AMDGPU: Fix crash when MachinePointerInfo invalid

The combine on a select of a load only triggers for
addrspace 0, and discards the MachinePointerInfo. The
conservative default needs to be used for this.

llvm-svn: 328652
diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
index 58afd16..51c27b0 100644
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -1087,7 +1087,7 @@
 bool SITargetLowering::isMemOpHasNoClobberedMemOperand(const SDNode *N) const {
   const MemSDNode *MemNode = cast<MemSDNode>(N);
   const Value *Ptr = MemNode->getMemOperand()->getValue();
-  const Instruction *I = dyn_cast<Instruction>(Ptr);
+  const Instruction *I = dyn_cast_or_null<Instruction>(Ptr);
   return I && I->getMetadata("amdgpu.noclobber");
 }