[llvm] [AArch64][FEAT_CMPBR] Codegen for Armv9.6-a compare-and-branch (PR #116465)

[via llvm-commits]

================
@@ -2427,6 +2430,150 @@ AArch64AsmPrinter::lowerBlockAddressConstant(const BlockAddress &BA) {
   return BAE;
 }
 
+void AArch64AsmPrinter::emitCBPseudoExpansion(const MachineInstr *MI) {
+  bool IsImm = false;
+  bool Is32Bit = false;
+
+  switch (MI->getOpcode()) {
+  default:
+    llvm_unreachable("This is not a CB pseudo instruction");
+  case AArch64::CBWPrr:
+    IsImm = false;
+    Is32Bit = true;
+    break;
+  case AArch64::CBXPrr:
+    IsImm = false;
+    Is32Bit = false;
+    break;
+  case AArch64::CBWPri:
+    IsImm = true;
+    Is32Bit = true;
+    break;
+  case AArch64::CBXPri:
+    IsImm = true;
+    Is32Bit = false;
+    break;
+  }
+
+  AArch64CC::CondCode CC =
+      static_cast<AArch64CC::CondCode>(MI->getOperand(0).getImm());
+  bool NeedsRegSwap = false;
+  bool NeedsImmDec = false;
+  bool NeedsImmInc = false;
+
+  unsigned MCOpC;
+  switch (CC) {
+  default:
+    llvm_unreachable("Invalid CB condition code");
+  case AArch64CC::EQ:
+    MCOpC = IsImm ? (Is32Bit ? AArch64::CBEQWri : AArch64::CBEQXri)
+                  : (Is32Bit ? AArch64::CBEQWrr : AArch64::CBEQXrr);
+    NeedsRegSwap = false;
+    NeedsImmDec = false;
+    NeedsImmInc = false;
+    break;
+  case AArch64CC::NE:
+    MCOpC = IsImm ? (Is32Bit ? AArch64::CBNEWri : AArch64::CBNEXri)
+                  : (Is32Bit ? AArch64::CBNEWrr : AArch64::CBNEXrr);
+    NeedsRegSwap = false;
+    NeedsImmDec = false;
+    NeedsImmInc = false;
+    break;
+  case AArch64CC::HS:
+    MCOpC = IsImm ? (Is32Bit ? AArch64::CBHIWri : AArch64::CBHIXri)
+                  : (Is32Bit ? AArch64::CBHSWrr : AArch64::CBHSXrr);
+    NeedsRegSwap = false;
+    NeedsImmDec = true;
+    NeedsImmInc = false;
+    break;
+  case AArch64CC::LO:
+    MCOpC = IsImm ? (Is32Bit ? AArch64::CBLOWri : AArch64::CBLOXri)
+                  : (Is32Bit ? AArch64::CBHIWrr : AArch64::CBHIXrr);
+    NeedsRegSwap = true;
+    NeedsImmDec = false;
+    NeedsImmInc = false;
+    break;
+  case AArch64CC::HI:
+    MCOpC = IsImm ? (Is32Bit ? AArch64::CBHIWri : AArch64::CBHIXri)
+                  : (Is32Bit ? AArch64::CBHIWrr : AArch64::CBHIXrr);
+    NeedsRegSwap = false;
+    NeedsImmDec = false;
+    NeedsImmInc = false;
+    break;
+  case AArch64CC::LS:
+    MCOpC = IsImm ? (Is32Bit ? AArch64::CBLOWri : AArch64::CBLOXri)
+                  : (Is32Bit ? AArch64::CBHSWrr : AArch64::CBHSXrr);
+    NeedsRegSwap = !IsImm;
+    NeedsImmDec = false;
+    NeedsImmInc = IsImm;
+    break;
+  case AArch64CC::GE:
+    MCOpC = IsImm ? (Is32Bit ? AArch64::CBGTWri : AArch64::CBGTXri)
+                  : (Is32Bit ? AArch64::CBGEWrr : AArch64::CBGEXrr);
+    NeedsRegSwap = false;
+    NeedsImmDec = IsImm;
+    NeedsImmInc = false;
+    break;
+  case AArch64CC::LT:
+    MCOpC = IsImm ? (Is32Bit ? AArch64::CBLTWri : AArch64::CBLTXri)
+                  : (Is32Bit ? AArch64::CBGTWrr : AArch64::CBGTXrr);
+    NeedsRegSwap = !IsImm;
+    NeedsImmDec = false;
+    NeedsImmInc = false;
+    break;
+  case AArch64CC::GT:
+    MCOpC = IsImm ? (Is32Bit ? AArch64::CBGTWri : AArch64::CBGTXri)
+                  : (Is32Bit ? AArch64::CBGTWrr : AArch64::CBGTXrr);
+    NeedsRegSwap = false;
+    NeedsImmDec = false;
+    NeedsImmInc = false;
+    break;
+  case AArch64CC::LE:
+    MCOpC = IsImm ? (Is32Bit ? AArch64::CBLTWri : AArch64::CBLTXri)
+                  : (Is32Bit ? AArch64::CBGEWrr : AArch64::CBGEXrr);
+    NeedsRegSwap = !IsImm;
+    NeedsImmDec = false;
+    NeedsImmInc = IsImm;
+    break;
+  }
+
+  MCInst Inst;
+  Inst.setOpcode(MCOpC);
+
+  MCOperand Lhs, Rhs, Trgt;
+  lowerOperand(MI->getOperand(1), Lhs);
+  lowerOperand(MI->getOperand(2), Rhs);
+  lowerOperand(MI->getOperand(3), Trgt);
+
+  if (NeedsRegSwap) {
+    assert(
+        !IsImm &&
+        "Unexpected register swap for CB instruction with immediate operand");
+    assert(Lhs.isReg() && "Expected register operand for CB");
+    assert(Rhs.isReg() && "Expected register operand for CB");
+    // Swap register operands
+    Inst.addOperand(Rhs);
+    Inst.addOperand(Lhs);
+  } else if (IsImm && NeedsImmDec) {
+    assert(IsImm && "Unexpected immediate decrement for CB instruction with "
+                    "reg-reg operands");
----------------
SpencerAbson wrote:

I'm not sure this assertion makes sense given the condition required to enter this section. This might have been intended to be:
```suggestion
  } else if (NeedsImmDec) {
    assert(IsImm && "Unexpected immediate decrement for CB instruction with "
                    "reg-reg operands");
```

https://github.com/llvm/llvm-project/pull/116465