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    /* In the case that any outputs/inputs have unsized types, then we need to
  50     * guess the bit-size. In this case, the validator ensures that all
  51     * bit-sizes match so we can just take the bit-size from first
  52     * output/input with an unsized type. If all the outputs/inputs are sized
  53     * then we don't need to guess the bit-size at all because the code we
  54     * generate for constant opcodes in this case already knows the sizes of
  55     * the types involved and does not need the provided bit-size for anything
  56     * (although it still requires to receive a valid bit-size).
  57     */
  58    unsigned bit_size = 0;
  59    if (!nir_alu_type_get_type_size(nir_op_infos[instr->op].output_type))
  60       bit_size = instr->dest.dest.ssa.bit_size;
  61
  62    for (unsigned i = 0; i < nir_op_infos[instr->op].num_inputs; i++) {
  63       if (!instr->src[i].src.is_ssa)
  64          return false;
  65
  66       if (bit_size == 0 &&
  67           !nir_alu_type_get_type_size(nir_op_infos[instr->op].input_sizes[i])) {
  68          bit_size = instr->src[i].src.ssa->bit_size;
  69       }
  70
  71       nir_instr *src_instr = instr->src[i].src.ssa->parent_instr;
  72
  73       if (src_instr->type != nir_instr_type_load_const)
  74          return false;
  75       nir_load_const_instr* load_const = nir_instr_as_load_const(src_instr);
  76
  77       for (unsigned j = 0; j < nir_ssa_alu_instr_src_components(instr, i);
  78            j++) {
  79          if (load_const->def.bit_size == 64)
  80             src[i].u64[j] = load_const->value.u64[instr->src[i].swizzle[j]];
  81          else
  82             src[i].u32[j] = load_const->value.u32[instr->src[i].swizzle[j]];
  83       }
  84
  85       /* We shouldn't have any source modifiers in the optimization loop. */
  86       assert(!instr->src[i].abs && !instr->src[i].negate);
  87    }
  88
  89    if (bit_size == 0)
  90       bit_size = 32;
  91
  92    /* We shouldn't have any saturate modifiers in the optimization loop. */
  93    assert(!instr->dest.saturate);
  94
  95    nir_const_value dest =
  96       nir_eval_const_opcode(instr->op, instr->dest.dest.ssa.num_components,
  97                             bit_size, src);
  98
  99    nir_load_const_instr *new_instr =
 100       nir_load_const_instr_create(mem_ctx,
 101                                   instr->dest.dest.ssa.num_components);
 102
 103    new_instr->def.bit_size = instr->dest.dest.ssa.bit_size;
 104    new_instr->value = dest;
 105
 106    nir_instr_insert_before(&instr->instr, &new_instr->instr);
 107
 108    nir_ssa_def_rewrite_uses(&instr->dest.dest.ssa,
 109                             nir_src_for_ssa(&new_instr->def));
 110
 111    nir_instr_remove(&instr->instr);
 112    ralloc_free(instr);
 113
 114    return true;
 115 }
 116
 117 static bool
 118 constant_fold_deref(nir_instr *instr, nir_deref_var *deref)
 119 {
 120    bool progress = false;
 121
 122    for (nir_deref *tail = deref->deref.child; tail; tail = tail->child) {
 123       if (tail->deref_type != nir_deref_type_array)
 124          continue;
 125
 126       nir_deref_array *arr = nir_deref_as_array(tail);
 127
 128       if (arr->deref_array_type == nir_deref_array_type_indirect &&
 129           arr->indirect.is_ssa &&
 130           arr->indirect.ssa->parent_instr->type == nir_instr_type_load_const) {
 131          nir_load_const_instr *indirect =
 132             nir_instr_as_load_const(arr->indirect.ssa->parent_instr);
 133
 134          arr->base_offset += indirect->value.u32[0];
 135
 136          /* Clear out the source */
 137          nir_instr_rewrite_src(instr, &arr->indirect, nir_src_for_ssa(NULL));
 138
 139          arr->deref_array_type = nir_deref_array_type_direct;
 140
 141          progress = true;
 142       }
 143    }
 144
 145    return progress;
 146 }
 147
 148 static bool
 149 constant_fold_intrinsic_instr(nir_intrinsic_instr *instr)
 150 {
 151    bool progress = false;
 152
 153    unsigned num_vars = nir_intrinsic_infos[instr->intrinsic].num_variables;
 154    for (unsigned i = 0; i < num_vars; i++) {
 155       progress |= constant_fold_deref(&instr->instr, instr->variables[i]);
 156    }
 157
 158    return progress;
 159 }
 160
 161 static bool
 162 constant_fold_tex_instr(nir_tex_instr *instr)
 163 {
 164    bool progress = false;
 165
 166    if (instr->texture)
 167       progress |= constant_fold_deref(&instr->instr, instr->texture);
 168
 169    if (instr->sampler)
 170       progress |= constant_fold_deref(&instr->instr, instr->sampler);
 171
 172    return progress;
 173 }
 174
 175 static bool
 176 constant_fold_block(nir_block *block, void *void_state)
 177 {
 178    struct constant_fold_state *state = void_state;
 179
 180    nir_foreach_instr_safe(block, instr) {
 181       switch (instr->type) {
 182       case nir_instr_type_alu:
 183          state->progress |= constant_fold_alu_instr(nir_instr_as_alu(instr),
 184                                                     state->mem_ctx);
 185          break;
 186       case nir_instr_type_intrinsic:
 187          state->progress |=
 188             constant_fold_intrinsic_instr(nir_instr_as_intrinsic(instr));
 189          break;
 190       case nir_instr_type_tex:
 191          state->progress |= constant_fold_tex_instr(nir_instr_as_tex(instr));
 192          break;
 193       default:
 194          /* Don't know how to constant fold */
 195          break;
 196       }
 197    }
 198
 199    return true;
 200 }
 201
 202 static bool
 203 nir_opt_constant_folding_impl(nir_function_impl *impl)
 204 {
 205    struct constant_fold_state state;
 206
 207    state.mem_ctx = ralloc_parent(impl);
 208    state.impl = impl;
 209    state.progress = false;
 210
 211    nir_foreach_block(impl, constant_fold_block, &state);
 212
 213    if (state.progress)
 214       nir_metadata_preserve(impl, nir_metadata_block_index |
 215                                   nir_metadata_dominance);
 216
 217    return state.progress;
 218 }
 219
 220 bool
 221 nir_opt_constant_folding(nir_shader *shader)
 222 {
 223    bool progress = false;
 224
 225    nir_foreach_function(shader, function) {
 226       if (function->impl)
 227          progress |= nir_opt_constant_folding_impl(function->impl);
 228    }
 229
 230    return progress;
 231 }