[Bug rtl-optimization/99905] [8/9/10/11 Regression] wrong code with -mno-mmx -mno-sse since r7-4540-gb229ab2a712ccd44

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99905

--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:ffc4155b6e45b8ab71d49a4b584f7cacb693e6b9

commit r11-8140-gffc4155b6e45b8ab71d49a4b584f7cacb693e6b9
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Apr 13 01:01:45 2021 +0200

    combine: Fix up expand_compound_operation [PR99905]

    The following testcase is miscompiled on x86_64-linux.
    expand_compound_operation is called on
    (zero_extract:DI (mem/c:TI (reg/f:DI 16 argp) [3 i+0 S16 A128])
        (const_int 16 [0x10])
        (const_int 63 [0x3f]))
    so mode is DImode, inner_mode is TImode, pos 63, len 16 and modewidth 64.

    A couple of lines above the problematic spot we have:
      if (modewidth >= pos + len)
        {
          tem = gen_lowpart (mode, XEXP (x, 0));
    where the code uses gen_lowpart and then shift left/right to extract it
    in mode.  But the guarding condition is false - 64 >= 63 + 16
    and so we enter the next condition, where the code shifts XEXP (x, 0)
    right by pos and then adds AND.  It does so incorrectly though.
    Given the modewidth < pos + len, inner_mode must be necessarily larger
    than mode and XEXP (x, 0) has the innermode, but it was calling
    simplify_shift_const with mode rather than inner_mode, which meant
    inconsistent arguments to simplify_shift_const and in this case made
    a DImode MEM shift out of it.

    The following patch fixes it, by doing the shift in inner_mode properly
    and then after the shift doing the lowpart subreg and masking already
    in mode.

    2021-04-13  Jakub Jelinek  <jakub@redhat.com>

            PR rtl-optimization/99905
            * combine.c (expand_compound_operation): If pos + len > modewidth,
            perform the right shift by pos in inner_mode and then convert to
mode,
            instead of trying to simplify a shift of rtx with inner_mode by pos
            as if it was a shift in mode.

            * gcc.target/i386/pr99905.c: New test.