src/glsl/nir/nir_split_var_copies.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.h"
  29
  30 /*
  31  * Implements "copy splitting" which is similar to structure splitting only
  32  * it works on copy operations rather than the datatypes themselves.  The
  33  * GLSL language allows you to copy one variable to another an entire
  34  * structure (which may contain arrays or other structures) at a time.
  35  * Normally, in a language such as C this would be handled by a "structure
  36  * splitting" pass that breaks up the structures.  Unfortunately for us,
  37  * structures used in inputs or outputs can't be split.  Therefore,
  38  * regardlesss of what we do, we have to be able to copy to/from
  39  * structures.
  40  *
  41  * The primary purpose of structure splitting is to allow you to better
  42  * optimize variable access and lower things to registers where you can.
  43  * The primary issue here is that, if you lower the copy to a bunch of
  44  * loads and stores, you loose a lot of information about the copy
  45  * operation that you would like to keep around.  To solve this problem, we
  46  * have a "copy splitting" pass that, instead of splitting the structures
  47  * or lowering the copy into loads and storres, splits the copy operation
  48  * into a bunch of copy operations one for each leaf of the structure tree.
  49  * If an intermediate array is encountered, it is referenced with a
  50  * wildcard reference to indicate that the entire array is to be copied.
  51  *
  52  * As things become direct, array copies may be able to be losslessly
  53  * lowered to having fewer and fewer wildcards.  However, until that
  54  * happens we want to keep the information about the arrays intact.
  55  *
  56  * Prior to the copy splitting pass, there are no wildcard references but
  57  * there may be incomplete references where the tail of the deref chain is
  58  * an array or a structure and not a specific element.  After the copy
  59  * splitting pass has completed, every variable deref will be a full-length
  60  * dereference pointing to a single leaf in the structure type tree with
  61  * possibly a few wildcard array dereferences.
  62  */
  63
  64 struct split_var_copies_state {
  65    void *mem_ctx;
  66    void *dead_ctx;
  67    bool progress;
  68 };
  69
  70 static nir_deref *
  71 get_deref_tail(nir_deref *deref)
  72 {
  73    while (deref->child != NULL)
  74       deref = deref->child;
  75    return deref;
  76 }
  77
  78 /* Recursively constructs deref chains to split a copy instruction into
  79  * multiple (if needed) copy instructions with full-length deref chains.
  80  * External callers of this function should pass the tail and head of the
  81  * deref chains found as the source and destination of the copy instruction
  82  * into this function.
  83  *
  84  * \param  old_copy  The copy instruction we are splitting
  85  * \param  dest_head The head of the destination deref chain we are building
  86  * \param  src_head  The head of the source deref chain we are building
  87  * \param  dest_tail The tail of the destination deref chain we are building
  88  * \param  src_tail  The tail of the source deref chain we are building
  89  * \param  state     The current split_var_copies_state object
  90  */
  91 static void
  92 split_var_copy_instr(nir_intrinsic_instr *old_copy,
  93                      nir_deref *dest_head, nir_deref *src_head,
  94                      nir_deref *dest_tail, nir_deref *src_tail,
  95                      struct split_var_copies_state *state)
  96 {
  97    assert(src_tail->type == dest_tail->type);
  98
  99    /* Make sure these really are the tails of the deref chains */
 100    assert(dest_tail->child == NULL);
 101    assert(src_tail->child == NULL);
 102
 103    switch (glsl_get_base_type(src_tail->type)) {
 104    case GLSL_TYPE_ARRAY: {
 105       /* Make a wildcard dereference */
 106       nir_deref_array *deref = nir_deref_array_create(state->dead_ctx);
 107       deref->deref.type = glsl_get_array_element(src_tail->type);
 108       deref->deref_array_type = nir_deref_array_type_wildcard;
 109
 110       /* Set the tail of both as the newly created wildcard deref.  It is
 111        * safe to use the same wildcard in both places because a) we will be
 112        * copying it before we put it in an actual instruction and b)
 113        * everything that will potentially add another link in the deref
 114        * chain will also add the same thing to both chains.
 115        */
 116       src_tail->child = &deref->deref;
 117       dest_tail->child = &deref->deref;
 118
 119       split_var_copy_instr(old_copy, dest_head, src_head,
 120                            dest_tail->child, src_tail->child, state);
 121
 122       /* Set it back to the way we found it */
 123       src_tail->child = NULL;
 124       dest_tail->child = NULL;
 125       break;
 126    }
 127
 128    case GLSL_TYPE_STRUCT:
 129       /* This is the only part that actually does any interesting
 130        * splitting.  For array types, we just use wildcards and resolve
 131        * them later.  For structure types, we need to emit one copy
 132        * instruction for every structure element.  Because we may have
 133        * structs inside structs, we just recurse and let the next level
 134        * take care of any additional structures.
 135        */
 136       for (unsigned i = 0; i < glsl_get_length(src_tail->type); i++) {
 137          nir_deref_struct *deref = nir_deref_struct_create(state->dead_ctx, i);
 138          deref->deref.type = glsl_get_struct_field(src_tail->type, i);
 139
 140          /* Set the tail of both as the newly created structure deref.  It
 141           * is safe to use the same wildcard in both places because a) we
 142           * will be copying it before we put it in an actual instruction
 143           * and b) everything that will potentially add another link in the
 144           * deref chain will also add the same thing to both chains.
