Inconsistent treatment of constant expressions evaluation.

[blishko]

Description

The compiler exhibits an inconsistent treatment of constant expressions evaluation.

When applying bitwise negation on uint256 max value (0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF), the compiler reports error for some expressions, but does not report an error in others.

When the expression appears as part of division, an error is reported.

contract BitwiseSolver {
    uint256 constant largeConstant = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF;
    function test() public returns (uint256) {
        return 1/(~largeConstant);
    }
}

Error reported:

Error: Arithmetic error when computing constant value.
 --> test2.sol:5:19:
  |
5 |         return 1/(~largeConstant);
  |                   ^^^^^^^^^^^^^^

However, when the expression stands on its own, no error is reported.

contract BitwiseSolver {
    uint256 constant largeConstant = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF;
    function test() public returns (uint256) {
        return ~largeConstant;
    }
}

Note that if the definition is inlined and the bitwise negation is applied directly to a literal a conversion error is reported:

contract BitwiseSolver {
    function test() public returns (uint256) {
        return ~0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF;
    }
}

Error: Return argument type int_const -115...(71 digits omitted)...9936 is not implicitly convertible to expected type (type of first return variable) uint256. Cannot implicitly convert signed literal to unsigned type.
 --> test2.sol:3:16:
  |
3 |         return ~0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF;
  |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[blishko]

This has been distilled out of #15600 where the current behaviour of constant evaluation causes SMTChecker to crash.