https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90693
--- Comment #10 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:0152637c74c9eab7658483b1cca4e3d584dd4262 commit r14-6940-g0152637c74c9eab7658483b1cca4e3d584dd4262 Author: Jakub Jelinek <ja...@redhat.com> Date: Fri Jan 5 11:16:58 2024 +0100 Improve __builtin_popcount* (x) == 1 generation if x is known != 0 [PR90693] We expand __builtin_popcount* (x) == 1 as x ^ (x - 1) > x - 1, either unconditionally in tree-ssa-math-opts.cc if we don't have a direct optab support for popcount, or during expansion where we compare the costs of comparison of the popcount against one vs. the above expression. As mentioned in the PR, if we know from ranger that the argument is not zero, we can emit x & (x - 1) == 0 test which is same number of GIMPLE statements, but on many targets cheaper (e.g. whenever an AND instruction can also set flags on whether result was zero or not). The following patch does that. 2024-01-05 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/90693 * tree-ssa-math-opts.cc (match_single_bit_test): If tree_expr_nonzero_p (arg), remember it in the second argument to IFN_POPCOUNT or lower it as arg & (arg - 1) == 0 rather than arg ^ (arg - 1) > arg - 1. * internal-fn.cc (expand_POPCOUNT): If second argument to IFN_POPCOUNT suggests arg is non-zero, try to expand it as arg & (arg - 1) == 0 rather than arg ^ (arg - 1) > arg - 1. * gcc.target/i386/pr90693-2.c: New test.
