On Sat, May 9, 2026 at 10:28 AM H.J. Lu <[email protected]> wrote:
>
> On Sat, May 9, 2026 at 10:20 AM H.J. Lu <[email protected]> wrote:
> >
> > On Sat, May 9, 2026 at 9:10 AM Liu, Hongtao <[email protected]> wrote:
> > >
> > >
> > >
> > > > -----Original Message-----
> > > > From: H.J. Lu <[email protected]>
> > > > Sent: Saturday, May 9, 2026 7:57 AM
> > > > To: GCC Patches <[email protected]>; Uros Bizjak
> > > > <[email protected]>; Liu, Hongtao <[email protected]>
> > > > Subject: [PATCH] x86_cse: Check CONST0_RTX and CONSTM1_RTX for
> > > > X86_CSE_VEC_DUP
> > > >
> > > > Check CONST0_RTX and CONSTM1_RTX when placing
> > > >
> > > > (insn 32 2 7 2 (set (reg:V2DI 114)
> > > > (const_vector:V2DI [
> > > > (const_int 0 [0]) repeated x2
> > > > ])) -1
> > > > (nil))
> > > >
> > > > after
> > > >
> > > > (note 2 3 32 2 NOTE_INSN_FUNCTION_BEG)
> > > >
> > > > for X86_CSE_VEC_DUP, not X86_CSE_CONST0_VECTOR or
> > > > X86_CSE_CONSTM1_VECTOR, after replacing redundant vector loads:
> > > >
> > > > (insn 31 15 16 2 (set (reg/v/f:DI 99 [ d ])
> > > > (const_int 0 [0])) "x.c":5:16 -1
> > > > (nil))
> > > > ...
> > > > (insn 18 17 19 2 (set (reg:V2DI 111 [ _22 ])
> > > > (vec_duplicate:V2DI (reg/v/f:DI 99 [ d ]))) "x.c":5:16 9345
> > > > {*vec_dupv2di}
> > > > (nil))
> > > >
> > > > ...
> > > > (insn 29 12 15 2 (set (reg/v/f:DI 98 [ c ])
> > > > (const_int 0 [0])) "x.c":5:16 -1
> > > > (nil))
> > > > ...
> > > > (insn 20 19 21 2 (set (reg:V2DI 112 [ _20 ])
> > > > (vec_duplicate:V2DI (reg/v/f:DI 98 [ c ]))) "x.c":5:16 9345
> > > > {*vec_dupv2di}
> > > > (nil))
> > > >
> > > > with
> > > >
> > > > (insn 18 17 19 2 (set (reg:V2DI 111 [ _22 ])
> > > > (reg:V2DI 114)) "x.c":5:16 2454 {movv2di_internal}
> > > > (nil))
> > > >
> > > > and
> > > >
> > > > (insn 20 19 21 2 (set (reg:V2DI 112 [ _20 ])
> > > > (reg:V2DI 114)) "x.c":5:16 2454 {movv2di_internal}
> > > > (nil))
> > > >
> > > > gcc/
> > > >
> > > > PR target/125239
> > > > * config/i386/i386-features.cc (ix86_place_single_vector_set):
> > > > Check CONST0_RTX and CONSTM1_RTX for X86_CSE_VEC_DUP.
> > >
> > > Can we detect it in ix86_broadcast_inner, set *kind_p to
> > > X86_CSE_CONST0_VECTOR, instead of handle it in
> > > ix86_place_single_vector_set.
> >
> > Done. I am testing this patch.
>
> The condition should be
>
> else if (CONST_VECTOR_P (src))
> {
> /* The only possible CONST_VECTORs of SRC are CONST0_RTX and
> CONSTM1_RTX. Otherwise,
>
> rtx set = gen_rtx_SET (dest, src);
>
> won't be a valid instruction. */
> machine_mode mode = GET_MODE (dest);
> if (!((src == CONST0_RTX (mode)
> && load->kind == X86_CSE_CONST0_VECTOR)
> || (src == CONSTM1_RTX (mode)
> && load->kind == X86_CSE_CONSTM1_VECTOR)))
> gcc_unreachable ();
I think for CONST_VECTOR size > UNITS_PER_WORD, we now constructed the
const_vector(line and assigned it to broadcast_source)
4910 else
4911 {
4912 int nunits = GET_MODE_NUNITS (mode);
4913 rtvec v = rtvec_alloc (nunits);
4914 for (int j = 0; j < nunits ; j++)
4915 RTVEC_ELT (v, j) = load->val;
4916 broadcast_source = gen_rtx_CONST_VECTOR (mode, v);
4917 }
And it will be passed to ix86_place_single_vector_set and cause
invalid insn, it's a bug that needs to be fixed.
> }
>
> > > Also, I wonder why pass_combine(or fwprop) doesn't catch this miss
> > > optimization. Set with CONST0_VECTOR should be cheaper than with
> > > vec_duplicate.
> >
> > Because of -fno-tree-dse -fno-tree-dce?
> >
> > > >
> > > > gcc/testsuite/
> > > >
> > > > PR target/125239
> > > > * gcc.target/i386/pr125239.c: New test.
> > > >
> > > >
> > > > --
> > > > H.J.
> >
> >
> >
> > --
> > H.J.
>
>
>
> --
> H.J.
--
BR,
Hongtao
