[llvm] Promote 32bit pseudo instr that infer extsw removal to 64bit in PPCMIPeephole (PR #85451)

[Lei Huang via llvm-commits]

================
@@ -5234,6 +5234,218 @@ bool PPCInstrInfo::isTOCSaveMI(const MachineInstr &MI) const {
 // We limit the max depth to track incoming values of PHIs or binary ops
 // (e.g. AND) to avoid excessive cost.
 const unsigned MAX_BINOP_DEPTH = 1;
+
+// This function will promote the instruction which defines the register `Reg`
+// in the parameter from a 32-bit to a 64-bit instruction if needed. The logic
+// used to check whether an instruction needs to be promoted or not is similar
+// to the logic used to check whether or not a defined register is sign or zero
+// extended within the function PPCInstrInfo::isSignOrZeroExtended.
+// Additionally, the `promoteInstr32To64ForElimEXTSW` function is recursive.
+// BinOpDepth does not count all of the recursions. The parameter BinOpDepth is
+// incremented  only when `promoteInstr32To64ForElimEXTSW` calls itself more
+// than once. This is done to prevent exponential recursion.
+void PPCInstrInfo::promoteInstr32To64ForElimEXTSW(const Register &Reg,
+                                                  MachineRegisterInfo *MRI,
+                                                  unsigned BinOpDepth,
+                                                  LiveVariables *LV) const {
+  if (!Reg.isVirtual())
+    return;
+
+  MachineInstr *MI = MRI->getVRegDef(Reg);
+  if (!MI)
+    return;
+
+  unsigned Opcode = MI->getOpcode();
+
+  switch (Opcode) {
+  case PPC::OR:
+  case PPC::ISEL:
+  case PPC::OR8:
+  case PPC::PHI: {
+    if (BinOpDepth >= MAX_BINOP_DEPTH)
+      break;
+    unsigned OperandEnd = 3, OperandStride = 1;
+    if (Opcode == PPC::PHI) {
+      OperandEnd = MI->getNumOperands();
+      OperandStride = 2;
+    }
+
+    for (unsigned I = 1; I < OperandEnd; I += OperandStride) {
+      assert(MI->getOperand(I).isReg() && "Operand must be register");
+      promoteInstr32To64ForElimEXTSW(MI->getOperand(I).getReg(), MRI,
+                                     BinOpDepth + 1, LV);
+    }
+
+    break;
+  }
+  case PPC::COPY: {
+    // Refers to the logic of the `case PPC::COPY` statement in the function
+    // PPCInstrInfo::isSignOrZeroExtended().
+
+    Register SrcReg = MI->getOperand(1).getReg();
+    // In both ELFv1 and v2 ABI, method parameters and the return value
+    // are sign- or zero-extended.
+    const MachineFunction *MF = MI->getMF();
+    if (!MF->getSubtarget<PPCSubtarget>().isSVR4ABI()) {
+      // If this is a copy from another register, we recursively promote the
+      // source.
+      promoteInstr32To64ForElimEXTSW(SrcReg, MRI, BinOpDepth, LV);
+      return;
+    }
+
+    // From here on everything is SVR4ABI. COPY will be eliminated in the other
+    // pass, we do not need promote the COPY pseudo opcode.
+
+    if (SrcReg != PPC::X3)
+      // If this is a copy from another register, we recursively promote the
+      // source.
+      promoteInstr32To64ForElimEXTSW(SrcReg, MRI, BinOpDepth, LV);
+    return;
+  }
+  case PPC::ORI:
+  case PPC::XORI:
+  case PPC::ORIS:
+  case PPC::XORIS:
+  case PPC::ORI8:
+  case PPC::XORI8:
+  case PPC::ORIS8:
+  case PPC::XORIS8:
+    promoteInstr32To64ForElimEXTSW(MI->getOperand(1).getReg(), MRI, BinOpDepth,
+                                   LV);
+    break;
+  case PPC::AND:
+  case PPC::AND8:
+    if (BinOpDepth >= MAX_BINOP_DEPTH)
+      break;
+
+    promoteInstr32To64ForElimEXTSW(MI->getOperand(1).getReg(), MRI,
+                                   BinOpDepth + 1, LV);
+    promoteInstr32To64ForElimEXTSW(MI->getOperand(2).getReg(), MRI,
+                                   BinOpDepth + 1, LV);
+    break;
+  }
+
