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

Alias metadata may no longer be valid after replacing the call argument.
Fix this by merging it with the memcpy alias metadata.

This fixes a miscompilation encountered in
https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/Failing.20tests.20when.20rustc.20is.20compiled.20with.201.20CGU.

(cherry picked from commit 4e6e476)

llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp

@@ -332,6 +332,17 @@ 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
@@ -1086,16 +1097,9 @@ 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;
@@ -1694,6 +1698,7 @@ 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;

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