diff --git a/compiler/forget/src/HIR/InferMutableLifetimes.ts b/compiler/forget/src/HIR/InferMutableLifetimes.ts
index 17c17c79fd..9a188b0bb8 100644
--- a/compiler/forget/src/HIR/InferMutableLifetimes.ts
+++ b/compiler/forget/src/HIR/InferMutableLifetimes.ts
@@ -5,10 +5,11 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import invariant from "invariant";
 import { assertExhaustive } from "../Common/utils";
 import { Effect, HIRFunction, Instruction, Place } from "./HIR";
-import { eachInstructionOperand } from "./visitors";
 import { printInstruction, printPlace } from "./PrintHIR";
+import { eachInstructionOperand } from "./visitors";
 
 /**
  * For each usage of a value in the given function, determines if the usage
@@ -77,9 +78,19 @@ function inferPlace(place: Place, instr: Instruction) {
 export function inferMutableRanges(func: HIRFunction) {
   for (const [_, block] of func.body.blocks) {
     for (const phi of block.phis) {
+      let start = Number.MAX_SAFE_INTEGER;
+      let end = Number.MIN_SAFE_INTEGER;
+      for (const [_, operand] of phi.operands) {
+        start = Math.min(start, operand.mutableRange.start);
+        end = Math.max(end, operand.mutableRange.end);
+      }
+      invariant(
+        start !== Number.MAX_SAFE_INTEGER && end !== Number.MIN_SAFE_INTEGER,
+        "Expected phi to have set start/end range values"
+      );
       phi.id.mutableRange = {
-        start: -1, // TODO(gsn): This is a hack, we should assign proper ids to phis.
-        end: -1,
+        start,
+        end,
       };
     }
 
diff --git a/compiler/forget/src/HIR/InferReactiveScopeVariables.ts b/compiler/forget/src/HIR/InferReactiveScopeVariables.ts
index 854e765581..0295a63a9b 100644
--- a/compiler/forget/src/HIR/InferReactiveScopeVariables.ts
+++ b/compiler/forget/src/HIR/InferReactiveScopeVariables.ts
@@ -11,6 +11,7 @@ import {
   Identifier,
   Instruction,
   makeScopeId,
+  MutableRange,
   Place,
   ScopeId,
 } from "./HIR";
@@ -94,10 +95,20 @@ export function inferReactiveScopeVariables(fn: HIRFunction) {
 
   // Maps each scope (by its identifying member) to a ScopeId value
   const scopeIds: Map<Identifier, ScopeId> = new Map();
+  // Store the mutable range and set of identifiers for each scope
+  const scopeVariables: Map<
+    ScopeId,
+    { range: MutableRange; variables: Set<Identifier> }
+  > = new Map();
 
-  // Iterate over all the identifiers in all scopes, and assign each
-  // identifier to its group's scope id. The first identifier in each
-  // group assigns the scope id for that group.
+  /**
+   * Iterate over all the identifiers and assign a unique ScopeId
+   * for each scope (based on the set identifier).
+   *
+   * At the same time, group the identifiers in each scope and
+   * build a MutableRange that describes the span of mutations
+   * across all identifiers in each scope.
+   */
   scopes.forEach((identifier, groupIdentifier) => {
     let scopeId = scopeIds.get(groupIdentifier);
     if (scopeId == null) {
@@ -105,7 +116,31 @@ export function inferReactiveScopeVariables(fn: HIRFunction) {
       scopeIds.set(groupIdentifier, scopeId);
     }
     identifier.scope = scopeId;
+
+    let scope = scopeVariables.get(scopeId);
+    if (scope === undefined) {
+      scope = {
+        range: { ...identifier.mutableRange },
+        variables: new Set(),
+      };
+      scopeVariables.set(scopeId, scope);
+    } else {
+      scope.range.start = Math.min(
+        scope.range.start,
+        identifier.mutableRange.start
+      );
+      scope.range.end = Math.max(scope.range.end, identifier.mutableRange.end);
+    }
+    scope.variables.add(identifier);
   });
+
+  // Update all the identifiers for each scope now that we know
+  // the scope's full range.
+  for (const [_, scope] of scopeVariables) {
+    for (const identifier of scope.variables) {
+      identifier.mutableRange = scope.range;
+    }
+  }
 }
 
