src/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 "program/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 class output_read_remover : public ir_hierarchical_visitor {
  41 protected:
  42    /**
  43     * A hash table mapping from the original ir_variable shader outputs
  44     * (ir_var_shader_out mode) to the new temporaries to be used instead.
  45     */
  46    hash_table *replacements;
  47
  48    void *mem_ctx;
  49 public:
  50    output_read_remover();
  51    ~output_read_remover();
  52    virtual ir_visitor_status visit(class ir_dereference_variable *);
  53    virtual ir_visitor_status visit_leave(class ir_return *);
  54    virtual ir_visitor_status visit_leave(class ir_function_signature *);
  55 };
  56
  57 /**
  58  * Hash function for the output variables - computes the hash of the name.
  59  * NOTE: We're using the name string to ensure that the hash doesn't depend
  60  * on any random factors, otherwise the output_read_remover could produce
  61  * the random order of the assignments.
  62  *
  63  * NOTE: If you want to reuse this function please take into account that
  64  * generally the names of the variables are non-unique.
  65  */
  66 static unsigned
  67 hash_table_var_hash(const void *key)
  68 {
  69    const ir_variable * var = static_cast<const ir_variable *>(key);
  70    return hash_table_string_hash(var->name);
  71 }
  72
  73 output_read_remover::output_read_remover()
  74 {
  75    mem_ctx = ralloc_context(NULL);
  76    replacements =
  77       hash_table_ctor(0, hash_table_var_hash, hash_table_pointer_compare);
  78 }
  79
  80 output_read_remover::~output_read_remover()
  81 {
  82    hash_table_dtor(replacements);
  83    ralloc_free(mem_ctx);
  84 }
  85
  86 ir_visitor_status
  87 output_read_remover::visit(ir_dereference_variable *ir)
  88 {
  89    if (ir->var->mode != ir_var_shader_out)
  90       return visit_continue;
  91
  92    ir_variable *temp = (ir_variable *) hash_table_find(replacements, ir->var);
  93
  94    /* If we don't have an existing temporary, create one. */
  95    if (temp == NULL) {
  96       void *var_ctx = ralloc_parent(ir->var);
  97       temp = new(var_ctx) ir_variable(ir->var->type, ir->var->name,
  98                                       ir_var_temporary);
  99       hash_table_insert(replacements, temp, ir->var);
 100       ir->var->insert_after(temp);
 101    }
 102
 103    /* Update the dereference to use the temporary */
 104    ir->var = temp;
 105
 106    return visit_continue;
 107 }
 108
 109 /**
 110  * Create an assignment to copy a temporary value back to the actual output.
 111  */
 112 static ir_assignment *
 113 copy(void *ctx, ir_variable *output, ir_variable *temp)
 114 {
 115    ir_dereference_variable *lhs = new(ctx) ir_dereference_variable(output);
 116    ir_dereference_variable *rhs = new(ctx) ir_dereference_variable(temp);
 117    return new(ctx) ir_assignment(lhs, rhs);
 118 }
 119
 120 /** Insert a copy-back assignment before a "return" statement */
 121 static void
 122 emit_return_copy(const void *key, void *data, void *closure)
 123 {
 124    ir_return *ir = (ir_return *) closure;
 125    ir->insert_before(copy(ir, (ir_variable *) key, (ir_variable *) data));
 126 }
 127
 128 /** Insert a copy-back assignment at the end of the main() function */
 129 static void
 130 emit_main_copy(const void *key, void *data, void *closure)
 131 {
 132    ir_function_signature *sig = (ir_function_signature *) closure;
 133    sig->body.push_tail(copy(sig, (ir_variable *) key, (ir_variable *) data));
 134 }
 135
 136 ir_visitor_status
 137 output_read_remover::visit_leave(ir_return *ir)
 138 {
 139    hash_table_call_foreach(replacements, emit_return_copy, ir);
 140    return visit_continue;
 141 }
 142
 143 ir_visitor_status
 144 output_read_remover::visit_leave(ir_function_signature *sig)
 145 {
 146    if (strcmp(sig->function_name(), "main") != 0)
 147       return visit_continue;
 148
 149    hash_table_call_foreach(replacements, emit_main_copy, sig);
 150    return visit_continue;
 151 }
 152
 153 void
 154 lower_output_reads(exec_list *instructions)
 155 {
 156    output_read_remover v;
 157    visit_list_elements(&v, instructions);
 158 }