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    struct exec_list new_outputs;
  43    struct exec_list new_inputs;
  44
  45    /* map from temporary to new input */
  46    struct hash_table *input_map;
  47 };
  48
  49 static void
  50 emit_copies(nir_builder *b, struct exec_list *dest_vars,
  51             struct exec_list *src_vars)
  52 {
  53    assert(exec_list_length(dest_vars) == exec_list_length(src_vars));
  54
  55    foreach_two_lists(dest_node, dest_vars, src_node, src_vars) {
  56       nir_variable *dest = exec_node_data(nir_variable, dest_node, node);
  57       nir_variable *src = exec_node_data(nir_variable, src_node, node);
  58
  59       /* No need to copy the contents of a non-fb_fetch_output output variable
  60        * to the temporary allocated for it, since its initial value is
  61        * undefined.
  62        */
  63       if (src->data.mode == nir_var_shader_out &&
  64           !src->data.fb_fetch_output)
  65          continue;
  66
  67       /* Can't copy the contents of the temporary back to a read-only
  68        * interface variable.  The value of the temporary won't have been
  69        * modified by the shader anyway.
  70        */
  71       if (dest->data.read_only)
  72          continue;
  73
  74       nir_copy_var(b, dest, src);
  75    }
  76 }
  77
  78 static void
  79 emit_output_copies_impl(struct lower_io_state *state, nir_function_impl *impl)
  80 {
  81    nir_builder b;
  82    nir_builder_init(&b, impl);
  83
  84    if (state->shader->info.stage == MESA_SHADER_GEOMETRY) {
  85       /* For geometry shaders, we have to emit the output copies right
  86        * before each EmitVertex call.
  87        */
  88       nir_foreach_block(block, impl) {
  89          nir_foreach_instr(instr, block) {
  90             if (instr->type != nir_instr_type_intrinsic)
  91                continue;
  92
  93             nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
  94             if (intrin->intrinsic == nir_intrinsic_emit_vertex ||
  95                 intrin->intrinsic == nir_intrinsic_emit_vertex_with_counter) {
  96                b.cursor = nir_before_instr(&intrin->instr);
  97                emit_copies(&b, &state->new_outputs, &state->old_outputs);
  98             }
  99          }
 100       }
 101    } else if (impl == state->entrypoint) {
 102       b.cursor = nir_before_block(nir_start_block(impl));
 103       emit_copies(&b, &state->old_outputs, &state->new_outputs);
 104
 105       /* For all other shader types, we need to do the copies right before
 106        * the jumps to the end block.
 107        */
 108       set_foreach(impl->end_block->predecessors, block_entry) {
 109          struct nir_block *block = (void *)block_entry->key;
 110          b.cursor = nir_after_block_before_jump(block);
 111          emit_copies(&b, &state->new_outputs, &state->old_outputs);
 112       }
 113    }
 114 }
 115
 116 /* For fragment shader inputs, when we lower to temporaries we'll invalidate
 117  * interpolateAt*() because now they'll be pointing to the temporary instead
 118  * of the actual variable. Since the caller presumably doesn't support
 119  * indirect indexing of inputs, we'll need to lower something like:
 120  *
 121  * in vec4 foo[3];
 122  *
 123  * ... = interpolateAtCentroid(foo[i]);
 124  *
 125  * to a sequence of interpolations that store to our temporary, then a
 126  * load at the end:
 127  *
 128  * in vec4 foo[3];
 129  * vec4 foo_tmp[3];
 130  *
 131  * foo_tmp[0] = interpolateAtCentroid(foo[0]);
 132  * foo_tmp[1] = interpolateAtCentroid(foo[1]);
 133  * ... = foo_tmp[i];
 134  */
 135
 136 /*
 137  * Recursively emit the interpolation instructions. Here old_interp_deref
 138  * refers to foo[i], temp_deref is foo_tmp[0/1], and new_interp_deref is
 139  * foo[0/1].
 140  */
 141
 142 static void
 143 emit_interp(nir_builder *b, nir_deref_instr **old_interp_deref,
 144             nir_deref_instr *temp_deref, nir_deref_instr *new_interp_deref,
 145             nir_intrinsic_instr *interp)
 146 {
 147    while (*old_interp_deref) {
 148       switch ((*old_interp_deref)->deref_type) {
 149       case nir_deref_type_struct:
 150          temp_deref =
 151             nir_build_deref_struct(b, temp_deref,
 152                                    (*old_interp_deref)->strct.index);
 153          new_interp_deref =
 154             nir_build_deref_struct(b, new_interp_deref,
 155                                    (*old_interp_deref)->strct.index);
 156          break;
 157       case nir_deref_type_array:
 158          if (nir_src_is_const((*old_interp_deref)->arr.index)) {
 159             temp_deref =
 160                nir_build_deref_array(b, temp_deref,
 161                                      (*old_interp_deref)->arr.index.ssa);
 162             new_interp_deref =
 163                nir_build_deref_array(b, new_interp_deref,
 164                                      (*old_interp_deref)->arr.index.ssa);
 165             break;
 166          } else {
 167             /* We have an indirect deref, so we have to emit interpolations
 168              * for every index. Recurse in case we have an array of arrays.
