Re: [aarch64] Code-gen for vector initialization involving constants

[Prathamesh Kulkarni <prathamesh.kulkarni@linaro.org>]

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On Tue, 2 May 2023 at 17:32, Richard Sandiford
<richard.sandiford@arm.com> wrote:
>
> Prathamesh Kulkarni <prathamesh.kulkarni@linaro.org> writes:
> > On Tue, 2 May 2023 at 14:56, Richard Sandiford
> > <richard.sandiford@arm.com> wrote:
> >> > [aarch64] Improve code-gen for vector initialization with single constant element.
> >> >
> >> > gcc/ChangeLog:
> >> >       * config/aarch64/aarc64.cc (aarch64_expand_vector_init): Tweak condition
> >> >       if (n_var == n_elts && n_elts <= 16) to allow a single constant,
> >> >       and if maxv == 1, use constant element for duplicating into register.
> >> >
> >> > gcc/testsuite/ChangeLog:
> >> >       * gcc.target/aarch64/vec-init-single-const.c: New test.
> >> >
> >> > diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
> >> > index 2b0de7ca038..f46750133a6 100644
> >> > --- a/gcc/config/aarch64/aarch64.cc
> >> > +++ b/gcc/config/aarch64/aarch64.cc
> >> > @@ -22167,7 +22167,7 @@ aarch64_expand_vector_init (rtx target, rtx vals)
> >> >       and matches[X][1] with the count of duplicate elements (if X is the
> >> >       earliest element which has duplicates).  */
> >> >
> >> > -  if (n_var == n_elts && n_elts <= 16)
> >> > +  if ((n_var >= n_elts - 1) && n_elts <= 16)
> >> >      {
> >> >        int matches[16][2] = {0};
> >> >        for (int i = 0; i < n_elts; i++)
> >> > @@ -22227,6 +22227,18 @@ aarch64_expand_vector_init (rtx target, rtx vals)
> >> >            vector register.  For big-endian we want that position to hold
> >> >            the last element of VALS.  */
> >> >         maxelement = BYTES_BIG_ENDIAN ? n_elts - 1 : 0;
> >> > +
> >> > +       /* If we have a single constant element, use that for duplicating
> >> > +          instead.  */
> >> > +       if (n_var == n_elts - 1)
> >> > +         for (int i = 0; i < n_elts; i++)
> >> > +           if (CONST_INT_P (XVECEXP (vals, 0, i))
> >> > +               || CONST_DOUBLE_P (XVECEXP (vals, 0, i)))
> >> > +             {
> >> > +               maxelement = i;
> >> > +               break;
> >> > +             }
> >> > +
> >> >         rtx x = force_reg (inner_mode, XVECEXP (vals, 0, maxelement));
> >> >         aarch64_emit_move (target, lowpart_subreg (mode, x, inner_mode));
> >>
> >> We don't want to force the constant into a register though.
> > OK right, sorry.
> > With the attached patch, for the following test-case:
> > int64x2_t f_s64(int64_t x)
> > {
> >   return (int64x2_t) { x, 1 };
> > }
> >
> > it loads constant from memory (same code-gen as without patch).
> > f_s64:
> >         adrp    x1, .LC0
> >         ldr     q0, [x1, #:lo12:.LC0]
> >         ins     v0.d[0], x0
> >         ret
> >
> > Does the patch look OK ?
> >
> > Thanks,
> > Prathamesh
> > [...]
> > [aarch64] Improve code-gen for vector initialization with single constant element.
> >
> > gcc/ChangeLog:
> >       * config/aarch64/aarc64.cc (aarch64_expand_vector_init): Tweak condition
> >       if (n_var == n_elts && n_elts <= 16) to allow a single constant,
> >       and if maxv == 1, use constant element for duplicating into register.
> >
> > gcc/testsuite/ChangeLog:
> >       * gcc.target/aarch64/vec-init-single-const.c: New test.
> >
> > diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
> > index 2b0de7ca038..97309ddec4f 100644
> > --- a/gcc/config/aarch64/aarch64.cc
> > +++ b/gcc/config/aarch64/aarch64.cc
> > @@ -22167,7 +22167,7 @@ aarch64_expand_vector_init (rtx target, rtx vals)
> >       and matches[X][1] with the count of duplicate elements (if X is the
> >       earliest element which has duplicates).  */
> >
> > -  if (n_var == n_elts && n_elts <= 16)
> > +  if ((n_var >= n_elts - 1) && n_elts <= 16)
>
> No need for the extra brackets.
Adjusted, thanks. Sorry if this sounds like a silly question, but why
do we need the n_elts <= 16 check ?
Won't n_elts be always <= 16 since max number of elements in a vector
would be 16 for V16QI ?
>
> >      {
> >        int matches[16][2] = {0};
> >        for (int i = 0; i < n_elts; i++)
> > @@ -22227,8 +22227,26 @@ aarch64_expand_vector_init (rtx target, rtx vals)
> >            vector register.  For big-endian we want that position to hold
> >            the last element of VALS.  */
> >         maxelement = BYTES_BIG_ENDIAN ? n_elts - 1 : 0;
> > -       rtx x = force_reg (inner_mode, XVECEXP (vals, 0, maxelement));
> > -       aarch64_emit_move (target, lowpart_subreg (mode, x, inner_mode));
> > +
> > +       /* If we have a single constant element, use that for duplicating
> > +          instead.  */
> > +       if (n_var == n_elts - 1)
> > +         for (int i = 0; i < n_elts; i++)
> > +           if (CONST_INT_P (XVECEXP (vals, 0, i))
> > +               || CONST_DOUBLE_P (XVECEXP (vals, 0, i)))
> > +             {
> > +               maxelement = i;
> > +               break;
> > +             }
> > +
> > +       rtx maxval = XVECEXP (vals, 0, maxelement);
> > +       if (!(CONST_INT_P (maxval) || CONST_DOUBLE_P (maxval)))
> > +         {
> > +           rtx x = force_reg (inner_mode, XVECEXP (vals, 0, maxelement));
> > +           aarch64_emit_move (target, lowpart_subreg (mode, x, inner_mode));
> > +         }
> > +       else
> > +         aarch64_emit_move (target, gen_vec_duplicate (mode, maxval));
> >       }
> >        else
> >       {
>
> This seems a bit convoluted.  It might be easier to record whether
> we see a CONST_INT_P or a CONST_DOUBLE_P during the previous loop,
> and if so what the constant is.  Then handle that case first,
> as a separate arm of the "if".
Adjusted in the attached patch. Does it look OK ?
>
> > diff --git a/gcc/testsuite/gcc.target/aarch64/vec-init-single-const.c b/gcc/testsuite/gcc.target/aarch64/vec-init-single-const.c
> > new file mode 100644
> > index 00000000000..682fd43439a
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.target/aarch64/vec-init-single-const.c
> > @@ -0,0 +1,66 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-O2" } */
> > +/* { dg-final { check-function-bodies "**" "" "" } } */
> > +
> > +#include <arm_neon.h>
> > +
> > +/*
> > +** f_s8:
> > +**   ...
> > +**   dup     v[0-9]+\.16b, w[0-9]+
> > +**   movi    v[0-9]+\.8b, 0x1
> > +**   ins     v[0-9]+\.b\[15\], v[0-9]+\.b\[0\]
> > +**   ...
> > +**   ret
>
> Like with the divide-and-conquer patch, there's nothing that requires
> the first two instructions to be in that order.
Hmm, will it be OK to disable scheduling by passing
-fno-schedule-insns -fno-schedule-insns2
for the test ?
>
> What is the second ... hiding?  What sequences do we actually generate?
Sorry, added them by mistake. They were the exact sequences. Adjusted
tests in the patch.
>
> BTW, remember to say how patches were tested :-)
Right, sorry. The patch is under bootstrap+test on aarch64-linux-gnu.
OK to commit if passes ?

