On Thu, 22 Jan 2026, Hongtao Liu wrote:
> On Thu, Jan 22, 2026 at 6:37 PM Richard Biener <[email protected]> wrote:
> >
> > On Tue, 20 Jan 2026, liuhongt wrote:
> >
> > > /* X86_TUNE_PREFER_BCST_FROM_INTEGER: Enable broadcast from integer for
> > > 128/256/512-bit vector, if disabled, the move will be done by
> > > broadcast/load from constant pool
> > >
> > > broadcast from integer:
> > > mov $0xa,%eax
> > > vmovd %eax,%xmm0
> > > vpbroadcastd %xmm0,%xmm0
> > >
> > > broadcast/load from constant pool:
> > > vpbroadcastd CST.0(%rip), %xmm0 */
> > >
> > > The tune is on by default.
> >
> > Thanks!
> >
> > I wonder if the broadcast/load from constnat pool could be late
> > split in to the former when a GPR is available (and the tune
> > indicates it's profitable).
> Good point, maybe the implementation of this tune could also be
> changed to convert the load of const_vector into broadcast from memory
> before RA, and then decide after RA whether we need to use a GPR to
> avoid this load. I'm not sure if doing this optimization after RA
> might have potential issues, I suspect there could be some level of
> conflict between this and RA.
I'd say it will clearly help the case when there's a lot of GPR
register pressure. OTOH possibly the bcast from memory pattern
could have an alternative with a scratch GPR for later use in
spliting so the RA would have choice? That alternative could be
disabled when !X86_TUNE_PREFER_BCST_FROM_INTEGER?
> >
> > > gcc/ChangeLog:
> > >
> > > PR target/123631
> > > * config/i386/i386-expand.cc (ix86_vector_duplicate_value):
> > > Don't force CONST_INT to reg !TARGET_PREFER_BCST_FROM_INTEGER,
> > > force it to mem instead.
> > > * config/i386/i386.h (TARGET_PREFER_BCST_FROM_INTEGER): New macro.
> > > * config/i386/x86-tune.def
> > > (X86_TUNE_PREFER_BCST_FROM_INTEGER): New tune.
> > > ---
> > > gcc/config/i386/i386-expand.cc | 17 +++++++++++++----
> > > gcc/config/i386/i386.h | 3 +++
> > > gcc/config/i386/x86-tune.def | 15 +++++++++++++++
> > > 3 files changed, 31 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/gcc/config/i386/i386-expand.cc
> > > b/gcc/config/i386/i386-expand.cc
> > > index d6525ddcdd0..a82bb4399c9 100644
> > > --- a/gcc/config/i386/i386-expand.cc
> > > +++ b/gcc/config/i386/i386-expand.cc
> > > @@ -17361,12 +17361,21 @@ ix86_vector_duplicate_value (machine_mode mode,
> > > rtx target, rtx val)
> > > machine_mode innermode = GET_MODE_INNER (mode);
> > > rtx reg;
> > >
> > > - /* If that fails, force VAL into a register. */
> > > + /* If that fails, force VAL into a register or mem. */
> > >
> > > start_sequence ();
> > > - reg = force_reg (innermode, val);
> > > - if (GET_MODE (reg) != innermode)
> > > - reg = gen_lowpart (innermode, reg);
> > > +
> > > + if (!TARGET_PREFER_BCST_FROM_INTEGER && CONST_INT_P (val)
> > > + && GET_MODE_BITSIZE (innermode) <= HOST_BITS_PER_WIDE_INT
> > > + && GET_MODE_BITSIZE(mode) >= 128)
> > > + reg = validize_mem (force_const_mem (innermode, val));
> > > + else
> > > + {
> > > + reg = force_reg (innermode, val);
> > > + if (GET_MODE (reg) != innermode)
> > > + reg = gen_lowpart (innermode, reg);
> > > + }
> > > +
> > > SET_SRC (PATTERN (insn)) = gen_vec_duplicate (mode, reg);
> > > seq = end_sequence ();
> > > if (seq)
> > > diff --git a/gcc/config/i386/i386.h b/gcc/config/i386/i386.h
> > > index 71bacc22052..888edfed88f 100644
> > > --- a/gcc/config/i386/i386.h
> > > +++ b/gcc/config/i386/i386.h
> > > @@ -409,6 +409,9 @@ extern unsigned char
> > > ix86_tune_features[X86_TUNE_LAST];
> > > ix86_tune_features[X86_TUNE_INTER_UNIT_MOVES_FROM_VEC]
> > > #define TARGET_INTER_UNIT_CONVERSIONS \
> > > ix86_tune_features[X86_TUNE_INTER_UNIT_CONVERSIONS]
> > > +#define TARGET_PREFER_BCST_FROM_INTEGER \
> > > + ix86_tune_features[X86_TUNE_PREFER_BCST_FROM_INTEGER]
> > > +
> > > #define TARGET_FOUR_JUMP_LIMIT
> > > ix86_tune_features[X86_TUNE_FOUR_JUMP_LIMIT]
> > > #define TARGET_SCHEDULE
> > > ix86_tune_features[X86_TUNE_SCHEDULE]
> > > #define TARGET_USE_BT ix86_tune_features[X86_TUNE_USE_BT]
> > > diff --git a/gcc/config/i386/x86-tune.def b/gcc/config/i386/x86-tune.def
> > > index a1944620daf..53cf1a19433 100644
> > > --- a/gcc/config/i386/x86-tune.def
> > > +++ b/gcc/config/i386/x86-tune.def
> > > @@ -488,6 +488,21 @@ DEF_TUNE (X86_TUNE_INTER_UNIT_MOVES_FROM_VEC,
> > > "inter_unit_moves_from_vec",
> > > DEF_TUNE (X86_TUNE_INTER_UNIT_CONVERSIONS, "inter_unit_conversions",
> > > ~(m_AMDFAM10 | m_BDVER))
> > >
> > > +/* X86_TUNE_PREFER_BCST_FROM_INTEGER: Enable broadcast from integer for
> > > + 128/256/512-bit vector, if disabled, the move will be done by
> > > + broadcast/load from constant pool
> > > +
> > > + broadcast from integer:
> > > + mov $0xa,%eax
> > > + vmovd %eax,%xmm0
> > > + vpbroadcastd %xmm0,%xmm0
> > > +
> > > + broadcast/load from constant pool:
> > > + vpbroadcastd CST.0(%rip), %xmm0 */
> > > +
> > > +DEF_TUNE (X86_TUNE_PREFER_BCST_FROM_INTEGER, "prefer_bcst_from_integer",
> > > + m_ALL)
> > > +
> > > /* X86_TUNE_SPLIT_MEM_OPND_FOR_FP_CONVERTS: Try to split memory operand
> > > for
> > > fp converts to destination register. */
> > > DEF_TUNE (X86_TUNE_SPLIT_MEM_OPND_FOR_FP_CONVERTS,
> > > "split_mem_opnd_for_fp_converts",
> > >
> >
> > --
> > Richard Biener <[email protected]>
> > SUSE Software Solutions Germany GmbH,
> > Frankenstrasse 146, 90461 Nuernberg, Germany;
> > GF: Jochen Jaser, Andrew McDonald, Werner Knoblich; (HRB 36809, AG
> > Nuernberg)
>
>
>
>
--
Richard Biener <[email protected]>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
