src/compiler/nir/nir_propagate_invariant.c

   1 /*
   2  * Copyright © 2016 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
  21  * DEALINGS IN THE SOFTWARE.
  22  */
  23
  24 #include "nir.h"
  25
  26 static void
  27 add_src(nir_src *src, struct set *invariants)
  28 {
  29    if (src->is_ssa) {
  30       _mesa_set_add(invariants, src->ssa);
  31    } else {
  32       _mesa_set_add(invariants, src->reg.reg);
  33    }
  34 }
  35
  36 static bool
  37 add_src_cb(nir_src *src, void *state)
  38 {
  39    add_src(src, state);
  40    return true;
  41 }
  42
  43 static bool
  44 dest_is_invariant(nir_dest *dest, struct set *invariants)
  45 {
  46    if (dest->is_ssa) {
  47       return _mesa_set_search(invariants, &dest->ssa);
  48    } else {
  49       return _mesa_set_search(invariants, dest->reg.reg);
  50    }
  51 }
  52
  53 static void
  54 add_cf_node(nir_cf_node *cf, struct set *invariants)
  55 {
  56    if (cf->type == nir_cf_node_if) {
  57       nir_if *if_stmt = nir_cf_node_as_if(cf);
  58       add_src(&if_stmt->condition, invariants);
  59    }
  60
  61    if (cf->parent)
  62       add_cf_node(cf->parent, invariants);
  63 }
  64
  65 static void
  66 add_var(nir_variable *var, struct set *invariants)
  67 {
  68    /* Because we pass the result of nir_intrinsic_get_var directly to this
  69     * function, it's possible for var to be NULL if, for instance, there's a
  70     * cast somewhere in the chain.
  71     */
  72    if (var != NULL)
  73       _mesa_set_add(invariants, var);
  74 }
  75
  76 static bool
  77 var_is_invariant(nir_variable *var, struct set * invariants)
  78 {
  79    /* Because we pass the result of nir_intrinsic_get_var directly to this
  80     * function, it's possible for var to be NULL if, for instance, there's a
  81     * cast somewhere in the chain.
  82     */
  83    return var && (var->data.invariant || _mesa_set_search(invariants, var));
  84 }
  85
  86 static void
  87 propagate_invariant_instr(nir_instr *instr, struct set *invariants)
  88 {
  89    switch (instr->type) {
  90    case nir_instr_type_alu: {
  91       nir_alu_instr *alu = nir_instr_as_alu(instr);
  92       if (!dest_is_invariant(&alu->dest.dest, invariants))
  93          break;
  94
  95       alu->exact = true;
  96       nir_foreach_src(instr, add_src_cb, invariants);
  97       break;
  98    }
  99
 100    case nir_instr_type_tex: {
 101       nir_tex_instr *tex = nir_instr_as_tex(instr);
 102       if (dest_is_invariant(&tex->dest, invariants))
 103          nir_foreach_src(instr, add_src_cb, invariants);
 104       break;
 105    }
 106
 107    case nir_instr_type_intrinsic: {
 108       nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
 109       switch (intrin->intrinsic) {
 110       case nir_intrinsic_copy_deref:
 111          /* If the destination is invariant then so is the source */
 112          if (var_is_invariant(nir_intrinsic_get_var(intrin, 0), invariants))
 113             add_var(nir_intrinsic_get_var(intrin, 1), invariants);
 114          break;
 115
 116       case nir_intrinsic_load_deref:
 117          if (dest_is_invariant(&intrin->dest, invariants))
 118             add_var(nir_intrinsic_get_var(intrin, 0), invariants);
 119          break;
 120
 121       case nir_intrinsic_store_deref:
 122          if (var_is_invariant(nir_intrinsic_get_var(intrin, 0), invariants))
 123             add_src(&intrin->src[1], invariants);
 124          break;
 125
 126       default:
 127          /* Nothing to do */
 128          break;
 129       }
 130    }
 131
 132    case nir_instr_type_deref:
 133    case nir_instr_type_jump:
 134    case nir_instr_type_ssa_undef:
 135    case nir_instr_type_load_const:
 136       break; /* Nothing to do */
 137
 138    case nir_instr_type_phi: {
 139       nir_phi_instr *phi = nir_instr_as_phi(instr);
 140       if (!dest_is_invariant(&phi->dest, invariants))
 141          break;
 142
 143       nir_foreach_phi_src(src, phi) {
 144          add_src(&src->src, invariants);
 145          add_cf_node(&src->pred->cf_node, invariants);
 146       }
 147       break;
 148    }
 149
 150    case nir_instr_type_call:
 151       unreachable("This pass must be run after function inlining");
 152
 153    case nir_instr_type_parallel_copy:
 154    default:
 155       unreachable("Cannot have this instruction type");
 156    }
 157 }
 158
 159 static bool
 160 propagate_invariant_impl(nir_function_impl *impl, struct set *invariants)
 161 {
 162    bool progress = false;
 163
 164    while (true) {
 165       uint32_t prev_entries = invariants->entries;
 166
 167       nir_foreach_block_reverse(block, impl) {
 168          nir_foreach_instr_reverse(instr, block)
 169             propagate_invariant_instr(instr, invariants);
 170       }
 171
 172       /* Keep running until we make no more progress. */
 173       if (invariants->entries > prev_entries) {
 174          progress = true;
 175          continue;
 176       } else {
 177          break;
 178       }
 179    }
 180
 181    if (progress) {
 182       nir_metadata_preserve(impl, nir_metadata_block_index |
 183                                   nir_metadata_dominance |
 184                                   nir_metadata_live_ssa_defs);
 185    }
 186
 187    return progress;
 188 }
 189
 190 bool
 191 nir_propagate_invariant(nir_shader *shader)
 192 {
 193    /* Hash set of invariant things */
 194    struct set *invariants = _mesa_pointer_set_create(NULL);
 195
 196    bool progress = false;
 197    nir_foreach_function(function, shader) {
 198       if (function->impl && propagate_invariant_impl(function->impl, invariants))
 199          progress = true;
 200    }
 201
 202    _mesa_set_destroy(invariants, NULL);
 203
 204    return progress;
 205 }