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 unsigned stage;
51 public:
52 output_read_remover(unsigned stage);
53 ~output_read_remover();
54 virtual ir_visitor_status visit(class ir_dereference_variable *);
55 virtual ir_visitor_status visit_leave(class ir_emit_vertex *);
56 virtual ir_visitor_status visit_leave(class ir_return *);
57 virtual ir_visitor_status visit_leave(class ir_function_signature *);
58 };
59
60 } /* anonymous namespace */
61
62 /**
63 * Hash function for the output variables - computes the hash of the name.
64 * NOTE: We're using the name string to ensure that the hash doesn't depend
65 * on any random factors, otherwise the output_read_remover could produce
66 * the random order of the assignments.
67 *
68 * NOTE: If you want to reuse this function please take into account that
69 * generally the names of the variables are non-unique.
70 */
71 static unsigned
hash_table_var_hash(const void * key)72 hash_table_var_hash(const void *key)
73 {
74 const ir_variable * var = static_cast<const ir_variable *>(key);
75 return _mesa_hash_string(var->name);
76 }
77
output_read_remover(unsigned stage)78 output_read_remover::output_read_remover(unsigned stage)
79 {
80 this->stage = stage;
81 replacements = _mesa_hash_table_create(NULL, hash_table_var_hash,
82 _mesa_key_pointer_equal);
83 }
84
~output_read_remover()85 output_read_remover::~output_read_remover()
86 {
87 _mesa_hash_table_destroy(replacements, NULL);
88 }
89
90 ir_visitor_status
visit(ir_dereference_variable * ir)91 output_read_remover::visit(ir_dereference_variable *ir)
92 {
93 if (ir->var->data.mode != ir_var_shader_out || ir->var->data.fb_fetch_output)
94 return visit_continue;
95
96 hash_entry *entry = _mesa_hash_table_search(replacements, ir->var);
97 ir_variable *temp = entry ? (ir_variable *) entry->data : NULL;
98
99 /* If we don't have an existing temporary, create one. */
100 if (temp == NULL) {
101 void *var_ctx = ralloc_parent(ir->var);
102 temp = new(var_ctx) ir_variable(ir->var->type, ir->var->name,
103 ir_var_temporary);
104 /* copy flags which affect arithematical precision */
105 temp->data.invariant = ir->var->data.invariant;
106 temp->data.precise = ir->var->data.precise;
107 temp->data.precision = ir->var->data.precision;
108 _mesa_hash_table_insert(replacements, ir->var, temp);
109 ir->var->insert_after(temp);
110 }
111
112 /* Update the dereference to use the temporary */
113 ir->var = temp;
114
115 return visit_continue;
116 }
117
118 /**
119 * Create an assignment to copy a temporary value back to the actual output.
120 */
121 static ir_assignment *
copy(void * ctx,ir_variable * output,ir_variable * temp)122 copy(void *ctx, ir_variable *output, ir_variable *temp)
123 {
124 ir_dereference_variable *lhs = new(ctx) ir_dereference_variable(output);
125 ir_dereference_variable *rhs = new(ctx) ir_dereference_variable(temp);
126 return new(ctx) ir_assignment(lhs, rhs);
127 }
128
129 /** Insert a copy-back assignment before a "return" statement or a call to
130 * EmitVertex().
131 */
132 static void
emit_return_copy(const void * key,void * data,void * closure)133 emit_return_copy(const void *key, void *data, void *closure)
134 {
135 ir_return *ir = (ir_return *) closure;
136 ir->insert_before(copy(ir, (ir_variable *) key, (ir_variable *) data));
137 }
138
139 /** Insert a copy-back assignment at the end of the main() function */
140 static void
emit_main_copy(const void * key,void * data,void * closure)141 emit_main_copy(const void *key, void *data, void *closure)
142 {
143 ir_function_signature *sig = (ir_function_signature *) closure;
144 sig->body.push_tail(copy(sig, (ir_variable *) key, (ir_variable *) data));
145 }
146
147 ir_visitor_status
visit_leave(ir_return * ir)148 output_read_remover::visit_leave(ir_return *ir)
149 {
150 hash_table_call_foreach(replacements, emit_return_copy, ir);
151 return visit_continue;
152 }
153
154 ir_visitor_status
visit_leave(ir_emit_vertex * ir)155 output_read_remover::visit_leave(ir_emit_vertex *ir)
156 {
157 hash_table_call_foreach(replacements, emit_return_copy, ir);
158 return visit_continue;
159 }
160
161 ir_visitor_status
visit_leave(ir_function_signature * sig)162 output_read_remover::visit_leave(ir_function_signature *sig)
163 {
164 if (strcmp(sig->function_name(), "main") != 0)
165 return visit_continue;
166
167 hash_table_call_foreach(replacements, emit_main_copy, sig);
168 return visit_continue;
169 }
170
171 void
lower_output_reads(unsigned stage,exec_list * instructions)172 lower_output_reads(unsigned stage, exec_list *instructions)
173 {
174 /* Due to the possible interactions between multiple tessellation control
175 * shader invocations, we leave output variables as-is.
176 */
177 if (stage == MESA_SHADER_TESS_CTRL)
178 return;
179
180 output_read_remover v(stage);
181 visit_list_elements(&v, instructions);
182 }
183