Thanks,
Prathamesh
>
> Thanks,
> Richard
>
> > +*/
> > +
> > +int8x16_t f_s8(int8_t x)
> > +{
> > +  return (int8x16_t) { x, x, x, x, x, x, x, x,
> > +                       x, x, x, x, x, x, x, 1 };
> > +}
> > +
> > +/*
> > +** f_s16:
> > +**   ...
> > +**   dup     v[0-9]+\.8h, w[0-9]+
> > +**   movi    v[0-9]+\.4h, 0x1
> > +**   ins     v[0-9]+\.h\[7\], v[0-9]+\.h\[0\]
> > +**   ...
> > +**   ret
> > +*/
> > +
> > +int16x8_t f_s16(int16_t x)
> > +{
> > +  return (int16x8_t) { x, x, x, x, x, x, x, 1 };
> > +}
> > +
> > +/*
> > +** f_s32:
> > +**   ...
> > +**   movi    v[0-9]\.2s, 0x1
> > +**   dup     v[0-9]\.4s, w[0-9]+
> > +**   ins     v[0-9]+\.s\[3\], v[0-9]+\.s\[0\]
> > +**   ...
> > +**   ret
> > +*/
> > +
> > +int32x4_t f_s32(int32_t x)
> > +{
> > +  return (int32x4_t) { x, x, x, 1 };
> > +}
> > +
> > +/*
> > +** f_s64:
> > +**   ...
> > +**   adrp    x[0-9]+, .LC[0-9]+
> > +**   ldr     q[0-9]+, \[x[0-9]+, #:lo12:.LC[0-9]+\]
> > +**   ins     v[0-9]+\.d\[0\], x[0-9]+
> > +**   ...
> > +**   ret
> > +*/
> > +
> > +int64x2_t f_s64(int64_t x)
> > +{
> > +  return (int64x2_t) { x, 1 };
> > +}

