diff --git a/compiler/forget/src/HIR/EnterSSA.ts b/compiler/forget/src/HIR/EnterSSA.ts
index 2d1c0f795c..30a0891606 100644
--- a/compiler/forget/src/HIR/EnterSSA.ts
+++ b/compiler/forget/src/HIR/EnterSSA.ts
@@ -51,7 +51,6 @@ class SSABuilder {
   makeId(oldId: Identifier): Identifier {
     return {
       id: this.nextSsaId,
-      preSsaId: oldId.id,
       name: oldId.name,
       mutableRange: {
         start: makeInstructionId(0),
diff --git a/compiler/forget/src/HIR/HIR.ts b/compiler/forget/src/HIR/HIR.ts
index 01692cd791..eab9a26334 100644
--- a/compiler/forget/src/HIR/HIR.ts
+++ b/compiler/forget/src/HIR/HIR.ts
@@ -298,8 +298,6 @@ export type MutableRange = {
  * Represents a user-defined variable (has a name) or a temporary variable (no name).
  */
 export type Identifier = {
-  // the original `id` value prior to entering SSA form
-  preSsaId: IdentifierId | null;
   // unique value to distinguish a variable, since name is not guaranteed to exist or be unique
   id: IdentifierId;
   // null for temporaries. name is primarily used for debugging.
diff --git a/compiler/forget/src/HIR/HIRBuilder.ts b/compiler/forget/src/HIR/HIRBuilder.ts
index 15d1308eea..49a11189b3 100644
--- a/compiler/forget/src/HIR/HIRBuilder.ts
+++ b/compiler/forget/src/HIR/HIRBuilder.ts
@@ -111,7 +111,6 @@ export default class HIRBuilder {
   makeTemporary(): Identifier {
     const id = this.nextIdentifierId;
     return {
-      preSsaId: null,
       id,
       name: null,
       mutableRange: { start: makeInstructionId(0), end: makeInstructionId(0) },
@@ -124,7 +123,6 @@ export default class HIRBuilder {
     if (identifier == null) {
       const id = this.nextIdentifierId;
       identifier = {
-        preSsaId: null,
         id,
         name: node.name,
         mutableRange: {
diff --git a/compiler/forget/src/HIR/LeaveSSA.ts b/compiler/forget/src/HIR/LeaveSSA.ts
index f8a0df78f2..19f62f21bf 100644
--- a/compiler/forget/src/HIR/LeaveSSA.ts
+++ b/compiler/forget/src/HIR/LeaveSSA.ts
@@ -1,24 +1,153 @@
-import { HIRFunction } from "./HIR";
-import { eachBlockOperand } from "./visitors";
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {
+  Effect,
+  GeneratedSource,
+  HIRFunction,
+  Identifier,
+  Instruction,
+  InstructionKind,
+  Phi,
+} from "./HIR";
+import { eachInstructionValueOperand, eachTerminalOperand } from "./visitors";
 
 /**
- * Removes SSA form by restoring each `Identifier.id` value to its pre-SSA value,
- * and removing all phi nodes.
+ * Removes SSA form by creating unique variable declarations for the versions of each variables.
+ * - Versions of a variable that do not flow into a phi node are each assigned their own const variable
+ * declaration.
+ * - If multiple versions of a variable flow into some phi node, then all those versions are reassigned to
+ * the phi version. A single declaration is created at the same block scope as the phi, prior to any of the
+ * assignments.
  */
-export default function leaveSSA(fn: HIRFunction) {
-  const ir = fn.body;
+export function leaveSSA(fn: HIRFunction) {
+  // Maps identifiers that appear as a phi or phi operand to a single canonical identifier
+  // for all instances.
+  const variableMapping: Map<Identifier, Identifier> = new Map();
 
-  for (const param of fn.params) {
-    param.identifier.id = param.identifier.preSsaId ?? param.identifier.id;
-  }
+  for (const [, block] of fn.body.blocks) {
+    // Identifiers (from phis) that *may* need a new `let` declaration created. If the original
+    // variable declaration flows into the phi, then we can reuse its declaration - this is
+    // discovered during iteration of instructions.
+    const needsDeclaration: Set<Identifier> = new Set();
+
+    // Find any phi nodes which need a variable declaration in the current block
+    // This includes phis in fallthrough nodes, or blocks that form part of control flow
+    // such as for or while (and later if/switch).
+    const phis: Array<Phi> = [];
+    const terminal = block.terminal;
+    if (
+      (terminal.kind === "if" ||
+        terminal.kind === "switch" ||
+        terminal.kind === "while" ||
+        terminal.kind === "for") &&
+      terminal.fallthrough !== null
+    ) {
+      const fallthrough = fn.body.blocks.get(terminal.fallthrough)!;
+      phis.push(...fallthrough.phis);
+    }
+    if (terminal.kind === "while" || terminal.kind === "for") {
+      const test = fn.body.blocks.get(terminal.test)!;
+      phis.push(...test.phis);
+      const loop = fn.body.blocks.get(terminal.loop)!;
+      phis.push(...loop.phis);
+    }
+    if (terminal.kind === "for") {
+      const update = fn.body.blocks.get(terminal.update)!;
+      phis.push(...update.phis);
+    }
+
+    // For each phi, determine a canonical identifier to use for versions of the variable
+    // that appear in the phi (as its output id and operands). If this is the first time
+    // we're seeing the phi id, then we may need to generate a new variable declaration
+    // Note that there can be multiple phi nodes for the same variable, we capture the
+    // outermost scope by visiting predecessor blocks first.
+    for (const phi of phis) {
+      let canonicalId = variableMapping.get(phi.id);
+      if (canonicalId === undefined) {
+        // Determine a new canonical id. We use the id/operand whose id is lowest,
+        // which ensures that _if_ the original variable declaration is one of the
+        // options we'll choose it and can reuse the declaration.
+        canonicalId = phi.id;
+        for (const [, operand] of phi.operands) {
+          if (operand.id < canonicalId.id) {
+            canonicalId = operand;
+          }
+        }
+        variableMapping.set(phi.id, canonicalId);
+        needsDeclaration.add(canonicalId);
+      }
+      // all versions of the variable need to be remapped to the canonical id
+      for (const [, operand] of phi.operands) {
+        variableMapping.set(operand, canonicalId);
+      }
+    }
+
+    // Visit instructions and rewrite identifiers based on the variable mapping
+    // updated above.
+    for (const instr of block.instructions) {
+      const { lvalue, value } = instr;
+      if (lvalue !== null) {
+        lvalue.place.identifier =
+          variableMapping.get(lvalue.place.identifier) ??
+          lvalue.place.identifier;
+        if (lvalue.place.memberPath === null) {
+          if (!variableMapping.has(lvalue.place.identifier)) {
+            // This variable does not flow into a phi, therefore there
+            // is no reassignment. Convert the declaration to a const.
+            lvalue.kind = InstructionKind.Const;
+          } else if (
+            variableMapping.get(lvalue.place.identifier) ===
+            lvalue.place.identifier
+          ) {
+            // This is an existing declaration we can reuse as the canonical declaration for its
+            // phi. Note, the declaration must already be a `let` or else it would be invalid to
+            // reassign the variable in the first place.
+            needsDeclaration.delete(lvalue.place.identifier);
+          }
+        }
+      }
+      for (const operand of eachInstructionValueOperand(value)) {
+        operand.identifier =
+          variableMapping.get(operand.identifier) ?? operand.identifier;
+      }
+    }
+
+    for (const operand of eachTerminalOperand(terminal)) {
+      operand.identifier =
+        variableMapping.get(operand.identifier) ?? operand.identifier;
+    }
+
+    // Generate new let declarations for any remaining phi variables
+    for (const identifier of needsDeclaration) {
+      const instr: Instruction = {
+        // NOTE: reuse the terminal id since these lets must be scoped with the terminal anyway
+        // the only reason they exist is that there is a scope that will span the control flow.
+        id: block.terminal.id,
+        lvalue: {
+          place: {
+            kind: "Identifier",
+            memberPath: null,
+            identifier,
+            effect: Effect.Mutate,
+            loc: GeneratedSource,
+          },
+          kind: InstructionKind.Let,
+        },
+        value: {
+          kind: "Primitive",
+          value: undefined,
+          loc: GeneratedSource,
+        },
+        loc: GeneratedSource,
+      };
+      block.instructions.push(instr);
+    }
 
-  for (const [, block] of ir.blocks) {
     block.phis.clear();
   }
-
-  for (const [, block] of ir.blocks) {
-    for (const place of eachBlockOperand(block)) {
-      place.identifier.id = place.identifier.preSsaId ?? place.identifier.id;
-    }
-  }
 }
diff --git a/compiler/forget/src/HIR/Pipeline.ts b/compiler/forget/src/HIR/Pipeline.ts
index 306cb5206d..ba745275b8 100644
--- a/compiler/forget/src/HIR/Pipeline.ts
+++ b/compiler/forget/src/HIR/Pipeline.ts
@@ -12,7 +12,7 @@ import enterSSA from "../HIR/EnterSSA";
 import { Environment } from "../HIR/HIRBuilder";
 import { inferMutableRanges } from "../HIR/InferMutableLifetimes";
 import inferReferenceEffects from "../HIR/InferReferenceEffects";
-import leaveSSA from "../HIR/LeaveSSA";
+import { leaveSSA } from "../HIR/LeaveSSA";
 import codegen from "./Codegen";
 import { HIRFunction } from "./HIR";
 import { inferReactiveScopeDependencies } from "./InferReactiveScopeDependencies";
diff --git a/compiler/forget/src/HIR/PrintHIR.ts b/compiler/forget/src/HIR/PrintHIR.ts
index 337c535c1c..a450ff0d0f 100644
--- a/compiler/forget/src/HIR/PrintHIR.ts
+++ b/compiler/forget/src/HIR/PrintHIR.ts
@@ -128,7 +128,9 @@ export function printTerminal(terminal: Terminal): Array<string> | string {
     case "if": {
       value = `[${terminal.id}] If (${printPlace(terminal.test)}) then:bb${
         terminal.consequent
-      } else:bb${terminal.alternate}`;
+      } else:bb${terminal.alternate}${
+        terminal.fallthrough ? ` fallthrough=bb${terminal.fallthrough}` : ""
+      }`;
       break;
     }
     case "throw": {
@@ -157,6 +159,9 @@ export function printTerminal(terminal: Terminal): Array<string> | string {
           output.push(`  Default: bb${case_.block}`);
         }
       });
+      if (terminal.fallthrough) {
+        output.push(`  Fallthrough: bb${terminal.fallthrough}`);
+      }
       value = output;
       break;
     }
diff --git a/compiler/forget/src/__tests__/fixtures/hir/_bug_expression-with-assignment.expect.md b/compiler/forget/src/__tests__/fixtures/hir/_bug_expression-with-assignment.expect.md
index 2e6274626d..a703b6e9bf 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/_bug_expression-with-assignment.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/_bug_expression-with-assignment.expect.md
@@ -51,9 +51,9 @@ flowchart TB
 
 ```javascript
 function f$0() {
-  let x$1 = 1;
-  x$1 = 2;
-  return x$1 + x$1 + x$1;
+  const x$4 = 1;
+  const x$5 = 2;
+  return x$5 + x$5 + x$5;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/_bug_inverted-if-else.expect.md b/compiler/forget/src/__tests__/fixtures/hir/_bug_inverted-if-else.expect.md
new file mode 100644
index 0000000000..89989d051e
--- /dev/null
+++ b/compiler/forget/src/__tests__/fixtures/hir/_bug_inverted-if-else.expect.md
@@ -0,0 +1,91 @@
+
+## Input
+
+```javascript
+function foo(a, b, c) {
+  let x = null;
+  label: {
+    if (a) {
+      x = b;
+      break label;
+    }
+    x = c;
+  }
+  return x;
+}
+
+```
+
+## HIR
+
+```
+bb0:
+  [1] Let mutate x$8_@0 = null
+  [2] If (read a$5) then:bb3 else:bb2 fallthrough=bb2
+bb3:
+  predecessor blocks: bb0
+  [3] Reassign mutate x$9_@1[3:6] = read b$6
+  [4] Goto bb1
+bb2:
+  predecessor blocks: bb0
+  [5] Reassign mutate x$10_@1[3:6] = read c$7
+  [6] Goto bb1
+bb1:
+  predecessor blocks: bb3 bb2
+  x$11_@1[3:6]: phi(bb3: x$9_@1, bb2: x$10_@1)
+  [7] Return read x$11_@1
+scope1 [3:6]:
+ - read b$6
+ - read a$5
+ - read c$7
+```
+
+### CFG
+
+```mermaid
+flowchart TB
+  %% Basic Blocks
+  subgraph bb0
+    bb0_instrs["
+      [1] Let mutate x$8_@0 = null
+    "]
+    bb0_instrs --> bb0_terminal(["If (read a$5)"])
+  end
+  subgraph bb3
+    bb3_instrs["
+      [3] Reassign mutate x$9_@1[3:6] = read b$6
+    "]
+    bb3_instrs --> bb3_terminal(["Goto"])
+  end
+  subgraph bb2
+    bb2_instrs["
+      [5] Reassign mutate x$10_@1[3:6] = read c$7
+    "]
+    bb2_instrs --> bb2_terminal(["Goto"])
+  end
+  subgraph bb1
+    bb1_terminal(["Return read x$11_@1"])
+  end
+
+  %% Jumps
+  bb0_terminal -- "then" --> bb3
+  bb0_terminal -- "else" --> bb2
+  bb3_terminal --> bb1
+  bb2_terminal --> bb1
+
+```
+
+## Code
+
+```javascript
+function foo$0(a$5, b$6, c$7) {
+  const x$8 = null;
+  bb2: if (a$5) {
+    const x$9 = b$6;
+  }
+
+  const x$10 = c$7;
+}
+
+```
+      
\ No newline at end of file
diff --git a/compiler/forget/src/__tests__/fixtures/hir/_bug_inverted-if-else.js b/compiler/forget/src/__tests__/fixtures/hir/_bug_inverted-if-else.js
new file mode 100644
index 0000000000..574de55c64
--- /dev/null
+++ b/compiler/forget/src/__tests__/fixtures/hir/_bug_inverted-if-else.js
@@ -0,0 +1,11 @@
+function foo(a, b, c) {
+  let x = null;
+  label: {
+    if (a) {
+      x = b;
+      break label;
+    }
+    x = c;
+  }
+  return x;
+}
diff --git a/compiler/forget/src/__tests__/fixtures/hir/_bug_while-with-assignment.expect.md b/compiler/forget/src/__tests__/fixtures/hir/_bug_while-with-assignment.expect.md
deleted file mode 100644
index 5a5062c6ed..0000000000
--- a/compiler/forget/src/__tests__/fixtures/hir/_bug_while-with-assignment.expect.md
+++ /dev/null
@@ -1,106 +0,0 @@
-
-## Input
-
-```javascript
-function f(reader) {
-  const queue = [1, 2, 3];
-  let value = 0;
-  let sum = 0;
-  // BUG: we need to codegen the complex test expression
-  while ((value = queue.pop()) != null) {
-    sum += value;
-  }
-  return sum;
-}
-
-```
-
-## HIR
-
-```
-bb0:
-  [1] Const mutate $11_@0 = 1
-  [2] Const mutate $12_@1 = 2
-  [3] Const mutate $13_@2 = 3
-  [4] Const mutate queue$14_@3[0:14] = Array [read $11_@0, read $12_@1, read $13_@2]
-  [5] Let mutate value$15_@4 = 0
-  [6] Let mutate sum$16_@3[0:14] = 0
-  [7] While test=bb1 loop=bb3 fallthrough=bb2
-bb1:
-  predecessor blocks: bb0 bb3
-  sum$21_@3[0:14]: phi(bb0: sum$16_@3, bb3: sum$22_@3)
-  [8] Reassign mutate value$18_@3[0:14] = Call mutate queue$14_@3.pop()
-  [9] Const mutate $19_@6 = null
-  [10] Const mutate $20_@7[10:12] = Binary read value$18_@3 != read $19_@6
-  [11] If (read $20_@7) then:bb3 else:bb2
-bb3:
-  predecessor blocks: bb1
-  [12] Reassign mutate sum$22_@3[0:14] = Binary read sum$21_@3 + read value$18_@3
-  [13] Goto(Continue) bb1
-bb2:
-  predecessor blocks: bb1
-  [14] Return read sum$21_@3
-scope7 [10:12]:
- - read $19_@6
-```
-
-### CFG
-
-```mermaid
-flowchart TB
-  %% Basic Blocks
-  subgraph bb0
-    bb0_instrs["
-      [1] Const mutate $11_@0 = 1
-      [2] Const mutate $12_@1 = 2
-      [3] Const mutate $13_@2 = 3
-      [4] Const mutate queue$14_@3[0:14] = Array [read $11_@0, read $12_@1, read $13_@2]
-      [5] Let mutate value$15_@4 = 0
-      [6] Let mutate sum$16_@3[0:14] = 0
-    "]
-    bb0_instrs --> bb0_terminal(["While"])
-  end
-  subgraph bb1
-    bb1_instrs["
-      [8] Reassign mutate value$18_@3[0:14] = Call mutate queue$14_@3.pop()
-      [9] Const mutate $19_@6 = null
-      [10] Const mutate $20_@7[10:12] = Binary read value$18_@3 != read $19_@6
-    "]
-    bb1_instrs --> bb1_terminal(["If (read $20_@7)"])
-  end
-  subgraph bb3
-    bb3_instrs["
-      [12] Reassign mutate sum$22_@3[0:14] = Binary read sum$21_@3 + read value$18_@3
-    "]
-    bb3_instrs --> bb3_terminal(["Goto"])
-  end
-  subgraph bb2
-    bb2_terminal(["Return read sum$21_@3"])
-  end
-
-  %% Jumps
-  bb0_terminal -- "test" --> bb1
-  bb0_terminal -- "loop" --> bb3
-  bb0_terminal -- "fallthrough" --> bb2
-  bb1_terminal -- "then" --> bb3
-  bb1_terminal -- "else" --> bb2
-  bb3_terminal --> bb1
-
-```
-
-## Code
-
-```javascript
-function f$0(reader$1) {
-  const queue$2 = [1, 2, 3];
-  let value$6 = 0;
-  let sum$7 = 0;
-  bb2: while (((value$6 = queue$2.pop()), value$6 != null)) {
-    sum$7 = sum$7 + value$6;
-  }
-
-  return sum$7;
-}
-
-```
-      
\ No newline at end of file
diff --git a/compiler/forget/src/__tests__/fixtures/hir/alias-while.expect.md b/compiler/forget/src/__tests__/fixtures/hir/alias-while.expect.md
index c7746aa18f..b2cb6cb033 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/alias-while.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/alias-while.expect.md
@@ -36,7 +36,7 @@ bb1:
   a$12_@0[0:12]: phi(bb0: a$8_@0, bb3: a$15_@0)
   b$14_@0[0:12]: phi(bb0: b$9_@0, bb3: b$17_@0)
   c$16_@0[0:12]: phi(bb0: c$10_@0, bb3: c$18_@0)
-  [5] If (read cond$7) then:bb3 else:bb2
+  [5] If (read cond$7) then:bb3 else:bb2 fallthrough=bb2
 bb3:
   predecessor blocks: bb1
   [6] Let mutate z$13_@0[0:12] = read a$12_@0
@@ -102,22 +102,22 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(cond$1) {
-  let a$2 = {};
-  let b$3 = {};
-  let c$4 = {};
-  bb2: while (cond$1) {
-    let z$5 = a$2;
-    a$2 = b$3;
-    b$3 = c$4;
-    c$4 = z$5;
-    mutate$6(a$2, b$3);
+function foo$0(cond$7) {
+  let a$8 = {};
+  let b$9 = {};
+  let c$10 = {};
+  bb2: while (cond$7) {
+    const z$13 = a$8;
+    a$8 = b$9;
+    b$9 = c$10;
+    c$10 = z$13;
+    mutate$6(a$8, b$9);
   }
 
-  a$2;
-  b$3;
-  c$4;
-  return a$2;
+  a$8;
+  b$9;
+  c$10;
+  return a$8;
 }
 
