loopTransform.cpp revision 113:ba764ed4b6f2
1/* 2 * Copyright 2000-2007 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, 20 * CA 95054 USA or visit www.sun.com if you need additional information or 21 * have any questions. 22 * 23 */ 24 25#include "incls/_precompiled.incl" 26#include "incls/_loopTransform.cpp.incl" 27 28//------------------------------is_loop_exit----------------------------------- 29// Given an IfNode, return the loop-exiting projection or NULL if both 30// arms remain in the loop. 31Node *IdealLoopTree::is_loop_exit(Node *iff) const { 32 if( iff->outcnt() != 2 ) return NULL; // Ignore partially dead tests 33 PhaseIdealLoop *phase = _phase; 34 // Test is an IfNode, has 2 projections. If BOTH are in the loop 35 // we need loop unswitching instead of peeling. 36 if( !is_member(phase->get_loop( iff->raw_out(0) )) ) 37 return iff->raw_out(0); 38 if( !is_member(phase->get_loop( iff->raw_out(1) )) ) 39 return iff->raw_out(1); 40 return NULL; 41} 42 43 44//============================================================================= 45 46 47//------------------------------record_for_igvn---------------------------- 48// Put loop body on igvn work list 49void IdealLoopTree::record_for_igvn() { 50 for( uint i = 0; i < _body.size(); i++ ) { 51 Node *n = _body.at(i); 52 _phase->_igvn._worklist.push(n); 53 } 54} 55 56//------------------------------compute_profile_trip_cnt---------------------------- 57// Compute loop trip count from profile data as 58// (backedge_count + loop_exit_count) / loop_exit_count 59void IdealLoopTree::compute_profile_trip_cnt( PhaseIdealLoop *phase ) { 60 if (!_head->is_CountedLoop()) { 61 return; 62 } 63 CountedLoopNode* head = _head->as_CountedLoop(); 64 if (head->profile_trip_cnt() != COUNT_UNKNOWN) { 65 return; // Already computed 66 } 67 float trip_cnt = (float)max_jint; // default is big 68 69 Node* back = head->in(LoopNode::LoopBackControl); 70 while (back != head) { 71 if ((back->Opcode() == Op_IfTrue || back->Opcode() == Op_IfFalse) && 72 back->in(0) && 73 back->in(0)->is_If() && 74 back->in(0)->as_If()->_fcnt != COUNT_UNKNOWN && 75 back->in(0)->as_If()->_prob != PROB_UNKNOWN) { 76 break; 77 } 78 back = phase->idom(back); 79 } 80 if (back != head) { 81 assert((back->Opcode() == Op_IfTrue || back->Opcode() == Op_IfFalse) && 82 back->in(0), "if-projection exists"); 83 IfNode* back_if = back->in(0)->as_If(); 84 float loop_back_cnt = back_if->_fcnt * back_if->_prob; 85 86 // Now compute a loop exit count 87 float loop_exit_cnt = 0.0f; 88 for( uint i = 0; i < _body.size(); i++ ) { 89 Node *n = _body[i]; 90 if( n->is_If() ) { 91 IfNode *iff = n->as_If(); 92 if( iff->_fcnt != COUNT_UNKNOWN && iff->_prob != PROB_UNKNOWN ) { 93 Node *exit = is_loop_exit(iff); 94 if( exit ) { 95 float exit_prob = iff->_prob; 96 if (exit->Opcode() == Op_IfFalse) exit_prob = 1.0 - exit_prob; 97 if (exit_prob > PROB_MIN) { 98 float exit_cnt = iff->_fcnt * exit_prob; 99 loop_exit_cnt += exit_cnt; 100 } 101 } 102 } 103 } 104 } 105 if (loop_exit_cnt > 0.0f) { 106 trip_cnt = (loop_back_cnt + loop_exit_cnt) / loop_exit_cnt; 107 } else { 108 // No exit count so use 109 trip_cnt = loop_back_cnt; 110 } 111 } 112#ifndef PRODUCT 113 if (TraceProfileTripCount) { 114 tty->print_cr("compute_profile_trip_cnt lp: %d cnt: %f\n", head->_idx, trip_cnt); 115 } 116#endif 117 head->set_profile_trip_cnt(trip_cnt); 118} 119 120//---------------------is_invariant_addition----------------------------- 121// Return nonzero index of invariant operand for an Add or Sub 122// of (nonconstant) invariant and variant values. Helper for reassoicate_invariants. 123int IdealLoopTree::is_invariant_addition(Node* n, PhaseIdealLoop *phase) { 124 int op = n->Opcode(); 125 if (op == Op_AddI || op == Op_SubI) { 126 bool in1_invar = this->is_invariant(n->in(1)); 127 bool in2_invar = this->is_invariant(n->in(2)); 128 if (in1_invar && !in2_invar) return 1; 129 if (!in1_invar && in2_invar) return 2; 130 } 131 return 0; 132} 133 134//---------------------reassociate_add_sub----------------------------- 135// Reassociate invariant add and subtract expressions: 136// 137// inv1 + (x + inv2) => ( inv1 + inv2) + x 138// (x + inv2) + inv1 => ( inv1 + inv2) + x 139// inv1 + (x - inv2) => ( inv1 - inv2) + x 140// inv1 - (inv2 - x) => ( inv1 - inv2) + x 141// (x + inv2) - inv1 => (-inv1 + inv2) + x 142// (x - inv2) + inv1 => ( inv1 - inv2) + x 143// (x - inv2) - inv1 => (-inv1 - inv2) + x 144// inv1 + (inv2 - x) => ( inv1 + inv2) - x 145// inv1 - (x - inv2) => ( inv1 + inv2) - x 146// (inv2 - x) + inv1 => ( inv1 + inv2) - x 147// (inv2 - x) - inv1 => (-inv1 + inv2) - x 148// inv1 - (x + inv2) => ( inv1 - inv2) - x 149// 150Node* IdealLoopTree::reassociate_add_sub(Node* n1, PhaseIdealLoop *phase) { 151 if (!n1->is_Add() && !n1->is_Sub() || n1->outcnt() == 0) return NULL; 152 if (is_invariant(n1)) return NULL; 153 int inv1_idx = is_invariant_addition(n1, phase); 154 if (!inv1_idx) return NULL; 155 // Don't mess with add of constant (igvn moves them to expression tree root.) 156 if (n1->is_Add() && n1->in(2)->is_Con()) return NULL; 157 Node* inv1 = n1->in(inv1_idx); 158 Node* n2 = n1->in(3 - inv1_idx); 159 int inv2_idx = is_invariant_addition(n2, phase); 160 if (!inv2_idx) return NULL; 161 Node* x = n2->in(3 - inv2_idx); 162 Node* inv2 = n2->in(inv2_idx); 163 164 bool neg_x = n2->is_Sub() && inv2_idx == 1; 165 bool neg_inv2 = n2->is_Sub() && inv2_idx == 2; 166 bool neg_inv1 = n1->is_Sub() && inv1_idx == 2; 167 if (n1->is_Sub() && inv1_idx == 1) { 168 neg_x = !neg_x; 169 neg_inv2 = !neg_inv2; 170 } 171 Node* inv1_c = phase->get_ctrl(inv1); 172 Node* inv2_c = phase->get_ctrl(inv2); 173 Node* n_inv1; 174 if (neg_inv1) { 175 Node *zero = phase->_igvn.intcon(0); 176 phase->set_ctrl(zero, phase->C->root()); 177 n_inv1 = new (phase->C, 3) SubINode(zero, inv1); 178 phase->register_new_node(n_inv1, inv1_c); 179 } else { 180 n_inv1 = inv1; 181 } 182 Node* inv; 183 if (neg_inv2) { 184 inv = new (phase->C, 3) SubINode(n_inv1, inv2); 185 } else { 186 inv = new (phase->C, 3) AddINode(n_inv1, inv2); 187 } 188 phase->register_new_node(inv, phase->get_early_ctrl(inv)); 189 190 Node* addx; 191 if (neg_x) { 192 addx = new (phase->C, 3) SubINode(inv, x); 193 } else { 194 addx = new (phase->C, 3) AddINode(x, inv); 195 } 196 phase->register_new_node(addx, phase->get_ctrl(x)); 197 phase->_igvn.hash_delete(n1); 198 phase->_igvn.subsume_node(n1, addx); 199 return addx; 200} 201 202//---------------------reassociate_invariants----------------------------- 203// Reassociate invariant expressions: 204void IdealLoopTree::reassociate_invariants(PhaseIdealLoop *phase) { 205 for (int i = _body.size() - 1; i >= 0; i--) { 206 Node *n = _body.at(i); 207 for (int j = 0; j < 5; j++) { 208 Node* nn = reassociate_add_sub(n, phase); 209 if (nn == NULL) break; 210 n = nn; // again 211 }; 212 } 213} 214 215//------------------------------policy_peeling--------------------------------- 216// Return TRUE or FALSE if the loop should be peeled or not. Peel if we can 217// make some loop-invariant test (usually a null-check) happen before the loop. 218bool IdealLoopTree::policy_peeling( PhaseIdealLoop *phase ) const { 219 Node *test = ((IdealLoopTree*)this)->tail(); 220 int body_size = ((IdealLoopTree*)this)->_body.size(); 221 int uniq = phase->C->unique(); 222 // Peeling does loop cloning which can result in O(N^2) node construction 223 if( body_size > 255 /* Prevent overflow for large body_size */ 224 || (body_size * body_size + uniq > MaxNodeLimit) ) { 225 return false; // too large to safely clone 226 } 227 while( test != _head ) { // Scan till run off top of loop 228 if( test->is_If() ) { // Test? 229 Node *ctrl = phase->get_ctrl(test->in(1)); 230 if (ctrl->is_top()) 231 return false; // Found dead test on live IF? No peeling! 