From b0096264315bd4efe9f404c8b65039120c5e8a49 Mon Sep 17 00:00:00 2001
From: Joe Savona <joesavona@fb.com>
Date: Fri, 3 Feb 2023 15:46:00 -0800
Subject: [PATCH] Improve DCE to handle unused loop phis

Improves DCE, using fixpoint iteration to detect values that are updated across
loops but otherwise never read. There is still some further optimization we can
do (the dce-loop case could optimize out `y`), but this seems like plenty for
now.

Actually, we probably have to add some return statements to our fixtures before
landing this, because otherwise most of the code goes away.
---
 .../src/Optimization/DeadCodeElimination.ts   | 105 +++++++-----------
 .../fixtures/hir/alias-while.expect.md        |  13 +--
 .../hir/assignment-variations.expect.md       |   9 +-
 .../hir/constant-propagation-phi.expect.md    |  14 ---
 .../__tests__/fixtures/hir/dce-loop.expect.md |  27 +++++
 .../src/__tests__/fixtures/hir/dce-loop.js    |   8 ++
 .../hir/destructuring-assignment.expect.md    |  12 +-
 .../fixtures/hir/destructuring.expect.md      |   8 +-
 .../hir/infer-phi-primitive.expect.md         |  19 ++--
 .../obj-literal-cached-in-if-else.expect.md   |  31 +++---
 ...bj-literal-mutated-after-if-else.expect.md |  21 ++--
 .../hir/primitive-alias-mutate.expect.md      |  19 ++--
 .../fixtures/hir/reverse-postorder.expect.md  |  61 +++-------
 .../fixtures/hir/ssa-call-jsx-2.expect.md     |   1 -
 .../hir/ssa-complex-multiple-if.expect.md     |  13 +--
 .../hir/ssa-complex-single-if.expect.md       |  11 +-
 .../fixtures/hir/ssa-if-else.expect.md        |   7 +-
 .../ssa-nested-loops-no-reassign.expect.md    |   5 +-
 .../hir/ssa-nested-partial-phi.expect.md      |  16 +--
 .../fixtures/hir/ssa-sibling-phis.expect.md   |   9 +-
 .../fixtures/hir/ssa-simple-phi.expect.md     |  10 +-
 .../fixtures/hir/ssa-simple.expect.md         |   5 +-
 .../fixtures/hir/ssa-single-if.expect.md      |   7 +-
 .../fixtures/hir/ssa-switch.expect.md         |  38 ++-----
 .../hir/ssa-while-no-reassign.expect.md       |   5 +-
 .../hir/switch-with-fallthrough.expect.md     |   6 -
 .../type-args-test-binary-operator.expect.md  |   1 -
 .../hir/type-binary-operator.expect.md        |   1 -
 .../fixtures/hir/type-field-load.expect.md    |  12 +-
 .../type-test-field-load-binary-op.expect.md  |   3 -
 .../hir/type-test-primitive.expect.md         |   5 +-
 .../type-test-return-type-inference.expect.md |   1 -
 32 files changed, 157 insertions(+), 346 deletions(-)
 create mode 100644 compiler/forget/src/__tests__/fixtures/hir/dce-loop.expect.md
 create mode 100644 compiler/forget/src/__tests__/fixtures/hir/dce-loop.js

diff --git a/compiler/forget/src/Optimization/DeadCodeElimination.ts b/compiler/forget/src/Optimization/DeadCodeElimination.ts
index e97fbd70bb..23a6394bb0 100644
--- a/compiler/forget/src/Optimization/DeadCodeElimination.ts
+++ b/compiler/forget/src/Optimization/DeadCodeElimination.ts
@@ -5,18 +5,12 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {
-  BlockId,
-  HIRFunction,
-  Identifier,
-  Instruction,
-  InstructionValue,
-} from "../HIR";
+import { HIRFunction, Identifier, InstructionValue } from "../HIR";
 import {
   eachInstructionValueOperand,
   eachTerminalOperand,
 } from "../HIR/visitors";
-import { assertExhaustive } from "../Utils/utils";
+import { assertExhaustive, retainWhere } from "../Utils/utils";
 
