1 /*
2 * Copyright (c) 1997, 2021, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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23 */
24
25 #include "precompiled.hpp"
26 #include "libadt/vectset.hpp"
27 #include "memory/allocation.inline.hpp"
28 #include "memory/resourceArea.hpp"
29 #include "opto/block.hpp"
30 #include "opto/c2compiler.hpp"
31 #include "opto/callnode.hpp"
32 #include "opto/cfgnode.hpp"
33 #include "opto/machnode.hpp"
34 #include "opto/opcodes.hpp"
35 #include "opto/phaseX.hpp"
36 #include "opto/rootnode.hpp"
37 #include "opto/runtime.hpp"
38 #include "opto/chaitin.hpp"
39 #include "runtime/deoptimization.hpp"
40
41 // Portions of code courtesy of Clifford Click
42
43 // Optimization - Graph Style
44
45 // To avoid float value underflow
46 #define MIN_BLOCK_FREQUENCY 1.e-35f
47
48 //----------------------------schedule_node_into_block-------------------------
49 // Insert node n into block b. Look for projections of n and make sure they
50 // are in b also.
51 void PhaseCFG::schedule_node_into_block( Node *n, Block *b ) {
52 // Set basic block of n, Add n to b,
53 map_node_to_block(n, b);
54 b->add_inst(n);
55
56 // After Matching, nearly any old Node may have projections trailing it.
57 // These are usually machine-dependent flags. In any case, they might
58 // float to another block below this one. Move them up.
59 for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax; i++) {
60 Node* use = n->fast_out(i);
61 if (use->is_Proj()) {
62 Block* buse = get_block_for_node(use);
63 if (buse != b) { // In wrong block?
64 if (buse != NULL) {
65 buse->find_remove(use); // Remove from wrong block
66 }
67 map_node_to_block(use, b);
68 b->add_inst(use);
69 }
70 }
71 }
72 }
73
74 //----------------------------replace_block_proj_ctrl-------------------------
75 // Nodes that have is_block_proj() nodes as their control need to use
76 // the appropriate Region for their actual block as their control since
77 // the projection will be in a predecessor block.
78 void PhaseCFG::replace_block_proj_ctrl( Node *n ) {
79 const Node *in0 = n->in(0);
80 assert(in0 != NULL, "Only control-dependent");
81 const Node *p = in0->is_block_proj();
82 if (p != NULL && p != n) { // Control from a block projection?
83 assert(!n->pinned() || n->is_MachConstantBase(), "only pinned MachConstantBase node is expected here");
84 // Find trailing Region
85 Block *pb = get_block_for_node(in0); // Block-projection already has basic block
86 uint j = 0;
87 if (pb->_num_succs != 1) { // More then 1 successor?
88 // Search for successor
89 uint max = pb->number_of_nodes();
90 assert( max > 1, "" );
91 uint start = max - pb->_num_succs;
92 // Find which output path belongs to projection
93 for (j = start; j < max; j++) {
94 if( pb->get_node(j) == in0 )
95 break;
96 }
97 assert( j < max, "must find" );
98 // Change control to match head of successor basic block
99 j -= start;
100 }
101 n->set_req(0, pb->_succs[j]->head());
102 }
103 }
104
105 bool PhaseCFG::is_dominator(Node* dom_node, Node* node) {
106 assert(is_CFG(node) && is_CFG(dom_node), "node and dom_node must be CFG nodes");
107 if (dom_node == node) {
108 return true;
109 }
110 Block* d = find_block_for_node(dom_node);
111 Block* n = find_block_for_node(node);
112 assert(n != NULL && d != NULL, "blocks must exist");
113
114 if (d == n) {
115 if (dom_node->is_block_start()) {
116 return true;
117 }
118 if (node->is_block_start()) {
119 return false;
120 }
121 if (dom_node->is_block_proj()) {
122 return false;
123 }
124 if (node->is_block_proj()) {
125 return true;
126 }
127
128 assert(is_control_proj_or_safepoint(node), "node must be control projection or safepoint");
129 assert(is_control_proj_or_safepoint(dom_node), "dom_node must be control projection or safepoint");
130
131 // Neither 'node' nor 'dom_node' is a block start or block projection.
132 // Check if 'dom_node' is above 'node' in the control graph.
133 if (is_dominating_control(dom_node, node)) {
134 return true;
135 }
136
137 #ifdef ASSERT
138 // If 'dom_node' does not dominate 'node' then 'node' has to dominate 'dom_node'
139 if (!is_dominating_control(node, dom_node)) {
140 node->dump();
141 dom_node->dump();
142 assert(false, "neither dom_node nor node dominates the other");
143 }
144 #endif
145
146 return false;
147 }
148 return d->dom_lca(n) == d;
149 }
150
151 bool PhaseCFG::is_CFG(Node* n) {
152 return n->is_block_proj() || n->is_block_start() || is_control_proj_or_safepoint(n);
153 }
154
155 bool PhaseCFG::is_control_proj_or_safepoint(Node* n) const {
156 bool result = (n->is_Mach() && n->as_Mach()->ideal_Opcode() == Op_SafePoint) || (n->is_Proj() && n->as_Proj()->bottom_type() == Type::CONTROL);
157 assert(!result || (n->is_Mach() && n->as_Mach()->ideal_Opcode() == Op_SafePoint)
158 || (n->is_Proj() && n->as_Proj()->_con == 0), "If control projection, it must be projection 0");
159 return result;
160 }
161
162 Block* PhaseCFG::find_block_for_node(Node* n) const {
163 if (n->is_block_start() || n->is_block_proj()) {
164 return get_block_for_node(n);
165 } else {
166 // Walk the control graph up if 'n' is not a block start nor a block projection. In this case 'n' must be
167 // an unmatched control projection or a not yet matched safepoint precedence edge in the middle of a block.
168 assert(is_control_proj_or_safepoint(n), "must be control projection or safepoint");
169 Node* ctrl = n->in(0);
170 while (!ctrl->is_block_start()) {
171 ctrl = ctrl->in(0);
172 }
173 return get_block_for_node(ctrl);
174 }
175 }
176
177 // Walk up the control graph from 'n' and check if 'dom_ctrl' is found.
178 bool PhaseCFG::is_dominating_control(Node* dom_ctrl, Node* n) {
179 Node* ctrl = n->in(0);
180 while (!ctrl->is_block_start()) {
181 if (ctrl == dom_ctrl) {
182 return true;
183 }
184 ctrl = ctrl->in(0);
185 }
186 return false;
187 }
188
189
190 //------------------------------schedule_pinned_nodes--------------------------
191 // Set the basic block for Nodes pinned into blocks
192 void PhaseCFG::schedule_pinned_nodes(VectorSet &visited) {
193 // Allocate node stack of size C->live_nodes()+8 to avoid frequent realloc
194 GrowableArray <Node*> spstack(C->live_nodes() + 8);
195 spstack.push(_root);
196 while (spstack.is_nonempty()) {
197 Node* node = spstack.pop();
198 if (!visited.test_set(node->_idx)) { // Test node and flag it as visited
199 if (node->pinned() && !has_block(node)) { // Pinned? Nail it down!
200 assert(node->in(0), "pinned Node must have Control");
201 // Before setting block replace block_proj control edge
202 replace_block_proj_ctrl(node);
203 Node* input = node->in(0);
204 while (!input->is_block_start()) {
205 input = input->in(0);
206 }
207 Block* block = get_block_for_node(input); // Basic block of controlling input
208 schedule_node_into_block(node, block);
209 }
210
211 // If the node has precedence edges (added when CastPP nodes are
212 // removed in final_graph_reshaping), fix the control of the
213 // node to cover the precedence edges and remove the
214 // dependencies.
215 Node* n = NULL;
216 for (uint i = node->len()-1; i >= node->req(); i--) {
217 Node* m = node->in(i);
218 if (m == NULL) continue;
219
220 // Only process precedence edges that are CFG nodes. Safepoints and control projections can be in the middle of a block
221 if (is_CFG(m)) {
222 node->rm_prec(i);
223 if (n == NULL) {
224 n = m;
225 } else {
226 assert(is_dominator(n, m) || is_dominator(m, n), "one must dominate the other");
227 n = is_dominator(n, m) ? m : n;
228 }
229 } else {
230 assert(node->is_Mach(), "sanity");
231 assert(node->as_Mach()->ideal_Opcode() == Op_StoreCM, "must be StoreCM node");
232 }
233 }
234 if (n != NULL) {
235 assert(node->in(0), "control should have been set");
236 assert(is_dominator(n, node->in(0)) || is_dominator(node->in(0), n), "one must dominate the other");
237 if (!is_dominator(n, node->in(0))) {
238 node->set_req(0, n);
239 }
240 }
241
242 // process all inputs that are non NULL
243 for (int i = node->len()-1; i >= 0; --i) {
244 if (node->in(i) != NULL) {
245 spstack.push(node->in(i));
246 }
247 }
248 }
249 }
250 }
251
252 #ifdef ASSERT
253 // Assert that new input b2 is dominated by all previous inputs.
254 // Check this by by seeing that it is dominated by b1, the deepest
255 // input observed until b2.
256 static void assert_dom(Block* b1, Block* b2, Node* n, const PhaseCFG* cfg) {
257 if (b1 == NULL) return;
258 assert(b1->_dom_depth < b2->_dom_depth, "sanity");
259 Block* tmp = b2;
260 while (tmp != b1 && tmp != NULL) {
261 tmp = tmp->_idom;
262 }
263 if (tmp != b1) {
264 // Detected an unschedulable graph. Print some nice stuff and die.
265 tty->print_cr("!!! Unschedulable graph !!!");
266 for (uint j=0; j<n->len(); j++) { // For all inputs
267 Node* inn = n->in(j); // Get input
268 if (inn == NULL) continue; // Ignore NULL, missing inputs
269 Block* inb = cfg->get_block_for_node(inn);
270 tty->print("B%d idom=B%d depth=%2d ",inb->_pre_order,
271 inb->_idom ? inb->_idom->_pre_order : 0, inb->_dom_depth);
272 inn->dump();
273 }
274 tty->print("Failing node: ");
275 n->dump();
276 assert(false, "unscheduable graph");
277 }
278 }
279 #endif
280
281 static Block* find_deepest_input(Node* n, const PhaseCFG* cfg) {
282 // Find the last input dominated by all other inputs.
283 Block* deepb = NULL; // Deepest block so far
284 int deepb_dom_depth = 0;
285 for (uint k = 0; k < n->len(); k++) { // For all inputs
286 Node* inn = n->in(k); // Get input
287 if (inn == NULL) continue; // Ignore NULL, missing inputs
288 Block* inb = cfg->get_block_for_node(inn);
289 assert(inb != NULL, "must already have scheduled this input");
290 if (deepb_dom_depth < (int) inb->_dom_depth) {
291 // The new inb must be dominated by the previous deepb.
292 // The various inputs must be linearly ordered in the dom
293 // tree, or else there will not be a unique deepest block.
294 DEBUG_ONLY(assert_dom(deepb, inb, n, cfg));
295 deepb = inb; // Save deepest block
296 deepb_dom_depth = deepb->_dom_depth;
297 }
298 }
299 assert(deepb != NULL, "must be at least one input to n");
300 return deepb;
301 }
302
303
304 //------------------------------schedule_early---------------------------------
305 // Find the earliest Block any instruction can be placed in. Some instructions
306 // are pinned into Blocks. Unpinned instructions can appear in last block in
307 // which all their inputs occur.
