[llvm] [TableGen][RISCV][GlobalISel] Select G_ICMP, G_SELECT, G_PTR_ADD (PR #67185)

[Michael Maitland via llvm-commits]

================
@@ -214,6 +237,41 @@ bool RISCVInstructionSelector::select(MachineInstr &MI) {
   return true;
 }
 
+bool RISCVInstructionSelector::replacePtrWithInt(MachineOperand &Op,
+                                                 MachineIRBuilder &MIB,
+                                                 MachineRegisterInfo &MRI) {
+  assert(Op.isReg() && "Operand is not a register!");
+  Register PtrReg = Op.getReg();
+  assert(MRI.getType(PtrReg).isPointer() && "Operand is not a pointer!");
+
+  const LLT XLenLLT = LLT::scalar(STI.getXLen());
+  auto PtrToInt = MIB.buildPtrToInt(XLenLLT, PtrReg);
+  MRI.setRegBank(PtrToInt.getReg(0), RBI.getRegBank(RISCV::GPRRegBankID));
+  MRI.setType(PtrReg, XLenLLT);
+  Op.setReg(PtrToInt.getReg(0));
+  return select(*PtrToInt);
+}
+
+bool RISCVInstructionSelector::preISelLower(MachineInstr &MI,
+                                            MachineIRBuilder &MIB,
+                                            MachineRegisterInfo &MRI) {
+  switch (MI.getOpcode()) {
+  case TargetOpcode::G_PTR_ADD: {
+    Register DstReg = MI.getOperand(0).getReg();
+    const LLT XLenLLT = LLT::scalar(STI.getXLen());
+
+    replacePtrWithInt(MI.getOperand(1), MIB, MRI);
+    MI.setDesc(TII.get(TargetOpcode::G_ADD));
+    MRI.setType(DstReg, XLenLLT);
+    break;
+  }
+  default:
+    return false;
+  }
+
+  return true;
----------------
michaelmaitland wrote:

> Can you simplify and return true? You know at this point in the code that the instruction was changed.
> nit: should this be return false and allow each case to return true if it was changed?

These two comments sort of go together. If you know you should return true on line 266, return true at that point instead of breaking to the bottom of a switch to immediately return true. To be honest, it doesn't matter what you return on line 272 since its unreachable if you did return true on line 266 and can be removed.

https://github.com/llvm/llvm-project/pull/67185