This is a subset of #68288, with hopefully narrower scope. It does not
support bitcasting to non-integral types yet.
Bitfields are supported, but only if they result in a full byte-sized
final buffer. It does not support casting from null-pointers yet or
casting from indeterminate bits.
The tests are from #68288 and partially from #74775.
The `BitcastBuffer` struct is currently always working in single bits,
but I plan to (try to) optimize this for the common full-byte case.
According to [P0533R9](https://wg21.link/P0533R9), the C++ standard
library functions corresponding to the C macros in `[c.math.abs]` are
now `constexpr`.
To implement this feature in libc++, we must make the built-in abs
function `constexpr`. This patch adds the implementation of a
`constexpr` abs function for the current constant evaluator and the new
bytecode interpreter.
It is important to note that in 2's complement systems, the absolute
value of the most negative value is out of range. In gcc, it will result
in an out-of-range error and will not be evaluated as constants. We
follow the same approach here.
And fix the diagnostics for __builtin_is_constant_evaluated(). We can be
in a non-constant context, but calling an immediate function always
makes the context constant for the duration of that call.
The new constant interpreter's `clang::interp::InterpState` contains
both `clang::interp::Context` and `clang::ASTContext`. So using `S.Ctx`
and `S.getCtx()` was a bit confusing. This PR rename `getCtx()` to
`getASTContext` to make things more clearer.
Signed-off-by: yronglin <yronglin777@gmail.com>
As per [P0533R9](https://wg21.link/P0533R9), the corresponding C++
`[c.math.fpclass]` standard library functions for the C macros are now
`constexpr`.
The only classification function that wasn't already `constexpr` was
`__builtin_signbit`.
The floating point comparison functions `__builtin_isgreater`,
`__builtin_isgreaterequal`, `__builtin_isless`, `__builtin_islessequal`,
`__builtin_islessgreater` and `__builtin_isunordered` are now
`constexpr`.
The C23 macro `iseqsig` is not currently supported because
`__bulitin_iseqsig` doesn't exist yet (and C++26 is still currently
based on C18).
This also allows them to be constant folded in C, matching the behaviour
of GCC.
