On Tue, Sep 16, 2025 at 4:59 PM Richard Biener
<[email protected]> wrote:
>
> On Tue, Sep 16, 2025 at 9:53 AM Liu, Hongtao <[email protected]> wrote:
> >
> >
> >
> > > -----Original Message-----
> > > From: Richard Biener <[email protected]>
> > > Sent: Tuesday, September 16, 2025 3:03 PM
> > > To: Liu, Hongtao <[email protected]>
> > > Cc: [email protected]; [email protected]
> > > Subject: Re: [PATCH] Remove SPR/GNR/DMR from avx512_{move,store}_by
> > > pieces tune.
> > >
> > > On Tue, Sep 16, 2025 at 7:53 AM liuhongt <[email protected]> wrote:
> > > >
> > > > From: "hongtao.liu" <[email protected]>
> > > >
> > > > Align move_max with prefer_vector_width for SPR/GNR/DMR to avoid STLF
> > > issue.
> > > > It's similar as previous commit.
> > > >
> > > > commit 6ea25c041964bf63014fcf7bb68fb1f5a0a4e123
> > > > Author: liuhongt <[email protected]>
> > > > Date: Thu Aug 15 12:54:07 2024 +0800
> > > >
> > > > Align ix86_{move_max,store_max} with vectorizer.
> > > >
> > > > When none of mprefer-vector-width, avx256_optimal/avx128_optimal,
> > > > avx256_store_by_pieces/avx512_store_by_pieces is specified, GCC will
> > > > set ix86_{move_max,store_max} as max available vector length except
> > > > for AVX part.
> > > >
> > > > if (TARGET_AVX512F_P (opts->x_ix86_isa_flags)
> > > > && TARGET_EVEX512_P (opts->x_ix86_isa_flags2))
> > > > opts->x_ix86_move_max = PVW_AVX512;
> > > > else
> > > > opts->x_ix86_move_max = PVW_AVX128;
> > > >
> > > > So for -mavx2, vectorizer will choose 256-bit for vectorization, but
> > > > 128-bit is used for struct copy, there could be a potential STLF
> > > > issue
> > > > due to this "misalign".
> > > >
> > > >
> > > > Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}.
> > > > Ready push to trunk.
> > >
> > > Not an objection to this patch, but I wonder if we have too many tunables
> > > where these kind of interactions cause more problems than positives by
> > > having them?
> > My experience is we should align MOVE_MAX with prefer_vector_width,
> > vectorization and memcpy are 2 main parts which create vector load/store,
> > they'd better align with each other.
> > >
> > > As general comment I'd say store-by-pieces with larger modes is always
> > > good,
> > > but the read part for move-by-pieces can cause STLF fails, not only from
> > Yes, avx512_store_by_piece is still good, I'll adjust my patch.
> >
> > > vectorization but of course also from (non-contigous) scalar stores
> > > performed
> > > by user code.
> > >
> > > I'm always advising CPU implementors to reduce STLF fail penalties (or
> > > allow
> > > more forwarding cases). On the compilers side we'd have to see to do less
> > > "local" (per stmt) decisions on what modes to use but take into account
> > > context - the post-fact fixup by the avoid-store-forwarding pass is
> > > likely not
> > > very effective?
> > I think the pass can't handle inter-procedure pointer analysis, and
> > there're memcpy and vectorization in caller/callee with different size,
> > worst case is small store in the caller followed by big load in the callee.
>
> True, IIRC this happened in 538.imagick_r at some point.
>
> There's also __attribute__((target)), so caller/callee could disagree
> about vector ISA
> (and/or size preference). But I guess that's not happening too often
> to be of concern.
Regarding target_clone,
It could even have different ABI(one return in memory , one return in
vector register) and hit a gcc_assert. .i.e pr101017
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101017
But it's a different issue.
>
> Richard.
>
> > >
> > > > gcc/ChangeLog:
> > > >
> > > > * config/i386/x86-tune.def (X86_TUNE_AVX512_MOVE_BY_PIECES):
> > > > (X86_TUNE_AVX512_STORE_BY_PIECES):
> > > >
> > > > gcc/testsuite/ChangeLog:
> > > >
> > > > * gcc.target/i386/pieces-memcpy-18.c: Use -mtune=znver5
> > > > instead of -mtune=sapphirerapids.
> > > > * gcc.target/i386/pieces-memcpy-21.c: Ditto.
> > > > * gcc.target/i386/pieces-memset-46.c: Ditto.
> > > > * gcc.target/i386/pieces-memset-49.c: Ditto.