 ```
@@ -145,7 +145,7 @@ flowchart TB
 ## Code
 
 ```javascript
-function mutate$0(x$1, y$2) {}
+function mutate$0(x$3, y$4) {}
 
 ```
       
\ No newline at end of file
diff --git a/compiler/forget/src/__tests__/fixtures/hir/assignment-variations.expect.md b/compiler/forget/src/__tests__/fixtures/hir/assignment-variations.expect.md
index b9deb6ca80..c4208f4695 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/assignment-variations.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/assignment-variations.expect.md
@@ -65,10 +65,10 @@ flowchart TB
 
 ```javascript
 function f$0() {
-  let x$1 = 1;
-  x$1 = x$1 + 1;
-  x$1 = x$1 + 1;
-  x$1 = x$1 >>> 1;
+  const x$5 = 1;
+  const x$7 = x$5 + 1;
+  const x$9 = x$7 + 1;
+  const x$11 = x$9 >>> 1;
 }
 
 ```
@@ -107,9 +107,9 @@ flowchart TB
 ## Code
 
 ```javascript
-function g$0(a$1) {
-  a$1.c.b = a$1.b.c + 1;
-  a$1.c.b = a$1.b.c * 2;
+function g$0(a$4) {
+  a$4.c.b = a$4.b.c + 1;
+  a$4.c.b = a$4.b.c * 2;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/call.expect.md b/compiler/forget/src/__tests__/fixtures/hir/call.expect.md
index d943297060..e7eb75ae26 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/call.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/call.expect.md
@@ -89,14 +89,14 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const a$2 = [];
-  const b$3 = {};
-  foo$4(a$2, b$3);
-  let _$5 = <div a={a$2}></div>;
+function Component$0(props$9) {
+  const a$10 = [];
+  const b$11 = {};
+  foo$4(a$10, b$11);
+  const _$13 = <div a={a$10}></div>;
 
-  foo$4(b$3);
-  return <div a={a$2} b={b$3}></div>;
+  foo$4(b$11);
+  return <div a={a$10} b={b$11}></div>;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/complex-while.expect.md b/compiler/forget/src/__tests__/fixtures/hir/complex-while.expect.md
index a132078235..3897cada95 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/complex-while.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/complex-while.expect.md
@@ -18,16 +18,16 @@ function foo(a, b, c) {
 
 ```
 bb0:
-  [1] If (read a$4) then:bb3 else:bb1
+  [1] If (read a$4) then:bb3 else:bb1 fallthrough=bb1
 bb3:
   predecessor blocks: bb0
   [2] While test=bb4 loop=bb6 fallthrough=bb1
 bb4:
   predecessor blocks: bb3 bb7
-  [3] If (read b$5) then:bb6 else:bb1
+  [3] If (read b$5) then:bb6 else:bb1 fallthrough=bb1
 bb6:
   predecessor blocks: bb4
-  [4] If (read c$6) then:bb1 else:bb7
+  [4] If (read c$6) then:bb1 else:bb7 fallthrough=bb7
 bb7:
   predecessor blocks: bb6
   [5] Goto(Continue) bb4
@@ -78,10 +78,10 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(a$1, b$2, c$3) {
-  bb1: if (a$1) {
-    while (b$2) {
-      bb7: if (c$3) break;
+function foo$0(a$4, b$5, c$6) {
+  bb1: if (a$4) {
+    while (b$5) {
+      bb7: if (c$6) break;
     }
   }
 }
diff --git a/compiler/forget/src/__tests__/fixtures/hir/component.expect.md b/compiler/forget/src/__tests__/fixtures/hir/component.expect.md
index 1e4074ec71..e959a98117 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/component.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/component.expect.md
@@ -44,12 +44,12 @@ bb0:
   [7] Goto bb1
 bb1:
   predecessor blocks: bb0 bb5 bb10
-  [8] If (read items$27_@0) then:bb3 else:bb2
+  [8] If (read items$27_@0) then:bb3 else:bb2 fallthrough=bb2
 bb3:
   predecessor blocks: bb1
   [9] Const mutate $34_@6 = null
   [10] Const mutate $36_@3[0:19] = Binary read item$10_@3 == read $34_@6
-  [11] If (read $36_@3) then:bb8 else:bb9
+  [11] If (read $36_@3) then:bb8 else:bb9 fallthrough=bb7
 bb8:
   predecessor blocks: bb3
   [12] Const mutate $37_@3[0:19] = read $36_@3
@@ -61,7 +61,7 @@ bb9:
 bb7:
   predecessor blocks: bb8 bb9
   $40_@3[0:19]: phi(bb8: $37_@3, bb9: $39_@3)
-  [16] If (read $40_@3) then:bb5 else:bb4
+  [16] If (read $40_@3) then:bb5 else:bb4 fallthrough=bb4
 bb5:
   predecessor blocks: bb7
   [17] Goto(Continue) bb1
@@ -72,7 +72,7 @@ bb4:
   [20] Const mutate $44_@8 = JSX <read $43_@7>{read item$10_@3}</read $43_@7>
   [21] Call mutate renderedItems$29_@2.push(read $44_@8)
   [22] Const mutate $49_@2[3:26] = Binary read renderedItems$29_@2.length >= read max$32_@5
-  [23] If (read $49_@2) then:bb2 else:bb10
+  [23] If (read $49_@2) then:bb2 else:bb10 fallthrough=bb10
 bb10:
   predecessor blocks: bb4
   [24] Goto(Continue) bb1
@@ -187,12 +187,12 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const items$2 = props$1.items;
-  const maxItems$3 = props$1.maxItems;
-  const renderedItems$4 = [];
-  const seen$5 = new Set$6();
-  const max$7 = Math$8.max(0, maxItems$3);
+function Component$0(props$26) {
+  const items$27 = props$26.items;
+  const maxItems$28 = props$26.maxItems;
+  const renderedItems$29 = [];
+  const seen$30 = new Set$6();
+  const max$32 = Math$8.max(0, maxItems$28);
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/conditional-break.expect.md b/compiler/forget/src/__tests__/fixtures/hir/conditional-break.expect.md
index a6f1237b15..bf49d3078d 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/conditional-break.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/conditional-break.expect.md
@@ -80,7 +80,7 @@ function Component(props) {
 bb0:
   [1] Const mutate a_DEBUG$5_@0[1:7] = Array []
   [2] Call mutate a_DEBUG$5_@0.push(read props$4.a)
-  [3] If (read props$4.b) then:bb2 else:bb1
+  [3] If (read props$4.b) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [4] Const mutate $6_@1 = null
@@ -129,15 +129,15 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const a_DEBUG$2 = [];
-  a_DEBUG$2.push(props$1.a);
-  bb1: if (props$1.b) {
+function Component$0(props$4) {
+  const a_DEBUG$5 = [];
+  a_DEBUG$5.push(props$4.a);
+  bb1: if (props$4.b) {
     return null;
   }
 
-  a_DEBUG$2.push(props$1.d);
-  return a_DEBUG$2;
+  a_DEBUG$5.push(props$4.d);
+  return a_DEBUG$5;
 }
 
 ```
@@ -147,7 +147,7 @@ function Component$0(props$1) {
 bb0:
   [1] Const mutate a$4_@0[1:7] = Array []
   [2] Call mutate a$4_@0.push(read props$3.a)
-  [3] If (read props$3.b) then:bb2 else:bb1
+  [3] If (read props$3.b) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [4] Call mutate a$4_@0.push(read props$3.c)
@@ -198,15 +198,15 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const a$2 = [];
-  a$2.push(props$1.a);
-  bb1: if (props$1.b) {
-    a$2.push(props$1.c);
+function Component$0(props$3) {
+  const a$4 = [];
+  a$4.push(props$3.a);
+  bb1: if (props$3.b) {
+    a$4.push(props$3.c);
   }
 
-  a$2.push(props$1.d);
-  return a$2;
+  a$4.push(props$3.d);
+  return a$4;
 }
 
 ```
@@ -216,7 +216,7 @@ function Component$0(props$1) {
 bb0:
   [1] Const mutate a$5_@0[1:8] = Array []
   [2] Call mutate a$5_@0.push(read props$4.a)
-  [3] If (read props$4.b) then:bb2 else:bb1
+  [3] If (read props$4.b) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [4] Call mutate a$5_@0.push(read props$4.c)
@@ -268,16 +268,16 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const a$2 = [];
-  a$2.push(props$1.a);
-  bb1: if (props$1.b) {
-    a$2.push(props$1.c);
+function Component$0(props$4) {
+  const a$5 = [];
+  a$5.push(props$4.a);
+  bb1: if (props$4.b) {
+    a$5.push(props$4.c);
     return null;
   }
 
-  a$2.push(props$1.d);
-  return a$2;
+  a$5.push(props$4.d);
+  return a$5;
 }
 
 ```
@@ -287,7 +287,7 @@ function Component$0(props$1) {
 bb0:
   [1] Const mutate a$4_@0[1:7] = Array []
   [2] Call mutate a$4_@0.push(read props$3.a)
-  [3] If (read props$3.b) then:bb2 else:bb1
+  [3] If (read props$3.b) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [4] Call mutate a$4_@0.push(read props$3.c)
@@ -337,16 +337,16 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const a$2 = [];
-  a$2.push(props$1.a);
-  bb1: if (props$1.b) {
-    a$2.push(props$1.c);
-    return a$2;
+function Component$0(props$3) {
+  const a$4 = [];
+  a$4.push(props$3.a);
+  bb1: if (props$3.b) {
+    a$4.push(props$3.c);
+    return a$4;
   }
 
-  a$2.push(props$1.d);
-  return a$2;
+  a$4.push(props$3.d);
+  return a$4;
 }
 
 ```
@@ -356,7 +356,7 @@ function Component$0(props$1) {
 bb0:
   [1] Const mutate a$4_@0[1:7] = Array []
   [2] Call mutate a$4_@0.push(read props$3.a)
-  [3] If (read props$3.b) then:bb1 else:bb2
+  [3] If (read props$3.b) then:bb1 else:bb2 fallthrough=bb2
 bb2:
   predecessor blocks: bb0
   [4] Call mutate a$4_@0.push(read props$3.c)
@@ -406,15 +406,15 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const a$2 = [];
-  a$2.push(props$1.a);
-  bb2: if (props$1.b) {
-    a$2.push(props$1.d);
-    return a$2;
+function Component$0(props$3) {
+  const a$4 = [];
+  a$4.push(props$3.a);
+  bb2: if (props$3.b) {
+    a$4.push(props$3.d);
+    return a$4;
   }
 
-  a$2.push(props$1.c);
+  a$4.push(props$3.c);
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/conditional-on-mutable.expect.md b/compiler/forget/src/__tests__/fixtures/hir/conditional-on-mutable.expect.md
index a0be2fc143..b61fd849fd 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/conditional-on-mutable.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/conditional-on-mutable.expect.md
@@ -37,14 +37,14 @@ function mayMutate() {}
 bb0:
   [1] Const mutate a$7_@0[1:9] = Array []
   [2] Const mutate b$8_@0[1:9] = Array []
-  [3] If (read b$8_@0) then:bb2 else:bb1
+  [3] If (read b$8_@0) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [4] Call mutate a$7_@0.push(read props$6.p0)
   [5] Goto bb1
 bb1:
   predecessor blocks: bb2 bb0
-  [6] If (read props$6.p1) then:bb4 else:bb3
+  [6] If (read props$6.p1) then:bb4 else:bb3 fallthrough=bb3
 bb4:
   predecessor blocks: bb1
   [7] Call mutate b$8_@0.push(read props$6.p2)
@@ -109,18 +109,18 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const a$2 = [];
-  const b$3 = [];
-  bb1: if (b$3) {
-    a$2.push(props$1.p0);
+function Component$0(props$6) {
+  const a$7 = [];
+  const b$8 = [];
+  bb1: if (b$8) {
+    a$7.push(props$6.p0);
   }
 
-  bb3: if (props$1.p1) {
-    b$3.push(props$1.p2);
+  bb3: if (props$6.p1) {
+    b$8.push(props$6.p2);
   }
 