 // Is the operand mutable at this given instruction
diff --git a/compiler/forget/src/__tests__/fixtures/hir/call.expect.md b/compiler/forget/src/__tests__/fixtures/hir/call.expect.md
index 56a9835c54..a2b8206209 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/call.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/call.expect.md
@@ -47,8 +47,8 @@ function foo$0() {
 
 ```
 bb0:
-  [1] Const mutate a$2_@0[1:3] = Array []
-  [2] Const mutate b$3_@0[2:6] = Object {  }
+  [1] Const mutate a$2_@0[0:6] = Array []
+  [2] Const mutate b$3_@0[0:6] = Object {  }
   [3] Call mutate foo$4_@0(mutate a$2_@0, mutate b$3_@0)
   [4] Const mutate $6_@1 = "div"
   [5] Let mutate _$5_@2 = JSX <read $6_@1 a={freeze a$2_@0} ></read $6_@1>
@@ -65,8 +65,8 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Const mutate a$2_@0[1:3] = Array []
-      [2] Const mutate b$3_@0[2:6] = Object {  }
+      [1] Const mutate a$2_@0[0:6] = Array []
+      [2] Const mutate b$3_@0[0:6] = Object {  }
       [3] Call mutate foo$4_@0(mutate a$2_@0, mutate b$3_@0)
       [4] Const mutate $6_@1 = 'div'
       [5] Let mutate _$5_@2 = JSX <read $6_@1 a={freeze a$2_@0} ></read $6_@1>
diff --git a/compiler/forget/src/__tests__/fixtures/hir/component.expect.md b/compiler/forget/src/__tests__/fixtures/hir/component.expect.md
index c69f71bf45..372e0cb70b 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/component.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/component.expect.md
@@ -38,9 +38,9 @@ bb0:
   [1] Const mutate items$2_@0 = read props$1.items
   [2] Const mutate maxItems$3_@1 = read props$1.maxItems
   [3] Const mutate renderedItems$4_@2[3:14] = Array []
-  [4] Const mutate seen$5_@3[4:11] = New mutate Set$6_@3()
+  [4] Const mutate seen$5_@3[0:11] = New mutate Set$6_@3()
   [5] Const mutate $9_@4 = 0
-  [6] Const mutate max$7_@5 = Call mutate Math$8_@5.max(read $9_@4, read maxItems$3_@1)
+  [6] Const mutate max$7_@5[0:6] = Call mutate Math$8_@5.max(read $9_@4, read maxItems$3_@1)
   Goto bb1
 bb1:
   predecessor blocks: bb0 bb5 bb10
@@ -48,15 +48,15 @@ bb1:
 bb3:
   predecessor blocks: bb1
   [7] Const mutate $11_@6 = null
-  [8] Const mutate $12_@3 = Binary read item$10_@3 == read $11_@6
+  [8] Const mutate $12_@3[0:11] = Binary read item$10_@3 == read $11_@6
   If (read $12_@3) then:bb8 else:bb9
 bb8:
   predecessor blocks: bb3
-  [9] Const mutate $13_@3 = read $12_@3
+  [9] Const mutate $13_@3[0:11] = read $12_@3
   Goto bb7
 bb9:
   predecessor blocks: bb3
-  [10] Const mutate $13_@3 = Call mutate seen$5_@3.has(mutate item$10_@3)
+  [10] Const mutate $13_@3[0:11] = Call mutate seen$5_@3.has(mutate item$10_@3)
   Goto bb7
 bb7:
   predecessor blocks: bb8 bb9
@@ -99,9 +99,9 @@ flowchart TB
       [1] Const mutate items$2_@0 = read props$1.items
       [2] Const mutate maxItems$3_@1 = read props$1.maxItems
       [3] Const mutate renderedItems$4_@2[3:14] = Array []
-      [4] Const mutate seen$5_@3[4:11] = New mutate Set$6_@3()
+      [4] Const mutate seen$5_@3[0:11] = New mutate Set$6_@3()
       [5] Const mutate $9_@4 = 0
-      [6] Const mutate max$7_@5 = Call mutate Math$8_@5.max(read $9_@4, read maxItems$3_@1)
+      [6] Const mutate max$7_@5[0:6] = Call mutate Math$8_@5.max(read $9_@4, read maxItems$3_@1)
     "]
     bb0_instrs --> bb0_terminal(["Goto"])
   end
@@ -111,19 +111,19 @@ flowchart TB
   subgraph bb3
     bb3_instrs["
       [7] Const mutate $11_@6 = null
-      [8] Const mutate $12_@3 = Binary read item$10_@3 == read $11_@6
+      [8] Const mutate $12_@3[0:11] = Binary read item$10_@3 == read $11_@6
     "]
     bb3_instrs --> bb3_terminal(["If (read $12_@3)"])
   end
   subgraph bb8
     bb8_instrs["
-      [9] Const mutate $13_@3 = read $12_@3
+      [9] Const mutate $13_@3[0:11] = read $12_@3
     "]
     bb8_instrs --> bb8_terminal(["Goto"])
   end
   subgraph bb9
     bb9_instrs["
-      [10] Const mutate $13_@3 = Call mutate seen$5_@3.has(mutate item$10_@3)
+      [10] Const mutate $13_@3[0:11] = Call mutate seen$5_@3.has(mutate item$10_@3)
     "]
     bb9_instrs --> bb9_terminal(["Goto"])
   end
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 ca992ca580..a653b86e6d 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
@@ -154,8 +154,8 @@ function Component$0(props$1) {
 ```
 bb0:
   [1] Const mutate a$2_@0[1:4] = Array []
-  [2] Const mutate b$3_@1[2:5] = Array []
-  [3] Const mutate $5_@1 = Call mutate mayMutate$4_@1(mutate b$3_@1)
+  [2] Const mutate b$3_@1[0:5] = Array []
+  [3] Const mutate $5_@1[0:5] = Call mutate mayMutate$4_@1(mutate b$3_@1)
   If (read $5_@1) then:bb2 else:bb1
 bb2:
   predecessor blocks: bb0
@@ -182,8 +182,8 @@ flowchart TB
   subgraph bb0
     bb0_instrs["
       [1] Const mutate a$2_@0[1:4] = Array []
-      [2] Const mutate b$3_@1[2:5] = Array []
-      [3] Const mutate $5_@1 = Call mutate mayMutate$4_@1(mutate b$3_@1)
+      [2] Const mutate b$3_@1[0:5] = Array []
+      [3] Const mutate $5_@1[0:5] = Call mutate mayMutate$4_@1(mutate b$3_@1)
     "]
     bb0_instrs --> bb0_terminal(["If (read $5_@1)"])
   end
diff --git a/compiler/forget/src/__tests__/fixtures/hir/constructor.expect.md b/compiler/forget/src/__tests__/fixtures/hir/constructor.expect.md
index 4911b0ee41..37d84e1536 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/constructor.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/constructor.expect.md
@@ -47,8 +47,8 @@ function Foo$0() {
 
 ```
 bb0:
-  [1] Const mutate a$2_@0[1:3] = Array []
-  [2] Const mutate b$3_@0[2:6] = Object {  }
+  [1] Const mutate a$2_@0[0:6] = Array []
+  [2] Const mutate b$3_@0[0:6] = Object {  }
   [3] New mutate Foo$4_@0(mutate a$2_@0, mutate b$3_@0)
   [4] Const mutate $6_@1 = "div"
   [5] Let mutate _$5_@2 = JSX <read $6_@1 a={freeze a$2_@0} ></read $6_@1>
@@ -65,8 +65,8 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Const mutate a$2_@0[1:3] = Array []
-      [2] Const mutate b$3_@0[2:6] = Object {  }
+      [1] Const mutate a$2_@0[0:6] = Array []
+      [2] Const mutate b$3_@0[0:6] = Object {  }
       [3] New mutate Foo$4_@0(mutate a$2_@0, mutate b$3_@0)
       [4] Const mutate $6_@1 = 'div'
       [5] Let mutate _$5_@2 = JSX <read $6_@1 a={freeze a$2_@0} ></read $6_@1>
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 a71f744317..0de74857d1 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
@@ -32,11 +32,11 @@ bb0:
   If (read cond$2_@0) then:bb2 else:bb3
 bb2:
   predecessor blocks: bb0
-  [4] Reassign mutate a$4_@3 = read x$3_@1
+  [4] Reassign mutate a$4_@3[4:5] = read x$3_@1
   Goto bb1
 bb3:
   predecessor blocks: bb0
-  [5] Reassign mutate a$4_@3 = Array []
+  [5] Reassign mutate a$4_@3[4:5] = Array []
   Goto bb1
 bb1:
   predecessor blocks: bb2 bb3
@@ -61,13 +61,13 @@ flowchart TB
   end
   subgraph bb2
     bb2_instrs["
-      [4] Reassign mutate a$4_@3 = read x$3_@1
+      [4] Reassign mutate a$4_@3[4:5] = read x$3_@1
     "]
     bb2_instrs --> bb2_terminal(["Goto"])
   end
   subgraph bb3
     bb3_instrs["
-      [5] Reassign mutate a$4_@3 = Array []
+      [5] Reassign mutate a$4_@3[4:5] = Array []
     "]
     bb3_instrs --> bb3_terminal(["Goto"])
   end
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 e2185eda83..7de35eb6a1 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
@@ -149,8 +149,8 @@ function Foo$0() {
 
