1 /* 2 * Copyright (c) 1997, 2024, 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. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 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). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 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 != nullptr) { 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 != nullptr, "Only control-dependent"); 81 const Node *p = in0->is_block_proj(); 82 if (p != nullptr && 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 != nullptr && d != nullptr, "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 = nullptr; 216 for (uint i = node->len()-1; i >= node->req(); i--) { 217 Node* m = node->in(i); 218 if (m == nullptr) 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 == nullptr) { 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 != nullptr) { 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) != nullptr) { 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 == nullptr) return; 258 assert(b1->_dom_depth < b2->_dom_depth, "sanity"); 259 Block* tmp = b2; 260 while (tmp != b1 && tmp != nullptr) { 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 == nullptr) 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 = nullptr; // 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 == nullptr) continue; // Ignore null, missing inputs 288 Block* inb = cfg->get_block_for_node(inn); 289 assert(inb != nullptr, "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 != nullptr, "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 != nullptr) { 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 == nullptr) { 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 == nullptr || 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 == nullptr) 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 != nullptr) mem_inputs[mem_inputs_length++] = base; 511 if (index != nullptr) mem_inputs[mem_inputs_length++] = index; 512 if (store != nullptr) mem_inputs[mem_inputs_length++] = store; 513 514 // In the comparison 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) != nullptr) mem_inputs[mem_inputs_length++] = load->in(0); 523 524 Block* deepb = nullptr; // 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 != nullptr, "null check without null projection"); 558 Node* null_block_region = if_true->find_out_with(Op_Region); 559 assert(null_block_region != nullptr, "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 != nullptr, ""); 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->do_aliasing() && 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(nullptr); 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 = nullptr; // 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 == nullptr) { 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 != nullptr, "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 nullptr; 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 = nullptr; // 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() : nullptr; 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 == nullptr) { 1210 // Bailout without retry 1211 assert(false, "graph should be schedulable"); 1212 C->record_method_not_compilable("late schedule failed: LCA is 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() : nullptr; 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 != nullptr && 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 = nullptr; 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 != nullptr, "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 != nullptr && 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 != nullptr, "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 != nullptr && must_clone[mach->ideal_Opcode()]) 1449 try_to_hoist = false; 1450 1451 Block* late = nullptr; 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 assert(false, "early schedule failed"); 1504 C->record_method_not_compilable("early schedule failed"); 1505 return; 1506 } 1507 1508 // Build Def-Use edges. 