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[rs6000] More efficient vector permute for little endian

Message ID 1395365894.3599.35.camel@gnopaine
State New
Headers show

Commit Message

Bill Schmidt March 21, 2014, 1:38 a.m. UTC 
Hi,

The original workaround for vector permute on a little endian platform
includes subtracting each element of the permute control vector from 31.
Because the upper 3 bits of each element are unimportant, this was
implemented as subtracting the whole vector from a splat of -1.  On
reflection this can be done more efficiently with a vector nor
operation.  This patch makes that change.

Bootstrapped and tested on powerpc64le-unknown-linux-gnu with no
regressions.  Is this ok for trunk?

Thanks,
Bill


2014-03-20  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>

	* config/rs6000/rs6000.c (rs6000_expand_vector_set): Generate a
	pattern for vector nor instead of subtract from splat(-1).
	(altivec_expand_vec_perm_const_le): Likewise.

Comments

David Edelsohn March 21, 2014, 1:39 p.m. UTC | #1 
On Thu, Mar 20, 2014 at 9:38 PM, Bill Schmidt
<wschmidt@linux.vnet.ibm.com> wrote:
> Hi,
>
> The original workaround for vector permute on a little endian platform
> includes subtracting each element of the permute control vector from 31.
> Because the upper 3 bits of each element are unimportant, this was
> implemented as subtracting the whole vector from a splat of -1.  On
> reflection this can be done more efficiently with a vector nor
> operation.  This patch makes that change.
>
> Bootstrapped and tested on powerpc64le-unknown-linux-gnu with no
> regressions.  Is this ok for trunk?
>
> Thanks,
> Bill
>
>
> 2014-03-20  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
>
>         * config/rs6000/rs6000.c (rs6000_expand_vector_set): Generate a
>         pattern for vector nor instead of subtract from splat(-1).
>         (altivec_expand_vec_perm_const_le): Likewise.

Okay.

Thanks, David
Richard Henderson March 21, 2014, 7:04 p.m. UTC | #2 
On 03/20/2014 06:38 PM, Bill Schmidt wrote:
> -      rtx splat = gen_rtx_VEC_DUPLICATE (V16QImode,
> -					 gen_rtx_CONST_INT (QImode, -1));
> +      rtx notx = gen_rtx_NOT (V16QImode, force_reg (V16QImode, x));
> +      rtx andx = gen_rtx_AND (V16QImode, notx, notx);
>        rtx tmp = gen_reg_rtx (V16QImode);
> -      emit_move_insn (tmp, splat);
> -      x = gen_rtx_MINUS (V16QImode, tmp, force_reg (V16QImode, x));
> -      emit_move_insn (tmp, x);
> +      emit_move_insn (tmp, andx);

Existing problem, and I know it's done all over that backend, but one shouldn't
use emit_move_insn on expressions like that.  Moves should be between RTX_OBJ
things: registers, constants, and memory.

Better to just do "emit_insn (gen_rtx_SET (VOIDmode, tmp, andx));".


r~
diff mbox

Patch

Index: gcc/config/rs6000/rs6000.c
===================================================================
--- gcc/config/rs6000/rs6000.c	(revision 208704)
+++ gcc/config/rs6000/rs6000.c	(working copy)
@@ -5622,12 +5622,10 @@  rs6000_expand_vector_set (rtx target, rtx val, int
   else 
     {
       /* Invert selector.  */
-      rtx splat = gen_rtx_VEC_DUPLICATE (V16QImode,
-					 gen_rtx_CONST_INT (QImode, -1));
+      rtx notx = gen_rtx_NOT (V16QImode, force_reg (V16QImode, x));
+      rtx andx = gen_rtx_AND (V16QImode, notx, notx);
       rtx tmp = gen_reg_rtx (V16QImode);
-      emit_move_insn (tmp, splat);
-      x = gen_rtx_MINUS (V16QImode, tmp, force_reg (V16QImode, x));
-      emit_move_insn (tmp, x);
+      emit_move_insn (tmp, andx);
 
       /* Permute with operands reversed and adjusted selector.  */
       x = gen_rtx_UNSPEC (mode, gen_rtvec (3, reg, target, tmp),
@@ -30321,18 +30319,18 @@  altivec_expand_vec_perm_const_le (rtx operands[4])
 
 /* Similarly to altivec_expand_vec_perm_const_le, we must adjust the
    permute control vector.  But here it's not a constant, so we must
-   generate a vector splat/subtract to do the adjustment.  */
+   generate a vector NOR to do the adjustment.  */
 
 void
 altivec_expand_vec_perm_le (rtx operands[4])
 {
-  rtx splat, unspec;
+  rtx notx, andx, unspec;
   rtx target = operands[0];
   rtx op0 = operands[1];
   rtx op1 = operands[2];
   rtx sel = operands[3];
   rtx tmp = target;
-  rtx splatreg = gen_reg_rtx (V16QImode);
+  rtx norreg = gen_reg_rtx (V16QImode);
   enum machine_mode mode = GET_MODE (target);
 
   /* Get everything in regs so the pattern matches.  */
@@ -30345,18 +30343,14 @@  altivec_expand_vec_perm_le (rtx operands[4])
   if (!REG_P (target))
     tmp = gen_reg_rtx (mode);
 
-  /* SEL = splat(31) - SEL.  */
-  /* We want to subtract from 31, but we can't vspltisb 31 since
-     it's out of range.  -1 works as well because only the low-order
-     five bits of the permute control vector elements are used.  */
-  splat = gen_rtx_VEC_DUPLICATE (V16QImode,
-				 gen_rtx_CONST_INT (QImode, -1));
-  emit_move_insn (splatreg, splat);
-  sel = gen_rtx_MINUS (V16QImode, splatreg, sel);
-  emit_move_insn (splatreg, sel);
+  /* Invert the selector with a VNOR.  */
+  notx = gen_rtx_NOT (V16QImode, sel);
+  andx = gen_rtx_AND (V16QImode, notx, notx);
+  emit_move_insn (norreg, andx);
 
   /* Permute with operands reversed and adjusted selector.  */
-  unspec = gen_rtx_UNSPEC (mode, gen_rtvec (3, op1, op0, splatreg), UNSPEC_VPERM);
+  unspec = gen_rtx_UNSPEC (mode, gen_rtvec (3, op1, op0, norreg),
+			   UNSPEC_VPERM);
 
   /* Copy into target, possibly by way of a register.  */
   if (!REG_P (target))