[llvm] [MemCpyOpt] Merge alias metadatas when replacing arguments (PR #67539)

[Nikita Popov via llvm-commits]

https://github.com/nikic updated https://github.com/llvm/llvm-project/pull/67539

>From 5ea4b651c4fb5b3fabdd2f5a086d19a2d249230f Mon Sep 17 00:00:00 2001
From: DianQK <dianqk at dianqk.net>
Date: Wed, 27 Sep 2023 18:45:21 +0800
Subject: [PATCH] [MemCpyOpt] Merge alias metadatas when replacing arguments

---
 .../lib/Transforms/Scalar/MemCpyOptimizer.cpp | 23 +++++++++++--------
 llvm/test/Transforms/MemCpyOpt/memcpy.ll      |  5 ++--
 2 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index 4db9d1b6d309afd..e818f6d4e84627d 100644
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -336,6 +336,17 @@ static bool writtenBetween(MemorySSA *MSSA, BatchAAResults &AA,
   return !MSSA->dominates(Clobber, Start);
 }
 
+// Update AA metadata
+static void combineAAMetadata(Instruction *ReplInst, Instruction *I) {
+  // FIXME: MD_tbaa_struct and MD_mem_parallel_loop_access should also be
+  // handled here, but combineMetadata doesn't support them yet
+  unsigned KnownIDs[] = {LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope,
+                         LLVMContext::MD_noalias,
+                         LLVMContext::MD_invariant_group,
+                         LLVMContext::MD_access_group};
+  combineMetadata(ReplInst, I, KnownIDs, true);
+}
+
 /// When scanning forward over instructions, we look for some other patterns to
 /// fold away. In particular, this looks for stores to neighboring locations of
 /// memory. If it sees enough consecutive ones, it attempts to merge them
@@ -1096,16 +1107,9 @@ bool MemCpyOptPass::performCallSlotOptzn(Instruction *cpyLoad,
                       MSSA->getMemoryAccess(C));
   }
 
-  // Update AA metadata
-  // FIXME: MD_tbaa_struct and MD_mem_parallel_loop_access should also be
-  // handled here, but combineMetadata doesn't support them yet
-  unsigned KnownIDs[] = {LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope,
-                         LLVMContext::MD_noalias,
-                         LLVMContext::MD_invariant_group,
-                         LLVMContext::MD_access_group};
-  combineMetadata(C, cpyLoad, KnownIDs, true);
+  combineAAMetadata(C, cpyLoad);
   if (cpyLoad != cpyStore)
-    combineMetadata(C, cpyStore, KnownIDs, true);
+    combineAAMetadata(C, cpyStore);
 
   ++NumCallSlot;
   return true;
@@ -1961,6 +1965,7 @@ bool MemCpyOptPass::processImmutArgument(CallBase &CB, unsigned ArgNo) {
                     << "  " << CB << "\n");
 
   // Otherwise we're good!  Update the immut argument.
+  combineAAMetadata(&CB, MDep);
   CB.setArgOperand(ArgNo, MDep->getSource());
   ++NumMemCpyInstr;
   return true;
diff --git a/llvm/test/Transforms/MemCpyOpt/memcpy.ll b/llvm/test/Transforms/MemCpyOpt/memcpy.ll
index d7475e7f5ea5913..f7c1c85517ffa32 100644
--- a/llvm/test/Transforms/MemCpyOpt/memcpy.ll
+++ b/llvm/test/Transforms/MemCpyOpt/memcpy.ll
@@ -695,10 +695,11 @@ define void @immut_valid_align_branched(i1 %c, ptr noalias align 4 %val) {
   ret void
 }
 
-; FIXME: This is a miscompile.
+; Merge/drop noalias metadata when replacing parameter.
 define void @immut_param_noalias_metadata(ptr align 4 byval(i32) %ptr) {
 ; CHECK-LABEL: @immut_param_noalias_metadata(
-; CHECK-NEXT:    call void @f(ptr noalias nocapture readonly [[PTR:%.*]]), !alias.scope !0
+; CHECK-NEXT:    store i32 1, ptr [[PTR:%.*]], align 4, !noalias !0
+; CHECK-NEXT:    call void @f(ptr noalias nocapture readonly [[PTR]])
 ; CHECK-NEXT:    ret void
 ;
   %tmp = alloca i32, align 4