[Bug tree-optimization/99204] [8/9 Regression] ICE in fold_read_from_constant_string, at fold-const.c:15441

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

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
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:f843203ea2c65d6319d784079baa8375c406a52c

commit r8-10890-gf843203ea2c65d6319d784079baa8375c406a52c
Author: Jakub Jelinek <jakub@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  <jakub@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)