1/*
2 * Copyright © 2012 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 DEALINGS
21 * IN THE SOFTWARE.
22 *
23 * Authors:
24 *    Eric Anholt <eric@anholt.net>
25 *
26 */
27
28#include "brw_cfg.h"
29#include "brw_fs_live_variables.h"
30
31using namespace brw;
32
33#define MAX_INSTRUCTION (1 << 30)
34
35/** @file brw_fs_live_variables.cpp
36 *
37 * Support for calculating liveness information about virtual GRFs.
38 *
39 * This produces a live interval for each whole virtual GRF.  We could
40 * choose to expose per-component live intervals for VGRFs of size > 1,
41 * but we currently do not.  It is easier for the consumers of this
42 * information to work with whole VGRFs.
43 *
44 * However, we internally track use/def information at the per-GRF level for
45 * greater accuracy.  Large VGRFs may be accessed piecemeal over many
46 * (possibly non-adjacent) instructions.  In this case, examining a single
47 * instruction is insufficient to decide whether a whole VGRF is ultimately
48 * used or defined.  Tracking individual components allows us to easily
49 * assemble this information.
50 *
51 * See Muchnick's Advanced Compiler Design and Implementation, section
52 * 14.1 (p444).
53 */
54
55void
56fs_live_variables::setup_one_read(struct block_data *bd, fs_inst *inst,
57                                  int ip, const fs_reg &reg)
58{
59   int var = var_from_reg(reg);
60   assert(var < num_vars);
61
62   start[var] = MIN2(start[var], ip);
63   end[var] = MAX2(end[var], ip);
64
65   /* The use[] bitset marks when the block makes use of a variable (VGRF
66    * channel) without having completely defined that variable within the
67    * block.
68    */
69   if (!BITSET_TEST(bd->def, var))
70      BITSET_SET(bd->use, var);
71}
72
73void
74fs_live_variables::setup_one_write(struct block_data *bd, fs_inst *inst,
75                                   int ip, const fs_reg &reg)
76{
77   int var = var_from_reg(reg);
78   assert(var < num_vars);
79
80   start[var] = MIN2(start[var], ip);
81   end[var] = MAX2(end[var], ip);
82
83   /* The def[] bitset marks when an initialization in a block completely
84    * screens off previous updates of that variable (VGRF channel).
85    */
86   if (inst->dst.file == VGRF && !inst->is_partial_write()) {
87      if (!BITSET_TEST(bd->use, var))
88         BITSET_SET(bd->def, var);
89   }
90}
91
92/**
93 * Sets up the use[] and def[] bitsets.
94 *
95 * The basic-block-level live variable analysis needs to know which
96 * variables get used before they're completely defined, and which
97 * variables are completely defined before they're used.
98 *
99 * These are tracked at the per-component level, rather than whole VGRFs.
100 */
101void
102fs_live_variables::setup_def_use()
103{
104   int ip = 0;
105
106   foreach_block (block, cfg) {
107      assert(ip == block->start_ip);
108      if (block->num > 0)
109	 assert(cfg->blocks[block->num - 1]->end_ip == ip - 1);
110
111      struct block_data *bd = &block_data[block->num];
112
113      foreach_inst_in_block(fs_inst, inst, block) {
114	 /* Set use[] for this instruction */
115	 for (unsigned int i = 0; i < inst->sources; i++) {
116            fs_reg reg = inst->src[i];
117
118            if (reg.file != VGRF)
119               continue;
120
121            for (unsigned j = 0; j < regs_read(inst, i); j++) {
122               setup_one_read(bd, inst, ip, reg);
123               reg.offset += REG_SIZE;
124            }
125	 }
126
127         bd->flag_use[0] |= inst->flags_read(v->devinfo) & ~bd->flag_def[0];
128
129         /* Set def[] for this instruction */
130         if (inst->dst.file == VGRF) {
131            fs_reg reg = inst->dst;
132            for (unsigned j = 0; j < regs_written(inst); j++) {
133               setup_one_write(bd, inst, ip, reg);
134               reg.offset += REG_SIZE;
135            }
136	 }
137
138         if (!inst->predicate && inst->exec_size >= 8)
139            bd->flag_def[0] |= inst->flags_written() & ~bd->flag_use[0];
140
141	 ip++;
142      }
143   }
144}
145
146/**
147 * The algorithm incrementally sets bits in liveout and livein,
148 * propagating it through control flow.  It will eventually terminate
149 * because it only ever adds bits, and stops when no bits are added in
150 * a pass.
151 */
152void
153fs_live_variables::compute_live_variables()
154{
155   bool cont = true;
156
157   while (cont) {
158      cont = false;
159
160      foreach_block_reverse (block, cfg) {
161         struct block_data *bd = &block_data[block->num];
162
163	 /* Update liveout */
164	 foreach_list_typed(bblock_link, child_link, link, &block->children) {
165            struct block_data *child_bd = &block_data[child_link->block->num];
166
167	    for (int i = 0; i < bitset_words; i++) {
168               BITSET_WORD new_liveout = (child_bd->livein[i] &
169                                          ~bd->liveout[i]);
170               if (new_liveout) {
171                  bd->liveout[i] |= new_liveout;
172                  cont = true;
173               }
174	    }
175            BITSET_WORD new_liveout = (child_bd->flag_livein[0] &
176                                       ~bd->flag_liveout[0]);
177            if (new_liveout) {
178               bd->flag_liveout[0] |= new_liveout;
179               cont = true;
180            }
181	 }
182
183         /* Update livein */
184         for (int i = 0; i < bitset_words; i++) {
185            BITSET_WORD new_livein = (bd->use[i] |
186                                      (bd->liveout[i] &
187                                       ~bd->def[i]));
188            if (new_livein & ~bd->livein[i]) {
189               bd->livein[i] |= new_livein;
190               cont = true;
191            }
192         }
193         BITSET_WORD new_livein = (bd->flag_use[0] |
194                                   (bd->flag_liveout[0] &
195                                    ~bd->flag_def[0]));
196         if (new_livein & ~bd->flag_livein[0]) {
197            bd->flag_livein[0] |= new_livein;
198            cont = true;
199         }
200      }
201   }
202}
203
204/**
205 * Extend the start/end ranges for each variable to account for the
206 * new information calculated from control flow.