 ```
 bb0:
-  [1] Const mutate a$2_@0[1:3] = Call mutate compute$3_@0(read props$1.a)
-  [2] Const mutate b$4_@0[2:4] = Call mutate compute$3_@0(read props$1.b)
+  [1] Const mutate a$2_@0[0:4] = Call mutate compute$3_@0(read props$1.a)
+  [2] Const mutate b$4_@0[0:4] = Call mutate compute$3_@0(read props$1.b)
   If (read props$1.c) then:bb2 else:bb1
 bb2:
   predecessor blocks: bb0
@@ -170,8 +170,8 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Const mutate a$2_@0[1:3] = Call mutate compute$3_@0(read props$1.a)
-      [2] Const mutate b$4_@0[2:4] = Call mutate compute$3_@0(read props$1.b)
+      [1] Const mutate a$2_@0[0:4] = Call mutate compute$3_@0(read props$1.a)
+      [2] Const mutate b$4_@0[0:4] = Call mutate compute$3_@0(read props$1.b)
     "]
     bb0_instrs --> bb0_terminal(["If (read props$1.c)"])
   end
diff --git a/compiler/forget/src/__tests__/fixtures/hir/independent.expect.md b/compiler/forget/src/__tests__/fixtures/hir/independent.expect.md
index f8be029c6d..9205c2653c 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/independent.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/independent.expect.md
@@ -28,8 +28,8 @@ function Foo() {}
 
 ```
 bb0:
-  [1] Const mutate a$2_@0 = Call mutate compute$3_@0(read props$1.a)
-  [2] Const mutate b$4_@0 = Call mutate compute$3_@0(read props$1.b)
+  [1] Const mutate a$2_@0[0:2] = Call mutate compute$3_@0(read props$1.a)
+  [2] Const mutate b$4_@0[0:2] = Call mutate compute$3_@0(read props$1.b)
   [3] Const mutate $6_@1 = JSX <read Foo$5 a={freeze a$2_@0} b={freeze b$4_@0} ></read Foo$5>
   Return read $6_@1
 ```
@@ -41,8 +41,8 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Const mutate a$2_@0 = Call mutate compute$3_@0(read props$1.a)
-      [2] Const mutate b$4_@0 = Call mutate compute$3_@0(read props$1.b)
+      [1] Const mutate a$2_@0[0:2] = Call mutate compute$3_@0(read props$1.a)
+      [2] Const mutate b$4_@0[0:2] = Call mutate compute$3_@0(read props$1.b)
       [3] Const mutate $6_@1 = JSX <read Foo$5 a={freeze a$2_@0} b={freeze b$4_@0} ></read Foo$5>
     "]
     bb0_instrs --> bb0_terminal(["Return read $6_@1"])
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 77555ebcba..1c97f779d6 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
@@ -115,8 +115,8 @@ function Foo$0() {
 
 ```
 bb0:
-  [1] Const mutate a$2_@0[1:3] = Call mutate compute$3_@0(read props$1.a)
-  [2] Const mutate b$4_@0[2:3] = Call mutate compute$3_@0(read props$1.b)
+  [1] Const mutate a$2_@0[0:3] = Call mutate compute$3_@0(read props$1.a)
+  [2] Const mutate b$4_@0[0:3] = Call mutate compute$3_@0(read props$1.b)
   If (read props$1.c) then:bb2 else:bb1
 bb2:
   predecessor blocks: bb0
@@ -135,8 +135,8 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Const mutate a$2_@0[1:3] = Call mutate compute$3_@0(read props$1.a)
-      [2] Const mutate b$4_@0[2:3] = Call mutate compute$3_@0(read props$1.b)
+      [1] Const mutate a$2_@0[0:3] = Call mutate compute$3_@0(read props$1.a)
+      [2] Const mutate b$4_@0[0:3] = Call mutate compute$3_@0(read props$1.b)
     "]
     bb0_instrs --> bb0_terminal(["If (read props$1.c)"])
   end
diff --git a/compiler/forget/src/__tests__/fixtures/hir/interdependent.expect.md b/compiler/forget/src/__tests__/fixtures/hir/interdependent.expect.md
index 317a224450..061fe93e36 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/interdependent.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/interdependent.expect.md
@@ -28,8 +28,8 @@ function Foo() {}
 
 ```
 bb0:
-  [1] Const mutate a$2_@0[1:3] = Call mutate compute$3_@0(read props$1.a)
-  [2] Const mutate b$4_@0[2:3] = Call mutate compute$3_@0(read props$1.b)
+  [1] Const mutate a$2_@0[0:3] = Call mutate compute$3_@0(read props$1.a)
+  [2] Const mutate b$4_@0[0:3] = Call mutate compute$3_@0(read props$1.b)
   [3] Call mutate foo$5_@0(mutate a$2_@0, mutate b$4_@0)
   [4] Const mutate $7_@1 = JSX <read Foo$6 a={freeze a$2_@0} b={freeze b$4_@0} ></read Foo$6>
   Return read $7_@1
@@ -42,8 +42,8 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Const mutate a$2_@0[1:3] = Call mutate compute$3_@0(read props$1.a)
-      [2] Const mutate b$4_@0[2:3] = Call mutate compute$3_@0(read props$1.b)
+      [1] Const mutate a$2_@0[0:3] = Call mutate compute$3_@0(read props$1.a)
+      [2] Const mutate b$4_@0[0:3] = Call mutate compute$3_@0(read props$1.b)
       [3] Call mutate foo$5_@0(mutate a$2_@0, mutate b$4_@0)
       [4] Const mutate $7_@1 = JSX <read Foo$6 a={freeze a$2_@0} b={freeze b$4_@0} ></read Foo$6>
     "]
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 a59714410a..c310f9173d 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/logical-expression.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/logical-expression.expect.md
@@ -23,15 +23,15 @@ function g() {}
 
 ```
 bb0:
-  [1] Const mutate $2_@0 = Call mutate f$1_@0()
+  [1] Const mutate $2_@0[0:1] = Call mutate f$1_@0()
   If (read $2_@0) then:bb2 else:bb3
 bb2:
   predecessor blocks: bb0
-  [2] Const mutate $3_@1 = Call mutate g$4_@1()
+  [2] Const mutate $3_@1[0:3] = Call mutate g$4_@1()
   Goto bb1
 bb3:
   predecessor blocks: bb0
-  [3] Const mutate $3_@1 = read $2_@0
+  [3] Const mutate $3_@1[0:3] = read $2_@0
   Goto bb1
 bb1:
   predecessor blocks: bb2 bb3
@@ -45,19 +45,19 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Const mutate $2_@0 = Call mutate f$1_@0()
+      [1] Const mutate $2_@0[0:1] = Call mutate f$1_@0()
     "]
     bb0_instrs --> bb0_terminal(["If (read $2_@0)"])
   end
   subgraph bb2
     bb2_instrs["
-      [2] Const mutate $3_@1 = Call mutate g$4_@1()
+      [2] Const mutate $3_@1[0:3] = Call mutate g$4_@1()
     "]
     bb2_instrs --> bb2_terminal(["Goto"])
   end
   subgraph bb3
     bb3_instrs["
-      [3] Const mutate $3_@1 = read $2_@0
+      [3] Const mutate $3_@1[0:3] = read $2_@0
     "]
     bb3_instrs --> bb3_terminal(["Goto"])
   end
@@ -89,15 +89,15 @@ function And$0() {
 
 ```
 bb0:
-  [1] Const mutate $2_@0 = Call mutate f$1_@0()
+  [1] Const mutate $2_@0[0:1] = Call mutate f$1_@0()
   If (read $2_@0) then:bb2 else:bb3
 bb2:
   predecessor blocks: bb0
-  [2] Const mutate $3_@1 = read $2_@0
+  [2] Const mutate $3_@1[0:3] = read $2_@0
   Goto bb1
 bb3:
   predecessor blocks: bb0
-  [3] Const mutate $3_@1 = Call mutate g$4_@1()
+  [3] Const mutate $3_@1[0:3] = Call mutate g$4_@1()
   Goto bb1
 bb1:
   predecessor blocks: bb2 bb3
@@ -111,19 +111,19 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Const mutate $2_@0 = Call mutate f$1_@0()
+      [1] Const mutate $2_@0[0:1] = Call mutate f$1_@0()
     "]
     bb0_instrs --> bb0_terminal(["If (read $2_@0)"])
   end
   subgraph bb2
     bb2_instrs["
-      [2] Const mutate $3_@1 = read $2_@0
+      [2] Const mutate $3_@1[0:3] = read $2_@0
     "]
     bb2_instrs --> bb2_terminal(["Goto"])
   end
   subgraph bb3
     bb3_instrs["
-      [3] Const mutate $3_@1 = Call mutate g$4_@1()
+      [3] Const mutate $3_@1[0:3] = Call mutate g$4_@1()
     "]
     bb3_instrs --> bb3_terminal(["Goto"])
   end
@@ -155,17 +155,17 @@ function Or$0() {
 
 ```
 bb0:
-  [1] Const mutate $3_@0 = Call mutate f$2_@0()
+  [1] Const mutate $3_@0[0:1] = Call mutate f$2_@0()
   [2] Const mutate $4_@1 = null
   [3] Const mutate $5_@2 = Binary read $3_@0 != read $4_@1
   If (read $5_@2) then:bb2 else:bb3
 bb2:
   predecessor blocks: bb0
-  [4] Const mutate $6_@3 = read $3_@0
+  [4] Const mutate $6_@3[0:5] = read $3_@0
   Goto bb1
 bb3:
   predecessor blocks: bb0
-  [5] Const mutate $6_@3 = Call mutate g$7_@3()
+  [5] Const mutate $6_@3[0:5] = Call mutate g$7_@3()
   Goto bb1
 bb1:
   predecessor blocks: bb2 bb3
@@ -179,7 +179,7 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Const mutate $3_@0 = Call mutate f$2_@0()
+      [1] Const mutate $3_@0[0:1] = Call mutate f$2_@0()
       [2] Const mutate $4_@1 = null
       [3] Const mutate $5_@2 = Binary read $3_@0 != read $4_@1
     "]
@@ -187,13 +187,13 @@ flowchart TB
   end
   subgraph bb2
     bb2_instrs["
-      [4] Const mutate $6_@3 = read $3_@0
+      [4] Const mutate $6_@3[0:5] = read $3_@0
     "]
     bb2_instrs --> bb2_terminal(["Goto"])
   end
   subgraph bb3
     bb3_instrs["
-      [5] Const mutate $6_@3 = Call mutate g$7_@3()
+      [5] Const mutate $6_@3[0:5] = Call mutate g$7_@3()
     "]
     bb3_instrs --> bb3_terminal(["Goto"])
   end
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 fa3dc0e3a1..b575a7d3d8 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
@@ -99,10 +99,10 @@ function cond$0(x$1) {
 