-  return <Foo$4 a={a$2} b={b$3}></Foo$4>;
+  return <Foo$4 a={a$7} b={b$8}></Foo$4>;
 }
 
 ```
@@ -131,14 +131,14 @@ bb0:
   [1] Const mutate a$9_@0[0:10] = Array []
   [2] Const mutate b$10_@0[0:10] = Array []
   [3] Const mutate $11_@0[0:10] = Call mutate mayMutate$4_@0(mutate b$10_@0)
-  [4] If (read $11_@0) then:bb2 else:bb1
+  [4] If (read $11_@0) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [5] Call mutate a$9_@0.push(read props$8.p0)
   [6] Goto bb1
 bb1:
   predecessor blocks: bb2 bb0
-  [7] If (read props$8.p1) then:bb4 else:bb3
+  [7] If (read props$8.p1) then:bb4 else:bb3 fallthrough=bb3
 bb4:
   predecessor blocks: bb1
   [8] Call mutate b$10_@0.push(read props$8.p2)
@@ -200,18 +200,18 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const a$2 = [];
-  const b$3 = [];
-  bb1: if (mayMutate$4(b$3)) {
-    a$2.push(props$1.p0);
+function Component$0(props$8) {
+  const a$9 = [];
+  const b$10 = [];
+  bb1: if (mayMutate$4(b$10)) {
+    a$9.push(props$8.p0);
   }
 
-  bb3: if (props$1.p1) {
-    b$3.push(props$1.p2);
+  bb3: if (props$8.p1) {
+    b$10.push(props$8.p2);
   }
 
-  return <Foo$6 a={a$2} b={b$3}></Foo$6>;
+  return <Foo$6 a={a$9} b={b$10}></Foo$6>;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/constructor.expect.md b/compiler/forget/src/__tests__/fixtures/hir/constructor.expect.md
index 9c05ae4ac8..46b5471b1d 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/constructor.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/constructor.expect.md
@@ -89,14 +89,14 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const a$2 = [];
-  const b$3 = {};
-  new Foo$4(a$2, b$3);
-  let _$5 = <div a={a$2}></div>;
+function Component$0(props$9) {
+  const a$10 = [];
+  const b$11 = {};
+  new Foo$4(a$10, b$11);
+  const _$13 = <div a={a$10}></div>;
 
-  new Foo$4(b$3);
-  return <div a={a$2} b={b$3}></div>;
+  new Foo$4(b$11);
+  return <div a={a$10} b={b$11}></div>;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/dependencies-outputs.expect.md b/compiler/forget/src/__tests__/fixtures/hir/dependencies-outputs.expect.md
index f8c609764b..5199b4ef6e 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/dependencies-outputs.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/dependencies-outputs.expect.md
@@ -27,14 +27,14 @@ bb0:
   [3] Const mutate $9_@1 = "div"
   [4] JSX <read $9_@1>{freeze x$8_@0}</read $9_@1>
   [5] Const mutate y$10_@2[5:12] = Array []
-  [6] If (read x$8_@0.length) then:bb2 else:bb1
+  [6] If (read x$8_@0.length) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [7] Call mutate y$10_@2.push(read x$8_@0)
   [8] Goto bb1
 bb1:
   predecessor blocks: bb2 bb0
-  [9] If (read b$7) then:bb4 else:bb3
+  [9] If (read b$7) then:bb4 else:bb3 fallthrough=bb3
 bb4:
   predecessor blocks: bb1
   [10] Call mutate y$10_@2.push(read b$7)
@@ -100,17 +100,17 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(a$1, b$2) {
-  const x$3 = [];
-  x$3.push(a$1);
-  <div>{x$3}</div>;
-  const y$5 = [];
-  bb1: if (x$3.length) {
-    y$5.push(x$3);
+function foo$0(a$6, b$7) {
+  const x$8 = [];
+  x$8.push(a$6);
+  <div>{x$8}</div>;
+  const y$10 = [];
+  bb1: if (x$8.length) {
+    y$10.push(x$8);
   }
 
-  bb3: if (b$2) {
-    y$5.push(b$2);
+  bb3: if (b$7) {
+    y$10.push(b$7);
   }
 }
 
diff --git a/compiler/forget/src/__tests__/fixtures/hir/dependencies.expect.md b/compiler/forget/src/__tests__/fixtures/hir/dependencies.expect.md
index 739f36a5e7..1fc0a646bb 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/dependencies.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/dependencies.expect.md
@@ -27,14 +27,14 @@ bb0:
   [1] Const mutate items$9_@0[1:10] = Array [read z$8]
   [2] Call mutate items$9_@0.push(read x$6)
   [3] Const mutate items2$10_@1[3:7] = Array []
-  [4] If (read x$6) then:bb2 else:bb1
+  [4] If (read x$6) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [5] Call mutate items2$10_@1.push(read y$7)
   [6] Goto bb1
 bb1:
   predecessor blocks: bb2 bb0
-  [7] If (read y$7) then:bb4 else:bb3
+  [7] If (read y$7) then:bb4 else:bb3 fallthrough=bb3
 bb4:
   predecessor blocks: bb1
   [8] Call mutate items$9_@0.push(read x$6)
@@ -97,19 +97,19 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(x$1, y$2, z$3) {
-  const items$4 = [z$3];
-  items$4.push(x$1);
-  const items2$5 = [];
-  bb1: if (x$1) {
-    items2$5.push(y$2);
+function foo$0(x$6, y$7, z$8) {
+  const items$9 = [z$8];
+  items$9.push(x$6);
+  const items2$10 = [];
+  bb1: if (x$6) {
+    items2$10.push(y$7);
   }
 
-  bb3: if (y$2) {
-    items$4.push(x$1);
+  bb3: if (y$7) {
+    items$9.push(x$6);
   }
 
-  return items2$5;
+  return items2$10;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/error.while-with-assignment-in-test.expect.md b/compiler/forget/src/__tests__/fixtures/hir/error.while-with-assignment-in-test.expect.md
new file mode 100644
index 0000000000..5dc68ff63f
--- /dev/null
+++ b/compiler/forget/src/__tests__/fixtures/hir/error.while-with-assignment-in-test.expect.md
@@ -0,0 +1,25 @@
+
+## Input
+
+```javascript
+function f(reader) {
+  const queue = [1, 2, 3];
+  let value = 0;
+  let sum = 0;
+  // BUG: we need to codegen the complex test expression
+  while ((value = queue.pop()) != null) {
+    sum += value;
+  }
+  return sum;
+}
+
+```
+
+
+## Error
+
+```
+TODO: Handle conversion of VariableDeclaration to expression
+```
+          
+      
\ No newline at end of file
diff --git a/compiler/forget/src/__tests__/fixtures/hir/_bug_while-with-assignment.js b/compiler/forget/src/__tests__/fixtures/hir/error.while-with-assignment-in-test.js
similarity index 100%
rename from compiler/forget/src/__tests__/fixtures/hir/_bug_while-with-assignment.js
rename to compiler/forget/src/__tests__/fixtures/hir/error.while-with-assignment-in-test.js
diff --git a/compiler/forget/src/__tests__/fixtures/hir/extend-scopes-if.expect.md b/compiler/forget/src/__tests__/fixtures/hir/extend-scopes-if.expect.md
index b70dcde797..3e3438bab5 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/extend-scopes-if.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/extend-scopes-if.expect.md
@@ -24,13 +24,13 @@ function foo(a, b, c) {
 ```
 bb0:
   [1] Let mutate x$10_@0[1:8] = Array []
-  [2] If (read a$7) then:bb2 else:bb1
+  [2] If (read a$7) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
-  [3] If (read b$8) then:bb4 else:bb1
+  [3] If (read b$8) then:bb4 else:bb1 fallthrough=bb1
 bb4:
   predecessor blocks: bb2
-  [4] If (read c$9) then:bb6 else:bb1
+  [4] If (read c$9) then:bb6 else:bb1 fallthrough=bb1
 bb6:
   predecessor blocks: bb4
   [5] Const mutate $11_@1 = 0
@@ -38,7 +38,7 @@ bb6:
   [7] Goto bb1
 bb1:
   predecessor blocks: bb6 bb4 bb2 bb0
-  [8] If (read a$7.length) then:bb8 else:bb7
+  [8] If (read a$7.length) then:bb8 else:bb7 fallthrough=bb7
 bb8:
   predecessor blocks: bb1
   [9] Return read a$7
@@ -105,18 +105,18 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(a$1, b$2, c$3) {
-  let x$4 = [];
-  bb1: if (a$1) {
-    if (b$2) {
-      if (c$3) {
-        x$4.push(0);
+function foo$0(a$7, b$8, c$9) {
+  const x$10 = [];
+  bb1: if (a$7) {
+    if (b$8) {
+      if (c$9) {
+        x$10.push(0);
       }
     }
   }
 
-  bb7: if (a$1.length) {
-    return a$1;
+  bb7: if (a$7.length) {
+    return a$7;
   }
 
   return null;
diff --git a/compiler/forget/src/__tests__/fixtures/hir/frozen-after-alias.expect.md b/compiler/forget/src/__tests__/fixtures/hir/frozen-after-alias.expect.md
index 94852ad18c..7ceeea4df1 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/frozen-after-alias.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/frozen-after-alias.expect.md
@@ -51,10 +51,10 @@ flowchart TB
 
 ```javascript
 function Component$0() {
-  const a$1 = [];
-  const b$2 = a$1;
-  useFreeze$3(a$1);
-  foo$4(b$2);
+  const a$5 = [];
+  const b$6 = a$5;
+  useFreeze$3(a$5);
+  foo$4(b$6);
 }
 
 ```
@@ -109,7 +109,7 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(x$1) {}
+function foo$0(x$2) {}
 
 ```
       
\ No newline at end of file
diff --git a/compiler/forget/src/__tests__/fixtures/hir/hook-call.expect.md b/compiler/forget/src/__tests__/fixtures/hir/hook-call.expect.md
index 11a8b2bf95..a5151d72ed 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/hook-call.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/hook-call.expect.md
@@ -121,14 +121,14 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const x$2 = [];
-  const y$3 = useFreeze$4(x$2);
-  foo$5(y$3, x$2);
+function Component$0(props$10) {
+  const x$11 = [];
+  const y$12 = useFreeze$4(x$11);
+  foo$5(y$12, x$11);
   return (
     <Component$0>
-      {x$2}
-      {y$3}
+      {x$11}
+      {y$12}
     </Component$0>
   );
 }
diff --git a/compiler/forget/src/__tests__/fixtures/hir/hooks-freeze-arguments.expect.md b/compiler/forget/src/__tests__/fixtures/hir/hooks-freeze-arguments.expect.md
index a2a6c14e6d..ae4e7defa9 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/hooks-freeze-arguments.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/hooks-freeze-arguments.expect.md
@@ -50,11 +50,11 @@ flowchart TB
 
 ```javascript
 function Component$0() {
-  const a$1 = [];
-  useFreeze$2(a$1);
-  useFreeze$2(a$1);
-  call$3(a$1);
-  return a$1;
+  const a$4 = [];
+  useFreeze$2(a$4);
+  useFreeze$2(a$4);
+  call$3(a$4);
+  return a$4;
 }
 
 ```
@@ -82,7 +82,7 @@ flowchart TB
 ## Code
 
 ```javascript
-function useFreeze$0(x$1) {}
+function useFreeze$0(x$2) {}
 
 ```
 ## HIR
@@ -109,7 +109,7 @@ flowchart TB
 ## Code
 
 ```javascript
-function call$0(x$1) {}
+function call$0(x$2) {}
 
 ```
       
\ No newline at end of file
diff --git a/compiler/forget/src/__tests__/fixtures/hir/hooks-freeze-possibly-mutable-arguments.expect.md b/compiler/forget/src/__tests__/fixtures/hir/hooks-freeze-possibly-mutable-arguments.expect.md
index 4b570c3214..c662505eeb 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/hooks-freeze-possibly-mutable-arguments.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/hooks-freeze-possibly-mutable-arguments.expect.md
@@ -29,7 +29,7 @@ bb0:
   [1] Const mutate cond$8_@0 = read props$7.cond
   [2] Const mutate x$9_@1 = read props$7.x
   [3] Let mutate a$10_@2 = undefined
-  [4] If (read cond$8_@0) then:bb2 else:bb3
+  [4] If (read cond$8_@0) then:bb2 else:bb3 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [5] Reassign mutate a$11_@3[5:8] = read x$9_@1
@@ -99,20 +99,21 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const cond$2 = props$1.cond;
-  const x$3 = props$1.x;
-  let a$4 = undefined;
-  bb1: if (cond$2) {
-    a$4 = x$3;
+function Component$0(props$7) {
+  const cond$8 = props$7.cond;
+  const x$9 = props$7.x;
+  const a$10 = undefined;
+  let a$11 = undefined;
+  bb1: if (cond$8) {
+    a$11 = x$9;
   } else {
-    a$4 = [];
+    a$11 = [];
   }
 
-  useFreeze$5(a$4);
-  useFreeze$5(a$4);
-  call$6(a$4);
-  return a$4;
+  useFreeze$5(a$11);
+  useFreeze$5(a$11);
+  call$6(a$11);
+  return a$11;
 }
 
 ```
@@ -140,7 +141,7 @@ flowchart TB
 ## Code
 
 ```javascript
-function useFreeze$0(x$1) {}
+function useFreeze$0(x$2) {}
 
 ```
 ## HIR
@@ -167,7 +168,7 @@ flowchart TB
 ## Code
 
 ```javascript
-function call$0(x$1) {}
+function call$0(x$2) {}
 
 ```
       
\ No newline at end of file
diff --git a/compiler/forget/src/__tests__/fixtures/hir/independent-across-if.expect.md b/compiler/forget/src/__tests__/fixtures/hir/independent-across-if.expect.md
index 22e6b60d64..1da79760d0 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/independent-across-if.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/independent-across-if.expect.md
@@ -147,7 +147,7 @@ function Foo$0() {}
 bb0:
   [1] Const mutate a$9_@0[0:7] = Call mutate compute$3_@0(read props$8.a)
   [2] Const mutate b$10_@0[0:7] = Call mutate compute$3_@0(read props$8.b)
-  [3] If (read props$8.c) then:bb2 else:bb1
+  [3] If (read props$8.c) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [4] Call mutate mutate$5_@0(mutate a$9_@0)
@@ -198,15 +198,15 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const a$2 = compute$3(props$1.a);
-  const b$4 = compute$3(props$1.b);
-  bb1: if (props$1.c) {
-    mutate$5(a$2);
-    mutate$5(b$4);
+function Component$0(props$8) {
+  const a$9 = compute$3(props$8.a);
+  const b$10 = compute$3(props$8.b);
+  bb1: if (props$8.c) {
+    mutate$5(a$9);
+    mutate$5(b$10);
   }
 
-  return <Foo$6 a={a$2} b={b$4}></Foo$6>;
+  return <Foo$6 a={a$9} b={b$10}></Foo$6>;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/independent.expect.md b/compiler/forget/src/__tests__/fixtures/hir/independent.expect.md
index 796fd04a74..e2de083090 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/independent.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/independent.expect.md
@@ -58,10 +58,10 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const a$2 = compute$3(props$1.a);
-  const b$4 = compute$3(props$1.b);
-  return <Foo$5 a={a$2} b={b$4}></Foo$5>;
+function Component$0(props$7) {
+  const a$8 = compute$3(props$7.a);
+  const b$9 = compute$3(props$7.b);
+  return <Foo$5 a={a$8} b={b$9}></Foo$5>;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/interdependent-across-if.expect.md b/compiler/forget/src/__tests__/fixtures/hir/interdependent-across-if.expect.md
index 9faec8686e..45773e510c 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/interdependent-across-if.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/interdependent-across-if.expect.md
@@ -114,7 +114,7 @@ function Foo$0() {}
 bb0:
   [1] Const mutate a$9_@0[0:6] = Call mutate compute$3_@0(read props$8.a)
   [2] Const mutate b$10_@0[0:6] = Call mutate compute$3_@0(read props$8.b)
-  [3] If (read props$8.c) then:bb2 else:bb1
+  [3] If (read props$8.c) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [4] Call mutate foo$5_@0(mutate a$9_@0, mutate b$10_@0)
@@ -163,14 +163,14 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const a$2 = compute$3(props$1.a);
-  const b$4 = compute$3(props$1.b);
-  bb1: if (props$1.c) {
-    foo$5(a$2, b$4);
+function Component$0(props$8) {
+  const a$9 = compute$3(props$8.a);
+  const b$10 = compute$3(props$8.b);
+  bb1: if (props$8.c) {
+    foo$5(a$9, b$10);
   }
 
