Revert r133285.  Causing odd failures on Dragonegg.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@133301 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 48a747d..601d9b4 100644
--- a/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -29,10 +29,6 @@
     return ConstantInt::get(Val->getType(), 0);
   }
   
-  // Insist that the amount-to-allocate not overflow.
-  OverflowingBinaryOperator *OBI = dyn_cast<OverflowingBinaryOperator>(Val);
-  if (OBI && !OBI->hasNoUnsignedWrap()) return 0;
-
   if (BinaryOperator *I = dyn_cast<BinaryOperator>(Val)) {
     if (ConstantInt *RHS = dyn_cast<ConstantInt>(I->getOperand(1))) {
       if (I->getOpcode() == Instruction::Shl) {
@@ -75,6 +71,11 @@
   // This requires TargetData to get the alloca alignment and size information.
   if (!TD) return 0;
 
+  // Insist that the amount-to-allocate not overflow.
+  OverflowingBinaryOperator *OBI =
+    dyn_cast<OverflowingBinaryOperator>(AI.getOperand(0));
+  if (OBI && !(OBI->hasNoSignedWrap() || OBI->hasNoUnsignedWrap())) return 0;
+
   const PointerType *PTy = cast<PointerType>(CI.getType());
   
   BuilderTy AllocaBuilder(*Builder);