232 // Standard IF only has one input value to check for loop invariance 233 assert( test->Opcode() == Op_If || test->Opcode() == Op_CountedLoopEnd, "Check this code when new subtype is added"); 234 // Condition is not a member of this loop? 235 if( !is_member(phase->get_loop(ctrl)) && 236 is_loop_exit(test) ) 237 return true; // Found reason to peel! 238 } 239 // Walk up dominators to loop _head looking for test which is 240 // executed on every path thru loop. 241 test = phase->idom(test); 242 } 243 return false; 244} 245 246//------------------------------peeled_dom_test_elim--------------------------- 247// If we got the effect of peeling, either by actually peeling or by making 248// a pre-loop which must execute at least once, we can remove all 249// loop-invariant dominated tests in the main body. 250void PhaseIdealLoop::peeled_dom_test_elim( IdealLoopTree *loop, Node_List &old_new ) { 251 bool progress = true; 252 while( progress ) { 253 progress = false; // Reset for next iteration 254 Node *prev = loop->_head->in(LoopNode::LoopBackControl);//loop->tail(); 255 Node *test = prev->in(0); 256 while( test != loop->_head ) { // Scan till run off top of loop 257 258 int p_op = prev->Opcode(); 259 if( (p_op == Op_IfFalse || p_op == Op_IfTrue) && 260 test->is_If() && // Test? 261 !test->in(1)->is_Con() && // And not already obvious? 262 // Condition is not a member of this loop? 263 !loop->is_member(get_loop(get_ctrl(test->in(1))))){ 264 // Walk loop body looking for instances of this test 265 for( uint i = 0; i < loop->_body.size(); i++ ) { 266 Node *n = loop->_body.at(i); 267 if( n->is_If() && n->in(1) == test->in(1) /*&& n != loop->tail()->in(0)*/ ) { 268 // IfNode was dominated by version in peeled loop body 269 progress = true; 270 dominated_by( old_new[prev->_idx], n ); 271 } 272 } 273 } 274 prev = test; 275 test = idom(test); 276 } // End of scan tests in loop 277 278 } // End of while( progress ) 279} 280 281//------------------------------do_peeling------------------------------------- 282// Peel the first iteration of the given loop. 283// Step 1: Clone the loop body. The clone becomes the peeled iteration. 284// The pre-loop illegally has 2 control users (old & new loops). 285// Step 2: Make the old-loop fall-in edges point to the peeled iteration. 286// Do this by making the old-loop fall-in edges act as if they came 287// around the loopback from the prior iteration (follow the old-loop 288// backedges) and then map to the new peeled iteration. This leaves 289// the pre-loop with only 1 user (the new peeled iteration), but the 290// peeled-loop backedge has 2 users. 291// Step 3: Cut the backedge on the clone (so its not a loop) and remove the 292// extra backedge user. 293void PhaseIdealLoop::do_peeling( IdealLoopTree *loop, Node_List &old_new ) { 294 295 C->set_major_progress(); 296 // Peeling a 'main' loop in a pre/main/post situation obfuscates the 297 // 'pre' loop from the main and the 'pre' can no longer have it's 298 // iterations adjusted. Therefore, we need to declare this loop as 299 // no longer a 'main' loop; it will need new pre and post loops before 300 // we can do further RCE. 301 Node *h = loop->_head; 302 if( h->is_CountedLoop() ) { 303 CountedLoopNode *cl = h->as_CountedLoop(); 304 assert(cl->trip_count() > 0, "peeling a fully unrolled loop"); 305 cl->set_trip_count(cl->trip_count() - 1); 306 if( cl->is_main_loop() ) { 307 cl->set_normal_loop(); 308#ifndef PRODUCT 309 if( PrintOpto && VerifyLoopOptimizations ) { 310 tty->print("Peeling a 'main' loop; resetting to 'normal' "); 311 loop->dump_head(); 312 } 313#endif 314 } 315 } 316 317 // Step 1: Clone the loop body. The clone becomes the peeled iteration. 318 // The pre-loop illegally has 2 control users (old & new loops). 319 clone_loop( loop, old_new, dom_depth(loop->_head) ); 320 321 322 // Step 2: Make the old-loop fall-in edges point to the peeled iteration. 323 // Do this by making the old-loop fall-in edges act as if they came 324 // around the loopback from the prior iteration (follow the old-loop 325 // backedges) and then map to the new peeled iteration. This leaves 326 // the pre-loop with only 1 user (the new peeled iteration), but the 327 // peeled-loop backedge has 2 users. 328 for (DUIterator_Fast jmax, j = loop->_head->fast_outs(jmax); j < jmax; j++) { 329 Node* old = loop->_head->fast_out(j); 330 if( old->in(0) == loop->_head && old->req() == 3 && 331 (old->is_Loop() || old->is_Phi()) ) { 332 Node *new_exit_value = old_new[old->in(LoopNode::LoopBackControl)->_idx]; 333 if( !new_exit_value ) // Backedge value is ALSO loop invariant? 334 // Then loop body backedge value remains the same. 335 new_exit_value = old->in(LoopNode::LoopBackControl); 336 _igvn.hash_delete(old); 337 old->set_req(LoopNode::EntryControl, new_exit_value); 338 } 339 } 340 341 342 // Step 3: Cut the backedge on the clone (so its not a loop) and remove the 343 // extra backedge user. 344 Node *nnn = old_new[loop->_head->_idx]; 345 _igvn.hash_delete(nnn); 346 nnn->set_req(LoopNode::LoopBackControl, C->top()); 347 for (DUIterator_Fast j2max, j2 = nnn->fast_outs(j2max); j2 < j2max; j2++) { 348 Node* use = nnn->fast_out(j2); 349 if( use->in(0) == nnn && use->req() == 3 && use->is_Phi() ) { 350 _igvn.hash_delete(use); 351 use->set_req(LoopNode::LoopBackControl, C->top()); 352 } 353 } 354 355 356 // Step 4: Correct dom-depth info. Set to loop-head depth. 357 int dd = dom_depth(loop->_head); 358 set_idom(loop->_head, loop->_head->in(1), dd); 359 for (uint j3 = 0; j3 < loop->_body.size(); j3++) { 360 Node *old = loop->_body.at(j3); 361 Node *nnn = old_new[old->_idx]; 362 if (!has_ctrl(nnn)) 363 set_idom(nnn, idom(nnn), dd-1); 364 // While we're at it, remove any SafePoints from the peeled code 365 if( old->Opcode() == Op_SafePoint ) { 366 Node *nnn = old_new[old->_idx]; 367 lazy_replace(nnn,nnn->in(TypeFunc::Control)); 368 } 369 } 370 371 // Now force out all loop-invariant dominating tests. The optimizer 372 // finds some, but we _know_ they are all useless. 373 peeled_dom_test_elim(loop,old_new); 374 375 loop->record_for_igvn(); 376} 377 378//------------------------------policy_maximally_unroll------------------------ 379// Return exact loop trip count, or 0 if not maximally unrolling 380bool IdealLoopTree::policy_maximally_unroll( PhaseIdealLoop *phase ) const { 381 CountedLoopNode *cl = _head->as_CountedLoop(); 382 assert( cl->is_normal_loop(), "" ); 383 384 Node *init_n = cl->init_trip(); 385 Node *limit_n = cl->limit(); 386 387 // Non-constant bounds 388 if( init_n == NULL || !init_n->is_Con() || 389 limit_n == NULL || !limit_n->is_Con() || 390 // protect against stride not being a constant 391 !cl->stride_is_con() ) { 392 return false; 393 } 394 int init = init_n->get_int(); 395 int limit = limit_n->get_int(); 396 int span = limit - init; 397 int stride = cl->stride_con(); 398 399 if (init >= limit || stride > span) { 400 // return a false (no maximally unroll) and the regular unroll/peel 401 // route will make a small mess which CCP will fold away. 402 return false; 403 } 404 uint trip_count = span/stride; // trip_count can be greater than 2 Gig. 405 assert( (int)trip_count*stride == span, "must divide evenly" ); 406 407 // Real policy: if we maximally unroll, does it get too big? 408 // Allow the unrolled mess to get larger than standard loop 409 // size. After all, it will no longer be a loop. 410 uint body_size = _body.size(); 411 uint unroll_limit = (uint)LoopUnrollLimit * 4; 412 assert( (intx)unroll_limit == LoopUnrollLimit * 4, "LoopUnrollLimit must fit in 32bits"); 413 cl->set_trip_count(trip_count); 414 if( trip_count <= unroll_limit && body_size <= unroll_limit ) { 415 uint new_body_size = body_size * trip_count; 416 if (new_body_size <= unroll_limit && 417 body_size == new_body_size / trip_count && 418 // Unrolling can result in a large amount of node construction 419 new_body_size < MaxNodeLimit - phase->C->unique()) { 420 return true; // maximally unroll 421 } 422 } 423 424 return false; // Do not maximally unroll 425} 426 427 428//------------------------------policy_unroll---------------------------------- 429// Return TRUE or FALSE if the loop should be unrolled or not. Unroll if 430// the loop is a CountedLoop and the body is small enough. 431bool IdealLoopTree::policy_unroll( PhaseIdealLoop *phase ) const { 432 433 CountedLoopNode *cl = _head->as_CountedLoop(); 434 assert( cl->is_normal_loop() || cl->is_main_loop(), "" ); 435 436 // protect against stride not being a constant 437 if( !cl->stride_is_con() ) return false; 438 439 // protect against over-unrolling 440 if( cl->trip_count() <= 1 ) return false; 441 442 int future_unroll_ct = cl->unrolled_count() * 2; 443 444 // Don't unroll if the next round of unrolling would push us 445 // over the expected trip count of the loop. One is subtracted 446 // from the expected trip count because the pre-loop normally 447 // executes 1 iteration. 