[IR] Memory Model Relaxation Annotations (#78569)

Implements the core/target-agnostic components of Memory Model
Relaxation Annotations.

RFC:
https://discourse.llvm.org/t/rfc-mmras-memory-model-relaxation-annotations/76361/5

1 files changed, 16 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index a42ef0c..0a7b7a6 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -59,6 +59,7 @@
 #include "llvm/IR/IntrinsicsWebAssembly.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/MDBuilder.h"
+#include "llvm/IR/MemoryModelRelaxationAnnotations.h"
 #include "llvm/IR/Metadata.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/PatternMatch.h"
@@ -3284,6 +3285,9 @@ void llvm::combineMetadata(Instruction *K, const Instruction *J,
       case LLVMContext::MD_invariant_group:
         // Preserve !invariant.group in K.
         break;
+      case LLVMContext::MD_mmra:
+        // Combine MMRAs
+        break;
       case LLVMContext::MD_align:
         if (DoesKMove || !K->hasMetadata(LLVMContext::MD_noundef))
           K->setMetadata(
@@ -3322,6 +3326,16 @@ void llvm::combineMetadata(Instruction *K, const Instruction *J,
   if (auto *JMD = J->getMetadata(LLVMContext::MD_invariant_group))
     if (isa<LoadInst>(K) || isa<StoreInst>(K))
       K->setMetadata(LLVMContext::MD_invariant_group, JMD);
+
+  // Merge MMRAs.
+  // This is handled separately because we also want to handle cases where K
+  // doesn't have tags but J does.
+  auto JMMRA = J->getMetadata(LLVMContext::MD_mmra);
+  auto KMMRA = K->getMetadata(LLVMContext::MD_mmra);
+  if (JMMRA || KMMRA) {
+    K->setMetadata(LLVMContext::MD_mmra,
+                   MMRAMetadata::combine(K->getContext(), JMMRA, KMMRA));
+  }
 }
 
 void llvm::combineMetadataForCSE(Instruction *K, const Instruction *J,
@@ -3341,7 +3355,8 @@ void llvm::combineMetadataForCSE(Instruction *K, const Instruction *J,
                          LLVMContext::MD_preserve_access_index,
                          LLVMContext::MD_prof,
                          LLVMContext::MD_nontemporal,
-                         LLVMContext::MD_noundef};
+                         LLVMContext::MD_noundef,
+                         LLVMContext::MD_mmra};
   combineMetadata(K, J, KnownIDs, KDominatesJ);
 }