 /**
  * Implements dead-code elimination, eliminating instructions whose values are unused.
@@ -26,71 +20,54 @@ import { assertExhaustive } from "../Utils/utils";
 export function deadCodeElimination(fn: HIRFunction): void {
   const used = new Set<Identifier>();
 
-  // Find any phi operands involved in a loop, which might otherwise appear as dead
-  // code when using a reverse iteration.
-  //
-  // A more advanced algorithm could still prune some of these operands
-  // let's keep it simple for now
-  const seen = new Set<BlockId>();
-  for (const [, block] of fn.body.blocks) {
-    for (const phi of block.phis) {
-      for (const [pred, operand] of phi.operands) {
-        if (!seen.has(pred)) {
-          used.add(operand);
-        }
-      }
-    }
-    seen.add(block.id);
-  }
+  // TODO: ensure a single iteration of the CFG if there are no back-edges,
+  // see EliminateRedundantPhi.ts for an example
+  let lastSize = -1;
+  while (used.size > lastSize) {
+    lastSize = used.size;
 
-  // Iterate blocks in postorder (successors before predecessors, excepting loops)
-  // to find usages before declarations
-  const reversedBlocks = [...fn.body.blocks.values()].reverse();
-  for (const block of reversedBlocks) {
-    for (const operand of eachTerminalOperand(block.terminal)) {
-      used.add(operand.identifier);
-    }
-
-    let nextInstructions: Array<Instruction> | null = null;
-    for (let i = block.instructions.length - 1; i >= 0; i--) {
-      const instr = block.instructions[i]!;
-      if (
-        !used.has(instr.lvalue.place.identifier) &&
-        pruneableValue(instr.value) &&
-        // Can't prune the last value of a value block, that's its value!
-        !(block.kind !== "block" && i === block.instructions.length - 1)
-      ) {
-        continue;
-      }
-      used.add(instr.lvalue.place.identifier);
-      nextInstructions ??= [];
-      nextInstructions.push(instr);
-      for (const operand of eachInstructionValueOperand(instr.value)) {
+    // Iterate blocks in postorder (successors before predecessors, excepting loops)
+    // to find usages before declarations
+    const reversedBlocks = [...fn.body.blocks.values()].reverse();
+    for (const block of reversedBlocks) {
+      for (const operand of eachTerminalOperand(block.terminal)) {
         used.add(operand.identifier);
       }
-    }
-    if (nextInstructions !== null) {
-      nextInstructions.reverse();
-      block.instructions = nextInstructions;
-    }
-    for (const phi of block.phis) {
-      if (used.has(phi.id)) {
-        for (const [, operand] of phi.operands) {
-          used.add(operand);
+
+      for (let i = block.instructions.length - 1; i >= 0; i--) {
+        const instr = block.instructions[i]!;
+        if (
+          !used.has(instr.lvalue.place.identifier) &&
+          pruneableValue(instr.value) &&
+          // Can't prune the last value of a value block, that's its value!
+          !(block.kind !== "block" && i === block.instructions.length - 1)
+        ) {
+          continue;
         }
-      } else {
-        for (const [, operand] of phi.operands) {
-          if (used.has(operand)) {
-            used.add(phi.id);
-            for (const [, operand] of phi.operands) {
-              used.add(operand);
-            }
-            break;
+        used.add(instr.lvalue.place.identifier);
+        for (const operand of eachInstructionValueOperand(instr.value)) {
+          used.add(operand.identifier);
+        }
+      }
+      for (const phi of block.phis) {
+        if (used.has(phi.id)) {
+          for (const [pred, operand] of phi.operands) {
+            used.add(operand);
           }
         }
       }
     }
   }
+  for (const [, block] of fn.body.blocks) {
+    for (const phi of block.phis) {
+      if (!used.has(phi.id)) {
+        block.phis.delete(phi);
+      }
+    }
+    retainWhere(block.instructions, (instr) =>
+      used.has(instr.lvalue.place.identifier)
+    );
+  }
 }
 
