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[NIR_MAX_VEC_COMPONENTS][NIR_MAX_VEC_COMPONENTS];
  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_types[i]))
  68          bit_size = instr->src[i].src.ssa->bit_size;
  69
  70       nir_instr *src_instr = instr->src[i].src.ssa->parent_instr;
  71
  72       if (src_instr->type != nir_instr_type_load_const)
  73          return false;
  74       nir_load_const_instr* load_const = nir_instr_as_load_const(src_instr);
  75
  76       for (unsigned j = 0; j < nir_ssa_alu_instr_src_components(instr, i);
  77            j++) {
  78          src[i][j] = load_const->value[instr->src[i].swizzle[j]];
  79       }
  80
  81       /* We shouldn't have any source modifiers in the optimization loop. */
  82       assert(!instr->src[i].abs && !instr->src[i].negate);
  83    }
  84
  85    if (bit_size == 0)
  86       bit_size = 32;
  87
  88    /* We shouldn't have any saturate modifiers in the optimization loop. */
  89    assert(!instr->dest.saturate);
  90
  91    nir_const_value dest[NIR_MAX_VEC_COMPONENTS];
  92    nir_const_value *srcs[NIR_MAX_VEC_COMPONENTS];
  93    memset(dest, 0, sizeof(dest));
  94    for (unsigned i = 0; i < nir_op_infos[instr->op].num_inputs; ++i)
  95       srcs[i] = src[i];
  96    nir_eval_const_opcode(instr->op, dest, instr->dest.dest.ssa.num_components,
  97                          bit_size, srcs);
  98
  99    nir_load_const_instr *new_instr =
 100       nir_load_const_instr_create(mem_ctx,
 101                                   instr->dest.dest.ssa.num_components,
 102                                   instr->dest.dest.ssa.bit_size);
 103
 104    memcpy(new_instr->value, dest, sizeof(*new_instr->value) * new_instr->def.num_components);
 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_intrinsic_instr(nir_intrinsic_instr *instr)
 119 {
 120    bool progress = false;
 121
 122    if ((instr->intrinsic == nir_intrinsic_demote_if ||
 123         instr->intrinsic == nir_intrinsic_discard_if) &&
 124        nir_src_is_const(instr->src[0])) {
 125       if (nir_src_as_bool(instr->src[0])) {
 126          /* This method of getting a nir_shader * from a nir_instr is
 127           * admittedly gross, but given the rarity of hitting this case I think
 128           * it's preferable to plumbing an otherwise unused nir_shader *
 129           * parameter through four functions to get here.
 130           */
 131          nir_cf_node *cf_node = &instr->instr.block->cf_node;
 132          nir_function_impl *impl = nir_cf_node_get_function(cf_node);
 133          nir_shader *shader = impl->function->shader;
 134
 135          nir_intrinsic_op op = instr->intrinsic == nir_intrinsic_discard_if ?
 136                                nir_intrinsic_discard :
 137                                nir_intrinsic_demote;
 138          nir_intrinsic_instr *new_instr = nir_intrinsic_instr_create(shader, op);
 139          nir_instr_insert_before(&instr->instr, &new_instr->instr);
 140          nir_instr_remove(&instr->instr);
 141          progress = true;
 142       } else {
 143          /* We're not discarding, just delete the instruction */
 144          nir_instr_remove(&instr->instr);
 145          progress = true;
 146       }
 147    }
 148
 149    return progress;
 150 }
 151
 152 static bool
 153 constant_fold_block(nir_block *block, void *mem_ctx)
 154 {
 155    bool progress = false;
 156
 157    nir_foreach_instr_safe(instr, block) {
 158       switch (instr->type) {
 159       case nir_instr_type_alu:
 160          progress |= constant_fold_alu_instr(nir_instr_as_alu(instr), mem_ctx);
 161          break;
 162       case nir_instr_type_intrinsic:
 163          progress |=
 164             constant_fold_intrinsic_instr(nir_instr_as_intrinsic(instr));
 165          break;
 166       default:
 167          /* Don't know how to constant fold */
 168          break;
 169       }
 170    }
 171
 172    return progress;
 173 }
 174
 175 static bool
 176 nir_opt_constant_folding_impl(nir_function_impl *impl)
 177 {
 178    void *mem_ctx = ralloc_parent(impl);
 179    bool progress = false;
 180
 181    nir_foreach_block(block, impl) {
 182       progress |= constant_fold_block(block, mem_ctx);
 183    }
 184
 185    if (progress) {
 186       nir_metadata_preserve(impl, nir_metadata_block_index |
 187                                   nir_metadata_dominance);
 188    } else {
 189 #ifndef NDEBUG
 190       impl->valid_metadata &= ~nir_metadata_not_properly_reset;
 191 #endif
 192    }
 193
 194    return progress;
 195 }
 196
 197 bool
 198 nir_opt_constant_folding(nir_shader *shader)
 199 {
 200    bool progress = false;
 201
 202    nir_foreach_function(function, shader) {
 203       if (function->impl)
 204          progress |= nir_opt_constant_folding_impl(function->impl);
 205    }
 206
 207    return progress;
 208 }