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

[Latchesar Ionkov <lucho@ionkov.net>]

Also
	ADDL	$-1, AX

is not equivalent to

	SUBL	$1, AX

The CF flag is different.

Thanks,
	Lucho

On Wed, Dec 17, 2003 at 12:59:58PM -0500, Latchesar Ionkov said:
> Hi,
>
> I am working on making gcc to support the standard Plan9 object format. I
> noticed something that IMO is a bug.
>
> If I try to compile:
>
> TEXT	main(SB), $0
> 	ADDL	$-1, AX
> 	ADCL	$-1, DX
> 	RET
>
> the result from
>
> 	8l -a t.8
> is:
>
> 001020  (1)	TEXT	main+0(SB),$0
> 001020 48	(2)	SUBL	$1, AX
> 001021 83d2ff	(3)	ADCL	$-1, DX
>
> According to my ia32 instruction set reference 0x48 is
> 	DECL AX
>
> not
> 	SUBL $1, AX
>
> Unlike SUBL, DECL doesn't change CF flag, so the ADCL instruction is not
> working correctly.
>
> Where are these types of optimizations made? Is it possible to turn them off
> completely?
>
> Thanks,
> 	Lucho