-  return <Foo$6 a={a$2} b={b$4}></Foo$6>;
+  return <Foo$6 a={a$9} b={b$10}></Foo$6>;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/interdependent.expect.md b/compiler/forget/src/__tests__/fixtures/hir/interdependent.expect.md
index 6e9508ee13..065a9d8099 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/interdependent.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/interdependent.expect.md
@@ -60,11 +60,11 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const a$2 = compute$3(props$1.a);
-  const b$4 = compute$3(props$1.b);
-  foo$5(a$2, b$4);
-  return <Foo$6 a={a$2} b={b$4}></Foo$6>;
+function Component$0(props$8) {
+  const a$9 = compute$3(props$8.a);
+  const b$10 = compute$3(props$8.b);
+  foo$5(a$9, b$10);
+  return <Foo$6 a={a$9} b={b$10}></Foo$6>;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/inverted-if.expect.md b/compiler/forget/src/__tests__/fixtures/hir/inverted-if.expect.md
index 9b20e7e8d2..da7e9ce49f 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/inverted-if.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/inverted-if.expect.md
@@ -19,10 +19,10 @@ function foo(a, b, c) {
 ```
 bb0:
   [1] Let mutate y$8_@0[1:6] = Array []
-  [2] If (read a$5) then:bb3 else:bb1
+  [2] If (read a$5) then:bb3 else:bb1 fallthrough=bb1
 bb3:
   predecessor blocks: bb0
-  [3] If (read b$6) then:bb5 else:bb1
+  [3] If (read b$6) then:bb5 else:bb1 fallthrough=bb1
 bb5:
   predecessor blocks: bb3
   [4] Call mutate y$8_@0.push(read c$7)
@@ -72,11 +72,11 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(a$1, b$2, c$3) {
-  let y$4 = [];
-  bb1: if (a$1) {
-    if (b$2) {
-      y$4.push(c$3);
+function foo$0(a$5, b$6, c$7) {
+  const y$8 = [];
+  bb1: if (a$5) {
+    if (b$6) {
+      y$8.push(c$7);
     }
   }
 }
diff --git a/compiler/forget/src/__tests__/fixtures/hir/jsx-fragment.expect.md b/compiler/forget/src/__tests__/fixtures/hir/jsx-fragment.expect.md
index f47d28c59d..d98c2ec93b 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/jsx-fragment.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/jsx-fragment.expect.md
@@ -76,10 +76,10 @@ flowchart TB
 ## Code
 
 ```javascript
-function Foo$0(props$1) {
+function Foo$0(props$13) {
   return (
     <>
-      Hello {props$1.greeting}
+      Hello {props$13.greeting}
       {<div>{<>Text</>}</div>}
     </>
   );
diff --git a/compiler/forget/src/__tests__/fixtures/hir/logical-expression.expect.md b/compiler/forget/src/__tests__/fixtures/hir/logical-expression.expect.md
index c806987d47..c20f685f1f 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/logical-expression.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/logical-expression.expect.md
@@ -24,7 +24,7 @@ function g() {}
 ```
 bb0:
   [1] Const mutate $5_@0[0:2] = Call mutate f$1_@0()
-  [2] If (read $5_@0) then:bb2 else:bb3
+  [2] If (read $5_@0) then:bb2 else:bb3 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [3] Const mutate $6_@1[0:6] = Call mutate g$4_@1()
@@ -92,7 +92,7 @@ function And$0() {
 ```
 bb0:
   [1] Const mutate $5_@0[0:2] = Call mutate f$1_@0()
-  [2] If (read $5_@0) then:bb2 else:bb3
+  [2] If (read $5_@0) then:bb2 else:bb3 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [3] Const mutate $6_@1[0:6] = read $5_@0
@@ -162,7 +162,7 @@ bb0:
   [1] Const mutate $9_@0[0:2] = Call mutate f$2_@0()
   [2] Const mutate $10_@1 = null
   [3] Const mutate $11_@2 = Binary read $9_@0 != read $10_@1
-  [4] If (read $11_@2) then:bb2 else:bb3
+  [4] If (read $11_@2) then:bb2 else:bb3 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [5] Const mutate $12_@3[0:8] = read $9_@0
@@ -221,7 +221,7 @@ flowchart TB
 ## Code
 
 ```javascript
-function QuestionQuestion$0(props$1) {
+function QuestionQuestion$0(props$8) {
   bb1: if (f$2() != null) {
   } else {
   }
diff --git a/compiler/forget/src/__tests__/fixtures/hir/mutable-lifetime-loops.expect.md b/compiler/forget/src/__tests__/fixtures/hir/mutable-lifetime-loops.expect.md
index f10d9bb39d..1c3331937f 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/mutable-lifetime-loops.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/mutable-lifetime-loops.expect.md
@@ -63,7 +63,7 @@ flowchart TB
 ## Code
 
 ```javascript
-function mutate$0(x$1, y$2) {}
+function mutate$0(x$3, y$4) {}
 
 ```
 ## HIR
@@ -90,7 +90,7 @@ flowchart TB
 ## Code
 
 ```javascript
-function cond$0(x$1) {}
+function cond$0(x$2) {}
 
 ```
 ## HIR
@@ -109,7 +109,7 @@ bb1:
   c$22_@0[0:23]: phi(bb0: c$15_@0, bb4: c$25_@0)
   d$24_@0[0:23]: phi(bb0: d$16_@0, bb4: d$26_@0)
   [6] Const mutate $17_@1[6:8] = true
-  [7] If (read $17_@1) then:bb3 else:bb2
+  [7] If (read $17_@1) then:bb3 else:bb2 fallthrough=bb2
 bb3:
   predecessor blocks: bb1
   [8] Let mutate z$19_@0[0:23] = read a$18_@0
@@ -119,7 +119,7 @@ bb3:
   [12] Reassign mutate d$26_@0[0:23] = read z$19_@0
   [13] Call mutate mutate$7_@0(mutate a$21_@0, mutate b$23_@0)
   [14] Const mutate $29_@0[0:23] = Call mutate cond$8_@0(mutate a$21_@0)
-  [15] If (read $29_@0) then:bb2 else:bb4
+  [15] If (read $29_@0) then:bb2 else:bb4 fallthrough=bb4
 bb4:
   predecessor blocks: bb3
   [16] Goto(Continue) bb1
@@ -129,16 +129,16 @@ bb2:
   b$31_@0[0:23]: phi(bb3: b$23_@0, bb1: b$20_@0)
   c$32_@0[0:23]: phi(bb3: c$25_@0, bb1: c$22_@0)
   d$33_@0[0:23]: phi(bb3: d$26_@0, bb1: d$24_@0)
-  [17] If (read a$30_@0) then:bb7 else:bb7
+  [17] If (read a$30_@0) then:bb7 else:bb7 fallthrough=bb7
 bb7:
   predecessor blocks: bb2
-  [18] If (read b$31_@0) then:bb9 else:bb9
+  [18] If (read b$31_@0) then:bb9 else:bb9 fallthrough=bb9
 bb9:
   predecessor blocks: bb7
-  [19] If (read c$32_@0) then:bb11 else:bb11
+  [19] If (read c$32_@0) then:bb11 else:bb11 fallthrough=bb11
 bb11:
   predecessor blocks: bb9
-  [20] If (read d$33_@0) then:bb13 else:bb13
+  [20] If (read d$33_@0) then:bb13 else:bb13 fallthrough=bb13
 bb13:
   predecessor blocks: bb11
   [21] Const mutate $34_@2 = null
@@ -225,35 +225,35 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  let a$2 = {};
-  let b$3 = {};
-  let c$4 = {};
-  let d$5 = {};
+function Component$0(props$12) {
+  let a$18 = {};
+  let b$20 = {};
+  let c$22 = {};
+  let d$24 = {};
   bb2: while (true) {
-    let z$6 = a$2;
-    a$2 = b$3;
-    b$3 = c$4;
-    c$4 = d$5;
-    d$5 = z$6;
-    mutate$7(a$2, b$3);
+    const z$19 = a$18;
+    a$18 = b$20;
+    b$20 = c$22;
+    c$22 = d$24;
+    d$24 = z$19;
+    mutate$7(a$18, b$20);
 
-    bb4: if (cond$8(a$2)) break;
+    bb4: if (cond$8(a$18)) break;
   }
 
-  bb7: if (a$2) {
+  bb7: if (a$18) {
   }
 
-  bb9: if (b$3) {
+  bb9: if (b$20) {
   }
 
-  bb11: if (c$4) {
+  bb11: if (c$22) {
   }
 
-  bb13: if (d$5) {
+  bb13: if (d$24) {
   }
 
-  mutate$7(d$5, null);
+  mutate$7(d$24, null);
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/mutable-lifetime-with-aliasing.expect.md b/compiler/forget/src/__tests__/fixtures/hir/mutable-lifetime-with-aliasing.expect.md
index b1dfa768c4..eb555749f2 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/mutable-lifetime-with-aliasing.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/mutable-lifetime-with-aliasing.expect.md
@@ -59,7 +59,7 @@ flowchart TB
 ## Code
 
 ```javascript
-function mutate$0(x$1, y$2) {}
+function mutate$0(x$3, y$4) {}
 
 ```
 ## HIR
@@ -73,19 +73,19 @@ bb0:
   [5] Const mutate x$15_@1[0:15] = Object {  }
   [6] Reassign mutate x$15_@1.b[0:15] = read b$12_@1
   [7] Const mutate y$16_@1[0:15] = Call mutate mutate$8_@1(mutate x$15_@1, mutate d$14_@1)
-  [8] If (read a$11_@0) then:bb1 else:bb1
+  [8] If (read a$11_@0) then:bb1 else:bb1 fallthrough=bb1
 bb1:
   predecessor blocks: bb0
-  [9] If (read b$12_@1) then:bb3 else:bb3
+  [9] If (read b$12_@1) then:bb3 else:bb3 fallthrough=bb3
 bb3:
   predecessor blocks: bb1
-  [10] If (read c$13_@2) then:bb5 else:bb5
+  [10] If (read c$13_@2) then:bb5 else:bb5 fallthrough=bb5
 bb5:
   predecessor blocks: bb3
-  [11] If (read d$14_@1) then:bb7 else:bb7
+  [11] If (read d$14_@1) then:bb7 else:bb7 fallthrough=bb7
 bb7:
   predecessor blocks: bb5
-  [12] If (read y$16_@1) then:bb9 else:bb9
+  [12] If (read y$16_@1) then:bb9 else:bb9 fallthrough=bb9
 bb9:
   predecessor blocks: bb7
   [13] Const mutate $17_@3 = null
@@ -148,32 +148,32 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const a$2 = {};
-  const b$3 = [a$2];
-  const c$4 = {};
-  const d$5 = {
-    c: c$4,
+function Component$0(props$10) {
+  const a$11 = {};
+  const b$12 = [a$11];
+  const c$13 = {};
+  const d$14 = {
+    c: c$13,
   };
-  const x$6 = {};
-  x$6.b = b$3;
-  const y$7 = mutate$8(x$6, d$5);
-  bb1: if (a$2) {
+  const x$15 = {};
+  x$15.b = b$12;
+  const y$16 = mutate$8(x$15, d$14);
+  bb1: if (a$11) {
   }
 
-  bb3: if (b$3) {
+  bb3: if (b$12) {
   }
 
-  bb5: if (c$4) {
+  bb5: if (c$13) {
   }
 
-  bb7: if (d$5) {
+  bb7: if (d$14) {
   }
 
-  bb9: if (y$7) {
+  bb9: if (y$16) {
   }
 
-  mutate$8(x$6, null);
+  mutate$8(x$15, null);
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/mutable-liverange-loop.expect.md b/compiler/forget/src/__tests__/fixtures/hir/mutable-liverange-loop.expect.md
index 63374ae199..58b79e8e30 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/mutable-liverange-loop.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/mutable-liverange-loop.expect.md
@@ -100,27 +100,27 @@ bb0:
 bb1:
   predecessor blocks: bb0 bb4
   [6] Const mutate $16_@2[6:8] = true
-  [7] If (read $16_@2) then:bb3 else:bb2
+  [7] If (read $16_@2) then:bb3 else:bb2 fallthrough=bb2
 bb3:
   predecessor blocks: bb1
   [8] Call mutate mutate$6_@0(mutate a$12_@0, mutate b$13_@0)
   [9] Const mutate $21_@0[0:18] = Call mutate cond$7_@0(mutate a$12_@0)
-  [10] If (read $21_@0) then:bb2 else:bb4
+  [10] If (read $21_@0) then:bb2 else:bb4 fallthrough=bb4
 bb4:
   predecessor blocks: bb3
   [11] Goto(Continue) bb1
 bb2:
   predecessor blocks: bb3 bb1
-  [12] If (read a$12_@0) then:bb7 else:bb7
+  [12] If (read a$12_@0) then:bb7 else:bb7 fallthrough=bb7
 bb7:
   predecessor blocks: bb2
-  [13] If (read b$13_@0) then:bb9 else:bb9
+  [13] If (read b$13_@0) then:bb9 else:bb9 fallthrough=bb9
 bb9:
   predecessor blocks: bb7
-  [14] If (read c$14_@1) then:bb11 else:bb11
+  [14] If (read c$14_@1) then:bb11 else:bb11 fallthrough=bb11
 bb11:
   predecessor blocks: bb9
-  [15] If (read d$15_@0) then:bb13 else:bb13
+  [15] If (read d$15_@0) then:bb13 else:bb13 fallthrough=bb13
 bb13:
   predecessor blocks: bb11
   [16] Const mutate $28_@3 = null
@@ -202,30 +202,30 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  let a$2 = {};
-  let b$3 = {};
-  let c$4 = {};
-  let d$5 = {};
+function Component$0(props$11) {
+  const a$12 = {};
+  const b$13 = {};
+  const c$14 = {};
+  const d$15 = {};
   bb2: while (true) {
-    mutate$6(a$2, b$3);
+    mutate$6(a$12, b$13);
 
-    bb4: if (cond$7(a$2)) break;
+    bb4: if (cond$7(a$12)) break;
   }
 
-  bb7: if (a$2) {
+  bb7: if (a$12) {
   }
 
-  bb9: if (b$3) {
+  bb9: if (b$13) {
   }
 
-  bb11: if (c$4) {
+  bb11: if (c$14) {
   }
 
-  bb13: if (d$5) {
+  bb13: if (d$15) {
   }
 
-  mutate$6(d$5, null);
+  mutate$6(d$15, null);
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-interleaved-by-terminal.expect.md b/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-interleaved-by-terminal.expect.md
index a1cb864a20..f78fcdc0a9 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-interleaved-by-terminal.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-interleaved-by-terminal.expect.md
@@ -21,7 +21,7 @@ function foo(a, b, c) {
 bb0:
   [1] Const mutate x$9_@0[1:6] = Array []
   [2] Const mutate y$10_@0[1:6] = Array []
-  [3] If (read x$9_@0) then:bb1 else:bb1
+  [3] If (read x$9_@0) then:bb1 else:bb1 fallthrough=bb1
 bb1:
   predecessor blocks: bb0
   [4] Call mutate y$10_@0.push(read a$6)
@@ -61,14 +61,14 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(a$1, b$2, c$3) {
-  const x$4 = [];
-  const y$5 = [];
-  bb1: if (x$4) {
+function foo$0(a$6, b$7, c$8) {
+  const x$9 = [];
+  const y$10 = [];
+  bb1: if (x$9) {
   }
 
-  y$5.push(a$1);
-  x$4.push(b$2);
+  y$10.push(a$6);
+  x$9.push(b$7);
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-interleaved.expect.md b/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-interleaved.expect.md
index 6803ea0884..97cc7a29ec 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-interleaved.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-interleaved.expect.md
@@ -47,11 +47,11 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(a$1, b$2) {
-  let x$3 = [];
-  let y$4 = [];
-  x$3.push(a$1);
-  y$4.push(b$2);
+function foo$0(a$5, b$6) {
+  const x$7 = [];
+  const y$8 = [];
+  x$7.push(a$5);
+  y$8.push(b$6);
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-shadowed.expect.md b/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-shadowed.expect.md
index 774fc10534..e31eebbaa1 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-shadowed.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-shadowed.expect.md
@@ -47,11 +47,11 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(a$1, b$2) {
-  let x$3 = [];
-  let y$4 = [];
-  y$4.push(b$2);
-  x$3.push(a$1);
+function foo$0(a$5, b$6) {
+  const x$7 = [];
+  const y$8 = [];
+  y$8.push(b$6);
+  x$7.push(a$5);
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-shadowing-within-block.expect.md b/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-shadowing-within-block.expect.md
index 78046cb56c..43f7316eb8 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-shadowing-within-block.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-shadowing-within-block.expect.md
@@ -22,11 +22,11 @@ function foo(a, b, c) {
 ```
 bb0:
   [1] Let mutate x$11_@0[1:11] = Array []
-  [2] If (read a$8) then:bb2 else:bb1
+  [2] If (read a$8) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [3] Let mutate y$12_@1[3:7] = Array []
-  [4] If (read b$9) then:bb4 else:bb3
+  [4] If (read b$9) then:bb4 else:bb3 fallthrough=bb3
 bb4:
   predecessor blocks: bb2
   [5] Call mutate y$12_@1.push(read c$10)
@@ -98,19 +98,19 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(a$1, b$2, c$3) {
-  let x$4 = [];
-  bb1: if (a$1) {
-    let y$5 = [];
+function foo$0(a$8, b$9, c$10) {
+  const x$11 = [];
+  bb1: if (a$8) {
+    const y$12 = [];
 
