[Bug tree-optimization/114965] [13/14/15 Regression] wrong code generated for Emacs/Gnulib strftime (regression from 13.2)

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114965

--- Comment #14 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-14 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:d54151df3ba0ee3203e0b8cb8f8fcd168a766c51

commit r14-10184-gd54151df3ba0ee3203e0b8cb8f8fcd168a766c51
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed May 8 10:17:32 2024 +0200

    reassoc: Fix up optimize_range_tests_to_bit_test [PR114965]

    The optimize_range_tests_to_bit_test optimization normally emits a range
    test first:
              if (entry_test_needed)
                {
                  tem = build_range_check (loc, optype, unshare_expr (exp),
                                           false, lowi, high);
                  if (tem == NULL_TREE || is_gimple_val (tem))
                    continue;
                }
    so during the bit test we already know that exp is in the [lowi, high]
    range, but skips it if we have range info which tells us this isn't
    necessary.
    Also, normally it emits shifts by exp - lowi counter, but has an
    optimization to use just exp counter if the mask isn't a more expensive
    constant in that case and lowi is > 0 and high is smaller than prec.

    The following testcase is miscompiled because the two abnormal cases
    are triggered.  The range of exp is [43, 43][48, 48][95, 95], so we on
    64-bit arch decide we don't need the entry test, because 95 - 43 < 64.
    And we also decide to use just exp as counter, because the range test
    tests just for exp == 43 || exp == 48, so high is smaller than 64 too.
    Because 95 is in the exp range, we can't do that, we'd either need to
    do a range test first, i.e.
    if (exp - 43U <= 48U - 43U) if ((1UL << exp) & mask1))
    or need to subtract lowi from the shift counter, i.e.
    if ((1UL << (exp - 43)) & mask2)
    but can't do both unless r.upper_bound () is < prec.

    The following patch ensures that.

    2024-05-08  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/114965
            * tree-ssa-reassoc.cc (optimize_range_tests_to_bit_test): Don't try
to
            optimize away exp - lowi subtraction from shift count unless entry
            test is emitted or unless r.upper_bound () is smaller than prec.

            * gcc.c-torture/execute/pr114965.c: New test.

    (cherry picked from commit 9adec2d91e62a479474ae79df5b455fd4b8463ba)