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

[Eric Botcazou]

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?

Thanks in advance.

-- 
Eric Botcazou