From ae5224d468f8e4ebe8d1f72bfee8bcc4c36806db Mon Sep 17 00:00:00 2001
From: "Duncan P. N. Exon Smith" <dexonsmith@apple.com>
Date: Tue, 9 Dec 2014 23:04:59 +0000
Subject: [PATCH] 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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223849 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/IR/Metadata.h | 5 +++--
 lib/IR/Metadata.cpp        | 9 +++++++++
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/llvm/IR/Metadata.h b/include/llvm/IR/Metadata.h
index ffdd7002cea..573e49fbb06 100644
--- a/include/llvm/IR/Metadata.h
+++ b/include/llvm/IR/Metadata.h
@@ -49,6 +49,7 @@ class Metadata {
 protected:
   /// \brief Storage flag for non-uniqued, otherwise unowned, metadata.
   bool IsDistinctInContext : 1;
+  bool InRAUW : 1;
   // TODO: expose remaining bits to subclasses.
 
   unsigned short SubclassData16;
@@ -65,8 +66,8 @@ public:
 
 protected:
   Metadata(unsigned ID)
-      : SubclassID(ID), IsDistinctInContext(false), SubclassData16(0),
-        SubclassData32(0) {}
+      : SubclassID(ID), IsDistinctInContext(false), InRAUW(false),
+        SubclassData16(0), SubclassData32(0) {}
   ~Metadata() {}
 
   /// \brief Store this in a big non-uniqued untyped bucket.
diff --git a/lib/IR/Metadata.cpp b/lib/IR/Metadata.cpp
index 805b7377bce..7a354c42c4c 100644
--- a/lib/IR/Metadata.cpp
+++ b/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;