[llvm] [GlobalIsel] Combine ADDE (PR #82413)

[Amara Emerson via llvm-commits]

================
@@ -6906,3 +6923,195 @@ bool CombinerHelper::matchOr(MachineInstr &MI, BuildFnTy &MatchInfo) {
 
   return false;
 }
+
+bool CombinerHelper::isZExtOrTruncLegal(LLT ToTy, LLT FromTy) const {
+  // Copy.
+  if (ToTy == FromTy)
+    return true;
+
+  if (isLegalOrBeforeLegalizer({TargetOpcode::G_ZEXT, {ToTy, FromTy}}))
+    return true;
+
+  if (isLegalOrBeforeLegalizer({TargetOpcode::G_TRUNC, {ToTy, FromTy}}))
+    return true;
+
+  return false;
+}
+
+bool CombinerHelper::matchAddCarryInOut(MachineInstr &MI,
+                                        BuildFnTy &MatchInfo) {
+  GAddCarryInOut *Add = cast<GAddCarryInOut>(&MI);
+
+  // adde has no flags.
+  Register Dst = Add->getDstReg();
+  Register Carry = Add->getCarryOutReg();
+  Register CarryIn = Add->getCarryInReg();
+  Register LHS = Add->getLHSReg();
+  Register RHS = Add->getRHSReg();
+  bool IsSigned = Add->isSigned();
+  LLT DstTy = MRI.getType(Dst);
+  LLT CarryTy = MRI.getType(Carry);
+  LLT OperandTy = MRI.getType(LHS);
+  LLT CarryInTy = MRI.getType(CarryIn);
+
+  // FIXME: handle undef
+
+  // fold sadde, if the carry is dead -> add(add(LHS, RHS),
+  // zextOrTrunc(CarryIn)), undef.
----------------
aemerson wrote:

If you put the pattern onto it's own line it's clearer to the reader:
``` ->
add(add(LHS, RHS), zextOrTrunc(CarryIn)), undef.
```

https://github.com/llvm/llvm-project/pull/82413