Revert "add support for PHI nodes to ObjectSizeOffsetVisitor"

This reverts r171298. Breaks clang selfhost.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171318 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/MemoryBuiltins.cpp b/lib/Analysis/MemoryBuiltins.cpp
index a565617..1481580 100644
--- a/lib/Analysis/MemoryBuiltins.cpp
+++ b/lib/Analysis/MemoryBuiltins.cpp
@@ -543,20 +543,9 @@
   return unknown();
 }
 
-SizeOffsetType ObjectSizeOffsetVisitor::visitPHINode(PHINode &PHI) {
-  if (PHI.getNumIncomingValues() == 0)
-    return unknown();
-
-  SizeOffsetType Ret = compute(PHI.getIncomingValue(0));
-  if (!bothKnown(Ret))
-    return unknown();
-
-  // verify that all PHI incoming pointers have the same size and offset
-  for (unsigned i = 1, e = PHI.getNumIncomingValues(); i != e; ++i) {
-    if (compute(PHI.getIncomingValue(i)) != Ret)
-      return unknown();
-  }
-  return Ret;
+SizeOffsetType ObjectSizeOffsetVisitor::visitPHINode(PHINode&) {
+  // too complex to analyze statically.
+  return unknown();
 }
 
 SizeOffsetType ObjectSizeOffsetVisitor::visitSelectInst(SelectInst &I) {