 /**
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 983b62fdcb..fa37177f0c 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/alias-while.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/alias-while.expect.md
@@ -30,12 +30,10 @@ function foo(cond) {
   const $ = React.useMemoCache();
   const c_0 = $[0] !== cond;
   let a;
-  let b;
-  let c;
   if (c_0) {
     a = {};
-    b = {};
-    c = {};
+    let b = {};
+    let c = {};
     while (cond) {
       const z = a;
       a = b;
@@ -45,16 +43,9 @@ function foo(cond) {
     }
     $[0] = cond;
     $[1] = a;
-    $[2] = b;
-    $[3] = c;
   } else {
     a = $[1];
-    b = $[2];
-    c = $[3];
   }
-  a;
-  b;
-  c;
   return a;
 }
 
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 dc12b49c37..edb9c4e0fa 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/assignment-variations.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/assignment-variations.expect.md
@@ -14,14 +14,7 @@ function f() {
 ## Code
 
 ```javascript
-function f() {
-  const x = 1;
-  1;
-  const x$0 = 2;
-  1;
-  const x$1 = 3;
-  const x$2 = x$1 >>> 1;
-}
+function f() {}
 
 ```
       
\ No newline at end of file
diff --git a/compiler/forget/src/__tests__/fixtures/hir/constant-propagation-phi.expect.md b/compiler/forget/src/__tests__/fixtures/hir/constant-propagation-phi.expect.md
index aa96bdf0a9..a0a4f00831 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/constant-propagation-phi.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/constant-propagation-phi.expect.md
@@ -22,23 +22,9 @@ function foo(a, b, c) {
 
 ```javascript
 function foo(a, b, c) {
-  const x = undefined;
-  let x$0 = undefined;
   if (a) {
-    2;
-    1;
-
-    const x$1 = 1;
-    x$0 = x$1;
   } else {
-    0;
-    1;
-
-    const x$2 = 1;
-    x$0 = x$2;
   }
-  1;
-  true;
   return b;
 }
 
diff --git a/compiler/forget/src/__tests__/fixtures/hir/dce-loop.expect.md b/compiler/forget/src/__tests__/fixtures/hir/dce-loop.expect.md
new file mode 100644
index 0000000000..9377023a0b
--- /dev/null
+++ b/compiler/forget/src/__tests__/fixtures/hir/dce-loop.expect.md
@@ -0,0 +1,27 @@
+
+## Input
+
+```javascript
+function foo(props) {
+  let x = 0;
+  let y = 0;
+  while (y < props.max) {
+    x++;
+    y++;
+  }
+}
+
+```
+
+## Code
+
+```javascript
+function foo(props) {
+  let y = 0;
+  while (y < props.max) {
+    y = y + 1;
+  }
+}
+
+```
+      
\ No newline at end of file
diff --git a/compiler/forget/src/__tests__/fixtures/hir/dce-loop.js b/compiler/forget/src/__tests__/fixtures/hir/dce-loop.js
new file mode 100644
index 0000000000..1ce81fe2c6
--- /dev/null
+++ b/compiler/forget/src/__tests__/fixtures/hir/dce-loop.js
@@ -0,0 +1,8 @@
+function foo(props) {
+  let x = 0;
+  let y = 0;
+  while (y < props.max) {
+    x++;
+    y++;
+  }
+}
diff --git a/compiler/forget/src/__tests__/fixtures/hir/destructuring-assignment.expect.md b/compiler/forget/src/__tests__/fixtures/hir/destructuring-assignment.expect.md
index 67a7954a80..b49d9d73cb 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/destructuring-assignment.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/destructuring-assignment.expect.md
@@ -25,17 +25,7 @@ function foo(a, b, c) {
 ## Code
 
 ```javascript
-function foo(a, b, c) {
-  const d = undefined;
-  const g = undefined;
-  const n = undefined;
-  const o = undefined;
-  const d$0 = a[0];
-  const g$1 = a[1][0].e.f;
-
-  const n$2 = b.l.m[0][0];
-  const o$3 = b.o;
-}
+function foo(a, b, c) {}
 
 ```
       
\ No newline at end of file
diff --git a/compiler/forget/src/__tests__/fixtures/hir/destructuring.expect.md b/compiler/forget/src/__tests__/fixtures/hir/destructuring.expect.md
index 2c26bd28c9..d153e036f2 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/destructuring.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/destructuring.expect.md
@@ -24,13 +24,7 @@ function foo(a, b, c) {
 ## Code
 
