Simplify CAMLalign and use C11 max_align_t
#13139
Open
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
dustanddreams
approved these changes
May 2, 2024
MisterDA
force-pushed
the
alignas-simplify-CAMLalign
branch
from
0d98742
to
a49b31b
Compare
In our public headers, we're using either: - C23 where `alignas` is a keyword; - C++11 or later where `alignas` is also available; - C11/C17 where `_Alignas` is available.
Unfortunately, MSVC C11 suppport is incomplete and doesn't define it. - https://developercommunity.visualstudio.com/t/max_align_t-is-not-provided-by-stddefh/10299797 - https://developercommunity.visualstudio.com/t/stdc11-should-add-max-align-t-to-stddefh/1386891
For C++, MSVC defines `using max_align_t = double`. Take inspiration
from GCC and LLVM for the fallback implementation.
It's unlikely that we need to carry a fallback implementation for
other compilers. If so, the following could be used:
#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202311L || \
defined(__cplusplus)
#define CAMLalignof(n) alignof(n)
#else
#define CAMLalignof(n) _Alignof(n)
#endif
typedef struct {
long long ll CAMLalign(CAMLalignof(long long));
long double ld CAMLalign(CAMLalignof(long double));
} max_align_t;
https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/ginclude/stddef.h
https://github.com/llvm/llvm-project/blob/main/clang/lib/Headers/__stddef_max_align_t.h
https://en.cppreference.com/w/c/types/max_align_t
MisterDA
force-pushed
the
alignas-simplify-CAMLalign
branch
from
a49b31b
to
d226d67
Compare
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Some cleanups removing checks and workarounds for older compilers, assuming that the compiler supports C11 or C++11 out of the box. We may use
_Alignas(since C11) oralignas(since C23) directly, and use themax_align_ttype. Unfortunately, support formax_align_tis missing from the Windows C standard library.