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[aarch64] Improve code-gen for vector initialization with single constant element.

gcc/ChangeLog:
	* config/aarch64/aarc64.cc (aarch64_expand_vector_init): Tweak condition
	if (n_var == n_elts && n_elts <= 16) to allow a single constant,
	and if maxv == 1, use constant element for duplicating into register.

gcc/testsuite/ChangeLog:
	* gcc.target/aarch64/vec-init-single-const.c: New test.

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 2b0de7ca038..31319977ffd 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -22167,7 +22167,7 @@ aarch64_expand_vector_init (rtx target, rtx vals)
      and matches[X][1] with the count of duplicate elements (if X is the
      earliest element which has duplicates).  */
 
-  if (n_var == n_elts && n_elts <= 16)
+  if (n_var >= n_elts - 1 && n_elts <= 16)
     {
       int matches[16][2] = {0};
       for (int i = 0; i < n_elts; i++)
@@ -22227,8 +22227,27 @@ aarch64_expand_vector_init (rtx target, rtx vals)
 	     vector register.  For big-endian we want that position to hold
 	     the last element of VALS.  */
 	  maxelement = BYTES_BIG_ENDIAN ? n_elts - 1 : 0;
-	  rtx x = force_reg (inner_mode, XVECEXP (vals, 0, maxelement));
-	  aarch64_emit_move (target, lowpart_subreg (mode, x, inner_mode));
+
+	  /* If we have a single constant element, use that for duplicating
+	     instead.  */
+	  if (n_var == n_elts - 1)
+	    {
+	      for (int i = 0; i < n_elts; i++)
+		if (CONST_INT_P (XVECEXP (vals, 0, i))
+		    || CONST_DOUBLE_P (XVECEXP (vals, 0, i)))
+		  {
+		    maxelement = i;
+		    rtx const_elem = XVECEXP (vals, 0, maxelement);
+		    aarch64_emit_move (target,
+				       gen_vec_duplicate (mode, const_elem));
+		    break;
+		  }
+	    }
+	  else
+	    {
+	      rtx x = force_reg (inner_mode, XVECEXP (vals, 0, maxelement));
+	      aarch64_emit_move (target, lowpart_subreg (mode, x, inner_mode));
+	    }
 	}
       else
 	{
diff --git a/gcc/testsuite/gcc.target/aarch64/vec-init-single-const.c b/gcc/testsuite/gcc.target/aarch64/vec-init-single-const.c
new file mode 100644
index 00000000000..790c90b48ce
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/vec-init-single-const.c
@@ -0,0 +1,58 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-schedule-insns -fno-schedule-insns2" } */
+/* { dg-final { check-function-bodies "**" "" "" } } */
+
+#include <arm_neon.h>
+
+/*
+** f_s8:
+**	dup	v[0-9]+\.16b, w[0-9]+
+**	movi	v[0-9]+\.8b, 0x1
+**	ins	v[0-9]+\.b\[15\], v[0-9]+\.b\[0\]
+**	ret
+*/
+
+int8x16_t f_s8(int8_t x)
+{
+  return (int8x16_t) { x, x, x, x, x, x, x, x,
+                       x, x, x, x, x, x, x, 1 };
+}
+
+/*
+** f_s16:
+**	dup	v[0-9]+\.8h, w[0-9]+
+**	movi	v[0-9]+\.4h, 0x1
+**	ins	v[0-9]+\.h\[7\], v[0-9]+\.h\[0\]
+**	ret
+*/
+
+int16x8_t f_s16(int16_t x)
+{
+  return (int16x8_t) { x, x, x, x, x, x, x, 1 };
+}
+
+/*
+** f_s32:
+**	dup	v[0-9]\.4s, w[0-9]+
+**	movi	v[0-9]\.2s, 0x1
+**	ins	v[0-9]+\.s\[3\], v[0-9]+\.s\[0\]
+**	ret
+*/
+
+int32x4_t f_s32(int32_t x)
+{
+  return (int32x4_t) { x, x, x, 1 };
+}
+
+/*
+** f_s64:
+**	adrp	x[0-9]+, .LC[0-9]+
+**	ldr	q[0-9]+, \[x[0-9]+, #:lo12:.LC[0-9]+\]
+**	ins	v[0-9]+\.d\[0\], x[0-9]+
+**	ret
+*/
+
+int64x2_t f_s64(int64_t x)
+{
+  return (int64x2_t) { x, 1 };
+}