@mgehre-amd pointed out the following post-commit review feedback on
the changes in 8cba72177dcd8de5d37177dbaf2347e5c1f0f1e8:
As an example, the paper says 3wb /* Yields an _BitInt(3); two value
bits, one sign bit */.
So I would expect that 0xFwb gives _BitInt(5); four value bits, one
sign bit, but with this implementation I get _BitInt(2).
This is because ResultVal as 4 bits, and getMinSignedBits() inteprets
it as negative and thus says that 1 bit is enough to represent -1.
This corrects the behavior for calculating the bit-width and adds some
test coverage.
WG14 adopted N2775 (http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2775.pdf)
at our Feb 2022 meeting. This paper adds a literal suffix for
bit-precise types that automatically sizes the bit-precise type to be
the smallest possible legal _BitInt type that can represent the literal
value. The suffix chosen is wb (for a signed bit-precise type) which
can be combined with the u suffix (for an unsigned bit-precise type).
The preprocessor continues to operate as-if all integer types were
intmax_t/uintmax_t, including bit-precise integer types. It is a
constraint violation if the bit-precise literal is too large to fit
within that type in the context of the preprocessor (when still using
a pp-number preprocessing token), but it is not a constraint violation
in other circumstances. This allows you to make bit-precise integer
literals that are wider than what the preprocessor currently supports
in order to initialize variables, etc.
Aaron Ballman