Re: [x86 PATCH] Avoid andn and generate shorter not;and with -Oz.

[Michael Matz via Gcc-patches]

Hello,

On Wed, 13 Apr 2022, Roger Sayle wrote:

> The x86 instruction encoding for SImode andn is longer than the
> equivalent notl/andl sequence when the source for the not operand
> is the same register as the destination.

_And_ when no REX prefixes are necessary for the notl,andn, which they are 
if the respective registers are %r8 or beyond.  As you seem to be fine 
with saving just a byte you ought to test that as well to not waste one 
again :-)


Ciao,
Michael.