aboutsummaryrefslogtreecommitdiff
path: root/mesalib/src/glsl/loop_unroll.cpp
blob: 6eced17365b859f1276a2227be90cfc9a8c885b6 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
/*
 * Copyright © 2010 Intel Corporation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */

#include "glsl_types.h"
#include "loop_analysis.h"
#include "ir_hierarchical_visitor.h"

namespace {

class loop_unroll_visitor : public ir_hierarchical_visitor {
public:
   loop_unroll_visitor(loop_state *state, unsigned max_iterations)
   {
      this->state = state;
      this->progress = false;
      this->max_iterations = max_iterations;
   }

   virtual ir_visitor_status visit_leave(ir_loop *ir);
   void simple_unroll(ir_loop *ir, int iterations);
   void complex_unroll(ir_loop *ir, int iterations,
                       bool continue_from_then_branch);
   void splice_post_if_instructions(ir_if *ir_if, exec_list *splice_dest);

   loop_state *state;

   bool progress;
   unsigned max_iterations;
};

} /* anonymous namespace */

static bool
is_break(ir_instruction *ir)
{
   return ir != NULL && ir->ir_type == ir_type_loop_jump
		     && ((ir_loop_jump *) ir)->is_break();
}

class loop_unroll_count : public ir_hierarchical_visitor {
public:
   int nodes;
   bool fail;

   loop_unroll_count(exec_list *list)
   {
      nodes = 0;
      fail = false;

      run(list);
   }

   virtual ir_visitor_status visit_enter(ir_assignment *ir)
   {
      nodes++;
      return visit_continue;
   }

   virtual ir_visitor_status visit_enter(ir_expression *ir)
   {
      nodes++;
      return visit_continue;
   }

   virtual ir_visitor_status visit_enter(ir_loop *ir)
   {
      fail = true;
      return visit_continue;
   }
};


/**
 * Unroll a loop which does not contain any jumps.  For example, if the input
 * is:
 *
 *     (loop (...) ...instrs...)
 *
 * And the iteration count is 3, the output will be:
 *
 *     ...instrs... ...instrs... ...instrs...
 */
void
loop_unroll_visitor::simple_unroll(ir_loop *ir, int iterations)
{
   void *const mem_ctx = ralloc_parent(ir);

   for (int i = 0; i < iterations; i++) {
      exec_list copy_list;

      copy_list.make_empty();
      clone_ir_list(mem_ctx, &copy_list, &ir->body_instructions);

      ir->insert_before(&copy_list);
   }

   /* The loop has been replaced by the unrolled copies.  Remove the original
    * loop from the IR sequence.
    */
   ir->remove();

   this->progress = true;
}


/**
 * Unroll a loop whose last statement is an ir_if.  If \c
 * continue_from_then_branch is true, the loop is repeated only when the
 * "then" branch of the if is taken; otherwise it is repeated only when the
 * "else" branch of the if is taken.
 *
 * For example, if the input is:
 *
 *     (loop (...)
 *      ...body...
 *      (if (cond)
 *          (...then_instrs...)
 *        (...else_instrs...)))
 *
 * And the iteration count is 3, and \c continue_from_then_branch is true,
 * then the output will be:
 *
 *     ...body...
 *     (if (cond)
 *         (...then_instrs...
 *          ...body...
 *          (if (cond)
 *              (...then_instrs...
 *               ...body...
 *               (if (cond)
 *                   (...then_instrs...)
 *                 (...else_instrs...)))
 *            (...else_instrs...)))
 *       (...else_instrs))
 */
void
loop_unroll_visitor::complex_unroll(ir_loop *ir, int iterations,
                                    bool continue_from_then_branch)
{
   void *const mem_ctx = ralloc_parent(ir);
   ir_instruction *ir_to_replace = ir;

   for (int i = 0; i < iterations; i++) {
      exec_list copy_list;

      copy_list.make_empty();
      clone_ir_list(mem_ctx, &copy_list, &ir->body_instructions);

      ir_if *ir_if = ((ir_instruction *) copy_list.get_tail())->as_if();
      assert(ir_if != NULL);

      ir_to_replace->insert_before(&copy_list);
      ir_to_replace->remove();

