RE: [PATCH 3/4]AArch64 Add SVE2 implementation for pow2 bitmask division

[Tamar Christina <Tamar.Christina@arm.com>]

Ping

> -----Original Message-----
> From: Tamar Christina <tamar.christina@arm.com>
> Sent: Friday, September 23, 2022 10:34 AM
> To: gcc-patches@gcc.gnu.org
> Cc: nd <nd@arm.com>; Richard Earnshaw <Richard.Earnshaw@arm.com>;
> Marcus Shawcroft <Marcus.Shawcroft@arm.com>; Kyrylo Tkachov
> <Kyrylo.Tkachov@arm.com>; Richard Sandiford
> <Richard.Sandiford@arm.com>
> Subject: [PATCH 3/4]AArch64 Add SVE2 implementation for pow2 bitmask
> division
> 
> Hi All,
> 
> In plenty of image and video processing code it's common to modify pixel
> values by a widening operation and then scale them back into range by
> dividing by 255.
> 
> This patch adds an named function to allow us to emit an optimized
> sequence when doing an unsigned division that is equivalent to:
> 
>    x = y / (2 ^ (bitsize (y)/2)-1)
> 
> For SVE2 this means we generate for:
> 
> void draw_bitmap1(uint8_t* restrict pixel, uint8_t level, int n) {
>   for (int i = 0; i < (n & -16); i+=1)
>     pixel[i] = (pixel[i] * level) / 0xff; }
> 
> the following:
> 
>         mov     z3.b, #1
> .L3:
>         ld1b    z0.h, p0/z, [x0, x3]
>         mul     z0.h, p1/m, z0.h, z2.h
>         addhnb  z1.b, z0.h, z3.h
>         addhnb  z0.b, z0.h, z1.h
>         st1b    z0.h, p0, [x0, x3]
>         inch    x3
>         whilelo p0.h, w3, w2
>         b.any   .L3
> 
> instead of:
> 
> .L3:
>         ld1b    z0.h, p1/z, [x0, x3]
>         mul     z0.h, p0/m, z0.h, z1.h
>         umulh   z0.h, p0/m, z0.h, z2.h
>         lsr     z0.h, z0.h, #7
>         st1b    z0.h, p1, [x0, x3]
>         inch    x3
>         whilelo p1.h, w3, w2
>         b.any   .L3
> 
> Which results in significantly faster code.
> 
> Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.
> 
> Ok for master?
> 
> Thanks,
> Tamar
> 
> gcc/ChangeLog:
> 
> 	* config/aarch64/aarch64-sve2.md
> (@aarch64_bitmask_udiv<mode>3): New.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* gcc.target/aarch64/sve2/div-by-bitmask_1.c: New test.
> 
> --- inline copy of patch --
> diff --git a/gcc/config/aarch64/aarch64-sve2.md
> b/gcc/config/aarch64/aarch64-sve2.md
> index
> f138f4be4bcf74c1a4a6d5847ed831435246737f..4d097f7c405cc68a1d6cda5c234
> a1023a6eba0d1 100644
> --- a/gcc/config/aarch64/aarch64-sve2.md
> +++ b/gcc/config/aarch64/aarch64-sve2.md
> @@ -71,6 +71,7 @@
>  ;; ---- [INT] Reciprocal approximation
>  ;; ---- [INT<-FP] Base-2 logarithm
>  ;; ---- [INT] Polynomial multiplication
> +;; ---- [INT] Misc optab implementations
>  ;;
>  ;; == Permutation
>  ;; ---- [INT,FP] General permutes
> @@ -2312,6 +2313,47 @@ (define_insn "@aarch64_sve_<optab><mode>"
>    "<sve_int_op>\t%0.<Vewtype>, %1.<Vetype>, %2.<Vetype>"
>  )
> 
> +;;
> +-----------------------------------------------------------------------
> +-- ;; ---- [INT] Misc optab implementations ;;
> +-----------------------------------------------------------------------
> +--
> +;; Includes:
> +;; - aarch64_bitmask_udiv
> +;;
> +-----------------------------------------------------------------------
> +--
> +
> +;; div optimizations using narrowings
> +;; we can do the division e.g. shorts by 255 faster by calculating it
> +as ;; (x + ((x + 257) >> 8)) >> 8 assuming the operation is done in ;;
