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_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
hash_table_var_hash(const void * key)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
output_read_remover()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
~output_read_remover()80 output_read_remover::~output_read_remover()
81 {
82 hash_table_dtor(replacements);
83 ralloc_free(mem_ctx);
84 }
85
86 ir_visitor_status
visit(ir_dereference_variable * ir)87 output_read_remover::visit(ir_dereference_variable *ir)
88 {
89 if (ir->var->mode != ir_var_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 }
101
102 /* Update the dereference to use the temporary */
103 ir->var = temp;
104
105 return visit_continue;
106 }
107
108 /**
109 * Create an assignment to copy a temporary value back to the actual output.
110 */
111 static ir_assignment *
copy(void * ctx,ir_variable * output,ir_variable * temp)112 copy(void *ctx, ir_variable *output, ir_variable *temp)
113 {
114 ir_dereference_variable *lhs = new(ctx) ir_dereference_variable(output);
115 ir_dereference_variable *rhs = new(ctx) ir_dereference_variable(temp);
116 return new(ctx) ir_assignment(lhs, rhs);
117 }
118
119 /** Insert a copy-back assignment before a "return" statement */
120 static void
emit_return_copy(const void * key,void * data,void * closure)121 emit_return_copy(const void *key, void *data, void *closure)
122 {
123 ir_return *ir = (ir_return *) closure;
124 ir->insert_before(copy(ir, (ir_variable *) key, (ir_variable *) data));
125 }
126
127 /** Insert a copy-back assignment at the end of the main() function */
128 static void
emit_main_copy(const void * key,void * data,void * closure)129 emit_main_copy(const void *key, void *data, void *closure)
130 {
131 ir_function_signature *sig = (ir_function_signature *) closure;
132 sig->body.push_tail(copy(sig, (ir_variable *) key, (ir_variable *) data));
133 }
134
135 ir_visitor_status
visit_leave(ir_return * ir)136 output_read_remover::visit_leave(ir_return *ir)
137 {
138 hash_table_call_foreach(replacements, emit_return_copy, ir);
139 return visit_continue;
140 }
141
142 ir_visitor_status
visit_leave(ir_function_signature * sig)143 output_read_remover::visit_leave(ir_function_signature *sig)
144 {
145 if (strcmp(sig->function_name(), "main") != 0)
146 return visit_continue;
147
148 hash_table_call_foreach(replacements, emit_main_copy, sig);
149 return visit_continue;
150 }
151
152 void
lower_output_reads(exec_list * instructions)153 lower_output_reads(exec_list *instructions)
154 {
155 output_read_remover v;
156 visit_list_elements(&v, instructions);
157 }
158