+  bool HasNonSignedExtInstrPromoted = false;
+  int NewOpcode = -1;
+
+  // Map the opcode of instructions (which are not sign- or zero-extended
+  // themselves,but have operands that are destination registers of sign- or
+  // zero-extended instructions) to their 64-bit equivalents.
+  std::unordered_map<unsigned, unsigned> OpcodeMap = {
+      {PPC::OR, PPC::OR8},     {PPC::ISEL, PPC::ISEL8},
+      {PPC::ORI, PPC::ORI8},   {PPC::XORI, PPC::XORI8},
+      {PPC::ORIS, PPC::ORIS8}, {PPC::XORIS, PPC::XORIS8},
+      {PPC::AND, PPC::AND8}};
+
+  auto It = OpcodeMap.find(Opcode);
+  if (It != OpcodeMap.end()) {
+    // Set the new opcode to the mapped 64-bit version.
+    NewOpcode = It->second;
+    HasNonSignedExtInstrPromoted = true;
+  }
+
+  const PPCInstrInfo *TII =
+      MI->getMF()->getSubtarget<PPCSubtarget>().getInstrInfo();
+  if (!TII->isSExt32To64(Opcode) && !HasNonSignedExtInstrPromoted)
+    return;
+
+  const TargetRegisterClass *RC = MRI->getRegClass(Reg);
+  if (RC == &PPC::G8RCRegClass || RC == &PPC::G8RC_and_G8RC_NOX0RegClass)
+    return;
+
+  // The TableGen function `get64BitInstrFromSignedExt32BitInstr` is used to
+  // map the 32-bit instruction with the `SExt32To64` flag to the 64-bit
+  // instruction with the same opcode.
+  if (!HasNonSignedExtInstrPromoted)
+    NewOpcode = PPC::get64BitInstrFromSignedExt32BitInstr(Opcode);
+
+  assert(NewOpcode != -1 &&
+         "Must have a 64-bit opcode to map the 32-bit opcode!");
+
+  const TargetRegisterInfo *TRI = MRI->getTargetRegisterInfo();
+  const MCInstrDesc &MCID = TII->get(NewOpcode);
+  const TargetRegisterClass *NewRC =
+      TRI->getRegClass(MCID.operands()[0].RegClass);
+
+  Register SrcReg = MI->getOperand(0).getReg();
+  const TargetRegisterClass *SrcRC = MRI->getRegClass(SrcReg);
+
+  // If the register class of the defined register in the 32-bit instruction
+  // is the same as the register class of the defined register in the promoted
+  // 64-bit instruction, we do not need to promote the instruction.
+  if (NewRC == SrcRC)
+    return;
+
+  DebugLoc DL = MI->getDebugLoc();
+  auto MBB = MI->getParent();
+
+  // Since the pseudo-opcode of the instruction is promoted from 32-bit to
+  // 64-bit, if the source reg class of the original instruction belongs to
+  // PPC::GRCRegClass or PPC::GPRC_and_GPRC_NOR0RegClass, we need to promote
+  // the operand to PPC::G8CRegClass or PPC::G8RC_and_G8RC_NOR0RegClass,
+  // respectively.
+  DenseMap<unsigned, Register> PromoteRegs;
+  for (unsigned i = 1; i < MI->getNumOperands(); i++) {
+    MachineOperand &Operand = MI->getOperand(i);
+    if (!Operand.isReg())
+      continue;
+
+    Register OperandReg = Operand.getReg();
+    if (!OperandReg.isVirtual())
+      continue;
+
+    const TargetRegisterClass *NewUsedRegRC =
+        TRI->getRegClass(MCID.operands()[i].RegClass);
+    const TargetRegisterClass *OrgRC = MRI->getRegClass(OperandReg);
+    if (NewUsedRegRC != OrgRC && (OrgRC == &PPC::GPRCRegClass ||
+                                  OrgRC == &PPC::GPRC_and_GPRC_NOR0RegClass)) {
+      // Promote the used 32-bit register to 64-bit register.
+      Register TmpReg = MRI->createVirtualRegister(NewUsedRegRC);
+      Register DstTmpReg = MRI->createVirtualRegister(NewUsedRegRC);
+      BuildMI(*MBB, MI, DL, TII->get(PPC::IMPLICIT_DEF), TmpReg);
+      BuildMI(*MBB, MI, DL, TII->get(PPC::INSERT_SUBREG), DstTmpReg)
+          .addReg(TmpReg)
+          .addReg(OperandReg)
+          .addImm(PPC::sub_32);
+      PromoteRegs[i] = DstTmpReg;
+    }
+  }
+
+    Register NewDefinedReg = MRI->createVirtualRegister(NewRC);
----------------
lei137 wrote:

I think the indentation from here to `return` is a bit off.

https://github.com/llvm/llvm-project/pull/85451