2 * Copyright © 2012 Intel Corporation
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:
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
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
24 * Eric Anholt <eric@anholt.net>
32 * Walks the shader instructions generated and creates a set of basic
33 * blocks with successor/predecessor edges connecting them.
37 pop_stack(exec_list
*list
)
39 bblock_link
*link
= (bblock_link
*)list
->get_tail();
40 bblock_t
*block
= link
->block
;
47 link(void *mem_ctx
, bblock_t
*block
, enum bblock_link_kind kind
)
49 bblock_link
*l
= new(mem_ctx
) bblock_link(block
, kind
);
54 push_stack(exec_list
*list
, void *mem_ctx
, bblock_t
*block
)
56 /* The kind of the link is immaterial, but we need to provide one since
57 * this is (ab)using the edge data structure in order to implement a stack.
59 list
->push_tail(link(mem_ctx
, block
, bblock_link_logical
));
62 bblock_t::bblock_t(cfg_t
*cfg
) :
63 cfg(cfg
), idom(NULL
), start_ip(0), end_ip(0), num(0), cycle_count(0)
65 instructions
.make_empty();
67 children
.make_empty();
71 bblock_t::add_successor(void *mem_ctx
, bblock_t
*successor
,
72 enum bblock_link_kind kind
)
74 successor
->parents
.push_tail(::link(mem_ctx
, this, kind
));
75 children
.push_tail(::link(mem_ctx
, successor
, kind
));
79 bblock_t::is_predecessor_of(const bblock_t
*block
,
80 enum bblock_link_kind kind
) const
82 foreach_list_typed_safe (bblock_link
, parent
, link
, &block
->parents
) {
83 if (parent
->block
== this && parent
->kind
<= kind
) {
92 bblock_t::is_successor_of(const bblock_t
*block
,
93 enum bblock_link_kind kind
) const
95 foreach_list_typed_safe (bblock_link
, child
, link
, &block
->children
) {
96 if (child
->block
== this && child
->kind
<= kind
) {
105 ends_block(const backend_instruction
*inst
)
107 enum opcode op
= inst
->opcode
;
109 return op
== BRW_OPCODE_IF
||
110 op
== BRW_OPCODE_ELSE
||
111 op
== BRW_OPCODE_CONTINUE
||
112 op
== BRW_OPCODE_BREAK
||
113 op
== BRW_OPCODE_DO
||
114 op
== BRW_OPCODE_WHILE
;
118 starts_block(const backend_instruction
*inst
)
120 enum opcode op
= inst
->opcode
;
122 return op
== BRW_OPCODE_DO
||
123 op
== BRW_OPCODE_ENDIF
;
127 bblock_t::can_combine_with(const bblock_t
*that
) const
129 if ((const bblock_t
*)this->link
.next
!= that
)
132 if (ends_block(this->end()) ||
133 starts_block(that
->start()))
140 bblock_t::combine_with(bblock_t
*that
)
142 assert(this->can_combine_with(that
));
143 foreach_list_typed (bblock_link
, link
, link
, &that
->parents
) {
144 assert(link
->block
== this);
147 this->end_ip
= that
->end_ip
;
148 this->instructions
.append_list(&that
->instructions
);
150 this->cfg
->remove_block(that
);
154 bblock_t::dump(backend_shader
*s
) const
156 int ip
= this->start_ip
;
157 foreach_inst_in_block(backend_instruction
, inst
, this) {
158 fprintf(stderr
, "%5d: ", ip
);
159 s
->dump_instruction(inst
);
164 cfg_t::cfg_t(exec_list
*instructions
)
166 mem_ctx
= ralloc_context(NULL
);
167 block_list
.make_empty();
173 bblock_t
*cur
= NULL
;
176 bblock_t
*entry
= new_block();
177 bblock_t
*cur_if
= NULL
; /**< BB ending with IF. */
178 bblock_t
*cur_else
= NULL
; /**< BB ending with ELSE. */
179 bblock_t
*cur_endif
= NULL
; /**< BB starting with ENDIF. */
180 bblock_t
*cur_do
= NULL
; /**< BB starting with DO. */
181 bblock_t
