https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99204
--- Comment #12 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-8 branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:f843203ea2c65d6319d784079baa8375c406a52c commit r8-10890-gf843203ea2c65d6319d784079baa8375c406a52c Author: Jakub Jelinek <ja...@redhat.com> Date: Tue Feb 23 09:49:48 2021 +0100 fold-const: Fix ICE in fold_read_from_constant_string on invalid code [PR99204] fold_read_from_constant_string and expand_expr_real_1 have code to optimize constant reads from string (tree vs. rtl). If the STRING_CST array type has zero low bound, index is fold converted to sizetype and so the compare_tree_int works fine, but if it has some other low bound, it calls size_diffop_loc and that function from 2 sizetype operands creates a ssizetype difference. expand_expr_real_1 then uses tree_fits_uhwi_p + compare_tree_int and so works fine, but fold-const.c only checked if index is INTEGER_CST and calls compare_tree_int, which means for negative index it will succeed and result in UB in the compiler. 2021-02-23 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/99204 * fold-const.c (fold_read_from_constant_string): Check that tree_fits_uhwi_p (index) rather than just that index is INTEGER_CST. * gfortran.dg/pr99204.f90: New test. (cherry picked from commit f53a9b563b5017af179f1fd900189c0ba83aa2ec)
