[PATCH/RFC] Fix PR optimization/11304

[Eric Botcazou]

Hi,

This is a regression from GCC 3.0.4, present in all released versions since 
then but already fixed on mainline. The function

int hux(int x)
{
  if (x)
  {
    set_eax(0);
    return x;
  }

  foo(x);
}

is miscompiled at -O -fomit-frame-pointer on x86: if x is not null, the 
function will return 0 anyway, because it fails to restore %eax after the 
call to set_eax().

The problem comes from the cross-jumping pass: it considers that the 
predecessors of two edges with the same destination block share common code. 
Now the first one sets %eax, while the second one only clobbers %eax. So we 
end up with a SET before a CLOBBER and the SET is deleted.

This was recently fixed on mainline by

2003-04-18  Richard Kenner  <kenner@vlsi1.ultra.nyu.edu>

	* cfgcleanup.c (flow_find_cross_jump): Use INSN_P, not active_insn_p.

but Jan seemed to have some reserve:
http://gcc.gnu.org/ml/gcc-patches/2003-04/msg01445.html
http://gcc.gnu.org/ml/gcc-patches/2003-04/msg01482.html


Is this patch appropriate for a backport? Do we want to fix the bug on the 
3.3 branch?


-- 
Eric Botcazou


2003-06-24  Eric Botcazou  <ebotcazou@libertysurf.fr>

	PR optimization/11304
	Backport from mainline:

	2003-04-18  Richard Kenner  <kenner@vlsi1.ultra.nyu.edu>

	* cfgcleanup.c (flow_find_cross_jump): Use INSN_P, not active_insn_p.


2003-06-24  Eric Botcazou  <ebotcazou@libertysurf.fr>

	* gcc.dg/i386-call-1.c: New test.
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