 145           */
 146          src_tail->child = &deref->deref;
 147          dest_tail->child = &deref->deref;
 148
 149          split_var_copy_instr(old_copy, dest_head, src_head,
 150                               dest_tail->child, src_tail->child, state);
 151       }
 152       /* Set it back to the way we found it */
 153       src_tail->child = NULL;
 154       dest_tail->child = NULL;
 155       break;
 156
 157    case GLSL_TYPE_UINT:
 158    case GLSL_TYPE_INT:
 159    case GLSL_TYPE_FLOAT:
 160    case GLSL_TYPE_BOOL:
 161       if (glsl_type_is_matrix(src_tail->type)) {
 162          nir_deref_array *deref = nir_deref_array_create(state->dead_ctx);
 163          deref->deref.type = glsl_get_column_type(src_tail->type);
 164          deref->deref_array_type = nir_deref_array_type_wildcard;
 165
 166          /* Set the tail of both as the newly created wildcard deref.  It
 167           * is safe to use the same wildcard in both places because a) we
 168           * will be copying it before we put it in an actual instruction
 169           * and b) everything that will potentially add another link in the
 170           * deref chain will also add the same thing to both chains.
 171           */
 172          src_tail->child = &deref->deref;
 173          dest_tail->child = &deref->deref;
 174
 175          split_var_copy_instr(old_copy, dest_head, src_head,
 176                               dest_tail->child, src_tail->child, state);
 177
 178          /* Set it back to the way we found it */
 179          src_tail->child = NULL;
 180          dest_tail->child = NULL;
 181       } else {
 182          /* At this point, we have fully built our deref chains and can
 183           * actually add the new copy instruction.
 184           */
 185          nir_intrinsic_instr *new_copy =
 186             nir_intrinsic_instr_create(state->mem_ctx, nir_intrinsic_copy_var);
 187
 188          /* We need to make copies because a) this deref chain actually
 189           * belongs to the copy instruction and b) the deref chains may
 190           * have some of the same links due to the way we constructed them
 191           */
 192          nir_deref *src = nir_copy_deref(new_copy, src_head);
 193          nir_deref *dest = nir_copy_deref(new_copy, dest_head);
 194
 195          new_copy->variables[0] = nir_deref_as_var(dest);
 196          new_copy->variables[1] = nir_deref_as_var(src);
 197
 198          /* Emit the copy instruction after the old instruction.  We'll
 199           * remove the old one later.
 200           */
 201          nir_instr_insert_after(&old_copy->instr, &new_copy->instr);
 202          state->progress = true;
 203       }
 204       break;
 205
 206    case GLSL_TYPE_SAMPLER:
 207    case GLSL_TYPE_IMAGE:
 208    case GLSL_TYPE_ATOMIC_UINT:
 209    case GLSL_TYPE_INTERFACE:
 210    default:
 211       unreachable("Cannot copy these types");
 212    }
 213 }
 214
 215 static bool
 216 split_var_copies_block(nir_block *block, void *void_state)
 217 {
 218    struct split_var_copies_state *state = void_state;
 219
 220    nir_foreach_instr_safe(block, instr) {
 221       if (instr->type != nir_instr_type_intrinsic)
 222          continue;
 223
 224       nir_intrinsic_instr *intrinsic = nir_instr_as_intrinsic(instr);
 225       if (intrinsic->intrinsic != nir_intrinsic_copy_var)
 226          continue;
 227
 228       nir_deref *dest_head = &intrinsic->variables[0]->deref;
 229       nir_deref *src_head = &intrinsic->variables[1]->deref;
 230       nir_deref *dest_tail = get_deref_tail(dest_head);
 231       nir_deref *src_tail = get_deref_tail(src_head);
 232
 233       switch (glsl_get_base_type(src_tail->type)) {
 234       case GLSL_TYPE_ARRAY:
 235       case GLSL_TYPE_STRUCT:
 236          split_var_copy_instr(intrinsic, dest_head, src_head,
 237                               dest_tail, src_tail, state);
 238          nir_instr_remove(&intrinsic->instr);
 239          ralloc_steal(state->dead_ctx, instr);
 240          break;
 241       case GLSL_TYPE_FLOAT:
 242       case GLSL_TYPE_INT:
 243       case GLSL_TYPE_UINT:
 244       case GLSL_TYPE_BOOL:
 245          if (glsl_type_is_matrix(src_tail->type)) {
 246             split_var_copy_instr(intrinsic, dest_head, src_head,
 247                                  dest_tail, src_tail, state);
 248             nir_instr_remove(&intrinsic->instr);
 249             ralloc_steal(state->dead_ctx, instr);
 250          }
 251          break;
 252       default:
 253          unreachable("Invalid type");
 254          break;
 255       }
 256    }
 257
 258    return true;
 259 }
 260
 261 static bool
 262 split_var_copies_impl(nir_function_impl *impl)
 263 {
 264    struct split_var_copies_state state;
 265
 266    state.mem_ctx = ralloc_parent(impl);
 267    state.dead_ctx = ralloc_context(NULL);
 268    state.progress = false;
 269
 270    nir_foreach_block(impl, split_var_copies_block, &state);
 271
 272    ralloc_free(state.dead_ctx);
 273
 274    return state.progress;
 275 }
 276
 277 bool
 278 nir_split_var_copies(nir_shader *shader)
 279 {
 280    bool progress = false;
 281
 282    nir_foreach_overload(shader, overload) {
 283       if (overload->impl)
 284          progress = split_var_copies_impl(overload->impl) || progress;
 285    }
 286
 287    return progress;
 288 }