1509 // Compute the latency information (via backwards walk) for all the 1510 // instructions in the graph 1511 _node_latency = new GrowableArray<uint>(); // resource_area allocation 1512 1513 if (C->do_scheduling()) { 1514 compute_latencies_backwards(visited, stack); 1515 } 1516 1517 // Now schedule all codes as LATE as possible. This is the LCA in the 1518 // dominator tree of all USES of a value. Pick the block with the least 1519 // loop nesting depth that is lowest in the dominator tree. 1520 // ( visited.clear() called in schedule_late()->Node_Backward_Iterator() ) 1521 schedule_late(visited, stack); 1522 if (C->failing()) { 1523 return; 1524 } 1525 1526 #ifndef PRODUCT 1527 if (trace_opto_pipelining()) { 1528 tty->print("\n---- Detect implicit null checks ----\n"); 1529 } 1530 #endif 1531 1532 // Detect implicit-null-check opportunities. Basically, find null checks 1533 // with suitable memory ops nearby. Use the memory op to do the null check. 1534 // I can generate a memory op if there is not one nearby. 1535 if (C->is_method_compilation()) { 1536 // By reversing the loop direction we get a very minor gain on mpegaudio. 1537 // Feel free to revert to a forward loop for clarity. 1538 // for( int i=0; i < (int)matcher._null_check_tests.size(); i+=2 ) { 1539 for (int i = _matcher._null_check_tests.size() - 2; i >= 0; i -= 2) { 1540 Node* proj = _matcher._null_check_tests[i]; 1541 Node* val = _matcher._null_check_tests[i + 1]; 1542 Block* block = get_block_for_node(proj); 1543 implicit_null_check(block, proj, val, C->allowed_deopt_reasons()); 1544 // The implicit_null_check will only perform the transformation 1545 // if the null branch is truly uncommon, *and* it leads to an 1546 // uncommon trap. Combined with the too_many_traps guards 1547 // above, this prevents SEGV storms reported in 6366351, 1548 // by recompiling offending methods without this optimization. 1549 } 1550 } 1551 1552 bool block_size_threshold_ok = false; 1553 intptr_t *recalc_pressure_nodes = nullptr; 1554 if (OptoRegScheduling) { 1555 for (uint i = 0; i < number_of_blocks(); i++) { 1556 Block* block = get_block(i); 1557 if (block->number_of_nodes() > 10) { 1558 block_size_threshold_ok = true; 1559 break; 1560 } 1561 } 1562 } 1563 1564 // Enabling the scheduler for register pressure plus finding blocks of size to schedule for it 1565 // is key to enabling this feature. 1566 PhaseChaitin regalloc(C->unique(), *this, _matcher, true); 1567 ResourceArea live_arena(mtCompiler); // Arena for liveness 1568 ResourceMark rm_live(&live_arena); 1569 PhaseLive live(*this, regalloc._lrg_map.names(), &live_arena, true); 1570 PhaseIFG ifg(&live_arena); 1571 if (OptoRegScheduling && block_size_threshold_ok) { 1572 regalloc.mark_ssa(); 1573 Compile::TracePhase tp("computeLive", &timers[_t_computeLive]); 1574 rm_live.reset_to_mark(); // Reclaim working storage 1575 IndexSet::reset_memory(C, &live_arena); 1576 uint node_size = regalloc._lrg_map.max_lrg_id(); 1577 ifg.init(node_size); // Empty IFG 1578 regalloc.set_ifg(ifg); 1579 regalloc.set_live(live); 1580 regalloc.gather_lrg_masks(false); // Collect LRG masks 1581 live.compute(node_size); // Compute liveness 1582 1583 recalc_pressure_nodes = NEW_RESOURCE_ARRAY(intptr_t, node_size); 1584 for (uint i = 0; i < node_size; i++) { 1585 recalc_pressure_nodes[i] = 0; 1586 } 1587 } 1588 _regalloc = ®alloc; 1589 1590 #ifndef PRODUCT 1591 if (trace_opto_pipelining()) { 1592 tty->print("\n---- Start Local Scheduling ----\n"); 1593 } 1594 #endif 1595 1596 // Schedule locally. Right now a simple topological sort. 1597 // Later, do a real latency aware scheduler. 