448 if (UnrollLimitForProfileCheck > 0 && 449 cl->profile_trip_cnt() != COUNT_UNKNOWN && 450 future_unroll_ct > UnrollLimitForProfileCheck && 451 (float)future_unroll_ct > cl->profile_trip_cnt() - 1.0) { 452 return false; 453 } 454 455 // When unroll count is greater than LoopUnrollMin, don't unroll if: 456 // the residual iterations are more than 10% of the trip count 457 // and rounds of "unroll,optimize" are not making significant progress 458 // Progress defined as current size less than 20% larger than previous size. 459 if (UseSuperWord && cl->node_count_before_unroll() > 0 && 460 future_unroll_ct > LoopUnrollMin && 461 (future_unroll_ct - 1) * 10.0 > cl->profile_trip_cnt() && 462 1.2 * cl->node_count_before_unroll() < (double)_body.size()) { 463 return false; 464 } 465 466 Node *init_n = cl->init_trip(); 467 Node *limit_n = cl->limit(); 468 // Non-constant bounds. 469 // Protect against over-unrolling when init or/and limit are not constant 470 // (so that trip_count's init value is maxint) but iv range is known. 471 if( init_n == NULL || !init_n->is_Con() || 472 limit_n == NULL || !limit_n->is_Con() ) { 473 Node* phi = cl->phi(); 474 if( phi != NULL ) { 475 assert(phi->is_Phi() && phi->in(0) == _head, "Counted loop should have iv phi."); 476 const TypeInt* iv_type = phase->_igvn.type(phi)->is_int(); 477 int next_stride = cl->stride_con() * 2; // stride after this unroll 478 if( next_stride > 0 ) { 479 if( iv_type->_lo + next_stride <= iv_type->_lo || // overflow 480 iv_type->_lo + next_stride > iv_type->_hi ) { 481 return false; // over-unrolling 482 } 483 } else if( next_stride < 0 ) { 484 if( iv_type->_hi + next_stride >= iv_type->_hi || // overflow 485 iv_type->_hi + next_stride < iv_type->_lo ) { 486 return false; // over-unrolling 487 } 488 } 489 } 490 } 491 492 // Adjust body_size to determine if we unroll or not 493 uint body_size = _body.size(); 494 // Key test to unroll CaffeineMark's Logic test 495 int xors_in_loop = 0; 496 // Also count ModL, DivL and MulL which expand mightly 497 for( uint k = 0; k < _body.size(); k++ ) { 498 switch( _body.at(k)->Opcode() ) { 499 case Op_XorI: xors_in_loop++; break; // CaffeineMark's Logic test 500 case Op_ModL: body_size += 30; break; 501 case Op_DivL: body_size += 30; break; 502 case Op_MulL: body_size += 10; break; 503 } 504 } 505 506 // Check for being too big 507 if( body_size > (uint)LoopUnrollLimit ) { 508 if( xors_in_loop >= 4 && body_size < (uint)LoopUnrollLimit*4) return true; 509 // Normal case: loop too big 510 return false; 511 } 512 513 // Check for stride being a small enough constant 514 if( abs(cl->stride_con()) > (1<<3) ) return false; 515 516 // Unroll once! (Each trip will soon do double iterations) 517 return true; 518} 519 520//------------------------------policy_align----------------------------------- 521// Return TRUE or FALSE if the loop should be cache-line aligned. Gather the 522// expression that does the alignment. Note that only one array base can be 523// aligned in a loop (unless the VM guarentees mutual alignment). Note that 524// if we vectorize short memory ops into longer memory ops, we may want to 525// increase alignment. 526bool IdealLoopTree::policy_align( PhaseIdealLoop *phase ) const { 527 return false; 528} 529 530//------------------------------policy_range_check----------------------------- 531// Return TRUE or FALSE if the loop should be range-check-eliminated. 532// Actually we do iteration-splitting, a more powerful form of RCE. 533bool IdealLoopTree::policy_range_check( PhaseIdealLoop *phase ) const { 534 if( !RangeCheckElimination ) return false; 535 536 CountedLoopNode *cl = _head->as_CountedLoop(); 537 // If we unrolled with no intention of doing RCE and we later 538 // changed our minds, we got no pre-loop. Either we need to 539 // make a new pre-loop, or we gotta disallow RCE. 540 if( cl->is_main_no_pre_loop() ) return false; // Disallowed for now. 541 Node *trip_counter = cl->phi(); 542 543 // Check loop body for tests of trip-counter plus loop-invariant vs 544 // loop-invariant. 545 for( uint i = 0; i < _body.size(); i++ ) { 546 Node *iff = _body[i]; 547 if( iff->Opcode() == Op_If ) { // Test? 548 549 // Comparing trip+off vs limit 550 Node *bol = iff->in(1); 551 if( bol->req() != 2 ) continue; // dead constant test 552 Node *cmp = bol->in(1); 553 554 Node *rc_exp = cmp->in(1); 555 Node *limit = cmp->in(2); 556 557 Node *limit_c = phase->get_ctrl(limit); 558 if( limit_c == phase->C->top() ) 559 return false; // Found dead test on live IF? No RCE! 560 if( is_member(phase->get_loop(limit_c) ) ) { 561 // Compare might have operands swapped; commute them 562 rc_exp = cmp->in(2); 563 limit = cmp->in(1); 564 limit_c = phase->get_ctrl(limit); 565 if( is_member(phase->get_loop(limit_c) ) ) 566 continue; // Both inputs are loop varying; cannot RCE 567 } 568 569 if (!phase->is_scaled_iv_plus_offset(rc_exp, trip_counter, NULL, NULL)) { 570 continue; 571 } 572 // Yeah! Found a test like 'trip+off vs limit' 573 // Test is an IfNode, has 2 projections. If BOTH are in the loop 574 // we need loop unswitching instead of iteration splitting. 575 if( is_loop_exit(iff) ) 576 return true; // Found reason to split iterations 577 } // End of is IF 578 } 579 580 return false; 581} 582 583//------------------------------policy_peel_only------------------------------- 584// Return TRUE or FALSE if the loop should NEVER be RCE'd or aligned. Useful 585// for unrolling loops with NO array accesses. 586bool IdealLoopTree::policy_peel_only( PhaseIdealLoop *phase ) const { 587 588 for( uint i = 0; i < _body.size(); i++ ) 589 if( _body[i]->is_Mem() ) 590 return false; 591 592 // No memory accesses at all! 593 return true; 594} 595 596//------------------------------clone_up_backedge_goo-------------------------- 597// If Node n lives in the back_ctrl block and cannot float, we clone a private 598// version of n in preheader_ctrl block and return that, otherwise return n. 599Node *PhaseIdealLoop::clone_up_backedge_goo( Node *back_ctrl, Node *preheader_ctrl, Node *n ) { 600 if( get_ctrl(n) != back_ctrl ) return n; 601 602 Node *x = NULL; // If required, a clone of 'n' 603 // Check for 'n' being pinned in the backedge. 604 if( n->in(0) && n->in(0) == back_ctrl ) { 605 x = n->clone(); // Clone a copy of 'n' to preheader 606 x->set_req( 0, preheader_ctrl ); // Fix x's control input to preheader 607 } 608 609 // Recursive fixup any other input edges into x. 610 // If there are no changes we can just return 'n', otherwise 611 // we need to clone a private copy and change it. 612 for( uint i = 1; i < n->req(); i++ ) { 613 Node *g = clone_up_backedge_goo( back_ctrl, preheader_ctrl, n->in(i) ); 614 if( g != n->in(i) ) { 615 if( !x ) 616 x = n->clone(); 617 x->set_req(i, g); 618 } 619 } 620 if( x ) { // x can legally float to pre-header location 621 register_new_node( x, preheader_ctrl ); 622 return x; 623 } else { // raise n to cover LCA of uses 624 set_ctrl( n, find_non_split_ctrl(back_ctrl->in(0)) ); 625 } 626 return n; 627} 628 629//------------------------------insert_pre_post_loops-------------------------- 630// Insert pre and post loops. If peel_only is set, the pre-loop can not have 631// more iterations added. It acts as a 'peel' only, no lower-bound RCE, no 632// alignment. Useful to unroll loops that do no array accesses. 633void PhaseIdealLoop::insert_pre_post_loops( IdealLoopTree *loop, Node_List &old_new, bool peel_only ) { 634 635 C->set_major_progress(); 636 637 // Find common pieces of the loop being guarded with pre & post loops 638 CountedLoopNode *main_head = loop->_head->as_CountedLoop(); 639 assert( main_head->is_normal_loop(), "" ); 640 CountedLoopEndNode *main_end = main_head->loopexit(); 641 assert( main_end->outcnt() == 2, "1 true, 1 false path only" ); 642 uint dd_main_head = dom_depth(main_head); 643 uint max = main_head->outcnt(); 644 645 Node *pre_header= main_head->in(LoopNode::EntryControl); 646 Node *init = main_head->init_trip(); 647 Node *incr = main_end ->incr(); 648 Node *limit = main_end ->limit(); 649 Node *stride = main_end ->stride(); 650 Node *cmp = main_end ->cmp_node(); 651 BoolTest::mask b_test = main_end->test_trip(); 652 653 // Need only 1 user of 'bol' because I will be hacking the loop bounds. 