[Bug tree-optimization/23855] loop header should also be pulled out of the inner loop too

[rakdver at gcc dot gnu dot org]

------- Comment #15 from rakdver at gcc dot gnu dot org  2006-04-09 23:51 -------
(In reply to comment #14)
> (In reply to comment #11)
> > I updated the patch for current mainline, but it still has issues for some
> > common uses of loops:
> > 
> > void foo(int *ie, int *je, double *x)
> > {
> >   int i, j;
> >   for (j=0; j<*je; ++j)
> >     for (i=0; i<*ie; ++i)
> >       x[i+j] = 0.0;
> > }
> > 
> > After loop header copying we have
> > 
> >   if (*je > 0)
> >     for (j=0; j<*je; ++j)
> >       if (*ie > 0)
> >         for (i=0; i<*ie; ++i)
> >           x[i+j ] = 0.0;
> > 
> > note how in this form we see the condition *ie > 0 not invariant wrt the
> > outer loop (because it does a memory load), but if we would run load-PRE
> > between loop header copying and guard hoisting we would get
> 
> actually, thinking about it again, it should suffice to teach
> invariant_without_guard_p about invariant memory loads, and this should just
> work.

It basically does, the only other problem is that we are not able to determine
that the outer loop is not infinite.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23855