Utils: Keep distinct MDNodes distinct in MapMetadata()

Create new copies of distinct `MDNode`s instead of following the
uniquing `MDNode` logic.

Just like self-references (or other cycles), `MapMetadata()` creates a
new node.  In practice most calls use `RF_NoModuleLevelChanges`, in
which case nothing is duplicated anyway.

Part of PR22111.

llvm-svn: 225476

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/ValueMapper.cpp b/llvm/lib/Transforms/Utils/ValueMapper.cpp
index a2eb1a07253..064cc575548 100644
--- a/llvm/lib/Transforms/Utils/ValueMapper.cpp
+++ b/llvm/lib/Transforms/Utils/ValueMapper.cpp
@@ -212,6 +212,20 @@ static Metadata *MapMetadataImpl(const Metadata *MD, ValueToValueMapTy &VM,
   if (Flags & RF_NoModuleLevelChanges)
     return mapToSelf(VM, MD);
 
+  // Distinct nodes are always recreated.
+  if (Node->isDistinct()) {
+    // Create the node first so it's available for cyclical references.
+    SmallVector<Metadata *, 4> EmptyOps(Node->getNumOperands());
+    MDNode *NewMD = MDNode::getDistinct(Node->getContext(), EmptyOps);
+    mapToMetadata(VM, Node, NewMD);
+
+    // Fix the operands.
+    for (unsigned I = 0, E = Node->getNumOperands(); I != E; ++I)
+      NewMD->replaceOperandWith(I, getMappedOp(Node->getOperand(I)));
+
+    return NewMD;
+  }
+
   // Create a dummy node in case we have a metadata cycle.
   MDNodeFwdDecl *Dummy = MDNode::getTemporary(Node->getContext(), None);
   mapToMetadata(VM, Node, Dummy);