 ```
 bb0:
-  [1] Let mutate a$2_@0 = Object {  }
-  [2] Let mutate b$3_@0 = Object {  }
-  [3] Let mutate c$4_@1 = Object {  }
-  [4] Let mutate d$5_@0 = Object {  }
+  [1] Let mutate a$2_@0[0:14] = Object {  }
+  [2] Let mutate b$3_@0[0:14] = Object {  }
+  [3] Let mutate c$4_@1[0:9] = Object {  }
+  [4] Let mutate d$5_@0[0:14] = Object {  }
   While test=bb1 loop=bb3 fallthrough=bb2
 bb1:
   predecessor blocks: bb0 bb4
@@ -111,12 +111,12 @@ bb1:
 bb3:
   predecessor blocks: bb1
   [6] Let mutate z$6_@3 = read a$2_@0
-  [7] Reassign mutate a$2_@0[7:12] = read b$3_@0
-  [8] Reassign mutate b$3_@0[8:11] = read c$4_@1
-  [9] Reassign mutate c$4_@1 = read d$5_@0
-  [10] Reassign mutate d$5_@0 = read z$6_@3
+  [7] Reassign mutate a$2_@0[0:14] = read b$3_@0
+  [8] Reassign mutate b$3_@0[0:14] = read c$4_@1
+  [9] Reassign mutate c$4_@1[0:9] = read d$5_@0
+  [10] Reassign mutate d$5_@0[0:14] = read z$6_@3
   [11] Call mutate mutate$7_@0(mutate a$2_@0, mutate b$3_@0)
-  [12] Const mutate $9_@0 = Call mutate cond$8_@0(mutate a$2_@0)
+  [12] Const mutate $9_@0[0:14] = Call mutate cond$8_@0(mutate a$2_@0)
   If (read $9_@0) then:bb2 else:bb4
 bb4:
   predecessor blocks: bb3
@@ -147,10 +147,10 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Let mutate a$2_@0 = Object {  }
-      [2] Let mutate b$3_@0 = Object {  }
-      [3] Let mutate c$4_@1 = Object {  }
-      [4] Let mutate d$5_@0 = Object {  }
+      [1] Let mutate a$2_@0[0:14] = Object {  }
+      [2] Let mutate b$3_@0[0:14] = Object {  }
+      [3] Let mutate c$4_@1[0:9] = Object {  }
+      [4] Let mutate d$5_@0[0:14] = Object {  }
     "]
     bb0_instrs --> bb0_terminal(["While"])
   end
@@ -163,12 +163,12 @@ flowchart TB
   subgraph bb3
     bb3_instrs["
       [6] Let mutate z$6_@3 = read a$2_@0
-      [7] Reassign mutate a$2_@0[7:12] = read b$3_@0
-      [8] Reassign mutate b$3_@0[8:11] = read c$4_@1
-      [9] Reassign mutate c$4_@1 = read d$5_@0
-      [10] Reassign mutate d$5_@0 = read z$6_@3
+      [7] Reassign mutate a$2_@0[0:14] = read b$3_@0
+      [8] Reassign mutate b$3_@0[0:14] = read c$4_@1
+      [9] Reassign mutate c$4_@1[0:9] = read d$5_@0
+      [10] Reassign mutate d$5_@0[0:14] = read z$6_@3
       [11] Call mutate mutate$7_@0(mutate a$2_@0, mutate b$3_@0)
-      [12] Const mutate $9_@0 = Call mutate cond$8_@0(mutate a$2_@0)
+      [12] Const mutate $9_@0[0:14] = Call mutate cond$8_@0(mutate a$2_@0)
     "]
     bb3_instrs --> bb3_terminal(["If (read $9_@0)"])
   end
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 17edc95bcb..08ef4d0d70 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
@@ -70,10 +70,10 @@ bb0:
   [1] Const mutate a$2_@0 = Object {  }
   [2] Const mutate b$3_@1 = Array [read a$2_@0]
   [3] Const mutate c$4_@2 = Object {  }
-  [4] Const mutate d$5_@3[4:7] = Object { c: read c$4_@2 }
-  [5] Const mutate x$6_@3[5:9] = Object {  }
-  [6] Reassign mutate x$6_@3.b[5:9] = read b$3_@1
-  [7] Const mutate y$7_@3 = Call mutate mutate$8_@3(mutate x$6_@3, mutate d$5_@3)
+  [4] Const mutate d$5_@3[0:9] = Object { c: read c$4_@2 }
+  [5] Const mutate x$6_@3[0:9] = Object {  }
+  [6] Reassign mutate x$6_@3.b[0:9] = read b$3_@1
+  [7] Const mutate y$7_@3[0:9] = Call mutate mutate$8_@3(mutate x$6_@3, mutate d$5_@3)
   If (read a$2_@0) then:bb1 else:bb1
 bb1:
   predecessor blocks: bb0
@@ -104,10 +104,10 @@ flowchart TB
       [1] Const mutate a$2_@0 = Object {  }
       [2] Const mutate b$3_@1 = Array [read a$2_@0]
       [3] Const mutate c$4_@2 = Object {  }
-      [4] Const mutate d$5_@3[4:7] = Object { c: read c$4_@2 }
-      [5] Const mutate x$6_@3[5:9] = Object {  }
-      [6] Reassign mutate x$6_@3.b[5:9] = read b$3_@1
-      [7] Const mutate y$7_@3 = Call mutate mutate$8_@3(mutate x$6_@3, mutate d$5_@3)
+      [4] Const mutate d$5_@3[0:9] = Object { c: read c$4_@2 }
+      [5] Const mutate x$6_@3[0:9] = Object {  }
+      [6] Reassign mutate x$6_@3.b[0:9] = read b$3_@1
+      [7] Const mutate y$7_@3[0:9] = Call mutate mutate$8_@3(mutate x$6_@3, mutate d$5_@3)
     "]
     bb0_instrs --> bb0_terminal(["If (read a$2_@0)"])
   end
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 f44edb3295..c507918163 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
@@ -94,10 +94,10 @@ function cond$0() {
 
 ```
 bb0:
-  [1] Let mutate a$2_@0[1:7] = Object {  }
-  [2] Let mutate b$3_@0[2:6] = Object {  }
+  [1] Let mutate a$2_@0[0:9] = Object {  }
+  [2] Let mutate b$3_@0[0:9] = Object {  }
   [3] Let mutate c$4_@1 = Object {  }
-  [4] Let mutate d$5_@0[4:9] = Object {  }
+  [4] Let mutate d$5_@0[0:9] = Object {  }
   While test=bb1 loop=bb3 fallthrough=bb2
 bb1:
   predecessor blocks: bb0 bb4
@@ -106,7 +106,7 @@ bb1:
 bb3:
   predecessor blocks: bb1
   [6] Call mutate mutate$6_@0(mutate a$2_@0, mutate b$3_@0)
-  [7] Const mutate $8_@0 = Call mutate cond$7_@0(mutate a$2_@0)
+  [7] Const mutate $8_@0[0:9] = Call mutate cond$7_@0(mutate a$2_@0)
   If (read $8_@0) then:bb2 else:bb4
 bb4:
   predecessor blocks: bb3
@@ -137,10 +137,10 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Let mutate a$2_@0[1:7] = Object {  }
-      [2] Let mutate b$3_@0[2:6] = Object {  }
+      [1] Let mutate a$2_@0[0:9] = Object {  }
+      [2] Let mutate b$3_@0[0:9] = Object {  }
       [3] Let mutate c$4_@1 = Object {  }
-      [4] Let mutate d$5_@0[4:9] = Object {  }
+      [4] Let mutate d$5_@0[0:9] = Object {  }
     "]
     bb0_instrs --> bb0_terminal(["While"])
   end
@@ -153,7 +153,7 @@ flowchart TB
   subgraph bb3
     bb3_instrs["
       [6] Call mutate mutate$6_@0(mutate a$2_@0, mutate b$3_@0)
-      [7] Const mutate $8_@0 = Call mutate cond$7_@0(mutate a$2_@0)
+      [7] Const mutate $8_@0[0:9] = Call mutate cond$7_@0(mutate a$2_@0)
     "]
     bb3_instrs --> bb3_terminal(["If (read $8_@0)"])
   end
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 7864105d7b..ec77ba9396 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
@@ -20,7 +20,7 @@ function foo() {
 bb0:
   [1] Let mutate x$1_@0[1:5] = Object {  }
   [2] Let mutate y$2_@1[2:4] = Array []
-  [3] Let mutate z$3_@1[3:4] = Object {  }
+  [3] Let mutate z$3_@1[2:4] = Object {  }
   [4] Call mutate y$2_@1.push(mutate z$3_@1)
   [5] Reassign mutate x$1_@0.y[1:5] = read y$2_@1
   Return freeze x$1_@0
@@ -35,7 +35,7 @@ flowchart TB
     bb0_instrs["
       [1] Let mutate x$1_@0[1:5] = Object {  }
       [2] Let mutate y$2_@1[2:4] = Array []
-      [3] Let mutate z$3_@1[3:4] = Object {  }
+      [3] Let mutate z$3_@1[2:4] = Object {  }
       [4] Call mutate y$2_@1.push(mutate z$3_@1)
       [5] Reassign mutate x$1_@0.y[1:5] = read y$2_@1
     "]
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 b1e9e0ce19..ccd4b3dcfc 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/reassignment-conditional.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/reassignment-conditional.expect.md
@@ -23,13 +23,13 @@ function Component(props) {
 
