src/compiler/glsl/lower_output_reads.cpp

   1 /*
   2  * Copyright © 2012 Vincent Lejeune
   3  * Copyright © 2012 Intel Corporation
   4  *
   5  * Permission is hereby granted, free of charge, to any person obtaining a
   6  * copy of this software and associated documentation files (the "Software"),
   7  * to deal in the Software without restriction, including without limitation
   8  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   9  * and/or sell copies of the Software, and to permit persons to whom the
  10  * Software is furnished to do so, subject to the following conditions:
  11  *
  12  * The above copyright notice and this permission notice (including the next
  13  * paragraph) shall be included in all copies or substantial portions of the
  14  * Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  21  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  22  * DEALINGS IN THE SOFTWARE.
  23  */
  24
  25 #include "ir.h"
  26 #include "util/hash_table.h"
  27
  28 /**
  29  * \file lower_output_reads.cpp
  30  *
  31  * In GLSL, shader output variables (such as varyings) can be both read and
  32  * written.  However, on some hardware, reading an output register causes
  33  * trouble.
  34  *
  35  * This pass creates temporary shadow copies of every (used) shader output,
  36  * and replaces all accesses to use those instead.  It also adds code to the
  37  * main() function to copy the final values to the actual shader outputs.
  38  */
  39
  40 namespace {
  41
  42 class output_read_remover : public ir_hierarchical_visitor {
  43 protected:
  44    /**
  45     * A hash table mapping from the original ir_variable shader outputs
  46     * (ir_var_shader_out mode) to the new temporaries to be used instead.
  47     */
  48    hash_table *replacements;
  49
  50    void *mem_ctx;
  51
  52    unsigned stage;
  53 public:
  54    output_read_remover(unsigned stage);
  55    ~output_read_remover();
  56    virtual ir_visitor_status visit(class ir_dereference_variable *);
  57    virtual ir_visitor_status visit_leave(class ir_emit_vertex *);
  58    virtual ir_visitor_status visit_leave(class ir_return *);
  59    virtual ir_visitor_status visit_leave(class ir_function_signature *);
  60 };
  61
  62 } /* anonymous namespace */
  63
  64 /**
  65  * Hash function for the output variables - computes the hash of the name.
  66  * NOTE: We're using the name string to ensure that the hash doesn't depend
  67  * on any random factors, otherwise the output_read_remover could produce
  68  * the random order of the assignments.
  69  *
  70  * NOTE: If you want to reuse this function please take into account that
  71  * generally the names of the variables are non-unique.
  72  */
  73 static unsigned
  74 hash_table_var_hash(const void *key)
  75 {
  76    const ir_variable * var = static_cast<const ir_variable *>(key);
  77    return _mesa_key_hash_string(var->name);
  78 }
  79
  80 output_read_remover::output_read_remover(unsigned stage)
  81 {
  82    this->stage = stage;
  83    mem_ctx = ralloc_context(NULL);
  84    replacements = _mesa_hash_table_create(NULL, hash_table_var_hash,
  85                                           _mesa_key_pointer_equal);
  86 }
  87
  88 output_read_remover::~output_read_remover()
  89 {
  90    _mesa_hash_table_destroy(replacements, NULL);
  91    ralloc_free(mem_ctx);
  92 }
  93
  94 ir_visitor_status
  95 output_read_remover::visit(ir_dereference_variable *ir)
  96 {
  97    if (ir->var->data.mode != ir_var_shader_out)
  98       return visit_continue;
  99    if (stage == MESA_SHADER_TESS_CTRL)
 100       return visit_continue;
 101
 102    hash_entry *entry = _mesa_hash_table_search(replacements, ir->var);
 103    ir_variable *temp = entry ? (ir_variable *) entry->data : NULL;
 104
 105    /* If we don't have an existing temporary, create one. */
 106    if (temp == NULL) {
 107       void *var_ctx = ralloc_parent(ir->var);
 108       temp = new(var_ctx) ir_variable(ir->var->type, ir->var->name,
 109                                       ir_var_temporary);
 110       _mesa_hash_table_insert(replacements, ir->var, temp);
 111       ir->var->insert_after(temp);
 112    }
 113
 114    /* Update the dereference to use the temporary */
 115    ir->var = temp;
 116
 117    return visit_continue;
 118 }
 119
 120 /**
 121  * Create an assignment to copy a temporary value back to the actual output.
 122  */
 123 static ir_assignment *
 124 copy(void *ctx, ir_variable *output, ir_variable *temp)
 125 {
 126    ir_dereference_variable *lhs = new(ctx) ir_dereference_variable(output);
 127    ir_dereference_variable *rhs = new(ctx) ir_dereference_variable(temp);
 128    return new(ctx) ir_assignment(lhs, rhs);
 129 }
 130
 131 /** Insert a copy-back assignment before a "return" statement or a call to
 132  * EmitVertex().
 133  */
 134 static void
 135 emit_return_copy(const void *key, void *data, void *closure)
 136 {
 137    ir_return *ir = (ir_return *) closure;
 138    ir->insert_before(copy(ir, (ir_variable *) key, (ir_variable *) data));
 139 }
 140
 141 /** Insert a copy-back assignment at the end of the main() function */
 142 static void
 143 emit_main_copy(const void *key, void *data, void *closure)
 144 {
 145    ir_function_signature *sig = (ir_function_signature *) closure;
 146    sig->body.push_tail(copy(sig, (ir_variable *) key, (ir_variable *) data));
 147 }
 148
 149 ir_visitor_status
 150 output_read_remover::visit_leave(ir_return *ir)
 151 {
 152    hash_table_call_foreach(replacements, emit_return_copy, ir);
 153    return visit_continue;
 154 }
 155
 156 ir_visitor_status
 157 output_read_remover::visit_leave(ir_emit_vertex *ir)
 158 {
 159    hash_table_call_foreach(replacements, emit_return_copy, ir);
 160    _mesa_hash_table_clear(replacements, NULL);
 161    return visit_continue;
 162 }
 163
 164 ir_visitor_status
 165 output_read_remover::visit_leave(ir_function_signature *sig)
 166 {
 167    if (strcmp(sig->function_name(), "main") != 0)
 168       return visit_continue;
 169
 170    hash_table_call_foreach(replacements, emit_main_copy, sig);
 171    return visit_continue;
 172 }
 173
 174 void
 175 lower_output_reads(unsigned stage, exec_list *instructions)
 176 {
 177    output_read_remover v(stage);
 178    visit_list_elements(&v, instructions);
 179 }