Re: Should it be reported as a bug? (-O2 and cmpxchg instruction)

[Andrew Haley <aph at redhat dot com>]

Martin Sustrik wrote:
> Andrew Haley wrote:
> > Please don't top-post.
> >
> > Martin Sustrik wrote:
> > > Andrew,
> > >
> > > Thanks for prompt response. However, I am not sure how to use the 
> > > earlyclobber modifier - this is actually the first gcc inline asembly 
> > > code I've ever written.
> > >
> > > Do you mean that I should add '&' sign to every operand in input 
> > > operand list, or should I add the sign when using the operands or what?
> >
> > Use "=&a" on the first operand.
> Ok, I've modified the code this way:
>
>            __asm__ volatile (
>                "lock; cmpxchgl %1, %3\n\t"
>                "jz 1f\n\t"
>                "mov %2, %%eax\n\t"
>                "lock; xchgl %%eax, %3\n\t"
>                "1:\n\t"
>                : "=&a" (oldval)
>                : "r" (thenval_), "r" (elseval_), "m" (value), "0" (0)

Ah, maybe I told you wrong: I see that Opernad 0 is also an input.  Sorry.

>                : "memory", "cc");
>
> However, the generated code is exactly the same as before.

I certainly don't get that.  Please post a complete test case, with
assembly output.  We also need to know exactly your version of gcc.

Andrew.