 ```
 bb0:
-  [1] Let mutate x$2_@0[1:2] = Array []
+  [1] Let mutate x$2_@0[1:4] = Array []
   [2] Call mutate x$2_@0.push(read props$1.p0)
   [3] Let mutate y$3_@1 = read x$2_@0
   If (read props$1.p1) then:bb2 else:bb1
 bb2:
   predecessor blocks: bb0
-  [4] Reassign mutate x$2_@0 = Array []
+  [4] Reassign mutate x$2_@0[1:4] = Array []
   Goto bb1
 bb1:
   predecessor blocks: bb2 bb0
@@ -46,7 +46,7 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Let mutate x$2_@0[1:2] = Array []
+      [1] Let mutate x$2_@0[1:4] = Array []
       [2] Call mutate x$2_@0.push(read props$1.p0)
       [3] Let mutate y$3_@1 = read x$2_@0
     "]
@@ -54,7 +54,7 @@ flowchart TB
   end
   subgraph bb2
     bb2_instrs["
-      [4] Reassign mutate x$2_@0 = Array []
+      [4] Reassign mutate x$2_@0[1:4] = Array []
     "]
     bb2_instrs --> bb2_terminal(["Goto"])
   end
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 c09610bbce..2c2bb901a5 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/reverse-postorder.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/reverse-postorder.expect.md
@@ -50,26 +50,26 @@ bb2:
     Default: bb4
 bb8:
   predecessor blocks: bb2
-  [5] Reassign mutate x$2_@4 = read props$1.v0
+  [5] Reassign mutate x$2_@4[5:9] = read props$1.v0
   Goto bb1
 bb6:
   predecessor blocks: bb2
-  [6] Reassign mutate x$2_@4 = read props$1.v1
+  [6] Reassign mutate x$2_@4[5:9] = read props$1.v1
   Goto bb1
 bb4:
   predecessor blocks: bb2
-  [7] Reassign mutate x$2_@4 = read props$1.v2
+  [7] Reassign mutate x$2_@4[5:9] = read props$1.v2
   Goto bb1
 bb10:
   predecessor blocks: bb0
   If (read props$1.cond2) then:bb12 else:bb13
 bb12:
   predecessor blocks: bb10
-  [8] Reassign mutate x$2_@4 = read props$1.b
+  [8] Reassign mutate x$2_@4[5:9] = read props$1.b
   Goto bb1
 bb13:
   predecessor blocks: bb10
-  [9] Reassign mutate x$2_@4 = read props$1.c
+  [9] Reassign mutate x$2_@4[5:9] = read props$1.c
   Goto bb1
 bb1:
   predecessor blocks: bb8 bb6 bb4 bb12 bb13
@@ -98,19 +98,19 @@ flowchart TB
   end
   subgraph bb8
     bb8_instrs["
-      [5] Reassign mutate x$2_@4 = read props$1.v0
+      [5] Reassign mutate x$2_@4[5:9] = read props$1.v0
     "]
     bb8_instrs --> bb8_terminal(["Goto"])
   end
   subgraph bb6
     bb6_instrs["
-      [6] Reassign mutate x$2_@4 = read props$1.v1
+      [6] Reassign mutate x$2_@4[5:9] = read props$1.v1
     "]
     bb6_instrs --> bb6_terminal(["Goto"])
   end
   subgraph bb4
     bb4_instrs["
-      [7] Reassign mutate x$2_@4 = read props$1.v2
+      [7] Reassign mutate x$2_@4[5:9] = read props$1.v2
     "]
     bb4_instrs --> bb4_terminal(["Goto"])
   end
@@ -119,13 +119,13 @@ flowchart TB
   end
   subgraph bb12
     bb12_instrs["
-      [8] Reassign mutate x$2_@4 = read props$1.b
+      [8] Reassign mutate x$2_@4[5:9] = read props$1.b
     "]
     bb12_instrs --> bb12_terminal(["Goto"])
   end
   subgraph bb13
     bb13_instrs["
-      [9] Reassign mutate x$2_@4 = read props$1.c
+      [9] Reassign mutate x$2_@4[5:9] = read props$1.c
     "]
     bb13_instrs --> bb13_terminal(["Goto"])
   end
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 3427e0efd4..507d15cbde 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
@@ -50,10 +50,10 @@ function foo$0() {
 
 ```
 bb0:
-  [1] Const mutate a$2_@0[1:3] = Array []
-  [2] Const mutate b$3_@0[2:7] = Object {  }
+  [1] Const mutate a$2_@0[0:7] = Array []
+  [2] Const mutate b$3_@0[0:7] = Object {  }
   [3] Call mutate foo$4_@0(mutate a$2_@0, mutate b$3_@0)
-  [4] Const mutate $7_@0 = Call mutate foo$4_@0()
+  [4] Const mutate $7_@0[0:7] = Call mutate foo$4_@0()
   If (read $7_@0) then:bb2 else:bb1
 bb2:
   predecessor blocks: bb0
@@ -75,10 +75,10 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Const mutate a$2_@0[1:3] = Array []
-      [2] Const mutate b$3_@0[2:7] = Object {  }
+      [1] Const mutate a$2_@0[0:7] = Array []
+      [2] Const mutate b$3_@0[0:7] = Object {  }
       [3] Call mutate foo$4_@0(mutate a$2_@0, mutate b$3_@0)
-      [4] Const mutate $7_@0 = Call mutate foo$4_@0()
+      [4] Const mutate $7_@0[0:7] = Call mutate foo$4_@0()
     "]
     bb0_instrs --> bb0_terminal(["If (read $7_@0)"])
   end
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 285a805d1a..beac169a6b 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
@@ -47,8 +47,8 @@ function foo$0() {
 
