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[libc++] constexpr is_sufficiently_aligned #146787

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[libc++] constexpr is_sufficiently_aligned #146787

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f6e9679
[libc++] constexpr is_sufficiently_aligned
dalg24 Jul 2, 2025
35ccbe6
Use __builtin_is_aligned with Clang and fix GCC implemtation
dalg24 Jul 3, 2025
bfaccf2
Prefer if consteval
dalg24 Jul 3, 2025
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6 changes: 3 additions & 3 deletions libcxx/include/__memory/is_sufficiently_aligned.h
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Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,6 @@

#include <__config>
#include <__cstddef/size_t.h>
#include <__type_traits/is_constant_evaluated.h>
#include <cstdint>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
Expand All @@ -28,10 +27,11 @@ _LIBCPP_HIDE_FROM_ABI constexpr bool is_sufficiently_aligned(_Tp* __ptr) {
# ifdef _LIBCPP_COMPILER_CLANG_BASED
return __builtin_is_aligned(__ptr, _Alignment);
# 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.

else
} else {
return reinterpret_cast<uintptr_t>(__ptr) % _Alignment == 0;
}
# endif
}

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