-    bb3: if (b$2) {
-      y$5.push(c$3);
+    bb3: if (b$9) {
+      y$12.push(c$10);
     }
 
-    x$4.push(<div>{y$5}</div>);
+    x$11.push(<div>{y$12}</div>);
   }
 
-  return x$4;
+  return x$11;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-while.expect.md b/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-while.expect.md
index 433734e79d..9bb61e3ccc 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-while.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-while.expect.md
@@ -22,7 +22,7 @@ bb0:
   [3] While test=bb1 loop=bb3 fallthrough=bb2
 bb1:
   predecessor blocks: bb0 bb3
-  [4] If (read c$8) then:bb3 else:bb2
+  [4] If (read c$8) then:bb3 else:bb2 fallthrough=bb2
 bb3:
   predecessor blocks: bb1
   [5] Call mutate y$10_@0.push(read b$7)
@@ -76,12 +76,12 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(a$1, b$2, c$3) {
-  let x$4 = [];
-  let y$5 = [];
-  bb2: while (c$3) {
-    y$5.push(b$2);
-    x$4.push(a$1);
+function foo$0(a$6, b$7, c$8) {
+  const x$9 = [];
+  const y$10 = [];
+  bb2: while (c$8) {
+    y$10.push(b$7);
+    x$9.push(a$6);
   }
 }
 
diff --git a/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-within-block.expect.md b/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-within-block.expect.md
index ab02513d1b..fdf3a1010d 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-within-block.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/overlapping-scopes-within-block.expect.md
@@ -22,11 +22,11 @@ function foo(a, b, c) {
 ```
 bb0:
   [1] Let mutate x$9_@0[1:9] = Array []
-  [2] If (read a$6) then:bb2 else:bb1
+  [2] If (read a$6) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [3] Let mutate y$10_@0[1:9] = Array []
-  [4] If (read b$7) then:bb4 else:bb3
+  [4] If (read b$7) then:bb4 else:bb3 fallthrough=bb3
 bb4:
   predecessor blocks: bb2
   [5] Call mutate y$10_@0.push(read c$8)
@@ -90,19 +90,19 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(a$1, b$2, c$3) {
-  let x$4 = [];
-  bb1: if (a$1) {
-    let y$5 = [];
+function foo$0(a$6, b$7, c$8) {
+  const x$9 = [];
+  bb1: if (a$6) {
+    const y$10 = [];
 
-    bb3: if (b$2) {
-      y$5.push(c$3);
+    bb3: if (b$7) {
+      y$10.push(c$8);
     }
 
-    x$4.push(y$5);
+    x$9.push(y$10);
   }
 
-  return x$4;
+  return x$9;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/property-assignment.expect.md b/compiler/forget/src/__tests__/fixtures/hir/property-assignment.expect.md
index 74ea0ae523..f410249c7e 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/property-assignment.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/property-assignment.expect.md
@@ -57,13 +57,13 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const x$2 = {};
-  const y$3 = [];
-  x$2.y = y$3;
-  const child$4 = <Component$0 data={y$3}></Component$0>;
-  x$2.y.push(props$1.p0);
-  return <Component$0 data={x$2}>{child$4}</Component$0>;
+function Component$0(props$6) {
+  const x$7 = {};
+  const y$8 = [];
+  x$7.y = y$8;
+  const child$9 = <Component$0 data={y$8}></Component$0>;
+  x$7.y.push(props$6.p0);
+  return <Component$0 data={x$7}>{child$9}</Component$0>;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/reactive-scope-grouping.expect.md b/compiler/forget/src/__tests__/fixtures/hir/reactive-scope-grouping.expect.md
index 8b413bb7ca..0b4516c790 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/reactive-scope-grouping.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/reactive-scope-grouping.expect.md
@@ -51,12 +51,12 @@ flowchart TB
 
 ```javascript
 function foo$0() {
-  let x$1 = {};
-  let y$2 = [];
-  let z$3 = {};
-  y$2.push(z$3);
-  x$1.y = y$2;
-  return x$1;
+  const x$4 = {};
+  const y$5 = [];
+  const z$6 = {};
+  y$5.push(z$6);
+  x$4.y = y$5;
+  return x$4;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/reactive-scopes.expect.md b/compiler/forget/src/__tests__/fixtures/hir/reactive-scopes.expect.md
index ef5a0a4dd9..6aa83da0dd 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/reactive-scopes.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/reactive-scopes.expect.md
@@ -22,10 +22,10 @@ bb0:
   [1] Let mutate x$10_@0[1:8] = Array []
   [2] Const mutate $11_@1 = 1
   [3] Const mutate $12_@2 = Binary read a$8.length === read $11_@1
-  [4] If (read $12_@2) then:bb2 else:bb1
+  [4] If (read $12_@2) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
-  [5] If (read b$9) then:bb4 else:bb1
+  [5] If (read b$9) then:bb4 else:bb1 fallthrough=bb1
 bb4:
   predecessor blocks: bb2
   [6] Call mutate x$10_@0.push(read b$9)
@@ -88,15 +88,15 @@ flowchart TB
 ## Code
 
 ```javascript
-function f$0(a$1, b$2) {
-  let x$3 = [];
-  bb1: if (a$1.length === 1) {
-    if (b$2) {
-      x$3.push(b$2);
+function f$0(a$8, b$9) {
+  const x$10 = [];
+  bb1: if (a$8.length === 1) {
+    if (b$9) {
+      x$10.push(b$9);
     }
   }
 
-  return <div>{x$3}</div>;
+  return <div>{x$10}</div>;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/reassignment-conditional.expect.md b/compiler/forget/src/__tests__/fixtures/hir/reassignment-conditional.expect.md
index 8c0260e471..fcefff2c63 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/reassignment-conditional.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/reassignment-conditional.expect.md
@@ -26,7 +26,7 @@ bb0:
   [1] Let mutate x$7_@0[1:7] = Array []
   [2] Call mutate x$7_@0.push(read props$6.p0)
   [3] Let mutate y$8_@0[1:7] = read x$7_@0
-  [4] If (read props$6.p1) then:bb2 else:bb1
+  [4] If (read props$6.p1) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [5] Reassign mutate x$9_@0[1:7] = Array []
@@ -88,18 +88,18 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  let x$2 = [];
-  x$2.push(props$1.p0);
-  let y$3 = x$2;
-  bb1: if (props$1.p1) {
-    x$2 = [];
+function Component$0(props$6) {
+  let x$7 = [];
+  x$7.push(props$6.p0);
+  const y$8 = x$7;
+  bb1: if (props$6.p1) {
+    x$7 = [];
   }
 
-  let _$4 = <Component$0 x={x$2}></Component$0>;
+  const _$12 = <Component$0 x={x$7}></Component$0>;
 
-  y$3.push(props$1.p2);
-  return <Component$0 x={x$2} y={y$3}></Component$0>;
+  y$8.push(props$6.p2);
+  return <Component$0 x={x$7} y={y$8}></Component$0>;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/reassignment-separate-scopes.expect.md b/compiler/forget/src/__tests__/fixtures/hir/reassignment-separate-scopes.expect.md
index d978caf4b8..c15bd7a239 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/reassignment-separate-scopes.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/reassignment-separate-scopes.expect.md
@@ -35,7 +35,7 @@ function foo(a, b, c) {
 ```
 bb0:
   [1] Let mutate x$16_@0[1:5] = Array []
-  [2] If (read a$13) then:bb2 else:bb1
+  [2] If (read a$13) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [3] Call mutate x$16_@0.push(read a$13)
@@ -48,6 +48,7 @@ bb1:
   [8] Switch (read b$14)
     Case read $20_@3: bb5
     Default: bb4
+    Fallthrough: bb3
 bb5:
   predecessor blocks: bb1
   [9] Reassign mutate x$22_@4[9:14] = Array []
@@ -150,31 +151,32 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(a$1, b$2, c$3) {
-  let x$4 = [];
-  bb1: if (a$1) {
-    x$4.push(a$1);
+function foo$0(a$13, b$14, c$15) {
+  const x$16 = [];
+  bb1: if (a$13) {
+    x$16.push(a$13);
   }
 
-  let y$5 = <div>{x$4}</div>;
+  const y$19 = <div>{x$16}</div>;
+  let x$22 = undefined;
 
-  bb3: switch (b$2) {
+  bb3: switch (b$14) {
     case 0: {
-      x$4 = [];
-      x$4.push(b$2);
+      x$22 = [];
+      x$22.push(b$14);
       break bb3;
     }
 
     default: {
-      x$4 = [];
-      x$4.push(c$3);
+      x$22 = [];
+      x$22.push(c$15);
     }
   }
 
   return (
     <div>
-      {y$5}
-      {x$4}
+      {y$19}
+      {x$22}
     </div>
   );
 }
diff --git a/compiler/forget/src/__tests__/fixtures/hir/reassignment.expect.md b/compiler/forget/src/__tests__/fixtures/hir/reassignment.expect.md
index 678e22ed47..2b5d7d45de 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/reassignment.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/reassignment.expect.md
@@ -66,15 +66,15 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  let x$2 = [];
-  x$2.push(props$1.p0);
-  let y$3 = x$2;
-  x$2 = [];
-  let _$4 = <Component$0 x={x$2}></Component$0>;
+function Component$0(props$6) {
+  const x$7 = [];
+  x$7.push(props$6.p0);
+  const y$8 = x$7;
+  const x$9 = [];
+  const _$10 = <Component$0 x={x$9}></Component$0>;
 
-  y$3.push(props$1.p1);
-  return <Component$0 x={x$2} y={y$3}></Component$0>;
+  y$8.push(props$6.p1);
+  return <Component$0 x={x$9} y={y$8}></Component$0>;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/reverse-postorder.expect.md b/compiler/forget/src/__tests__/fixtures/hir/reverse-postorder.expect.md
index 243ee6ce67..4133c31866 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/reverse-postorder.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/reverse-postorder.expect.md
@@ -37,7 +37,7 @@ function Component(props) {
 ```
 bb0:
   [1] Let mutate x$7_@0 = undefined
-  [2] If (read props$6.cond) then:bb2 else:bb10
+  [2] If (read props$6.cond) then:bb2 else:bb10 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [3] Const mutate $8_@1 = 2
@@ -48,6 +48,7 @@ bb2:
     Case read $9_@2: bb6
     Case read $8_@1: bb4
     Default: bb4
+    Fallthrough: bb1
 bb8:
   predecessor blocks: bb2
   [7] Reassign mutate x$11_@4[7:17] = read props$6.v0
@@ -62,7 +63,7 @@ bb4:
   [12] Goto bb1
 bb10:
   predecessor blocks: bb0
-  [13] If (read props$6.cond2) then:bb12 else:bb13
+  [13] If (read props$6.cond2) then:bb12 else:bb13 fallthrough=bb1
 bb12:
   predecessor blocks: bb10
   [14] Reassign mutate x$14_@4[7:17] = read props$6.b
@@ -167,17 +168,18 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  let x$2 = undefined;
-  bb1: if (props$1.cond) {
-    switch (props$1.test) {
+function Component$0(props$6) {
+  const x$7 = undefined;
+  let x$11 = undefined;
+  bb1: if (props$6.cond) {
+    switch (props$6.test) {
       case 0: {
-        x$2 = props$1.v0;
+        x$11 = props$6.v0;
         break bb1;
       }
 
       case 1: {
-        x$2 = props$1.v1;
+        x$11 = props$6.v1;
         break bb1;
       }
 
@@ -185,18 +187,18 @@ function Component$0(props$1) {
       }
 
       default: {
-        x$2 = props$1.v2;
+        x$11 = props$6.v2;
       }
     }
   } else {
-    if (props$1.cond2) {
-      x$2 = props$1.b;
+    if (props$6.cond2) {
+      x$11 = props$6.b;
     } else {
-      x$2 = props$1.c;
+      x$11 = props$6.c;
     }
   }
 
-  x$2;
+  x$11;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/simple-alias.expect.md b/compiler/forget/src/__tests__/fixtures/hir/simple-alias.expect.md
index 907b8254f9..f2ad814ebd 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/simple-alias.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/simple-alias.expect.md
@@ -84,14 +84,14 @@ flowchart TB
 
 ```javascript
 function foo$0() {
-  let a$1 = {};
-  let b$2 = {};
-  let c$3 = {};
-  a$1 = b$2;
-  b$2 = c$3;
-  c$3 = a$1;
-  mutate$4(a$1, b$2);
-  return c$3;
+  const a$5 = {};
+  const b$6 = {};
+  const c$7 = {};
+  const a$8 = b$6;
+  const b$9 = c$7;
+  const c$10 = a$8;
+  mutate$4(a$8, b$9);
+  return c$10;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/simple.expect.md b/compiler/forget/src/__tests__/fixtures/hir/simple.expect.md
index d925fc326d..3d6174d171 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/simple.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/simple.expect.md
@@ -15,7 +15,7 @@ function foo(x, y) {
 
 ```
 bb0:
-  [1] If (read x$8) then:bb2 else:bb1
+  [1] If (read x$8) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [2] Const mutate $10_@0 = false
@@ -71,11 +71,11 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(x$1, y$2) {
-  bb1: if (x$1) {
-    return foo$0(false, y$2);
+function foo$0(x$8, y$9) {
+  bb1: if (x$8) {
+    return foo$0(false, y$9);
   }
-  return [y$2 * 10];
+  return [y$9 * 10];
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-arrayexpression.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-arrayexpression.expect.md
index f78d6502e2..899cbf7728 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-arrayexpression.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-arrayexpression.expect.md
@@ -45,11 +45,11 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const a$2 = 1;
-  const b$3 = 2;
-  const x$4 = [a$2, b$3];
-  return x$4;
+function Component$0(props$5) {
+  const a$6 = 1;
+  const b$7 = 2;
+  const x$8 = [a$6, b$7];
+  return x$8;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-call-jsx-2.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-call-jsx-2.expect.md
index 4c325410d3..1112def4d9 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-call-jsx-2.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-call-jsx-2.expect.md
@@ -53,7 +53,7 @@ bb0:
   [2] Const mutate b$12_@0[0:10] = Object {  }
   [3] Call mutate foo$4_@0(mutate a$11_@0, mutate b$12_@0)
   [4] Const mutate $13_@0[0:10] = Call mutate foo$4_@0()
-  [5] If (read $13_@0) then:bb2 else:bb1
+  [5] If (read $13_@0) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [6] Const mutate $14_@1 = "div"
@@ -113,16 +113,16 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const a$2 = [];
-  const b$3 = {};
-  foo$4(a$2, b$3);
+function Component$0(props$10) {
+  const a$11 = [];
+  const b$12 = {};
+  foo$4(a$11, b$12);
   bb1: if (foo$4()) {
-    let _$5 = <div a={a$2}></div>;
+    const _$15 = <div a={a$11}></div>;
   }
 
-  foo$4(a$2, b$3);
-  return <div a={a$2} b={b$3}></div>;
+  foo$4(a$11, b$12);
+  return <div a={a$11} b={b$12}></div>;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-call-jsx.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-call-jsx.expect.md
index 33937f5de1..002fba21e2 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-call-jsx.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-call-jsx.expect.md
@@ -89,14 +89,14 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const a$2 = [];
-  const b$3 = {};
-  foo$4(a$2, b$3);
-  let _$5 = <div a={a$2}></div>;
+function Component$0(props$9) {
+  const a$10 = [];
+  const b$11 = {};
+  foo$4(a$10, b$11);
+  const _$13 = <div a={a$10}></div>;
 
-  foo$4(a$2, b$3);
-  return <div a={a$2} b={b$3}></div>;
+  foo$4(a$10, b$11);
+  return <div a={a$10} b={b$11}></div>;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-complex-multiple-if.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-complex-multiple-if.expect.md
index 0b4da48098..9a5d73f716 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-complex-multiple-if.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-complex-multiple-if.expect.md
@@ -25,7 +25,7 @@ bb0:
   [2] Let mutate y$8_@1 = 2
   [3] Const mutate $9_@2 = 2
   [4] Const mutate $10_@3 = Binary read y$8_@1 === read $9_@2
-  [5] If (read $10_@3) then:bb2 else:bb1
+  [5] If (read $10_@3) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [6] Reassign mutate x$11_@0[1:14] = 3
@@ -35,7 +35,7 @@ bb1:
   x$17_@0[1:14]: phi(bb2: x$11_@0, bb0: x$7_@0)
   [8] Const mutate $12_@4 = 3
   [9] Const mutate $14_@5 = Binary read y$8_@1 === read $12_@4
-  [10] If (read $14_@5) then:bb4 else:bb3
+  [10] If (read $14_@5) then:bb4 else:bb3 fallthrough=bb3
 bb4:
   predecessor blocks: bb1
   [11] Reassign mutate x$15_@0[1:14] = 5
@@ -107,17 +107,19 @@ flowchart TB
 
