AMDGPU: Stop reporting is-noop addrspacecast for constant 32-bit

[arsenm]

Summary

This will require something to cast. Before this would eliminate
the cast, which would result in copies of $noreg.

[nhaehnle]

LGTM

[arsenm]

r341803

lib/Target/AMDGPU/SIISelLowering.cpp

EVT SITargetLowering::getOptimalMemOpType(uint64_t Size, unsigned DstAlign,
 
   // Use the default.
   return MVT::Other;
 }
 
 static bool isFlatGlobalAddrSpace(unsigned AS) {
   return AS == AMDGPUAS::GLOBAL_ADDRESS ||
          AS == AMDGPUAS::FLAT_ADDRESS ||
-         AS == AMDGPUAS::CONSTANT_ADDRESS ||
-         AS == AMDGPUAS::CONSTANT_ADDRESS_32BIT;
+         AS == AMDGPUAS::CONSTANT_ADDRESS;
 }
 
 bool SITargetLowering::isNoopAddrSpaceCast(unsigned SrcAS,
                                            unsigned DestAS) const {
   return isFlatGlobalAddrSpace(SrcAS) && isFlatGlobalAddrSpace(DestAS);
 }
 
 bool SITargetLowering::isMemOpHasNoClobberedMemOperand(const SDNode *N) const {

test/CodeGen/AMDGPU/invalid-addrspacecast.ll

 ; RUN: not llc -march=amdgcn -mcpu=bonaire -mattr=-promote-alloca < %s 2>&1 | FileCheck -check-prefix=ERROR %s
 
 ; ERROR: error: <unknown>:0:0: in function use_group_to_global_addrspacecast void (i32 addrspace(3)*): invalid addrspacecast
 define amdgpu_kernel void @use_group_to_global_addrspacecast(i32 addrspace(3)* %ptr) {
   %stof = addrspacecast i32 addrspace(3)* %ptr to i32 addrspace(1)*
   store volatile i32 0, i32 addrspace(1)* %stof
   ret void
 }
+
+; ERROR: error: <unknown>:0:0: in function use_constant32bit_to_flat_addrspacecast void (i32 addrspace(6)*): invalid addrspacecast
+define amdgpu_kernel void @use_constant32bit_to_flat_addrspacecast(i32 addrspace(6)* %ptr) #0 {
+  %stof = addrspacecast i32 addrspace(6)* %ptr to i32*
+  store volatile i32 7, i32* %stof
+  ret void
+}