src/glsl/nir/nir_lower_load_const_to_scalar.c

   1 /*
   2  * Copyright © 2015 Broadcom
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  21  * IN THE SOFTWARE.
  22  */
  23
  24 #include "util/macros.h"
  25 #include "nir.h"
  26 #include "nir_builder.h"
  27
  28 /** @file nir_lower_load_const_to_scalar.c
  29  *
  30  * Replaces vector nir_load_const instructions with a series of loads and a
  31  * vec[234] to reconstruct the original vector (on the assumption that
  32  * nir_lower_alu_to_scalar() will then be used to split it up).
  33  *
  34  * This gives NIR a chance to CSE more operations on a scalar shader, when the
  35  * same value was used in different vector contant loads.
  36  */
  37
  38 static void
  39 lower_load_const_instr_scalar(nir_load_const_instr *lower)
  40 {
  41    if (lower->def.num_components == 1)
  42       return;
  43
  44    nir_builder b;
  45    nir_builder_init(&b, nir_cf_node_get_function(&lower->instr.block->cf_node));
  46    b.cursor = nir_before_instr(&lower->instr);
  47
  48    /* Emit the individual loads. */
  49    nir_ssa_def *loads[4];
  50    for (unsigned i = 0; i < lower->def.num_components; i++) {
  51       nir_load_const_instr *load_comp = nir_load_const_instr_create(b.shader, 1);
  52       load_comp->value.u[0] = lower->value.u[i];
  53       nir_builder_instr_insert(&b, &load_comp->instr);
  54       loads[i] = &load_comp->def;
  55    }
  56
  57    /* Batch things back together into a vector. */
  58    nir_ssa_def *vec;
  59    switch (lower->def.num_components) {
  60    case 2:
  61       vec = nir_vec2(&b, loads[0], loads[1]);
  62       break;
  63    case 3:
  64       vec = nir_vec3(&b, loads[0], loads[1], loads[2]);
  65       break;
  66    case 4:
  67       vec = nir_vec4(&b, loads[0], loads[1], loads[2], loads[3]);
  68       break;
  69    default:
  70       unreachable("Unknown load_const component count.");
  71    }
  72
  73    /* Replace the old load with a reference to our reconstructed vector. */
  74    nir_ssa_def_rewrite_uses(&lower->def, nir_src_for_ssa(vec),
  75                             ralloc_parent(b.impl));
  76    nir_instr_remove(&lower->instr);
  77 }
  78
  79 static bool
  80 lower_load_const_to_scalar_block(nir_block *block, void *data)
  81 {
  82    nir_foreach_instr_safe(block, instr) {
  83       if (instr->type == nir_instr_type_load_const)
  84          lower_load_const_instr_scalar(nir_instr_as_load_const(instr));
  85    }
  86
  87    return true;
  88 }
  89
  90 static void
  91 nir_lower_load_const_to_scalar_impl(nir_function_impl *impl)
  92 {
  93    nir_foreach_block(impl, lower_load_const_to_scalar_block, NULL);
  94 }
  95
  96 void
  97 nir_lower_load_const_to_scalar(nir_shader *shader)
  98 {
  99    nir_foreach_overload(shader, overload) {
 100       if (overload->impl)
 101          nir_lower_load_const_to_scalar_impl(overload->impl);
 102    }
 103 }