Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
mir: add unchecked signed-integer arithmetic ops (#1164)
## Summary Which signed integer arithmetic operation are checked for overflow is now made explicit within the MIR. This: * makes the exceptional control-flow arising from overflow checks visible to data-flow analysis, fixing destructors sometimes not being run * moves decision-making regarding overflow checks out of the code generators and into a central place (the AST -> MIR translation) ## Details In order to give the code generators more freedom over how they implement the overflow checks, no separate magics that implement the checks are introduced. ### MIR additions * add built-in signed integer arithmetic unary operators (negation) * add built-in signed integer arithmetic binary operators (addition, subtraction, multiplication, division, and remainder) * the behaviour of the built-in operators regarding over- and underflow, as well as division-by-zero, is undefined ### General architecture * when overflow checks are enabled, signed integer arithmetic operations are kept as magic calls (using `mnkCheckedCall` if panics are disabled) * when overflow checks are disabled, signed integer arithmetic operations are translated to use the MIR built-in operators * signed integer arithmetic operators kept as magic calls are unconditionally translated to checked operations by the code generators * the built-in arithmetic operators are unconditionally translated to unchecked operations (if available) by the code generators * the overflow check behaviour of `abs` is still controlled individually by each code generator ### AST-to-MIR translation * `mSucc` (successor) and `mPred` (predecessor) are lowered into normal addition and subtraction operators, respectively. This was previously left to the code generators ### MIR-to-CGIR translation * built-in operations equivalent to the ones added to the MIR are added to the `CgNode` IR * the MIR's arithmetic operations have a one-to-one correspondence with the `CgNode` ones ### Code generation * `vmgen` generates `Addu`, `Subu`, and `Mulu` for unchecked signed additions, subtractions, and multiplications. For a lack of unchecked versions, negation, division, and remainder still use the checked opcodes * `cgen` and `jsgen` generate the same code for the unchecked built-in operators as they previously did for unchecked arithmetic magics * all three code generators ignore `mSucc` and `mPred` ### Other * `mirexec` treats the built-in arithmetic operations operands as usages * the MIR built-in arithmetic operators are rendered as how they would look like in the high-level language (`+`, `*`, `div`, etc.) --------- Co-authored-by: Saem Ghani <saemghani+github@gmail.com>
- Loading branch information
