src/compiler/nir/nir_lower_io_to_temporaries.c

   1 /*
   2  * Copyright © 2015 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
  24 /*
  25  * Implements a pass that lowers output and/or input variables to a
  26  * temporary plus an output variable with a single copy at each exit
  27  * point of the shader and/or an input variable with a single copy
  28  * at the entrance point of the shader.  This way the output variable
  29  * is only ever written once and/or input is only read once, and there
  30  * are no indirect outut/input accesses.
  31  */
  32
  33 #include "nir.h"
  34 #include "nir_builder.h"
  35 #include "nir_deref.h"
  36
  37 struct lower_io_state {
  38    nir_shader *shader;
  39    nir_function_impl *entrypoint;
  40    struct exec_list old_outputs;
  41    struct exec_list old_inputs;
  42
  43    /* map from temporary to new input */
  44    struct hash_table *input_map;
  45 };
  46
  47 static void
  48 emit_copies(nir_builder *b, struct exec_list *dest_vars,
  49             struct exec_list *src_vars)
  50 {
  51    assert(exec_list_length(dest_vars) == exec_list_length(src_vars));
  52
  53    foreach_two_lists(dest_node, dest_vars, src_node, src_vars) {
  54       nir_variable *dest = exec_node_data(nir_variable, dest_node, node);
  55       nir_variable *src = exec_node_data(nir_variable, src_node, node);
  56
  57       /* No need to copy the contents of a non-fb_fetch_output output variable
  58        * to the temporary allocated for it, since its initial value is
  59        * undefined.
  60        */
  61       if (src->data.mode == nir_var_shader_out &&
  62           !src->data.fb_fetch_output)
  63          continue;
  64
  65       /* Can't copy the contents of the temporary back to a read-only
  66        * interface variable.  The value of the temporary won't have been
  67        * modified by the shader anyway.
  68        */
  69       if (dest->data.read_only)
  70          continue;
  71
  72       nir_copy_var(b, dest, src);
  73    }
  74 }
  75
  76 static void
  77 emit_output_copies_impl(struct lower_io_state *state, nir_function_impl *impl)
  78 {
  79    nir_builder b;
  80    nir_builder_init(&b, impl);
  81
  82    if (state->shader->info.stage == MESA_SHADER_GEOMETRY) {
  83       /* For geometry shaders, we have to emit the output copies right
  84        * before each EmitVertex call.
  85        */
  86       nir_foreach_block(block, impl) {
  87          nir_foreach_instr(instr, block) {
  88             if (instr->type != nir_instr_type_intrinsic)
  89                continue;
  90
  91             nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
  92             if (intrin->intrinsic == nir_intrinsic_emit_vertex ||
  93                 intrin->intrinsic == nir_intrinsic_emit_vertex_with_counter) {
  94                b.cursor = nir_before_instr(&intrin->instr);
  95                emit_copies(&b, &state->shader->outputs, &state->old_outputs);
  96             }
  97          }
  98       }
  99    } else if (impl == state->entrypoint) {
 100       b.cursor = nir_before_block(nir_start_block(impl));
 101       emit_copies(&b, &state->old_outputs, &state->shader->outputs);
 102
 103       /* For all other shader types, we need to do the copies right before
 104        * the jumps to the end block.
 105        */
 106       set_foreach(impl->end_block->predecessors, block_entry) {
 107          struct nir_block *block = (void *)block_entry->key;
 108          b.cursor = nir_after_block_before_jump(block);
 109          emit_copies(&b, &state->shader->outputs, &state->old_outputs);
 110       }
 111    }
 112 }
 113
 114 /* For fragment shader inputs, when we lower to temporaries we'll invalidate
 115  * interpolateAt*() because now they'll be pointing to the temporary instead
 116  * of the actual variable. Since the caller presumably doesn't support
 117  * indirect indexing of inputs, we'll need to lower something like:
 118  *
 119  * in vec4 foo[3];
 120  *
 121  * ... = interpolateAtCentroid(foo[i]);
 122  *
 123  * to a sequence of interpolations that store to our temporary, then a
 124  * load at the end:
 125  *
 126  * in vec4 foo[3];
 127  * vec4 foo_tmp[3];
 128  *
 129  * foo_tmp[0] = interpolateAtCentroid(foo[0]);
 130  * foo_tmp[1] = interpolateAtCentroid(foo[1]);
 131  * ... = foo_tmp[i];
 132  */
 133
 134 /*
 135  * Recursively emit the interpolation instructions. Here old_interp_deref
 136  * refers to foo[i], temp_deref is foo_tmp[0/1], and new_interp_deref is
 137  * foo[0/1].