> +double the precision of x.
> +;;
> +;; See aarch64-simd.md for bigger explanation.
> +(define_expand "@aarch64_bitmask_udiv<mode>3"
> +  [(match_operand:SVE_FULL_HSDI 0 "register_operand")
> +   (match_operand:SVE_FULL_HSDI 1 "register_operand")
> +   (match_operand:SVE_FULL_HSDI 2 "immediate_operand")]
> +  "TARGET_SVE2"
> +{
> +  unsigned HOST_WIDE_INT size
> +    = (1ULL << GET_MODE_UNIT_BITSIZE (<VNARROW>mode)) - 1;
> +  if (!CONST_VECTOR_P (operands[2])
> +      || const_vector_encoded_nelts (operands[2]) != 1
> +      || size != UINTVAL (CONST_VECTOR_ELT (operands[2], 0)))
> +    FAIL;
> +
> +  rtx addend = gen_reg_rtx (<MODE>mode);
> +  rtx tmp1 = gen_reg_rtx (<VNARROW>mode);
> +  rtx tmp2 = gen_reg_rtx (<VNARROW>mode);
> +  rtx val = aarch64_simd_gen_const_vector_dup (<VNARROW>mode, 1);
> +  emit_move_insn (addend, lowpart_subreg (<MODE>mode, val,
> +<VNARROW>mode));
> +  emit_insn (gen_aarch64_sve (UNSPEC_ADDHNB, <MODE>mode, tmp1,
> operands[1],
> +			      addend));
> +  emit_insn (gen_aarch64_sve (UNSPEC_ADDHNB, <MODE>mode, tmp2,
> operands[1],
> +			      lowpart_subreg (<MODE>mode, tmp1,
> +					      <VNARROW>mode)));
> +  emit_move_insn (operands[0],
> +		  lowpart_subreg (<MODE>mode, tmp2,
> <VNARROW>mode));
> +  DONE;
> +})
> +
>  ;;
> ==========================================================
> ===============
>  ;; == Permutation
>  ;;
> ==========================================================
> ===============
> diff --git a/gcc/testsuite/gcc.target/aarch64/sve2/div-by-bitmask_1.c
> b/gcc/testsuite/gcc.target/aarch64/sve2/div-by-bitmask_1.c
> new file mode 100644
> index
> 0000000000000000000000000000000000000000..e6f5098c30f4e2eb8ed1af153c
> 0bb0d204cda6d9
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/sve2/div-by-bitmask_1.c
> @@ -0,0 +1,53 @@
> +/* { dg-do compile } */
> +/* { dg-additional-options "-O2 -std=c99" } */
> +/* { dg-final { check-function-bodies "**" "" "" { target { le } } } }
> +*/
> +
> +#include <stdint.h>
> +
> +/*
> +** draw_bitmap1:
> +** ...
> +**	mul	z[0-9]+.h, p[0-9]+/m, z[0-9]+.h, z[0-9]+.h
> +**	addhnb	z[0-9]+.b, z[0-9]+.h, z[0-9]+.h
> +**	addhnb	z[0-9]+.b, z[0-9]+.h, z[0-9]+.h
> +** ...
> +*/
> +void draw_bitmap1(uint8_t* restrict pixel, uint8_t level, int n) {
> +  for (int i = 0; i < (n & -16); i+=1)
> +    pixel[i] = (pixel[i] * level) / 0xff; }
> +
> +void draw_bitmap2(uint8_t* restrict pixel, uint8_t level, int n) {
> +  for (int i = 0; i < (n & -16); i+=1)
> +    pixel[i] = (pixel[i] * level) / 0xfe; }
> +
> +/*
> +** draw_bitmap3:
> +** ...
> +**	mul	z[0-9]+.s, p[0-9]+/m, z[0-9]+.s, z[0-9]+.s
> +**	addhnb	z[0-9]+.h, z[0-9]+.s, z[0-9]+.s
> +**	addhnb	z[0-9]+.h, z[0-9]+.s, z[0-9]+.s
> +** ...
> +*/
> +void draw_bitmap3(uint16_t* restrict pixel, uint16_t level, int n) {
> +  for (int i = 0; i < (n & -16); i+=1)
> +    pixel[i] = (pixel[i] * level) / 0xffffU; }
> +
> +/*
> +** draw_bitmap4:
> +** ...
> +**	mul	z[0-9]+.d, p[0-9]+/m, z[0-9]+.d, z[0-9]+.d
> +**	addhnb	z[0-9]+.s, z[0-9]+.d, z[0-9]+.d
> +**	addhnb	z[0-9]+.s, z[0-9]+.d, z[0-9]+.d
> +** ...
> +*/
> +void draw_bitmap4(uint32_t* restrict pixel, uint32_t level, int n) {
> +  for (int i = 0; i < (n & -16); i+=1)
> +    pixel[i] = (pixel[i] * (uint64_t)level) / 0xffffffffUL; }
> 
> 
> 
> 
> --