[PATCH] Fix -ftree-ter -O0 (PR tree-optimization/43655)

[Jakub Jelinek]

On Wed, Dec 15, 2010 at 03:26:52AM +0100, Richard Guenther wrote:
> On Tue, Dec 14, 2010 at 2:56 PM, Jeff Law <law@redhat.com> wrote:
> > I'm a little confused as to why TER is running when we're not optimizing.
> > Â There's no doubt more bugs of this nature lying around if we allow specific
> > optimizers to be turned on at -O0.

I think the reason we allow it is unit testing, plus, eventually we want
some (limited) TER at -O0 for inline asm operands to get rid of the
regressions tree-SSA and tuplification caused.

> > If we're going to allow optimizers to run at -O0, wouldn't it be better to
> > fix gimple_references_memory_p rather than have to twiddle each of its
> > callers to DTRT at -O0. Â At least one of the other users of
> > gimple_references_memory_p seems to be prone to a similar bug
> > (tree-tailcall.c).
> 
> I originally wanted to get rid of gimple_references_memory_p.  For the specific
> test is_gimple_val (rhs) is probably enough (given that we don't TER aggregate
> copies).

You mean
  if (!optimized
      && gimple_assign_single_p (stmt)
      && !is_gimple_val (gimple_assign_rhs1 (stmt)))
    return false;
?

As for the other uses of gimple_references_memory_p, I guess most if not all
are never called for -O0, because neither gate_all_optimizations nor
gate_all_early_optimizations allows most of the late tree passes (and early
optimization passes) at all at -O0, no matter if they are enabled or not.
That includes ccp, dom, loop opts, tail call/recursion which use that
function.  And also pre, ealias and alias which use TODO_rebuild_alias.
So I think tree-ter was the only -O0 user of that function.

	Jakub