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
  35 struct lower_io_state {
  36    nir_shader *shader;
  37    nir_function *entrypoint;
  38    struct exec_list old_outputs;
  39    struct exec_list old_inputs;
  40 };
  41
  42 static void
  43 emit_copies(nir_cursor cursor, nir_shader *shader, struct exec_list *new_vars,
  44           struct exec_list *old_vars)
  45 {
  46    assert(exec_list_length(new_vars) == exec_list_length(old_vars));
  47
  48    foreach_two_lists(new_node, new_vars, old_node, old_vars) {
  49       nir_variable *newv = exec_node_data(nir_variable, new_node, node);
  50       nir_variable *temp = exec_node_data(nir_variable, old_node, node);
  51
  52       nir_intrinsic_instr *copy =
  53          nir_intrinsic_instr_create(shader, nir_intrinsic_copy_var);
  54       copy->variables[0] = nir_deref_var_create(copy, newv);
  55       copy->variables[1] = nir_deref_var_create(copy, temp);
  56
  57       nir_instr_insert(cursor, &copy->instr);
  58    }
  59 }
  60
  61 static void
  62 emit_output_copies_impl(struct lower_io_state *state, nir_function_impl *impl)
  63 {
  64    if (state->shader->stage == MESA_SHADER_GEOMETRY) {
  65       /* For geometry shaders, we have to emit the output copies right
  66        * before each EmitVertex call.
  67        */
  68       nir_foreach_block(block, impl) {
  69          nir_foreach_instr(instr, block) {
  70             if (instr->type != nir_instr_type_intrinsic)
  71                continue;
  72
  73             nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
  74             if (intrin->intrinsic == nir_intrinsic_emit_vertex) {
  75                nir_cursor cursor = nir_before_instr(&intrin->instr);
  76                emit_copies(cursor, state->shader, &state->shader->outputs,
  77                            &state->old_outputs);
  78             }
  79          }
  80       }
  81    } else if (impl->function == state->entrypoint) {
  82       /* For all other shader types, we need to do the copies right before
  83        * the jumps to the end block.
  84        */
  85       struct set_entry *block_entry;
  86       set_foreach(impl->end_block->predecessors, block_entry) {
  87          struct nir_block *block = (void *)block_entry->key;
  88          nir_cursor cursor = nir_after_block_before_jump(block);
  89          emit_copies(cursor, state->shader, &state->shader->outputs,
  90                      &state->old_outputs);
  91       }
  92    }
  93 }
  94
  95 static void
  96 emit_input_copies_impl(struct lower_io_state *state, nir_function_impl *impl)
  97 {
  98    if (impl->function == state->entrypoint) {
  99       nir_cursor cursor = nir_before_block(nir_start_block(impl));
 100       emit_copies(cursor, state->shader, &state->old_inputs,
 101                   &state->shader->inputs);
 102    }
 103 }
 104
 105 static nir_variable *
 106 create_shadow_temp(struct lower_io_state *state, nir_variable *var)
 107 {
 108    nir_variable *nvar = ralloc(state->shader, nir_variable);
 109    memcpy(nvar, var, sizeof *nvar);
 110
 111    /* The original is now the temporary */
 112    nir_variable *temp = var;
 113
 114    /* Reparent the name to the new variable */
 115    ralloc_steal(nvar, nvar->name);
 116
 117    /* Reparent the constant initializer (if any) */
 118    ralloc_steal(nvar, nvar->constant_initializer);
 119
 120    /* Give the original a new name with @<mode>-temp appended */
 121    const char *mode = (temp->data.mode == nir_var_shader_in) ? "in" : "out";
 122    temp->name = ralloc_asprintf(var, "%s@%s-temp", mode, nvar->name);
 123    temp->data.mode = nir_var_global;
 124    temp->constant_initializer = NULL;
 125
 126    return nvar;
 127 }
 128
 129 void
 130 nir_lower_io_to_temporaries(nir_shader *shader, nir_function *entrypoint,
 131                             bool outputs, bool inputs)
 132 {
 133    struct lower_io_state state;
 134
 135    if (shader->stage == MESA_SHADER_TESS_CTRL)
 136       return;
 137
 138    state.shader = shader;
 139    state.entrypoint = entrypoint;
 140
 141    if (inputs)
 142       exec_list_move_nodes_to(&shader->inputs, &state.old_inputs);
 143    else
 144       exec_list_make_empty(&state.old_inputs);
 145
 146    if (outputs)
 147       exec_list_move_nodes_to(&shader->outputs, &state.old_outputs);
 148    else
 149       exec_list_make_empty(&state.old_outputs);
 150
 151    /* Walk over all of the outputs turn each output into a temporary and
 152     * make a new variable for the actual output.
 153     */
 154    nir_foreach_variable(var, &state.old_outputs) {
 155       nir_variable *output = create_shadow_temp(&state, var);
 156       exec_list_push_tail(&shader->outputs, &output->node);
 157    }
 158
 159    /* and same for inputs: */
 160    nir_foreach_variable(var, &state.old_inputs) {
 161       nir_variable *input = create_shadow_temp(&state, var);
 162       exec_list_push_tail(&shader->inputs, &input->node);
 163    }
 164
 165    nir_foreach_function(function, shader) {
 166       if (function->impl == NULL)
 167          continue;
 168
 169       if (inputs)
 170          emit_input_copies_impl(&state, function->impl);
 171
 172       if (outputs)
 173          emit_output_copies_impl(&state, function->impl);
 174
 175       nir_metadata_preserve(function->impl, nir_metadata_block_index |
 176                                             nir_metadata_dominance);
 177    }
 178
 179    exec_list_append(&shader->globals, &state.old_inputs);
 180    exec_list_append(&shader->globals, &state.old_outputs);
 181 }