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Re: movmem pattern and missed alignment
On Tue, Oct 9, 2018 at 1:53 PM Joseph Myers <joseph@codesourcery.com> wrote:
>
> On Tue, 9 Oct 2018, Richard Biener wrote:
>
> > It was repeatedly suggested that we _could_ derive alignment info from
> > function parameter types since we rely on precise typing there for example
> > for points-to analysis (albeit only for restrict qualification processing and
> > for DECL_BY_REFERENCE "pointers"). That would fix the simple testcase
> > that was presented here.
>
> Even in that case you mustn't assume alignment for pointer comparisons,
> only for dereferences. Assuming it for comparisons breaks e.g. glibc's
>
> # define LC_GLOBAL_LOCALE ((locale_t) -1L)
>
> (locale_t is a pointer-to-pointer-aligned-struct) and other similar
> constructs involving magic constants (not dereferenced) of pointer type;
> comparisons of a locale_t value against LC_GLOBAL_LOCALE need to work.
Heh! That's non-conforming!
But yes, looks like it won't fly after all.
Richard.
> --
> Joseph S. Myers
> joseph@codesourcery.com