Teach ValueMapper to use ODR uniqued types when available

Summary:
This is exposed during ThinLTO compilation, when we import an alias by
creating a clone of the aliasee. Without this fix the debug type is
unnecessarily cloned and we get a duplicate, undoing the uniquing.

Fixes PR36089.

Reviewers: mehdi_amini, pcc

Subscribers: eraman, JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D41669

llvm-svn: 323813

1 files changed, 15 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/Utils/ValueMapper.cpp b/llvm/lib/Transforms/Utils/ValueMapper.cpp
index 8c9ecbc3503..55fff3f3872 100644
--- a/llvm/lib/Transforms/Utils/ValueMapper.cpp
+++ b/llvm/lib/Transforms/Utils/ValueMapper.cpp
@@ -25,6 +25,7 @@
 #include "llvm/IR/CallSite.h"
 #include "llvm/IR/Constant.h"
 #include "llvm/IR/Constants.h"
+#include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GlobalAlias.h"
@@ -536,13 +537,23 @@ Optional<Metadata *> MDNodeMapper::tryToMapOperand(const Metadata *Op) {
   return None;
 }
 
+static Metadata *cloneOrBuildODR(const MDNode &N) {
+  auto *CT = dyn_cast<DICompositeType>(&N);
+  // If ODR type uniquing is enabled, we would have uniqued composite types
+  // with identifiers during bitcode reading, so we can just use CT.
+  if (CT && CT->getContext().isODRUniquingDebugTypes() &&
+      CT->getIdentifier() != "")
+    return const_cast<DICompositeType *>(CT);
+  return MDNode::replaceWithDistinct(N.clone());
+}
+
 MDNode *MDNodeMapper::mapDistinctNode(const MDNode &N) {
   assert(N.isDistinct() && "Expected a distinct node");
   assert(!M.getVM().getMappedMD(&N) && "Expected an unmapped node");
-  DistinctWorklist.push_back(cast<MDNode>(
-      (M.Flags & RF_MoveDistinctMDs)
-          ? M.mapToSelf(&N)
-          : M.mapToMetadata(&N, MDNode::replaceWithDistinct(N.clone()))));
+  DistinctWorklist.push_back(
+      cast<MDNode>((M.Flags & RF_MoveDistinctMDs)
+                       ? M.mapToSelf(&N)
+                       : M.mapToMetadata(&N, cloneOrBuildODR(N))));
   return DistinctWorklist.back();
 }