[llvm] r225665 - IR: Prevent handleChangedOperand() recursion

[Duncan P. N. Exon Smith]

Author: dexonsmith
Date: Mon Jan 12 13:36:35 2015
New Revision: 225665

URL: http://llvm.org/viewvc/llvm-project?rev=225665&view=rev
Log:
IR: Prevent handleChangedOperand() recursion

Instead of returning early on `handleChangedOperand()` recursion
(finally identified (and test added) in r225657), prevent it upfront by
releasing operands before RAUW.

Aside from massively different program flow, there should be no
functionality change ;).

Modified:
    llvm/trunk/include/llvm/IR/Metadata.h
    llvm/trunk/lib/IR/Metadata.cpp

Modified: llvm/trunk/include/llvm/IR/Metadata.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/IR/Metadata.h?rev=225665&r1=225664&r2=225665&view=diff
==============================================================================
--- llvm/trunk/include/llvm/IR/Metadata.h (original)
+++ llvm/trunk/include/llvm/IR/Metadata.h Mon Jan 12 13:36:35 2015
@@ -49,7 +49,6 @@ 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;
@@ -66,8 +65,8 @@ public:
 
 protected:
   Metadata(unsigned ID)
-      : SubclassID(ID), IsDistinctInContext(false), InRAUW(false),
-        SubclassData16(0), SubclassData32(0) {}
+      : SubclassID(ID), IsDistinctInContext(false), SubclassData16(0),
+        SubclassData32(0) {}
   ~Metadata() {}
 
   /// \brief Store this in a big non-uniqued untyped bucket.

Modified: llvm/trunk/lib/IR/Metadata.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Metadata.cpp?rev=225665&r1=225664&r2=225665&view=diff
==============================================================================
--- llvm/trunk/lib/IR/Metadata.cpp (original)
+++ llvm/trunk/lib/IR/Metadata.cpp Mon Jan 12 13:36:35 2015
@@ -534,12 +534,6 @@ void GenericMDNode::handleChangedOperand
     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.
-    setOperand(Op, New);
-    return;
-  }
 
   auto &Store = getContext().pImpl->MDNodeSet;
   Store.erase(this);
@@ -571,13 +565,17 @@ void GenericMDNode::handleChangedOperand
   // Collision.
   if (!isResolved()) {
     // Still unresolved, so RAUW.
-    InRAUW = true;
+    //
+    // First, clear out all operands to prevent any recursion (similar to
+    // dropAllReferences(), but we still need the use-list).
+    for (unsigned O = 0, E = getNumOperands(); O != E; ++O)
+      setOperand(O, nullptr);
     ReplaceableUses->replaceAllUsesWith(*I);
     delete this;
     return;
   }
 
-  // Store in non-uniqued form if this node has already been resolved.
+  // Store in non-uniqued form if RAUW isn't possible.
   storeDistinctInContext();
 }