308 bool PhaseCFG::schedule_early(VectorSet &visited, Node_Stack &roots) {
309 // Allocate stack with enough space to avoid frequent realloc
310 Node_Stack nstack(roots.size() + 8);
311 // _root will be processed among C->top() inputs
312 roots.push(C->top(), 0);
313 visited.set(C->top()->_idx);
314
315 while (roots.size() != 0) {
316 // Use local variables nstack_top_n & nstack_top_i to cache values
317 // on stack's top.
318 Node* parent_node = roots.node();
319 uint input_index = 0;
320 roots.pop();
321
322 while (true) {
323 if (input_index == 0) {
324 // Fixup some control. Constants without control get attached
325 // to root and nodes that use is_block_proj() nodes should be attached
326 // to the region that starts their block.
327 const Node* control_input = parent_node->in(0);
328 if (control_input != NULL) {
329 replace_block_proj_ctrl(parent_node);
330 } else {
331 // Is a constant with NO inputs?
332 if (parent_node->req() == 1) {
333 parent_node->set_req(0, _root);
334 }
335 }
336 }
337
338 // First, visit all inputs and force them to get a block. If an
339 // input is already in a block we quit following inputs (to avoid
340 // cycles). Instead we put that Node on a worklist to be handled
341 // later (since IT'S inputs may not have a block yet).
342
343 // Assume all n's inputs will be processed
344 bool done = true;
345
346 while (input_index < parent_node->len()) {
347 Node* in = parent_node->in(input_index++);
348 if (in == NULL) {
349 continue;
350 }
351
352 int is_visited = visited.test_set(in->_idx);
353 if (!has_block(in)) {
354 if (is_visited) {
355 assert(false, "graph should be schedulable");
356 return false;
357 }
358 // Save parent node and next input's index.
359 nstack.push(parent_node, input_index);
360 // Process current input now.
361 parent_node = in;
362 input_index = 0;
363 // Not all n's inputs processed.
364 done = false;
365 break;
366 } else if (!is_visited) {
367 // Visit this guy later, using worklist
368 roots.push(in, 0);
369 }
370 }
371
372 if (done) {
373 // All of n's inputs have been processed, complete post-processing.
374
375 // Some instructions are pinned into a block. These include Region,
376 // Phi, Start, Return, and other control-dependent instructions and
377 // any projections which depend on them.
378 if (!parent_node->pinned()) {
379 // Set earliest legal block.
380 Block* earliest_block = find_deepest_input(parent_node, this);
381 map_node_to_block(parent_node, earliest_block);
382 } else {
383 assert(get_block_for_node(parent_node) == get_block_for_node(parent_node->in(0)), "Pinned Node should be at the same block as its control edge");
384 }
385
386 if (nstack.is_empty()) {
387 // Finished all nodes on stack.
388 // Process next node on the worklist 'roots'.
389 break;
390 }
391 // Get saved parent node and next input's index.
392 parent_node = nstack.node();
393 input_index = nstack.index();
394 nstack.pop();
395 }
396 }
397 }
398 return true;
399 }
400
401 //------------------------------dom_lca----------------------------------------
402 // Find least common ancestor in dominator tree
403 // LCA is a current notion of LCA, to be raised above 'this'.
404 // As a convenient boundary condition, return 'this' if LCA is NULL.
405 // Find the LCA of those two nodes.
406 Block* Block::dom_lca(Block* LCA) {
407 if (LCA == NULL || LCA == this) return this;
408
409 Block* anc = this;
410 while (anc->_dom_depth > LCA->_dom_depth)
411 anc = anc->_idom; // Walk up till anc is as high as LCA
412
413 while (LCA->_dom_depth > anc->_dom_depth)
414 LCA = LCA->_idom; // Walk up till LCA is as high as anc
415
416 while (LCA != anc) { // Walk both up till they are the same
417 LCA = LCA->_idom;
418 anc = anc->_idom;
419 }
420
421 return LCA;
422 }
423
424 //--------------------------raise_LCA_above_use--------------------------------
425 // We are placing a definition, and have been given a def->use edge.
426 // The definition must dominate the use, so move the LCA upward in the
427 // dominator tree to dominate the use. If the use is a phi, adjust
428 // the LCA only with the phi input paths which actually use this def.
429 static Block* raise_LCA_above_use(Block* LCA, Node* use, Node* def, const PhaseCFG* cfg) {
430 Block* buse = cfg->get_block_for_node(use);
431 if (buse == NULL) return LCA; // Unused killing Projs have no use block
432 if (!use->is_Phi()) return buse->dom_lca(LCA);
433 uint pmax = use->req(); // Number of Phi inputs
434 // Why does not this loop just break after finding the matching input to
435 // the Phi? Well...it's like this. I do not have true def-use/use-def
436 // chains. Means I cannot distinguish, from the def-use direction, which
437 // of many use-defs lead from the same use to the same def. That is, this
438 // Phi might have several uses of the same def. Each use appears in a
439 // different predecessor block. But when I enter here, I cannot distinguish
440 // which use-def edge I should find the predecessor block for. So I find
441 // them all. Means I do a little extra work if a Phi uses the same value
442 // more than once.
443 for (uint j=1; j<pmax; j++) { // For all inputs
444 if (use->in(j) == def) { // Found matching input?
445 Block* pred = cfg->get_block_for_node(buse->pred(j));
446 LCA = pred->dom_lca(LCA);
447 }
448 }
449 return LCA;
450 }
451
452 //----------------------------raise_LCA_above_marks----------------------------
453 // Return a new LCA that dominates LCA and any of its marked predecessors.
454 // Search all my parents up to 'early' (exclusive), looking for predecessors
455 // which are marked with the given index. Return the LCA (in the dom tree)
456 // of all marked blocks. If there are none marked, return the original
457 // LCA.
458 static Block* raise_LCA_above_marks(Block* LCA, node_idx_t mark, Block* early, const PhaseCFG* cfg) {
459 Block_List worklist;
460 worklist.push(LCA);
461 while (worklist.size() > 0) {
462 Block* mid = worklist.pop();
463 if (mid == early) continue; // stop searching here
464
465 // Test and set the visited bit.
466 if (mid->raise_LCA_visited() == mark) continue; // already visited
467
468 // Don't process the current LCA, otherwise the search may terminate early
469 if (mid != LCA && mid->raise_LCA_mark() == mark) {
470 // Raise the LCA.
471 LCA = mid->dom_lca(LCA);
472 if (LCA == early) break; // stop searching everywhere
473 assert(early->dominates(LCA), "early is high enough");
474 // Resume searching at that point, skipping intermediate levels.
475 worklist.push(LCA);
476 if (LCA == mid)
477 continue; // Don't mark as visited to avoid early termination.
478 } else {
479 // Keep searching through this block's predecessors.
480 for (uint j = 1, jmax = mid->num_preds(); j < jmax; j++) {
481 Block* mid_parent = cfg->get_block_for_node(mid->pred(j));
482 worklist.push(mid_parent);
483 }
484 }
485 mid->set_raise_LCA_visited(mark);
486 }
487 return LCA;
488 }
489
490 //--------------------------memory_early_block--------------------------------
491 // This is a variation of find_deepest_input, the heart of schedule_early.
492 // Find the "early" block for a load, if we considered only memory and
493 // address inputs, that is, if other data inputs were ignored.
494 //
495 // Because a subset of edges are considered, the resulting block will
496 // be earlier (at a shallower dom_depth) than the true schedule_early
497 // point of the node. We compute this earlier block as a more permissive
498 // site for anti-dependency insertion, but only if subsume_loads is enabled.
499 static Block* memory_early_block(Node* load, Block* early, const PhaseCFG* cfg) {
500 Node* base;
501 Node* index;
502 Node* store = load->in(MemNode::Memory);
503 load->as_Mach()->memory_inputs(base, index);
504
505 assert(base != NodeSentinel && index != NodeSentinel,
506 "unexpected base/index inputs");
507
508 Node* mem_inputs[4];
509 int mem_inputs_length = 0;
510 if (base != NULL) mem_inputs[mem_inputs_length++] = base;
511 if (index != NULL) mem_inputs[mem_inputs_length++] = index;
512 if (store != NULL) mem_inputs[mem_inputs_length++] = store;
513
514 // In the comparision below, add one to account for the control input,
515 // which may be null, but always takes up a spot in the in array.
516 if (mem_inputs_length + 1 < (int) load->req()) {
517 // This "load" has more inputs than just the memory, base and index inputs.
518 // For purposes of checking anti-dependences, we need to start
519 // from the early block of only the address portion of the instruction,
520 // and ignore other blocks that may have factored into the wider
521 // schedule_early calculation.
522 if (load->in(0) != NULL) mem_inputs[mem_inputs_length++] = load->in(0);
523
524 Block* deepb = NULL; // Deepest block so far
525 int deepb_dom_depth = 0;
526 for (int i = 0; i < mem_inputs_length; i++) {
527 Block* inb = cfg->get_block_for_node(mem_inputs[i]);
528 if (deepb_dom_depth < (int) inb->_dom_depth) {
529 // The new inb must be dominated by the previous deepb.
530 // The various inputs must be linearly ordered in the dom
531 // tree, or else there will not be a unique deepest block.
532 DEBUG_ONLY(assert_dom(deepb, inb, load, cfg));
533 deepb = inb; // Save deepest block
534 deepb_dom_depth = deepb->_dom_depth;
535 }
536 }
537 early = deepb;
538 }
539
540 return early;
541 }
542
543 // This function is used by insert_anti_dependences to find unrelated loads for stores in implicit null checks.
544 bool PhaseCFG::unrelated_load_in_store_null_block(Node* store, Node* load) {
545 // We expect an anti-dependence edge from 'load' to 'store', except when
546 // implicit_null_check() has hoisted 'store' above its early block to
547 // perform an implicit null check, and 'load' is placed in the null
548 // block. In this case it is safe to ignore the anti-dependence, as the
549 // null block is only reached if 'store' tries to write to null object and
550 // 'load' read from non-null object (there is preceding check for that)
551 // These objects can't be the same.
552 Block* store_block = get_block_for_node(store);
553 Block* load_block = get_block_for_node(load);
554 Node* end = store_block->end();
555 if (end->is_MachNullCheck() && (end->in(1) == store) && store_block->dominates(load_block)) {
556 Node* if_true = end->find_out_with(Op_IfTrue);
557 assert(if_true != NULL, "null check without null projection");
558 Node* null_block_region = if_true->find_out_with(Op_Region);
559 assert(null_block_region != NULL, "null check without null region");
560 return get_block_for_node(null_block_region) == load_block;
561 }
562 return false;
563 }
564
565 //--------------------------insert_anti_dependences---------------------------
566 // A load may need to witness memory that nearby stores can overwrite.
567 // For each nearby store, either insert an "anti-dependence" edge
568 // from the load to the store, or else move LCA upward to force the
569 // load to (eventually) be scheduled in a block above the store.
570 //
571 // Do not add edges to stores on distinct control-flow paths;
572 // only add edges to stores which might interfere.
573 //
574 // Return the (updated) LCA. There will not be any possibly interfering
575 // store between the load's "early block" and the updated LCA.
