389 lines
11 KiB
C
389 lines
11 KiB
C
/*
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* Copyright © 2020 Google LLC
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*
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files (the "Software"),
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* to deal in the Software without restriction, including without limitation
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* the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice (including the next
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* paragraph) shall be included in all copies or substantial portions of the
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* Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
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* IN THE SOFTWARE.
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*/
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/**
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* @file
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*
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* Removes unused components of SSA defs.
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*
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* Due to various optimization passes (or frontend implementations,
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* particularly prog_to_nir), we may have instructions generating vectors
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* whose components don't get read by any instruction.
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*
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* For memory loads, while it can be tricky to eliminate unused low components
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* or channels in the middle of a writemask (you might need to increment some
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* offset from a load_uniform, for example), it is trivial to just drop the
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* trailing components.
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* For vector ALU and load_const, only used by other ALU instructions,
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* this pass eliminates arbitrary channels as well as duplicate channels,
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* and reswizzles the uses.
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*
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* This pass is probably only of use to vector backends -- scalar backends
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* typically get unused def channel trimming by scalarizing and dead code
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* elimination.
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*/
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#include "nir.h"
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#include "nir_builder.h"
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#include "util/u_math.h"
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/*
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* Round up a vector size to a vector size that's valid in NIR. At present, NIR
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* supports only vec2-5, vec8, and vec16. Attempting to generate other sizes
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* will fail validation.
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*/
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static unsigned
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round_up_components(unsigned n)
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{
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return (n > 5) ? util_next_power_of_two(n) : n;
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}
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static bool
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shrink_dest_to_read_mask(nir_ssa_def *def)
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{
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/* early out if there's nothing to do. */
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if (def->num_components == 1)
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return false;
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/* don't remove any channels if used by an intrinsic */
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nir_foreach_use(use_src, def) {
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if (use_src->parent_instr->type == nir_instr_type_intrinsic)
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return false;
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}
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unsigned mask = nir_ssa_def_components_read(def);
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int last_bit = util_last_bit(mask);
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/* If nothing was read, leave it up to DCE. */
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if (!mask)
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return false;
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unsigned rounded = round_up_components(last_bit);
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assert(rounded <= def->num_components);
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last_bit = rounded;
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if (def->num_components > last_bit) {
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def->num_components = last_bit;
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return true;
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}
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return false;
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}
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static void
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reswizzle_alu_uses(nir_ssa_def *def, uint8_t *reswizzle)
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{
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nir_foreach_use(use_src, def) {
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/* all uses must be ALU instructions */
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assert(use_src->parent_instr->type == nir_instr_type_alu);
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nir_alu_src *alu_src = (nir_alu_src*)use_src;
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/* reswizzle ALU sources */
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for (unsigned i = 0; i < NIR_MAX_VEC_COMPONENTS; i++)
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alu_src->swizzle[i] = reswizzle[alu_src->swizzle[i]];
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}
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}
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static bool
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is_only_used_by_alu(nir_ssa_def *def)
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{
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nir_foreach_use(use_src, def) {
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if (use_src->parent_instr->type != nir_instr_type_alu)
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return false;
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}
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return true;
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}
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static bool
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opt_shrink_vector(nir_builder *b, nir_alu_instr *instr)
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{
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nir_ssa_def *def = &instr->dest.dest.ssa;
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unsigned mask = nir_ssa_def_components_read(def);
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/* If nothing was read, leave it up to DCE. */
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if (mask == 0)
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return false;
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/* don't remove any channels if used by non-ALU */
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if (!is_only_used_by_alu(def))
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return false;
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uint8_t reswizzle[NIR_MAX_VEC_COMPONENTS] = { 0 };
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nir_ssa_scalar srcs[NIR_MAX_VEC_COMPONENTS] = { 0 };
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unsigned num_components = 0;
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for (unsigned i = 0; i < def->num_components; i++) {
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if (!((mask >> i) & 0x1))
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continue;
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nir_ssa_scalar scalar = nir_get_ssa_scalar(instr->src[i].src.ssa, instr->src[i].swizzle[0]);
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/* Try reuse a component with the same value */
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unsigned j;
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for (j = 0; j < num_components; j++) {
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if (scalar.def == srcs[j].def && scalar.comp == srcs[j].comp) {
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reswizzle[i] = j;
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break;
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}
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}
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/* Otherwise, just append the value */
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if (j == num_components) {
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srcs[num_components] = scalar;
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reswizzle[i] = num_components++;
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}
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}
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/* return if no component was removed */
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if (num_components == def->num_components)
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return false;
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/* create new vecN and replace uses */
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nir_ssa_def *new_vec = nir_vec_scalars(b, srcs, num_components);
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nir_ssa_def_rewrite_uses(def, new_vec);
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reswizzle_alu_uses(new_vec, reswizzle);
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return true;
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}
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static bool
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opt_shrink_vectors_alu(nir_builder *b, nir_alu_instr *instr)
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{
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nir_ssa_def *def = &instr->dest.dest.ssa;
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/* Nothing to shrink */
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if (def->num_components == 1)
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return false;
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switch (instr->op) {
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/* don't use nir_op_is_vec() as not all vector sizes are supported. */
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case nir_op_vec4:
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case nir_op_vec3:
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case nir_op_vec2:
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return opt_shrink_vector(b, instr);
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default:
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if (nir_op_infos[instr->op].output_size != 0)
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return false;
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break;
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}
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/* don't remove any channels if used by non-ALU */
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if (!is_only_used_by_alu(def))
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return false;
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unsigned mask = nir_ssa_def_components_read(def);
