Re: 4 GCC regressions, 2 new, with your patch on 2002-07-18T09:56:17Z.

[Geoff Keating <geoffk at geoffk dot org>]

> Date: Mon, 22 Jul 2002 03:05:58 +0200
> From: Jan Hubicka <jh@suse.cz>

> > > With your recent patch, GCC has some regression test failures, which
> > > used to pass.  There are 2 new failures, and 2
> > > failures that existed before and after that patch; 0 failures
> > > have been fixed.
> > > 
> > > The new failures are:
> > > powerpc-eabisim gcc.sum gcc.dg/20010822-1.c
> > > native gcc.sum gcc.dg/20010822-1.c
> > 
> > I guess I would have to conclude that these are mines however strange it
> > looks.  I will check what is going on.
> 
> Hi,
> this is another interesting problem. What happends is that code hoisting
> (insert_insn_end_bb) inserts load in between flags set and conditional
> jump instruction. This is valid, since load does not clobber flags, but
> not very sane as we lose optimizaiton opurtunities.

We really shouldn't be losing any optimisation opportunities by doing
this; if we do, it probably means that some piece of code is looking
at the RTL sequence instead of using def/use chains or whatever.  What
goes wrong?

This code really doesn't feel right to me.  There could be many
unexpected consequences.

> However, the code gets wrong in ifcvt as ifcvt insert new code before
> the flags set and uses uninitialized register.

Why does the code in ifcvt think this is valid?

> This patch fixes the gcse part by avoiding code hoisting to insert
> instructions as such a crazy places.  I believe this is good thing to
> do, but still I would like to know what to do with ifcvt.

I think it would be best to fix ifcvt.

> Regtested bootstrapped mainline.  I am now rerunning bootstrap with -Os.
> OK for mainline?

I don't think this code is a good idea.

> Mon Jul 22 03:02:47 CEST 2002  Jan Hubicka  <jh@suse.cz>
> 	* gcse.c (insert_insn_end_bb): Do not insert in between flags setter
> 	and user.
-- 
- Geoffrey Keating <geoffk@geoffk.org> <geoffk@redhat.com>