From 5b9992075c7127ff4e2b5361dd57b732f86b97ad Mon Sep 17 00:00:00 2001
From: Joe Savona <joesavona@fb.com>
Date: Wed, 26 Apr 2023 11:27:41 -0700
Subject: [PATCH] Driveby optimization of DCE

Lift a constant evaluation out of a loop
---
 compiler/forget/src/Optimization/DeadCodeElimination.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler/forget/src/Optimization/DeadCodeElimination.ts b/compiler/forget/src/Optimization/DeadCodeElimination.ts
index c7a9b3272e..bc6aabafe9 100644
--- a/compiler/forget/src/Optimization/DeadCodeElimination.ts
+++ b/compiler/forget/src/Optimization/DeadCodeElimination.ts
@@ -33,13 +33,13 @@ export function deadCodeElimination(fn: HIRFunction): void {
   // of the blocks
   const hasLoop = hasBackEdge(fn);
 
+  const reversedBlocks = [...fn.body.blocks.values()].reverse();
   let size = state.count;
   do {
     size = state.count;
 
     // 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)) {
         state.reference(operand.identifier);