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Subject: [Bug target/109973] [13/14 Regression] Wrong code for AVX2 since
 13.1 by combining VPAND and VPTEST since r13-2006-ga56c1641e9d25e
Date: Thu, 22 Jun 2023 06:44:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109973

--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Roger Sayle <sayle@gcc.gnu.org>:

https://gcc.gnu.org/g:5322f009e8f7d1c7a1c9aab7cb4c90c433398fdd

commit r14-2030-g5322f009e8f7d1c7a1c9aab7cb4c90c433398fdd
Author: Roger Sayle <roger@nextmovesoftware.com>
Date:   Thu Jun 22 07:43:07 2023 +0100

    i386: Convert ptestz of pandn into ptestc.

    This patch is the next installment in a set of backend patches around
    improvements to ptest/vptest.  A previous patch optimized the sequence
    t=3Dpand(x,y); ptestz(t,t) into the equivalent ptestz(x,y), using the
    property that ZF is set to (X&Y) =3D=3D 0.  This patch performs a simil=
ar
    transformation, converting t=3Dpandn(x,y); ptestz(t,t) into the (almost)
    equivalent ptestc(y,x), using the property that the CF flags is set to
    (~X&Y) =3D=3D 0.  The tricky bit is that this sets the CF flag instead =
of
    the ZF flag, so we can only perform this transformation when we can
    also convert the flags consumer, as well as the producer.

    For the test case:

    int foo (__m128i x, __m128i y)
    {
      __m128i a =3D x & ~y;
      return __builtin_ia32_ptestz128 (a, a);
    }

    With -O2 -msse4.1 we previously generated:

    foo:    pandn   %xmm0, %xmm1
            xorl    %eax, %eax
            ptest   %xmm1, %xmm1
            sete    %al
            ret

    with this patch we now generate:

    foo:    xorl    %eax, %eax
            ptest   %xmm0, %xmm1
            setc    %al
            ret

    At the same time, this patch also provides alternative fixes for
    PR target/109973 and PR target/110118, by recognizing that ptestc(x,x)
    always sets the carry flag (X&~X is always zero).  This is achieved
    both by recognizing the special case in ix86_expand_sse_ptest and with
    a splitter to convert an eligible ptest into an stc.

    2023-06-22  Roger Sayle  <roger@nextmovesoftware.com>
                Uros Bizjak  <ubizjak@gmail.com>

    gcc/ChangeLog
            * config/i386/i386-expand.cc (ix86_expand_sse_ptest): Recognize
            expansion of ptestc with equal operands as producing const1_rtx.
            * config/i386/i386.cc (ix86_rtx_costs): Provide accurate cost
            estimates of UNSPEC_PTEST, where the ptest performs the PAND
            or PAND of its operands.
            * config/i386/sse.md (define_split): Transform CCCmode UNSPEC_P=
TEST
            of reg_equal_p operands into an x86_stc instruction.
            (define_split): Split pandn/ptestz/set{n?}e into ptestc/set{n?}=
c.
            (define_split): Similar to above for strict_low_part destinatio=
ns.
            (define_split): Split pandn/ptestz/j{n?}e into ptestc/j{n?}c.

    gcc/testsuite/ChangeLog
            * gcc.target/i386/avx-vptest-4.c: New test case.
            * gcc.target/i386/avx-vptest-5.c: Likewise.
            * gcc.target/i386/avx-vptest-6.c: Likewise.
            * gcc.target/i386/pr109973-1.c: Update test case.
            * gcc.target/i386/pr109973-2.c: Likewise.
            * gcc.target/i386/sse4_1-ptest-4.c: New test case.
            * gcc.target/i386/sse4_1-ptest-5.c: Likewise.
            * gcc.target/i386/sse4_1-ptest-6.c: Likewise.=