654 Node *bol = main_end->in(CountedLoopEndNode::TestValue); 655 if( bol->outcnt() != 1 ) { 656 bol = bol->clone(); 657 register_new_node(bol,main_end->in(CountedLoopEndNode::TestControl)); 658 _igvn.hash_delete(main_end); 659 main_end->set_req(CountedLoopEndNode::TestValue, bol); 660 } 661 // Need only 1 user of 'cmp' because I will be hacking the loop bounds. 662 if( cmp->outcnt() != 1 ) { 663 cmp = cmp->clone(); 664 register_new_node(cmp,main_end->in(CountedLoopEndNode::TestControl)); 665 _igvn.hash_delete(bol); 666 bol->set_req(1, cmp); 667 } 668 669 //------------------------------ 670 // Step A: Create Post-Loop. 671 Node* main_exit = main_end->proj_out(false); 672 assert( main_exit->Opcode() == Op_IfFalse, "" ); 673 int dd_main_exit = dom_depth(main_exit); 674 675 // Step A1: Clone the loop body. The clone becomes the post-loop. The main 676 // loop pre-header illegally has 2 control users (old & new loops). 677 clone_loop( loop, old_new, dd_main_exit ); 678 assert( old_new[main_end ->_idx]->Opcode() == Op_CountedLoopEnd, "" ); 679 CountedLoopNode *post_head = old_new[main_head->_idx]->as_CountedLoop(); 680 post_head->set_post_loop(main_head); 681 682 // Build the main-loop normal exit. 683 IfFalseNode *new_main_exit = new (C, 1) IfFalseNode(main_end); 684 _igvn.register_new_node_with_optimizer( new_main_exit ); 685 set_idom(new_main_exit, main_end, dd_main_exit ); 686 set_loop(new_main_exit, loop->_parent); 687 688 // Step A2: Build a zero-trip guard for the post-loop. After leaving the 689 // main-loop, the post-loop may not execute at all. We 'opaque' the incr 690 // (the main-loop trip-counter exit value) because we will be changing 691 // the exit value (via unrolling) so we cannot constant-fold away the zero 692 // trip guard until all unrolling is done. 693 Node *zer_opaq = new (C, 2) Opaque1Node(incr); 694 Node *zer_cmp = new (C, 3) CmpINode( zer_opaq, limit ); 695 Node *zer_bol = new (C, 2) BoolNode( zer_cmp, b_test ); 696 register_new_node( zer_opaq, new_main_exit ); 697 register_new_node( zer_cmp , new_main_exit ); 698 register_new_node( zer_bol , new_main_exit ); 699 700 // Build the IfNode 701 IfNode *zer_iff = new (C, 2) IfNode( new_main_exit, zer_bol, PROB_FAIR, COUNT_UNKNOWN ); 702 _igvn.register_new_node_with_optimizer( zer_iff ); 703 set_idom(zer_iff, new_main_exit, dd_main_exit); 704 set_loop(zer_iff, loop->_parent); 705 706 // Plug in the false-path, taken if we need to skip post-loop 707 _igvn.hash_delete( main_exit ); 708 main_exit->set_req(0, zer_iff); 709 _igvn._worklist.push(main_exit); 710 set_idom(main_exit, zer_iff, dd_main_exit); 711 set_idom(main_exit->unique_out(), zer_iff, dd_main_exit); 712 // Make the true-path, must enter the post loop 713 Node *zer_taken = new (C, 1) IfTrueNode( zer_iff ); 714 _igvn.register_new_node_with_optimizer( zer_taken ); 715 set_idom(zer_taken, zer_iff, dd_main_exit); 716 set_loop(zer_taken, loop->_parent); 717 // Plug in the true path 718 _igvn.hash_delete( post_head ); 719 post_head->set_req(LoopNode::EntryControl, zer_taken); 720 set_idom(post_head, zer_taken, dd_main_exit); 721 722 // Step A3: Make the fall-in values to the post-loop come from the 723 // fall-out values of the main-loop. 724 for (DUIterator_Fast imax, i = main_head->fast_outs(imax); i < imax; i++) { 725 Node* main_phi = main_head->fast_out(i); 726 if( main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() >0 ) { 727 Node *post_phi = old_new[main_phi->_idx]; 728 Node *fallmain = clone_up_backedge_goo(main_head->back_control(), 729 post_head->init_control(), 730 main_phi->in(LoopNode::LoopBackControl)); 731 _igvn.hash_delete(post_phi); 732 post_phi->set_req( LoopNode::EntryControl, fallmain ); 733 } 734 } 735 736 // Update local caches for next stanza 737 main_exit = new_main_exit; 738 739 740 //------------------------------ 741 // Step B: Create Pre-Loop. 742 743 // Step B1: Clone the loop body. The clone becomes the pre-loop. The main 744 // loop pre-header illegally has 2 control users (old & new loops). 745 clone_loop( loop, old_new, dd_main_head ); 746 CountedLoopNode* pre_head = old_new[main_head->_idx]->as_CountedLoop(); 747 CountedLoopEndNode* pre_end = old_new[main_end ->_idx]->as_CountedLoopEnd(); 748 pre_head->set_pre_loop(main_head); 749 Node *pre_incr = old_new[incr->_idx]; 750 751 // Find the pre-loop normal exit. 752 Node* pre_exit = pre_end->proj_out(false); 753 assert( pre_exit->Opcode() == Op_IfFalse, "" ); 754 IfFalseNode *new_pre_exit = new (C, 1) IfFalseNode(pre_end); 755 _igvn.register_new_node_with_optimizer( new_pre_exit ); 756 set_idom(new_pre_exit, pre_end, dd_main_head); 757 set_loop(new_pre_exit, loop->_parent); 758 759 // Step B2: Build a zero-trip guard for the main-loop. After leaving the 760 // pre-loop, the main-loop may not execute at all. Later in life this 761 // zero-trip guard will become the minimum-trip guard when we unroll 762 // the main-loop. 763 Node *min_opaq = new (C, 2) Opaque1Node(limit); 764 Node *min_cmp = new (C, 3) CmpINode( pre_incr, min_opaq ); 765 Node *min_bol = new (C, 2) BoolNode( min_cmp, b_test ); 766 register_new_node( min_opaq, new_pre_exit ); 767 register_new_node( min_cmp , new_pre_exit ); 768 register_new_node( min_bol , new_pre_exit ); 769 770 // Build the IfNode 771 IfNode *min_iff = new (C, 2) IfNode( new_pre_exit, min_bol, PROB_FAIR, COUNT_UNKNOWN ); 772 _igvn.register_new_node_with_optimizer( min_iff ); 773 set_idom(min_iff, new_pre_exit, dd_main_head); 774 set_loop(min_iff, loop->_parent); 775 776 // Plug in the false-path, taken if we need to skip main-loop 777 _igvn.hash_delete( pre_exit ); 778 pre_exit->set_req(0, min_iff); 779 set_idom(pre_exit, min_iff, dd_main_head); 780 set_idom(pre_exit->unique_out(), min_iff, dd_main_head); 781 // Make the true-path, must enter the main loop 782 Node *min_taken = new (C, 1) IfTrueNode( min_iff ); 783 _igvn.register_new_node_with_optimizer( min_taken ); 784 set_idom(min_taken, min_iff, dd_main_head); 785 set_loop(min_taken, loop->_parent); 786 // Plug in the true path 787 _igvn.hash_delete( main_head ); 788 main_head->set_req(LoopNode::EntryControl, min_taken); 789 set_idom(main_head, min_taken, dd_main_head); 790 791 // Step B3: Make the fall-in values to the main-loop come from the 792 // fall-out values of the pre-loop. 793 for (DUIterator_Fast i2max, i2 = main_head->fast_outs(i2max); i2 < i2max; i2++) { 794 Node* main_phi = main_head->fast_out(i2); 795 if( main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() > 0 ) { 796 Node *pre_phi = old_new[main_phi->_idx]; 797 Node *fallpre = clone_up_backedge_goo(pre_head->back_control(), 798 main_head->init_control(), 799 pre_phi->in(LoopNode::LoopBackControl)); 800 _igvn.hash_delete(main_phi); 801 main_phi->set_req( LoopNode::EntryControl, fallpre ); 802 } 803 } 804 805 // Step B4: Shorten the pre-loop to run only 1 iteration (for now). 806 // RCE and alignment may change this later. 807 Node *cmp_end = pre_end->cmp_node(); 808 assert( cmp_end->in(2) == limit, "" ); 809 Node *pre_limit = new (C, 3) AddINode( init, stride ); 810 811 // Save the original loop limit in this Opaque1 node for 812 // use by range check elimination. 