*cur_while
= NULL
; /**< BB immediately following WHILE. */
182 exec_list if_stack
, else_stack
, do_stack
, while_stack
;
185 set_next_block(&cur
, entry
, ip
);
187 foreach_in_list_safe(backend_instruction
, inst
, instructions
) {
188 /* set_next_block wants the post-incremented ip */
191 inst
->exec_node::remove();
193 switch (inst
->opcode
) {
195 cur
->instructions
.push_tail(inst
);
197 /* Push our information onto a stack so we can recover from
200 push_stack(&if_stack
, mem_ctx
, cur_if
);
201 push_stack(&else_stack
, mem_ctx
, cur_else
);
207 /* Set up our immediately following block, full of "then"
211 cur_if
->add_successor(mem_ctx
, next
, bblock_link_logical
);
213 set_next_block(&cur
, next
, ip
);
216 case BRW_OPCODE_ELSE
:
217 cur
->instructions
.push_tail(inst
);
222 assert(cur_if
!= NULL
);
223 cur_if
->add_successor(mem_ctx
, next
, bblock_link_logical
);
225 set_next_block(&cur
, next
, ip
);
228 case BRW_OPCODE_ENDIF
: {
229 if (cur
->instructions
.is_empty()) {
230 /* New block was just created; use it. */
233 cur_endif
= new_block();
235 cur
->add_successor(mem_ctx
, cur_endif
, bblock_link_logical
);
237 set_next_block(&cur
, cur_endif
, ip
- 1);
240 cur
->instructions
.push_tail(inst
);
243 cur_else
->add_successor(mem_ctx
, cur_endif
, bblock_link_logical
);
245 assert(cur_if
!= NULL
);
246 cur_if
->add_successor(mem_ctx
, cur_endif
, bblock_link_logical
);
249 assert(cur_if
->end()->opcode
== BRW_OPCODE_IF
);
250 assert(!cur_else
|| cur_else
->end()->opcode
== BRW_OPCODE_ELSE
);
252 /* Pop the stack so we're in the previous if/else/endif */
253 cur_if
= pop_stack(&if_stack
);
254 cur_else
= pop_stack(&else_stack
);
258 /* Push our information onto a stack so we can recover from
261 push_stack(&do_stack
, mem_ctx
, cur_do
);
262 push_stack(&while_stack
, mem_ctx
, cur_while
);
264 /* Set up the block just after the while. Don't know when exactly
265 * it will start, yet.
267 cur_while
= new_block();
269 if (cur
->instructions
.is_empty()) {
270 /* New block was just created; use it. */
273 cur_do
= new_block();
275 cur
->add_successor(mem_ctx
, cur_do
, bblock_link_logical
);
277 set_next_block(&cur
, cur_do
, ip
- 1);
280 cur
->instructions
.push_tail(inst
);
282 /* Represent divergent execution of the loop as a pair of alternative
283 * edges coming out of the DO instruction: For any physical iteration
284 * of the loop a given logical thread can either start off enabled
285 * (which is represented as the "next" successor), or disabled (if it
286 * has reached a non-uniform exit of the loop during a previous
287 * iteration, which is represented as the "cur_while" successor).
289 * The disabled edge will be taken by the logical thread anytime we
290 * arrive at the DO instruction through a back-edge coming from a
291 * conditional exit of the loop where divergent control flow started.
293 * This guarantees that there is a control-flow path from any
294 * divergence point of the loop into the convergence point
295 * (immediately past the WHILE instruction) such that it overlaps the
296 * whole IP region of divergent control flow (potentially the whole
297 * loop) *and* doesn't imply the execution of any instructions part
298 * of the loop (since the corresponding execution mask bit will be
299 * disabled for a diverging thread).
