This is a preparatory step for D34515 This patch: - makes nodes `ISD::ADDCARRY` and `ISD::SUBCARRY` legal for `i32` - lowering is done by first converting the boolean value into the carry flag using `(_, C) ← (ARMISD::ADDC R, -1)` and converted back to an integer value using `(R, _) ← (ARMISD::ADDE 0, 0, C)`. An `ARMISD::ADDE` between the two operations does the actual addition. - for subtraction, given that `ISD::SUBCARRY` second result is actually a borrow, we need to invert the value of the second operand and result before and after using `ARMISD::SUBE` - given that the generic combiner may lower `ISD::ADDCARRY` and `ISD::SUBCARRY`into `ISD::UADDO` and `ISD::USUBO` we need to update their lowering as well otherwise `i64` operations now would require branches. This implies updating the corresponding test for unsigned. - adds new target specific combiners for sequences that conceptually do `R1 ← carryToReg(C0); C1 ← regToCarry(R1)` (just use `C0`) and their dual `C1 ← regToCarry(R0); R1 ← carryToReg(C1)` (just use `R0`)

This is a preparatory step for D34515 This patch: - makes nodes `ISD::ADDCARRY` and `ISD::SUBCARRY` legal for `i32` - lowering is done by first converting the boolean value into the carry flag using `(_, C) ← (ARMISD::ADDC R, -1)` and converted back to an integer value using `(R, _) ← (ARMISD::ADDE 0, 0, C)`. An `ARMISD::ADDE` between the two operations does the actual addition. - for subtraction, given that `ISD::SUBCARRY` second result is actually a borrow, we need to invert the value of the second operand and result before and after using `ARMISD::SUBE`. We need to invert the carry result of `ARMISD::SUBE` to preserve the semantics. - given that the generic combiner may lower `ISD::ADDCARRY` and `ISD::SUBCARRY`into `ISD::UADDO` and `ISD::USUBO` we need to update their lowering as well otherwise `i64` operations now would require branches. This implies updating the corresponding test for unsigned. - add new combiner to remove the redundant conversions from/to carry flags to/from boolean values `(ARMISD::ADDC (ARMISD::ADDE 0, 0, C), -1)` → `C`

This is a preparatory step for D34515 This patch: - makes nodes `ISD::ADDCARRY` and `ISD::SUBCARRY` legal for `i32` - lowering is done by first converting the boolean value into the carry flag using `(_, C) ← (ARMISD::ADDC R, -1)` and converted back to an integer value using `(R, _) ← (ARMISD::ADDE 0, 0, C)`. An `ARMISD::ADDE` between the two operations does the actual addition. - for subtraction, given that `ISD::SUBCARRY` second result is actually a borrow, we need to invert the value of the second operand and result before and after using `ARMISD::SUBE`. We need to invert the carry result of `ARMISD::SUBE` to preserve the semantics. - given that the generic combiner may lower `ISD::ADDCARRY` and `ISD::SUBCARRY`into `ISD::UADDO` and `ISD::USUBO` we need to update their lowering as well otherwise `i64` operations now would require branches. This implies updating the corresponding test for unsigned. - adds new target specific combiners for sequences that conceptually do `R1 ← carryToReg(C0); new combiner to remove the redundant conversions from/to carry flags to/from boolean values `(ARMISD::ADDC (ARMISD::ADDE 0, 0, C1 ← regToCarry(R1)` (just use `C0`) and their dual `C1 ← regToCarry(R0);C), R1 ← carryToReg(C1)` (just use `R0`)-1)` → `C`