 ```javascript
-function foo(a, b, c) {
-  const d = a[0];
-  const f = a[1][0].e.f;
-
-  const n = b.l.m[0][0];
-  const o = b.o;
-}
+function foo(a, b, c) {}
 
 ```
       
\ No newline at end of file
diff --git a/compiler/forget/src/__tests__/fixtures/hir/infer-phi-primitive.expect.md b/compiler/forget/src/__tests__/fixtures/hir/infer-phi-primitive.expect.md
index e00fdab235..1a2e72575f 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/infer-phi-primitive.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/infer-phi-primitive.expect.md
@@ -21,25 +21,24 @@ function foo(a, b) {
 ```javascript
 function foo(a, b) {
   const $ = React.useMemoCache();
-  const x = undefined;
   const c_0 = $[0] !== a;
-  let x$0;
+  let x;
   if (c_0) {
-    x$0 = undefined;
+    x = undefined;
     if (a) {
-      const x$1 = 1;
-      x$0 = x$1;
+      const x$0 = 1;
+      x = x$0;
     } else {
-      const x$2 = 2;
-      x$0 = x$2;
+      const x$1 = 2;
+      x = x$1;
     }
     $[0] = a;
-    $[1] = x$0;
+    $[1] = x;
   } else {
-    x$0 = $[1];
+    x = $[1];
   }
 
-  const y = x$0;
+  const y = x;
   return y;
 }
 
diff --git a/compiler/forget/src/__tests__/fixtures/hir/obj-literal-cached-in-if-else.expect.md b/compiler/forget/src/__tests__/fixtures/hir/obj-literal-cached-in-if-else.expect.md
index 5927fc3de3..6d71a7389a 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/obj-literal-cached-in-if-else.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/obj-literal-cached-in-if-else.expect.md
@@ -20,42 +20,41 @@ function foo(a, b, c, d) {
 ```javascript
 function foo(a, b, c, d) {
   const $ = React.useMemoCache();
-  const x = {};
   const c_0 = $[0] !== b;
   const c_1 = $[1] !== c;
-  let x$0;
+  let x;
   if (c_0 || c_1) {
-    x$0 = undefined;
+    x = undefined;
     if (someVal) {
       const c_3 = $[3] !== b;
-      let x$1;
+      let x$0;
       if (c_3) {
-        x$1 = { b: b };
+        x$0 = { b: b };
         $[3] = b;
-        $[4] = x$1;
+        $[4] = x$0;
       } else {
-        x$1 = $[4];
+        x$0 = $[4];
       }
-      x$0 = x$1;
+      x = x$0;
     } else {
       const c_5 = $[5] !== c;
-      let x$2;
+      let x$1;
       if (c_5) {
-        x$2 = { c: c };
+        x$1 = { c: c };
         $[5] = c;
-        $[6] = x$2;
+        $[6] = x$1;
       } else {
-        x$2 = $[6];
+        x$1 = $[6];
       }
-      x$0 = x$2;
+      x = x$1;
     }
     $[0] = b;
     $[1] = c;
-    $[2] = x$0;
+    $[2] = x;
   } else {
-    x$0 = $[2];
+    x = $[2];
   }
-  return x$0;
+  return x;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/obj-literal-mutated-after-if-else.expect.md b/compiler/forget/src/__tests__/fixtures/hir/obj-literal-mutated-after-if-else.expect.md
index 853a25b354..9e980329a7 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/obj-literal-mutated-after-if-else.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/obj-literal-mutated-after-if-else.expect.md
@@ -21,27 +21,26 @@ function foo(a, b, c, d) {
 ```javascript
 function foo(a, b, c, d) {
   const $ = React.useMemoCache();
-  const x = {};
   const c_0 = $[0] !== b;
   const c_1 = $[1] !== c;
-  let x$0;
+  let x;
   if (c_0 || c_1) {
-    x$0 = undefined;
+    x = undefined;
     if (someVal) {
-      const x$1 = { b: b };
-      x$0 = x$1;
+      const x$0 = { b: b };
+      x = x$0;
     } else {
-      const x$2 = { c: c };
-      x$0 = x$2;
+      const x$1 = { c: c };
+      x = x$1;
     }
-    x$0.f = 1;
+    x.f = 1;
     $[0] = b;
     $[1] = c;
-    $[2] = x$0;
+    $[2] = x;
   } else {
-    x$0 = $[2];
+    x = $[2];
   }
-  return x$0;
+  return x;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/primitive-alias-mutate.expect.md b/compiler/forget/src/__tests__/fixtures/hir/primitive-alias-mutate.expect.md
index 9b48a260e8..66fb0da09c 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/primitive-alias-mutate.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/primitive-alias-mutate.expect.md
@@ -21,25 +21,24 @@ function component(a) {
 ```javascript
 function component(a) {
   const $ = React.useMemoCache();
-  const x = "foo";
   const c_0 = $[0] !== a;
-  let x$0;
+  let x;
   if (c_0) {
-    x$0 = undefined;
+    x = undefined;
     if (a) {
-      const x$1 = "bar";
-      x$0 = x$1;
+      const x$0 = "bar";
+      x = x$0;
     } else {
-      const x$2 = "baz";
-      x$0 = x$2;
+      const x$1 = "baz";
+      x = x$1;
     }
     $[0] = a;
-    $[1] = x$0;
+    $[1] = x;
   } else {
-    x$0 = $[1];
+    x = $[1];
   }
 
-  const y = x$0;
+  const y = x;
   mutate(y);
   return y;
 }
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 383b4814e5..2530479763 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/reverse-postorder.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/reverse-postorder.expect.md
@@ -36,59 +36,24 @@ function Component(props) {
 
