https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113281
--- Comment #30 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-13 branch has been updated by Richard Sandiford <rsand...@gcc.gnu.org>: https://gcc.gnu.org/g:2602b71103d5ef2ef86000cac832b31dad3dfe2b commit r13-8813-g2602b71103d5ef2ef86000cac832b31dad3dfe2b Author: Richard Sandiford <richard.sandif...@arm.com> Date: Fri May 31 15:56:05 2024 +0100 vect: Tighten vect_determine_precisions_from_range [PR113281] This was another PR caused by the way that vect_determine_precisions_from_range handles shifts. We tried to narrow 32768 >> x to a 16-bit shift based on range information for the inputs and outputs, with vect_recog_over_widening_pattern (after PR110828) adjusting the shift amount. But this doesn't work for the case where x is in [16, 31], since then 32-bit 32768 >> x is a well-defined zero, whereas no well-defined 16-bit 32768 >> y will produce 0. We could perhaps generate x < 16 ? 32768 >> x : 0 instead, but since vect_determine_precisions_from_range was never really supposed to rely on fix-ups, it seems better to fix that instead. The patch also makes the code more selective about which codes can be narrowed based on input and output ranges. This showed that vect_truncatable_operation_p was missing cases for BIT_NOT_EXPR (equivalent to BIT_XOR_EXPR of -1) and NEGATE_EXPR (equivalent to BIT_NOT_EXPR followed by a PLUS_EXPR of 1). pr113281-1.c is the original testcase. pr113281-[23].c failed before the patch due to overly optimistic narrowing. pr113281-[45].c previously passed and are meant to protect against accidental optimisation regressions. gcc/ PR target/113281 * tree-vect-patterns.cc (vect_recog_over_widening_pattern): Remove workaround for right shifts. (vect_truncatable_operation_p): Handle NEGATE_EXPR and BIT_NOT_EXPR. (vect_determine_precisions_from_range): Be more selective about which codes can be narrowed based on their input and output ranges. For shifts, require at least one more bit of precision than the maximum shift amount. gcc/testsuite/ PR target/113281 * gcc.dg/vect/pr113281-1.c: New test. * gcc.dg/vect/pr113281-2.c: Likewise. * gcc.dg/vect/pr113281-3.c: Likewise. * gcc.dg/vect/pr113281-4.c: Likewise. * gcc.dg/vect/pr113281-5.c: Likewise. (cherry picked from commit 1a8261e047f7a2c2b0afb95716f7615cba718cd1)