 169              */
 170             unsigned length = glsl_get_length(temp_deref->type);
 171             for (unsigned i = 0; i < length; i++) {
 172                nir_deref_instr *new_temp =
 173                   nir_build_deref_array_imm(b, temp_deref, i);
 174                nir_deref_instr *new_interp =
 175                   nir_build_deref_array_imm(b, new_interp_deref, i);
 176
 177                emit_interp(b, old_interp_deref + 1, new_temp, new_interp,
 178                            interp);
 179             }
 180
 181             return;
 182          }
 183
 184       case nir_deref_type_var:
 185       case nir_deref_type_array_wildcard:
 186       case nir_deref_type_ptr_as_array:
 187       case nir_deref_type_cast:
 188          unreachable("bad deref type");
 189       }
 190
 191       old_interp_deref++;
 192    }
 193
 194    /* Now that we've constructed a fully-qualified deref with all the indirect
 195     * derefs replaced with direct ones, it's time to actually emit the new
 196     * interpolation instruction.
 197     */
 198
 199    nir_intrinsic_instr *new_interp =
 200       nir_intrinsic_instr_create(b->shader, interp->intrinsic);
 201
 202    new_interp->src[0] = nir_src_for_ssa(&new_interp_deref->dest.ssa);
 203    if (interp->intrinsic == nir_intrinsic_interp_deref_at_sample ||
 204        interp->intrinsic == nir_intrinsic_interp_deref_at_offset ||
 205        interp->intrinsic == nir_intrinsic_interp_deref_at_vertex) {
 206       new_interp->src[1] = interp->src[1];
 207    }
 208
 209    new_interp->num_components = interp->num_components;
 210    nir_ssa_dest_init(&new_interp->instr, &new_interp->dest,
 211                      interp->dest.ssa.num_components,
 212                      interp->dest.ssa.bit_size, NULL);
 213
 214    nir_builder_instr_insert(b, &new_interp->instr);
 215    nir_store_deref(b, temp_deref, &new_interp->dest.ssa,
 216                    (1 << interp->dest.ssa.num_components) - 1);
 217 }
 218
 219 static void
 220 fixup_interpolation_instr(struct lower_io_state *state,
 221                           nir_intrinsic_instr *interp, nir_builder *b)
 222 {
 223    nir_deref_path interp_path;
 224    nir_deref_path_init(&interp_path, nir_src_as_deref(interp->src[0]), NULL);
 225
 226    b->cursor = nir_before_instr(&interp->instr);
 227
 228    /* The original interpolation instruction should contain a deref path
 229     * starting with the original variable, which is now the temporary.
 230     */
 231    nir_deref_instr *temp_root = interp_path.path[0];
 232
 233    /* Fish out the newly-created input variable. */
 234    assert(temp_root->deref_type == nir_deref_type_var);
 235    struct hash_entry *entry = _mesa_hash_table_search(state->input_map,
 236                                                       temp_root->var);
 237    assert(entry);
 238    nir_variable *input = entry->data;
 239    nir_deref_instr *input_root = nir_build_deref_var(b, input);
 240
 241    /* Emit the interpolation instructions. */
 242    emit_interp(b, interp_path.path + 1, temp_root, input_root, interp);
 243
 244    /* Now the temporary contains the interpolation results, and we can just
 245     * load from it. We can reuse the original deref, since it points to the
 246     * correct part of the temporary.