 ```javascript
 function Component(props) {
-  const $ = React.useMemoCache();
-  const c_0 = $[0] !== props.cond;
-  const c_1 = $[1] !== props.test;
-  const c_2 = $[2] !== props.v0;
-  const c_3 = $[3] !== props.v1;
-  const c_4 = $[4] !== props.v2;
-  const c_5 = $[5] !== props.cond2;
-  const c_6 = $[6] !== props.b;
-  const c_7 = $[7] !== props.c;
-  let x;
-  if (c_0 || c_1 || c_2 || c_3 || c_4 || c_5 || c_6 || c_7) {
-    x = undefined;
-    bb1: if (props.cond) {
-      switch (props.test) {
-        case 0: {
-          const x$0 = props.v0;
-          x = x$0;
-          break bb1;
-        }
-        case 1: {
-          const x$1 = props.v1;
-          x = x$1;
-          break bb1;
-        }
-        case 2: {
-        }
-        default: {
-          const x$2 = props.v2;
-          x = x$2;
-        }
+  bb1: if (props.cond) {
+    switch (props.test) {
+      case 0: {
+        break bb1;
       }
-    } else {
-      if (props.cond2) {
-        const x$3 = props.b;
-        x = x$3;
-      } else {
-        const x$4 = props.c;
-        x = x$4;
+      case 1: {
+        break bb1;
+      }
+      case 2: {
+      }
+      default: {
       }
     }
-    $[0] = props.cond;
-    $[1] = props.test;
-    $[2] = props.v0;
-    $[3] = props.v1;
-    $[4] = props.v2;
-    $[5] = props.cond2;
-    $[6] = props.b;
-    $[7] = props.c;
-    $[8] = x;
   } else {
-    x = $[8];
+    if (props.cond2) {
+    } else {
+    }
   }
-  x;
 }
 
 ```
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 ba8d2049fb..b77594b2f4 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
@@ -40,7 +40,6 @@ function Component(props) {
       t0 = $[2];
     }
     if (t0) {
-      const _ = <div a={a}></div>;
     }
 
     foo(a, b);
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 c906c69d4d..f55c93b742 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
@@ -20,18 +20,7 @@ function foo() {
 ## Code
 
