[X86] Limit getTargetConstantFromNode to only work on NormalLoads not extending loads.

This seems to fix a failure reported by Jordan Rupprecht, but we
don't have a reduced test case yet.

llvm-svn: 365589

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -5788,7 +5788,7 @@ static SDValue getShuffleVectorZeroOrUndef(SDValue V2, int Idx,
 }
 
 static const Constant *getTargetConstantFromNode(LoadSDNode *Load) {
-  if (!Load)
+  if (!Load || !ISD::isNormalLoad(Load))
     return nullptr;
 
   SDValue Ptr = Load->getBasePtr();