[Bug gas/22871] Encode instructions of 64-bit registers without the REX_W bit

[jbeulich at novell dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=22871

Jan Beulich <jbeulich at novell dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |jbeulich at novell dot com

--- Comment #1 from Jan Beulich <jbeulich at novell dot com> ---
subq %r64, %r64 and testq $imm31, %r64 could similarly benefit. Whether
converting test{q,l,w} $imm8,%r{64,32,16} to testb $imm8,%r8 isn't as clear,
but I think reads of 8-bit registers are commonly not causing stalls (only
writes do).

Along those lines test{q,l,w} $imm,mem might allow conversion if all set bits
in imm fall within a single byte. Of course care needs to be taken that the
adjustment to the displacement won't break addressability of the object.

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