3 files changed, 30 insertions, 6 deletions

diff --git a/llvm/include/llvm/IR/Metadata.h b/llvm/include/llvm/IR/Metadata.h
index 4a8557d074f..df8ce354bb7 100644
--- a/llvm/include/llvm/IR/Metadata.h
+++ b/llvm/include/llvm/IR/Metadata.h
@@ -915,11 +915,21 @@ public:
   /// \brief Resolve cycles.
   ///
   /// Once all forward declarations have been resolved, force cycles to be
-  /// resolved. If \p AllowTemps is true, then any temporary metadata
-  /// is ignored, otherwise it asserts when encountering temporary metadata.
+  /// resolved. This interface is used when there are no more temporaries,
+  /// and thus unresolved nodes are part of cycles and no longer need RAUW
+  /// support.
   ///
   /// \pre No operands (or operands' operands, etc.) have \a isTemporary().
-  void resolveCycles(bool AllowTemps = false);
+  void resolveCycles() { resolveRecursivelyImpl(/* AllowTemps */ false); }
+
+  /// \brief Resolve cycles while ignoring temporaries.
+  ///
+  /// This drops RAUW support for any temporaries, which can no longer
+  /// be uniqued.
+  ///
+  void resolveNonTemporaries() {
+    resolveRecursivelyImpl(/* AllowTemps */ true);
+  }
 
   /// \brief Replace a temporary node with a permanent one.
   ///
@@ -977,6 +987,11 @@ private:
   void decrementUnresolvedOperandCount();
   unsigned countUnresolvedOperands();
 
+  /// Resolve cycles recursively. If \p AllowTemps is true, then any temporary
+  /// metadata is ignored, otherwise it asserts when encountering temporary
+  /// metadata.
+  void resolveRecursivelyImpl(bool AllowTemps);
+
   /// \brief Mutate this to be "uniqued".
   ///
   /// Mutate this so that \a isUniqued().
diff --git a/llvm/lib/IR/Metadata.cpp b/llvm/lib/IR/Metadata.cpp
index d8eaceb9ea2..9a9a5017841 100644
--- a/llvm/lib/IR/Metadata.cpp
+++ b/llvm/lib/IR/Metadata.cpp
@@ -557,7 +557,7 @@ void MDNode::decrementUnresolvedOperandCount() {
     resolve();
 }
 
-void MDNode::resolveCycles(bool AllowTemps) {
+void MDNode::resolveRecursivelyImpl(bool AllowTemps) {
   if (isResolved())
     return;
 
diff --git a/llvm/lib/Transforms/Utils/ValueMapper.cpp b/llvm/lib/Transforms/Utils/ValueMapper.cpp
index 2e361d38ed0..f47ddb9f064 100644
--- a/llvm/lib/Transforms/Utils/ValueMapper.cpp
+++ b/llvm/lib/Transforms/Utils/ValueMapper.cpp
@@ -222,8 +222,17 @@ static void resolveCycles(Metadata *MD, bool AllowTemps) {
   if (auto *N = dyn_cast_or_null<MDNode>(MD)) {
     if (AllowTemps && N->isTemporary())
       return;
-    if (!N->isResolved())
-      N->resolveCycles(AllowTemps);
+    if (!N->isResolved()) {
+      if (AllowTemps)
+        // Note that this will drop RAUW support on any temporaries, which
+        // blocks uniquing. If this ends up being an issue, in the future
+        // we can experiment with delaying resolving these nodes until
+        // after metadata is fully materialized (i.e. when linking metadata
+        // as a postpass after function importing).
+        N->resolveNonTemporaries();
+      else
+        N->resolveCycles();
+    }
   }
 }