From 98d66a7d31ea690d8e8e2c60330616fcda6c71e8 Mon Sep 17 00:00:00 2001
From: Hyxogen <8938732+Hyxogen@users.noreply.github.com>
Date: Fri, 3 Nov 2023 11:04:31 +0100
Subject: [PATCH] icf: compare alloca position for testing equivalence

This fixes an incorrect detection of identical code involving alloca
ordering.

Previously for allocas, we only checked if the allocated type, operands
and alignment were the same. However this doesn't take into account that
two identical alloca instructions at different relative points in the
function can not be taken for the same.

Fixed by adding a map that keeps track of allocas that take place at
relatively the same position, and using that map to check alloca
equivalence.
---
 llvm/include/llvm/Cheerp/IdenticalCodeFolding.h |  1 +
 llvm/lib/CheerpUtils/IdenticalCodeFolding.cpp   | 12 ++++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/llvm/include/llvm/Cheerp/IdenticalCodeFolding.h b/llvm/include/llvm/Cheerp/IdenticalCodeFolding.h
index 5f15e277f5ff..934bacd48be3 100644
--- a/llvm/include/llvm/Cheerp/IdenticalCodeFolding.h
+++ b/llvm/include/llvm/Cheerp/IdenticalCodeFolding.h
@@ -68,6 +68,7 @@ class IdenticalCodeFolding
 	std::unordered_map<std::pair<const llvm::Function*, const llvm::Function*>, bool, pair_hash> functionEquivalence;
 	std::unordered_map<const llvm::Function*, bool> externalFunctionMapping;
 	std::vector<llvm::Function*> deleteList;
+	std::unordered_map<const llvm::AllocaInst*, const llvm::AllocaInst*> allocaPairs;
 };
 
 class HashAccumulator64 {
diff --git a/llvm/lib/CheerpUtils/IdenticalCodeFolding.cpp b/llvm/lib/CheerpUtils/IdenticalCodeFolding.cpp
index b0f682614c45..c1cb5b8fc22d 100644
--- a/llvm/lib/CheerpUtils/IdenticalCodeFolding.cpp
+++ b/llvm/lib/CheerpUtils/IdenticalCodeFolding.cpp
@@ -92,6 +92,8 @@ bool IdenticalCodeFolding::equivalentFunction(const llvm::Function* A, const llv
 	llvm::errs() << "function A: " << A->getName() << '\n';
 	llvm::errs() << "function B: " << B->getName() << '\n';
 #endif
+	// Clear up equivalent allocas of previous function
+	allocaPairs.clear();
 
 	// Do not fold wasm/asmjs with generic JS functions.
 	if (A->getSection() != StringRef("asmjs") || B->getSection() != StringRef("asmjs"))
@@ -232,9 +234,15 @@ bool IdenticalCodeFolding::equivalentInstruction(const llvm::Instruction* A, con
 		{
 			const AllocaInst* a = cast<AllocaInst>(A);
 			const AllocaInst* b = cast<AllocaInst>(B);
-			return CacheAndReturn(equivalentType(a->getAllocatedType(), b->getAllocatedType()) &&
+			if ((allocaPairs.count(a) && allocaPairs[a] != b) || (allocaPairs.count(b) && allocaPairs[b] != a))
+				return false;
+			const bool equivalent =  equivalentType(a->getAllocatedType(), b->getAllocatedType()) &&
 				equivalentOperand(a->getArraySize(), b->getArraySize()) &&
-				a->getAlign() == b->getAlign());
+				a->getAlign() == b->getAlign();
+
+			if (equivalent)
+				allocaPairs[a] = b;
+			return CacheAndReturn(equivalent);
 		}
 		case Instruction::Unreachable:
 		{