 ```
 bb0:
-  [1] Const mutate a$2_@0[1:3] = Array []
-  [2] Const mutate b$3_@0[2:6] = Object {  }
+  [1] Const mutate a$2_@0[0:6] = Array []
+  [2] Const mutate b$3_@0[0:6] = Object {  }
   [3] Call mutate foo$4_@0(mutate a$2_@0, mutate b$3_@0)
   [4] Const mutate $6_@1 = "div"
   [5] Let mutate _$5_@2 = JSX <read $6_@1 a={freeze a$2_@0} ></read $6_@1>
@@ -65,8 +65,8 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Const mutate a$2_@0[1:3] = Array []
-      [2] Const mutate b$3_@0[2:6] = Object {  }
+      [1] Const mutate a$2_@0[0:6] = Array []
+      [2] Const mutate b$3_@0[0:6] = Object {  }
       [3] Call mutate foo$4_@0(mutate a$2_@0, mutate b$3_@0)
       [4] Const mutate $6_@1 = 'div'
       [5] Let mutate _$5_@2 = JSX <read $6_@1 a={freeze a$2_@0} ></read $6_@1>
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 4807737597..401618fad1 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
@@ -21,14 +21,14 @@ function foo() {
 
 ```
 bb0:
-  [1] Let mutate x$1_@0 = 1
+  [1] Let mutate x$1_@0[1:8] = 1
   [2] Let mutate y$2_@1 = 2
   [3] Const mutate $3_@2 = 2
   [4] Const mutate $4_@3 = Binary read y$2_@1 === read $3_@2
   If (read $4_@3) then:bb2 else:bb1
 bb2:
   predecessor blocks: bb0
-  [5] Reassign mutate x$1_@0 = 3
+  [5] Reassign mutate x$1_@0[1:8] = 3
   Goto bb1
 bb1:
   predecessor blocks: bb2 bb0
@@ -37,7 +37,7 @@ bb1:
   If (read $6_@5) then:bb4 else:bb3
 bb4:
   predecessor blocks: bb1
-  [8] Reassign mutate x$1_@0 = 5
+  [8] Reassign mutate x$1_@0[1:8] = 5
   Goto bb3
 bb3:
   predecessor blocks: bb4 bb1
@@ -52,7 +52,7 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Let mutate x$1_@0 = 1
+      [1] Let mutate x$1_@0[1:8] = 1
       [2] Let mutate y$2_@1 = 2
       [3] Const mutate $3_@2 = 2
       [4] Const mutate $4_@3 = Binary read y$2_@1 === read $3_@2
@@ -61,7 +61,7 @@ flowchart TB
   end
   subgraph bb2
     bb2_instrs["
-      [5] Reassign mutate x$1_@0 = 3
+      [5] Reassign mutate x$1_@0[1:8] = 3
     "]
     bb2_instrs --> bb2_terminal(["Goto"])
   end
@@ -74,7 +74,7 @@ flowchart TB
   end
   subgraph bb4
     bb4_instrs["
-      [8] Reassign mutate x$1_@0 = 5
+      [8] Reassign mutate x$1_@0[1:8] = 5
     "]
     bb4_instrs --> bb4_terminal(["Goto"])
   end
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 53af4d4f12..49bf4281f6 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
@@ -18,14 +18,14 @@ function foo() {
 
 ```
 bb0:
-  [1] Let mutate x$1_@0 = 1
+  [1] Let mutate x$1_@0[1:5] = 1
   [2] Let mutate y$2_@1 = 2
   [3] Const mutate $3_@2 = 2
   [4] Const mutate $4_@3 = Binary read y$2_@1 === read $3_@2
   If (read $4_@3) then:bb2 else:bb1
 bb2:
   predecessor blocks: bb0
-  [5] Reassign mutate x$1_@0 = 3
+  [5] Reassign mutate x$1_@0[1:5] = 3
   Goto bb1
 bb1:
   predecessor blocks: bb2 bb0
@@ -40,7 +40,7 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Let mutate x$1_@0 = 1
+      [1] Let mutate x$1_@0[1:5] = 1
       [2] Let mutate y$2_@1 = 2
       [3] Const mutate $3_@2 = 2
       [4] Const mutate $4_@3 = Binary read y$2_@1 === read $3_@2
@@ -49,7 +49,7 @@ flowchart TB
   end
   subgraph bb2
     bb2_instrs["
-      [5] Reassign mutate x$1_@0 = 3
+      [5] Reassign mutate x$1_@0[1:5] = 3
     "]
     bb2_instrs --> bb2_terminal(["Goto"])
   end
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 d750634c9a..a3a3846dde 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-for.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-for.expect.md
@@ -16,7 +16,7 @@ function foo() {
 
 ```
 bb0:
-  [1] Let mutate x$1_@0 = 0
+  [1] Let mutate x$1_@0[0:5] = 0
   Goto bb1
 bb1:
   predecessor blocks: bb0 bb4
@@ -26,7 +26,7 @@ bb1:
 bb4:
   predecessor blocks: bb1
   [4] Const mutate $2_@3 = 1
-  [5] Reassign mutate x$1_@0 = Binary read x$1_@0 + read $2_@3
+  [5] Reassign mutate x$1_@0[0:5] = Binary read x$1_@0 + read $2_@3
   Goto(Continue) bb1
 bb2:
   predecessor blocks: bb1
@@ -40,7 +40,7 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Let mutate x$1_@0 = 0
+      [1] Let mutate x$1_@0[0:5] = 0
     "]
     bb0_instrs --> bb0_terminal(["Goto"])
   end
@@ -54,7 +54,7 @@ flowchart TB
   subgraph bb4
     bb4_instrs["
       [4] Const mutate $2_@3 = 1
-      [5] Reassign mutate x$1_@0 = Binary read x$1_@0 + read $2_@3
+      [5] Reassign mutate x$1_@0[0:5] = Binary read x$1_@0 + read $2_@3
     "]
     bb4_instrs --> bb4_terminal(["Goto"])
   end
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 40550e4071..62e8e181bd 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-newexpression.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-newexpression.expect.md
@@ -45,9 +45,9 @@ function Foo$0() {
 
 ```
 bb0:
-  [1] Const mutate a$2_@0[1:3] = Array []
-  [2] Const mutate b$3_@0[2:3] = Object {  }
-  [3] Let mutate c$4_@0 = New mutate Foo$5_@0(mutate a$2_@0, mutate b$3_@0)
+  [1] Const mutate a$2_@0[0:3] = Array []
+  [2] Const mutate b$3_@0[0:3] = Object {  }
+  [3] Let mutate c$4_@0[0:3] = New mutate Foo$5_@0(mutate a$2_@0, mutate b$3_@0)
   Return freeze c$4_@0
 ```
 
@@ -58,9 +58,9 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Const mutate a$2_@0[1:3] = Array []
-      [2] Const mutate b$3_@0[2:3] = Object {  }
-      [3] Let mutate c$4_@0 = New mutate Foo$5_@0(mutate a$2_@0, mutate b$3_@0)
+      [1] Const mutate a$2_@0[0:3] = Array []
+      [2] Const mutate b$3_@0[0:3] = Object {  }
+      [3] Let mutate c$4_@0[0:3] = New mutate Foo$5_@0(mutate a$2_@0, mutate b$3_@0)
     "]
     bb0_instrs --> bb0_terminal(["Return freeze c$4_@0"])
   end
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 4596a48ce1..eab076d40f 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
@@ -22,18 +22,18 @@ function foo() {
 
