[Bug rtl-optimization/98037] ICE in dse.c:find_shift_sequence for large non-integer modes

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98037

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Richard Sandiford
<rsandifo@gcc.gnu.org>:

https://gcc.gnu.org/g:fb9ee3e7419178e6530c09b99272022d062b50f3

commit r10-9108-gfb9ee3e7419178e6530c09b99272022d062b50f3
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Wed Dec 2 16:20:34 2020 +0000

    dse: Cope with bigger-than-integer modes [PR98037]

    dse.c:find_shift_sequence tries to represent a store and load
    back as a shift right followed by a truncation.  It therefore
    needs to find an integer mode in which to do the shift right.
    The loop it uses has the form:

      FOR_EACH_MODE_FROM (new_mode_iter,
                          smallest_int_mode_for_size (GET_MODE_BITSIZE
(read_mode)))

    which implicitly assumes that read_mode has an equivalent integer mode.
    As shown in the testcase, not all modes have such an integer mode.

    This patch just makes the code start from the smallest integer mode and
    skip modes that are too small.  The loop already breaks at the first
    mode wider than word_mode.

    gcc/
            PR rtl-optimization/98037
            * dse.c (find_shift_sequence): Iterate over all integers and
            skip modes that are too small.

    gcc/testsuite/
            PR rtl-optimization/98037
            * gcc.target/aarch64/sve/acle/general/pr98037.c: New test.

    (cherry picked from commit f835e9f6562dda9c8a1384be2c9d4e45c112ed8e)