1598 GrowableArray<int> ready_cnt(C->unique(), C->unique(), -1); 1599 visited.reset(); 1600 for (uint i = 0; i < number_of_blocks(); i++) { 1601 Block* block = get_block(i); 1602 if (!schedule_local(block, ready_cnt, visited, recalc_pressure_nodes)) { 1603 if (!C->failure_reason_is(C2Compiler::retry_no_subsuming_loads())) { 1604 assert(false, "local schedule failed"); 1605 C->record_method_not_compilable("local schedule failed"); 1606 } 1607 _regalloc = nullptr; 1608 return; 1609 } 1610 } 1611 _regalloc = nullptr; 1612 1613 // If we inserted any instructions between a Call and his CatchNode, 1614 // clone the instructions on all paths below the Catch. 1615 for (uint i = 0; i < number_of_blocks(); i++) { 1616 Block* block = get_block(i); 1617 call_catch_cleanup(block); 1618 } 1619 1620 #ifndef PRODUCT 1621 if (trace_opto_pipelining()) { 1622 tty->print("\n---- After GlobalCodeMotion ----\n"); 1623 for (uint i = 0; i < number_of_blocks(); i++) { 1624 Block* block = get_block(i); 1625 block->dump(); 1626 } 1627 } 1628 #endif 1629 // Dead. 1630 _node_latency = (GrowableArray<uint> *)((intptr_t)0xdeadbeef); 1631 } 1632 1633 bool PhaseCFG::do_global_code_motion() { 1634 1635 build_dominator_tree(); 1636 if (C->failing()) { 1637 return false; 1638 } 1639 1640 NOT_PRODUCT( C->verify_graph_edges(); ) 1641 1642 estimate_block_frequency(); 1643 1644 global_code_motion(); 1645 1646 if (C->failing()) { 1647 return false; 1648 } 1649 1650 return true; 1651 } 1652 1653 //------------------------------Estimate_Block_Frequency----------------------- 1654 // Estimate block frequencies based on IfNode probabilities. 1655 void PhaseCFG::estimate_block_frequency() { 1656 1657 // Force conditional branches leading to uncommon traps to be unlikely, 1658 // not because we get to the uncommon_trap with less relative frequency, 1659 // but because an uncommon_trap typically causes a deopt, so we only get 1660 // there once. 1661 if (C->do_freq_based_layout()) { 1662 Block_List worklist; 1663 Block* root_blk = get_block(0); 1664 for (uint i = 1; i < root_blk->num_preds(); i++) { 1665 Block *pb = get_block_for_node(root_blk->pred(i)); 1666 if (pb->has_uncommon_code()) { 1667 worklist.push(pb); 1668 } 1669 } 1670 while (worklist.size() > 0) { 1671 Block* uct = worklist.pop(); 1672 if (uct == get_root_block()) { 1673 continue; 1674 } 1675 for (uint i = 1; i < uct->num_preds(); i++) { 1676 Block *pb = get_block_for_node(uct->pred(i)); 1677 if (pb->_num_succs == 1) { 1678 worklist.push(pb); 1679 } else if (pb->num_fall_throughs() == 2) { 1680 pb->update_uncommon_branch(uct); 1681 } 1682 } 1683 } 1684 } 1685 1686 // Create the loop tree and calculate loop depth. 1687 _root_loop = create_loop_tree(); 1688 _root_loop->compute_loop_depth(0); 1689 1690 // Compute block frequency of each block, relative to a single loop entry. 1691 _root_loop->compute_freq(); 1692 1693 // Adjust all frequencies to be relative to a single method entry 1694 _root_loop->_freq = 1.0; 1695 _root_loop->scale_freq(); 1696 1697 // Save outmost loop frequency for LRG frequency threshold 1698 _outer_loop_frequency = _root_loop->outer_loop_freq(); 1699 1700 // force paths ending at uncommon traps to be infrequent 1701 if (!C->do_freq_based_layout()) { 1702 Block_List worklist; 1703 Block* root_blk = get_block(0); 1704 for (uint i = 1; i < root_blk->num_preds(); i++) { 1705 Block *pb = get_block_for_node(root_blk->pred(i)); 1706 if (pb->has_uncommon_code()) { 1707 worklist.push(pb); 1708 } 1709 } 1710 while (worklist.size() > 0) { 1711 Block* uct = worklist.pop(); 1712 uct->_freq = PROB_MIN; 1713 for (uint i = 1; i < uct->num_preds(); i++) { 1714 Block *pb = get_block_for_node(uct->pred(i)); 1715 if (pb->_num_succs == 1 && pb->_freq > PROB_MIN) { 1716 worklist.push(pb); 1717 } 1718 } 1719 } 1720 } 1721 1722 #ifdef ASSERT 1723 for (uint i = 0; i < number_of_blocks(); i++) { 1724 Block* b = get_block(i); 1725 assert(b->_freq >= MIN_BLOCK_FREQUENCY, "Register Allocator requires meaningful block frequency"); 1726 } 1727 #endif 1728 1729 #ifndef PRODUCT 1730 if (PrintCFGBlockFreq) { 1731 tty->print_cr("CFG Block Frequencies"); 1732 _root_loop->dump_tree(); 1733 if (Verbose) { 1734 tty->print_cr("PhaseCFG dump"); 1735 dump(); 1736 tty->print_cr("Node dump"); 1737 _root->dump(99999); 1738 } 1739 } 1740 #endif 1741 } 1742 1743 //----------------------------create_loop_tree-------------------------------- 1744 // Create a loop tree from the CFG 1745 CFGLoop* PhaseCFG::create_loop_tree() { 1746 1747 #ifdef ASSERT 1748 assert(get_block(0) == get_root_block(), "first block should be root block"); 1749 for (uint i = 0; i < number_of_blocks(); i++) { 1750 Block* block = get_block(i); 1751 // Check that _loop field are clear...we could clear them if not. 1752 assert(block->_loop == nullptr, "clear _loop expected"); 1753 // Sanity check that the RPO numbering is reflected in the _blocks array. 1754 // It doesn't have to be for the loop tree to be built, but if it is not, 1755 // then the blocks have been reordered since dom graph building...which 1756 // may question the RPO numbering 1757 assert(block->_rpo == i, "unexpected reverse post order number"); 1758 } 1759 #endif 1760 1761 int idct = 0; 1762 CFGLoop* root_loop = new CFGLoop(idct++); 1763 1764 Block_List worklist; 1765 1766 // Assign blocks to loops 1767 for(uint i = number_of_blocks() - 1; i > 0; i-- ) { // skip Root block 1768 Block* block = get_block(i); 1769 1770 if (block->head()->is_Loop()) { 1771 Block* loop_head = block; 1772 assert(loop_head->num_preds() - 1 == 2, "loop must have 2 predecessors"); 1773 Node* tail_n = loop_head->pred(LoopNode::LoopBackControl); 1774 Block* tail = get_block_for_node(tail_n); 1775 1776 // Defensively filter out Loop nodes for non-single-entry loops. 1777 // For all reasonable loops, the head occurs before the tail in RPO. 1778 if (i <= tail->_rpo) { 1779 1780 // The tail and (recursive) predecessors of the tail 1781 // are made members of a new loop. 1782 1783 assert(worklist.size() == 0, "nonempty worklist"); 1784 CFGLoop* nloop = new CFGLoop(idct++); 1785 assert(loop_head->_loop == nullptr, "just checking"); 1786 loop_head->_loop = nloop; 1787 // Add to nloop so push_pred() will skip over inner loops 1788 nloop->add_member(loop_head); 1789 nloop->push_pred(loop_head, LoopNode::LoopBackControl, worklist, this); 1790 1791 while (worklist.size() > 0) { 1792 Block* member = worklist.pop(); 1793 if (member != loop_head) { 1794 for (uint j = 1; j < member->num_preds(); j++) { 1795 nloop->push_pred(member, j, worklist, this); 1796 } 1797 } 1798 } 1799 } 1800 } 1801 } 1802 1803 // Create a member list for each loop consisting 1804 // of both blocks and (immediate child) loops. 1805 for (uint i = 0; i < number_of_blocks(); i++) { 1806 Block* block = get_block(i); 1807 CFGLoop* lp = block->_loop; 1808 if (lp == nullptr) { 1809 // Not assigned to a loop. Add it to the method's pseudo loop. 1810 block->_loop = root_loop; 1811 lp = root_loop; 1812 } 1813 if (lp == root_loop || block != lp->head()) { // loop heads are already members 1814 lp->add_member(block); 1815 } 1816 if (lp != root_loop) { 1817 if (lp->parent() == nullptr) { 1818 // Not a nested loop. Make it a child of the method's pseudo loop. 1819 root_loop->add_nested_loop(lp); 1820 } 1821 if (block == lp->head()) { 1822 // Add nested loop to member list of parent loop. 1823 lp->parent()->add_member(lp); 1824 } 1825 } 1826 } 1827 1828 return root_loop; 1829 } 1830 1831 //------------------------------push_pred-------------------------------------- 1832 void CFGLoop::push_pred(Block* blk, int i, Block_List& worklist, PhaseCFG* cfg) { 1833 Node* pred_n = blk->pred(i); 1834 Block* pred = cfg->get_block_for_node(pred_n); 1835 CFGLoop *pred_loop = pred->_loop; 1836 if (pred_loop == nullptr) { 1837 // Filter out blocks for non-single-entry loops. 