AMDGPU: Move spill pseudo special case out of adjustAllocatableRegClass (#158246)

This is special for the same reason av_mov_b64_imm_pseudo is special.

Author: arsenm

llvm/lib/Target/AMDGPU/SIInstrInfo.cpp

@@ -5976,8 +5976,7 @@ SIInstrInfo::getWholeWaveFunctionSetup(MachineFunction &MF) const {
 static const TargetRegisterClass *
 adjustAllocatableRegClass(const GCNSubtarget &ST, const SIRegisterInfo &RI,
                           const MCInstrDesc &TID, unsigned RCID) {
-  if (!ST.hasGFX90AInsts() && (((TID.mayLoad() || TID.mayStore()) &&
-                                !(TID.TSFlags & SIInstrFlags::Spill)))) {
+  if (!ST.hasGFX90AInsts() && (TID.mayLoad() || TID.mayStore())) {
     switch (RCID) {
     case AMDGPU::AV_32RegClassID:
       RCID = AMDGPU::VGPR_32RegClassID;
@@ -6012,10 +6011,9 @@ const TargetRegisterClass *SIInstrInfo::getRegClass(const MCInstrDesc &TID,
   if (OpNum >= TID.getNumOperands())
     return nullptr;
   auto RegClass = TID.operands()[OpNum].RegClass;
-  if (TID.getOpcode() == AMDGPU::AV_MOV_B64_IMM_PSEUDO) {
-    // Special pseudos have no alignment requirement
+  // Special pseudos have no alignment requirement.
+  if (TID.getOpcode() == AMDGPU::AV_MOV_B64_IMM_PSEUDO || isSpill(TID))
     return RI.getRegClass(RegClass);
-  }
 
   return adjustAllocatableRegClass(ST, RI, TID, RegClass);
 }

llvm/lib/Target/AMDGPU/SIInstrInfo.h

@@ -797,10 +797,12 @@ class SIInstrInfo final : public AMDGPUGenInstrInfo {
     return get(Opcode).TSFlags & SIInstrFlags::Spill;
   }
 
-  static bool isSpill(const MachineInstr &MI) {
-    return MI.getDesc().TSFlags & SIInstrFlags::Spill;
+  static bool isSpill(const MCInstrDesc &Desc) {
+    return Desc.TSFlags & SIInstrFlags::Spill;
   }
 
+  static bool isSpill(const MachineInstr &MI) { return isSpill(MI.getDesc()); }
+
   static bool isWWMRegSpillOpcode(uint16_t Opcode) {
     return Opcode == AMDGPU::SI_SPILL_WWM_V32_SAVE ||
            Opcode == AMDGPU::SI_SPILL_WWM_AV32_SAVE ||