[libc++] constexpr is_sufficiently_aligned #146787
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This is indended as support for filing a LWG issue. The implementation was suggested by Nikolas in https://github.com/llvm/llvm-project/pull/122603/files#r2035285951
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FYI, I'm not sure this approach is actually conforming. I was looking into this and came up with this test case: extern int z;
alignas(8) int z;
bool test() {
const bool is_aligned = is_sufficiently_aligned<8>(&z);
assert(is_sufficiently_aligned<8>(&z) == is_aligned); // fails
} |
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We have __builtin_is_aligned, which I think is what you want? |
Thanks for pointing that one out. That looks that the way to go for Clang but it is not provided by GCC. |
EricWF
reviewed
Jul 3, 2025
| # else | ||
| if constexpr (is_constant_evaluated()) | ||
| if consteval { | ||
| return __builtin_constant_p(__builtin_assume_aligned(__ptr, _Alignment) != nullptr); |
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I would prefer simply not supporting constexpr with GCC here.
It seems better to fail loudly than to give the wrong result.
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The goal was to determine whether or not it is implementable, and potentially opening a LWG issue before C++26 is shipped.
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This is indended as support for filing a LWG issue. The implementation was suggested by Nikolas in https://github.com/llvm/llvm-project/pull/122603/files#r2035285951