1838 // For all reasonable loops, the head occurs before the tail in RPO. 1839 if (pred->_rpo > head()->_rpo) { 1840 pred->_loop = this; 1841 worklist.push(pred); 1842 } 1843 } else if (pred_loop != this) { 1844 // Nested loop. 1845 while (pred_loop->_parent != nullptr && pred_loop->_parent != this) { 1846 pred_loop = pred_loop->_parent; 1847 } 1848 // Make pred's loop be a child 1849 if (pred_loop->_parent == nullptr) { 1850 add_nested_loop(pred_loop); 1851 // Continue with loop entry predecessor. 1852 Block* pred_head = pred_loop->head(); 1853 assert(pred_head->num_preds() - 1 == 2, "loop must have 2 predecessors"); 1854 assert(pred_head != head(), "loop head in only one loop"); 1855 push_pred(pred_head, LoopNode::EntryControl, worklist, cfg); 1856 } else { 1857 assert(pred_loop->_parent == this && _parent == nullptr, "just checking"); 1858 } 1859 } 1860 } 1861 1862 //------------------------------add_nested_loop-------------------------------- 1863 // Make cl a child of the current loop in the loop tree. 1864 void CFGLoop::add_nested_loop(CFGLoop* cl) { 1865 assert(_parent == nullptr, "no parent yet"); 1866 assert(cl != this, "not my own parent"); 1867 cl->_parent = this; 1868 CFGLoop* ch = _child; 1869 if (ch == nullptr) { 1870 _child = cl; 1871 } else { 1872 while (ch->_sibling != nullptr) { ch = ch->_sibling; } 1873 ch->_sibling = cl; 1874 } 1875 } 1876 1877 //------------------------------compute_loop_depth----------------------------- 1878 // Store the loop depth in each CFGLoop object. 1879 // Recursively walk the children to do the same for them. 1880 void CFGLoop::compute_loop_depth(int depth) { 1881 _depth = depth; 1882 CFGLoop* ch = _child; 1883 while (ch != nullptr) { 1884 ch->compute_loop_depth(depth + 1); 1885 ch = ch->_sibling; 1886 } 1887 } 1888 1889 //------------------------------compute_freq----------------------------------- 1890 // Compute the frequency of each block and loop, relative to a single entry 1891 // into the dominating loop head. 1892 void CFGLoop::compute_freq() { 1893 // Bottom up traversal of loop tree (visit inner loops first.) 1894 // Set loop head frequency to 1.0, then transitively 1895 // compute frequency for all successors in the loop, 1896 // as well as for each exit edge. Inner loops are 1897 // treated as single blocks with loop exit targets 1898 // as the successor blocks. 1899 1900 // Nested loops first 1901 CFGLoop* ch = _child; 1902 while (ch != nullptr) { 1903 ch->compute_freq(); 1904 ch = ch->_sibling; 1905 } 1906 assert (_members.length() > 0, "no empty loops"); 1907 Block* hd = head(); 1908 hd->_freq = 1.0; 1909 for (int i = 0; i < _members.length(); i++) { 1910 CFGElement* s = _members.at(i); 1911 double freq = s->_freq; 1912 if (s->is_block()) { 1913 Block* b = s->as_Block(); 1914 for (uint j = 0; j < b->_num_succs; j++) { 1915 Block* sb = b->_succs[j]; 1916 update_succ_freq(sb, freq * b->succ_prob(j)); 1917 } 1918 } else { 1919 CFGLoop* lp = s->as_CFGLoop(); 1920 assert(lp->_parent == this, "immediate child"); 1921 for (int k = 0; k < lp->_exits.length(); k++) { 1922 Block* eb = lp->_exits.at(k).get_target(); 1923 double prob = lp->_exits.at(k).get_prob(); 1924 update_succ_freq(eb, freq * prob); 1925 } 1926 } 1927 } 1928 1929 // For all loops other than the outer, "method" loop, 1930 // sum and normalize the exit probability. The "method" loop 1931 // should keep the initial exit probability of 1, so that 1932 // inner blocks do not get erroneously scaled. 