576 // Any stores in the updated LCA will have new precedence edges
577 // back to the load. The caller is expected to schedule the load
578 // in the LCA, in which case the precedence edges will make LCM
579 // preserve anti-dependences. The caller may also hoist the load
580 // above the LCA, if it is not the early block.
581 Block* PhaseCFG::insert_anti_dependences(Block* LCA, Node* load, bool verify) {
582 assert(load->needs_anti_dependence_check(), "must be a load of some sort");
583 assert(LCA != NULL, "");
584 DEBUG_ONLY(Block* LCA_orig = LCA);
585
586 // Compute the alias index. Loads and stores with different alias indices
587 // do not need anti-dependence edges.
588 int load_alias_idx = C->get_alias_index(load->adr_type());
589 #ifdef ASSERT
590 assert(Compile::AliasIdxTop <= load_alias_idx && load_alias_idx < C->num_alias_types(), "Invalid alias index");
591 if (load_alias_idx == Compile::AliasIdxBot && C->AliasLevel() > 0 &&
592 (PrintOpto || VerifyAliases ||
593 (PrintMiscellaneous && (WizardMode || Verbose)))) {
594 // Load nodes should not consume all of memory.
595 // Reporting a bottom type indicates a bug in adlc.
596 // If some particular type of node validly consumes all of memory,
597 // sharpen the preceding "if" to exclude it, so we can catch bugs here.
598 tty->print_cr("*** Possible Anti-Dependence Bug: Load consumes all of memory.");
599 load->dump(2);
600 if (VerifyAliases) assert(load_alias_idx != Compile::AliasIdxBot, "");
601 }
602 #endif
603
604 if (!C->alias_type(load_alias_idx)->is_rewritable()) {
605 // It is impossible to spoil this load by putting stores before it,
606 // because we know that the stores will never update the value
607 // which 'load' must witness.
608 return LCA;
609 }
610
611 node_idx_t load_index = load->_idx;
612
613 // Note the earliest legal placement of 'load', as determined by
614 // by the unique point in the dom tree where all memory effects
615 // and other inputs are first available. (Computed by schedule_early.)
616 // For normal loads, 'early' is the shallowest place (dom graph wise)
617 // to look for anti-deps between this load and any store.
618 Block* early = get_block_for_node(load);
619
620 // If we are subsuming loads, compute an "early" block that only considers
621 // memory or address inputs. This block may be different than the
622 // schedule_early block in that it could be at an even shallower depth in the
623 // dominator tree, and allow for a broader discovery of anti-dependences.
624 if (C->subsume_loads()) {
625 early = memory_early_block(load, early, this);
626 }
627
628 ResourceArea *area = Thread::current()->resource_area();
629 Node_List worklist_mem(area); // prior memory state to store
630 Node_List worklist_store(area); // possible-def to explore
631 Node_List worklist_visited(area); // visited mergemem nodes
632 Node_List non_early_stores(area); // all relevant stores outside of early
633 bool must_raise_LCA = false;
634
635 // 'load' uses some memory state; look for users of the same state.
636 // Recurse through MergeMem nodes to the stores that use them.
637
638 // Each of these stores is a possible definition of memory
639 // that 'load' needs to use. We need to force 'load'
640 // to occur before each such store. When the store is in
641 // the same block as 'load', we insert an anti-dependence
642 // edge load->store.
643
644 // The relevant stores "nearby" the load consist of a tree rooted
645 // at initial_mem, with internal nodes of type MergeMem.
646 // Therefore, the branches visited by the worklist are of this form:
647 // initial_mem -> (MergeMem ->)* store
648 // The anti-dependence constraints apply only to the fringe of this tree.
649
650 Node* initial_mem = load->in(MemNode::Memory);
651 worklist_store.push(initial_mem);
652 worklist_visited.push(initial_mem);
653 worklist_mem.push(NULL);
654 while (worklist_store.size() > 0) {
655 // Examine a nearby store to see if it might interfere with our load.
656 Node* mem = worklist_mem.pop();
657 Node* store = worklist_store.pop();
658 uint op = store->Opcode();
659
660 // MergeMems do not directly have anti-deps.
661 // Treat them as internal nodes in a forward tree of memory states,
662 // the leaves of which are each a 'possible-def'.
663 if (store == initial_mem // root (exclusive) of tree we are searching
664 || op == Op_MergeMem // internal node of tree we are searching
665 ) {
666 mem = store; // It's not a possibly interfering store.
667 if (store == initial_mem)
668 initial_mem = NULL; // only process initial memory once
669
670 for (DUIterator_Fast imax, i = mem->fast_outs(imax); i < imax; i++) {
671 store = mem->fast_out(i);
672 if (store->is_MergeMem()) {
673 // Be sure we don't get into combinatorial problems.
674 // (Allow phis to be repeated; they can merge two relevant states.)
675 uint j = worklist_visited.size();
676 for (; j > 0; j--) {
677 if (worklist_visited.at(j-1) == store) break;
678 }
679 if (j > 0) continue; // already on work list; do not repeat
680 worklist_visited.push(store);
681 }
682 worklist_mem.push(mem);
683 worklist_store.push(store);
684 }
685 continue;
686 }
687
688 if (op == Op_MachProj || op == Op_Catch) continue;
689 if (store->needs_anti_dependence_check()) continue; // not really a store
690
691 // Compute the alias index. Loads and stores with different alias
692 // indices do not need anti-dependence edges. Wide MemBar's are
693 // anti-dependent on everything (except immutable memories).
694 const TypePtr* adr_type = store->adr_type();
695 if (!C->can_alias(adr_type, load_alias_idx)) continue;
696
697 // Most slow-path runtime calls do NOT modify Java memory, but
698 // they can block and so write Raw memory.
699 if (store->is_Mach()) {
700 MachNode* mstore = store->as_Mach();
701 if (load_alias_idx != Compile::AliasIdxRaw) {
702 // Check for call into the runtime using the Java calling
703 // convention (and from there into a wrapper); it has no
704 // _method. Can't do this optimization for Native calls because
705 // they CAN write to Java memory.
706 if (mstore->ideal_Opcode() == Op_CallStaticJava) {
707 assert(mstore->is_MachSafePoint(), "");
708 MachSafePointNode* ms = (MachSafePointNode*) mstore;
709 assert(ms->is_MachCallJava(), "");
710 MachCallJavaNode* mcj = (MachCallJavaNode*) ms;
711 if (mcj->_method == NULL) {
712 // These runtime calls do not write to Java visible memory
713 // (other than Raw) and so do not require anti-dependence edges.
714 continue;
715 }
716 }
717 // Same for SafePoints: they read/write Raw but only read otherwise.
718 // This is basically a workaround for SafePoints only defining control
719 // instead of control + memory.
720 if (mstore->ideal_Opcode() == Op_SafePoint)
721 continue;
722 } else {
723 // Some raw memory, such as the load of "top" at an allocation,
724 // can be control dependent on the previous safepoint. See
725 // comments in GraphKit::allocate_heap() about control input.
726 // Inserting an anti-dep between such a safepoint and a use
727 // creates a cycle, and will cause a subsequent failure in
728 // local scheduling. (BugId 4919904)
729 // (%%% How can a control input be a safepoint and not a projection??)
730 if (mstore->ideal_Opcode() == Op_SafePoint && load->in(0) == mstore)
731 continue;
732 }
733 }
734
735 // Identify a block that the current load must be above,
736 // or else observe that 'store' is all the way up in the
737 // earliest legal block for 'load'. In the latter case,
738 // immediately insert an anti-dependence edge.
739 Block* store_block = get_block_for_node(store);
740 assert(store_block != NULL, "unused killing projections skipped above");
741
742 if (store->is_Phi()) {
743 // Loop-phis need to raise load before input. (Other phis are treated
744 // as store below.)
745 //
746 // 'load' uses memory which is one (or more) of the Phi's inputs.
747 // It must be scheduled not before the Phi, but rather before
748 // each of the relevant Phi inputs.
749 //
750 // Instead of finding the LCA of all inputs to a Phi that match 'mem',
751 // we mark each corresponding predecessor block and do a combined
752 // hoisting operation later (raise_LCA_above_marks).
753 //
754 // Do not assert(store_block != early, "Phi merging memory after access")
755 // PhiNode may be at start of block 'early' with backedge to 'early'
756 DEBUG_ONLY(bool found_match = false);
757 for (uint j = PhiNode::Input, jmax = store->req(); j < jmax; j++) {
758 if (store->in(j) == mem) { // Found matching input?
759 DEBUG_ONLY(found_match = true);
760 Block* pred_block = get_block_for_node(store_block->pred(j));
761 if (pred_block != early) {
762 // If any predecessor of the Phi matches the load's "early block",
763 // we do not need a precedence edge between the Phi and 'load'
764 // since the load will be forced into a block preceding the Phi.
765 pred_block->set_raise_LCA_mark(load_index);
766 assert(!LCA_orig->dominates(pred_block) ||
767 early->dominates(pred_block), "early is high enough");
768 must_raise_LCA = true;
769 } else {
770 // anti-dependent upon PHI pinned below 'early', no edge needed
771 LCA = early; // but can not schedule below 'early'
772 }
773 }
774 }
775 assert(found_match, "no worklist bug");
776 } else if (store_block != early) {
777 // 'store' is between the current LCA and earliest possible block.
778 // Label its block, and decide later on how to raise the LCA
779 // to include the effect on LCA of this store.
780 // If this store's block gets chosen as the raised LCA, we
781 // will find him on the non_early_stores list and stick him
782 // with a precedence edge.
783 // (But, don't bother if LCA is already raised all the way.)
784 if (LCA != early && !unrelated_load_in_store_null_block(store, load)) {
785 store_block->set_raise_LCA_mark(load_index);
786 must_raise_LCA = true;
787 non_early_stores.push(store);
788 }
789 } else {
790 // Found a possibly-interfering store in the load's 'early' block.
791 // This means 'load' cannot sink at all in the dominator tree.
792 // Add an anti-dep edge, and squeeze 'load' into the highest block.
793 assert(store != load->find_exact_control(load->in(0)), "dependence cycle found");
794 if (verify) {
795 assert(store->find_edge(load) != -1 || unrelated_load_in_store_null_block(store, load),
796 "missing precedence edge");
797 } else {
798 store->add_prec(load);
799 }
800 LCA = early;
801 // This turns off the process of gathering non_early_stores.
802 }
803 }
804 // (Worklist is now empty; all nearby stores have been visited.)
805
806 // Finished if 'load' must be scheduled in its 'early' block.
807 // If we found any stores there, they have already been given
808 // precedence edges.
809 if (LCA == early) return LCA;
810
811 // We get here only if there are no possibly-interfering stores
812 // in the load's 'early' block. Move LCA up above all predecessors
813 // which contain stores we have noted.
814 //
815 // The raised LCA block can be a home to such interfering stores,
816 // but its predecessors must not contain any such stores.
817 //
818 // The raised LCA will be a lower bound for placing the load,
819 // preventing the load from sinking past any block containing
820 // a store that may invalidate the memory state required by 'load'.
821 if (must_raise_LCA)
822 LCA = raise_LCA_above_marks(LCA, load->_idx, early, this);
823 if (LCA == early) return LCA;
824
825 // Insert anti-dependence edges from 'load' to each store
826 // in the non-early LCA block.
