R600/SI: Update tablegen defs to avoid restoring spilled sgprs to m0

We had code to do this in SIRegisterInfo::eliminateFrameIndex(), but
it is easier to just change the definition of SI_SPILL_S32_RESTORE to
only allow numbered sgprs.

llvm-svn: 237143

2 files changed, 4 insertions, 9 deletions

diff --git a/llvm/lib/Target/R600/SIInstructions.td b/llvm/lib/Target/R600/SIInstructions.td
index 24ebd5cf5fd..4c4e1aa76f4 100644
--- a/llvm/lib/Target/R600/SIInstructions.td
+++ b/llvm/lib/Target/R600/SIInstructions.td
@@ -2047,7 +2047,10 @@ multiclass SI_SPILL_SGPR <RegisterClass sgpr_class> {
   } // End UseNamedOperandTable = 1
 }
 
-defm SI_SPILL_S32  : SI_SPILL_SGPR <SReg_32>;
+// It's unclear whether you can use M0 as the output of v_readlane_b32
+// instructions, so use SGPR_32 register class for spills to prevent
+// this from happening.
+defm SI_SPILL_S32  : SI_SPILL_SGPR <SGPR_32>;
 defm SI_SPILL_S64  : SI_SPILL_SGPR <SReg_64>;
 defm SI_SPILL_S128 : SI_SPILL_SGPR <SReg_128>;
 defm SI_SPILL_S256 : SI_SPILL_SGPR <SReg_256>;
diff --git a/llvm/lib/Target/R600/SIRegisterInfo.cpp b/llvm/lib/Target/R600/SIRegisterInfo.cpp
index 13a89743677..db2ff0b1f95 100644
--- a/llvm/lib/Target/R600/SIRegisterInfo.cpp
+++ b/llvm/lib/Target/R600/SIRegisterInfo.cpp
@@ -245,7 +245,6 @@ void SIRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator MI,
       for (unsigned i = 0, e = NumSubRegs; i < e; ++i) {
         unsigned SubReg = getPhysRegSubReg(MI->getOperand(0).getReg(),
                                            &AMDGPU::SGPR_32RegClass, i);
-        bool isM0 = SubReg == AMDGPU::M0;
         struct SIMachineFunctionInfo::SpilledReg Spill =
             MFI->getSpilledReg(MF, Index, i);
 
@@ -254,19 +253,12 @@ void SIRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator MI,
            Ctx.emitError("Ran out of VGPRs for spilling SGPR");
         }
 
-        if (isM0)
-          SubReg = RS->scavengeRegister(&AMDGPU::SGPR_32RegClass, MI, 0);
-
         BuildMI(*MBB, MI, DL,
                 TII->getMCOpcodeFromPseudo(AMDGPU::V_READLANE_B32),
                 SubReg)
                 .addReg(Spill.VGPR)
                 .addImm(Spill.Lane)
                 .addReg(MI->getOperand(0).getReg(), RegState::ImplicitDefine);
-        if (isM0) {
-          BuildMI(*MBB, MI, DL, TII->get(AMDGPU::S_MOV_B32), AMDGPU::M0)
-                  .addReg(SubReg);
-        }
       }
 
       // TODO: only do this when it is needed