1 /*
2 * Copyright © 2010 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
21 * DEALINGS IN THE SOFTWARE.
22 */
23
24 #include <limits.h>
25 #include "main/compiler.h"
26 #include "compiler/glsl_types.h"
27 #include "loop_analysis.h"
28 #include "ir_hierarchical_visitor.h"
29
30 /**
31 * Find an initializer of a variable outside a loop
32 *
33 * Works backwards from the loop to find the pre-loop value of the variable.
34 * This is used, for example, to find the initial value of loop induction
35 * variables.
36 *
37 * \param loop Loop where \c var is an induction variable
38 * \param var Variable whose initializer is to be found
39 *
40 * \return
41 * The \c ir_rvalue assigned to the variable outside the loop. May return
42 * \c NULL if no initializer can be found.
43 */
44 ir_rvalue *
find_initial_value(ir_loop * loop,ir_variable * var)45 find_initial_value(ir_loop *loop, ir_variable *var)
46 {
47 for (exec_node *node = loop->prev;
48 !node->is_head_sentinel();
49 node = node->prev) {
50 ir_instruction *ir = (ir_instruction *) node;
51
52 switch (ir->ir_type) {
53 case ir_type_call:
54 case ir_type_loop:
55 case ir_type_loop_jump:
56 case ir_type_return:
57 case ir_type_if:
58 return NULL;
59
60 case ir_type_function:
61 case ir_type_function_signature:
62 assert(!"Should not get here.");
63 return NULL;
64
65 case ir_type_assignment: {
66 ir_assignment *assign = ir->as_assignment();
67 ir_variable *assignee = assign->lhs->whole_variable_referenced();
68
69 if (assignee == var)
70 return (assign->condition != NULL) ? NULL : assign->rhs;
71
72 break;
73 }
74
75 default:
76 break;
77 }
78 }
79
80 return NULL;
81 }
82
83
84 int
calculate_iterations(ir_rvalue * from,ir_rvalue * to,ir_rvalue * increment,enum ir_expression_operation op)85 calculate_iterations(ir_rvalue *from, ir_rvalue *to, ir_rvalue *increment,
86 enum ir_expression_operation op)
87 {
88 if (from == NULL || to == NULL || increment == NULL)
89 return -1;
90
91 void *mem_ctx = ralloc_context(NULL);
92
93 ir_expression *const sub =
94 new(mem_ctx) ir_expression(ir_binop_sub, from->type, to, from);
95
96 ir_expression *const div =
97 new(mem_ctx) ir_expression(ir_binop_div, sub->type, sub, increment);
98
99 ir_constant *iter = div->constant_expression_value();
100
101 if (iter == NULL)
102 return -1;
103
104 if (!iter->type->is_integer()) {
105 const ir_expression_operation op = iter->type->is_double()
106 ? ir_unop_d2i : ir_unop_f2i;
107 ir_rvalue *cast =
108 new(mem_ctx) ir_expression(op, glsl_type::int_type, iter, NULL);
109
110 iter = cast->constant_expression_value();
111 }
112
113 int iter_value = iter->get_int_component(0);
114
115 /* Make sure that the calculated number of iterations satisfies the exit
116 * condition. This is needed to catch off-by-one errors and some types of
117 * ill-formed loops. For example, we need to detect that the following
118 * loop does not have a maximum iteration count.
119 *
120 * for (float x = 0.0; x != 0.9; x += 0.2)
121 * ;
122 */
123 const int bias[] = { -1, 0, 1 };
124 bool valid_loop = false;
125
126 for (unsigned i = 0; i < ARRAY_SIZE(bias); i++) {
127 /* Increment may be of type int, uint or float. */
128 switch (increment->type->base_type) {
129 case GLSL_TYPE_INT:
130 iter = new(mem_ctx) ir_constant(iter_value + bias[i]);
131 break;
132 case GLSL_TYPE_UINT:
133 iter = new(mem_ctx) ir_constant(unsigned(iter_value + bias[i]));
134 break;
135 case GLSL_TYPE_FLOAT:
136 iter = new(mem_ctx) ir_constant(float(iter_value + bias[i]));
137 break;
138 case GLSL_TYPE_DOUBLE:
139 iter = new(mem_ctx) ir_constant(double(iter_value + bias[i]));
140 break;
141 default:
142 unreachable("Unsupported type for loop iterator.");
143 }
144
145 ir_expression *const mul =
146 new(mem_ctx) ir_expression(ir_binop_mul, increment->type, iter,
147 increment);
148
149 ir_expression *const add =
150 new(mem_ctx) ir_expression(ir_binop_add, mul->type, mul, from);
151
152 ir_expression *const cmp =
153 new(mem_ctx) ir_expression(op, glsl_type::bool_type, add, to);
154
155 ir_constant *const cmp_result = cmp->constant_expression_value();
156
157 assert(cmp_result != NULL);
158 if (cmp_result->get_bool_component(0)) {
159 iter_value += bias[i];
160 valid_loop = true;
161 break;
162 }
163 }
164
165 ralloc_free(mem_ctx);
166 return (valid_loop) ? iter_value : -1;
167 }
168
169 namespace {
170
171 class loop_control_visitor : public ir_hierarchical_visitor {
172 public:
loop_control_visitor(loop_state * state)173 loop_control_visitor(loop_state *state)
174 {
175 this->state = state;
176 this->progress = false;
177 }
178
179 virtual ir_visitor_status visit_leave(ir_loop *ir);
180
181 loop_state *state;
182
183 bool progress;
184 };
185
186 } /* anonymous namespace */
187
188 ir_visitor_status
visit_leave(ir_loop * ir)189 loop_control_visitor::visit_leave(ir_loop *ir)
190 {
191 loop_variable_state *const ls = this->state->get(ir);
192
193 /* If we've entered a loop that hasn't been analyzed, something really,
194 * really bad has happened.
195 */
196 if (ls == NULL) {
197 assert(ls != NULL);
198 return visit_continue;
199 }
200
201 if (ls->limiting_terminator != NULL) {
202 /* If the limiting terminator has an iteration count of zero, then we've
203 * proven that the loop cannot run, so delete it.
204 */
205 int iterations = ls->limiting_terminator->iterations;
206 if (iterations == 0) {
207 ir->remove();
208 this->progress = true;
209 return visit_continue;
210 }
211 }
212
213 /* Remove the conditional break statements associated with all terminators
214 * that are associated with a fixed iteration count, except for the one
215 * associated with the limiting terminator--that one needs to stay, since
216 * it terminates the loop. Exception: if the loop still has a normative
217 * bound, then that terminates the loop, so we don't even need the limiting
218 * terminator.
219 */
220 foreach_in_list(loop_terminator, t, &ls->terminators) {
221 if (t->iterations < 0)
222 continue;
223
224 if (t != ls->limiting_terminator) {
225 t->ir->remove();
226
227 assert(ls->num_loop_jumps > 0);
228 ls->num_loop_jumps--;
229
230 this->progress = true;
231 }
232 }
233
234 return visit_continue;
235 }
236
237
238 bool
set_loop_controls(exec_list * instructions,loop_state * ls)239 set_loop_controls(exec_list *instructions, loop_state *ls)
240 {
241 loop_control_visitor v(ls);
242
243 v.run(instructions);
244
245 return v.progress;
246 }
247