[x86_64 PATCH] PR target/109973: CCZmode and CCCmode variants of [v]ptest.

[Roger Sayle]

This is my proposed minimal fix for PR target/109973 (hopefully suitable
for backporting) that follows Jakub Jelinek's suggestion that we introduce
CCZmode and CCCmode variants of ptest and vptest, so that the i386
backend treats [v]ptest instructions similarly to testl instructions;
using different CCmodes to indicate which condition flags are desired,
and then relying on the RTL cmpelim pass to eliminate redundant tests.

This conveniently matches Intel's intrinsics, that provide different
functions for retrieving different flags, _mm_testz_si128 tests the
Z flag, _mm_testc_si128 tests the carry flag.  Currently we use the
same instruction (pattern) for both, and unfortunately the *ptest<mode>_and
optimization is only valid when the ptest/vptest instruction is used to
set/test the Z flag.

The downside, as predicted by Jakub, is that GCC's cmpelim pass is
currently COMPARE-centric and not able to merge the ptests from expressions
such as _mm256_testc_si256 (a, b) + _mm256_testz_si256 (a, b), which is a
known issue, PR target/80040.  I've some follow-up patches to improve
things, but this first patch fixes the wrong-code regression, replacing
it with a rare missed-optimization (hopefully suitable for GCC 13).

The only change that was unanticipated was the tweak to ix86_match_ccmode.
Oddly, CCZmode is allowable for CCmode, but CCCmode isn't.  Given that
CCZmode means just the Z flag, CCCmode means just the C flag, and
CCmode means all the flags, I'm guessing this asymmetry is unintentional.
Perhaps a super-safe fix is to explicitly test for CCZmode, CCCmode or
CCmode
in the *<sse4_1>_ptest<mode> pattern's predicate, and not attempt to
re-use ix86_match_ccmode?

This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check, both with and without --target_board=unix{-m32}
with no new failures.  Ok for mainline?


2023-05-29  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
        PR targt/109973
        * config/i386/i386-builtin.def (__builtin_ia32_ptestz128): Use new
        CODE_for_sse4_1_ptestzv2di.
        (__builtin_ia32_ptestc128): Use new CODE_for_sse4_1_ptestcv2di.
        (__builtin_ia32_ptestz256): Use new CODE_for_avx_ptestzv4di.
        (__builtin_ia32_ptestc256): Use new CODE_for_avx_ptestcv4di.
        * config/i386/i386-expand.cc (ix86_expand_branch): Use CCZmode
        when expanding UNSPEC_PTEST to compare against zero.
        * config/i386/i386-features.cc (scalar_chain::convert_compare):
        Likewise generate CCZmode UNSPEC_PTESTs when converting comparisons.
        (general_scalar_chain::convert_insn): Use CCZmode for COMPARE
result.
        (timode_scalar_chain::convert_insn): Use CCZmode for COMPARE result.
        * config/i386/i386.cc (ix86_match_ccmode): Allow the SET_SRC to be
        an UNSPEC, in addition to a COMPARE.  Consider CCCmode to be a form
        of CCmode.
        * config/i386/sse.md (define_split): When splitting UNSPEC_MOVMSK
        to UNSPEC_PTEST, preserve the FLAG_REG mode as CCZ.
        (*<sse4_1>_ptest<mode>): Add asterisk to hide define_insn.
        Remove ":CC" flags specification, and use ix86_match_ccmode instead.
        (<sse4_1>_ptestz<mode>): New define_expand to specify CCZ.
        (<sse4_1>_ptestc<mode>): New define_expand to specify CCC.
        (<sse4_1>_ptest<mode>): A define_expand using CC to preserve the
        current behavior.
        (*ptest<mode>_and): Specify CCZ to only perform this optimization
        when only the Z flag is required.

gcc/testsuite/ChangeLog
        PR targt/109973
        * gcc.target/i386/pr109973-1.c: New test case.
        * gcc.target/i386/pr109973-2.c: Likewise.


Thanks,
Roger
--

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