827 // Mine the non_early_stores list for such stores.
828 if (LCA->raise_LCA_mark() == load_index) {
829 while (non_early_stores.size() > 0) {
830 Node* store = non_early_stores.pop();
831 Block* store_block = get_block_for_node(store);
832 if (store_block == LCA) {
833 // add anti_dependence from store to load in its own block
834 assert(store != load->find_exact_control(load->in(0)), "dependence cycle found");
835 if (verify) {
836 assert(store->find_edge(load) != -1, "missing precedence edge");
837 } else {
838 store->add_prec(load);
839 }
840 } else {
841 assert(store_block->raise_LCA_mark() == load_index, "block was marked");
842 // Any other stores we found must be either inside the new LCA
843 // or else outside the original LCA. In the latter case, they
844 // did not interfere with any use of 'load'.
845 assert(LCA->dominates(store_block)
846 || !LCA_orig->dominates(store_block), "no stray stores");
847 }
848 }
849 }
850
851 // Return the highest block containing stores; any stores
852 // within that block have been given anti-dependence edges.
853 return LCA;
854 }
855
856 // This class is used to iterate backwards over the nodes in the graph.
857
858 class Node_Backward_Iterator {
859
860 private:
861 Node_Backward_Iterator();
862
863 public:
864 // Constructor for the iterator
865 Node_Backward_Iterator(Node *root, VectorSet &visited, Node_Stack &stack, PhaseCFG &cfg);
866
867 // Postincrement operator to iterate over the nodes
868 Node *next();
869
870 private:
871 VectorSet &_visited;
872 Node_Stack &_stack;
873 PhaseCFG &_cfg;
874 };
875
876 // Constructor for the Node_Backward_Iterator
877 Node_Backward_Iterator::Node_Backward_Iterator( Node *root, VectorSet &visited, Node_Stack &stack, PhaseCFG &cfg)
878 : _visited(visited), _stack(stack), _cfg(cfg) {
879 // The stack should contain exactly the root
880 stack.clear();
881 stack.push(root, root->outcnt());
882
883 // Clear the visited bits
884 visited.clear();
885 }
886
887 // Iterator for the Node_Backward_Iterator
888 Node *Node_Backward_Iterator::next() {
889
890 // If the _stack is empty, then just return NULL: finished.
891 if ( !_stack.size() )
892 return NULL;
893
894 // I visit unvisited not-anti-dependence users first, then anti-dependent
895 // children next. I iterate backwards to support removal of nodes.
896 // The stack holds states consisting of 3 values:
897 // current Def node, flag which indicates 1st/2nd pass, index of current out edge
898 Node *self = (Node*)(((uintptr_t)_stack.node()) & ~1);
899 bool iterate_anti_dep = (((uintptr_t)_stack.node()) & 1);
900 uint idx = MIN2(_stack.index(), self->outcnt()); // Support removal of nodes.
901 _stack.pop();
902
903 // I cycle here when I am entering a deeper level of recursion.
904 // The key variable 'self' was set prior to jumping here.
905 while( 1 ) {
906
907 _visited.set(self->_idx);
908
909 // Now schedule all uses as late as possible.
910 const Node* src = self->is_Proj() ? self->in(0) : self;
911 uint src_rpo = _cfg.get_block_for_node(src)->_rpo;
912
913 // Schedule all nodes in a post-order visit
914 Node *unvisited = NULL; // Unvisited anti-dependent Node, if any
915
916 // Scan for unvisited nodes
917 while (idx > 0) {
918 // For all uses, schedule late
919 Node* n = self->raw_out(--idx); // Use
920
921 // Skip already visited children
922 if ( _visited.test(n->_idx) )
923 continue;
924
925 // do not traverse backward control edges
926 Node *use = n->is_Proj() ? n->in(0) : n;
927 uint use_rpo = _cfg.get_block_for_node(use)->_rpo;
928
929 if ( use_rpo < src_rpo )
930 continue;
931
932 // Phi nodes always precede uses in a basic block
933 if ( use_rpo == src_rpo && use->is_Phi() )
934 continue;
935
936 unvisited = n; // Found unvisited
937
938 // Check for possible-anti-dependent
939 // 1st pass: No such nodes, 2nd pass: Only such nodes.
940 if (n->needs_anti_dependence_check() == iterate_anti_dep) {
941 unvisited = n; // Found unvisited
942 break;
943 }
944 }
945
946 // Did I find an unvisited not-anti-dependent Node?
947 if (!unvisited) {
948 if (!iterate_anti_dep) {
949 // 2nd pass: Iterate over nodes which needs_anti_dependence_check.
950 iterate_anti_dep = true;
951 idx = self->outcnt();
952 continue;
953 }
954 break; // All done with children; post-visit 'self'
955 }
956
957 // Visit the unvisited Node. Contains the obvious push to
958 // indicate I'm entering a deeper level of recursion. I push the
959 // old state onto the _stack and set a new state and loop (recurse).
960 _stack.push((Node*)((uintptr_t)self | (uintptr_t)iterate_anti_dep), idx);
961 self = unvisited;
962 iterate_anti_dep = false;
963 idx = self->outcnt();
964 } // End recursion loop
965
966 return self;
967 }
968
969 //------------------------------ComputeLatenciesBackwards----------------------
970 // Compute the latency of all the instructions.
971 void PhaseCFG::compute_latencies_backwards(VectorSet &visited, Node_Stack &stack) {
972 #ifndef PRODUCT
973 if (trace_opto_pipelining())
974 tty->print("\n#---- ComputeLatenciesBackwards ----\n");
975 #endif
976
977 Node_Backward_Iterator iter((Node *)_root, visited, stack, *this);
978 Node *n;
979
980 // Walk over all the nodes from last to first
981 while ((n = iter.next())) {
982 // Set the latency for the definitions of this instruction
983 partial_latency_of_defs(n);
984 }
985 } // end ComputeLatenciesBackwards
986
987 //------------------------------partial_latency_of_defs------------------------
988 // Compute the latency impact of this node on all defs. This computes
989 // a number that increases as we approach the beginning of the routine.
990 void PhaseCFG::partial_latency_of_defs(Node *n) {
991 // Set the latency for this instruction
992 #ifndef PRODUCT
993 if (trace_opto_pipelining()) {
994 tty->print("# latency_to_inputs: node_latency[%d] = %d for node", n->_idx, get_latency_for_node(n));
995 dump();
996 }
997 #endif
998
999 if (n->is_Proj()) {
1000 n = n->in(0);
1001 }
1002
1003 if (n->is_Root()) {
1004 return;
1005 }
1006
1007 uint nlen = n->len();
1008 uint use_latency = get_latency_for_node(n);
1009 uint use_pre_order = get_block_for_node(n)->_pre_order;
1010
1011 for (uint j = 0; j < nlen; j++) {
1012 Node *def = n->in(j);
1013
1014 if (!def || def == n) {
1015 continue;
1016 }
1017
1018 // Walk backwards thru projections
1019 if (def->is_Proj()) {
1020 def = def->in(0);
1021 }
1022
1023 #ifndef PRODUCT
1024 if (trace_opto_pipelining()) {
1025 tty->print("# in(%2d): ", j);
1026 def->dump();
1027 }
1028 #endif
1029
1030 // If the defining block is not known, assume it is ok
1031 Block *def_block = get_block_for_node(def);
1032 uint def_pre_order = def_block ? def_block->_pre_order : 0;
1033
1034 if ((use_pre_order < def_pre_order) || (use_pre_order == def_pre_order && n->is_Phi())) {
1035 continue;
1036 }
1037
1038 uint delta_latency = n->latency(j);
1039 uint current_latency = delta_latency + use_latency;
1040
1041 if (get_latency_for_node(def) < current_latency) {
1042 set_latency_for_node(def, current_latency);
1043 }
1044
1045 #ifndef PRODUCT
1046 if (trace_opto_pipelining()) {
1047 tty->print_cr("# %d + edge_latency(%d) == %d -> %d, node_latency[%d] = %d", use_latency, j, delta_latency, current_latency, def->_idx, get_latency_for_node(def));
1048 }
1049 #endif
1050 }
1051 }
1052
1053 //------------------------------latency_from_use-------------------------------
1054 // Compute the latency of a specific use
1055 int PhaseCFG::latency_from_use(Node *n, const Node *def, Node *use) {
1056 // If self-reference, return no latency
1057 if (use == n || use->is_Root()) {
1058 return 0;
1059 }
1060
1061 uint def_pre_order = get_block_for_node(def)->_pre_order;
1062 uint latency = 0;
1063
1064 // If the use is not a projection, then it is simple...
1065 if (!use->is_Proj()) {
1066 #ifndef PRODUCT
1067 if (trace_opto_pipelining()) {
1068 tty->print("# out(): ");
1069 use->dump();
1070 }
1071 #endif
1072
1073 uint use_pre_order = get_block_for_node(use)->_pre_order;
1074
1075 if (use_pre_order < def_pre_order)
1076 return 0;
1077
1078 if (use_pre_order == def_pre_order && use->is_Phi())
1079 return 0;
1080
1081 uint nlen = use->len();
1082 uint nl = get_latency_for_node(use);
1083
1084 for ( uint j=0; j<nlen; j++ ) {
1085 if (use->in(j) == n) {
1086 // Change this if we want local latencies
1087 uint ul = use->latency(j);
1088 uint l = ul + nl;
1089 if (latency < l) latency = l;
1090 #ifndef PRODUCT
1091 if (trace_opto_pipelining()) {
1092 tty->print_cr("# %d + edge_latency(%d) == %d -> %d, latency = %d",
1093 nl, j, ul, l, latency);
1094 }
1095 #endif
1096 }
1097 }
1098 } else {
1099 // This is a projection, just grab the latency of the use(s)
1100 for (DUIterator_Fast jmax, j = use->fast_outs(jmax); j < jmax; j++) {
1101 uint l = latency_from_use(use, def, use->fast_out(j));
1102 if (latency < l) latency = l;
1103 }
1104 }
1105
1106 return latency;
1107 }
1108
1109 //------------------------------latency_from_uses------------------------------
1110 // Compute the latency of this instruction relative to all of it's uses.
1111 // This computes a number that increases as we approach the beginning of the
1112 // routine.
1113 void PhaseCFG::latency_from_uses(Node *n) {
1114 // Set the latency for this instruction
1115 #ifndef PRODUCT
1116 if (trace_opto_pipelining()) {
1117 tty->print("# latency_from_outputs: node_latency[%d] = %d for node", n->_idx, get_latency_for_node(n));
1118 dump();
1119 }
1120 #endif
1121 uint latency=0;
1122 const Node *def = n->is_Proj() ? n->in(0): n;
1123
1124 for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax; i++) {
1125 uint l = latency_from_use(n, def, n->fast_out(i));
1126
1127 if (latency < l) latency = l;
1128 }
1129
1130 set_latency_for_node(n, latency);
1131 }
1132
1133 //------------------------------is_cheaper_block-------------------------
1134 // Check if a block between early and LCA block of uses is cheaper by
1135 // frequency-based policy, latency-based policy and random-based policy
1136 bool PhaseCFG::is_cheaper_block(Block* LCA, Node* self, uint target_latency,
1137 uint end_latency, double least_freq,
1138 int cand_cnt, bool in_latency) {
1139 if (StressGCM) {
1140 // Should be randomly accepted in stress mode
1141 return C->randomized_select(cand_cnt);
1142 }
1143
1144 // Better Frequency
1145 if (LCA->_freq < least_freq) {
1146 return true;
1147 }
1148
1149 // Otherwise, choose with latency
1150 const double delta = 1 + PROB_UNLIKELY_MAG(4);
1151 if (!in_latency && // No block containing latency
1152 LCA->_freq < least_freq * delta && // No worse frequency
1153 target_latency >= end_latency && // within latency range
1154 !self->is_iteratively_computed() // But don't hoist IV increments
1155 // because they may end up above other uses of their phi forcing
1156 // their result register to be different from their input.
