AMDGPU: Fix verifier error when spilling SGPRs

The current SGPR spilling test does not stress this
because it is using s_buffer_load instructions to
increase SGPR pressure and spill, but their output
operands have the same SReg_32_XM0 constraint. This fixes
an error when the SReg_32 output from most instructions
is spilled.

llvm-svn: 270301

llvm/lib/Target/AMDGPU/SIInstrInfo.cpp

@@ -584,6 +584,12 @@ void SIInstrInfo::storeRegToStackSlot(MachineBasicBlock &MBB,
   if (RI.isSGPRClass(RC)) {
     MFI->setHasSpilledSGPRs();
 
+    if (TargetRegisterInfo::isVirtualRegister(SrcReg) && RC->getSize() == 4) {
+      // m0 may not be allowed for readlane.
+      MachineRegisterInfo &MRI = MF->getRegInfo();
+      MRI.constrainRegClass(SrcReg, &AMDGPU::SReg_32_XM0RegClass);
+    }
+
     // We are only allowed to create one new instruction when spilling
     // registers, so we need to use pseudo instruction for spilling
     // SGPRs.
@@ -677,6 +683,13 @@ void SIInstrInfo::loadRegFromStackSlot(MachineBasicBlock &MBB,
     // FIXME: Maybe this should not include a memoperand because it will be
     // lowered to non-memory instructions.
     unsigned Opcode = getSGPRSpillRestoreOpcode(RC->getSize());
+
+    if (TargetRegisterInfo::isVirtualRegister(DestReg) && RC->getSize() == 4) {
+      // m0 may not be allowed for readlane.
+      MachineRegisterInfo &MRI = MF->getRegInfo();
+      MRI.constrainRegClass(DestReg, &AMDGPU::SReg_32_XM0RegClass);
+    }
+
     BuildMI(MBB, MI, DL, get(Opcode), DestReg)
       .addFrameIndex(FrameIndex) // frame_idx
       .addMemOperand(MMO);

llvm/test/CodeGen/AMDGPU/si-sgpr-spill.ll

@@ -1,5 +1,5 @@
-; RUN: llc -march=amdgcn -mcpu=SI < %s | FileCheck %s
-; RUN: llc -march=amdgcn -mcpu=tonga < %s | FileCheck %s
+; RUN: llc -march=amdgcn -verify-machineinstrs < %s | FileCheck %s
+; RUN: llc -march=amdgcn -mcpu=tonga -verify-machineinstrs < %s | FileCheck %s
 
 ; These tests check that the compiler won't crash when it needs to spill
 ; SGPRs.