1933 if (_depth != 0) { 1934 // Total the exit probabilities for this loop. 1935 double exits_sum = 0.0f; 1936 for (int i = 0; i < _exits.length(); i++) { 1937 exits_sum += _exits.at(i).get_prob(); 1938 } 1939 1940 // Normalize the exit probabilities. Until now, the 1941 // probabilities estimate the possibility of exit per 1942 // a single loop iteration; afterward, they estimate 1943 // the probability of exit per loop entry. 1944 for (int i = 0; i < _exits.length(); i++) { 1945 Block* et = _exits.at(i).get_target(); 1946 float new_prob = 0.0f; 1947 if (_exits.at(i).get_prob() > 0.0f) { 1948 new_prob = _exits.at(i).get_prob() / exits_sum; 1949 } 1950 BlockProbPair bpp(et, new_prob); 1951 _exits.at_put(i, bpp); 1952 } 1953 1954 // Save the total, but guard against unreasonable probability, 1955 // as the value is used to estimate the loop trip count. 1956 // An infinite trip count would blur relative block 1957 // frequencies. 1958 if (exits_sum > 1.0f) exits_sum = 1.0; 1959 if (exits_sum < PROB_MIN) exits_sum = PROB_MIN; 1960 _exit_prob = exits_sum; 1961 } 1962 } 1963 1964 //------------------------------succ_prob------------------------------------- 1965 // Determine the probability of reaching successor 'i' from the receiver block. 1966 float Block::succ_prob(uint i) { 1967 int eidx = end_idx(); 1968 Node *n = get_node(eidx); // Get ending Node 1969 1970 int op = n->Opcode(); 1971 if (n->is_Mach()) { 1972 if (n->is_MachNullCheck()) { 1973 // Can only reach here if called after lcm. The original Op_If is gone, 1974 // so we attempt to infer the probability from one or both of the 1975 // successor blocks. 1976 assert(_num_succs == 2, "expecting 2 successors of a null check"); 1977 // If either successor has only one predecessor, then the 1978 // probability estimate can be derived using the 1979 // relative frequency of the successor and this block. 1980 if (_succs[i]->num_preds() == 2) { 1981 return _succs[i]->_freq / _freq; 1982 } else if (_succs[1-i]->num_preds() == 2) { 1983 return 1 - (_succs[1-i]->_freq / _freq); 1984 } else { 1985 // Estimate using both successor frequencies 1986 float freq = _succs[i]->_freq; 1987 return freq / (freq + _succs[1-i]->_freq); 1988 } 1989 } 1990 op = n->as_Mach()->ideal_Opcode(); 1991 } 1992 1993 1994 // Switch on branch type 1995 switch( op ) { 1996 case Op_CountedLoopEnd: 1997 case Op_If: { 1998 assert (i < 2, "just checking"); 1999 // Conditionals pass on only part of their frequency 2000 float prob = n->as_MachIf()->_prob; 2001 assert(prob >= 0.0 && prob <= 1.0, "out of range probability"); 2002 // If succ[i] is the FALSE branch, invert path info 2003 if( get_node(i + eidx + 1)->Opcode() == Op_IfFalse ) { 2004 return 1.0f - prob; // not taken 2005 } else { 2006 return prob; // taken 2007 } 2008 } 2009 2010 case Op_Jump: 2011 return n->as_MachJump()->_probs[get_node(i + eidx + 1)->as_JumpProj()->_con]; 2012 2013 case Op_Catch: { 2014 const CatchProjNode *ci = get_node(i + eidx + 1)->as_CatchProj(); 2015 if (ci->_con == CatchProjNode::fall_through_index) { 2016 // Fall-thru path gets the lion's share. 