Re: -fnon-call-exceptions + -fprofile-arcs on x86

[Andrew Pinski <pinskia at physics dot uc dot edu>]

On May 10, 2004, at 07:54, Eric Botcazou wrote:

> Hi,
>
> We ran into a problem with -fnon-call-exceptions + -fprofile-arcs on 
> x86.
> Now -fnon-call-exception is the default for Ada, so the problem is 
> already
> present with -fprofile-arcs for the Ada compiler (and further 
> exacerbated by
> -fstack-check).
>
> -fprofile-arcs needs to add increment insns on some edges of the CFG.  
> The
> 'add' insns on x86 clobber the condition code register so 
> -fprofile-arcs
> wreaks havoc when the condition code register is live on the edges it 
> adds
> insns on.
>
> It's possible (and very easy with -fstack-check) to have the condition 
> code
> register live on edges with -fnon-call-exceptions: a compare-and-jump
> construct whose operands are trapping MEMs is sufficient.  This leads 
> to
> wrong code because the compare is eventually deleted.
>
> Now to the question: is this fixable in profile.c?  If no, would a 
> patch that
> prevents the middle-end from generating compare-and-jump constructs 
> that
> span two basic blocks be acceptable?


I thought this was fixed when PR 11767 was fixed.

Thanks,
Andrew Pinski