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 "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 ir_rvalue *cast =
106 new(mem_ctx) ir_expression(ir_unop_f2i, glsl_type::int_type, iter,
107 NULL);
108
109 iter = cast->constant_expression_value();
110 }
111
112 int iter_value = iter->get_int_component(0);
113
114 /* Make sure that the calculated number of iterations satisfies the exit
115 * condition. This is needed to catch off-by-one errors and some types of
116 * ill-formed loops. For example, we need to detect that the following
117 * loop does not have a maximum iteration count.
118 *
119 * for (float x = 0.0; x != 0.9; x += 0.2)
120 * ;
121 */
122 const int bias[] = { -1, 0, 1 };
123 bool valid_loop = false;
124
125 for (unsigned i = 0; i < Elements(bias); i++) {
126 iter = (increment->type->is_integer())
127 ? new(mem_ctx) ir_constant(iter_value + bias[i])
128 : new(mem_ctx) ir_constant(float(iter_value + bias[i]));
129
130 ir_expression *const mul =
131 new(mem_ctx) ir_expression(ir_binop_mul, increment->type, iter,
132 increment);
133
134 ir_expression *const add =
135 new(mem_ctx) ir_expression(ir_binop_add, mul->type, mul, from);
136
137 ir_expression *const cmp =
138 new(mem_ctx) ir_expression(op, glsl_type::bool_type, add, to);
139
140 ir_constant *const cmp_result = cmp->constant_expression_value();
141
142 assert(cmp_result != NULL);
143 if (cmp_result->get_bool_component(0)) {
144 iter_value += bias[i];
145 valid_loop = true;
146 break;
147 }
148 }
149
150 ralloc_free(mem_ctx);
151 return (valid_loop) ? iter_value : -1;
152 }
153
154
155 class loop_control_visitor : public ir_hierarchical_visitor {
156 public:
loop_control_visitor(loop_state * state)157 loop_control_visitor(loop_state *state)
158 {
159 this->state = state;
160 this->progress = false;
161 }
162
163 virtual ir_visitor_status visit_leave(ir_loop *ir);
164
165 loop_state *state;
166
167 bool progress;
168 };
169
170
171 ir_visitor_status
visit_leave(ir_loop * ir)172 loop_control_visitor::visit_leave(ir_loop *ir)
173 {
174 loop_variable_state *const ls = this->state->get(ir);
175
176 /* If we've entered a loop that hasn't been analyzed, something really,
177 * really bad has happened.
178 */
179 if (ls == NULL) {
180 assert(ls != NULL);
181 return visit_continue;
182 }
183
184 /* Search the loop terminating conditions for one of the form 'i < c' where
185 * i is a loop induction variable, c is a constant, and < is any relative
186 * operator.
187 */
188 int max_iterations = ls->max_iterations;
189
190 if(ir->from && ir->to && ir->increment)
191 max_iterations = calculate_iterations(ir->from, ir->to, ir->increment, (ir_expression_operation)ir->cmp);
192
193 if(max_iterations < 0)
194 max_iterations = INT_MAX;
195
196 foreach_list(node, &ls->terminators) {
197 loop_terminator *t = (loop_terminator *) node;
198 ir_if *if_stmt = t->ir;
199
200 /* If-statements can be either 'if (expr)' or 'if (deref)'. We only care
201 * about the former here.
202 */
203 ir_expression *cond = if_stmt->condition->as_expression();
204 if (cond == NULL)
205 continue;
206
207 switch (cond->operation) {
208 case ir_binop_less:
209 case ir_binop_greater:
210 case ir_binop_lequal:
211 case ir_binop_gequal: {
212 /* The expressions that we care about will either be of the form
213 * 'counter < limit' or 'limit < counter'. Figure out which is
214 * which.
215 */
216 ir_rvalue *counter = cond->operands[0]->as_dereference_variable();
217 ir_constant *limit = cond->operands[1]->as_constant();
218 enum ir_expression_operation cmp = cond->operation;
219
220 if (limit == NULL) {
221 counter = cond->operands[1]->as_dereference_variable();
222 limit = cond->operands[0]->as_constant();
223
224 switch (cmp) {
225 case ir_binop_less: cmp = ir_binop_gequal; break;
226 case ir_binop_greater: cmp = ir_binop_lequal; break;
227 case ir_binop_lequal: cmp = ir_binop_greater; break;
228 case ir_binop_gequal: cmp = ir_binop_less; break;
229 default: assert(!"Should not get here.");
230 }
231 }
232
233 if ((counter == NULL) || (limit == NULL))
234 break;
235
236 ir_variable *var = counter->variable_referenced();
237
238 ir_rvalue *init = find_initial_value(ir, var);
239
240 foreach_list(iv_node, &ls->induction_variables) {
241 loop_variable *lv = (loop_variable *) iv_node;
242
243 if (lv->var == var) {
244 const int iterations = calculate_iterations(init, limit,
245 lv->increment,
246 cmp);
247 if (iterations >= 0) {
248 /* If the new iteration count is lower than the previously
249 * believed iteration count, update the loop control values.
250 */
251 if (iterations < max_iterations) {
252 ir->from = init->clone(ir, NULL);
253 ir->to = limit->clone(ir, NULL);
254 ir->increment = lv->increment->clone(ir, NULL);
255 ir->counter = lv->var;
256 ir->cmp = cmp;
257
258 max_iterations = iterations;
259 }
260
261 /* Remove the conditional break statement. The loop
262 * controls are now set such that the exit condition will be
263 * satisfied.
264 */
265 if_stmt->remove();
266
267 assert(ls->num_loop_jumps > 0);
268 ls->num_loop_jumps--;
269
270 this->progress = true;
271 }
272
273 break;
274 }
275 }
276 break;
277 }
278
279 default:
280 break;
281 }
282 }
283
284 /* If we have proven the one of the loop exit conditions is satisifed before
285 * running the loop once, remove the loop.
286 */
287 if (max_iterations == 0)
288 ir->remove();
289 else
290 ls->max_iterations = max_iterations;
291
292 return visit_continue;
293 }
294
295
296 bool
set_loop_controls(exec_list * instructions,loop_state * ls)297 set_loop_controls(exec_list *instructions, loop_state *ls)
298 {
299 loop_control_visitor v(ls);
300
301 v.run(instructions);
302
303 return v.progress;
304 }
305