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
  36 struct lower_io_state {
  37    nir_shader *shader;
  38    nir_function_impl *entrypoint;
  39    struct exec_list old_outputs;
  40    struct exec_list old_inputs;
  41 };
  42
  43 static void
  44 emit_copies(nir_builder *b, struct exec_list *dest_vars,
  45             struct exec_list *src_vars)
  46 {
  47    assert(exec_list_length(dest_vars) == exec_list_length(src_vars));
  48
  49    foreach_two_lists(dest_node, dest_vars, src_node, src_vars) {
  50       nir_variable *dest = exec_node_data(nir_variable, dest_node, node);
  51       nir_variable *src = exec_node_data(nir_variable, src_node, node);
  52
  53       /* No need to copy the contents of a non-fb_fetch_output output variable
  54        * to the temporary allocated for it, since its initial value is
  55        * undefined.
  56        */
  57       if (src->data.mode == nir_var_shader_out &&
  58           !src->data.fb_fetch_output)
  59          continue;
  60
  61       /* Can't copy the contents of the temporary back to a read-only
  62        * interface variable.  The value of the temporary won't have been
  63        * modified by the shader anyway.
  64        */
  65       if (dest->data.read_only)
  66          continue;
  67
  68       nir_copy_var(b, dest, src);
  69    }
  70 }
  71
  72 static void
  73 emit_output_copies_impl(struct lower_io_state *state, nir_function_impl *impl)
  74 {
  75    nir_builder b;
  76    nir_builder_init(&b, impl);
  77
  78    if (state->shader->info.stage == MESA_SHADER_GEOMETRY) {
  79       /* For geometry shaders, we have to emit the output copies right
  80        * before each EmitVertex call.
  81        */
  82       nir_foreach_block(block, impl) {
  83          nir_foreach_instr(instr, block) {
  84             if (instr->type != nir_instr_type_intrinsic)
  85                continue;
  86
  87             nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
  88             if (intrin->intrinsic == nir_intrinsic_emit_vertex ||
  89                 intrin->intrinsic == nir_intrinsic_emit_vertex_with_counter) {
  90                b.cursor = nir_before_instr(&intrin->instr);
  91                emit_copies(&b, &state->shader->outputs, &state->old_outputs);
  92             }
  93          }
  94       }
  95    } else if (impl == state->entrypoint) {
  96       b.cursor = nir_before_block(nir_start_block(impl));
  97       emit_copies(&b, &state->old_outputs, &state->shader->outputs);
  98
  99       /* For all other shader types, we need to do the copies right before
 100        * the jumps to the end block.
 101        */
 102       set_foreach(impl->end_block->predecessors, block_entry) {
 103          struct nir_block *block = (void *)block_entry->key;
 104          b.cursor = nir_after_block_before_jump(block);
 105          emit_copies(&b, &state->shader->outputs, &state->old_outputs);
 106       }
 107    }
 108 }
 109
 110 static void
 111 emit_input_copies_impl(struct lower_io_state *state, nir_function_impl *impl)
 112 {
 113    if (impl == state->entrypoint) {
 114       nir_builder b;
 115       nir_builder_init(&b, impl);
 116       b.cursor = nir_before_block(nir_start_block(impl));
 117       emit_copies(&b, &state->old_inputs, &state->shader->inputs);
 118    }
 119 }
 120
 121 static nir_variable *
 122 create_shadow_temp(struct lower_io_state *state, nir_variable *var)
 123 {
 124    nir_variable *nvar = ralloc(state->shader, nir_variable);
 125    memcpy(nvar, var, sizeof *nvar);
 126
 127    /* The original is now the temporary */
 128    nir_variable *temp = var;
 129
 130    /* Reparent the name to the new variable */
 131    ralloc_steal(nvar, nvar->name);
 132
 133    assert(nvar->constant_initializer == NULL);
 134
 135    /* Give the original a new name with @<mode>-temp appended */
 136    const char *mode = (temp->data.mode == nir_var_shader_in) ? "in" : "out";
 137    temp->name = ralloc_asprintf(var, "%s@%s-temp", mode, nvar->name);
 138    temp->data.mode = nir_var_shader_temp;
 139    temp->data.read_only = false;
 140    temp->data.fb_fetch_output = false;
 141    temp->data.compact = false;
 142
 143    return nvar;
 144 }
 145
 146 void
 147 nir_lower_io_to_temporaries(nir_shader *shader, nir_function_impl *entrypoint,
 148                             bool outputs, bool inputs)
 149 {
 150    struct lower_io_state state;
 151
 152    if (shader->info.stage == MESA_SHADER_TESS_CTRL)
 153       return;
 154
 155    state.shader = shader;
 156    state.entrypoint = entrypoint;
 157
 158    if (inputs)
 159       exec_list_move_nodes_to(&shader->inputs, &state.old_inputs);
 160    else
 161       exec_list_make_empty(&state.old_inputs);
 162
 163    if (outputs)
 164       exec_list_move_nodes_to(&shader->outputs, &state.old_outputs);
 165    else
 166       exec_list_make_empty(&state.old_outputs);
 167
 168    /* Walk over all of the outputs turn each output into a temporary and
 169     * make a new variable for the actual output.
 170     */
 171    nir_foreach_variable(var, &state.old_outputs) {
 172       nir_variable *output = create_shadow_temp(&state, var);
 173       exec_list_push_tail(&shader->outputs, &output->node);
 174    }
 175
 176    /* and same for inputs: */
 177    nir_foreach_variable(var, &state.old_inputs) {
 178       nir_variable *input = create_shadow_temp(&state, var);
 179       exec_list_push_tail(&shader->inputs, &input->node);
 180    }
 181
 182    nir_foreach_function(function, shader) {
 183       if (function->impl == NULL)
 184          continue;
 185
 186       if (inputs)
 187          emit_input_copies_impl(&state, function->impl);
 188
 189       if (outputs)
 190          emit_output_copies_impl(&state, function->impl);
 191
 192       nir_metadata_preserve(function->impl, nir_metadata_block_index |
 193                                             nir_metadata_dominance);
 194    }
 195
 196    exec_list_append(&shader->globals, &state.old_inputs);
 197    exec_list_append(&shader->globals, &state.old_outputs);
 198
 199    nir_fixup_deref_modes(shader);
 200 }