813 Node *pre_opaq = new (C, 3) Opaque1Node(pre_limit, limit); 814 815 register_new_node( pre_limit, pre_head->in(0) ); 816 register_new_node( pre_opaq , pre_head->in(0) ); 817 818 // Since no other users of pre-loop compare, I can hack limit directly 819 assert( cmp_end->outcnt() == 1, "no other users" ); 820 _igvn.hash_delete(cmp_end); 821 cmp_end->set_req(2, peel_only ? pre_limit : pre_opaq); 822 823 // Special case for not-equal loop bounds: 824 // Change pre loop test, main loop test, and the 825 // main loop guard test to use lt or gt depending on stride 826 // direction: 827 // positive stride use < 828 // negative stride use > 829 830 if (pre_end->in(CountedLoopEndNode::TestValue)->as_Bool()->_test._test == BoolTest::ne) { 831 832 BoolTest::mask new_test = (main_end->stride_con() > 0) ? BoolTest::lt : BoolTest::gt; 833 // Modify pre loop end condition 834 Node* pre_bol = pre_end->in(CountedLoopEndNode::TestValue)->as_Bool(); 835 BoolNode* new_bol0 = new (C, 2) BoolNode(pre_bol->in(1), new_test); 836 register_new_node( new_bol0, pre_head->in(0) ); 837 _igvn.hash_delete(pre_end); 838 pre_end->set_req(CountedLoopEndNode::TestValue, new_bol0); 839 // Modify main loop guard condition 840 assert(min_iff->in(CountedLoopEndNode::TestValue) == min_bol, "guard okay"); 841 BoolNode* new_bol1 = new (C, 2) BoolNode(min_bol->in(1), new_test); 842 register_new_node( new_bol1, new_pre_exit ); 843 _igvn.hash_delete(min_iff); 844 min_iff->set_req(CountedLoopEndNode::TestValue, new_bol1); 845 // Modify main loop end condition 846 BoolNode* main_bol = main_end->in(CountedLoopEndNode::TestValue)->as_Bool(); 847 BoolNode* new_bol2 = new (C, 2) BoolNode(main_bol->in(1), new_test); 848 register_new_node( new_bol2, main_end->in(CountedLoopEndNode::TestControl) ); 849 _igvn.hash_delete(main_end); 850 main_end->set_req(CountedLoopEndNode::TestValue, new_bol2); 851 } 852 853 // Flag main loop 854 main_head->set_main_loop(); 855 if( peel_only ) main_head->set_main_no_pre_loop(); 856 857 // It's difficult to be precise about the trip-counts 858 // for the pre/post loops. They are usually very short, 859 // so guess that 4 trips is a reasonable value. 860 post_head->set_profile_trip_cnt(4.0); 861 pre_head->set_profile_trip_cnt(4.0); 862 863 // Now force out all loop-invariant dominating tests. The optimizer 864 // finds some, but we _know_ they are all useless. 865 peeled_dom_test_elim(loop,old_new); 866} 867 868//------------------------------is_invariant----------------------------- 869// Return true if n is invariant 870bool IdealLoopTree::is_invariant(Node* n) const { 871 Node *n_c = _phase->get_ctrl(n); 872 if (n_c->is_top()) return false; 873 return !is_member(_phase->get_loop(n_c)); 874} 875 876 877//------------------------------do_unroll-------------------------------------- 878// Unroll the loop body one step - make each trip do 2 iterations. 879void PhaseIdealLoop::do_unroll( IdealLoopTree *loop, Node_List &old_new, bool adjust_min_trip ) { 880 assert( LoopUnrollLimit, "" ); 881#ifndef PRODUCT 882 if( PrintOpto && VerifyLoopOptimizations ) { 883 tty->print("Unrolling "); 884 loop->dump_head(); 885 } 886#endif 887 CountedLoopNode *loop_head = loop->_head->as_CountedLoop(); 888 CountedLoopEndNode *loop_end = loop_head->loopexit(); 889 assert( loop_end, "" ); 890 891 // Remember loop node count before unrolling to detect 892 // if rounds of unroll,optimize are making progress 893 loop_head->set_node_count_before_unroll(loop->_body.size()); 894 895 Node *ctrl = loop_head->in(LoopNode::EntryControl); 896 Node *limit = loop_head->limit(); 897 Node *init = loop_head->init_trip(); 898 Node *strid = loop_head->stride(); 899 900 Node *opaq = NULL; 901 if( adjust_min_trip ) { // If not maximally unrolling, need adjustment 902 assert( loop_head->is_main_loop(), "" ); 903 assert( ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "" ); 904 Node *iff = ctrl->in(0); 905 assert( iff->Opcode() == Op_If, "" ); 906 Node *bol = iff->in(1); 907 assert( bol->Opcode() == Op_Bool, "" ); 908 Node *cmp = bol->in(1); 909 assert( cmp->Opcode() == Op_CmpI, "" ); 910 opaq = cmp->in(2); 911 // Occasionally it's possible for a pre-loop Opaque1 node to be 912 // optimized away and then another round of loop opts attempted. 913 // We can not optimize this particular loop in that case. 914 if( opaq->Opcode() != Op_Opaque1 ) 915 return; // Cannot find pre-loop! Bail out! 916 } 917 918 C->set_major_progress(); 919 920 // Adjust max trip count. The trip count is intentionally rounded 921 // down here (e.g. 15-> 7-> 3-> 1) because if we unwittingly over-unroll, 922 // the main, unrolled, part of the loop will never execute as it is protected 923 // by the min-trip test. See bug 4834191 for a case where we over-unrolled 924 // and later determined that part of the unrolled loop was dead. 925 loop_head->set_trip_count(loop_head->trip_count() / 2); 926 927 // Double the count of original iterations in the unrolled loop body. 928 loop_head->double_unrolled_count(); 929 930 // ----------- 931 // Step 2: Cut back the trip counter for an unroll amount of 2. 932 // Loop will normally trip (limit - init)/stride_con. Since it's a 933 // CountedLoop this is exact (stride divides limit-init exactly). 934 // We are going to double the loop body, so we want to knock off any 935 // odd iteration: (trip_cnt & ~1). Then back compute a new limit. 936 Node *span = new (C, 3) SubINode( limit, init ); 937 register_new_node( span, ctrl ); 938 Node *trip = new (C, 3) DivINode( 0, span, strid ); 939 register_new_node( trip, ctrl ); 940 Node *mtwo = _igvn.intcon(-2); 941 set_ctrl(mtwo, C->root()); 942 Node *rond = new (C, 3) AndINode( trip, mtwo ); 943 register_new_node( rond, ctrl ); 944 Node *spn2 = new (C, 3) MulINode( rond, strid ); 945 register_new_node( spn2, ctrl ); 946 Node *lim2 = new (C, 3) AddINode( spn2, init ); 947 register_new_node( lim2, ctrl ); 948 949 // Hammer in the new limit 950 Node *ctrl2 = loop_end->in(0); 951 Node *cmp2 = new (C, 3) CmpINode( loop_head->incr(), lim2 ); 952 register_new_node( cmp2, ctrl2 ); 953 Node *bol2 = new (C, 2) BoolNode( cmp2, loop_end->test_trip() ); 954 register_new_node( bol2, ctrl2 ); 955 _igvn.hash_delete(loop_end); 956 loop_end->set_req(CountedLoopEndNode::TestValue, bol2); 957 958 // Step 3: Find the min-trip test guaranteed before a 'main' loop. 959 // Make it a 1-trip test (means at least 2 trips). 960 if( adjust_min_trip ) { 961 // Guard test uses an 'opaque' node which is not shared. Hence I 962 // can edit it's inputs directly. Hammer in the new limit for the 963 // minimum-trip guard. 964 assert( opaq->outcnt() == 1, "" ); 965 _igvn.hash_delete(opaq); 966 opaq->set_req(1, lim2); 967 } 968 969 // --------- 970 // Step 4: Clone the loop body. Move it inside the loop. This loop body 971 // represents the odd iterations; since the loop trips an even number of 972 // times its backedge is never taken. Kill the backedge. 973 uint dd = dom_depth(loop_head); 974 clone_loop( loop, old_new, dd ); 975 976 // Make backedges of the clone equal to backedges of the original. 977 // Make the fall-in from the original come from the fall-out of the clone. 978 for (DUIterator_Fast jmax, j = loop_head->fast_outs(jmax); j < jmax; j++) { 979 Node* phi = loop_head->fast_out(j); 980 if( phi->is_Phi() && phi->in(0) == loop_head && phi->outcnt() > 0 ) { 981 Node *newphi = old_new[phi->_idx]; 982 _igvn.hash_delete( phi ); 983 _igvn.hash_delete( newphi ); 984 985 phi ->set_req(LoopNode:: EntryControl, newphi->in(LoopNode::LoopBackControl)); 986 newphi->set_req(LoopNode::LoopBackControl, phi ->in(LoopNode::LoopBackControl)); 987 phi ->set_req(LoopNode::LoopBackControl, C->top()); 988 } 989 } 990 Node *clone_head = old_new[loop_head->_idx]; 991 _igvn.hash_delete( clone_head ); 992 loop_head ->set_req(LoopNode:: EntryControl, clone_head->in(LoopNode::LoopBackControl)); 993 clone_head->set_req(LoopNode::LoopBackControl, loop_head ->in(LoopNode::LoopBackControl)); 994 loop_head ->set_req(LoopNode::LoopBackControl, C->top()); 995 loop->_head = clone_head; // New loop header 996 997 set_idom(loop_head, loop_head ->in(LoopNode::EntryControl), dd); 998 set_idom(clone_head, clone_head->in(LoopNode::EntryControl), dd); 999 1000 // Kill the clone's backedge 1001 Node *newcle = old_new[loop_end->_idx]; 1002 _igvn.hash_delete( newcle ); 1003 Node *one = _igvn.intcon(1); 1004 set_ctrl(one, C->root()); 1005 newcle->set_req(1, one); 1006 // Force clone into same loop body 1007 uint max = loop->_body.size(); 1008 for( uint k = 0; k < max; k++ ) { 1009 Node *old = loop->_body.at(k); 1010 Node *nnn = old_new[old->_idx]; 1011 loop->_body.push(nnn); 1012 if (!has_ctrl(old)) 1013 set_loop(nnn, loop); 1014 } 1015} 1016 1017//------------------------------do_maximally_unroll---------------------------- 1018 1019void PhaseIdealLoop::do_maximally_unroll( IdealLoopTree *loop, Node_List &old_new ) { 1020 CountedLoopNode *cl = loop->_head->as_CountedLoop(); 1021 assert( cl->trip_count() > 0, ""); 1022 1023 // If loop is tripping an odd number of times, peel odd iteration 1024 if( (cl->trip_count() & 1) == 1 ) { 1025 do_peeling( loop, old_new ); 1026 } 1027 1028 // Now its tripping an even number of times remaining. Double loop body. 1029 // Do not adjust pre-guards; they are not needed and do not exist. 