https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110914
--- Comment #5 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:398842e7038ea0f34054f0f694014d0ecd656846 commit r14-3564-g398842e7038ea0f34054f0f694014d0ecd656846 Author: Jakub Jelinek <ja...@redhat.com> Date: Wed Aug 30 11:21:45 2023 +0200 tree-ssa-strlen: Fix up handling of conditionally zero memcpy [PR110914] The following testcase is miscompiled since r279392 aka r10-5451-gef29b12cfbb4979 The strlen pass has adjust_last_stmt function, which performs mainly strcat or strcat-like optimizations (say strcpy (x, "abcd"); strcat (x, p); or equivalent memcpy (x, "abcd", strlen ("abcd") + 1); char *q = strchr (x, 0); memcpy (x, p, strlen (p)); etc. where the first stmt stores '\0' character at the end but next immediately overwrites it and so the first memcpy can be adjusted to store 1 fewer bytes. handle_builtin_memcpy called this function in two spots, the first one guarded like: if (olddsi != NULL && tree_fits_uhwi_p (len) && !integer_zerop (len)) adjust_last_stmt (olddsi, stmt, false); i.e. only for constant non-zero length. The other spot can call it even for non-constant length but in that case we punt before that if that length isn't length of some string + 1, so again non-zero. The r279392 change I assume wanted to add some warning stuff and changed it like if (olddsi != NULL - && tree_fits_uhwi_p (len) && !integer_zerop (len)) - adjust_last_stmt (olddsi, stmt, false); + { + maybe_warn_overflow (stmt, len, rvals, olddsi, false, true); + adjust_last_stmt (olddsi, stmt, false); + } While maybe_warn_overflow possibly handles non-constant length fine, adjust_last_stmt really relies on length to be non-zero, which !integer_zerop (len) alone doesn't guarantee. While we could for len being SSA_NAME ask the ranger or tree_expr_nonzero_p, I think adjust_last_stmt will not benefit from it much, so the following patch just restores the above condition/previous behavior for the adjust_last_stmt call only. 2023-08-30 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/110914 * tree-ssa-strlen.cc (strlen_pass::handle_builtin_memcpy): Don't call adjust_last_stmt unless len is known constant. * gcc.c-torture/execute/pr110914.c: New test.
