[Bug target/113255] [11/12/13/14 Regression] wrong code with -O2 -mtune=k8

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113255

--- Comment #12 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:a98d5130a6dcff2ed4db371e500550134777b8cf

commit r14-8346-ga98d5130a6dcff2ed4db371e500550134777b8cf
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Jan 15 12:55:20 2024 +0100

    rtl-optimization/113255 - base_alias_check vs. pointer difference

    When the x86 backend generates code for cpymem with the rep_8byte
    strathegy for the 8 byte aligned main rep movq it needs to compute
    an adjusted pointer to the source after doing a prologue aligning
    the destination.  It computes that via

      src_ptr + (dest_ptr - orig_dest_ptr)

    which is perfectly fine.  On RTL this is then

        8: r134:DI=const(`g'+0x44)
        9: {r133:DI=frame:DI-0x4c;clobber flags:CC;}
          REG_UNUSED flags:CC
       56: r129:DI=const(`g'+0x4c)
       57: {r129:DI=r129:DI&0xfffffffffffffff8;clobber flags:CC;}
          REG_UNUSED flags:CC
          REG_EQUAL const(`g'+0x4c)&0xfffffffffffffff8
       58: {r118:DI=r134:DI-r129:DI;clobber flags:CC;}
          REG_DEAD r134:DI
          REG_UNUSED flags:CC
          REG_EQUAL const(`g'+0x44)-r129:DI
       59: {r119:DI=r133:DI-r118:DI;clobber flags:CC;}
          REG_DEAD r133:DI
          REG_UNUSED flags:CC

    but as written find_base_term happily picks the first candidate
    it finds for the MINUS which means it picks const(`g') rather
    than the correct frame:DI.  This way find_base_term (but also
    the unfixed find_base_value used by init_alias_analysis to
    initialize REG_BASE_VALUE) performs pointer analysis isn't
    sound.  The following restricts the handling of multi-operand
    operations to the case we know only one can be a pointer.

    This for example causes gcc.dg/tree-ssa/pr94969.c to miss some
    RTL PRE (I've opened PR113395 for this).  A more drastic patch,
    removing base_alias_check results in only gcc.dg/guality/pr41447-1.c
    regressing (so testsuite coverage is bad).  I've looked at
    gcc.dg/tree-ssa tests and mostly scheduling changes are present,
    the cc1plus .text size is only 230 bytes worse.  With the this
    less drastic patch below most scheduling changes are gone.

    x86_64 might not the very best target to test for impact, but
    test coverage on other targets is unlikely to be very much better.

            PR rtl-optimization/113255
            * alias.cc (find_base_term): Remove PLUS/MINUS handling
            when both operands are not CONST_INT_P.

            * gcc.dg/torture/pr113255.c: New testcase.