 ```javascript
 function foo$0() {
-  let x$1 = 1;
-  let y$2 = 2;
-  bb1: if (y$2 === 2) {
-    x$1 = 3;
+  let x$7 = 1;
+  const y$8 = 2;
+  bb1: if (y$8 === 2) {
+    x$7 = 3;
   }
 
-  bb3: if (y$2 === 3) {
-    x$1 = 5;
+  let x$15 = undefined;
+
+  bb3: if (y$8 === 3) {
+    x$15 = 5;
   }
 
-  y$2 = x$1;
+  const y$18 = x$15;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-complex-single-if.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-complex-single-if.expect.md
index f6e9d49f66..8f2d5e5db9 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-complex-single-if.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-complex-single-if.expect.md
@@ -22,7 +22,7 @@ bb0:
   [2] Let mutate y$6_@1 = 2
   [3] Const mutate $7_@2 = 2
   [4] Const mutate $8_@3 = Binary read y$6_@1 === read $7_@2
-  [5] If (read $8_@3) then:bb2 else:bb1
+  [5] If (read $8_@3) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [6] Reassign mutate x$9_@0[1:9] = 3
@@ -75,13 +75,13 @@ flowchart TB
 
 ```javascript
 function foo$0() {
-  let x$1 = 1;
-  let y$2 = 2;
-  bb1: if (y$2 === 2) {
-    x$1 = 3;
+  let x$5 = 1;
+  const y$6 = 2;
+  bb1: if (y$6 === 2) {
+    x$5 = 3;
   }
 
-  y$2 = x$1;
+  const y$11 = x$5;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-for-of.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-for-of.expect.md
index cca1c44dbb..7aafc6d070 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-for-of.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-for-of.expect.md
@@ -23,11 +23,11 @@ bb0:
   [2] Goto bb1
 bb1:
   predecessor blocks: bb0 bb4
-  [3] If (read items$5_@0) then:bb3 else:bb2
+  [3] If (read items$5_@0) then:bb3 else:bb2 fallthrough=bb2
 bb3:
   predecessor blocks: bb1
   [4] Let mutate y$7_@1 = 0
-  [5] If (read cond$4) then:bb5 else:bb4
+  [5] If (read cond$4) then:bb5 else:bb4 fallthrough=bb4
 bb5:
   predecessor blocks: bb3
   [6] Reassign mutate y$9_@2 = 1
@@ -88,8 +88,8 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(cond$1) {
-  let items$2 = [];
+function foo$0(cond$4) {
+  const items$5 = [];
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-for.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-for.expect.md
index ca49eecaa4..6572b52fbd 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-for.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-for.expect.md
@@ -27,7 +27,7 @@ bb1:
   x$13_@0[0:13]: phi(bb3: x$7_@0, bb4: x$14_@0)
   [5] Const mutate $9_@2 = 10
   [6] Const mutate $11_@3[6:8] = Binary read i$8_@1 < read $9_@2
-  [7] If (read $11_@3) then:bb5 else:bb2
+  [7] If (read $11_@3) then:bb5 else:bb2 fallthrough=bb2
 bb5:
   predecessor blocks: bb1
   [8] Const mutate $12_@4 = 1
@@ -103,12 +103,12 @@ flowchart TB
 
 ```javascript
 function foo$0() {
-  let x$1 = 1;
-  bb2: for (let i$2 = 0; i$2 < 10; update$3()) {
-    x$1 = x$1 + 1;
+  let x$7 = 1;
+  bb2: for (const i$8 = 0; i$8 < 10; update$3()) {
+    x$7 = x$7 + 1;
   }
 
-  return x$1;
+  return x$7;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-if-else.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-if-else.expect.md
index 97a31f325a..cc530e4c59 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-if-else.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-if-else.expect.md
@@ -21,7 +21,7 @@ function foo() {
 bb0:
   [1] Let mutate x$5_@0 = 1
   [2] Let mutate y$6_@1 = 2
-  [3] If (read y$6_@1) then:bb2 else:bb3
+  [3] If (read y$6_@1) then:bb2 else:bb3 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [4] Let mutate z$7_@2 = Binary read x$5_@0 + read y$6_@1
@@ -81,12 +81,12 @@ flowchart TB
 
 ```javascript
 function foo$0() {
-  let x$1 = 1;
-  let y$2 = 2;
-  bb1: if (y$2) {
-    let z$3 = x$1 + y$2;
+  const x$5 = 1;
+  const y$6 = 2;
+  bb1: if (y$6) {
+    const z$7 = x$5 + y$6;
   } else {
-    let z$4 = x$1;
+    const z$8 = x$5;
   }
 }
 
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-multiple-phis.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-multiple-phis.expect.md
new file mode 100644
index 0000000000..9cc8ded1f7
--- /dev/null
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-multiple-phis.expect.md
@@ -0,0 +1,195 @@
+
+## Input
+
+```javascript
+function foo(a, b, c, d) {
+  let x = 0;
+  if (true) {
+    if (true) {
+      x = a;
+    } else {
+      x = b;
+    }
+    x;
+  } else {
+    if (true) {
+      x = c;
+    } else {
+      x = d;
+    }
+    x;
+  }
+  x;
+}
+
+```
+
+## HIR
+
+```
+bb0:
+  [1] Let mutate x$13_@0 = 0
+  [2] Const mutate $14_@1 = true
+  [3] If (read $14_@1) then:bb2 else:bb6 fallthrough=bb1
+bb2:
+  predecessor blocks: bb0
+  [4] Const mutate $15_@2 = true
+  [5] If (read $15_@2) then:bb4 else:bb5 fallthrough=bb3
+bb4:
+  predecessor blocks: bb2
+  [6] Reassign mutate x$16_@3[6:17] = read a$9
+  [7] Goto bb3
+bb5:
+  predecessor blocks: bb2
+  [8] Reassign mutate x$17_@3[6:17] = read b$10
+  [9] Goto bb3
+bb3:
+  predecessor blocks: bb4 bb5
+  x$18_@3[6:17]: phi(bb4: x$16_@3, bb5: x$17_@3)
+  [10] read x$18_@3
+  [11] Goto bb1
+bb6:
+  predecessor blocks: bb0
+  [12] Const mutate $19_@4 = true
+  [13] If (read $19_@4) then:bb8 else:bb9 fallthrough=bb7
+bb8:
+  predecessor blocks: bb6
+  [14] Reassign mutate x$20_@3[6:17] = read c$11
+  [15] Goto bb7
+bb9:
+  predecessor blocks: bb6
+  [16] Reassign mutate x$21_@3[6:17] = read d$12
+  [17] Goto bb7
+bb7:
+  predecessor blocks: bb8 bb9
+  x$22_@3[6:17]: phi(bb8: x$20_@3, bb9: x$21_@3)
+  [18] read x$22_@3
+  [19] Goto bb1
+bb1:
+  predecessor blocks: bb3 bb7
+  x$23_@3[6:17]: phi(bb3: x$18_@3, bb7: x$22_@3)
+  [20] read x$23_@3
+  [21] Return
+scope3 [6:17]:
+ - read a$9
+ - read b$10
+ - read $15_@2
+ - read c$11
+ - read d$12
+```
+
+### CFG
+
+```mermaid
+flowchart TB
+  %% Basic Blocks
+  subgraph bb0
+    bb0_instrs["
+      [1] Let mutate x$13_@0 = 0
+      [2] Const mutate $14_@1 = true
+    "]
+    bb0_instrs --> bb0_terminal(["If (read $14_@1)"])
+  end
+  subgraph bb2
+    bb2_instrs["
+      [4] Const mutate $15_@2 = true
+    "]
+    bb2_instrs --> bb2_terminal(["If (read $15_@2)"])
+  end
+  subgraph bb4
+    bb4_instrs["
+      [6] Reassign mutate x$16_@3[6:17] = read a$9
+    "]
+    bb4_instrs --> bb4_terminal(["Goto"])
+  end
+  subgraph bb5
+    bb5_instrs["
+      [8] Reassign mutate x$17_@3[6:17] = read b$10
+    "]
+    bb5_instrs --> bb5_terminal(["Goto"])
+  end
+  subgraph bb3
+    bb3_instrs["
+      [10] read x$18_@3
+    "]
+    bb3_instrs --> bb3_terminal(["Goto"])
+  end
+  subgraph bb6
+    bb6_instrs["
+      [12] Const mutate $19_@4 = true
+    "]
+    bb6_instrs --> bb6_terminal(["If (read $19_@4)"])
+  end
+  subgraph bb8
+    bb8_instrs["
+      [14] Reassign mutate x$20_@3[6:17] = read c$11
+    "]
+    bb8_instrs --> bb8_terminal(["Goto"])
+  end
+  subgraph bb9
+    bb9_instrs["
+      [16] Reassign mutate x$21_@3[6:17] = read d$12
+    "]
+    bb9_instrs --> bb9_terminal(["Goto"])
+  end
+  subgraph bb7
+    bb7_instrs["
+      [18] read x$22_@3
+    "]
+    bb7_instrs --> bb7_terminal(["Goto"])
+  end
+  subgraph bb1
+    bb1_instrs["
+      [20] read x$23_@3
+    "]
+    bb1_instrs --> bb1_terminal(["Return"])
+  end
+
+  %% Jumps
+  bb0_terminal -- "then" --> bb2
+  bb0_terminal -- "else" --> bb6
+  bb0_terminal -- "fallthrough" --> bb1
+  bb2_terminal -- "then" --> bb4
+  bb2_terminal -- "else" --> bb5
+  bb2_terminal -- "fallthrough" --> bb3
+  bb4_terminal --> bb3
+  bb5_terminal --> bb3
+  bb3_terminal --> bb1
+  bb6_terminal -- "then" --> bb8
+  bb6_terminal -- "else" --> bb9
+  bb6_terminal -- "fallthrough" --> bb7
+  bb8_terminal --> bb7
+  bb9_terminal --> bb7
+  bb7_terminal --> bb1
+
+```
+
+## Code
+
+```javascript
+function foo$0(a$9, b$10, c$11, d$12) {
+  const x$13 = 0;
+  let x$18 = undefined;
+  bb1: if (true) {
+    bb3: if (true) {
+      x$18 = a$9;
+    } else {
+      x$18 = b$10;
+    }
+
+    x$18;
+  } else {
+    bb7: if (true) {
+      x$18 = c$11;
+    } else {
+      x$18 = d$12;
+    }
+
+    x$18;
+  }
+
+  x$18;
+}
+
+```
+      
\ No newline at end of file
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-multiple-phis.js b/compiler/forget/src/__tests__/fixtures/hir/ssa-multiple-phis.js
new file mode 100644
index 0000000000..03ad0b030e
--- /dev/null
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-multiple-phis.js
@@ -0,0 +1,19 @@
+function foo(a, b, c, d) {
+  let x = 0;
+  if (true) {
+    if (true) {
+      x = a;
+    } else {
+      x = b;
+    }
+    x;
+  } else {
+    if (true) {
+      x = c;
+    } else {
+      x = d;
+    }
+    x;
+  }
+  x;
+}
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-nested-loops-no-reassign.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-nested-loops-no-reassign.expect.md
index ad442592f1..e0f0d190f6 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-nested-loops-no-reassign.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-nested-loops-no-reassign.expect.md
@@ -25,19 +25,19 @@ bb0:
   [2] While test=bb1 loop=bb3 fallthrough=bb2
 bb1:
   predecessor blocks: bb0 bb5
-  [3] If (read a$6) then:bb3 else:bb2
+  [3] If (read a$6) then:bb3 else:bb2 fallthrough=bb2
 bb3:
   predecessor blocks: bb1
   [4] While test=bb4 loop=bb6 fallthrough=bb5
 bb4:
   predecessor blocks: bb3 bb8
-  [5] If (read b$7) then:bb6 else:bb5
+  [5] If (read b$7) then:bb6 else:bb5 fallthrough=bb5
 bb6:
   predecessor blocks: bb4
   [6] While test=bb7 loop=bb9 fallthrough=bb8
 bb7:
   predecessor blocks: bb6 bb9
-  [7] If (read c$8) then:bb9 else:bb8
+  [7] If (read c$8) then:bb9 else:bb8 fallthrough=bb8
 bb9:
   predecessor blocks: bb7
   [8] Const mutate $13_@1 = 1
@@ -124,17 +124,17 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(a$1, b$2, c$3) {
-  let x$4 = 0;
-  bb2: while (a$1) {
-    bb5: while (b$2) {
-      bb8: while (c$3) {
-        x$4 + 1;
+function foo$0(a$6, b$7, c$8) {
+  const x$9 = 0;
+  bb2: while (a$6) {
+    bb5: while (b$7) {
+      bb8: while (c$8) {
+        x$9 + 1;
       }
     }
   }
 
-  return x$4;
+  return x$9;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-nested-partial-reassignment.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-nested-partial-reassignment.expect.md
new file mode 100644
index 0000000000..69b0c972f1
--- /dev/null
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-nested-partial-reassignment.expect.md
@@ -0,0 +1,105 @@
+
+## Input
+
+```javascript
+function foo(a, b, c, d, e) {
+  let x = null;
+  if (a) {
+    x = b;
+  } else {
+    if (c) {
+      x = d;
+    }
+  }
+  return x;
+}
+
+```
+
+## HIR
+
+```
+bb0:
+  [1] Let mutate x$12_@0[1:8] = null
+  [2] If (read a$7) then:bb2 else:bb3 fallthrough=bb1
+bb2:
+  predecessor blocks: bb0
+  [3] Reassign mutate x$13_@0[1:8] = read b$8
+  [4] Goto bb1
+bb3:
+  predecessor blocks: bb0
+  [5] If (read c$9) then:bb5 else:bb1 fallthrough=bb1
+bb5:
+  predecessor blocks: bb3
+  [6] Reassign mutate x$14_@0[1:8] = read d$10
+  [7] Goto bb1
+bb1:
+  predecessor blocks: bb2 bb5 bb3
+  x$15_@0[1:8]: phi(bb2: x$13_@0, bb5: x$14_@0, bb3: x$12_@0)
+  [8] Return read x$15_@0
+scope0 [1:8]:
+ - read b$8
+ - read d$10
+ - read c$9
+ - read a$7
+```
+
+### CFG
+
+```mermaid
+flowchart TB
+  %% Basic Blocks
+  subgraph bb0
+    bb0_instrs["
+      [1] Let mutate x$12_@0[1:8] = null
+    "]
+    bb0_instrs --> bb0_terminal(["If (read a$7)"])
+  end
+  subgraph bb2
+    bb2_instrs["
+      [3] Reassign mutate x$13_@0[1:8] = read b$8
+    "]
+    bb2_instrs --> bb2_terminal(["Goto"])
+  end
+  subgraph bb3
+    bb3_terminal(["If (read c$9)"])
+  end
+  subgraph bb5
+    bb5_instrs["
+      [6] Reassign mutate x$14_@0[1:8] = read d$10
+    "]
+    bb5_instrs --> bb5_terminal(["Goto"])
+  end
+  subgraph bb1
+    bb1_terminal(["Return read x$15_@0"])
+  end
+
+  %% Jumps
+  bb0_terminal -- "then" --> bb2
+  bb0_terminal -- "else" --> bb3
+  bb0_terminal -- "fallthrough" --> bb1
+  bb2_terminal --> bb1
+  bb3_terminal -- "then" --> bb5
+  bb3_terminal -- "else" --> bb1
+  bb5_terminal --> bb1
+
+```
+
+## Code
+
+```javascript
+function foo$0(a$7, b$8, c$9, d$10, e$11) {
+  let x$12 = null;
+  bb1: if (a$7) {
+    x$12 = b$8;
+  } else {
+    if (c$9) {
+      x$12 = d$10;
+    }
+  }
+
+  return x$12;
+}
+
+```
+      
\ No newline at end of file
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-nested-partial-reassignment.js b/compiler/forget/src/__tests__/fixtures/hir/ssa-nested-partial-reassignment.js
new file mode 100644
index 0000000000..00574a537c
--- /dev/null
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-nested-partial-reassignment.js
@@ -0,0 +1,11 @@
+function foo(a, b, c, d, e) {
+  let x = null;
+  if (a) {
+    x = b;
+  } else {
+    if (c) {
+      x = d;
+    }
+  }
+  return x;
+}
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-newexpression.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-newexpression.expect.md
index 48104c33af..c9bdd07aad 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-newexpression.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-newexpression.expect.md
@@ -72,11 +72,11 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const a$2 = [];
-  const b$3 = {};
-  let c$4 = new Foo$5(a$2, b$3);
-  return c$4;
+function Component$0(props$6) {
+  const a$7 = [];
+  const b$8 = {};
+  const c$9 = new Foo$5(a$7, b$8);
+  return c$9;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-objectexpression-phi.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-objectexpression-phi.expect.md
index 4d3e698300..65082830ad 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-objectexpression-phi.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-objectexpression-phi.expect.md
@@ -26,7 +26,7 @@ bb0:
   [2] Let mutate y$7_@0[1:10] = 2
   [3] Const mutate $8_@2 = 1
   [4] Const mutate $9_@3 = Binary read x$6_@0 > read $8_@2
-  [5] If (read $9_@3) then:bb2 else:bb3
+  [5] If (read $9_@3) then:bb2 else:bb3 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [6] Reassign mutate x$10_@0[1:10] = 2
@@ -91,19 +91,19 @@ flowchart TB
 