301 * This way we make sure that any variables that are live throughout
302 * the region of divergence for an inactive logical thread are also
303 * considered to interfere with any other variables assigned by
304 * active logical threads within the same physical region of the
305 * program, since otherwise we would risk cross-channel data
309 cur
->add_successor(mem_ctx
, next
, bblock_link_logical
);
310 cur
->add_successor(mem_ctx
, cur_while
, bblock_link_physical
);
311 set_next_block(&cur
, next
, ip
);
314 case BRW_OPCODE_CONTINUE
:
315 cur
->instructions
.push_tail(inst
);
317 /* A conditional CONTINUE may start a region of divergent control
318 * flow until the start of the next loop iteration (*not* until the
319 * end of the loop which is why the successor is not the top-level
320 * divergence point at cur_do). The live interval of any variable
321 * extending through a CONTINUE edge is guaranteed to overlap the
322 * whole region of divergent execution, because any variable live-out
323 * at the CONTINUE instruction will also be live-in at the top of the
324 * loop, and therefore also live-out at the bottom-most point of the
325 * loop which is reachable from the top (since a control flow path
326 * exists from a definition of the variable through this CONTINUE
327 * instruction, the top of the loop, the (reachable) bottom of the
328 * loop, the top of the loop again, into a use of the variable).
330 assert(cur_do
!= NULL
);
331 cur
->add_successor(mem_ctx
, cur_do
->next(), bblock_link_logical
);
335 cur
->add_successor(mem_ctx
, next
, bblock_link_logical
);
337 set_next_block(&cur
, next
, ip
);
340 case BRW_OPCODE_BREAK
:
341 cur
->instructions
.push_tail(inst
);
343 /* A conditional BREAK instruction may start a region of divergent
344 * control flow until the end of the loop if the condition is
345 * non-uniform, in which case the loop will execute additional
346 * iterations with the present channel disabled. We model this as a
347 * control flow path from the divergence point to the convergence
348 * point that overlaps the whole IP range of the loop and skips over
349 * the execution of any other instructions part of the loop.
351 * See the DO case for additional explanation.
353 assert(cur_do
!= NULL
);
354 cur
->add_successor(mem_ctx
, cur_do
, bblock_link_physical
);
355 cur
->add_successor(mem_ctx
, cur_while
, bblock_link_logical
);
359 cur
->add_successor(mem_ctx
, next
, bblock_link_logical
);
361 set_next_block(&cur
, next
, ip
);
364 case BRW_OPCODE_WHILE
:
365 cur
->instructions
.push_tail(inst
);
367 assert(cur_do
!= NULL
&& cur_while
!= NULL
);
369 /* A conditional WHILE instruction may start a region of divergent
370 * control flow until the end of the loop, just like the BREAK
371 * instruction. See the BREAK case for more details. OTOH an
372 * unconditional WHILE instruction is non-divergent (just like an
373 * unconditional CONTINUE), and will necessarily lead to the
374 * execution of an additional iteration of the loop for all enabled
375 * channels, so we may skip over the divergence point at the top of
376 * the loop to keep the CFG as unambiguous as possible.
378 if (inst
->predicate
) {
379 cur
->add_successor(mem_ctx
, cur_do
, bblock_link_logical
);
381 cur
->add_successor(mem_ctx
, cur_do
->next(), bblock_link_logical
);
384 set_next_block(&cur
, cur_while
, ip
);
386 /* Pop the stack so we're in the previous loop */
387 cur_do
= pop_stack(&do_stack
);
388 cur_while
= pop_stack(&while_stack
);
392 cur
->instructions
.push_tail(inst
);
397 cur
->end_ip
= ip
- 1;
404 ralloc_free(mem_ctx
);
408 cfg_t::remove_block(bblock_t
*block
)
410 foreach_list_typed_safe (bblock_link
, predecessor
, link
, &block
->parents
) {
411 /* Remove block from all of its predecessors' successor lists. */
412 foreach_list_typed_safe (bblock_link
, successor
, link
,
413 &predecessor
->block
->children
) {
414 if (block
== successor
->block
