bool f(int a, int b) { return a >= 0 && b >= 0; } This can be optimized to `return (a | b) >= 0;`. LLVM does this transformation, but GCC does not.

Confirmed. Two pieces depending on SHORT_CIRCUIT_... maybe_fold_and_comparisons for ifcombine and a match.pd pattern for _1 = a_3(D) >= 0; _2 = b_4(D) >= 0; _5 = _1 & _2; that should also make it work through maybe_fold_and_comparisons. We have something like this in fold-const.c btw.

Or reassoc could do it across different BBs.

(In reply to Gabriel Ravier from comment #0) > bool f(int a, int b) > { > return a >= 0 && b >= 0; > } > > This can be optimized to `return (a | b) >= 0;`. LLVM does this > transformation, but GCC does not. For orthogonality you also want: a < 0 && b < 0 -> (a & b) < 0 a >= 0 || b >= 0 -> (a & b) >= 0 a < 0 || b < 0 -> (a | b) < 0

I think doing it only in the last reassoc would have the advantage that it wouldn't break other optimizations done by reassoc. E.g. if (a >= 0 && b >= 0 && a < 32 && b < 128) which can be now optimized into a < 32U && b < 128U couldn't be optimized unless we teach the reassoc code that (a | b) >= 0 is equivalent to a >= 0 && b >= 0. The user can write it that way though: void bar (int, int); void foo (int a, int b) { if (a >= 0 && b >= 0 && a < 32 && b < 128) bar (a, b); } void baz (int a, int b) { if ((a | b) >= 0 && a < 32 && b < 128) bar (a, b); }

Created attachment 49938 [details] gcc11-pr95731.patch Untested fix.

The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>: https://gcc.gnu.org/g:13d47c37a2c043f3e5981e73e4c82158a39f41e8 commit r11-6609-g13d47c37a2c043f3e5981e73e4c82158a39f41e8 Author: Jakub Jelinek <jakub@redhat.com> Date: Tue Jan 12 11:03:40 2021 +0100 reassoc: Optimize in reassoc x < 0 && y < 0 to (x | y) < 0 etc. [PR95731] We already had x != 0 && y != 0 to (x | y) != 0 and x != -1 && y != -1 to (x & y) != -1 and x < 32U && y < 32U to (x | y) < 32U, this patch adds signed x < 0 && y < 0 to (x | y) < 0. In that case, the low/high seem to be always the same and just in_p indices whether it is >= 0 or < 0, also, all types in the same bucket (same precision) should be type compatible, but we can have some >= 0 and some < 0 comparison mixed, so the patch handles that by using the right BIT_IOR_EXPR or BIT_AND_EXPR and doing one set of < 0 or >= 0 first, then BIT_NOT_EXPR and then the other one. I had to move optimize_range_tests_var_bound before this optimization because that one deals with signed a >= 0 && a < b, and limited it to the last reassoc pass as reassoc itself can't virtually undo this optimization yet (and not sure if vrp would be able to). 2021-01-12 Jakub Jelinek <jakub@redhat.com> PR tree-optimization/95731 * tree-ssa-reassoc.c (optimize_range_tests_cmp_bitwise): Also optimize x < 0 && y < 0 && z < 0 into (x | y | z) < 0 for signed x, y, z. (optimize_range_tests): Call optimize_range_tests_cmp_bitwise only after optimize_range_tests_var_bound. * gcc.dg/tree-ssa/pr95731.c: New test. * gcc.c-torture/execute/pr95731.c: New test.

Fixed.

*** Bug 83123 has been marked as a duplicate of this bug. ***