2017 return 1.0f - PROB_UNLIKELY_MAG(5)*_num_succs; 2018 } else { 2019 // Presume exceptional paths are equally unlikely 2020 return PROB_UNLIKELY_MAG(5); 2021 } 2022 } 2023 2024 case Op_Root: 2025 case Op_Goto: 2026 // Pass frequency straight thru to target 2027 return 1.0f; 2028 2029 case Op_NeverBranch: 2030 return 0.0f; 2031 2032 case Op_TailCall: 2033 case Op_TailJump: 2034 case Op_ForwardException: 2035 case Op_Return: 2036 case Op_Halt: 2037 case Op_Rethrow: 2038 // Do not push out freq to root block 2039 return 0.0f; 2040 2041 default: 2042 ShouldNotReachHere(); 2043 } 2044 2045 return 0.0f; 2046 } 2047 2048 //------------------------------num_fall_throughs----------------------------- 2049 // Return the number of fall-through candidates for a block 2050 int Block::num_fall_throughs() { 2051 int eidx = end_idx(); 2052 Node *n = get_node(eidx); // Get ending Node 2053 2054 int op = n->Opcode(); 2055 if (n->is_Mach()) { 2056 if (n->is_MachNullCheck()) { 2057 // In theory, either side can fall-thru, for simplicity sake, 2058 // let's say only the false branch can now. 2059 return 1; 2060 } 2061 op = n->as_Mach()->ideal_Opcode(); 2062 } 2063 2064 // Switch on branch type 2065 switch( op ) { 2066 case Op_CountedLoopEnd: 2067 case Op_If: 2068 return 2; 2069 2070 case Op_Root: 2071 case Op_Goto: 2072 return 1; 2073 2074 case Op_Catch: { 2075 for (uint i = 0; i < _num_succs; i++) { 2076 const CatchProjNode *ci = get_node(i + eidx + 1)->as_CatchProj(); 2077 if (ci->_con == CatchProjNode::fall_through_index) { 2078 return 1; 2079 } 2080 } 2081 return 0; 2082 } 2083 2084 case Op_Jump: 2085 case Op_NeverBranch: 2086 case Op_TailCall: 2087 case Op_TailJump: 2088 case Op_ForwardException: 2089 case Op_Return: 2090 case Op_Halt: 2091 case Op_Rethrow: 2092 return 0; 2093 2094 default: 2095 ShouldNotReachHere(); 2096 } 2097 2098 return 0; 2099 } 2100 2101 //------------------------------succ_fall_through----------------------------- 2102 // Return true if a specific successor could be fall-through target. 2103 bool Block::succ_fall_through(uint i) { 2104 int eidx = end_idx(); 2105 Node *n = get_node(eidx); // Get ending Node 2106 2107 int op = n->Opcode(); 2108 if (n->is_Mach()) { 2109 if (n->is_MachNullCheck()) { 2110 // In theory, either side can fall-thru, for simplicity sake, 2111 // let's say only the false branch can now. 2112 return get_node(i + eidx + 1)->Opcode() == Op_IfFalse; 2113 } 2114 op = n->as_Mach()->ideal_Opcode(); 2115 } 2116 2117 // Switch on branch type 2118 switch( op ) { 2119 case Op_CountedLoopEnd: 2120 case Op_If: 2121 case Op_Root: 2122 case Op_Goto: 2123 return true; 2124 2125 case Op_Catch: { 2126 const CatchProjNode *ci = get_node(i + eidx + 1)->as_CatchProj(); 2127 return ci->_con == CatchProjNode::fall_through_index; 2128 } 2129 2130 case Op_Jump: 2131 case Op_NeverBranch: 2132 case Op_TailCall: 2133 case Op_TailJump: 2134 case Op_ForwardException: 2135 case Op_Return: 2136 case Op_Halt: 2137 case Op_Rethrow: 2138 return false; 2139 2140 default: 2141 ShouldNotReachHere(); 2142 } 2143 2144 return false; 2145 } 2146 2147 //------------------------------update_uncommon_branch------------------------ 2148 // Update the probability of a two-branch to be uncommon 2149 void Block::update_uncommon_branch(Block* ub) { 2150 int eidx = end_idx(); 2151 Node *n = get_node(eidx); // Get ending Node 2152 2153 int op = n->as_Mach()->ideal_Opcode(); 2154 2155 assert(op == Op_CountedLoopEnd || op == Op_If, "must be a If"); 2156 assert(num_fall_throughs() == 2, "must be a two way branch block"); 2157 2158 // Which successor is ub? 2159 uint s; 2160 for (s = 0; s <_num_succs; s++) { 2161 if (_succs[s] == ub) break; 2162 } 2163 assert(s < 2, "uncommon successor must be found"); 2164 2165 // If ub is the true path, make the proability small, else 2166 // ub is the false path, and make the probability large 2167 bool invert = (get_node(s + eidx + 1)->Opcode() == Op_IfFalse); 2168 2169 // Get existing probability 2170 float p = n->as_MachIf()->_prob; 2171 2172 if (invert) p = 1.0 - p; 2173 if (p > PROB_MIN) { 2174 p = PROB_MIN; 2175 } 2176 if (invert) p = 1.0 - p; 2177 2178 n->as_MachIf()->_prob = p; 2179 } 2180 2181 //------------------------------update_succ_freq------------------------------- 2182 // Update the appropriate frequency associated with block 'b', a successor of 2183 // a block in this loop. 2184 void CFGLoop::update_succ_freq(Block* b, double freq) { 2185 if (b->_loop == this) { 2186 if (b == head()) { 2187 // back branch within the loop 2188 // Do nothing now, the loop carried frequency will be 2189 // adjust later in scale_freq(). 