src/compiler/nir/nir_opt_constant_folding.c

   1 /*
   2  * Copyright © 2014 Intel Corporation
   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  * Authors:
  24  *    Jason Ekstrand (jason@jlekstrand.net)
  25  *
  26  */
  27
  28 #include "nir_constant_expressions.h"
  29 #include <math.h>
  30
  31 /*
  32  * Implements SSA-based constant folding.
  33  */
  34
  35 struct constant_fold_state {
  36    void *mem_ctx;
  37    nir_function_impl *impl;
  38    bool progress;
  39 };
  40
  41 static bool
  42 constant_fold_alu_instr(nir_alu_instr *instr, void *mem_ctx)
  43 {
  44    nir_const_value src[4];
  45
  46    if (!instr->dest.dest.is_ssa)
  47       return false;
  48
  49    for (unsigned i = 0; i < nir_op_infos[instr->op].num_inputs; i++) {
  50       if (!instr->src[i].src.is_ssa)
  51          return false;
  52
  53       nir_instr *src_instr = instr->src[i].src.ssa->parent_instr;
  54
  55       if (src_instr->type != nir_instr_type_load_const)
  56          return false;
  57       nir_load_const_instr* load_const = nir_instr_as_load_const(src_instr);
  58
  59       for (unsigned j = 0; j < nir_ssa_alu_instr_src_components(instr, i);
  60            j++) {
  61          src[i].u[j] = load_const->value.u[instr->src[i].swizzle[j]];
  62       }
  63
  64       /* We shouldn't have any source modifiers in the optimization loop. */
  65       assert(!instr->src[i].abs && !instr->src[i].negate);
  66    }
  67
  68    /* We shouldn't have any saturate modifiers in the optimization loop. */
  69    assert(!instr->dest.saturate);
  70
  71    nir_const_value dest =
  72       nir_eval_const_opcode(instr->op, instr->dest.dest.ssa.num_components,
  73                             src);
  74
  75    nir_load_const_instr *new_instr =
  76       nir_load_const_instr_create(mem_ctx,
  77                                   instr->dest.dest.ssa.num_components);
  78
  79    new_instr->value = dest;
  80
  81    nir_instr_insert_before(&instr->instr, &new_instr->instr);
  82
  83    nir_ssa_def_rewrite_uses(&instr->dest.dest.ssa,
  84                             nir_src_for_ssa(&new_instr->def));
  85
  86    nir_instr_remove(&instr->instr);
  87    ralloc_free(instr);
  88
  89    return true;
  90 }
  91
  92 static bool
  93 constant_fold_deref(nir_instr *instr, nir_deref_var *deref)
  94 {
  95    bool progress = false;
  96
  97    for (nir_deref *tail = deref->deref.child; tail; tail = tail->child) {
  98       if (tail->deref_type != nir_deref_type_array)
  99          continue;
 100
 101       nir_deref_array *arr = nir_deref_as_array(tail);
 102
 103       if (arr->deref_array_type == nir_deref_array_type_indirect &&
 104           arr->indirect.is_ssa &&
 105           arr->indirect.ssa->parent_instr->type == nir_instr_type_load_const) {
 106          nir_load_const_instr *indirect =
 107             nir_instr_as_load_const(arr->indirect.ssa->parent_instr);
 108
 109          arr->base_offset += indirect->value.u[0];
 110
 111          /* Clear out the source */
 112          nir_instr_rewrite_src(instr, &arr->indirect, nir_src_for_ssa(NULL));
 113
 114          arr->deref_array_type = nir_deref_array_type_direct;
 115
 116          progress = true;
 117       }
 118    }
 119
 120    return progress;
 121 }
 122
 123 static bool
 124 constant_fold_intrinsic_instr(nir_intrinsic_instr *instr)
 125 {
 126    bool progress = false;
 127
 128    unsigned num_vars = nir_intrinsic_infos[instr->intrinsic].num_variables;
 129    for (unsigned i = 0; i < num_vars; i++) {
 130       progress |= constant_fold_deref(&instr->instr, instr->variables[i]);
 131    }
 132
 133    return progress;
 134 }
 135
 136 static bool
 137 constant_fold_tex_instr(nir_tex_instr *instr)
 138 {
 139    if (instr->sampler)
 140       return constant_fold_deref(&instr->instr, instr->sampler);
 141    else
 142       return false;
 143 }
 144
 145 static bool
 146 constant_fold_block(nir_block *block, void *void_state)
 147 {
 148    struct constant_fold_state *state = void_state;
 149
 150    nir_foreach_instr_safe(block, instr) {
 151       switch (instr->type) {
 152       case nir_instr_type_alu:
 153          state->progress |= constant_fold_alu_instr(nir_instr_as_alu(instr),
 154                                                     state->mem_ctx);
 155          break;
 156       case nir_instr_type_intrinsic:
 157          state->progress |=
 158             constant_fold_intrinsic_instr(nir_instr_as_intrinsic(instr));
 159          break;
 160       case nir_instr_type_tex:
 161          state->progress |= constant_fold_tex_instr(nir_instr_as_tex(instr));
 162          break;
 163       default:
 164          /* Don't know how to constant fold */
 165          break;
 166       }
 167    }
 168
 169    return true;
 170 }
 171
 172 static bool
 173 nir_opt_constant_folding_impl(nir_function_impl *impl)
 174 {
 175    struct constant_fold_state state;
 176
 177    state.mem_ctx = ralloc_parent(impl);
 178    state.impl = impl;
 179    state.progress = false;
 180
 181    nir_foreach_block(impl, constant_fold_block, &state);
 182
 183    if (state.progress)
 184       nir_metadata_preserve(impl, nir_metadata_block_index |
 185                                   nir_metadata_dominance);
 186
 187    return state.progress;
 188 }
 189
 190 bool
 191 nir_opt_constant_folding(nir_shader *shader)
 192 {
 193    bool progress = false;
 194
 195    nir_foreach_function(shader, function) {
 196       if (function->impl)
 197          progress |= nir_opt_constant_folding_impl(function->impl);
 198    }
 199
 200    return progress;
 201 }