[Mesa-dev] [PATCH] radeonsi: don't preload constants at the beginning of shaders

[Bas Nieuwenhuizen]

Reviewed-by: Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl>

On Sat, Sep 10, 2016 at 12:40 AM, Marek Olšák <maraeo at gmail.com> wrote:
> From: Marek Olšák <marek.olsak at amd.com>
>
> LLVM can CSE the loads, thus we can always re-load constants before each
> use. The decrease in SGPR spilling is huge.
>
> The best improvements are the dumbest ones.
>
> 26011 shaders in 14651 tests
> Totals:
> SGPRS: 1453346 -> 1251920 (-13.86 %)
> VGPRS: 742576 -> 728421 (-1.91 %)
> Spilled SGPRs: 52298 -> 16644 (-68.17 %)
> Spilled VGPRs: 397 -> 369 (-7.05 %)
> Scratch VGPRs: 1372 -> 1344 (-2.04 %) dwords per thread
> Code Size: 36136488 -> 36001064 (-0.37 %) bytes
> LDS: 767 -> 767 (0.00 %) blocks
> Max Waves: 219315 -> 222221 (1.33 %)
> ---
>  src/gallium/drivers/radeonsi/si_shader.c | 30 +++++++++++-------------------
>  1 file changed, 11 insertions(+), 19 deletions(-)
>
> diff --git a/src/gallium/drivers/radeonsi/si_shader.c b/src/gallium/drivers/radeonsi/si_shader.c
> index 0b7de18..08e3cee 100644
> --- a/src/gallium/drivers/radeonsi/si_shader.c
> +++ b/src/gallium/drivers/radeonsi/si_shader.c
> @@ -1874,26 +1874,33 @@ static LLVMValueRef fetch_constant(
>                 for (chan = 0; chan < TGSI_NUM_CHANNELS; ++chan)
>                         values[chan] = fetch_constant(bld_base, reg, type, chan);
>
>                 return lp_build_gather_values(bld_base->base.gallivm, values, 4);
>         }
>
>         buf = reg->Register.Dimension ? reg->Dimension.Index : 0;
>         idx = reg->Register.Index * 4 + swizzle;
>
>         if (!reg->Register.Indirect && !reg->Dimension.Indirect) {
> +               LLVMValueRef c0, c1;
> +
> +               c0 = buffer_load_const(ctx, ctx->const_buffers[buf],
> +                                      LLVMConstInt(ctx->i32, idx * 4, 0));
> +
>                 if (!tgsi_type_is_64bit(type))
> -                       return bitcast(bld_base, type, ctx->constants[buf][idx]);
> +                       return bitcast(bld_base, type, c0);
>                 else {
> +                       c1 = buffer_load_const(ctx, ctx->const_buffers[buf],
> +                                              LLVMConstInt(ctx->i32,
> +                                                           (idx + 1) * 4, 0));
>                         return radeon_llvm_emit_fetch_64bit(bld_base, type,
> -                                                           ctx->constants[buf][idx],
> -                                                           ctx->constants[buf][idx + 1]);
> +                                                           c0, c1);
>                 }
>         }
>
>         if (reg->Register.Dimension && reg->Dimension.Indirect) {
>                 LLVMValueRef ptr = LLVMGetParam(ctx->radeon_bld.main_fn, SI_PARAM_CONST_BUFFERS);
>                 LLVMValueRef index;
>                 index = get_bounded_indirect_index(ctx, &reg->DimIndirect,
>                                                    reg->Dimension.Index,
>                                                    SI_NUM_CONST_BUFFERS);
>                 bufp = build_indexed_load_const(ctx, ptr, index);
> @@ -5789,39 +5796,26 @@ static void create_function(struct si_shader_context *ctx)
>
>  static void preload_constants(struct si_shader_context *ctx)
>  {
>         struct lp_build_tgsi_context *bld_base = &ctx->radeon_bld.soa.bld_base;
>         struct gallivm_state *gallivm = bld_base->base.gallivm;
>         const struct tgsi_shader_info *info = bld_base->info;
>         unsigned buf;
>         LLVMValueRef ptr = LLVMGetParam(ctx->radeon_bld.main_fn, SI_PARAM_CONST_BUFFERS);
>
>         for (buf = 0; buf < SI_NUM_CONST_BUFFERS; buf++) {
> -               unsigned i, num_const = info->const_file_max[buf] + 1;
> -
> -               if (num_const == 0)
> +               if (info->const_file_max[buf] == -1)
>                         continue;
>
> -               /* Allocate space for the constant values */
> -               ctx->constants[buf] = CALLOC(num_const * 4, sizeof(LLVMValueRef));
> -
>                 /* Load the resource descriptor */
>                 ctx->const_buffers[buf] =
>                         build_indexed_load_const(ctx, ptr, lp_build_const_int32(gallivm, buf));
> -
> -               /* Load the constants, we rely on the code sinking to do the rest */
> -               for (i = 0; i < num_const * 4; ++i) {
> -                       ctx->constants[buf][i] =
> -                               buffer_load_const(ctx,
> -                                       ctx->const_buffers[buf],
> -                                       lp_build_const_int32(gallivm, i * 4));
> -               }
>         }
>  }
>
>  static void preload_shader_buffers(struct si_shader_context *ctx)
>  {
>         struct gallivm_state *gallivm = &ctx->radeon_bld.gallivm;
>         LLVMValueRef ptr = LLVMGetParam(ctx->radeon_bld.main_fn, SI_PARAM_SHADER_BUFFERS);
>         int buf, maxbuf;
>
>         maxbuf = MIN2(ctx->shader->selector->info.file_max[TGSI_FILE_BUFFER],
> @@ -6898,22 +6892,20 @@ int si_compile_tgsi_shader(struct si_screen *sscreen,
>                 ctx.shader = shader->gs_copy_shader;
>                 if ((r = si_generate_gs_copy_shader(sscreen, &ctx,
>                                                     shader, debug))) {
>                         free(shader->gs_copy_shader);
>                         shader->gs_copy_shader = NULL;
>                         goto out;
>                 }
>         }
>
>  out:
> -       for (int i = 0; i < SI_NUM_CONST_BUFFERS; i++)
> -               FREE(ctx.constants[i]);
>         return r;
>  }
>
>  /**
>   * Create, compile and return a shader part (prolog or epilog).
>   *
>   * \param sscreen      screen
>   * \param list         list of shader parts of the same category
>   * \param key          shader part key
>   * \param tm           LLVM target machine
> --
> 2.7.4
>
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