2190 } else { 2191 // simple branch within the loop 2192 b->_freq += freq; 2193 } 2194 } else if (!in_loop_nest(b)) { 2195 // branch is exit from this loop 2196 BlockProbPair bpp(b, freq); 2197 _exits.append(bpp); 2198 } else { 2199 // branch into nested loop 2200 CFGLoop* ch = b->_loop; 2201 ch->_freq += freq; 2202 } 2203 } 2204 2205 //------------------------------in_loop_nest----------------------------------- 2206 // Determine if block b is in the receiver's loop nest. 2207 bool CFGLoop::in_loop_nest(Block* b) { 2208 int depth = _depth; 2209 CFGLoop* b_loop = b->_loop; 2210 int b_depth = b_loop->_depth; 2211 if (depth == b_depth) { 2212 return true; 2213 } 2214 while (b_depth > depth) { 2215 b_loop = b_loop->_parent; 2216 b_depth = b_loop->_depth; 2217 } 2218 return b_loop == this; 2219 } 2220 2221 //------------------------------scale_freq------------------------------------- 2222 // Scale frequency of loops and blocks by trip counts from outer loops 2223 // Do a top down traversal of loop tree (visit outer loops first.) 2224 void CFGLoop::scale_freq() { 2225 double loop_freq = _freq * trip_count(); 2226 _freq = loop_freq; 2227 for (int i = 0; i < _members.length(); i++) { 2228 CFGElement* s = _members.at(i); 2229 double block_freq = s->_freq * loop_freq; 2230 if (g_isnan(block_freq) || block_freq < MIN_BLOCK_FREQUENCY) 2231 block_freq = MIN_BLOCK_FREQUENCY; 2232 s->_freq = block_freq; 2233 } 2234 CFGLoop* ch = _child; 2235 while (ch != nullptr) { 2236 ch->scale_freq(); 2237 ch = ch->_sibling; 2238 } 2239 } 2240 2241 // Frequency of outer loop 2242 double CFGLoop::outer_loop_freq() const { 2243 if (_child != nullptr) { 2244 return _child->_freq; 2245 } 2246 return _freq; 2247 } 2248 2249 #ifndef PRODUCT 2250 //------------------------------dump_tree-------------------------------------- 2251 void CFGLoop::dump_tree() const { 2252 dump(); 2253 if (_child != nullptr) _child->dump_tree(); 2254 if (_sibling != nullptr) _sibling->dump_tree(); 2255 } 2256 2257 //------------------------------dump------------------------------------------- 2258 void CFGLoop::dump() const { 2259 for (int i = 0; i < _depth; i++) tty->print(" "); 2260 tty->print("%s: %d trip_count: %6.0f freq: %6.0f\n", 2261 _depth == 0 ? "Method" : "Loop", _id, trip_count(), _freq); 2262 for (int i = 0; i < _depth; i++) tty->print(" "); 2263 tty->print(" members:"); 2264 int k = 0; 2265 for (int i = 0; i < _members.length(); i++) { 2266 if (k++ >= 6) { 2267 tty->print("\n "); 2268 for (int j = 0; j < _depth+1; j++) tty->print(" "); 2269 k = 0; 2270 } 2271 CFGElement *s = _members.at(i); 2272 if (s->is_block()) { 2273 Block *b = s->as_Block(); 2274 tty->print(" B%d(%6.3f)", b->_pre_order, b->_freq); 2275 } else { 2276 CFGLoop* lp = s->as_CFGLoop(); 2277 tty->print(" L%d(%6.3f)", lp->_id, lp->_freq); 2278 } 2279 } 2280 tty->print("\n"); 2281 for (int i = 0; i < _depth; i++) tty->print(" "); 2282 tty->print(" exits: "); 2283 k = 0; 2284 for (int i = 0; i < _exits.length(); i++) { 2285 if (k++ >= 7) { 2286 tty->print("\n "); 2287 for (int j = 0; j < _depth+1; j++) tty->print(" "); 2288 k = 0; 2289 } 2290 Block *blk = _exits.at(i).get_target(); 2291 double prob = _exits.at(i).get_prob(); 2292 tty->print(" ->%d@%d%%", blk->_pre_order, (int)(prob*100)); 2293 } 2294 tty->print("\n"); 2295 } 2296 #endif