src/freedreno/ir3/ir3_nir_lower_tex_prefetch.c

/*
 * Copyright © 2019 Igalia S.L.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#include "ir3_nir.h"

/**
 * A pass which detects tex instructions which are candidate to be executed
 * prior to FS shader start, and change them to nir_texop_tex_prefetch.
 */

static int
coord_offset(nir_ssa_def *ssa)
{
	nir_instr *parent_instr = ssa->parent_instr;

	/* The coordinate of a texture sampling instruction eligible for
	 * pre-fetch is either going to be a load_interpolated_input/
	 * load_input, or a vec2 assembling non-swizzled components of
	 * a load_interpolated_input/load_input (due to varying packing)
	 */

	if (parent_instr->type == nir_instr_type_alu) {
		nir_alu_instr *alu = nir_instr_as_alu(parent_instr);

		if (alu->op != nir_op_vec2)
			return -1;

		if (!alu->src[0].src.is_ssa)
			return -1;

		int base_offset = coord_offset(alu->src[0].src.ssa) +
				alu->src[0].swizzle[0];

		/* NOTE it might be possible to support more than 2D? */
		for (int i = 1; i < 2; i++) {
			if (!alu->src[i].src.is_ssa)
				return -1;

			int nth_offset = coord_offset(alu->src[i].src.ssa) +
					alu->src[i].swizzle[0];

			if (nth_offset != (base_offset + i))
				return -1;
		}

		return base_offset;
	}

	if (parent_instr->type != nir_instr_type_intrinsic)
		return -1;

	nir_intrinsic_instr *input = nir_instr_as_intrinsic(parent_instr);

	if (input->intrinsic != nir_intrinsic_load_interpolated_input)
		return -1;

	/* limit to load_barycentric_pixel, other interpolation modes don't seem
	 * to be supported:
	 */
	if (!input->src[0].is_ssa)
		return -1;

	nir_intrinsic_instr *interp =
		nir_instr_as_intrinsic(input->src[0].ssa->parent_instr);

	if (interp->intrinsic != nir_intrinsic_load_barycentric_pixel)
		return -1;

	/* we also need a const input offset: */
	if (!nir_src_is_const(input->src[1]))
		return -1;

	unsigned base = nir_src_as_uint(input->src[1]) + nir_intrinsic_base(input);
	unsigned comp = nir_intrinsic_component(input);

	return (4 * base) + comp;
}

int
ir3_nir_coord_offset(nir_ssa_def *ssa)
{

	assert (ssa->num_components == 2);
	return coord_offset(ssa);
}

static bool
has_src(nir_tex_instr *tex, nir_tex_src_type type)
{
	return nir_tex_instr_src_index(tex, type) > 0;
}

static bool
lower_tex_prefetch_block(nir_block *block)
{
	bool progress = false;

	nir_foreach_instr_safe(instr, block) {
		if (instr->type != nir_instr_type_tex)
			continue;

		nir_tex_instr *tex = nir_instr_as_tex(instr);
		if (tex->op != nir_texop_tex)
			continue;

		if (has_src(tex, nir_tex_src_bias) ||
				has_src(tex, nir_tex_src_lod) ||
				has_src(tex, nir_tex_src_comparator) ||
				has_src(tex, nir_tex_src_projector) ||
				has_src(tex, nir_tex_src_offset) ||
				has_src(tex, nir_tex_src_ddx) ||
				has_src(tex, nir_tex_src_ddy) ||
				has_src(tex, nir_tex_src_ms_index) ||
				has_src(tex, nir_tex_src_texture_offset) ||
				has_src(tex, nir_tex_src_sampler_offset))
			continue;

		/* only prefetch for simple 2d tex fetch case */
		if (tex->sampler_dim != GLSL_SAMPLER_DIM_2D || tex->is_array)
			continue;

		int idx = nir_tex_instr_src_index(tex, nir_tex_src_coord);
		/* First source should be the sampling coordinate. */
		nir_tex_src *coord = &tex->src[idx];
		debug_assert(coord->src.is_ssa);

		if (ir3_nir_coord_offset(coord->src.ssa) >= 0) {
			tex->op = nir_texop_tex_prefetch;

			progress |= true;
		}
	}

	return progress;
}

static bool
lower_tex_prefetch_func(nir_function_impl *impl)
{
	/* Only instructions in the the outer-most block are considered
	 * eligible for pre-dispatch, because they need to be move-able
	 * to the beginning of the shader to avoid locking down the
	 * register holding the pre-fetched result for too long.
	 */
	nir_block *block = nir_start_block(impl);
	if (!block)
		return false;

	bool progress = lower_tex_prefetch_block(block);

	if (progress) {
		nir_metadata_preserve(impl, nir_metadata_block_index |
				nir_metadata_dominance);
	}

	return progress;
}

bool
ir3_nir_lower_tex_prefetch(nir_shader *shader)
{
	bool progress = false;

	assert(shader->info.stage == MESA_SHADER_FRAGMENT);

	nir_foreach_function(function, shader) {
		/* Only texture sampling instructions inside the main function
		 * are eligible for pre-dispatch.
		 */
		if (!function->impl || !function->is_entrypoint)
			continue;

		progress |= lower_tex_prefetch_func(function->impl);
	}

	return progress;
}