AMDGPU: Move a flawed assert when spilling SGPRs

[arsenm]

Summary

It's possible to validly spill the frame offset register
in a call sequence to a VGPR. There are definitely issues
with SGPR spilling to memory, so move the assert later.

[rampitec]

LGTM

[arsenm]

r330612

lib/Target/AMDGPU/SIInstrInfo.cpp

void SIInstrInfo::storeRegToStackSlot(MachineBasicBlock &MBB,
                                       int FrameIndex,
                                       const TargetRegisterClass *RC,
                                       const TargetRegisterInfo *TRI) const {
   MachineFunction *MF = MBB.getParent();
   SIMachineFunctionInfo *MFI = MF->getInfo<SIMachineFunctionInfo>();
   MachineFrameInfo &FrameInfo = MF->getFrameInfo();
   DebugLoc DL = MBB.findDebugLoc(MI);
 
-  assert(SrcReg != MFI->getStackPtrOffsetReg() &&
-         SrcReg != MFI->getFrameOffsetReg() &&
-         SrcReg != MFI->getScratchWaveOffsetReg());
-
   unsigned Size = FrameInfo.getObjectSize(FrameIndex);
   unsigned Align = FrameInfo.getObjectAlignment(FrameIndex);
   MachinePointerInfo PtrInfo
     = MachinePointerInfo::getFixedStack(*MF, FrameIndex);
   MachineMemOperand *MMO
     = MF->getMachineMemOperand(PtrInfo, MachineMemOperand::MOStore,
                                Size, Align);
   unsigned SpillSize = TRI->getSpillSize(*RC);

lib/Target/AMDGPU/SIRegisterInfo.cpp

bool SIRegisterInfo::spillSGPR(MachineBasicBlock::iterator MI,
   const DebugLoc &DL = MI->getDebugLoc();
 
   MachineFrameInfo &FrameInfo = MF->getFrameInfo();
 
   bool SpillToSMEM = spillSGPRToSMEM();
   if (SpillToSMEM && OnlyToVGPR)
     return false;
 
+  assert(SpillToVGPR || (SuperReg != MFI->getStackPtrOffsetReg() &&
+                         SuperReg != MFI->getFrameOffsetReg() &&
+                         SuperReg != MFI->getScratchWaveOffsetReg()));
+
   assert(SuperReg != AMDGPU::M0 && "m0 should never spill");
 
   unsigned OffsetReg = AMDGPU::M0;
   unsigned M0CopyReg = AMDGPU::NoRegister;
 
   if (SpillToSMEM) {
     if (RS->isRegUsed(AMDGPU::M0)) {
       M0CopyReg = MRI.createVirtualRegister(&AMDGPU::SReg_32_XM0RegClass);

test/CodeGen/AMDGPU/spill-csr-frame-ptr-reg-copy.ll

+; RUN: llc -mtriple=amdgcn-amd-amdhsa -verify-machineinstrs -stress-regalloc=1 < %s | FileCheck -check-prefix=GCN %s
+
+; For the CSR copy of s5, it may be possible to see it in
+; storeRegToStackSlot.
+
+; GCN-LABEL: {{^}}spill_csr_s5_copy:
+; GCN: buffer_store_dword v32, off, s[0:3], s5 offset:8 ; 4-byte Folded Spill
+; GCN: v_writelane_b32 v32, s5, 2
+; GCN: s_swappc_b64
+; GCN: v_readlane_b32 s5, v32, 2
+; GCN: v_mov_b32_e32 [[K:v[0-9]+]], 9
+; GCN: buffer_store_dword [[K]], off, s[0:3], s5 offset:4
+; GCN: buffer_load_dword v32, off, s[0:3], s5 offset:8 ; 4-byte Folded Reload
+; GCN: s_setpc_b64
+define void @spill_csr_s5_copy() #0 {
+bb:
+  %alloca = alloca i32, addrspace(5)
+  %tmp = tail call i64 @func() #1
+  %tmp1 = getelementptr inbounds i32, i32 addrspace(1)* null, i64 %tmp
+  %tmp2 = load i32, i32 addrspace(1)* %tmp1, align 4
+  %tmp3 = zext i32 %tmp2 to i64
+  store volatile i32 9, i32 addrspace(5)* %alloca
+  ret void
+}
+
+declare i64 @func()
+
+attributes #0 = { nounwind }
+attributes #1 = { nounwind readnone }