 ```javascript
-function foo() {
-  const x = 1;
-  const y = 2;
-  2;
-  true;
-
-  const x$0 = 3;
-  3;
-  false;
-
-  const y$1 = x$0;
-}
+function foo() {}
 
 ```
       
\ No newline at end of file
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 5f5a449489..8a47245f31 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
@@ -17,16 +17,7 @@ function foo() {
 ## Code
 
 ```javascript
-function foo() {
-  const x = 1;
-  const y = 2;
-  2;
-  true;
-
-  const x$0 = 3;
-
-  const y$1 = x$0;
-}
+function foo() {}
 
 ```
       
\ No newline at end of file
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 f48d8f744e..ef6a01f316 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
@@ -18,12 +18,7 @@ function foo() {
 ## Code
 
 ```javascript
-function foo() {
-  const x = 1;
-  const y = 2;
-
-  const z = 3;
-}
+function foo() {}
 
 ```
       
\ No newline at end of file
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 42b723ab2b..8ec987a29f 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
@@ -25,10 +25,7 @@ function foo(a, b, c) {
   const x = 0;
   while (a) {
     while (b) {
-      while (c) {
-        1;
-        1;
-      }
+      while (c) {}
     }
   }
   return x;
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-nested-partial-phi.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-nested-partial-phi.expect.md
index 9ac41d2f64..2c34709bfc 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-nested-partial-phi.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-nested-partial-phi.expect.md
@@ -18,23 +18,9 @@ function foo(a, b, c) {
 
 ```javascript
 function foo(a, b, c) {
-  const $ = React.useMemoCache();
-  const x = a;
   if (b) {
-    const c_0 = $[0] !== c;
-    let x$0;
-    if (c_0) {
-      x$0 = x;
-      if (c) {
-        const x$1 = c;
-        x$0 = x$1;
-      }
-      $[0] = c;
-      $[1] = x$0;
-    } else {
-      x$0 = $[1];
+    if (c) {
     }
-    x$0;
   }
 }
 
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
index cd80d386d6..80a1187c2e 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-sibling-phis.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-sibling-phis.expect.md
@@ -27,14 +27,7 @@ function foo(a, b, c, d) {
 ## Code
 
 ```javascript
-function foo(a, b, c, d) {
-  const x = 0;
-  true;
-  true;
-
-  const x$0 = a;
-  x$0;
-}
+function foo(a, b, c, d) {}
 
 ```
       
\ No newline at end of file
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 34bc4817c7..aee2c34aef 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
@@ -19,15 +19,7 @@ function foo() {
 ## Code
 
 ```javascript
-function foo() {
-  const y = 2;
-  1;
-  true;
-
-  const y$0 = 1;
-
-  const x = y$0;
-}
+function foo() {}
 
 ```
       
\ No newline at end of file
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 0048cc265f..ac778eaf49 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-simple.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-simple.expect.md
@@ -12,10 +12,7 @@ function foo() {
 ## Code
 
 ```javascript
-function foo() {
-  const x = 1;
-  const y = 2;
-}
+function foo() {}
 
 ```
       
\ No newline at end of file
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 fccc8db799..7e6ec830ec 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
@@ -16,12 +16,7 @@ function foo() {
 ## Code
 
 ```javascript
-function foo() {
-  const x = 1;
-  const y = 2;
-
-  const z = 3;
-}
+function foo() {}
 
 ```
       
\ No newline at end of file
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 3ae1276929..a1beb758ee 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-switch.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-switch.expect.md
@@ -28,39 +28,17 @@ function foo() {
 
 ```javascript
 function foo() {
-  const $ = React.useMemoCache();
   const x = 1;
-  let x$0;
-  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
-    x$0 = undefined;
-    bb1: switch (x) {
-      case 1: {
-        1;
-
-        const x$1 = 2;
-        x$0 = x$1;
-        break bb1;
-      }
-      case 2: {
-        2;
-
-        const x$2 = 3;
-        x$0 = x$2;
-        break bb1;
-      }
-      default: {
-        3;
-
-        const x$3 = 4;
-        x$0 = x$3;
-      }
+  bb1: switch (x) {
+    case 1: {
+      break bb1;
+    }
+    case 2: {
+      break bb1;
+    }
+    default: {
     }
-    $[0] = x$0;
-  } else {
-    x$0 = $[0];
   }
-
-  const y = x$0;
 }
 
