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Re: x86_64: Should the -mavx* options affected __alignof__ (max_align_t)?
- From: Joseph Myers <joseph at codesourcery dot com>
- To: Florian Weimer <fweimer at redhat dot com>
- Cc: GCC <gcc at gcc dot gnu dot org>
- Date: Mon, 23 Mar 2015 18:34:52 +0000
- Subject: Re: x86_64: Should the -mavx* options affected __alignof__ (max_align_t)?
- Authentication-results: sourceware.org; auth=none
- References: <55105B5B dot 50107 at redhat dot com>
On Mon, 23 Mar 2015, Florian Weimer wrote:
> __alignof__ (max_align_t) appears to be stuck at 16, even though some
> AVX512 operations require 512 byte alignment.
> Is this intentional? There are arguments for (more ABI compatibility)
> and against (max_align_t is misleading) this behavior.
max_align_t is only about fundamental alignments. See
<http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1892.htm#dr_445> for an
accepted cleanup of the alignment wording in C11.
It doesn't seem useful to increase the alignment requirements for malloc
beyond this, especially as all allocations, even 1-byte ones, have the
same alignment requirements.
Joseph S. Myers