      /* placeholder that will be removed in the next iteration */
      ir_to_replace =
         new(mem_ctx) ir_loop_jump(ir_loop_jump::jump_continue);

      exec_list *const list = (continue_from_then_branch)
         ? &ir_if->then_instructions : &ir_if->else_instructions;

      list->push_tail(ir_to_replace);
   }

   ir_to_replace->remove();

   this->progress = true;
}


/**
 * Move all of the instructions which follow \c ir_if to the end of
 * \c splice_dest.
 *
 * For example, in the code snippet:
 *
 *     (if (cond)
 *         (...then_instructions...
 *          break)
 *       (...else_instructions...))
 *     ...post_if_instructions...
 *
 * If \c ir_if points to the "if" instruction, and \c splice_dest points to
 * (...else_instructions...), the code snippet is transformed into:
 *
 *     (if (cond)
 *         (...then_instructions...
 *          break)
 *       (...else_instructions...
 *        ...post_if_instructions...))
 */
void
loop_unroll_visitor::splice_post_if_instructions(ir_if *ir_if,
                                                 exec_list *splice_dest)
{
   while (!ir_if->get_next()->is_tail_sentinel()) {
      ir_instruction *move_ir = (ir_instruction *) ir_if->get_next();

      move_ir->remove();
      splice_dest->push_tail(move_ir);
   }
}


ir_visitor_status
loop_unroll_visitor::visit_leave(ir_loop *ir)
{
   loop_variable_state *const ls = this->state->get(ir);
   int iterations;

   /* If we've entered a loop that hasn't been analyzed, something really,
    * really bad has happened.
    */
   if (ls == NULL) {
      assert(ls != NULL);
      return visit_continue;
   }

   /* Don't try to unroll loops where the number of iterations is not known
    * at compile-time.
    */
   if (ls->limiting_terminator == NULL)
      return visit_continue;

   iterations = ls->limiting_terminator->iterations;

   /* Don't try to unroll loops that have zillions of iterations either.
    */
   if (iterations > (int) max_iterations)
      return visit_continue;

   /* Don't try to unroll nested loops and loops with a huge body.
    */
   loop_unroll_count count(&ir->body_instructions);

   if (count.fail || count.nodes * iterations > (int)max_iterations * 5)
      return visit_continue;

   /* Note: the limiting terminator contributes 1 to ls->num_loop_jumps.
    * We'll be removing the limiting terminator before we unroll.
    */
   assert(ls->num_loop_jumps > 0);
   unsigned predicted_num_loop_jumps = ls->num_loop_jumps - 1;

   if (predicted_num_loop_jumps > 1)
      return visit_continue;

   if (predicted_num_loop_jumps == 0) {
      ls->limiting_terminator->ir->remove();
      simple_unroll(ir, iterations);
      return visit_continue;
   }

   ir_instruction *last_ir = (ir_instruction *) ir->body_instructions.get_tail();
   assert(last_ir != NULL);

   if (is_break(last_ir)) {
      /* If the only loop-jump is a break at the end of the loop, the loop
       * will execute exactly once.  Remove the break and use the simple
       * unroller with an iteration count of 1.
       */
      last_ir->remove();

      ls->limiting_terminator->ir->remove();
      simple_unroll(ir, 1);
      return visit_continue;
   }

   foreach_list(node, &ir->body_instructions) {
      /* recognize loops in the form produced by ir_lower_jumps */
      ir_instruction *cur_ir = (ir_instruction *) node;

      /* Skip the limiting terminator, since it will go away when we
       * unroll.
       */
      if (cur_ir == ls->limiting_terminator->ir)
         continue;

      ir_if *ir_if = cur_ir->as_if();
      if (ir_if != NULL) {
         /* Determine which if-statement branch, if any, ends with a
          * break.  The branch that did *not* have the break will get a
          * temporary continue inserted in each iteration of the loop
          * unroll.
          *
          * Note that since ls->num_loop_jumps is <= 1, it is impossible
          * for both branches to end with a break.
          */
         ir_instruction *ir_if_last =
            (ir_instruction *) ir_if->then_instructions.get_tail();

         if (is_break(ir_if_last)) {
            ls->limiting_terminator->ir->remove();
            splice_post_if_instructions(ir_if, &ir_if->else_instructions);
            ir_if_last->remove();
            complex_unroll(ir, iterations, false);
            return visit_continue;
         } else {
            ir_if_last =
               (ir_instruction *) ir_if->else_instructions.get_tail();

            if (is_break(ir_if_last)) {
               ls->limiting_terminator->ir->remove();
               splice_post_if_instructions(ir_if, &ir_if->then_instructions);
               ir_if_last->remove();
               complex_unroll(ir, iterations, true);
               return visit_continue;
            }
         }
      }
   }

   /* Did not find the break statement.  It must be in a complex if-nesting,
    * so don't try to unroll.
    */
   return visit_continue;
}


bool
unroll_loops(exec_list *instructions, loop_state *ls, unsigned max_iterations)
{
   loop_unroll_visitor v(ls, max_iterations);

   v.run(instructions);

   return v.progress;
}