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

3 files changed, 64 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);
diff --git a/llvm/test/Linker/Inputs/distinct.ll b/llvm/test/Linker/Inputs/distinct.ll
new file mode 100644
index 00000000000..07ae224d28a
--- /dev/null
+++ b/llvm/test/Linker/Inputs/distinct.ll
@@ -0,0 +1,13 @@
+@global = linkonce global i32 0
+
+!named = !{!0, !1, !2, !3, !4, !5, !6, !7, !8}
+
+!0 = !{}
+!1 = !{!0}
+!2 = !{i32* @global}
+!3 = distinct !{}
+!4 = distinct !{!0}
+!5 = distinct !{i32* @global}
+!6 = !{!3}
+!7 = !{!4}
+!8 = !{!5}
diff --git a/llvm/test/Linker/distinct.ll b/llvm/test/Linker/distinct.ll
new file mode 100644
index 00000000000..c8e5c89eb09
--- /dev/null
+++ b/llvm/test/Linker/distinct.ll
@@ -0,0 +1,37 @@
+; RUN: llvm-link %s %S/Inputs/distinct.ll -o - -S | FileCheck %s
+
+; Test that distinct nodes from other modules remain distinct.  The @global
+; cases are the most interesting, since the operands actually need to be
+; remapped.
+
+; CHECK: @global = linkonce global i32 0
+@global = linkonce global i32 0
+
+; CHECK: !named = !{!0, !1, !2, !3, !4, !5, !6, !7, !8, !0, !1, !2, !9, !10, !11, !12, !13, !14}
+!named = !{!0, !1, !2, !3, !4, !5, !6, !7, !8}
+
+; CHECK:      !0 = !{}
+; CHECK-NEXT: !1 = !{!0}
+; CHECK-NEXT: !2 = !{i32* @global}
+; CHECK-NEXT: !3 = distinct !{}
+; CHECK-NEXT: !4 = distinct !{!0}
+; CHECK-NEXT: !5 = distinct !{i32* @global}
+; CHECK-NEXT: !6 = !{!3}
+; CHECK-NEXT: !7 = !{!4}
+; CHECK-NEXT: !8 = !{!5}
+; CHECK-NEXT: !9 = distinct !{}
+; CHECK-NEXT: !10 = distinct !{!0}
+; CHECK-NEXT: !11 = distinct !{i32* @global}
+; CHECK-NEXT: !12 = !{!9}
+; CHECK-NEXT: !13 = !{!10}
+; CHECK-NEXT: !14 = !{!11}
+; CHECK-NOT:  !
+!0 = !{}
+!1 = !{!0}
+!2 = !{i32* @global}
+!3 = distinct !{}
+!4 = distinct !{!0}
+!5 = distinct !{i32* @global}
+!6 = !{!3}
+!7 = !{!4}
+!8 = !{!5}