https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102134
--- Comment #9 from CVS 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:06ac981ffb3c0d6997f2e1c01ffaf6253b6a244f commit r12-3246-g06ac981ffb3c0d6997f2e1c01ffaf6253b6a244f Author: Jakub Jelinek <ja...@redhat.com> Date: Tue Aug 31 10:29:23 2021 +0200 tree-ssa-ccp: Fix up bit_value_binop on RSHIFT_EXPR [PR102134] As mentioned in the PR, this hunk is guarded with !wi::neg_p (r1val | r1mask, sgn) which means if sgn is UNSIGNED, it is always true, but r1val | r1mask in widest_int is still sign-extended. That means wi::clz (arg) returns 0, wi::get_precision (arg) returns some very large number (WIDE_INT_MAX_PRECISION, on x86_64 576 bits) and width is 64, so we end up with lzcount of -512 where the code afterwards expects a non-negative lzcount. For arg without the sign bit set the code works right, those numbers are zero extended and so wi::clz must return wi::get_precision (arg) - width plus number of leading zero bits within the width precision. The patch fixes it by handling the sign-extension specially, either it could be done through wi::neg_p (arg) check, but lzcount == 0 works identically. 2021-08-31 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/102134 * tree-ssa-ccp.c (bit_value_binop) <case RSHIFT_EXPR>: If sgn is UNSIGNED and r1val | r1mask has MSB set, ensure lzcount doesn't become negative. * gcc.c-torture/execute/pr102134.c: New test.
