[Bug middle-end/97073] [8/9/10/11 Regression] Miscompilation with -m32 -O1 -march=i686

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97073

--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:9389e3abc1fc4881f22c7376aae2dd650af2b792

commit r10-8804-g9389e3abc1fc4881f22c7376aae2dd650af2b792
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Sun Sep 27 23:18:26 2020 +0200

    optabs: Don't reuse target for multi-word expansions if it overlaps
operand(s) [PR97073]

    The following testcase is miscompiled on i686-linux, because
    we try to expand a double-word bitwise logic operation with op0
    being a (mem:DI u) and target (mem:DI u+4), i.e. partial overlap, and
    thus end up with:
            movl    4(%esp), %eax
            andl    u, %eax
            movl    %eax, u+4
    ! movl u+4, %eax optimized out
            andl    8(%esp), %eax
            movl    %eax, u+8
    rather than with the desired:
            movl    4(%esp), %edx
            movl    8(%esp), %eax
            andl    u, %edx
            andl    u+4, %eax
            movl    %eax, u+8
            movl    %edx, u+4
    because the store of the first word to target overwrites the second word of
    the operand.
    expand_binop for this (and several similar places) already check for target
    == op0 or target == op1, this patch just adds reg_overlap_mentioned_p calls
    next to it.
    Pedantically, at least for some of these it might be sufficient to force
    a different target if there is overlap but target is not rtx_equal_p to
    the operand (e.g. in this bitwise logical case, but e.g. not in the shift
    cases where there is reordering), though that would go against the
    preexisting target == op? checks and the rationale that REG_EQUAL notes in
    that case isn't correct.

    2020-09-27  Jakub Jelinek  <jakub@redhat.com>

            PR middle-end/97073
            * optabs.c (expand_binop, expand_absneg_bit, expand_unop,
            expand_copysign_bit): Check reg_overlap_mentioned_p between target
            and operand(s) and if it returns true, force a pseudo as target.

            * gcc.c-torture/execute/pr97073.c: New test.

    (cherry picked from commit a4b31d5807f2bc67c8999b3d53369cf2a5c6e1ec)