[PATCH] gcc4: Add 'asm goto' miscompilation quirk

[Ingo Molnar]

* Jakub Jelinek <jakub@xxxxxxxxxx> wrote:

> On Thu, Oct 10, 2013 at 08:51:04AM +0200, Jakub Jelinek wrote:
> > @@ -8,6 +8,7 @@ foo (int a, int b)
> >    asm volatile goto ("bts $1, %0; jc %l[lab]" : : "m" (b) : "memory" : lab);
> >    return 0;
> >  lab:
> > +  asm ("");
> >    return 0;
> >  }
> 
> Or alternatively put the asm (""); right after asm goto,
>   asm volatile goto ("bts $1, %0; jc %l[lab]" : : "m" (b) : "memory" : lab);
>   asm ("");
>   return ...;
> lab;
>   return ...;
> What generates better code remains to be tested.  In any case, please
> conditionalize the hacks on non-fixed compilers once the fix is released.

Something like the patch below? (Totally untested and all that.)

Notes:

- If the bug is fixed in 4.8.3 then the version check can be sharpened
  from 99999 to 40803.

- I'd really prefer this quirk versus having to add the extra barrier to 
  the label, as it makes the actual usage sites a lot less painful.

Thanks,

	Ingo

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