 ```javascript
 function foo$0() {
-  let x$1 = 1;
-  let y$2 = 2;
-  bb1: if (x$1 > 1) {
-    x$1 = 2;
+  let x$6 = 1;
+  let y$7 = 2;
+  bb1: if (x$6 > 1) {
+    x$6 = 2;
   } else {
-    y$2 = 3;
+    y$7 = 3;
   }
 
-  let t$5 = {
-    x: x$1,
-    y: y$2,
+  const t$14 = {
+    x: x$6,
+    y: y$7,
   };
-  return t$5;
+  return t$14;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-objectexpression.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-objectexpression.expect.md
index 69f7933223..4bc5e82a50 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-objectexpression.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-objectexpression.expect.md
@@ -45,14 +45,14 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  const a$2 = 1;
-  const b$3 = 2;
-  const x$4 = {
-    a: a$2,
-    b: b$3,
+function Component$0(props$5) {
+  const a$6 = 1;
+  const b$7 = 2;
+  const x$8 = {
+    a: a$6,
+    b: b$7,
   };
-  return x$4;
+  return x$8;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-property-call.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-property-call.expect.md
index dfc1a42c1b..342e1cbe70 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-property-call.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-property-call.expect.md
@@ -47,12 +47,12 @@ flowchart TB
 
 ```javascript
 function foo$0() {
-  const x$1 = [];
-  const y$2 = {
-    x: x$1,
+  const x$4 = [];
+  const y$5 = {
+    x: x$4,
   };
-  y$2.x.push([]);
-  return y$2;
+  y$5.x.push([]);
+  return y$5;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-property.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-property.expect.md
index f9e4208798..6a2845e3ef 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-property.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-property.expect.md
@@ -44,10 +44,10 @@ flowchart TB
 
 ```javascript
 function foo$0() {
-  const x$1 = [];
-  const y$2 = {};
-  y$2.x = x$1;
-  return y$2;
+  const x$3 = [];
+  const y$4 = {};
+  y$4.x = x$3;
+  return y$4;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-reassign.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-reassign.expect.md
new file mode 100644
index 0000000000..e5c957e562
--- /dev/null
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-reassign.expect.md
@@ -0,0 +1,63 @@
+
+## Input
+
+```javascript
+function foo(a, b, c) {
+  let x = 0;
+  x = a;
+  x = b;
+  x = c;
+  return x;
+}
+
+```
+
+## HIR
+
+```
+bb0:
+  [1] Let mutate x$8_@0 = 0
+  [2] Reassign mutate x$9_@1 = read a$5
+  [3] Reassign mutate x$10_@2 = read b$6
+  [4] Reassign mutate x$11_@3 = read c$7
+  [5] Return read x$11_@3
+scope1 [2:3]:
+ - read a$5
+scope2 [3:4]:
+ - read b$6
+scope3 [4:5]:
+ - read c$7
+```
+
+### CFG
+
+```mermaid
+flowchart TB
+  %% Basic Blocks
+  subgraph bb0
+    bb0_instrs["
+      [1] Let mutate x$8_@0 = 0
+      [2] Reassign mutate x$9_@1 = read a$5
+      [3] Reassign mutate x$10_@2 = read b$6
+      [4] Reassign mutate x$11_@3 = read c$7
+    "]
+    bb0_instrs --> bb0_terminal(["Return read x$11_@3"])
+  end
+
+  %% Jumps
+  %% empty
+```
+
+## Code
+
+```javascript
+function foo$0(a$5, b$6, c$7) {
+  const x$8 = 0;
+  const x$9 = a$5;
+  const x$10 = b$6;
+  const x$11 = c$7;
+  return x$11;
+}
+
+```
+      
\ No newline at end of file
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-reassign.js b/compiler/forget/src/__tests__/fixtures/hir/ssa-reassign.js
new file mode 100644
index 0000000000..ea96f4a745
--- /dev/null
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-reassign.js
@@ -0,0 +1,7 @@
+function foo(a, b, c) {
+  let x = 0;
+  x = a;
+  x = b;
+  x = c;
+  return x;
+}
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-return.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-return.expect.md
index a9ec87d3b5..33be65cfc8 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-return.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-return.expect.md
@@ -20,7 +20,7 @@ bb0:
   [1] Let mutate x$4_@0[1:7] = 1
   [2] Const mutate $5_@1 = 1
   [3] Const mutate $6_@2 = Binary read x$4_@0 === read $5_@1
-  [4] If (read $6_@2) then:bb2 else:bb1
+  [4] If (read $6_@2) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [5] Reassign mutate x$7_@0[1:7] = 2
@@ -67,12 +67,12 @@ flowchart TB
 
 ```javascript
 function foo$0() {
-  let x$1 = 1;
-  bb1: if (x$1 === 1) {
-    x$1 = 2;
+  let x$4 = 1;
+  bb1: if (x$4 === 1) {
+    x$4 = 2;
   }
 
-  return x$1;
+  return x$4;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-shadowing.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-shadowing.expect.md
index 455c1f41c0..3e6d8ad457 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-shadowing.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-shadowing.expect.md
@@ -49,7 +49,7 @@ function log$0() {}
 ```
 bb0:
   [1] Let mutate str$6_@0[1:8] = ""
-  [2] If (read cond$5) then:bb2 else:bb3
+  [2] If (read cond$5) then:bb2 else:bb3 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [3] Let mutate str$7_@1 = "other test"
@@ -110,16 +110,16 @@ flowchart TB
 ## Code
 
 ```javascript
-function Foo$0(cond$1) {
-  let str$2 = "";
-  bb1: if (cond$1) {
-    let str$3 = "other test";
-    log$4(str$3);
+function Foo$0(cond$5) {
+  let str$6 = "";
+  bb1: if (cond$5) {
+    const str$7 = "other test";
+    log$4(str$7);
   } else {
-    str$2 = "fallthrough test";
+    str$6 = "fallthrough test";
   }
 
-  log$4(str$2);
+  log$4(str$6);
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-sibling-phis.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-sibling-phis.expect.md
new file mode 100644
index 0000000000..4b02019526
--- /dev/null
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-sibling-phis.expect.md
@@ -0,0 +1,191 @@
+
+## Input
+
+```javascript
+function foo(a, b, c, d) {
+  let x = 0;
+  if (true) {
+    if (true) {
+      x = a;
+    } else {
+      x = b;
+    }
+    x;
+  } else {
+    if (true) {
+      x = c;
+    } else {
+      x = d;
+    }
+    x;
+  }
+  // note: intentionally no phi here so that there are two distinct phis above
+}
+
+```
+
+## HIR
+
+```
+bb0:
+  [1] Let mutate x$13_@0 = 0
+  [2] Const mutate $14_@1 = true
+  [3] If (read $14_@1) then:bb2 else:bb6 fallthrough=bb1
+bb2:
+  predecessor blocks: bb0
+  [4] Const mutate $15_@2 = true
+  [5] If (read $15_@2) then:bb4 else:bb5 fallthrough=bb3
+bb4:
+  predecessor blocks: bb2
+  [6] Reassign mutate x$16_@3[6:9] = read a$9
+  [7] Goto bb3
+bb5:
+  predecessor blocks: bb2
+  [8] Reassign mutate x$17_@3[6:9] = read b$10
+  [9] Goto bb3
+bb3:
+  predecessor blocks: bb4 bb5
+  x$18_@3[6:9]: phi(bb4: x$16_@3, bb5: x$17_@3)
+  [10] read x$18_@3
+  [11] Goto bb1
+bb6:
+  predecessor blocks: bb0
+  [12] Const mutate $19_@4 = true
+  [13] If (read $19_@4) then:bb8 else:bb9 fallthrough=bb7
+bb8:
+  predecessor blocks: bb6
+  [14] Reassign mutate x$20_@5[14:17] = read c$11
+  [15] Goto bb7
+bb9:
+  predecessor blocks: bb6
+  [16] Reassign mutate x$21_@5[14:17] = read d$12
+  [17] Goto bb7
+bb7:
+  predecessor blocks: bb8 bb9
+  x$22_@5[14:17]: phi(bb8: x$20_@5, bb9: x$21_@5)
+  [18] read x$22_@5
+  [19] Goto bb1
+bb1:
+  predecessor blocks: bb3 bb7
+  [20] Return
+scope3 [6:9]:
+ - read a$9
+ - read b$10
+scope5 [14:17]:
+ - read c$11
+ - read d$12
+```
+
+### CFG
+
+```mermaid
+flowchart TB
+  %% Basic Blocks
+  subgraph bb0
+    bb0_instrs["
+      [1] Let mutate x$13_@0 = 0
+      [2] Const mutate $14_@1 = true
+    "]
+    bb0_instrs --> bb0_terminal(["If (read $14_@1)"])
+  end
+  subgraph bb2
+    bb2_instrs["
+      [4] Const mutate $15_@2 = true
+    "]
+    bb2_instrs --> bb2_terminal(["If (read $15_@2)"])
+  end
+  subgraph bb4
+    bb4_instrs["
+      [6] Reassign mutate x$16_@3[6:9] = read a$9
+    "]
+    bb4_instrs --> bb4_terminal(["Goto"])
+  end
+  subgraph bb5
+    bb5_instrs["
+      [8] Reassign mutate x$17_@3[6:9] = read b$10
+    "]
+    bb5_instrs --> bb5_terminal(["Goto"])
+  end
+  subgraph bb3
+    bb3_instrs["
+      [10] read x$18_@3
+    "]
+    bb3_instrs --> bb3_terminal(["Goto"])
+  end
+  subgraph bb6
+    bb6_instrs["
+      [12] Const mutate $19_@4 = true
+    "]
+    bb6_instrs --> bb6_terminal(["If (read $19_@4)"])
+  end
+  subgraph bb8
+    bb8_instrs["
+      [14] Reassign mutate x$20_@5[14:17] = read c$11
+    "]
+    bb8_instrs --> bb8_terminal(["Goto"])
+  end
+  subgraph bb9
+    bb9_instrs["
+      [16] Reassign mutate x$21_@5[14:17] = read d$12
+    "]
+    bb9_instrs --> bb9_terminal(["Goto"])
+  end
+  subgraph bb7
+    bb7_instrs["
+      [18] read x$22_@5
+    "]
+    bb7_instrs --> bb7_terminal(["Goto"])
+  end
+  subgraph bb1
+    bb1_terminal(["Return"])
+  end
+
+  %% Jumps
+  bb0_terminal -- "then" --> bb2
+  bb0_terminal -- "else" --> bb6
+  bb0_terminal -- "fallthrough" --> bb1
+  bb2_terminal -- "then" --> bb4
+  bb2_terminal -- "else" --> bb5
+  bb2_terminal -- "fallthrough" --> bb3
+  bb4_terminal --> bb3
+  bb5_terminal --> bb3
+  bb3_terminal --> bb1
+  bb6_terminal -- "then" --> bb8
+  bb6_terminal -- "else" --> bb9
+  bb6_terminal -- "fallthrough" --> bb7
+  bb8_terminal --> bb7
+  bb9_terminal --> bb7
+  bb7_terminal --> bb1
+
+```
+
+## Code
+
+```javascript
+function foo$0(a$9, b$10, c$11, d$12) {
+  const x$13 = 0;
+  bb1: if (true) {
+    let x$16 = undefined;
+
+    bb3: if (true) {
+      x$16 = a$9;
+    } else {
+      x$16 = b$10;
+    }
+
+    x$16;
+  } else {
+    let x$20 = undefined;
+
+    bb7: if (true) {
+      x$20 = c$11;
+    } else {
+      x$20 = d$12;
+    }
+
+    x$20;
+  }
+}
+
+```
+      
\ No newline at end of file
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-sibling-phis.js b/compiler/forget/src/__tests__/fixtures/hir/ssa-sibling-phis.js
new file mode 100644
index 0000000000..72d80d0ad1
--- /dev/null
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-sibling-phis.js
@@ -0,0 +1,19 @@
+function foo(a, b, c, d) {
+  let x = 0;
+  if (true) {
+    if (true) {
+      x = a;
+    } else {
+      x = b;
+    }
+    x;
+  } else {
+    if (true) {
+      x = c;
+    } else {
+      x = d;
+    }
+    x;
+  }
+  // note: intentionally no phi here so that there are two distinct phis above
+}
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-simple-phi.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-simple-phi.expect.md
index 081aec327f..90bdbee104 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-simple-phi.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-simple-phi.expect.md
@@ -23,7 +23,7 @@ bb0:
   [1] Let mutate y$5_@0 = 2
   [2] Const mutate $6_@1 = 1
   [3] Const mutate $7_@2 = Binary read y$5_@0 > read $6_@1
-  [4] If (read $7_@2) then:bb2 else:bb3
+  [4] If (read $7_@2) then:bb2 else:bb3 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [5] Reassign mutate y$8_@3[5:10] = 1
@@ -89,14 +89,15 @@ flowchart TB
 
 ```javascript
 function foo$0() {
-  let y$1 = 2;
-  bb1: if (y$1 > 1) {
-    y$1 = 1;
+  const y$5 = 2;
+  let y$8 = undefined;
+  bb1: if (y$5 > 1) {
+    y$8 = 1;
   } else {
-    y$1 = 2;
+    y$8 = 2;
   }
 
-  let x$4 = y$1;
+  const x$11 = y$8;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-simple.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-simple.expect.md
index cce524f1ce..cc17b32e36 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-simple.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-simple.expect.md
@@ -40,8 +40,8 @@ flowchart TB
 
 ```javascript
 function foo$0() {
-  let x$1 = 1;
-  let y$2 = 2;
+  const x$3 = 1;
+  const y$4 = 2;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-single-if.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-single-if.expect.md
index 06b0a5f5b5..8d0a4b4338 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-single-if.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-single-if.expect.md
@@ -19,7 +19,7 @@ function foo() {
 bb0:
   [1] Let mutate x$4_@0 = 1
   [2] Let mutate y$5_@1 = 2
-  [3] If (read y$5_@1) then:bb2 else:bb1
+  [3] If (read y$5_@1) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [4] Let mutate z$6_@2 = Binary read x$4_@0 + read y$5_@1
@@ -65,10 +65,10 @@ flowchart TB
 
 ```javascript
 function foo$0() {
-  let x$1 = 1;
-  let y$2 = 2;
-  bb1: if (y$2) {
-    let z$3 = x$1 + y$2;
+  const x$4 = 1;
+  const y$5 = 2;
+  bb1: if (y$5) {
+    const z$6 = x$4 + y$5;
   }
 }
 