1030 if( cl->trip_count() > 0 ) { 1031 do_unroll( loop, old_new, false ); 1032 } 1033} 1034 1035//------------------------------dominates_backedge--------------------------------- 1036// Returns true if ctrl is executed on every complete iteration 1037bool IdealLoopTree::dominates_backedge(Node* ctrl) { 1038 assert(ctrl->is_CFG(), "must be control"); 1039 Node* backedge = _head->as_Loop()->in(LoopNode::LoopBackControl); 1040 return _phase->dom_lca_internal(ctrl, backedge) == ctrl; 1041} 1042 1043//------------------------------add_constraint--------------------------------- 1044// Constrain the main loop iterations so the condition: 1045// scale_con * I + offset < limit 1046// always holds true. That is, either increase the number of iterations in 1047// the pre-loop or the post-loop until the condition holds true in the main 1048// loop. Stride, scale, offset and limit are all loop invariant. Further, 1049// stride and scale are constants (offset and limit often are). 1050void PhaseIdealLoop::add_constraint( int stride_con, int scale_con, Node *offset, Node *limit, Node *pre_ctrl, Node **pre_limit, Node **main_limit ) { 1051 1052 // Compute "I :: (limit-offset)/scale_con" 1053 Node *con = new (C, 3) SubINode( limit, offset ); 1054 register_new_node( con, pre_ctrl ); 1055 Node *scale = _igvn.intcon(scale_con); 1056 set_ctrl(scale, C->root()); 1057 Node *X = new (C, 3) DivINode( 0, con, scale ); 1058 register_new_node( X, pre_ctrl ); 1059 1060 // For positive stride, the pre-loop limit always uses a MAX function 1061 // and the main loop a MIN function. For negative stride these are 1062 // reversed. 1063 1064 // Also for positive stride*scale the affine function is increasing, so the 1065 // pre-loop must check for underflow and the post-loop for overflow. 1066 // Negative stride*scale reverses this; pre-loop checks for overflow and 1067 // post-loop for underflow. 1068 if( stride_con*scale_con > 0 ) { 1069 // Compute I < (limit-offset)/scale_con 1070 // Adjust main-loop last iteration to be MIN/MAX(main_loop,X) 1071 *main_limit = (stride_con > 0) 1072 ? (Node*)(new (C, 3) MinINode( *main_limit, X )) 1073 : (Node*)(new (C, 3) MaxINode( *main_limit, X )); 1074 register_new_node( *main_limit, pre_ctrl ); 1075 1076 } else { 1077 // Compute (limit-offset)/scale_con + SGN(-scale_con) <= I 1078 // Add the negation of the main-loop constraint to the pre-loop. 1079 // See footnote [++] below for a derivation of the limit expression. 1080 Node *incr = _igvn.intcon(scale_con > 0 ? -1 : 1); 1081 set_ctrl(incr, C->root()); 1082 Node *adj = new (C, 3) AddINode( X, incr ); 1083 register_new_node( adj, pre_ctrl ); 1084 *pre_limit = (scale_con > 0) 1085 ? (Node*)new (C, 3) MinINode( *pre_limit, adj ) 1086 : (Node*)new (C, 3) MaxINode( *pre_limit, adj ); 1087 register_new_node( *pre_limit, pre_ctrl ); 1088 1089// [++] Here's the algebra that justifies the pre-loop limit expression: 1090// 1091// NOT( scale_con * I + offset < limit ) 1092// == 1093// scale_con * I + offset >= limit 1094// == 1095// SGN(scale_con) * I >= (limit-offset)/|scale_con| 1096// == 1097// (limit-offset)/|scale_con| <= I * SGN(scale_con) 1098// == 1099// (limit-offset)/|scale_con|-1 < I * SGN(scale_con) 1100// == 1101// ( if (scale_con > 0) /*common case*/ 1102// (limit-offset)/scale_con - 1 < I 1103// else 1104// (limit-offset)/scale_con + 1 > I 1105// ) 1106// ( if (scale_con > 0) /*common case*/ 1107// (limit-offset)/scale_con + SGN(-scale_con) < I 1108// else 1109// (limit-offset)/scale_con + SGN(-scale_con) > I 1110 } 1111} 1112 1113 1114//------------------------------is_scaled_iv--------------------------------- 1115// Return true if exp is a constant times an induction var 1116bool PhaseIdealLoop::is_scaled_iv(Node* exp, Node* iv, int* p_scale) { 1117 if (exp == iv) { 1118 if (p_scale != NULL) { 1119 *p_scale = 1; 1120 } 1121 return true; 1122 } 1123 int opc = exp->Opcode(); 1124 if (opc == Op_MulI) { 1125 if (exp->in(1) == iv && exp->in(2)->is_Con()) { 1126 if (p_scale != NULL) { 1127 *p_scale = exp->in(2)->get_int(); 1128 } 1129 return true; 1130 } 1131 if (exp->in(2) == iv && exp->in(1)->is_Con()) { 1132 if (p_scale != NULL) { 1133 *p_scale = exp->in(1)->get_int(); 1134 } 1135 return true; 1136 } 1137 } else if (opc == Op_LShiftI) { 1138 if (exp->in(1) == iv && exp->in(2)->is_Con()) { 1139 if (p_scale != NULL) { 1140 *p_scale = 1 << exp->in(2)->get_int(); 1141 } 1142 return true; 1143 } 1144 } 1145 return false; 1146} 1147 1148//-----------------------------is_scaled_iv_plus_offset------------------------------ 1149// Return true if exp is a simple induction variable expression: k1*iv + (invar + k2) 1150bool PhaseIdealLoop::is_scaled_iv_plus_offset(Node* exp, Node* iv, int* p_scale, Node** p_offset, int depth) { 1151 if (is_scaled_iv(exp, iv, p_scale)) { 1152 if (p_offset != NULL) { 1153 Node *zero = _igvn.intcon(0); 1154 set_ctrl(zero, C->root()); 1155 *p_offset = zero; 1156 } 1157 return true; 1158 } 1159 int opc = exp->Opcode(); 1160 if (opc == Op_AddI) { 1161 if (is_scaled_iv(exp->in(1), iv, p_scale)) { 1162 if (p_offset != NULL) { 1163 *p_offset = exp->in(2); 1164 } 1165 return true; 1166 } 1167 if (exp->in(2)->is_Con()) { 1168 Node* offset2 = NULL; 1169 if (depth < 2 && 1170 is_scaled_iv_plus_offset(exp->in(1), iv, p_scale, 1171 p_offset != NULL ? &offset2 : NULL, depth+1)) { 1172 if (p_offset != NULL) { 1173 Node *ctrl_off2 = get_ctrl(offset2); 1174 Node* offset = new (C, 3) AddINode(offset2, exp->in(2)); 1175 register_new_node(offset, ctrl_off2); 1176 *p_offset = offset; 1177 } 1178 return true; 1179 } 1180 } 1181 } else if (opc == Op_SubI) { 1182 if (is_scaled_iv(exp->in(1), iv, p_scale)) { 1183 if (p_offset != NULL) { 1184 Node *zero = _igvn.intcon(0); 1185 set_ctrl(zero, C->root()); 1186 Node *ctrl_off = get_ctrl(exp->in(2)); 1187 Node* offset = new (C, 3) SubINode(zero, exp->in(2)); 1188 register_new_node(offset, ctrl_off); 1189 *p_offset = offset; 1190 } 1191 return true; 1192 } 1193 if (is_scaled_iv(exp->in(2), iv, p_scale)) { 1194 if (p_offset != NULL) { 1195 *p_scale *= -1; 1196 *p_offset = exp->in(1); 1197 } 1198 return true; 1199 } 1200 } 1201 return false; 1202} 1203 1204//------------------------------do_range_check--------------------------------- 1205// Eliminate range-checks and other trip-counter vs loop-invariant tests. 1206void PhaseIdealLoop::do_range_check( IdealLoopTree *loop, Node_List &old_new ) { 1207#ifndef PRODUCT 1208 if( PrintOpto && VerifyLoopOptimizations ) { 1209 tty->print("Range Check Elimination "); 1210 loop->dump_head(); 1211 } 1212#endif 1213 assert( RangeCheckElimination, "" ); 1214 CountedLoopNode *cl = loop->_head->as_CountedLoop(); 1215 assert( cl->is_main_loop(), "" ); 1216 1217 // Find the trip counter; we are iteration splitting based on it 1218 Node *trip_counter = cl->phi(); 1219 // Find the main loop limit; we will trim it's iterations 1220 // to not ever trip end tests 1221 Node *main_limit = cl->limit(); 1222 // Find the pre-loop limit; we will expand it's iterations to 1223 // not ever trip low tests. 1224 Node *ctrl = cl->in(LoopNode::EntryControl); 1225 assert( ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "" ); 1226 Node *iffm = ctrl->in(0); 1227 assert( iffm->Opcode() == Op_If, "" ); 1228 Node *p_f = iffm->in(0); 1229 assert( p_f->Opcode() == Op_IfFalse, "" ); 1230 CountedLoopEndNode *pre_end = p_f->in(0)->as_CountedLoopEnd(); 1231 assert( pre_end->loopnode()->is_pre_loop(), "" ); 1232 Node *pre_opaq1 = pre_end->limit(); 1233 // Occasionally it's possible for a pre-loop Opaque1 node to be 1234 // optimized away and then another round of loop opts attempted. 