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