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[Bug tree-optimization/51938] missed optimization: 2 comparisons
- From: "glisse at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Fri, 08 Jun 2012 13:06:52 +0000
- Subject: [Bug tree-optimization/51938] missed optimization: 2 comparisons
- Auto-submitted: auto-generated
- References: <bug-51938-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51938
--- Comment #5 from Marc Glisse <glisse at gcc dot gnu.org> 2012-06-08 13:06:52 UTC ---
The main difficulty is trapping math. It isn't hard to add to
tree-ssa-ifcombine an ifcombine_ifnotandif variant, and we could make it call
maybe_fold_and_comparisons (as ifcombine_ifandif does) with
invert_tree_comparison (gimple_cond_code (outer_cond),...), but unless we pass
-fno-trapping-math, it won't help.
combine_comparisons (fold-const.c) has relevant code to determine whether the
optimization is safe wrt trapping, but it does so with the semantic that
UNLT_EXPR never traps, whereas I am (wrongfully) using it for
TRUTH_NOT_EXPR(GE_EXPR). So I guess that means two more versions of
maybe_fold_and_comparisons/maybe_fold_or_comparisons are needed :-(