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 static bool
  36 constant_fold_alu_instr(nir_alu_instr *instr, void *mem_ctx, unsigned execution_mode)
  37 {
  38    nir_const_value src[NIR_MAX_VEC_COMPONENTS][NIR_MAX_VEC_COMPONENTS];
  39
  40    if (!instr->dest.dest.is_ssa)
  41       return false;
  42
  43    /* In the case that any outputs/inputs have unsized types, then we need to
  44     * guess the bit-size. In this case, the validator ensures that all
  45     * bit-sizes match so we can just take the bit-size from first
  46     * output/input with an unsized type. If all the outputs/inputs are sized
  47     * then we don't need to guess the bit-size at all because the code we
  48     * generate for constant opcodes in this case already knows the sizes of
  49     * the types involved and does not need the provided bit-size for anything
  50     * (although it still requires to receive a valid bit-size).
  51     */
  52    unsigned bit_size = 0;
  53    if (!nir_alu_type_get_type_size(nir_op_infos[instr->op].output_type))
  54       bit_size = instr->dest.dest.ssa.bit_size;
  55
  56    for (unsigned i = 0; i < nir_op_infos[instr->op].num_inputs; i++) {
  57       if (!instr->src[i].src.is_ssa)
  58          return false;
  59
  60       if (bit_size == 0 &&
  61           !nir_alu_type_get_type_size(nir_op_infos[instr->op].input_types[i]))
  62          bit_size = instr->src[i].src.ssa->bit_size;
  63
  64       nir_instr *src_instr = instr->src[i].src.ssa->parent_instr;
  65
  66       if (src_instr->type != nir_instr_type_load_const)
  67          return false;
  68       nir_load_const_instr* load_const = nir_instr_as_load_const(src_instr);
  69
  70       for (unsigned j = 0; j < nir_ssa_alu_instr_src_components(instr, i);
  71            j++) {
  72          src[i][j] = load_const->value[instr->src[i].swizzle[j]];
  73       }
  74
  75       /* We shouldn't have any source modifiers in the optimization loop. */
  76       assert(!instr->src[i].abs && !instr->src[i].negate);
  77    }
  78
  79    if (bit_size == 0)
  80       bit_size = 32;
  81
  82    /* We shouldn't have any saturate modifiers in the optimization loop. */
  83    assert(!instr->dest.saturate);
  84
  85    nir_const_value dest[NIR_MAX_VEC_COMPONENTS];
  86    nir_const_value *srcs[NIR_MAX_VEC_COMPONENTS];
  87    memset(dest, 0, sizeof(dest));
  88    for (unsigned i = 0; i < nir_op_infos[instr->op].num_inputs; ++i)
  89       srcs[i] = src[i];
  90    nir_eval_const_opcode(instr->op, dest, instr->dest.dest.ssa.num_components,
  91                          bit_size, srcs, execution_mode);
  92
  93    nir_load_const_instr *new_instr =
  94       nir_load_const_instr_create(mem_ctx,
  95                                   instr->dest.dest.ssa.num_components,
  96                                   instr->dest.dest.ssa.bit_size);
  97
  98    memcpy(new_instr->value, dest, sizeof(*new_instr->value) * new_instr->def.num_components);
  99
 100    nir_instr_insert_before(&instr->instr, &new_instr->instr);
 101
 102    nir_ssa_def_rewrite_uses(&instr->dest.dest.ssa,
 103                             nir_src_for_ssa(&new_instr->def));
 104
 105    nir_instr_remove(&instr->instr);
 106    ralloc_free(instr);
 107
 108    return true;
 109 }
 110
 111 static bool
 112 constant_fold_intrinsic_instr(nir_intrinsic_instr *instr)
 113 {
 114    bool progress = false;
 115
 116    if ((instr->intrinsic == nir_intrinsic_demote_if ||
 117         instr->intrinsic == nir_intrinsic_discard_if) &&
 118        nir_src_is_const(instr->src[0])) {
 119       if (nir_src_as_bool(instr->src[0])) {
 120          /* This method of getting a nir_shader * from a nir_instr is
 121           * admittedly gross, but given the rarity of hitting this case I think
 122           * it's preferable to plumbing an otherwise unused nir_shader *
 123           * parameter through four functions to get here.
 124           */
 125          nir_cf_node *cf_node = &instr->instr.block->cf_node;
 126          nir_function_impl *impl = nir_cf_node_get_function(cf_node);
 127          nir_shader *shader = impl->function->shader;
 128
 129          nir_intrinsic_op op = instr->intrinsic == nir_intrinsic_discard_if ?
 130                                nir_intrinsic_discard :
 131                                nir_intrinsic_demote;
 132          nir_intrinsic_instr *new_instr = nir_intrinsic_instr_create(shader, op);
 133          nir_instr_insert_before(&instr->instr, &new_instr->instr);
 134          nir_instr_remove(&instr->instr);
 135          progress = true;
 136       } else {
 137          /* We're not discarding, just delete the instruction */
 138          nir_instr_remove(&instr->instr);
 139          progress = true;
 140       }
 141    }
 142
 143    return progress;
 144 }
 145
 146 static bool
 147 constant_fold_block(nir_block *block, void *mem_ctx, unsigned execution_mode)
 148 {
 149    bool progress = false;
 150
 151    nir_foreach_instr_safe(instr, block) {
 152       switch (instr->type) {
 153       case nir_instr_type_alu:
 154          progress |= constant_fold_alu_instr(nir_instr_as_alu(instr), mem_ctx, execution_mode);
 155          break;
 156       case nir_instr_type_intrinsic:
 157          progress |=
 158             constant_fold_intrinsic_instr(nir_instr_as_intrinsic(instr));
 159          break;
 160       default:
 161          /* Don't know how to constant fold */
 162          break;
 163       }
 164    }
 165
 166    return progress;
 167 }
 168
 169 static bool
 170 nir_opt_constant_folding_impl(nir_function_impl *impl, unsigned execution_mode)
 171 {
 172    void *mem_ctx = ralloc_parent(impl);
 173    bool progress = false;
 174
 175    nir_foreach_block(block, impl) {
 176       progress |= constant_fold_block(block, mem_ctx, execution_mode);
 177    }
 178
 179    if (progress) {
 180       nir_metadata_preserve(impl, nir_metadata_block_index |
 181                                   nir_metadata_dominance);
 182    } else {
 183 #ifndef NDEBUG
 184       impl->valid_metadata &= ~nir_metadata_not_properly_reset;
 185 #endif
 186    }
 187
 188    return progress;
 189 }
 190
 191 bool
 192 nir_opt_constant_folding(nir_shader *shader)
 193 {
 194    bool progress = false;
 195    unsigned execution_mode = shader->info.float_controls_execution_mode;
 196
 197    nir_foreach_function(function, shader) {
 198       if (function->impl)
 199          progress |= nir_opt_constant_folding_impl(function->impl, execution_mode);
 200    }
 201
 202    return progress;
 203 }