 ```
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 5e69a4427a..8ec206869f 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
@@ -18,10 +18,7 @@ function foo() {
 ```javascript
 function foo() {
   const x = 1;
-  while (true) {
-    1;
-    2;
-  }
+  while (true) {}
   return x;
 }
 
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 2d5476f046..391d7e70e3 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
@@ -38,27 +38,21 @@ function foo(x) {
 function foo(x) {
   bb1: switch (x) {
     case 0: {
-      const y = 0;
     }
     case 1: {
-      const y = 1;
       break bb1;
     }
     case 2: {
       break bb1;
     }
     case 3: {
-      const y = 3;
       break bb1;
     }
     case 4: {
-      const y = 4;
     }
     case 5: {
-      const y = 5;
     }
     default: {
-      const y = 0;
     }
   }
 }
diff --git a/compiler/forget/src/__tests__/fixtures/hir/type-args-test-binary-operator.expect.md b/compiler/forget/src/__tests__/fixtures/hir/type-args-test-binary-operator.expect.md
index 16c53f63f1..a26dfe2180 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/type-args-test-binary-operator.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/type-args-test-binary-operator.expect.md
@@ -15,7 +15,6 @@ function component(a, b) {
 ```javascript
 function component(a, b) {
   if (a > b) {
-    const m = {};
   }
 }
 
diff --git a/compiler/forget/src/__tests__/fixtures/hir/type-binary-operator.expect.md b/compiler/forget/src/__tests__/fixtures/hir/type-binary-operator.expect.md
index e4a585eaa3..8c07bc201b 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/type-binary-operator.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/type-binary-operator.expect.md
@@ -32,7 +32,6 @@ function component() {
     b = $[1];
   }
   if (a > b) {
-    const m = {};
   }
 }
 
diff --git a/compiler/forget/src/__tests__/fixtures/hir/type-field-load.expect.md b/compiler/forget/src/__tests__/fixtures/hir/type-field-load.expect.md
index a093a2bc2c..44cdc18891 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/type-field-load.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/type-field-load.expect.md
@@ -12,17 +12,7 @@ function component() {
 ## Code
 
 ```javascript
-function component() {
-  const $ = React.useMemoCache();
-  let x;
-  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
-    x = { t: 1 };
-    $[0] = x;
-  } else {
-    x = $[0];
-  }
-  const p = x.t;
-}
+function component() {}
 
 ```
       
\ No newline at end of file
diff --git a/compiler/forget/src/__tests__/fixtures/hir/type-test-field-load-binary-op.expect.md b/compiler/forget/src/__tests__/fixtures/hir/type-test-field-load-binary-op.expect.md
index 783a26d730..bdf321a918 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/type-test-field-load-binary-op.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/type-test-field-load-binary-op.expect.md
@@ -45,9 +45,6 @@ function component() {
   const v = x.v;
   if (u > v) {
   }
-
-  const y = x.u;
-  const z = x.v;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/type-test-primitive.expect.md b/compiler/forget/src/__tests__/fixtures/hir/type-test-primitive.expect.md
index 12b481767a..72e1d42f6e 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/type-test-primitive.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/type-test-primitive.expect.md
@@ -12,10 +12,7 @@ function component() {
 ## Code
 
 ```javascript
-function component() {
-  const x = 1;
-  const y = 2;
-}
+function component() {}
 
 ```
       
\ No newline at end of file
diff --git a/compiler/forget/src/__tests__/fixtures/hir/type-test-return-type-inference.expect.md b/compiler/forget/src/__tests__/fixtures/hir/type-test-return-type-inference.expect.md
index b7b036b3bc..24ca54aeb0 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/type-test-return-type-inference.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/type-test-return-type-inference.expect.md
@@ -34,7 +34,6 @@ function component() {
     y = $[1];
   }
   if (x > y) {
-    const z = {};
   }
 
   const z_0 = foo();