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-switch.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-switch.expect.md
index da88ebc5f8..a358ffe9e7 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-switch.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-switch.expect.md
@@ -37,6 +37,7 @@ bb0:
     Case read $14_@4: bb5
     Case read $12_@2: bb3
     Default: bb2
+    Fallthrough: bb1
 bb5:
   predecessor blocks: bb0
   [7] Const mutate $15_@5 = 1
@@ -130,24 +131,25 @@ flowchart TB
 
 ```javascript
 function foo$0() {
-  let x$1 = 1;
-  bb1: switch (x$1) {
-    case x$1 === 1: {
-      x$1 = x$1 + 1;
+  const x$10 = 1;
+  let x$16 = undefined;
+  bb1: switch (x$10) {
+    case x$10 === 1: {
+      x$16 = x$10 + 1;
       break bb1;
     }
 
-    case x$1 === 2: {
-      x$1 = x$1 + 2;
+    case x$10 === 2: {
+      x$16 = x$10 + 2;
       break bb1;
     }
 
     default: {
-      x$1 = x$1 + 3;
+      x$16 = x$10 + 3;
     }
   }
 
-  let y$9 = x$1;
+  const y$22 = x$16;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-throw.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-throw.expect.md
index 7e1e0bb0db..669e36b3a7 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-throw.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-throw.expect.md
@@ -19,7 +19,7 @@ bb0:
   [1] Let mutate x$4_@0[1:7] = 1
   [2] Const mutate $5_@1 = 1
   [3] Const mutate $6_@2 = Binary read x$4_@0 === read $5_@1
-  [4] If (read $6_@2) then:bb2 else:bb1
+  [4] If (read $6_@2) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
   [5] Reassign mutate x$7_@0[1:7] = 2
@@ -66,12 +66,12 @@ flowchart TB
 
 ```javascript
 function foo$0() {
-  let x$1 = 1;
-  bb1: if (x$1 === 1) {
-    x$1 = 2;
+  let x$4 = 1;
+  bb1: if (x$4 === 1) {
+    x$4 = 2;
   }
 
-  throw x$1;
+  throw x$4;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-while-no-reassign.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-while-no-reassign.expect.md
index 31d2037c47..e20b65de8f 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-while-no-reassign.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-while-no-reassign.expect.md
@@ -23,7 +23,7 @@ bb1:
   predecessor blocks: bb0 bb3
   [3] Const mutate $6_@1 = 10
   [4] Const mutate $8_@2[4:6] = Binary read x$5_@0 < read $6_@1
-  [5] If (read $8_@2) then:bb3 else:bb2
+  [5] If (read $8_@2) then:bb3 else:bb2 fallthrough=bb2
 bb3:
   predecessor blocks: bb1
   [6] Const mutate $9_@3 = 1
@@ -82,12 +82,12 @@ flowchart TB
 
 ```javascript
 function foo$0() {
-  let x$1 = 1;
-  bb2: while (x$1 < 10) {
-    x$1 + 1;
+  const x$5 = 1;
+  bb2: while (x$5 < 10) {
+    x$5 + 1;
   }
 
-  return x$1;
+  return x$5;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-while.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-while.expect.md
index 8bb036c3d3..7af54f1cce 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-while.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-while.expect.md
@@ -24,7 +24,7 @@ bb1:
   x$7_@0[0:9]: phi(bb0: x$5_@0, bb3: x$10_@0)
   [3] Const mutate $6_@1 = 10
   [4] Const mutate $8_@2[4:6] = Binary read x$7_@0 < read $6_@1
-  [5] If (read $8_@2) then:bb3 else:bb2
+  [5] If (read $8_@2) then:bb3 else:bb2 fallthrough=bb2
 bb3:
   predecessor blocks: bb1
   [6] Const mutate $9_@3 = 1
@@ -80,12 +80,12 @@ flowchart TB
 
 ```javascript
 function foo$0() {
-  let x$1 = 1;
-  bb2: while (x$1 < 10) {
-    x$1 = x$1 + 1;
+  let x$5 = 1;
+  bb2: while (x$5 < 10) {
+    x$5 = x$5 + 1;
   }
 
-  return x$1;
+  return x$5;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/switch-non-final-default.expect.md b/compiler/forget/src/__tests__/fixtures/hir/switch-non-final-default.expect.md
index 454453f975..fdf868c6cc 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/switch-non-final-default.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/switch-non-final-default.expect.md
@@ -42,6 +42,7 @@ bb0:
     Case read $13_@2: bb6
     Default: bb1
     Case read $12_@1: bb2
+    Fallthrough: bb1
 bb6:
   predecessor blocks: bb0
   [7] Call mutate x$10_@0.push(read props$9.p2)
@@ -121,17 +122,17 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  let x$2 = [];
-  let y$3 = undefined;
-  bb1: switch (props$1.p0) {
+function Component$0(props$9) {
+  const x$10 = [];
+  let y$11 = undefined;
+  bb1: switch (props$9.p0) {
     case 1: {
       break bb1;
     }
 
     case true: {
-      x$2.push(props$1.p2);
-      y$3 = [];
+      x$10.push(props$9.p2);
+      y$11 = [];
       break bb1;
     }
 
@@ -140,13 +141,13 @@ function Component$0(props$1) {
     }
 
     case false: {
-      y$3 = x$2;
+      y$11 = x$10;
     }
   }
 
-  const child$7 = <Component$0 data={x$2}></Component$0>;
-  y$3.push(props$1.p4);
-  return <Component$0 data={y$3}>{child$7}</Component$0>;
+  const child$19 = <Component$0 data={x$10}></Component$0>;
+  y$11.push(props$9.p4);
+  return <Component$0 data={y$11}>{child$19}</Component$0>;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/switch-with-fallthrough.expect.md b/compiler/forget/src/__tests__/fixtures/hir/switch-with-fallthrough.expect.md
index 8186d5c74a..267fbbf5dc 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/switch-with-fallthrough.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/switch-with-fallthrough.expect.md
@@ -51,6 +51,7 @@ bb0:
     Case read $12_@2: bb4
     Case read $11_@1: bb3
     Default: bb2
+    Fallthrough: bb1
 bb10:
   predecessor blocks: bb0
   [9] Reassign mutate y$17_@7 = 0
@@ -159,15 +160,15 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(x$1) {
-  let y$2 = undefined;
-  bb1: switch (x$1) {
+function foo$0(x$9) {
+  const y$10 = undefined;
+  bb1: switch (x$9) {
     case 0: {
-      y$2 = 0;
+      const y$17 = 0;
     }
 
     case 1: {
-      y$2 = 1;
+      const y$18 = 1;
       break bb1;
     }
 
@@ -176,20 +177,20 @@ function foo$0(x$1) {
     }
 
     case 3: {
-      y$2 = 3;
+      const y$19 = 3;
       break bb1;
     }
 
     case 4: {
-      y$2 = 4;
+      const y$20 = 4;
     }
 
     case 5: {
-      y$2 = 5;
+      const y$21 = 5;
     }
 
     default: {
-      y$2 = 0;
+      const y$22 = 0;
     }
   }
 }
diff --git a/compiler/forget/src/__tests__/fixtures/hir/switch.expect.md b/compiler/forget/src/__tests__/fixtures/hir/switch.expect.md
index 8c9bfc2497..18676026ea 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/switch.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/switch.expect.md
@@ -36,6 +36,7 @@ bb0:
     Case read $12_@2: bb4
     Case read $11_@1: bb2
     Default: bb1
+    Fallthrough: bb1
 bb4:
   predecessor blocks: bb0
   [6] Call mutate x$9_@0.push(read props$8.p2)
@@ -116,24 +117,24 @@ flowchart TB
 ## Code
 
 ```javascript
-function Component$0(props$1) {
-  let x$2 = [];
-  let y$3 = undefined;
-  bb1: switch (props$1.p0) {
+function Component$0(props$8) {
+  const x$9 = [];
+  let y$10 = undefined;
+  bb1: switch (props$8.p0) {
     case true: {
-      x$2.push(props$1.p2);
-      x$2.push(props$1.p3);
-      y$3 = [];
+      x$9.push(props$8.p2);
+      x$9.push(props$8.p3);
+      const y$13 = [];
     }
 
     case false: {
-      y$3 = x$2;
+      y$10 = x$9;
     }
   }
 
-  const child$6 = <Component$0 data={x$2}></Component$0>;
-  y$3.push(props$1.p4);
-  return <Component$0 data={y$3}>{child$6}</Component$0>;
+  const child$19 = <Component$0 data={x$9}></Component$0>;
+  y$10.push(props$8.p4);
+  return <Component$0 data={y$10}>{child$19}</Component$0>;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/while-break.expect.md b/compiler/forget/src/__tests__/fixtures/hir/while-break.expect.md
index 4de197229b..bfcbbd99d8 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/while-break.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/while-break.expect.md
@@ -18,7 +18,7 @@ bb0:
   [1] While test=bb1 loop=bb2 fallthrough=bb2
 bb1:
   predecessor blocks: bb0
-  [2] If (read a$3) then:bb2 else:bb2
+  [2] If (read a$3) then:bb2 else:bb2 fallthrough=bb2
 bb2:
   predecessor blocks: bb1
   [3] Return read b$4
@@ -52,11 +52,11 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(a$1, b$2) {
-  bb2: while (a$1) {
+function foo$0(a$3, b$4) {
+  bb2: while (a$3) {
     break;
   }
-  return b$2;
+  return b$4;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/while-conditional-continue.expect.md b/compiler/forget/src/__tests__/fixtures/hir/while-conditional-continue.expect.md
index 016ff2f8de..8beb1687f4 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/while-conditional-continue.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/while-conditional-continue.expect.md
@@ -22,10 +22,10 @@ bb0:
   [1] While test=bb1 loop=bb3 fallthrough=bb2
 bb1:
   predecessor blocks: bb0 bb5 bb4
-  [2] If (read a$5) then:bb3 else:bb2
+  [2] If (read a$5) then:bb3 else:bb2 fallthrough=bb2
 bb3:
   predecessor blocks: bb1
-  [3] If (read b$6) then:bb5 else:bb4
+  [3] If (read b$6) then:bb5 else:bb4 fallthrough=bb4
 bb5:
   predecessor blocks: bb3
   [4] Goto(Continue) bb1
@@ -86,15 +86,15 @@ flowchart TB
 ## Code
 
 ```javascript
-function foo$0(a$1, b$2, c$3, d$4) {
-  bb2: while (a$1) {
-    bb4: if (b$2) {
+function foo$0(a$5, b$6, c$7, d$8) {
+  bb2: while (a$5) {
+    bb4: if (b$6) {
       continue;
     }
-    c$3();
+    c$7();
   }
 
-  d$4();
+  d$8();
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/hir-test.ts b/compiler/forget/src/__tests__/hir-test.ts
index ec77ac67ae..74f49383ed 100644
--- a/compiler/forget/src/__tests__/hir-test.ts
+++ b/compiler/forget/src/__tests__/hir-test.ts
@@ -48,61 +48,58 @@ describe("React Forget (HIR version)", () => {
         }
       }
 
-      const ast = parser.parse(input, {
-        sourceFilename: file,
-        plugins: ["typescript", "jsx"],
-      });
-      let items: Array<[string, string, string]> = [];
-      traverse(ast, {
-        FunctionDeclaration: {
-          enter(nodePath) {
-            const { ir } = run(nodePath, {
-              eliminateRedundantPhi: true,
-              inferReferenceEffects: true,
-              inferMutableRanges: true,
-              inferReactiveScopeVariables: true,
-              inferReactiveScopes: true,
-              inferReactiveScopeDependencies: true,
-              leaveSSA: false,
-              codegen: false,
-            });
+      let items: Array<[string, string, string]> | null = null;
+      let error: Error | null = null;
+      try {
+        items = transform(input, file);
+      } catch (e) {
+        error = e;
+      }
+      let outputs: Array<string>;
 
-            // Print the HIR before leaving SSA.
-            const textHIR = printFunction(ir);
-            const visualization = visualizeHIRMermaid(ir);
+      const expectError = file.startsWith("error.");
+      if (expectError) {
+        if (error === null) {
+          throw new Error(
+            `Expected an error to be thrown for fixture: '${file}', remove the 'error.' prefix if an error is not expected.`
+          );
+        } else {
+          outputs = [formatErrorOutput(error)];
+        }
+      } else {
+        if (error !== null) {
+          console.error(error);
+          throw new Error(
+            `Expected fixture '${file}' to succeed but it failed with error: '${error.message}'. See console output for details.`
+          );
+        }
+        if (items === null || items.length === 0) {
+          throw new Error(`Expected at least one output for file '${file}'.`);
+        }
+        outputs = formatOutput(items);
+      }
+      return `
+## Input
 
-            const { ast } = run(nodePath, {
-              eliminateRedundantPhi: true,
-              inferReferenceEffects: true,
-              inferMutableRanges: true,
-              inferReactiveScopeVariables: true,
-              inferReactiveScopes: true,
-              inferReactiveScopeDependencies: true,
-              leaveSSA: true,
-              codegen: true,
-            });
+${wrapWithTripleBackticks(input, "javascript")}
 
-            invariant(
-              ast !== null,
-              "ast is null when codegen option is enabled"
-            );
-            const text = prettier.format(
-              generate(ast).code.replace("\n\n", "\n"),
-              {
-                semi: true,
-                parser: "babel-ts",
-              }
-            );
-            items.push([textHIR, text, visualization]);
-          },
-        },
-      });
-      invariant(
-        items.length > 0,
-        "Visitor failed, check that the input has a function"
-      );
-      const outputs = items.map(([hir, text, visualization]) => {
-        return `
+${outputs.join("\n")}
+      `;
+    }
+  );
+});
+
+function formatErrorOutput(error: Error): string {
+  return `
+## Error
+
+${wrapWithTripleBackticks(error.message)}
+          `;
+}
+
+function formatOutput(items: Array<[string, string, string]>): Array<string> {
+  return items.map(([hir, text, visualization]) => {
+    return `
 ## HIR
 
 ${wrapWithTripleBackticks(hir)}
@@ -115,14 +112,55 @@ ${wrapWithTripleBackticks(visualization, "mermaid")}
 
 ${wrapWithTripleBackticks(text, "javascript")}
         `.trim();
-      });
-      return `
-## Input
+  });
+}
 
-${wrapWithTripleBackticks(input, "javascript")}
+function transform(
+  text: string,
+  file: string
+): Array<[string, string, string]> {
+  const items: Array<[string, string, string]> = [];
+  const ast = parser.parse(text, {
+    sourceFilename: file,
+    plugins: ["typescript", "jsx"],
+  });
+  traverse(ast, {
+    FunctionDeclaration: {
+      enter(nodePath) {
+        const { ir } = run(nodePath, {
+          eliminateRedundantPhi: true,
+          inferReferenceEffects: true,
+          inferMutableRanges: true,
+          inferReactiveScopeVariables: true,
+          inferReactiveScopes: true,
+          inferReactiveScopeDependencies: true,
+          leaveSSA: false,
+          codegen: false,
+        });
 
-${outputs.join("\n")}
-      `;
-    }
-  );
-});
+        // Print the HIR before leaving SSA.
+        const textHIR = printFunction(ir);
+        const visualization = visualizeHIRMermaid(ir);
+
+        const { ast } = run(nodePath, {
+          eliminateRedundantPhi: true,
+          inferReferenceEffects: true,
+          inferMutableRanges: true,
+          inferReactiveScopeVariables: true,
+          inferReactiveScopes: true,
+          inferReactiveScopeDependencies: true,
+          leaveSSA: true,
+          codegen: true,
+        });
+
+        invariant(ast !== null, "ast is null when codegen option is enabled");
+        const text = prettier.format(generate(ast).code.replace("\n\n", "\n"), {
+          semi: true,
+          parser: "babel-ts",
+        });
+        items.push([textHIR, text, visualization]);
+      },
+    },
+  });
+  return items;
+}
diff --git a/compiler/forget/src/index.ts b/compiler/forget/src/index.ts
index f143316c21..83cc7f9512 100644
--- a/compiler/forget/src/index.ts
+++ b/compiler/forget/src/index.ts
@@ -34,7 +34,7 @@ import { inferReactiveScopeDependencies } from "./HIR/InferReactiveScopeDependen
 import { inferReactiveScopes } from "./HIR/InferReactiveScopes";
 import { inferReactiveScopeVariables } from "./HIR/InferReactiveScopeVariables";
 import inferReferenceEffects from "./HIR/InferReferenceEffects";
-import leaveSSA from "./HIR/LeaveSSA";
+import { leaveSSA } from "./HIR/LeaveSSA";
 import printHIR from "./HIR/PrintHIR";
 
 function parseFunctions(