https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99142
--- Comment #1 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Hans-Peter Nilsson <h...@gcc.gnu.org>: https://gcc.gnu.org/g:a2ef38b1f94dd108046e702ad46dcd8e9b34625e commit r11-7277-ga2ef38b1f94dd108046e702ad46dcd8e9b34625e Author: Hans-Peter Nilsson <h...@axis.com> Date: Tue Feb 16 22:27:53 2021 +0100 match.pd: Restrict clz cmp 0 replacement by single_use, PR99142 If we're not going to eliminate the clz, it's better for the comparison to use that result than its input, so we don't extend the lifetime of the input. Also, an additional use of the result is more likely cheaper than a compare of the input, in particular considering that the clz may have made available a non-zero condition matching the original use. The "s" modifier doesn't stop this situation, as the transformation wouldn't result in "an expression with more than one operator"; a gating single_use condition on the result is necessary. gcc: PR tree-optimization/99142 * match.pd (clz cmp 0): Gate replacement on single_use of clz result. gcc/testsuite: PR tree-optimization/99142 * gcc.dg/tree-ssa/pr99142.c: New test.