 247     */
 248    nir_ssa_def *load = nir_load_deref(b, nir_src_as_deref(interp->src[0]));
 249    nir_ssa_def_rewrite_uses(&interp->dest.ssa, nir_src_for_ssa(load));
 250    nir_instr_remove(&interp->instr);
 251
 252    nir_deref_path_finish(&interp_path);
 253 }
 254
 255 static void
 256 fixup_interpolation(struct lower_io_state *state, nir_function_impl *impl,
 257                     nir_builder *b)
 258 {
 259    nir_foreach_block(block, impl) {
 260       nir_foreach_instr_safe(instr, block) {
 261          if (instr->type != nir_instr_type_intrinsic)
 262             continue;
 263
 264          nir_intrinsic_instr *interp = nir_instr_as_intrinsic(instr);
 265
 266          if (interp->intrinsic == nir_intrinsic_interp_deref_at_centroid ||
 267              interp->intrinsic == nir_intrinsic_interp_deref_at_sample ||
 268              interp->intrinsic == nir_intrinsic_interp_deref_at_offset ||
 269              interp->intrinsic == nir_intrinsic_interp_deref_at_vertex) {
 270             fixup_interpolation_instr(state, interp, b);
 271          }
 272       }
 273    }
 274 }
 275
 276 static void
 277 emit_input_copies_impl(struct lower_io_state *state, nir_function_impl *impl)
 278 {
 279    if (impl == state->entrypoint) {
 280       nir_builder b;
 281       nir_builder_init(&b, impl);
 282       b.cursor = nir_before_block(nir_start_block(impl));
 283       emit_copies(&b, &state->old_inputs, &state->new_inputs);
 284       if (state->shader->info.stage == MESA_SHADER_FRAGMENT)
 285          fixup_interpolation(state, impl, &b);
 286    }
 287 }
 288
 289 static nir_variable *
 290 create_shadow_temp(struct lower_io_state *state, nir_variable *var)
 291 {
 292    nir_variable *nvar = ralloc(state->shader, nir_variable);
 293    memcpy(nvar, var, sizeof *nvar);
 294    nvar->data.cannot_coalesce = true;
 295
 296    /* The original is now the temporary */
 297    nir_variable *temp = var;
 298
 299    /* Reparent the name to the new variable */
 300    ralloc_steal(nvar, nvar->name);
 301
 302    assert(nvar->constant_initializer == NULL && nvar->pointer_initializer == NULL);
 303
 304    /* Give the original a new name with @<mode>-temp appended */
 305    const char *mode = (temp->data.mode == nir_var_shader_in) ? "in" : "out";
 306    temp->name = ralloc_asprintf(var, "%s@%s-temp", mode, nvar->name);
 307    temp->data.mode = nir_var_shader_temp;
 308    temp->data.read_only = false;
 309    temp->data.fb_fetch_output = false;
 310    temp->data.compact = false;
 311
 312    return nvar;
 313 }
 314
 315 void
 316 nir_lower_io_to_temporaries(nir_shader *shader, nir_function_impl *entrypoint,
 317                             bool outputs, bool inputs)
 318 {
 319    struct lower_io_state state;
 320
 321    if (shader->info.stage == MESA_SHADER_TESS_CTRL)
 322       return;
 323
 324    state.shader = shader;
 325    state.entrypoint = entrypoint;
 326    state.input_map = _mesa_pointer_hash_table_create(NULL);
 327
 328    if (inputs)
 329       exec_list_move_nodes_to(&shader->inputs, &state.old_inputs);
 330    else
 331       exec_list_make_empty(&state.old_inputs);
 332
 333    if (outputs)
 334       exec_list_move_nodes_to(&shader->outputs, &state.old_outputs);
 335    else
 336       exec_list_make_empty(&state.old_outputs);
 337
 338    exec_list_make_empty(&state.new_inputs);
 339    exec_list_make_empty(&state.new_outputs);
 340
 341    /* Walk over all of the outputs turn each output into a temporary and
 342     * make a new variable for the actual output.
 343     */
 344    nir_foreach_variable(var, &state.old_outputs) {
 345       nir_variable *output = create_shadow_temp(&state, var);
 346       exec_list_push_tail(&state.new_outputs, &output->node);
 347    }
 348
 349    /* and same for inputs: */
 350    nir_foreach_variable(var, &state.old_inputs) {
 351       nir_variable *input = create_shadow_temp(&state, var);
 352       exec_list_push_tail(&state.new_inputs, &input->node);
 353       _mesa_hash_table_insert(state.input_map, var, input);
 354    }
 355
 356    nir_foreach_function(function, shader) {
 357       if (function->impl == NULL)
 358          continue;
 359
 360       if (inputs)
 361          emit_input_copies_impl(&state, function->impl);
 362
 363       if (outputs)
 364          emit_output_copies_impl(&state, function->impl);
 365
 366       nir_metadata_preserve(function->impl, nir_metadata_block_index |
 367                                             nir_metadata_dominance);
 368    }
 369
 370    exec_list_append(&shader->inputs, &state.new_inputs);
 371    exec_list_append(&shader->outputs, &state.new_outputs);
 372    exec_list_append(&shader->globals, &state.old_inputs);
 373    exec_list_append(&shader->globals, &state.old_outputs);
 374
 375    nir_fixup_deref_modes(shader);
 376
 377    _mesa_hash_table_destroy(state.input_map, NULL);
 378 }