inariant.group handling in GVN

The most important part required to make clang
devirtualization works ( ͡°͜ʖ ͡°).
The code is able to find non local dependencies, but unfortunatelly
because the caller can only handle local dependencies, I had to add
some restrictions to look for dependencies only in the same BB.

http://reviews.llvm.org/D12992

llvm-svn: 249196

2 files changed, 17 insertions, 7 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 1a74544045c..5be5a7df26b 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1386,7 +1386,8 @@ bool llvm::removeUnreachableBlocks(Function &F) {
   return true;
 }
 
-void llvm::combineMetadata(Instruction *K, const Instruction *J, ArrayRef<unsigned> KnownIDs) {
+void llvm::combineMetadata(Instruction *K, const Instruction *J,
+                           ArrayRef<unsigned> KnownIDs) {
   SmallVector<std::pair<unsigned, MDNode *>, 4> Metadata;
   K->dropUnknownNonDebugMetadata(KnownIDs);
   K->getAllMetadataOtherThanDebugLoc(Metadata);
@@ -1424,8 +1425,20 @@ void llvm::combineMetadata(Instruction *K, const Instruction *J, ArrayRef<unsign
         // Only set the !nonnull if it is present in both instructions.
         K->setMetadata(Kind, JMD);
         break;
+      case LLVMContext::MD_invariant_group:
+        // Preserve !invariant.group in K.
+        break;
     }
   }
+  // Set !invariant.group from J if J has it. If both instructions have it
+  // then we will just pick it from J - even when they are different.
+  // Also make sure that K is load or store - f.e. combining bitcast with load
+  // could produce bitcast with invariant.group metadata, which is invalid.
+  // FIXME: we should try to preserve both invariant.group md if they are
+  // different, but right now instruction can only have one invariant.group.
+  if (auto *JMD = J->getMetadata(LLVMContext::MD_invariant_group))
+    if (isa<LoadInst>(K) || isa<StoreInst>(K))
+      K->setMetadata(LLVMContext::MD_invariant_group, JMD);
 }
 
 unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 403356931ca..e2bd46e85c3 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1095,12 +1095,9 @@ static bool HoistThenElseCodeToIf(BranchInst *BI,
       I2->replaceAllUsesWith(I1);
     I1->intersectOptionalDataWith(I2);
     unsigned KnownIDs[] = {
-      LLVMContext::MD_tbaa,
-      LLVMContext::MD_range,
-      LLVMContext::MD_fpmath,
-      LLVMContext::MD_invariant_load,
-      LLVMContext::MD_nonnull
-    };
+        LLVMContext::MD_tbaa,    LLVMContext::MD_range,
+        LLVMContext::MD_fpmath,  LLVMContext::MD_invariant_load,
+        LLVMContext::MD_nonnull, LLVMContext::MD_invariant_group};
     combineMetadata(I1, I2, KnownIDs);
     I2->eraseFromParent();
     Changed = true;