From mboxrd@z Thu Jan  1 00:00:00 1970
From: Latchesar Ionkov <lucho@ionkov.net>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] 8a/8l bug
Message-ID: <20031217192636.GA7069@ionkov.net>
References: <20031217175958.GA6505@ionkov.net>
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Date: Wed, 17 Dec 2003 14:26:36 -0500
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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