Re: [Patch] PR 51938: extend ifcombine

[Marc Glisse <marc dot glisse at inria dot fr>]

On Wed, 20 Jun 2012, Richard Guenther wrote:

> On Sun, Jun 10, 2012 at 4:16 PM, Marc Glisse <marc.glisse@inria.fr> wrote:
> > Hello,
> >
> > currently, tree-ssa-ifcombine handles pairs of imbricated "if"s that share
> > the same then branch, or the same else branch. There is no particular reason
> > why it couldn't also handle the case where the then branch of one is the
> > else branch of the other, which is what I do here.
> >
> > Any comments?
>
> The general idea looks good, but I think the patch is too invasive.  As far
> as I can see the only callers with a non-zero 'inv' argument come from
> ifcombine_ifnotorif and ifcombine_ifnotandif (and both with inv == 2).
> I would rather see a more localized patch that makes use of
> invert_tree_comparison to perform the inversion on the call arguments
> of maybe_fold_and/or_comparisons.

Hello,

I finally went back to this version (which is where I started from, as 
shown in the PR). It is not very satisfying because:

* some bit tests could also be optimized (more generally, grouping a&&b 
and !a&&b on one side and a||b and !a||b on the other side is rather 
arbitrary),

* -ftrapping-math makes it useless for floating point,

but I guess it is better than nothing. Handling traps correctly is 
complicated because the current code is already a bit bogus (see 
http://gcc.gnu.org/ml/gcc-patches/2012-07/msg00924.html for an example), 
and even the definition of -ftrapping-math is not clear 
( http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53805 ).

If defaults are ever reconsidered, my default flags include 
-frounding-math -fno-trapping-math.


2012-06-10 ?Marc Glisse ?<marc.glisse@inria.fr>

gcc/
	PR tree-optimization/51938
	* tree-ssa-ifcombine.c (ifcombine_ifandif): New parameter for
	inverted outer condition.
	(ifcombine_iforif): Likewise.
	(tree_ssa_ifcombine_bb): Update calls to the above. Detect !a&&b
	and !a||b patterns.

gcc/testsuite/
	PR tree-optimization/51938
	* gcc.dg/tree-ssa/ssa-ifcombine-8.c: New testcase.
	* gcc.dg/tree-ssa/ssa-ifcombine-9.c: New testcase.

--
Marc Glisse

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