207 */
208void
209fs_live_variables::compute_start_end()
210{
211   foreach_block (block, cfg) {
212      struct block_data *bd = &block_data[block->num];
213
214      for (int i = 0; i < num_vars; i++) {
215         if (BITSET_TEST(bd->livein, i)) {
216            start[i] = MIN2(start[i], block->start_ip);
217            end[i] = MAX2(end[i], block->start_ip);
218         }
219
220         if (BITSET_TEST(bd->liveout, i)) {
221            start[i] = MIN2(start[i], block->end_ip);
222            end[i] = MAX2(end[i], block->end_ip);
223         }
224      }
225   }
226}
227
228fs_live_variables::fs_live_variables(fs_visitor *v, const cfg_t *cfg)
229   : v(v), cfg(cfg)
230{
231   mem_ctx = ralloc_context(NULL);
232
233   num_vgrfs = v->alloc.count;
234   num_vars = 0;
235   var_from_vgrf = rzalloc_array(mem_ctx, int, num_vgrfs);
236   for (int i = 0; i < num_vgrfs; i++) {
237      var_from_vgrf[i] = num_vars;
238      num_vars += v->alloc.sizes[i];
239   }
240
241   vgrf_from_var = rzalloc_array(mem_ctx, int, num_vars);
242   for (int i = 0; i < num_vgrfs; i++) {
243      for (unsigned j = 0; j < v->alloc.sizes[i]; j++) {
244         vgrf_from_var[var_from_vgrf[i] + j] = i;
245      }
246   }
247
248   start = ralloc_array(mem_ctx, int, num_vars);
249   end = rzalloc_array(mem_ctx, int, num_vars);
250   for (int i = 0; i < num_vars; i++) {
251      start[i] = MAX_INSTRUCTION;
252      end[i] = -1;
253   }
254
255   block_data= rzalloc_array(mem_ctx, struct block_data, cfg->num_blocks);
256
257   bitset_words = BITSET_WORDS(num_vars);
258   for (int i = 0; i < cfg->num_blocks; i++) {
259      block_data[i].def = rzalloc_array(mem_ctx, BITSET_WORD, bitset_words);
260      block_data[i].use = rzalloc_array(mem_ctx, BITSET_WORD, bitset_words);
261      block_data[i].livein = rzalloc_array(mem_ctx, BITSET_WORD, bitset_words);
262      block_data[i].liveout = rzalloc_array(mem_ctx, BITSET_WORD, bitset_words);
263
264      block_data[i].flag_def[0] = 0;
265      block_data[i].flag_use[0] = 0;
266      block_data[i].flag_livein[0] = 0;
267      block_data[i].flag_liveout[0] = 0;
268   }
269
270   setup_def_use();
271   compute_live_variables();
272   compute_start_end();
273}
274
275fs_live_variables::~fs_live_variables()
276{
277   ralloc_free(mem_ctx);
278}
279
280void
281fs_visitor::invalidate_live_intervals()
282{
283   ralloc_free(live_intervals);
284   live_intervals = NULL;
285}
286
287/**
288 * Compute the live intervals for each virtual GRF.
289 *
290 * This uses the per-component use/def data, but combines it to produce
291 * information about whole VGRFs.
292 */
293void
294fs_visitor::calculate_live_intervals()
295{
296   if (this->live_intervals)
297      return;
298
299   int num_vgrfs = this->alloc.count;
300   ralloc_free(this->virtual_grf_start);
301   ralloc_free(this->virtual_grf_end);
302   virtual_grf_start = ralloc_array(mem_ctx, int, num_vgrfs);
303   virtual_grf_end = ralloc_array(mem_ctx, int, num_vgrfs);
304
305   for (int i = 0; i < num_vgrfs; i++) {
306      virtual_grf_start[i] = MAX_INSTRUCTION;
307      virtual_grf_end[i] = -1;
308   }
309
310   this->live_intervals = new(mem_ctx) fs_live_variables(this, cfg);
311
312   /* Merge the per-component live ranges to whole VGRF live ranges. */
313   for (int i = 0; i < live_intervals->num_vars; i++) {
314      int vgrf = live_intervals->vgrf_from_var[i];
315      virtual_grf_start[vgrf] = MIN2(virtual_grf_start[vgrf],
316                                     live_intervals->start[i]);
317      virtual_grf_end[vgrf] = MAX2(virtual_grf_end[vgrf],
318                                   live_intervals->end[i]);
319   }
320}
321
322bool
323fs_live_variables::vars_interfere(int a, int b)
324{
325   return !(end[b] <= start[a] ||
326            end[a] <= start[b]);
327}
328
329bool
330fs_visitor::virtual_grf_interferes(int a, int b)
331{
332   return !(virtual_grf_end[a] <= virtual_grf_start[b] ||
333            virtual_grf_end[b] <= virtual_grf_start[a]);
334}
335