Guard MemoryBuiltins against self-looping GEPs, which can occur in unreachable code due to constant propagation.

Fixes PR13621.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162098 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/MemoryBuiltins.cpp b/lib/Analysis/MemoryBuiltins.cpp
index c0cc27b..e77d2ff 100644
--- a/lib/Analysis/MemoryBuiltins.cpp
+++ b/lib/Analysis/MemoryBuiltins.cpp
@@ -473,6 +473,10 @@
 }
 
 SizeOffsetType ObjectSizeOffsetVisitor::visitGEPOperator(GEPOperator &GEP) {
+  // Ignore self-referencing GEPs, they can occur in unreachable code.
+  if (&GEP == GEP.getPointerOperand())
+    return unknown();
+
   SizeOffsetType PtrData = compute(GEP.getPointerOperand());
   if (!bothKnown(PtrData) || !GEP.hasAllConstantIndices())
     return unknown();