1157 ) {
1158 return true;
1159 }
1160
1161 return false;
1162 }
1163
1164 //------------------------------hoist_to_cheaper_block-------------------------
1165 // Pick a block for node self, between early and LCA block of uses, that is a
1166 // cheaper alternative to LCA.
1167 Block* PhaseCFG::hoist_to_cheaper_block(Block* LCA, Block* early, Node* self) {
1168 Block* least = LCA;
1169 double least_freq = least->_freq;
1170 uint target = get_latency_for_node(self);
1171 uint start_latency = get_latency_for_node(LCA->head());
1172 uint end_latency = get_latency_for_node(LCA->get_node(LCA->end_idx()));
1173 bool in_latency = (target <= start_latency);
1174 const Block* root_block = get_block_for_node(_root);
1175
1176 // Turn off latency scheduling if scheduling is just plain off
1177 if (!C->do_scheduling())
1178 in_latency = true;
1179
1180 // Do not hoist (to cover latency) instructions which target a
1181 // single register. Hoisting stretches the live range of the
1182 // single register and may force spilling.
1183 MachNode* mach = self->is_Mach() ? self->as_Mach() : NULL;
1184 if (mach && mach->out_RegMask().is_bound1() && mach->out_RegMask().is_NotEmpty())
1185 in_latency = true;
1186
1187 #ifndef PRODUCT
1188 if (trace_opto_pipelining()) {
1189 tty->print("# Find cheaper block for latency %d: ", get_latency_for_node(self));
1190 self->dump();
1191 tty->print_cr("# B%d: start latency for [%4d]=%d, end latency for [%4d]=%d, freq=%g",
1192 LCA->_pre_order,
1193 LCA->head()->_idx,
1194 start_latency,
1195 LCA->get_node(LCA->end_idx())->_idx,
1196 end_latency,
1197 least_freq);
1198 }
1199 #endif
1200
1201 int cand_cnt = 0; // number of candidates tried
1202
1203 // Walk up the dominator tree from LCA (Lowest common ancestor) to
1204 // the earliest legal location. Capture the least execution frequency,
1205 // or choose a random block if -XX:+StressGCM, or using latency-based policy
1206 while (LCA != early) {
1207 LCA = LCA->_idom; // Follow up the dominator tree
1208
1209 if (LCA == NULL) {
1210 // Bailout without retry
1211 assert(false, "graph should be schedulable");
1212 C->record_method_not_compilable("late schedule failed: LCA == NULL");
1213 return least;
1214 }
1215
1216 // Don't hoist machine instructions to the root basic block
1217 if (mach && LCA == root_block)
1218 break;
1219
1220 if (self->is_memory_writer() &&
1221 (LCA->_loop->depth() > early->_loop->depth())) {
1222 // LCA is an invalid placement for a memory writer: choosing it would
1223 // cause memory interference, as illustrated in schedule_late().
1224 continue;
1225 }
1226 verify_memory_writer_placement(LCA, self);
1227
1228 uint start_lat = get_latency_for_node(LCA->head());
1229 uint end_idx = LCA->end_idx();
1230 uint end_lat = get_latency_for_node(LCA->get_node(end_idx));
1231 double LCA_freq = LCA->_freq;
1232 #ifndef PRODUCT
1233 if (trace_opto_pipelining()) {
1234 tty->print_cr("# B%d: start latency for [%4d]=%d, end latency for [%4d]=%d, freq=%g",
1235 LCA->_pre_order, LCA->head()->_idx, start_lat, end_idx, end_lat, LCA_freq);
1236 }
1237 #endif
1238 cand_cnt++;
1239 if (is_cheaper_block(LCA, self, target, end_lat, least_freq, cand_cnt, in_latency)) {
1240 least = LCA; // Found cheaper block
1241 least_freq = LCA_freq;
1242 start_latency = start_lat;
1243 end_latency = end_lat;
1244 if (target <= start_lat)
1245 in_latency = true;
1246 }
1247 }
1248
1249 #ifndef PRODUCT
1250 if (trace_opto_pipelining()) {
1251 tty->print_cr("# Choose block B%d with start latency=%d and freq=%g",
1252 least->_pre_order, start_latency, least_freq);
1253 }
1254 #endif
1255
1256 // See if the latency needs to be updated
1257 if (target < end_latency) {
1258 #ifndef PRODUCT
1259 if (trace_opto_pipelining()) {
1260 tty->print_cr("# Change latency for [%4d] from %d to %d", self->_idx, target, end_latency);
1261 }
1262 #endif
1263 set_latency_for_node(self, end_latency);
1264 partial_latency_of_defs(self);
1265 }
1266
1267 return least;
1268 }
1269
1270
1271 //------------------------------schedule_late-----------------------------------
1272 // Now schedule all codes as LATE as possible. This is the LCA in the
1273 // dominator tree of all USES of a value. Pick the block with the least
1274 // loop nesting depth that is lowest in the dominator tree.
1275 extern const char must_clone[];
1276 void PhaseCFG::schedule_late(VectorSet &visited, Node_Stack &stack) {
1277 #ifndef PRODUCT
1278 if (trace_opto_pipelining())
1279 tty->print("\n#---- schedule_late ----\n");
1280 #endif
1281
1282 Node_Backward_Iterator iter((Node *)_root, visited, stack, *this);
1283 Node *self;
1284
1285 // Walk over all the nodes from last to first
1286 while ((self = iter.next())) {
1287 Block* early = get_block_for_node(self); // Earliest legal placement
1288
1289 if (self->is_top()) {
1290 // Top node goes in bb #2 with other constants.
1291 // It must be special-cased, because it has no out edges.
1292 early->add_inst(self);
1293 continue;
1294 }
1295
1296 // No uses, just terminate
1297 if (self->outcnt() == 0) {
1298 assert(self->is_MachProj(), "sanity");
1299 continue; // Must be a dead machine projection
1300 }
1301
1302 // If node is pinned in the block, then no scheduling can be done.
1303 if( self->pinned() ) // Pinned in block?
1304 continue;
1305
1306 #ifdef ASSERT
1307 // Assert that memory writers (e.g. stores) have a "home" block (the block
1308 // given by their control input), and that this block corresponds to their
1309 // earliest possible placement. This guarantees that
1310 // hoist_to_cheaper_block() will always have at least one valid choice.
1311 if (self->is_memory_writer()) {
1312 assert(find_block_for_node(self->in(0)) == early,
1313 "The home of a memory writer must also be its earliest placement");
1314 }
1315 #endif
1316
1317 MachNode* mach = self->is_Mach() ? self->as_Mach() : NULL;
1318 if (mach) {
1319 switch (mach->ideal_Opcode()) {
1320 case Op_CreateEx:
1321 // Don't move exception creation
1322 early->add_inst(self);
1323 continue;
1324 break;
1325 case Op_CheckCastPP: {
1326 // Don't move CheckCastPP nodes away from their input, if the input
1327 // is a rawptr (5071820).
1328 Node *def = self->in(1);
1329 if (def != NULL && def->bottom_type()->base() == Type::RawPtr) {
1330 early->add_inst(self);
1331 #ifdef ASSERT
1332 _raw_oops.push(def);
1333 #endif
1334 continue;
1335 }
1336 break;
1337 }
1338 default:
1339 break;
1340 }
1341 if (C->has_irreducible_loop() && self->is_memory_writer()) {
1342 // If the CFG is irreducible, place memory writers in their home block.
1343 // This prevents hoist_to_cheaper_block() from accidentally placing such
1344 // nodes into deeper loops, as in the following example:
1345 //
1346 // Home placement of store in B1 (loop L1):
1347 //
1348 // B1 (L1):
1349 // m1 <- ..
1350 // m2 <- store m1, ..
1351 // B2 (L2):
1352 // jump B2
1353 // B3 (L1):
1354 // .. <- .. m2, ..
1355 //
1356 // Wrong "hoisting" of store to B2 (in loop L2, child of L1):
1357 //
1358 // B1 (L1):
1359 // m1 <- ..
1360 // B2 (L2):
1361 // m2 <- store m1, ..
1362 // # Wrong: m1 and m2 interfere at this point.
1363 // jump B2
1364 // B3 (L1):
1365 // .. <- .. m2, ..
1366 //
1367 // This "hoist inversion" can happen due to different factors such as
1368 // inaccurate estimation of frequencies for irreducible CFGs, and loops
1369 // with always-taken exits in reducible CFGs. In the reducible case,
1370 // hoist inversion is prevented by discarding invalid blocks (those in
1371 // deeper loops than the home block). In the irreducible case, the
1372 // invalid blocks cannot be identified due to incomplete loop nesting
1373 // information, hence a conservative solution is taken.
1374 #ifndef PRODUCT
1375 if (trace_opto_pipelining()) {
1376 tty->print_cr("# Irreducible loops: schedule in home block B%d:",
1377 early->_pre_order);
1378 self->dump();
1379 }
1380 #endif
1381 schedule_node_into_block(self, early);
1382 continue;
1383 }
1384 }
1385
1386 // Gather LCA of all uses
1387 Block *LCA = NULL;
1388 {
1389 for (DUIterator_Fast imax, i = self->fast_outs(imax); i < imax; i++) {
1390 // For all uses, find LCA
1391 Node* use = self->fast_out(i);
1392 LCA = raise_LCA_above_use(LCA, use, self, this);
1393 }
1394 guarantee(LCA != NULL, "There must be a LCA");
1395 } // (Hide defs of imax, i from rest of block.)
1396
1397 // Place temps in the block of their use. This isn't a
1398 // requirement for correctness but it reduces useless
1399 // interference between temps and other nodes.
1400 if (mach != NULL && mach->is_MachTemp()) {
1401 map_node_to_block(self, LCA);
1402 LCA->add_inst(self);
1403 continue;
1404 }
1405
1406 // Check if 'self' could be anti-dependent on memory
1407 if (self->needs_anti_dependence_check()) {
1408 // Hoist LCA above possible-defs and insert anti-dependences to
1409 // defs in new LCA block.
1410 LCA = insert_anti_dependences(LCA, self);
1411 }
1412
1413 if (early->_dom_depth > LCA->_dom_depth) {
1414 // Somehow the LCA has moved above the earliest legal point.
1415 // (One way this can happen is via memory_early_block.)
1416 if (C->subsume_loads() == true && !C->failing()) {
1417 // Retry with subsume_loads == false
1418 // If this is the first failure, the sentinel string will "stick"
1419 // to the Compile object, and the C2Compiler will see it and retry.