> > > > ---
> > > > gcc/config/i386/x86-tune.def | 6 ++----
> > > > gcc/testsuite/gcc.target/i386/pieces-memcpy-18.c | 2 +-
> > > > gcc/testsuite/gcc.target/i386/pieces-memcpy-21.c | 2 +-
> > > > gcc/testsuite/gcc.target/i386/pieces-memset-46.c | 2 +-
> > > > gcc/testsuite/gcc.target/i386/pieces-memset-49.c | 2 +-
> > > > 5 files changed, 6 insertions(+), 8 deletions(-)
> > > >
> > > > diff --git a/gcc/config/i386/x86-tune.def
> > > > b/gcc/config/i386/x86-tune.def index a86cbad281c..8e642aa92a2 100644
> > > > --- a/gcc/config/i386/x86-tune.def
> > > > +++ b/gcc/config/i386/x86-tune.def
> > > > @@ -625,14 +625,12 @@ DEF_TUNE
> > > (X86_TUNE_AVX256_STORE_BY_PIECES,
> > > > "avx256_store_by_pieces",
> > > > /* X86_TUNE_AVX512_MOVE_BY_PIECES: Optimize move_by_pieces with
> > > 512-bit
> > > > AVX instructions. */
> > > > DEF_TUNE (X86_TUNE_AVX512_MOVE_BY_PIECES,
> > > "avx512_move_by_pieces",
> > > > - m_SAPPHIRERAPIDS | m_GRANITERAPIDS | m_GRANITERAPIDS_D
> > > > - | m_DIAMONDRAPIDS | m_ZNVER4 | m_ZNVER5)
> > > > + m_ZNVER4 | m_ZNVER5)
> > > >
> > > > /* X86_TUNE_AVX512_STORE_BY_PIECES: Optimize store_by_pieces with
> > > 512-bit
> > > > AVX instructions. */
> > > > DEF_TUNE (X86_TUNE_AVX512_STORE_BY_PIECES,
> > > "avx512_store_by_pieces",
> > > > - m_SAPPHIRERAPIDS | m_GRANITERAPIDS | m_GRANITERAPIDS_D
> > > > - | m_DIAMONDRAPIDS | m_ZNVER4 | m_ZNVER5)
> > > > + m_ZNVER4 | m_ZNVER5)
> > > >
> > > > /* X86_TUNE_AVX512_TWO_EPILOGUES: Use two vector epilogues for
> > > 512-bit
> > > > vectorized loops. */
> > > > diff --git a/gcc/testsuite/gcc.target/i386/pieces-memcpy-18.c
> > > > b/gcc/testsuite/gcc.target/i386/pieces-memcpy-18.c
> > > > index b15a0db9ff0..b4995ac0598 100644
> > > > --- a/gcc/testsuite/gcc.target/i386/pieces-memcpy-18.c
> > > > +++ b/gcc/testsuite/gcc.target/i386/pieces-memcpy-18.c
> > > > @@ -1,5 +1,5 @@
> > > > /* { dg-do compile } */
> > > > -/* { dg-options "-O2 -march=sapphirerapids" } */
> > > > +/* { dg-options "-O2 -march=znver5" } */
> > > >
> > > > extern char *dst, *src;
> > > >
> > > > diff --git a/gcc/testsuite/gcc.target/i386/pieces-memcpy-21.c
> > > > b/gcc/testsuite/gcc.target/i386/pieces-memcpy-21.c
> > > > index ef439f20f74..804a2989d64 100644
> > > > --- a/gcc/testsuite/gcc.target/i386/pieces-memcpy-21.c
> > > > +++ b/gcc/testsuite/gcc.target/i386/pieces-memcpy-21.c
> > > > @@ -1,5 +1,5 @@
> > > > /* { dg-do compile } */
> > > > -/* { dg-options "-O2 -mtune=sapphirerapids -march=x86-64 -mavx2" } */
> > > > +/* { dg-options "-O2 -mtune=znver5 -march=x86-64 -mavx2" } */
> > > >
> > > > extern char *dst, *src;
> > > >
> > > > diff --git a/gcc/testsuite/gcc.target/i386/pieces-memset-46.c
> > > > b/gcc/testsuite/gcc.target/i386/pieces-memset-46.c
> > > > index be1b054eed2..43d636ee3ff 100644
> > > > --- a/gcc/testsuite/gcc.target/i386/pieces-memset-46.c
> > > > +++ b/gcc/testsuite/gcc.target/i386/pieces-memset-46.c
> > > > @@ -1,5 +1,5 @@
> > > > /* { dg-do compile } */
> > > > -/* { dg-options "-O2 -march=sapphirerapids" } */
> > > > +/* { dg-options "-O2 -march=znver5" } */
> > > >
> > > > extern char *dst;
> > > >
> > > > diff --git a/gcc/testsuite/gcc.target/i386/pieces-memset-49.c
> > > > b/gcc/testsuite/gcc.target/i386/pieces-memset-49.c
> > > > index ad43f89a9bd..ca4933ac1d8 100644
> > > > --- a/gcc/testsuite/gcc.target/i386/pieces-memset-49.c
> > > > +++ b/gcc/testsuite/gcc.target/i386/pieces-memset-49.c
> > > > @@ -1,5 +1,5 @@
> > > > /* { dg-do compile } */
> > > > -/* { dg-options "-O2 -mtune=sapphirerapids -march=x86-64 -mavx2" } */
> > > > +/* { dg-options "-O2 -mtune=znver5 -march=x86-64 -mavx2" } */
> > > >
> > > > extern char *dst;
> > > >
> > > > --
> > > > 2.34.1
> > > >
--
BR,
Hongtao