 ```
 bb0:
-  [1] Let mutate x$1_@0 = 1
-  [2] Let mutate y$2_@1 = 2
+  [1] Let mutate x$1_@0[1:5] = 1
+  [2] Let mutate y$2_@1[2:6] = 2
   [3] Const mutate $3_@2 = 1
   [4] Const mutate $4_@3 = Binary read x$1_@0 > read $3_@2
   If (read $4_@3) then:bb2 else:bb3
 bb2:
   predecessor blocks: bb0
-  [5] Reassign mutate x$1_@0 = 2
+  [5] Reassign mutate x$1_@0[1:5] = 2
   Goto bb1
 bb3:
   predecessor blocks: bb0
-  [6] Reassign mutate y$2_@1 = 3
+  [6] Reassign mutate y$2_@1[2:6] = 3
   Goto bb1
 bb1:
   predecessor blocks: bb2 bb3
@@ -48,8 +48,8 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Let mutate x$1_@0 = 1
-      [2] Let mutate y$2_@1 = 2
+      [1] Let mutate x$1_@0[1:5] = 1
+      [2] Let mutate y$2_@1[2:6] = 2
       [3] Const mutate $3_@2 = 1
       [4] Const mutate $4_@3 = Binary read x$1_@0 > read $3_@2
     "]
@@ -57,13 +57,13 @@ flowchart TB
   end
   subgraph bb2
     bb2_instrs["
-      [5] Reassign mutate x$1_@0 = 2
+      [5] Reassign mutate x$1_@0[1:5] = 2
     "]
     bb2_instrs --> bb2_terminal(["Goto"])
   end
   subgraph bb3
     bb3_instrs["
-      [6] Reassign mutate y$2_@1 = 3
+      [6] Reassign mutate y$2_@1[2:6] = 3
     "]
     bb3_instrs --> bb3_terminal(["Goto"])
   end
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 5aefad393a..f05cb7ce88 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
@@ -17,7 +17,7 @@ function foo() {
 bb0:
   [1] Const mutate x$1_@0 = Array []
   [2] Const mutate y$2_@1[2:4] = Object { x: read x$1_@0 }
-  [3] Const mutate $3_@1[3:4] = Array []
+  [3] Const mutate $3_@1[2:4] = Array []
   [4] Call mutate y$2_@1.x.push(mutate $3_@1)
   Return freeze y$2_@1
 ```
@@ -31,7 +31,7 @@ flowchart TB
     bb0_instrs["
       [1] Const mutate x$1_@0 = Array []
       [2] Const mutate y$2_@1[2:4] = Object { x: read x$1_@0 }
-      [3] Const mutate $3_@1[3:4] = Array []
+      [3] Const mutate $3_@1[2:4] = Array []
       [4] Call mutate y$2_@1.x.push(mutate $3_@1)
     "]
     bb0_instrs --> bb0_terminal(["Return freeze y$2_@1"])
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 ce8558cbb9..e4831fe2dc 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-return.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-return.expect.md
@@ -17,13 +17,13 @@ function foo() {
 
 ```
 bb0:
-  [1] Let mutate x$1_@0 = 1
+  [1] Let mutate x$1_@0[1:4] = 1
   [2] Const mutate $2_@1 = 1
   [3] Const mutate $3_@2 = Binary read x$1_@0 === read $2_@1
   If (read $3_@2) then:bb2 else:bb1
 bb2:
   predecessor blocks: bb0
-  [4] Reassign mutate x$1_@0 = 2
+  [4] Reassign mutate x$1_@0[1:4] = 2
   Goto bb1
 bb1:
   predecessor blocks: bb2 bb0
@@ -37,7 +37,7 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Let mutate x$1_@0 = 1
+      [1] Let mutate x$1_@0[1:4] = 1
       [2] Const mutate $2_@1 = 1
       [3] Const mutate $3_@2 = Binary read x$1_@0 === read $2_@1
     "]
@@ -45,7 +45,7 @@ flowchart TB
   end
   subgraph bb2
     bb2_instrs["
-      [4] Reassign mutate x$1_@0 = 2
+      [4] Reassign mutate x$1_@0[1:4] = 2
     "]
     bb2_instrs --> bb2_terminal(["Goto"])
   end
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 378af61469..699e72e7b2 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$2_@0 = ""
+  [1] Let mutate str$2_@0[1:4] = ""
   If (read cond$1) then:bb2 else:bb3
 bb2:
   predecessor blocks: bb0
@@ -58,7 +58,7 @@ bb2:
   Goto bb1
 bb3:
   predecessor blocks: bb0
-  [4] Reassign mutate str$2_@0 = "fallthrough test"
+  [4] Reassign mutate str$2_@0[1:4] = "fallthrough test"
   Goto bb1
 bb1:
   predecessor blocks: bb2 bb3
@@ -73,7 +73,7 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Let mutate str$2_@0 = ''
+      [1] Let mutate str$2_@0[1:4] = ''
     "]
     bb0_instrs --> bb0_terminal(["If (read cond$1)"])
   end
@@ -86,7 +86,7 @@ flowchart TB
   end
   subgraph bb3
     bb3_instrs["
-      [4] Reassign mutate str$2_@0 = 'fallthrough test'
+      [4] Reassign mutate str$2_@0[1:4] = 'fallthrough test'
     "]
     bb3_instrs --> bb3_terminal(["Goto"])
   end
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 030f14e678..fefd8c4465 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
@@ -26,11 +26,11 @@ bb0:
   If (read $3_@2) then:bb2 else:bb3
 bb2:
   predecessor blocks: bb0
-  [4] Reassign mutate y$1_@3 = 1
+  [4] Reassign mutate y$1_@3[4:5] = 1
   Goto bb1
 bb3:
   predecessor blocks: bb0
-  [5] Reassign mutate y$1_@3 = 2
+  [5] Reassign mutate y$1_@3[4:5] = 2
   Goto bb1
 bb1:
   predecessor blocks: bb2 bb3
@@ -53,13 +53,13 @@ flowchart TB
   end
   subgraph bb2
     bb2_instrs["
-      [4] Reassign mutate y$1_@3 = 1
+      [4] Reassign mutate y$1_@3[4:5] = 1
     "]
     bb2_instrs --> bb2_terminal(["Goto"])
   end
   subgraph bb3
     bb3_instrs["
-      [5] Reassign mutate y$1_@3 = 2
+      [5] Reassign mutate y$1_@3[4:5] = 2
     "]
     bb3_instrs --> bb3_terminal(["Goto"])
   end
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 1713025598..a796c43905 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-switch.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-switch.expect.md
@@ -40,17 +40,17 @@ bb0:
 bb5:
   predecessor blocks: bb0
   [6] Const mutate $6_@5 = 1
-  [7] Reassign mutate x$1_@6 = Binary read x$1_@0 + read $6_@5
+  [7] Reassign mutate x$1_@6[7:11] = Binary read x$1_@0 + read $6_@5
   Goto bb1
 bb3:
   predecessor blocks: bb0
   [8] Const mutate $3_@7 = 2
-  [9] Reassign mutate x$1_@6 = Binary read x$1_@0 + read $3_@7
+  [9] Reassign mutate x$1_@6[7:11] = Binary read x$1_@0 + read $3_@7
   Goto bb1
 bb2:
   predecessor blocks: bb0
   [10] Const mutate $2_@8 = 3
-  [11] Reassign mutate x$1_@6 = Binary read x$1_@0 + read $2_@8
+  [11] Reassign mutate x$1_@6[7:11] = Binary read x$1_@0 + read $2_@8
   Goto bb1
 bb1:
   predecessor blocks: bb5 bb3 bb2
@@ -76,21 +76,21 @@ flowchart TB
   subgraph bb5
     bb5_instrs["
       [6] Const mutate $6_@5 = 1
-      [7] Reassign mutate x$1_@6 = Binary read x$1_@0 + read $6_@5
+      [7] Reassign mutate x$1_@6[7:11] = Binary read x$1_@0 + read $6_@5
     "]
     bb5_instrs --> bb5_terminal(["Goto"])
   end
   subgraph bb3
     bb3_instrs["
       [8] Const mutate $3_@7 = 2
-      [9] Reassign mutate x$1_@6 = Binary read x$1_@0 + read $3_@7
+      [9] Reassign mutate x$1_@6[7:11] = Binary read x$1_@0 + read $3_@7
     "]
     bb3_instrs --> bb3_terminal(["Goto"])
   end
   subgraph bb2
     bb2_instrs["
       [10] Const mutate $2_@8 = 3
-      [11] Reassign mutate x$1_@6 = Binary read x$1_@0 + read $2_@8
+      [11] Reassign mutate x$1_@6[7:11] = Binary read x$1_@0 + read $2_@8
     "]
     bb2_instrs --> bb2_terminal(["Goto"])
   end
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 5d54773ea7..16b0784ec2 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-throw.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-throw.expect.md
@@ -16,13 +16,13 @@ function foo() {
 
 ```
 bb0:
-  [1] Let mutate x$1_@0 = 1
+  [1] Let mutate x$1_@0[1:4] = 1
   [2] Const mutate $2_@1 = 1
   [3] Const mutate $3_@2 = Binary read x$1_@0 === read $2_@1
   If (read $3_@2) then:bb2 else:bb1
 bb2:
   predecessor blocks: bb0
-  [4] Reassign mutate x$1_@0 = 2
+  [4] Reassign mutate x$1_@0[1:4] = 2
   Goto bb1
 bb1:
   predecessor blocks: bb2 bb0
@@ -36,7 +36,7 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Let mutate x$1_@0 = 1
+      [1] Let mutate x$1_@0[1:4] = 1
       [2] Const mutate $2_@1 = 1
       [3] Const mutate $3_@2 = Binary read x$1_@0 === read $2_@1
     "]
@@ -44,7 +44,7 @@ flowchart TB
   end
   subgraph bb2
     bb2_instrs["
-      [4] Reassign mutate x$1_@0 = 2
+      [4] Reassign mutate x$1_@0[1:4] = 2
     "]
     bb2_instrs --> bb2_terminal(["Goto"])
   end
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 560f33325f..c16a101817 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-while.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-while.expect.md
@@ -17,7 +17,7 @@ function foo() {
 