1420 C->record_failure(C2Compiler::retry_no_subsuming_loads());
1421 } else {
1422 // Bailout without retry when (early->_dom_depth > LCA->_dom_depth)
1423 assert(false, "graph should be schedulable");
1424 C->record_method_not_compilable("late schedule failed: incorrect graph");
1425 }
1426 return;
1427 }
1428
1429 if (self->is_memory_writer()) {
1430 // If the LCA of a memory writer is a descendant of its home loop, hoist
1431 // it into a valid placement.
1432 while (LCA->_loop->depth() > early->_loop->depth()) {
1433 LCA = LCA->_idom;
1434 }
1435 assert(LCA != NULL, "a valid LCA must exist");
1436 verify_memory_writer_placement(LCA, self);
1437 }
1438
1439 // If there is no opportunity to hoist, then we're done.
1440 // In stress mode, try to hoist even the single operations.
1441 bool try_to_hoist = StressGCM || (LCA != early);
1442
1443 // Must clone guys stay next to use; no hoisting allowed.
1444 // Also cannot hoist guys that alter memory or are otherwise not
1445 // allocatable (hoisting can make a value live longer, leading to
1446 // anti and output dependency problems which are normally resolved
1447 // by the register allocator giving everyone a different register).
1448 if (mach != NULL && must_clone[mach->ideal_Opcode()])
1449 try_to_hoist = false;
1450
1451 Block* late = NULL;
1452 if (try_to_hoist) {
1453 // Now find the block with the least execution frequency.
1454 // Start at the latest schedule and work up to the earliest schedule
1455 // in the dominator tree. Thus the Node will dominate all its uses.
1456 late = hoist_to_cheaper_block(LCA, early, self);
1457 } else {
1458 // Just use the LCA of the uses.
1459 late = LCA;
1460 }
1461
1462 // Put the node into target block
1463 schedule_node_into_block(self, late);
1464
1465 #ifdef ASSERT
1466 if (self->needs_anti_dependence_check()) {
1467 // since precedence edges are only inserted when we're sure they
1468 // are needed make sure that after placement in a block we don't
1469 // need any new precedence edges.
1470 verify_anti_dependences(late, self);
1471 }
1472 #endif
1473 } // Loop until all nodes have been visited
1474
1475 } // end ScheduleLate
1476
1477 //------------------------------GlobalCodeMotion-------------------------------
1478 void PhaseCFG::global_code_motion() {
1479 ResourceMark rm;
1480
1481 #ifndef PRODUCT
1482 if (trace_opto_pipelining()) {
1483 tty->print("\n---- Start GlobalCodeMotion ----\n");
1484 }
1485 #endif
1486
1487 // Initialize the node to block mapping for things on the proj_list
1488 for (uint i = 0; i < _matcher.number_of_projections(); i++) {
1489 unmap_node_from_block(_matcher.get_projection(i));
1490 }
1491
1492 // Set the basic block for Nodes pinned into blocks
1493 VectorSet visited;
1494 schedule_pinned_nodes(visited);
1495
1496 // Find the earliest Block any instruction can be placed in. Some
1497 // instructions are pinned into Blocks. Unpinned instructions can
1498 // appear in last block in which all their inputs occur.
1499 visited.clear();
1500 Node_Stack stack((C->live_nodes() >> 2) + 16); // pre-grow
1501 if (!schedule_early(visited, stack)) {
1502 // Bailout without retry
1503 C->record_method_not_compilable("early schedule failed");
1504 return;
1505 }
1506
1507 // Build Def-Use edges.
1508 // Compute the latency information (via backwards walk) for all the
1509 // instructions in the graph
1510 _node_latency = new GrowableArray<uint>(); // resource_area allocation
1511
1512 if (C->do_scheduling()) {
1513 compute_latencies_backwards(visited, stack);
1514 }
1515
1516 // Now schedule all codes as LATE as possible. This is the LCA in the
1517 // dominator tree of all USES of a value. Pick the block with the least
1518 // loop nesting depth that is lowest in the dominator tree.
1519 // ( visited.clear() called in schedule_late()->Node_Backward_Iterator() )
1520 schedule_late(visited, stack);
1521 if (C->failing()) {
1522 return;
1523 }
1524
1525 #ifndef PRODUCT
1526 if (trace_opto_pipelining()) {
1527 tty->print("\n---- Detect implicit null checks ----\n");
1528 }
1529 #endif
1530
1531 // Detect implicit-null-check opportunities. Basically, find NULL checks
1532 // with suitable memory ops nearby. Use the memory op to do the NULL check.
1533 // I can generate a memory op if there is not one nearby.
1534 if (C->is_method_compilation()) {
1535 // By reversing the loop direction we get a very minor gain on mpegaudio.
1536 // Feel free to revert to a forward loop for clarity.
1537 // for( int i=0; i < (int)matcher._null_check_tests.size(); i+=2 ) {
1538 for (int i = _matcher._null_check_tests.size() - 2; i >= 0; i -= 2) {
1539 Node* proj = _matcher._null_check_tests[i];
1540 Node* val = _matcher._null_check_tests[i + 1];
1541 Block* block = get_block_for_node(proj);
1542 implicit_null_check(block, proj, val, C->allowed_deopt_reasons());
1543 // The implicit_null_check will only perform the transformation
1544 // if the null branch is truly uncommon, *and* it leads to an
1545 // uncommon trap. Combined with the too_many_traps guards
1546 // above, this prevents SEGV storms reported in 6366351,
1547 // by recompiling offending methods without this optimization.
1548 }
1549 }
1550
1551 bool block_size_threshold_ok = false;
1552 intptr_t *recalc_pressure_nodes = NULL;
1553 if (OptoRegScheduling) {
1554 for (uint i = 0; i < number_of_blocks(); i++) {
1555 Block* block = get_block(i);
1556 if (block->number_of_nodes() > 10) {
1557 block_size_threshold_ok = true;
1558 break;
1559 }
1560 }
1561 }
1562
1563 // Enabling the scheduler for register pressure plus finding blocks of size to schedule for it
1564 // is key to enabling this feature.
1565 PhaseChaitin regalloc(C->unique(), *this, _matcher, true);
1566 ResourceArea live_arena(mtCompiler); // Arena for liveness
1567 ResourceMark rm_live(&live_arena);
1568 PhaseLive live(*this, regalloc._lrg_map.names(), &live_arena, true);
1569 PhaseIFG ifg(&live_arena);
1570 if (OptoRegScheduling && block_size_threshold_ok) {
1571 regalloc.mark_ssa();
1572 Compile::TracePhase tp("computeLive", &timers[_t_computeLive]);
1573 rm_live.reset_to_mark(); // Reclaim working storage
1574 IndexSet::reset_memory(C, &live_arena);
1575 uint node_size = regalloc._lrg_map.max_lrg_id();
1576 ifg.init(node_size); // Empty IFG
1577 regalloc.set_ifg(ifg);
1578 regalloc.set_live(live);
1579 regalloc.gather_lrg_masks(false); // Collect LRG masks
1580 live.compute(node_size); // Compute liveness
1581
1582 recalc_pressure_nodes = NEW_RESOURCE_ARRAY(intptr_t, node_size);
1583 for (uint i = 0; i < node_size; i++) {
1584 recalc_pressure_nodes[i] = 0;
1585 }
1586 }
1587 _regalloc = ®alloc;
1588
1589 #ifndef PRODUCT
1590 if (trace_opto_pipelining()) {
1591 tty->print("\n---- Start Local Scheduling ----\n");
1592 }
1593 #endif
1594
1595 // Schedule locally. Right now a simple topological sort.
1596 // Later, do a real latency aware scheduler.
1597 GrowableArray<int> ready_cnt(C->unique(), C->unique(), -1);
1598 visited.reset();
1599 for (uint i = 0; i < number_of_blocks(); i++) {
1600 Block* block = get_block(i);
1601 if (!schedule_local(block, ready_cnt, visited, recalc_pressure_nodes)) {
1602 if (!C->failure_reason_is(C2Compiler::retry_no_subsuming_loads())) {
1603 C->record_method_not_compilable("local schedule failed");
1604 }
1605 _regalloc = NULL;
1606 return;
1607 }
1608 }
1609 _regalloc = NULL;
1610
1611 // If we inserted any instructions between a Call and his CatchNode,
1612 // clone the instructions on all paths below the Catch.
1613 for (uint i = 0; i < number_of_blocks(); i++) {
1614 Block* block = get_block(i);
1615 call_catch_cleanup(block);
1616 }
1617
1618 #ifndef PRODUCT
1619 if (trace_opto_pipelining()) {
1620 tty->print("\n---- After GlobalCodeMotion ----\n");
1621 for (uint i = 0; i < number_of_blocks(); i++) {
1622 Block* block = get_block(i);
1623 block->dump();
1624 }
1625 }
1626 #endif
1627 // Dead.
1628 _node_latency = (GrowableArray<uint> *)((intptr_t)0xdeadbeef);
1629 }
1630
1631 bool PhaseCFG::do_global_code_motion() {
1632
1633 build_dominator_tree();
1634 if (C->failing()) {
1635 return false;
1636 }
1637
1638 NOT_PRODUCT( C->verify_graph_edges(); )
1639
1640 estimate_block_frequency();
1641
1642 global_code_motion();
1643
1644 if (C->failing()) {
1645 return false;
1646 }
1647
1648 return true;
1649 }
1650
1651 //------------------------------Estimate_Block_Frequency-----------------------
1652 // Estimate block frequencies based on IfNode probabilities.
1653 void PhaseCFG::estimate_block_frequency() {
1654
1655 // Force conditional branches leading to uncommon traps to be unlikely,
1656 // not because we get to the uncommon_trap with less relative frequency,
1657 // but because an uncommon_trap typically causes a deopt, so we only get
1658 // there once.
1659 if (C->do_freq_based_layout()) {
1660 Block_List worklist;
1661 Block* root_blk = get_block(0);
1662 for (uint i = 1; i < root_blk->num_preds(); i++) {
1663 Block *pb = get_block_for_node(root_blk->pred(i));
1664 if (pb->has_uncommon_code()) {
1665 worklist.push(pb);
1666 }
1667 }
1668 while (worklist.size() > 0) {
1669 Block* uct = worklist.pop();
1670 if (uct == get_root_block()) {
1671 continue;
1672 }
1673 for (uint i = 1; i < uct->num_preds(); i++) {
1674 Block *pb = get_block_for_node(uct->pred(i));
1675 if (pb->_num_succs == 1) {
1676 worklist.push(pb);
1677 } else if (pb->num_fall_throughs() == 2) {
1678 pb->update_uncommon_branch(uct);
1679 }
1680 }
1681 }
1682 }
1683
1684 // Create the loop tree and calculate loop depth.
1685 _root_loop = create_loop_tree();
1686 _root_loop->compute_loop_depth(0);
1687
1688 // Compute block frequency of each block, relative to a single loop entry.