 138  */
 139
 140 static void
 141 emit_interp(nir_builder *b, nir_deref_instr **old_interp_deref,
 142             nir_deref_instr *temp_deref, nir_deref_instr *new_interp_deref,
 143             nir_intrinsic_instr *interp)
 144 {
 145    while (*old_interp_deref) {
 146       switch ((*old_interp_deref)->deref_type) {
 147       case nir_deref_type_struct:
 148          temp_deref =
 149             nir_build_deref_struct(b, temp_deref,
 150                                    (*old_interp_deref)->strct.index);
 151          new_interp_deref =
 152             nir_build_deref_struct(b, new_interp_deref,
 153                                    (*old_interp_deref)->strct.index);
 154          break;
 155       case nir_deref_type_array:
 156          if (nir_src_is_const((*old_interp_deref)->arr.index)) {
 157             temp_deref =
 158                nir_build_deref_array(b, temp_deref,
 159                                      (*old_interp_deref)->arr.index.ssa);
 160             new_interp_deref =
 161                nir_build_deref_array(b, new_interp_deref,
 162                                      (*old_interp_deref)->arr.index.ssa);
 163             break;
 164          } else {
 165             /* We have an indirect deref, so we have to emit interpolations
 166              * for every index. Recurse in case we have an array of arrays.
 167              */
 168             unsigned length = glsl_get_length(temp_deref->type);
 169             for (unsigned i = 0; i < length; i++) {
 170                nir_deref_instr *new_temp =
 171                   nir_build_deref_array_imm(b, temp_deref, i);
 172                nir_deref_instr *new_interp =
 173                   nir_build_deref_array_imm(b, new_interp_deref, i);
 174
 175                emit_interp(b, old_interp_deref + 1, new_temp, new_interp,
 176                            interp);
 177             }
 178
 179             return;
 180          }
 181
 182       case nir_deref_type_var:
 183       case nir_deref_type_array_wildcard:
 184       case nir_deref_type_ptr_as_array:
 185       case nir_deref_type_cast:
 186          unreachable("bad deref type");
 187       }
 188
 189       old_interp_deref++;
 190    }
 191
 192    /* Now that we've constructed a fully-qualified deref with all the indirect
 193     * derefs replaced with direct ones, it's time to actually emit the new
 194     * interpolation instruction.
 195     */
 196
 197    nir_intrinsic_instr *new_interp =
 198       nir_intrinsic_instr_create(b->shader, interp->intrinsic);
 199
 200    new_interp->src[0] = nir_src_for_ssa(&new_interp_deref->dest.ssa);
 201    if (interp->intrinsic == nir_intrinsic_interp_deref_at_sample ||
 202        interp->intrinsic == nir_intrinsic_interp_deref_at_offset ||
 203        interp->intrinsic == nir_intrinsic_interp_deref_at_vertex) {
 204       new_interp->src[1] = interp->src[1];
 205    }
 206
 207    new_interp->num_components = interp->num_components;
 208    nir_ssa_dest_init(&new_interp->instr, &new_interp->dest,
 209                      interp->dest.ssa.num_components,
 210                      interp->dest.ssa.bit_size, NULL);
 211
 212    nir_builder_instr_insert(b, &new_interp->instr);
 213    nir_store_deref(b, temp_deref, &new_interp->dest.ssa,
 214                    (1 << interp->dest.ssa.num_components) - 1);
 215 }
 216
 217 static void
 218 fixup_interpolation_instr(struct lower_io_state *state,
 219                           nir_intrinsic_instr *interp, nir_builder *b)
 220 {
 221    nir_deref_path interp_path;
 222    nir_deref_path_init(&interp_path, nir_src_as_deref(interp->src[0]), NULL);
 223
 224    b->cursor = nir_before_instr(&interp->instr);
 225
 226    /* The original interpolation instruction should contain a deref path
 227     * starting with the original variable, which is now the temporary.
 228     */
 229    nir_deref_instr *temp_root = interp_path.path[0];
 230
 231    /* Fish out the newly-created input variable. */
 232    assert(temp_root->deref_type == nir_deref_type_var);
 233    struct hash_entry *entry = _mesa_hash_table_search(state->input_map,
 234                                                       temp_root->var);
 235    assert(entry);
 236    nir_variable *input = entry->data;
 237    nir_deref_instr *input_root = nir_build_deref_var(b, input);
 238
 239    /* Emit the interpolation instructions. */
 240    emit_interp(b, interp_path.path + 1, temp_root, input_root, interp);
 241
 242    /* Now the temporary contains the interpolation results, and we can just
 243     * load from it. We can reuse the original deref, since it points to the
 244     * correct part of the temporary.
