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Re: [PATCH, i386] Add prefixes avoidance tuning for silvermont target


Ilya Enkovich <enkovich.gnu@gmail.com> writes:

> Silvermont processors have penalty for instructions having 4+ bytes of
> prefixes (including escape bytes in opcode).  This situation happens
> when REX prefix is used in SSE4 instructions.  This patch tries to
> avoid such situation by preferring xmm0-xmm7 usage over xmm8-xmm15 in
> those instructions.  I achieved it by adding new tuning flag and new
> alternatives affected by tuning.

Why make it a tuning flag? Shouldn't this help unconditionally for code
size everywhere? Or is there some drawback? 

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only


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