shifts and rotates by 1 on ix86

[Maciej W. Rozycki]

On Wed, 10 May 2000, Alexander Sokolov wrote:

> > 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?

 Please note that both kinds of opcodes are available since 80186, so
unless assembling in the 16-bit mode this is a non-issue.  Well, unless
you implement .8086 as well.

 However, implicit 1-bit shifts and rotates do set flags differently than
the explicit forms.  So I don't think it's actually a good idea to choose
either opcode automatically -- let a compiler or a programmer make the
decision which behaviour suits their needs. 

-- 
+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+--------------------------------------------------------------+
+        e-mail: macro@ds2.pg.gda.pl, PGP key available        +