 ```
 bb0:
-  [1] Let mutate x$1_@0 = 1
+  [1] Let mutate x$1_@0[0:5] = 1
   While test=bb1 loop=bb3 fallthrough=bb2
 bb1:
   predecessor blocks: bb0 bb3
@@ -27,7 +27,7 @@ bb1:
 bb3:
   predecessor blocks: bb1
   [4] Const mutate $2_@3 = 1
-  [5] Reassign mutate x$1_@0 = Binary read x$1_@0 + read $2_@3
+  [5] Reassign mutate x$1_@0[0:5] = Binary read x$1_@0 + read $2_@3
   Goto(Continue) bb1
 bb2:
   predecessor blocks: bb1
@@ -41,7 +41,7 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Let mutate x$1_@0 = 1
+      [1] Let mutate x$1_@0[0:5] = 1
     "]
     bb0_instrs --> bb0_terminal(["While"])
   end
@@ -55,7 +55,7 @@ flowchart TB
   subgraph bb3
     bb3_instrs["
       [4] Const mutate $2_@3 = 1
-      [5] Reassign mutate x$1_@0 = Binary read x$1_@0 + read $2_@3
+      [5] Reassign mutate x$1_@0[0:5] = Binary read x$1_@0 + read $2_@3
     "]
     bb3_instrs --> bb3_terminal(["Goto"])
   end
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 0a860dd2f4..7a2375b0c1 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
@@ -33,7 +33,7 @@ function Component(props) {
 ```
 bb0:
   [1] Let mutate x$2_@0[1:6] = Array []
-  [2] Let mutate y$3_@1 = undefined
+  [2] Let mutate y$3_@1[2:8] = undefined
   [3] Const mutate $4_@2 = false
   [4] Const mutate $5_@3 = true
   [5] Const mutate $6_@4 = 1
@@ -45,11 +45,11 @@ bb0:
 bb6:
   predecessor blocks: bb0
   [6] Call mutate x$2_@0.push(read props$1.p2)
-  [7] Reassign mutate y$3_@1 = Array []
+  [7] Reassign mutate y$3_@1[2:8] = Array []
   Goto bb1
 bb2:
   predecessor blocks: bb0
-  [8] Reassign mutate y$3_@1 = read x$2_@0
+  [8] Reassign mutate y$3_@1[2:8] = read x$2_@0
   Goto bb1
 bb1:
   predecessor blocks: bb0 bb6 bb2
@@ -67,7 +67,7 @@ flowchart TB
   subgraph bb0
     bb0_instrs["
       [1] Let mutate x$2_@0[1:6] = Array []
-      [2] Let mutate y$3_@1 = undefined
+      [2] Let mutate y$3_@1[2:8] = undefined
       [3] Const mutate $4_@2 = false
       [4] Const mutate $5_@3 = true
       [5] Const mutate $6_@4 = 1
@@ -77,13 +77,13 @@ flowchart TB
   subgraph bb6
     bb6_instrs["
       [6] Call mutate x$2_@0.push(read props$1.p2)
-      [7] Reassign mutate y$3_@1 = Array []
+      [7] Reassign mutate y$3_@1[2:8] = Array []
     "]
     bb6_instrs --> bb6_terminal(["Goto"])
   end
   subgraph bb2
     bb2_instrs["
-      [8] Reassign mutate y$3_@1 = read x$2_@0
+      [8] Reassign mutate y$3_@1[2:8] = read x$2_@0
     "]
     bb2_instrs --> bb2_terminal(["Goto"])
   end
diff --git a/compiler/forget/src/__tests__/fixtures/hir/switch.expect.md b/compiler/forget/src/__tests__/fixtures/hir/switch.expect.md
index 58a3ac0103..65eec56240 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/switch.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/switch.expect.md
@@ -29,7 +29,7 @@ function Component(props) {
 ```
 bb0:
   [1] Let mutate x$2_@0[1:6] = Array []
-  [2] Let mutate y$3_@1 = undefined
+  [2] Let mutate y$3_@1[2:8] = undefined
   [3] Const mutate $4_@2 = false
   [4] Const mutate $5_@3 = true
   Switch (read props$1.p0)
@@ -44,7 +44,7 @@ bb4:
   Goto bb2
 bb2:
   predecessor blocks: bb4 bb0
-  [8] Reassign mutate y$3_@1 = read x$2_@0
+  [8] Reassign mutate y$3_@1[2:8] = read x$2_@0
   Goto bb1
 bb1:
   predecessor blocks: bb2 bb0
@@ -62,7 +62,7 @@ flowchart TB
   subgraph bb0
     bb0_instrs["
       [1] Let mutate x$2_@0[1:6] = Array []
-      [2] Let mutate y$3_@1 = undefined
+      [2] Let mutate y$3_@1[2:8] = undefined
       [3] Const mutate $4_@2 = false
       [4] Const mutate $5_@3 = true
     "]
@@ -78,7 +78,7 @@ flowchart TB
   end
   subgraph bb2
     bb2_instrs["
-      [8] Reassign mutate y$3_@1 = read x$2_@0
+      [8] Reassign mutate y$3_@1[2:8] = read x$2_@0
     "]
     bb2_instrs --> bb2_terminal(["Goto"])
   end