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 variables to a temporary plus an
  26  * output variable with a single copy at each exit point of the shader.
  27  * This way the output variable is only ever written.
  28  */
  29
  30 #include "nir.h"
  31
  32 struct lower_io_state {
  33    nir_shader *shader;
  34    struct exec_list old_outputs;
  35 };
  36
  37 static void
  38 emit_output_copies(nir_cursor cursor, struct lower_io_state *state)
  39 {
  40    assert(exec_list_length(&state->shader->outputs) ==
  41           exec_list_length(&state->old_outputs));
  42
  43    foreach_two_lists(out_node, &state->shader->outputs,
  44                      temp_node, &state->old_outputs) {
  45       nir_variable *output = exec_node_data(nir_variable, out_node, node);
  46       nir_variable *temp = exec_node_data(nir_variable, temp_node, node);
  47
  48       nir_intrinsic_instr *copy =
  49          nir_intrinsic_instr_create(state->shader, nir_intrinsic_copy_var);
  50       copy->variables[0] = nir_deref_var_create(copy, output);
  51       copy->variables[1] = nir_deref_var_create(copy, temp);
  52
  53       nir_instr_insert(cursor, &copy->instr);
  54    }
  55 }
  56
  57 void
  58 nir_lower_io_to_temporaries(nir_shader *shader, nir_function *entrypoint)
  59 {
  60    struct lower_io_state state;
  61
  62    if (shader->stage == MESA_SHADER_TESS_CTRL)
  63       return;
  64
  65    state.shader = shader;
  66    exec_list_move_nodes_to(&shader->outputs, &state.old_outputs);
  67
  68    /* Walk over all of the outputs turn each output into a temporary and
  69     * make a new variable for the actual output.
  70     */
  71    nir_foreach_variable(var, &state.old_outputs) {
  72       nir_variable *output = ralloc(shader, nir_variable);
  73       memcpy(output, var, sizeof *output);
  74
  75       /* The orignal is now the temporary */
  76       nir_variable *temp = var;
  77
  78       /* Reparent the name to the new variable */
  79       ralloc_steal(output, output->name);
  80
  81       /* Reparent the constant initializer (if any) */
  82       ralloc_steal(output, output->constant_initializer);
  83
  84       /* Give the output a new name with @out-temp appended */
  85       temp->name = ralloc_asprintf(var, "%s@out-temp", output->name);
  86       temp->data.mode = nir_var_global;
  87       temp->constant_initializer = NULL;
  88
  89       exec_list_push_tail(&shader->outputs, &output->node);
  90    }
  91
  92    nir_foreach_function(function, shader) {
  93       if (function->impl == NULL)
  94          continue;
  95
  96       if (shader->stage == MESA_SHADER_GEOMETRY) {
  97          /* For geometry shaders, we have to emit the output copies right
  98           * before each EmitVertex call.
  99           */
 100          nir_foreach_block(block, function->impl) {
 101             nir_foreach_instr(instr, block) {
 102                if (instr->type != nir_instr_type_intrinsic)
 103                   continue;
 104
 105                nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
 106                if (intrin->intrinsic == nir_intrinsic_emit_vertex) {
 107                   emit_output_copies(nir_before_instr(&intrin->instr),
 108                                      &state);
 109                }
 110             }
 111          }
 112       } else if (function == entrypoint) {
 113          /* For all other shader types, we need to do the copies right before
 114           * the jumps to the end block.
 115           */
 116          struct set_entry *block_entry;
 117          set_foreach(function->impl->end_block->predecessors, block_entry) {
 118             struct nir_block *block = (void *)block_entry->key;
 119             emit_output_copies(nir_after_block_before_jump(block), &state);
 120          }
 121       }
 122
 123       nir_metadata_preserve(function->impl, nir_metadata_block_index |
 124                                             nir_metadata_dominance);
 125    }
 126
 127    exec_list_append(&shader->globals, &state.old_outputs);
 128 }