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unsigned last_bit = util_last_bit(mask);
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unsigned num_components = util_bitcount(mask);
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unsigned rounded = round_up_components(num_components);
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assert(rounded <= def->num_components);
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num_components = rounded;
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/* return, if there is nothing to do */
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if (mask == 0 || num_components == def->num_components)
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return false;
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const bool is_bitfield_mask = last_bit == num_components;
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if (is_bitfield_mask) {
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/* just reduce the number of components and return */
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def->num_components = num_components;
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instr->dest.write_mask = mask;
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return true;
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}
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uint8_t reswizzle[NIR_MAX_VEC_COMPONENTS] = { 0 };
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unsigned index = 0;
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for (unsigned i = 0; i < last_bit; i++) {
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/* skip unused components */
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if (!((mask >> i) & 0x1))
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continue;
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/* reswizzle the sources */
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for (int k = 0; k < nir_op_infos[instr->op].num_inputs; k++) {
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instr->src[k].swizzle[index] = instr->src[k].swizzle[i];
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reswizzle[i] = index;
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}
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index++;
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}
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assert(index == num_components);
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/* update dest */
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def->num_components = num_components;
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instr->dest.write_mask = BITFIELD_MASK(num_components);
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/* update uses */
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reswizzle_alu_uses(def, reswizzle);
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return true;
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}
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static bool
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opt_shrink_vectors_intrinsic(nir_builder *b, nir_intrinsic_instr *instr)
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{
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switch (instr->intrinsic) {
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case nir_intrinsic_load_uniform:
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case nir_intrinsic_load_ubo:
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case nir_intrinsic_load_input:
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case nir_intrinsic_load_input_vertex:
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case nir_intrinsic_load_per_vertex_input:
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case nir_intrinsic_load_interpolated_input:
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case nir_intrinsic_load_ssbo:
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case nir_intrinsic_load_push_constant:
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case nir_intrinsic_load_constant:
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case nir_intrinsic_load_shared:
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case nir_intrinsic_load_global:
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case nir_intrinsic_load_global_constant:
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case nir_intrinsic_load_kernel_input:
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case nir_intrinsic_load_scratch:
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break;
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default:
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return false;
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}
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/* Must be a vectorized intrinsic that we can resize. */
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assert(instr->num_components != 0);
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/* Trim the dest to the used channels */
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if (shrink_dest_to_read_mask(&instr->dest.ssa)) {
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instr->num_components = instr->dest.ssa.num_components;
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return true;
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}
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return false;
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}
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static bool
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opt_shrink_vectors_load_const(nir_load_const_instr *instr)
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{
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nir_ssa_def *def = &instr->def;
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/* early out if there's nothing to do. */
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if (def->num_components == 1)
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return false;
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/* don't remove any channels if used by non-ALU */
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if (!is_only_used_by_alu(def))
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return false;
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unsigned mask = nir_ssa_def_components_read(def);
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/* If nothing was read, leave it up to DCE. */
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if (!mask)
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return false;
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uint8_t reswizzle[NIR_MAX_VEC_COMPONENTS] = { 0 };
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unsigned num_components = 0;
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for (unsigned i = 0; i < def->num_components; i++) {
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if (!((mask >> i) & 0x1))
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continue;
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/* Try reuse a component with the same constant */
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unsigned j;
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for (j = 0; j < num_components; j++) {
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if (instr->value[i].u64 == instr->value[j].u64) {
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reswizzle[i] = j;
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break;
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}
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}
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/* Otherwise, just append the value */
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if (j == num_components) {
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instr->value[num_components] = instr->value[i];
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reswizzle[i] = num_components++;
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}
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}
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unsigned rounded = round_up_components(num_components);
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assert(rounded <= def->num_components);
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num_components = rounded;
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if (num_components == def->num_components)
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return false;
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def->num_components = num_components;
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reswizzle_alu_uses(def, reswizzle);
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return true;
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}
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static bool
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opt_shrink_vectors_ssa_undef(nir_ssa_undef_instr *instr)
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{
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return shrink_dest_to_read_mask(&instr->def);
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}
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static bool
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opt_shrink_vectors_instr(nir_builder *b, nir_instr *instr)
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{
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b->cursor = nir_before_instr(instr);
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switch (instr->type) {
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case nir_instr_type_alu:
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return opt_shrink_vectors_alu(b, nir_instr_as_alu(instr));
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case nir_instr_type_intrinsic:
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return opt_shrink_vectors_intrinsic(b, nir_instr_as_intrinsic(instr));
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case nir_instr_type_load_const:
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return opt_shrink_vectors_load_const(nir_instr_as_load_const(instr));
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case nir_instr_type_ssa_undef:
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return opt_shrink_vectors_ssa_undef(nir_instr_as_ssa_undef(instr));
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default:
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return false;
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}
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return true;
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}
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bool
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nir_opt_shrink_vectors(nir_shader *shader)
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{
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bool progress = false;
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nir_foreach_function(function, shader) {
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if (!function->impl)
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continue;
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nir_builder b;
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nir_builder_init(&b, function->impl);
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nir_foreach_block_reverse(block, function->impl) {
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nir_foreach_instr_reverse(instr, block) {
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progress |= opt_shrink_vectors_instr(&b, instr);
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}
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}
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if (progress) {
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nir_metadata_preserve(function->impl,
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nir_metadata_block_index |
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nir_metadata_dominance);
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} else {
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nir_metadata_preserve(function->impl, nir_metadata_all);
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}
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}
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return progress;
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}
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