) {
415 successor
->link
.remove();
416 ralloc_free(successor
);
420 /* Add removed-block's successors to its predecessors' successor lists. */
421 foreach_list_typed (bblock_link
, successor
, link
, &block
->children
) {
422 if (!successor
->block
->is_successor_of(predecessor
->block
,
424 predecessor
->block
->children
.push_tail(link(mem_ctx
,
431 foreach_list_typed_safe (bblock_link
, successor
, link
, &block
->children
) {
432 /* Remove block from all of its childrens' parents lists. */
433 foreach_list_typed_safe (bblock_link
, predecessor
, link
,
434 &successor
->block
->parents
) {
435 if (block
== predecessor
->block
) {
436 predecessor
->link
.remove();
437 ralloc_free(predecessor
);
441 /* Add removed-block's predecessors to its successors' predecessor lists. */
442 foreach_list_typed (bblock_link
, predecessor
, link
, &block
->parents
) {
443 if (!predecessor
->block
->is_predecessor_of(successor
->block
,
444 predecessor
->kind
)) {
445 successor
->block
->parents
.push_tail(link(mem_ctx
,
452 block
->link
.remove();
454 for (int b
= block
->num
; b
< this->num_blocks
- 1; b
++) {
455 this->blocks
[b
] = this->blocks
[b
+ 1];
456 this->blocks
[b
]->num
= b
;
459 this->blocks
[this->num_blocks
- 1]->num
= this->num_blocks
- 2;
467 bblock_t
*block
= new(mem_ctx
) bblock_t(this);
473 cfg_t::set_next_block(bblock_t
**cur
, bblock_t
*block
, int ip
)
476 (*cur
)->end_ip
= ip
- 1;
479 block
->start_ip
= ip
;
480 block
->num
= num_blocks
++;
481 block_list
.push_tail(&block
->link
);
486 cfg_t::make_block_array()
488 blocks
= ralloc_array(mem_ctx
, bblock_t
*, num_blocks
);
491 foreach_block (block
, this) {
494 assert(i
== num_blocks
);
498 cfg_t::dump(backend_shader
*s
)
503 foreach_block (block
, this) {
505 fprintf(stderr
, "START B%d IDOM(B%d)", block
->num
, block
->idom
->num
);
507 fprintf(stderr
, "START B%d IDOM(none)", block
->num
);
509 foreach_list_typed(bblock_link
, link
, link
, &block
->parents
) {
510 fprintf(stderr
, " <%cB%d",
511 link
->kind
== bblock_link_logical
? '-' : '~',
514 fprintf(stderr
, "\n");
517 fprintf(stderr
, "END B%d", block
->num
);
518 foreach_list_typed(bblock_link
, link
, link
, &block
->children
) {
519 fprintf(stderr
, " %c>B%d",
520 link
->kind
== bblock_link_logical
? '-' : '~',
523 fprintf(stderr
, "\n");
527 /* Calculates the immediate dominator of each block, according to "A Simple,
528 * Fast Dominance Algorithm" by Keith D. Cooper, Timothy J. Harvey, and Ken
531 * The authors claim that for control flow graphs of sizes normally encountered
532 * (less than 1000 nodes) that this algorithm is significantly faster than
533 * others like Lengauer-Tarjan.
536 cfg_t::calculate_idom()
538 foreach_block(block
, this) {
541 blocks
[0]->idom
= blocks
[0];
547 foreach_block(block
, this) {
551 bblock_t
*new_idom
= NULL
;
552 foreach_list_typed(bblock_link
, parent
, link
, &block
->parents
) {
553 if (parent
->block
->idom
) {
554 if (new_idom
== NULL
) {
555 new_idom
= parent
->block
;
556 } else if (parent
->block
->idom
!= NULL
) {
557 new_idom
= intersect(parent
->block
, new_idom
);
562 if (block
->idom
!= new_idom
) {
563 block
->idom
= new_idom
;
573 cfg_t::intersect(bblock_t
*b1
, bblock_t
*b2
)
575 /* Note, the comparisons here are the opposite of what the paper says
576 * because we index blocks from beginning -> end (i.e. reverse post-order)
577 * instead of post-order like they assume.
579 while (b1
->num
!= b2
->num
) {
580 while (b1
->num
> b2
->num
)
582 while (b2
->num
> b1
->num
)
592 printf("digraph CFG {\n");
593 for (int b
= 0; b
< num_blocks
; b
++) {
594 bblock_t
*block
= this->blocks
[b
];
596 foreach_list_typed_safe (bblock_link
, child
, link
, &block
->children
) {
597 printf("\t%d -> %d\n", b
, child
->block
->num
);
604 cfg_t::dump_domtree()
606 printf("digraph DominanceTree {\n");
607 foreach_block(block
, this) {
609 printf("\t%d -> %d\n", block
->idom
->num
, block
->num
);