[Bug target/115891] [15 regression] libgcrypt tests segfault in crc32_less_than_16 with LTO with late-combine

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115891

--- Comment #4 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Richard Sandiford <rsandifo@gcc.gnu.org>:

https://gcc.gnu.org/g:9f9faebb8ebfc0103461641cc49ba0b21877b2b1

commit r15-2069-g9f9faebb8ebfc0103461641cc49ba0b21877b2b1
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Tue Jul 16 15:31:17 2024 +0100

    rtl-ssa: Enforce earlyclobbers on hard-coded clobbers [PR115891]

    The asm in the testcase has a memory operand and also clobbers ax.
    The clobber means that ax cannot be used to hold inputs, which
    extends to the address of the memory.

    I think I had an implicit assumption that constrain_operands
    would enforce this, but in hindsight, that clearly wasn't going
    to be true.  constrain_operands only looks at constraints, and
    these clobbers are by definition outside the constraint system.
    (And that's why they have to be handled conservatively, since there's
    no way to distinguish the earlyclobber and non-earlyclobber cases.)

    The semantics of hard-coded clobbers are generic enough that I think
    they should be handled directly by rtl-ssa, rather than by consumers.
    And in the context of rtl-ssa, the easiest way to check for a clash is
    to walk the list of input registers, which we already have to hand.
    It therefore seemed better not to push this down to a more generic
    rtl helper.

    The patch detects hard-coded clobbers in the same way as regrename:
    by temporarily stubbing out the operands with pc_rtx.

    gcc/
            PR rtl-optimization/115891
            * rtl-ssa/changes.cc (find_clobbered_access): New function.
            (recog_level2): Use it to check for overlap between input
            registers and hard-coded clobbers.  Conditionally reset
            recog_data.insn after changing the insn code.

    gcc/testsuite/
            PR rtl-optimization/115891
            * gcc.target/i386/pr115891.c: New test.