1689 _root_loop->compute_freq();
1690
1691 // Adjust all frequencies to be relative to a single method entry
1692 _root_loop->_freq = 1.0;
1693 _root_loop->scale_freq();
1694
1695 // Save outmost loop frequency for LRG frequency threshold
1696 _outer_loop_frequency = _root_loop->outer_loop_freq();
1697
1698 // force paths ending at uncommon traps to be infrequent
1699 if (!C->do_freq_based_layout()) {
1700 Block_List worklist;
1701 Block* root_blk = get_block(0);
1702 for (uint i = 1; i < root_blk->num_preds(); i++) {
1703 Block *pb = get_block_for_node(root_blk->pred(i));
1704 if (pb->has_uncommon_code()) {
1705 worklist.push(pb);
1706 }
1707 }
1708 while (worklist.size() > 0) {
1709 Block* uct = worklist.pop();
1710 uct->_freq = PROB_MIN;
1711 for (uint i = 1; i < uct->num_preds(); i++) {
1712 Block *pb = get_block_for_node(uct->pred(i));
1713 if (pb->_num_succs == 1 && pb->_freq > PROB_MIN) {
1714 worklist.push(pb);
1715 }
1716 }
1717 }
1718 }
1719
1720 #ifdef ASSERT
1721 for (uint i = 0; i < number_of_blocks(); i++) {
1722 Block* b = get_block(i);
1723 assert(b->_freq >= MIN_BLOCK_FREQUENCY, "Register Allocator requires meaningful block frequency");
1724 }
1725 #endif
1726
1727 #ifndef PRODUCT
1728 if (PrintCFGBlockFreq) {
1729 tty->print_cr("CFG Block Frequencies");
1730 _root_loop->dump_tree();
1731 if (Verbose) {
1732 tty->print_cr("PhaseCFG dump");
1733 dump();
1734 tty->print_cr("Node dump");
1735 _root->dump(99999);
1736 }
1737 }
1738 #endif
1739 }
1740
1741 //----------------------------create_loop_tree--------------------------------
1742 // Create a loop tree from the CFG
1743 CFGLoop* PhaseCFG::create_loop_tree() {
1744
1745 #ifdef ASSERT
1746 assert(get_block(0) == get_root_block(), "first block should be root block");
1747 for (uint i = 0; i < number_of_blocks(); i++) {
1748 Block* block = get_block(i);
1749 // Check that _loop field are clear...we could clear them if not.
1750 assert(block->_loop == NULL, "clear _loop expected");
1751 // Sanity check that the RPO numbering is reflected in the _blocks array.
1752 // It doesn't have to be for the loop tree to be built, but if it is not,
1753 // then the blocks have been reordered since dom graph building...which
1754 // may question the RPO numbering
1755 assert(block->_rpo == i, "unexpected reverse post order number");
1756 }
1757 #endif
1758
1759 int idct = 0;
1760 CFGLoop* root_loop = new CFGLoop(idct++);
1761
1762 Block_List worklist;
1763
1764 // Assign blocks to loops
1765 for(uint i = number_of_blocks() - 1; i > 0; i-- ) { // skip Root block
1766 Block* block = get_block(i);
1767
1768 if (block->head()->is_Loop()) {
1769 Block* loop_head = block;
1770 assert(loop_head->num_preds() - 1 == 2, "loop must have 2 predecessors");
1771 Node* tail_n = loop_head->pred(LoopNode::LoopBackControl);
1772 Block* tail = get_block_for_node(tail_n);
1773
1774 // Defensively filter out Loop nodes for non-single-entry loops.
1775 // For all reasonable loops, the head occurs before the tail in RPO.
1776 if (i <= tail->_rpo) {
1777
1778 // The tail and (recursive) predecessors of the tail
1779 // are made members of a new loop.
1780
1781 assert(worklist.size() == 0, "nonempty worklist");
1782 CFGLoop* nloop = new CFGLoop(idct++);
1783 assert(loop_head->_loop == NULL, "just checking");
1784 loop_head->_loop = nloop;
1785 // Add to nloop so push_pred() will skip over inner loops
1786 nloop->add_member(loop_head);
1787 nloop->push_pred(loop_head, LoopNode::LoopBackControl, worklist, this);
1788
1789 while (worklist.size() > 0) {
1790 Block* member = worklist.pop();
1791 if (member != loop_head) {
1792 for (uint j = 1; j < member->num_preds(); j++) {
1793 nloop->push_pred(member, j, worklist, this);
1794 }
1795 }
1796 }
1797 }
1798 }
1799 }
1800
1801 // Create a member list for each loop consisting
1802 // of both blocks and (immediate child) loops.
1803 for (uint i = 0; i < number_of_blocks(); i++) {
1804 Block* block = get_block(i);
1805 CFGLoop* lp = block->_loop;
1806 if (lp == NULL) {
1807 // Not assigned to a loop. Add it to the method's pseudo loop.
1808 block->_loop = root_loop;
1809 lp = root_loop;
1810 }
1811 if (lp == root_loop || block != lp->head()) { // loop heads are already members
1812 lp->add_member(block);
1813 }
1814 if (lp != root_loop) {
1815 if (lp->parent() == NULL) {
1816 // Not a nested loop. Make it a child of the method's pseudo loop.
1817 root_loop->add_nested_loop(lp);
1818 }
1819 if (block == lp->head()) {
1820 // Add nested loop to member list of parent loop.
1821 lp->parent()->add_member(lp);
1822 }
1823 }
1824 }
1825
1826 return root_loop;
1827 }
1828
1829 //------------------------------push_pred--------------------------------------
1830 void CFGLoop::push_pred(Block* blk, int i, Block_List& worklist, PhaseCFG* cfg) {
1831 Node* pred_n = blk->pred(i);
1832 Block* pred = cfg->get_block_for_node(pred_n);
1833 CFGLoop *pred_loop = pred->_loop;
1834 if (pred_loop == NULL) {
1835 // Filter out blocks for non-single-entry loops.
1836 // For all reasonable loops, the head occurs before the tail in RPO.
1837 if (pred->_rpo > head()->_rpo) {
1838 pred->_loop = this;
1839 worklist.push(pred);
1840 }
1841 } else if (pred_loop != this) {
1842 // Nested loop.
1843 while (pred_loop->_parent != NULL && pred_loop->_parent != this) {
1844 pred_loop = pred_loop->_parent;
1845 }
1846 // Make pred's loop be a child
1847 if (pred_loop->_parent == NULL) {
1848 add_nested_loop(pred_loop);
1849 // Continue with loop entry predecessor.
1850 Block* pred_head = pred_loop->head();
1851 assert(pred_head->num_preds() - 1 == 2, "loop must have 2 predecessors");
1852 assert(pred_head != head(), "loop head in only one loop");
1853 push_pred(pred_head, LoopNode::EntryControl, worklist, cfg);
1854 } else {
1855 assert(pred_loop->_parent == this && _parent == NULL, "just checking");
1856 }
1857 }
1858 }
1859
1860 //------------------------------add_nested_loop--------------------------------
1861 // Make cl a child of the current loop in the loop tree.
1862 void CFGLoop::add_nested_loop(CFGLoop* cl) {
1863 assert(_parent == NULL, "no parent yet");
1864 assert(cl != this, "not my own parent");
1865 cl->_parent = this;
1866 CFGLoop* ch = _child;
1867 if (ch == NULL) {
1868 _child = cl;
1869 } else {
1870 while (ch->_sibling != NULL) { ch = ch->_sibling; }
1871 ch->_sibling = cl;
1872 }
1873 }
1874
1875 //------------------------------compute_loop_depth-----------------------------
1876 // Store the loop depth in each CFGLoop object.
1877 // Recursively walk the children to do the same for them.
1878 void CFGLoop::compute_loop_depth(int depth) {
1879 _depth = depth;
1880 CFGLoop* ch = _child;
1881 while (ch != NULL) {
1882 ch->compute_loop_depth(depth + 1);
1883 ch = ch->_sibling;
1884 }
1885 }
1886
1887 //------------------------------compute_freq-----------------------------------
1888 // Compute the frequency of each block and loop, relative to a single entry
1889 // into the dominating loop head.
1890 void CFGLoop::compute_freq() {
1891 // Bottom up traversal of loop tree (visit inner loops first.)
1892 // Set loop head frequency to 1.0, then transitively
1893 // compute frequency for all successors in the loop,
1894 // as well as for each exit edge. Inner loops are
1895 // treated as single blocks with loop exit targets
1896 // as the successor blocks.
1897
1898 // Nested loops first
1899 CFGLoop* ch = _child;
1900 while (ch != NULL) {
1901 ch->compute_freq();
1902 ch = ch->_sibling;
1903 }
1904 assert (_members.length() > 0, "no empty loops");
1905 Block* hd = head();
1906 hd->_freq = 1.0;
1907 for (int i = 0; i < _members.length(); i++) {
1908 CFGElement* s = _members.at(i);
1909 double freq = s->_freq;
1910 if (s->is_block()) {
1911 Block* b = s->as_Block();
1912 for (uint j = 0; j < b->_num_succs; j++) {
1913 Block* sb = b->_succs[j];
1914 update_succ_freq(sb, freq * b->succ_prob(j));
1915 }
1916 } else {
1917 CFGLoop* lp = s->as_CFGLoop();
1918 assert(lp->_parent == this, "immediate child");
1919 for (int k = 0; k < lp->_exits.length(); k++) {
1920 Block* eb = lp->_exits.at(k).get_target();
1921 double prob = lp->_exits.at(k).get_prob();
1922 update_succ_freq(eb, freq * prob);
1923 }
1924 }
1925 }
1926
1927 // For all loops other than the outer, "method" loop,
1928 // sum and normalize the exit probability. The "method" loop
1929 // should keep the initial exit probability of 1, so that
1930 // inner blocks do not get erroneously scaled.
1931 if (_depth != 0) {
1932 // Total the exit probabilities for this loop.
1933 double exits_sum = 0.0f;
1934 for (int i = 0; i < _exits.length(); i++) {
1935 exits_sum += _exits.at(i).get_prob();
1936 }
1937
1938 // Normalize the exit probabilities. Until now, the
1939 // probabilities estimate the possibility of exit per
1940 // a single loop iteration; afterward, they estimate
1941 // the probability of exit per loop entry.
1942 for (int i = 0; i < _exits.length(); i++) {
1943 Block* et = _exits.at(i).get_target();
1944 float new_prob = 0.0f;
1945 if (_exits.at(i).get_prob() > 0.0f) {
1946 new_prob = _exits.at(i).get_prob() / exits_sum;
1947 }
1948 BlockProbPair bpp(et, new_prob);
1949 _exits.at_put(i, bpp);
1950 }
1951
1952 // Save the total, but guard against unreasonable probability,
1953 // as the value is used to estimate the loop trip count.
1954 // An infinite trip count would blur relative block
1955 // frequencies.
1956 if (exits_sum > 1.0f) exits_sum = 1.0;
1957 if (exits_sum < PROB_MIN) exits_sum = PROB_MIN;
1958 _exit_prob = exits_sum;
1959 }
1960 }
1961
1962 //------------------------------succ_prob-------------------------------------
1963 // Determine the probability of reaching successor 'i' from the receiver block.
1964 float Block::succ_prob(uint i) {
1965 int eidx = end_idx();
1966 Node *n = get_node(eidx); // Get ending Node
1967
1968 int op = n->Opcode();
1969 if (n->is_Mach()) {
1970 if (n->is_MachNullCheck()) {
1971 // Can only reach here if called after lcm. The original Op_If is gone,
1972 // so we attempt to infer the probability from one or both of the
1973 // successor blocks.
