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Re: shifts and rotates by 1 on ix86
- To: Alexander Sokolov <robocop at netlink dot ru>
- Subject: Re: shifts and rotates by 1 on ix86
- From: Alan Modra <alan at linuxcare dot com dot au>
- Date: Wed, 10 May 2000 19:59:05 +1000 (EST)
- cc: binutils <binutils at sourceware dot cygnus dot com>
On Wed, 10 May 2000, Alexander Sokolov wrote:
> On Wed, 10 May 2000, Alan Modra wrote:
>
> > You can get the smaller opcode sequence by writing "shll %eax".
>
> This should be documented in manual.
True. Along with a few of other details too.
> > The reason gas does not do this automatically is that on certain processors,
> > eg. 486, the D1 E0 opcode sequence is slower than C1 E0 01.
>
> Then why not to add directives like .386, .486 etc or a command line
> option to specify the target cpu type?
That's not such a bad idea, particularly if the directive also enabled
warnings when someone tried to use an instruction not available on the
chosen cpu.
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