 245     */
 246    nir_ssa_def *load = nir_load_deref(b, nir_src_as_deref(interp->src[0]));
 247    nir_ssa_def_rewrite_uses(&interp->dest.ssa, nir_src_for_ssa(load));
 248    nir_instr_remove(&interp->instr);
 249
 250    nir_deref_path_finish(&interp_path);
 251 }
 252
 253 static void
 254 fixup_interpolation(struct lower_io_state *state, nir_function_impl *impl,
 255                     nir_builder *b)
 256 {
 257    nir_foreach_block(block, impl) {
 258       nir_foreach_instr_safe(instr, block) {
 259          if (instr->type != nir_instr_type_intrinsic)
 260             continue;
 261
 262          nir_intrinsic_instr *interp = nir_instr_as_intrinsic(instr);
 263
 264          if (interp->intrinsic == nir_intrinsic_interp_deref_at_centroid ||
 265              interp->intrinsic == nir_intrinsic_interp_deref_at_sample ||
 266              interp->intrinsic == nir_intrinsic_interp_deref_at_offset ||
 267              interp->intrinsic == nir_intrinsic_interp_deref_at_vertex) {
 268             fixup_interpolation_instr(state, interp, b);
 269          }
 270       }
 271    }
 272 }
 273
 274 static void
 275 emit_input_copies_impl(struct lower_io_state *state, nir_function_impl *impl)
 276 {
 277    if (impl == state->entrypoint) {
 278       nir_builder b;
 279       nir_builder_init(&b, impl);
 280       b.cursor = nir_before_block(nir_start_block(impl));
 281       emit_copies(&b, &state->old_inputs, &state->shader->inputs);
 282       if (state->shader->info.stage == MESA_SHADER_FRAGMENT)
 283          fixup_interpolation(state, impl, &b);
 284    }
 285 }
 286
 287 static nir_variable *
 288 create_shadow_temp(struct lower_io_state *state, nir_variable *var)
 289 {
 290    nir_variable *nvar = ralloc(state->shader, nir_variable);
 291    memcpy(nvar, var, sizeof *nvar);
 292    nvar->data.cannot_coalesce = true;
 293
 294    /* The original is now the temporary */
 295    nir_variable *temp = var;
 296
 297    /* Reparent the name to the new variable */
 298    ralloc_steal(nvar, nvar->name);
 299
 300    assert(nvar->constant_initializer == NULL && nvar->pointer_initializer == NULL);
 301
 302    /* Give the original a new name with @<mode>-temp appended */
 303    const char *mode = (temp->data.mode == nir_var_shader_in) ? "in" : "out";
 304    temp->name = ralloc_asprintf(var, "%s@%s-temp", mode, nvar->name);
 305    temp->data.mode = nir_var_shader_temp;
 306    temp->data.read_only = false;
 307    temp->data.fb_fetch_output = false;
 308    temp->data.compact = false;
 309
 310    return nvar;
 311 }
 312
 313 void
 314 nir_lower_io_to_temporaries(nir_shader *shader, nir_function_impl *entrypoint,
 315                             bool outputs, bool inputs)
 316 {
 317    struct lower_io_state state;
 318
 319    if (shader->info.stage == MESA_SHADER_TESS_CTRL)
 320       return;
 321
 322    state.shader = shader;
 323    state.entrypoint = entrypoint;
 324    state.input_map = _mesa_pointer_hash_table_create(NULL);
 325
 326    if (inputs)
 327       exec_list_move_nodes_to(&shader->inputs, &state.old_inputs);
 328    else
 329       exec_list_make_empty(&state.old_inputs);
 330
 331    if (outputs)
 332       exec_list_move_nodes_to(&shader->outputs, &state.old_outputs);
 333    else
 334       exec_list_make_empty(&state.old_outputs);
 335
 336    /* Walk over all of the outputs turn each output into a temporary and
 337     * make a new variable for the actual output.
 338     */
 339    nir_foreach_variable(var, &state.old_outputs) {
 340       nir_variable *output = create_shadow_temp(&state, var);
 341       exec_list_push_tail(&shader->outputs, &output->node);
 342    }
 343
 344    /* and same for inputs: */
 345    nir_foreach_variable(var, &state.old_inputs) {
 346       nir_variable *input = create_shadow_temp(&state, var);
 347       exec_list_push_tail(&shader->inputs, &input->node);
 348       _mesa_hash_table_insert(state.input_map, var, input);
 349    }
 350
 351    nir_foreach_function(function, shader) {
 352       if (function->impl == NULL)
 353          continue;
 354
 355       if (inputs)
 356          emit_input_copies_impl(&state, function->impl);
 357
 358       if (outputs)
 359          emit_output_copies_impl(&state, function->impl);
 360
 361       nir_metadata_preserve(function->impl, nir_metadata_block_index |
 362                                             nir_metadata_dominance);
 363    }
 364
 365    exec_list_append(&shader->globals, &state.old_inputs);
 366    exec_list_append(&shader->globals, &state.old_outputs);
 367
 368    nir_fixup_deref_modes(shader);
 369
 370    _mesa_hash_table_destroy(state.input_map, NULL);
 371 }