This is the mail archive of the
mailing list for the GCC project.
Re: [patch] Fix tree-optimization/20139.
On Wed, 2005-02-23 at 12:43 -0500, Kazu Hirata wrote:
> Hi Jeff,
> > FWIW, we might consider just folding any expression that is subject
> > to TER. I've got a patch somewhere around here which does that.
> > Mostly it seems to eliminate casts, but from time to time it finds
> > something it can zap in complex expressions.
> > Thoughts?
> That would work, too. Could you dig up your patch please?
That required some serious digging :-)
I think all I did was put in the appropriate call to fold_stmt
in rewrite_trees. I suspect the code may have changed some, but
you can see what I was working with in this fragment from
FOR_EACH_SSA_DEF_OPERAND (def_p, stmt, iter, SSA_OP_DEF)
if (replace_def_variable (map, def_p, NULL))
changed = true;
/* If both SSA_NAMEs coalesce to the same variable,
mark the now redundant copy for removal. */
&& num_uses == 1
&& (DEF_FROM_PTR (def_p) == USE_OP (uses, 0)))
remove = 1;
if (changed && !remove)
fold_stmt (bsi_stmt_ptr (si));
> The only thing I am worried about is its effect on compile-time
> performance. Have you had a chance to take a look at that? I suppose
> calling fold once for every statement or so shouldn't hurt too much.
I never really looked at it. I was more interested in seeing what
folding opportunities were exposed by TER and whether or not it made
sense to beef up some optimizer earlier in the tree-ssa path.
Most of the stuff it found was useless casts.
Oh yea, to bootstrap we needed to remove a possibly bogus call to
STRIP_NOPS from maybe_fold_stmt_indirect.