[llvm] [WebAssembly] Use RefTypeMem2Local instead of Mem2Reg (PR #83196)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Heejin Ahn (aheejin)

<details>
<summary>Changes</summary>

When reference-types feature is enabled, forcing mem2reg unconditionally even in `-O0` has some problems described in #<!-- -->81575. This uses RefTypeMem2Local pass added in #<!-- -->81965 instead. This also removes `IsForced` parameter added in
https://github.com/llvm/llvm-project/commit/890146b19206827bc48ee1ae1dc1534ff2ff18d7 given that we don't need it anymore.

This may still hurt debug info related to reference type variables a little during the backend transformation given that they are not stored in memory anymore, but reference type variables are presumably rare and it would be still a lot less damage than forcing mem2reg on the whole program. Also this fixes the EH problem described in #<!-- -->81575.

Fixes #<!-- -->81575.

cc @<!-- -->xortoast 

---
Full diff: https://github.com/llvm/llvm-project/pull/83196.diff


4 Files Affected:

- (modified) llvm/include/llvm/Transforms/Utils.h (+1-1) 
- (modified) llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp (+3-2) 
- (modified) llvm/lib/Transforms/Utils/Mem2Reg.cpp (+4-8) 
- (modified) llvm/test/CodeGen/WebAssembly/ref-type-mem2local.ll (+1) 


``````````diff
diff --git a/llvm/include/llvm/Transforms/Utils.h b/llvm/include/llvm/Transforms/Utils.h
index 0fa6de3f67130a..c6a6a05f3fddb4 100644
--- a/llvm/include/llvm/Transforms/Utils.h
+++ b/llvm/include/llvm/Transforms/Utils.h
@@ -70,7 +70,7 @@ extern char &LCSSAID;
 //   %Y = load i32* %X
 //   ret i32 %Y
 //
-FunctionPass *createPromoteMemoryToRegisterPass(bool IsForced = false);
+FunctionPass *createPromoteMemoryToRegisterPass();
 
 //===----------------------------------------------------------------------===//
 //
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
index d088c7d925ddf0..cb6e9eef365dd4 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
@@ -487,8 +487,9 @@ void WebAssemblyPassConfig::addISelPrepare() {
       WasmTM->getSubtargetImpl(std::string(WasmTM->getTargetCPU()),
                                std::string(WasmTM->getTargetFeatureString()));
   if (Subtarget->hasReferenceTypes()) {
-    // We need to remove allocas for reference types
-    addPass(createPromoteMemoryToRegisterPass(true));
+    // We need to move reference type allocas to WASM_ADDRESS_SPACE_VAR so that
+    // loads and stores are promoted to local.gets/local.sets.
+    addPass(createWebAssemblyRefTypeMem2Local());
   }
   // Lower atomics and TLS if necessary
   addPass(new CoalesceFeaturesAndStripAtomics(&getWebAssemblyTargetMachine()));
diff --git a/llvm/lib/Transforms/Utils/Mem2Reg.cpp b/llvm/lib/Transforms/Utils/Mem2Reg.cpp
index fbc6dd7613deb8..5ad7aeb463ecb2 100644
--- a/llvm/lib/Transforms/Utils/Mem2Reg.cpp
+++ b/llvm/lib/Transforms/Utils/Mem2Reg.cpp
@@ -74,19 +74,15 @@ namespace {
 struct PromoteLegacyPass : public FunctionPass {
   // Pass identification, replacement for typeid
   static char ID;
-  bool ForcePass; /// If true, forces pass to execute, instead of skipping.
 
-  PromoteLegacyPass() : FunctionPass(ID), ForcePass(false) {
-    initializePromoteLegacyPassPass(*PassRegistry::getPassRegistry());
-  }
-  PromoteLegacyPass(bool IsForced) : FunctionPass(ID), ForcePass(IsForced) {
+  PromoteLegacyPass() : FunctionPass(ID) {
     initializePromoteLegacyPassPass(*PassRegistry::getPassRegistry());
   }
 
   // runOnFunction - To run this pass, first we calculate the alloca
   // instructions that are safe for promotion, then we promote each one.
   bool runOnFunction(Function &F) override {
-    if (!ForcePass && skipFunction(F))
+    if (skipFunction(F))
       return false;
 
     DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
@@ -115,6 +111,6 @@ INITIALIZE_PASS_END(PromoteLegacyPass, "mem2reg", "Promote Memory to Register",
                     false, false)
 
 // createPromoteMemoryToRegister - Provide an entry point to create this pass.
-FunctionPass *llvm::createPromoteMemoryToRegisterPass(bool IsForced) {
-  return new PromoteLegacyPass(IsForced);
+FunctionPass *llvm::createPromoteMemoryToRegisterPass() {
+  return new PromoteLegacyPass();
 }
diff --git a/llvm/test/CodeGen/WebAssembly/ref-type-mem2local.ll b/llvm/test/CodeGen/WebAssembly/ref-type-mem2local.ll
index a38243ca218cc1..31d37db5318930 100644
--- a/llvm/test/CodeGen/WebAssembly/ref-type-mem2local.ll
+++ b/llvm/test/CodeGen/WebAssembly/ref-type-mem2local.ll
@@ -1,4 +1,5 @@
 ; RUN: opt < %s -wasm-ref-type-mem2local -S | FileCheck %s
+; RUN: llc < %s -mattr=+reference-types -stop-after=wasm-ref-type-mem2local | FileCheck %s
 
 target triple = "wasm32-unknown-unknown"
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/83196