1235 // We can not optimize this particular loop in that case. 1236 if( pre_opaq1->Opcode() != Op_Opaque1 ) 1237 return; 1238 Opaque1Node *pre_opaq = (Opaque1Node*)pre_opaq1; 1239 Node *pre_limit = pre_opaq->in(1); 1240 1241 // Where do we put new limit calculations 1242 Node *pre_ctrl = pre_end->loopnode()->in(LoopNode::EntryControl); 1243 1244 // Ensure the original loop limit is available from the 1245 // pre-loop Opaque1 node. 1246 Node *orig_limit = pre_opaq->original_loop_limit(); 1247 if( orig_limit == NULL || _igvn.type(orig_limit) == Type::TOP ) 1248 return; 1249 1250 // Need to find the main-loop zero-trip guard 1251 Node *bolzm = iffm->in(1); 1252 assert( bolzm->Opcode() == Op_Bool, "" ); 1253 Node *cmpzm = bolzm->in(1); 1254 assert( cmpzm->is_Cmp(), "" ); 1255 Node *opqzm = cmpzm->in(2); 1256 if( opqzm->Opcode() != Op_Opaque1 ) 1257 return; 1258 assert( opqzm->in(1) == main_limit, "do not understand situation" ); 1259 1260 // Must know if its a count-up or count-down loop 1261 1262 // protect against stride not being a constant 1263 if ( !cl->stride_is_con() ) { 1264 return; 1265 } 1266 int stride_con = cl->stride_con(); 1267 Node *zero = _igvn.intcon(0); 1268 Node *one = _igvn.intcon(1); 1269 set_ctrl(zero, C->root()); 1270 set_ctrl(one, C->root()); 1271 1272 // Range checks that do not dominate the loop backedge (ie. 1273 // conditionally executed) can lengthen the pre loop limit beyond 1274 // the original loop limit. To prevent this, the pre limit is 1275 // (for stride > 0) MINed with the original loop limit (MAXed 1276 // stride < 0) when some range_check (rc) is conditionally 1277 // executed. 1278 bool conditional_rc = false; 1279 1280 // Check loop body for tests of trip-counter plus loop-invariant vs 1281 // loop-invariant. 1282 for( uint i = 0; i < loop->_body.size(); i++ ) { 1283 Node *iff = loop->_body[i]; 1284 if( iff->Opcode() == Op_If ) { // Test? 1285 1286 // Test is an IfNode, has 2 projections. If BOTH are in the loop 1287 // we need loop unswitching instead of iteration splitting. 1288 Node *exit = loop->is_loop_exit(iff); 1289 if( !exit ) continue; 1290 int flip = (exit->Opcode() == Op_IfTrue) ? 1 : 0; 1291 1292 // Get boolean condition to test 1293 Node *i1 = iff->in(1); 1294 if( !i1->is_Bool() ) continue; 1295 BoolNode *bol = i1->as_Bool(); 1296 BoolTest b_test = bol->_test; 1297 // Flip sense of test if exit condition is flipped 1298 if( flip ) 1299 b_test = b_test.negate(); 1300 1301 // Get compare 1302 Node *cmp = bol->in(1); 1303 1304 // Look for trip_counter + offset vs limit 1305 Node *rc_exp = cmp->in(1); 1306 Node *limit = cmp->in(2); 1307 jint scale_con= 1; // Assume trip counter not scaled 1308 1309 Node *limit_c = get_ctrl(limit); 1310 if( loop->is_member(get_loop(limit_c) ) ) { 1311 // Compare might have operands swapped; commute them 1312 b_test = b_test.commute(); 1313 rc_exp = cmp->in(2); 1314 limit = cmp->in(1); 1315 limit_c = get_ctrl(limit); 1316 if( loop->is_member(get_loop(limit_c) ) ) 1317 continue; // Both inputs are loop varying; cannot RCE 1318 } 1319 // Here we know 'limit' is loop invariant 1320 1321 // 'limit' maybe pinned below the zero trip test (probably from a 1322 // previous round of rce), in which case, it can't be used in the 1323 // zero trip test expression which must occur before the zero test's if. 1324 if( limit_c == ctrl ) { 1325 continue; // Don't rce this check but continue looking for other candidates. 1326 } 1327 1328 // Check for scaled induction variable plus an offset 1329 Node *offset = NULL; 1330 1331 if (!is_scaled_iv_plus_offset(rc_exp, trip_counter, &scale_con, &offset)) { 1332 continue; 1333 } 1334 1335 Node *offset_c = get_ctrl(offset); 1336 if( loop->is_member( get_loop(offset_c) ) ) 1337 continue; // Offset is not really loop invariant 1338 // Here we know 'offset' is loop invariant. 1339 1340 // As above for the 'limit', the 'offset' maybe pinned below the 1341 // zero trip test. 1342 if( offset_c == ctrl ) { 1343 continue; // Don't rce this check but continue looking for other candidates. 1344 } 1345 1346 // At this point we have the expression as: 1347 // scale_con * trip_counter + offset :: limit 1348 // where scale_con, offset and limit are loop invariant. Trip_counter 1349 // monotonically increases by stride_con, a constant. Both (or either) 1350 // stride_con and scale_con can be negative which will flip about the 1351 // sense of the test. 1352 1353 // Adjust pre and main loop limits to guard the correct iteration set 1354 if( cmp->Opcode() == Op_CmpU ) {// Unsigned compare is really 2 tests 1355 if( b_test._test == BoolTest::lt ) { // Range checks always use lt 1356 // The overflow limit: scale*I+offset < limit 1357 add_constraint( stride_con, scale_con, offset, limit, pre_ctrl, &pre_limit, &main_limit ); 1358 // The underflow limit: 0 <= scale*I+offset. 1359 // Some math yields: -scale*I-(offset+1) < 0 1360 Node *plus_one = new (C, 3) AddINode( offset, one ); 1361 register_new_node( plus_one, pre_ctrl ); 1362 Node *neg_offset = new (C, 3) SubINode( zero, plus_one ); 1363 register_new_node( neg_offset, pre_ctrl ); 1364 add_constraint( stride_con, -scale_con, neg_offset, zero, pre_ctrl, &pre_limit, &main_limit ); 1365 if (!conditional_rc) { 1366 conditional_rc = !loop->dominates_backedge(iff); 1367 } 1368 } else { 1369#ifndef PRODUCT 1370 if( PrintOpto ) 1371 tty->print_cr("missed RCE opportunity"); 1372#endif 1373 continue; // In release mode, ignore it 1374 } 1375 } else { // Otherwise work on normal compares 1376 switch( b_test._test ) { 1377 case BoolTest::ge: // Convert X >= Y to -X <= -Y 1378 scale_con = -scale_con; 1379 offset = new (C, 3) SubINode( zero, offset ); 1380 register_new_node( offset, pre_ctrl ); 1381 limit = new (C, 3) SubINode( zero, limit ); 1382 register_new_node( limit, pre_ctrl ); 1383 // Fall into LE case 1384 case BoolTest::le: // Convert X <= Y to X < Y+1 1385 limit = new (C, 3) AddINode( limit, one ); 1386 register_new_node( limit, pre_ctrl ); 1387 // Fall into LT case 1388 case BoolTest::lt: 1389 add_constraint( stride_con, scale_con, offset, limit, pre_ctrl, &pre_limit, &main_limit ); 1390 if (!conditional_rc) { 1391 conditional_rc = !loop->dominates_backedge(iff); 1392 } 1393 break; 1394 default: 1395#ifndef PRODUCT 1396 if( PrintOpto ) 1397 tty->print_cr("missed RCE opportunity"); 1398#endif 1399 continue; // Unhandled case 1400 } 1401 } 1402 1403 // Kill the eliminated test 1404 C->set_major_progress(); 1405 Node *kill_con = _igvn.intcon( 1-flip ); 1406 set_ctrl(kill_con, C->root()); 1407 _igvn.hash_delete(iff); 1408 iff->set_req(1, kill_con); 1409 _igvn._worklist.push(iff); 1410 // Find surviving projection 1411 assert(iff->is_If(), ""); 1412 ProjNode* dp = ((IfNode*)iff)->proj_out(1-flip); 1413 // Find loads off the surviving projection; remove their control edge 1414 for (DUIterator_Fast imax, i = dp->fast_outs(imax); i < imax; i++) { 1415 Node* cd = dp->fast_out(i); // Control-dependent node 1416 if( cd->is_Load() ) { // Loads can now float around in the loop 1417 _igvn.hash_delete(cd); 1418 // Allow the load to float around in the loop, or before it 1419 // but NOT before the pre-loop. 1420 cd->set_req(0, ctrl); // ctrl, not NULL 1421 _igvn._worklist.push(cd); 1422 --i; 1423 --imax; 1424 } 1425 } 1426 1427 } // End of is IF 1428 1429 } 1430 1431 // Update loop limits 1432 if (conditional_rc) { 1433 pre_limit = (stride_con > 0) ? (Node*)new (C,3) MinINode(pre_limit, orig_limit) 1434 : (Node*)new (C,3) MaxINode(pre_limit, orig_limit); 1435 register_new_node(pre_limit, pre_ctrl); 1436 } 1437 _igvn.hash_delete(pre_opaq); 1438 pre_opaq->set_req(1, pre_limit); 1439 1440 // Note:: we are making the main loop limit no longer precise; 1441 // need to round up based on stride. 1442 if( stride_con != 1 && stride_con != -1 ) { // Cutout for common case 1443 // "Standard" round-up logic: ([main_limit-init+(y-1)]/y)*y+init 1444 // Hopefully, compiler will optimize for powers of 2. 1445 Node *ctrl = get_ctrl(main_limit); 1446 Node *stride = cl->stride(); 1447 Node *init = cl->init_trip(); 1448 Node *span = new (C, 3) SubINode(main_limit,init); 1449 register_new_node(span,ctrl); 1450 Node *rndup = _igvn.intcon(stride_con + ((stride_con>0)?-1:1)); 1451 Node *add = new (C, 3) AddINode(span,rndup); 1452 register_new_node(add,ctrl); 1453 Node *div = new (C, 3) DivINode(0,add,stride); 1454 register_new_node(div,ctrl); 1455 Node *mul = new (C, 3) MulINode(div,stride); 1456 register_new_node(mul,ctrl); 1457 Node *newlim = new (C, 3) AddINode(mul,init); 1458 register_new_node(newlim,ctrl); 1459 main_limit = newlim; 1460 } 1461 1462 Node *main_cle = cl->loopexit(); 1463 Node *main_bol = main_cle->in(1); 1464 // Hacking loop bounds; need private copies of exit test 1465 if( main_bol->outcnt() > 1 ) {// BoolNode shared? 