AMDGPU/GlobalISel: Implement applyMappingImpl less incorrectly

We're checking the current register bank of the registers in the
instruction, but the mapping may have inserted cross bank copies and
is expecting to replace the registers.

We mostly get away with this currently, because VGPR->SGPR copies are
illegal, and we assume this won't happen. In a future change, we'll
start relying on more cross register bank copies being inserted, and
this starts to break down.

llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp

@@ -1069,11 +1069,11 @@ bool AMDGPURegisterBankInfo::applyMappingWideLoad(MachineInstr &MI,
 
   // If the pointer is an SGPR, we have nothing to do.
   if (SrcRegs.empty()) {
-    Register PtrReg = MI.getOperand(1).getReg();
-    const RegisterBank *PtrBank = getRegBank(PtrReg, MRI, *TRI);
+    const RegisterBank *PtrBank =
+      OpdMapper.getInstrMapping().getOperandMapping(1).BreakDown[0].RegBank;
     if (PtrBank == &AMDGPU::SGPRRegBank)
       return false;
-    SrcRegs.push_back(PtrReg);
+    SrcRegs.push_back(MI.getOperand(1).getReg());
   }
 
   assert(LoadSize % MaxNonSmrdLoadSize == 0);
@@ -1458,7 +1458,8 @@ void AMDGPURegisterBankInfo::applyMappingImpl(
     if (DstTy != LLT::scalar(16))
       break;
 
-    const RegisterBank *DstBank = getRegBank(DstReg, MRI, *TRI);
+    const RegisterBank *DstBank =
+      OpdMapper.getInstrMapping().getOperandMapping(0).BreakDown[0].RegBank;
     if (DstBank == &AMDGPU::VGPRRegBank)
       break;
 
@@ -1479,7 +1480,8 @@ void AMDGPURegisterBankInfo::applyMappingImpl(
   case AMDGPU::G_UMIN:
   case AMDGPU::G_UMAX: {
     Register DstReg = MI.getOperand(0).getReg();
-    const RegisterBank *DstBank = getRegBank(DstReg, MRI, *TRI);
+    const RegisterBank *DstBank =
+      OpdMapper.getInstrMapping().getOperandMapping(0).BreakDown[0].RegBank;
     if (DstBank == &AMDGPU::VGPRRegBank)
       break;
 
@@ -1516,7 +1518,8 @@ void AMDGPURegisterBankInfo::applyMappingImpl(
     bool Signed = Opc == AMDGPU::G_SEXT;
 
     MachineIRBuilder B(MI);
-    const RegisterBank *SrcBank = getRegBank(SrcReg, MRI, *TRI);
+    const RegisterBank *SrcBank =
+      OpdMapper.getInstrMapping().getOperandMapping(1).BreakDown[0].RegBank;
 
     Register DstReg = MI.getOperand(0).getReg();
     LLT DstTy = MRI.getType(DstReg);
@@ -1618,7 +1621,8 @@ void AMDGPURegisterBankInfo::applyMappingImpl(
     substituteSimpleCopyRegs(OpdMapper, 1);
     substituteSimpleCopyRegs(OpdMapper, 2);
 
-    const RegisterBank *DstBank = getRegBank(DstReg, MRI, *TRI);
+    const RegisterBank *DstBank =
+      OpdMapper.getInstrMapping().getOperandMapping(0).BreakDown[0].RegBank;
     if (DstBank == &AMDGPU::SGPRRegBank)
       break; // Can use S_PACK_* instructions.
 
@@ -1628,8 +1632,10 @@ void AMDGPURegisterBankInfo::applyMappingImpl(
     Register Hi = MI.getOperand(2).getReg();
     const LLT S32 = LLT::scalar(32);
 
-    const RegisterBank *BankLo = getRegBank(Lo, MRI, *TRI);
-    const RegisterBank *BankHi = getRegBank(Hi, MRI, *TRI);
+    const RegisterBank *BankLo =
+      OpdMapper.getInstrMapping().getOperandMapping(1).BreakDown[0].RegBank;
+    const RegisterBank *BankHi =
+      OpdMapper.getInstrMapping().getOperandMapping(2).BreakDown[0].RegBank;
 
     Register ZextLo;
     Register ShiftHi;
@@ -1710,7 +1716,8 @@ void AMDGPURegisterBankInfo::applyMappingImpl(
       = OpdMapper.getInstrMapping().getOperandMapping(0);
 
     // FIXME: Should be getting from mapping or not?
-    const RegisterBank *SrcBank = getRegBank(SrcReg, MRI, *TRI);
+    const RegisterBank *SrcBank =
+      OpdMapper.getInstrMapping().getOperandMapping(1).BreakDown[0].RegBank;
     MRI.setRegBank(DstReg, *DstMapping.BreakDown[0].RegBank);
     MRI.setRegBank(CastSrc.getReg(0), *SrcBank);
     MRI.setRegBank(One.getReg(0), AMDGPU::SGPRRegBank);
@@ -1775,9 +1782,12 @@ void AMDGPURegisterBankInfo::applyMappingImpl(
     auto InsHi = B.buildInsertVectorElement(Vec32, InsLo, InsRegs[1], IdxHi);
     B.buildBitcast(DstReg, InsHi);
 
-    const RegisterBank *DstBank = getRegBank(DstReg, MRI, *TRI);
-    const RegisterBank *SrcBank = getRegBank(SrcReg, MRI, *TRI);
-    const RegisterBank *InsSrcBank = getRegBank(InsReg, MRI, *TRI);
+    const RegisterBank *DstBank =
+      OpdMapper.getInstrMapping().getOperandMapping(0).BreakDown[0].RegBank;
+    const RegisterBank *SrcBank =
+      OpdMapper.getInstrMapping().getOperandMapping(1).BreakDown[0].RegBank;
+    const RegisterBank *InsSrcBank =
+      OpdMapper.getInstrMapping().getOperandMapping(2).BreakDown[0].RegBank;
 
     MRI.setRegBank(InsReg, *InsSrcBank);
     MRI.setRegBank(CastSrc.getReg(0), *SrcBank);