[llvm-commits] Review Request for modification to Instruction::IsIdenticalToWhenDefined

[Joel Jones]

Fix a problem with incomplete equality testing of PHINodes in Instruction::IsIdenticalToWhenDefined.

This manifested itself when inlining two calls to the same function.  The inlined function had a switch statement that returned one of a set of global variables.  Without this modification, the two phi instructions that chose values from the branches of the switch instruction inlined from the callee were considered equivalent and jump-threading replaced a load for the first switch value with a phi selecting from the second switch, thereby producing incorrect code.

This patch has been tested with "make check-all", "lnt runteste nt", and llvm self-hosted, and on the original program that had this problem, wireshark.

<rdar://problem/11025519>

Attached is a test case which will reside in test/Transforms/JumpThreading

Index: lib/VMCore/Instruction.cpp
===================================================================
--- lib/VMCore/Instruction.cpp	(revision 156460)
+++ lib/VMCore/Instruction.cpp	(working copy)
@@ -226,7 +226,15 @@
            RMWI->isVolatile() == cast<AtomicRMWInst>(I)->isVolatile() &&
            RMWI->getOrdering() == cast<AtomicRMWInst>(I)->getOrdering() &&
            RMWI->getSynchScope() == cast<AtomicRMWInst>(I)->getSynchScope();
-
+	if (const PHINode *thisPHI = dyn_cast<PHINode>(this)) {
+		// The check above ensures that the dyn_cast and getIncomingBlock calls
+		// below won't fail, as the type of otherPHI must be PHINode and the
+		// number of incoming blocks must be the same.
+		const PHINode *otherPHI = dyn_cast<PHINode>(I);
+		for (unsigned i = 0, e = thisPHI->getNumOperands(); i != e; ++i) 
+		  if (thisPHI->getIncomingBlock(i) != otherPHI->getIncomingBlock(i))
+			  return false;
+	}
   return true;
 }
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