Re: [9fans] 8a/8l bug

[Latchesar Ionkov <lucho@ionkov.net>]

Thanks,

I already found the code and changed it. Is it likely such changes to be
accepted in the standard Plan9 distribution?

Ideally there should be an option whether to do that type of optimizations.
Unfortunately it is hard to implement the option without introducing a flag
per row in the y* arrays. The flag will be also useful for opcodes that
translate to different types of instructions some of which have 0x0f prefix,
while others don't. Currently that is not supported and it is very hard to
add support for IMUL Reg, Imm8 for example.

Would you accept patch that:

1. Adds a new option whether to do instruction optimizations.
2. Modifies y* arrays to have a flag whether the instruction code should be
used if the optimizations are on.
3. Optionally the flag also holds information whether the specific
instruction has 0x0f/0x66 headers overriding the default specified in the
optab array.

Thanks,
	Lucho

On Wed, Dec 17, 2003 at 05:54:19PM -0500, Russ Cox said:
> > Also
> > 	ADDL	$-1, AX
> >
> > is not equivalent to
> >
> > 	SUBL	$1, AX
> >
> > The CF flag is different.
>
> The linker is doing the "optimizations" as part of
> instruction selection.  (The split of work between
> compiler and loader is different than it is with gcc.)
>
> In uchar yaddl[] = { ..., delete the two lines beginning
> with Yi1.
>
> Then you have to edit all the table entries in optab[]
> that reference yaddl to remove the offending inc/dec
> instructions.  But I can't remember how to decode
> that table.
>
> Russ