1974 assert(_num_succs == 2, "expecting 2 successors of a null check");
1975 // If either successor has only one predecessor, then the
1976 // probability estimate can be derived using the
1977 // relative frequency of the successor and this block.
1978 if (_succs[i]->num_preds() == 2) {
1979 return _succs[i]->_freq / _freq;
1980 } else if (_succs[1-i]->num_preds() == 2) {
1981 return 1 - (_succs[1-i]->_freq / _freq);
1982 } else {
1983 // Estimate using both successor frequencies
1984 float freq = _succs[i]->_freq;
1985 return freq / (freq + _succs[1-i]->_freq);
1986 }
1987 }
1988 op = n->as_Mach()->ideal_Opcode();
1989 }
1990
1991
1992 // Switch on branch type
1993 switch( op ) {
1994 case Op_CountedLoopEnd:
1995 case Op_If: {
1996 assert (i < 2, "just checking");
1997 // Conditionals pass on only part of their frequency
1998 float prob = n->as_MachIf()->_prob;
1999 assert(prob >= 0.0 && prob <= 1.0, "out of range probability");
2000 // If succ[i] is the FALSE branch, invert path info
2001 if( get_node(i + eidx + 1)->Opcode() == Op_IfFalse ) {
2002 return 1.0f - prob; // not taken
2003 } else {
2004 return prob; // taken
2005 }
2006 }
2007
2008 case Op_Jump:
2009 return n->as_MachJump()->_probs[get_node(i + eidx + 1)->as_JumpProj()->_con];
2010
2011 case Op_Catch: {
2012 const CatchProjNode *ci = get_node(i + eidx + 1)->as_CatchProj();
2013 if (ci->_con == CatchProjNode::fall_through_index) {
2014 // Fall-thru path gets the lion's share.
2015 return 1.0f - PROB_UNLIKELY_MAG(5)*_num_succs;
2016 } else {
2017 // Presume exceptional paths are equally unlikely
2018 return PROB_UNLIKELY_MAG(5);
2019 }
2020 }
2021
2022 case Op_Root:
2023 case Op_Goto:
2024 // Pass frequency straight thru to target
2025 return 1.0f;
2026
2027 case Op_NeverBranch:
2028 return 0.0f;
2029
2030 case Op_TailCall:
2031 case Op_TailJump:
2032 case Op_Return:
2033 case Op_Halt:
2034 case Op_Rethrow:
2035 // Do not push out freq to root block
2036 return 0.0f;
2037
2038 default:
2039 ShouldNotReachHere();
2040 }
2041
2042 return 0.0f;
2043 }
2044
2045 //------------------------------num_fall_throughs-----------------------------
2046 // Return the number of fall-through candidates for a block
2047 int Block::num_fall_throughs() {
2048 int eidx = end_idx();
2049 Node *n = get_node(eidx); // Get ending Node
2050
2051 int op = n->Opcode();
2052 if (n->is_Mach()) {
2053 if (n->is_MachNullCheck()) {
2054 // In theory, either side can fall-thru, for simplicity sake,
2055 // let's say only the false branch can now.
2056 return 1;
2057 }
2058 op = n->as_Mach()->ideal_Opcode();
2059 }
2060
2061 // Switch on branch type
2062 switch( op ) {
2063 case Op_CountedLoopEnd:
2064 case Op_If:
2065 return 2;
2066
2067 case Op_Root:
2068 case Op_Goto:
2069 return 1;
2070
2071 case Op_Catch: {
2072 for (uint i = 0; i < _num_succs; i++) {
2073 const CatchProjNode *ci = get_node(i + eidx + 1)->as_CatchProj();
2074 if (ci->_con == CatchProjNode::fall_through_index) {
2075 return 1;
2076 }
2077 }
2078 return 0;
2079 }
2080
2081 case Op_Jump:
2082 case Op_NeverBranch:
2083 case Op_TailCall:
2084 case Op_TailJump:
2085 case Op_Return:
2086 case Op_Halt:
2087 case Op_Rethrow:
2088 return 0;
2089
2090 default:
2091 ShouldNotReachHere();
2092 }
2093
2094 return 0;
2095 }
2096
2097 //------------------------------succ_fall_through-----------------------------
2098 // Return true if a specific successor could be fall-through target.
2099 bool Block::succ_fall_through(uint i) {
2100 int eidx = end_idx();
2101 Node *n = get_node(eidx); // Get ending Node
2102
2103 int op = n->Opcode();
2104 if (n->is_Mach()) {
2105 if (n->is_MachNullCheck()) {
2106 // In theory, either side can fall-thru, for simplicity sake,
2107 // let's say only the false branch can now.
2108 return get_node(i + eidx + 1)->Opcode() == Op_IfFalse;
2109 }
2110 op = n->as_Mach()->ideal_Opcode();
2111 }
2112
2113 // Switch on branch type
2114 switch( op ) {
2115 case Op_CountedLoopEnd:
2116 case Op_If:
2117 case Op_Root:
2118 case Op_Goto:
2119 return true;
2120
2121 case Op_Catch: {
2122 const CatchProjNode *ci = get_node(i + eidx + 1)->as_CatchProj();
2123 return ci->_con == CatchProjNode::fall_through_index;
2124 }
2125
2126 case Op_Jump:
2127 case Op_NeverBranch:
2128 case Op_TailCall:
2129 case Op_TailJump:
2130 case Op_Return:
2131 case Op_Halt:
2132 case Op_Rethrow:
2133 return false;
2134
2135 default:
2136 ShouldNotReachHere();
2137 }
2138
2139 return false;
2140 }
2141
2142 //------------------------------update_uncommon_branch------------------------
2143 // Update the probability of a two-branch to be uncommon
2144 void Block::update_uncommon_branch(Block* ub) {
2145 int eidx = end_idx();
2146 Node *n = get_node(eidx); // Get ending Node
2147
2148 int op = n->as_Mach()->ideal_Opcode();
2149
2150 assert(op == Op_CountedLoopEnd || op == Op_If, "must be a If");
2151 assert(num_fall_throughs() == 2, "must be a two way branch block");
2152
2153 // Which successor is ub?
2154 uint s;
2155 for (s = 0; s <_num_succs; s++) {
2156 if (_succs[s] == ub) break;
2157 }
2158 assert(s < 2, "uncommon successor must be found");
2159
2160 // If ub is the true path, make the proability small, else
2161 // ub is the false path, and make the probability large
2162 bool invert = (get_node(s + eidx + 1)->Opcode() == Op_IfFalse);
2163
2164 // Get existing probability
2165 float p = n->as_MachIf()->_prob;
2166
2167 if (invert) p = 1.0 - p;
2168 if (p > PROB_MIN) {
2169 p = PROB_MIN;
2170 }
2171 if (invert) p = 1.0 - p;
2172
2173 n->as_MachIf()->_prob = p;
2174 }
2175
2176 //------------------------------update_succ_freq-------------------------------
2177 // Update the appropriate frequency associated with block 'b', a successor of
2178 // a block in this loop.
2179 void CFGLoop::update_succ_freq(Block* b, double freq) {
2180 if (b->_loop == this) {
2181 if (b == head()) {
2182 // back branch within the loop
2183 // Do nothing now, the loop carried frequency will be
2184 // adjust later in scale_freq().
2185 } else {
2186 // simple branch within the loop
2187 b->_freq += freq;
2188 }
2189 } else if (!in_loop_nest(b)) {
2190 // branch is exit from this loop
2191 BlockProbPair bpp(b, freq);
2192 _exits.append(bpp);
2193 } else {
2194 // branch into nested loop
2195 CFGLoop* ch = b->_loop;
2196 ch->_freq += freq;
2197 }
2198 }
2199
2200 //------------------------------in_loop_nest-----------------------------------
2201 // Determine if block b is in the receiver's loop nest.
2202 bool CFGLoop::in_loop_nest(Block* b) {
2203 int depth = _depth;
2204 CFGLoop* b_loop = b->_loop;
2205 int b_depth = b_loop->_depth;
2206 if (depth == b_depth) {
2207 return true;
2208 }
2209 while (b_depth > depth) {
2210 b_loop = b_loop->_parent;
2211 b_depth = b_loop->_depth;
2212 }
2213 return b_loop == this;
2214 }
2215
2216 //------------------------------scale_freq-------------------------------------
2217 // Scale frequency of loops and blocks by trip counts from outer loops
2218 // Do a top down traversal of loop tree (visit outer loops first.)
2219 void CFGLoop::scale_freq() {
2220 double loop_freq = _freq * trip_count();
2221 _freq = loop_freq;
2222 for (int i = 0; i < _members.length(); i++) {
2223 CFGElement* s = _members.at(i);
2224 double block_freq = s->_freq * loop_freq;
2225 if (g_isnan(block_freq) || block_freq < MIN_BLOCK_FREQUENCY)
2226 block_freq = MIN_BLOCK_FREQUENCY;
2227 s->_freq = block_freq;
2228 }
2229 CFGLoop* ch = _child;
2230 while (ch != NULL) {
2231 ch->scale_freq();
2232 ch = ch->_sibling;
2233 }
2234 }
2235
2236 // Frequency of outer loop
2237 double CFGLoop::outer_loop_freq() const {
2238 if (_child != NULL) {
2239 return _child->_freq;
2240 }
2241 return _freq;
2242 }
2243
2244 #ifndef PRODUCT
2245 //------------------------------dump_tree--------------------------------------
2246 void CFGLoop::dump_tree() const {
2247 dump();
2248 if (_child != NULL) _child->dump_tree();
2249 if (_sibling != NULL) _sibling->dump_tree();
2250 }
2251
2252 //------------------------------dump-------------------------------------------
2253 void CFGLoop::dump() const {
2254 for (int i = 0; i < _depth; i++) tty->print(" ");
2255 tty->print("%s: %d trip_count: %6.0f freq: %6.0f\n",
2256 _depth == 0 ? "Method" : "Loop", _id, trip_count(), _freq);
2257 for (int i = 0; i < _depth; i++) tty->print(" ");
2258 tty->print(" members:");
2259 int k = 0;
2260 for (int i = 0; i < _members.length(); i++) {
2261 if (k++ >= 6) {
2262 tty->print("\n ");
2263 for (int j = 0; j < _depth+1; j++) tty->print(" ");
2264 k = 0;
2265 }
2266 CFGElement *s = _members.at(i);
2267 if (s->is_block()) {
2268 Block *b = s->as_Block();
2269 tty->print(" B%d(%6.3f)", b->_pre_order, b->_freq);
2270 } else {
2271 CFGLoop* lp = s->as_CFGLoop();
2272 tty->print(" L%d(%6.3f)", lp->_id, lp->_freq);
2273 }
2274 }
2275 tty->print("\n");
2276 for (int i = 0; i < _depth; i++) tty->print(" ");
2277 tty->print(" exits: ");
2278 k = 0;
2279 for (int i = 0; i < _exits.length(); i++) {
2280 if (k++ >= 7) {
2281 tty->print("\n ");
2282 for (int j = 0; j < _depth+1; j++) tty->print(" ");
2283 k = 0;
2284 }
2285 Block *blk = _exits.at(i).get_target();
2286 double prob = _exits.at(i).get_prob();
2287 tty->print(" ->%d@%d%%", blk->_pre_order, (int)(prob*100));
2288 }
2289 tty->print("\n");
2290 }
2291 #endif
--- EOF ---