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

[hjl.tools at gmail dot com]

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

--- Comment #5 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Linus Torvalds from comment #4)
> (In reply to H.J. Lu from comment #3)
> > 
> > We need to keep
> > 
> >     andq    imm31, mem
> 
> Yes.
> 
> > and optimize testq to
> > 
> >     testl   imm31, mem
> 
> This one isn't quite as obvious. There *may* be microarchitectures that
> could have problems doing store buffer forwarding of a previous 64-bit write
> to a the 32-bit read of the "testl".
> 

I updated users/hjl/optimize branch to encode

testq $imm31, mem

as

testl $imm31, mem

only at -O2.

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