https://sourceware.org/bugzilla/show_bug.cgi?id=22871
--- Comment #7 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Jan Beulich from comment #6)
> (In reply to H.J. Lu from comment #5)
> > I updated users/hjl/optimize branch to encode
> >
> > testq $imm31, mem
> >
> > as
> >
> > testl $imm31, mem
> >
> > only at -O2.
>
> I was about to suggest that, also because the memory access pattern changes
> (the shorter access may not fault when the longer one would, not to think of
> side effects when accessing MMIO). I'd even consider moving this higher up,
> to -O3.
Good point. I will remove "testq $imm31, mem". I will add
"test{q,l,w} $imm8,%r{64,32,16}" to "testb $imm8,%r8" to -O3.
> Another thing to consider here would be to encode e.g. vxorps %zmmM, %zmmM,
> %zmmN as vxorps %xmmM, %xmmM, %xmmN for the low 16 registers, as that'll be
> VEX encodable, i.e. shorter than the default EVEX variant. Same for vandnps
> (and of course all their flavors dealing with different data types).
We can do it at -O2.
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