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Re: Gcc extra alignment..
- To: egcs at tantalophile dot demon dot co dot uk
- Subject: Re: Gcc extra alignment..
- From: John Wehle <john at feith dot com>
- Date: Wed, 1 Nov 2000 19:43:48 -0500 (EST)
- Cc: rittle at latour dot rsch dot comm dot mot dot com, gcc at gcc dot gnu dot org, torvalds at transmeta dot com
> The stack is aligned to 16 bytes for some reason I don't entirely see
> the point in. (Like, why can't the few functions that use 128-bit SIMD
> use `and' to align their stack instead?)
Keeping the stack always aligned is felt to be cheaper than burning another
register in order to still access the arguments when using 'and' to align
the stack. I didn't have any benchmark numbers which clearly indicated the
best approach when I supplied the patches for both approaches in late 1998
/ early 1999 (in fact there may not be one best approach).
Of course both the stack and frame pointer are normally present unless
-fomit-frame-pointer is in use so really no additional registers are
needed to support using 'and' to align the stack. I don't believe that
there's any reason it can't be supported as an option if someone was to
update the my original patch and supply convincing benchmark numbers.
-- John
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