IR: Metadata: Detect an RAUW recursion

Speculatively handle a recursion in
`GenericMDNode::handleChangedOperand()`.  I'm hoping this fixes the
failing hexagon bot [1].

[1]: http://lab.llvm.org:8011/builders/llvm-hexagon-elf/builds/13434

llvm-svn: 223849

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/IR/Metadata.cpp b/llvm/lib/IR/Metadata.cpp
index 805b7377bce..7a354c42c4c 100644
--- a/llvm/lib/IR/Metadata.cpp
+++ b/llvm/lib/IR/Metadata.cpp
@@ -495,6 +495,14 @@ void GenericMDNode::handleChangedOperand(void *Ref, Metadata *New) {
     setOperand(Op, New);
     return;
   }
+  if (InRAUW) {
+    // We just hit a recursion due to RAUW.  Set the operand and move on, since
+    // we're about to be deleted.
+    //
+    // FIXME: Can this cycle really happen?
+    setOperand(Op, New);
+    return;
+  }
 
   auto &Store = getContext().pImpl->MDNodeSet;
   Store.erase(this);
@@ -550,6 +558,7 @@ void GenericMDNode::handleChangedOperand(void *Ref, Metadata *New) {
   // Collision.
   if (!isResolved()) {
     // Still unresolved, so RAUW.
+    InRAUW = true;
     ReplaceableUses->replaceAllUsesWith(*I);
     delete this;
     return;