1466 _igvn.hash_delete(main_cle); 1467 main_bol = main_bol->clone();// Clone a private BoolNode 1468 register_new_node( main_bol, main_cle->in(0) ); 1469 main_cle->set_req(1,main_bol); 1470 } 1471 Node *main_cmp = main_bol->in(1); 1472 if( main_cmp->outcnt() > 1 ) { // CmpNode shared? 1473 _igvn.hash_delete(main_bol); 1474 main_cmp = main_cmp->clone();// Clone a private CmpNode 1475 register_new_node( main_cmp, main_cle->in(0) ); 1476 main_bol->set_req(1,main_cmp); 1477 } 1478 // Hack the now-private loop bounds 1479 _igvn.hash_delete(main_cmp); 1480 main_cmp->set_req(2, main_limit); 1481 _igvn._worklist.push(main_cmp); 1482 // The OpaqueNode is unshared by design 1483 _igvn.hash_delete(opqzm); 1484 assert( opqzm->outcnt() == 1, "cannot hack shared node" ); 1485 opqzm->set_req(1,main_limit); 1486 _igvn._worklist.push(opqzm); 1487} 1488 1489//------------------------------DCE_loop_body---------------------------------- 1490// Remove simplistic dead code from loop body 1491void IdealLoopTree::DCE_loop_body() { 1492 for( uint i = 0; i < _body.size(); i++ ) 1493 if( _body.at(i)->outcnt() == 0 ) 1494 _body.map( i--, _body.pop() ); 1495} 1496 1497 1498//------------------------------adjust_loop_exit_prob-------------------------- 1499// Look for loop-exit tests with the 50/50 (or worse) guesses from the parsing stage. 1500// Replace with a 1-in-10 exit guess. 1501void IdealLoopTree::adjust_loop_exit_prob( PhaseIdealLoop *phase ) { 1502 Node *test = tail(); 1503 while( test != _head ) { 1504 uint top = test->Opcode(); 1505 if( top == Op_IfTrue || top == Op_IfFalse ) { 1506 int test_con = ((ProjNode*)test)->_con; 1507 assert(top == (uint)(test_con? Op_IfTrue: Op_IfFalse), "sanity"); 1508 IfNode *iff = test->in(0)->as_If(); 1509 if( iff->outcnt() == 2 ) { // Ignore dead tests 1510 Node *bol = iff->in(1); 1511 if( bol && bol->req() > 1 && bol->in(1) && 1512 ((bol->in(1)->Opcode() == Op_StorePConditional ) || 1513 (bol->in(1)->Opcode() == Op_StoreLConditional ) || 1514 (bol->in(1)->Opcode() == Op_CompareAndSwapI ) || 1515 (bol->in(1)->Opcode() == Op_CompareAndSwapL ) || 1516 (bol->in(1)->Opcode() == Op_CompareAndSwapP ) || 1517 (bol->in(1)->Opcode() == Op_CompareAndSwapN ))) 1518 return; // Allocation loops RARELY take backedge 1519 // Find the OTHER exit path from the IF 1520 Node* ex = iff->proj_out(1-test_con); 1521 float p = iff->_prob; 1522 if( !phase->is_member( this, ex ) && iff->_fcnt == COUNT_UNKNOWN ) { 1523 if( top == Op_IfTrue ) { 1524 if( p < (PROB_FAIR + PROB_UNLIKELY_MAG(3))) { 1525 iff->_prob = PROB_STATIC_FREQUENT; 1526 } 1527 } else { 1528 if( p > (PROB_FAIR - PROB_UNLIKELY_MAG(3))) { 1529 iff->_prob = PROB_STATIC_INFREQUENT; 1530 } 1531 } 1532 } 1533 } 1534 } 1535 test = phase->idom(test); 1536 } 1537} 1538 1539 1540//------------------------------policy_do_remove_empty_loop-------------------- 1541// Micro-benchmark spamming. Policy is to always remove empty loops. 1542// The 'DO' part is to replace the trip counter with the value it will 1543// have on the last iteration. This will break the loop. 1544bool IdealLoopTree::policy_do_remove_empty_loop( PhaseIdealLoop *phase ) { 1545 // Minimum size must be empty loop 1546 if( _body.size() > 7/*number of nodes in an empty loop*/ ) return false; 1547 1548 if( !_head->is_CountedLoop() ) return false; // Dead loop 1549 CountedLoopNode *cl = _head->as_CountedLoop(); 1550 if( !cl->loopexit() ) return false; // Malformed loop 1551 if( !phase->is_member(this,phase->get_ctrl(cl->loopexit()->in(CountedLoopEndNode::TestValue)) ) ) 1552 return false; // Infinite loop 1553#ifndef PRODUCT 1554 if( PrintOpto ) 1555 tty->print_cr("Removing empty loop"); 1556#endif 1557#ifdef ASSERT 1558 // Ensure only one phi which is the iv. 1559 Node* iv = NULL; 1560 for (DUIterator_Fast imax, i = cl->fast_outs(imax); i < imax; i++) { 1561 Node* n = cl->fast_out(i); 1562 if (n->Opcode() == Op_Phi) { 1563 assert(iv == NULL, "Too many phis" ); 1564 iv = n; 1565 } 1566 } 1567 assert(iv == cl->phi(), "Wrong phi" ); 1568#endif 1569 // Replace the phi at loop head with the final value of the last 1570 // iteration. Then the CountedLoopEnd will collapse (backedge never 1571 // taken) and all loop-invariant uses of the exit values will be correct. 1572 Node *phi = cl->phi(); 1573 Node *final = new (phase->C, 3) SubINode( cl->limit(), cl->stride() ); 1574 phase->register_new_node(final,cl->in(LoopNode::EntryControl)); 1575 phase->_igvn.hash_delete(phi); 1576 phase->_igvn.subsume_node(phi,final); 1577 phase->C->set_major_progress(); 1578 return true; 1579} 1580 1581 1582//============================================================================= 1583//------------------------------iteration_split_impl--------------------------- 1584void IdealLoopTree::iteration_split_impl( PhaseIdealLoop *phase, Node_List &old_new ) { 1585 // Check and remove empty loops (spam micro-benchmarks) 1586 if( policy_do_remove_empty_loop(phase) ) 1587 return; // Here we removed an empty loop 1588 1589 bool should_peel = policy_peeling(phase); // Should we peel? 1590 1591 bool should_unswitch = policy_unswitching(phase); 1592 1593 // Non-counted loops may be peeled; exactly 1 iteration is peeled. 1594 // This removes loop-invariant tests (usually null checks). 1595 if( !_head->is_CountedLoop() ) { // Non-counted loop 1596 if (PartialPeelLoop && phase->partial_peel(this, old_new)) { 1597 return; 1598 } 1599 if( should_peel ) { // Should we peel? 1600#ifndef PRODUCT 1601 if (PrintOpto) tty->print_cr("should_peel"); 1602#endif 1603 phase->do_peeling(this,old_new); 1604 } else if( should_unswitch ) { 1605 phase->do_unswitching(this, old_new); 1606 } 1607 return; 1608 } 1609 CountedLoopNode *cl = _head->as_CountedLoop(); 1610 1611 if( !cl->loopexit() ) return; // Ignore various kinds of broken loops 1612 1613 // Do nothing special to pre- and post- loops 1614 if( cl->is_pre_loop() || cl->is_post_loop() ) return; 1615 1616 // Compute loop trip count from profile data 1617 compute_profile_trip_cnt(phase); 1618 1619 // Before attempting fancy unrolling, RCE or alignment, see if we want 1620 // to completely unroll this loop or do loop unswitching. 1621 if( cl->is_normal_loop() ) { 1622 bool should_maximally_unroll = policy_maximally_unroll(phase); 1623 if( should_maximally_unroll ) { 1624 // Here we did some unrolling and peeling. Eventually we will 1625 // completely unroll this loop and it will no longer be a loop. 1626 phase->do_maximally_unroll(this,old_new); 1627 return; 1628 } 1629 if (should_unswitch) { 1630 phase->do_unswitching(this, old_new); 1631 return; 1632 } 1633 } 1634 1635 1636 // Counted loops may be peeled, may need some iterations run up 1637 // front for RCE, and may want to align loop refs to a cache 1638 // line. Thus we clone a full loop up front whose trip count is 1639 // at least 1 (if peeling), but may be several more. 1640 1641 // The main loop will start cache-line aligned with at least 1 1642 // iteration of the unrolled body (zero-trip test required) and 1643 // will have some range checks removed. 1644 1645 // A post-loop will finish any odd iterations (leftover after 1646 // unrolling), plus any needed for RCE purposes. 1647 1648 bool should_unroll = policy_unroll(phase); 1649 1650 bool should_rce = policy_range_check(phase); 1651 1652 bool should_align = policy_align(phase); 1653 1654 // If not RCE'ing (iteration splitting) or Aligning, then we do not 1655 // need a pre-loop. We may still need to peel an initial iteration but 1656 // we will not be needing an unknown number of pre-iterations. 1657 // 1658 // Basically, if may_rce_align reports FALSE first time through, 1659 // we will not be able to later do RCE or Aligning on this loop. 1660 bool may_rce_align = !policy_peel_only(phase) || should_rce || should_align; 1661 1662 // If we have any of these conditions (RCE, alignment, unrolling) met, then 1663 // we switch to the pre-/main-/post-loop model. This model also covers 1664 // peeling. 1665 if( should_rce || should_align || should_unroll ) { 1666 if( cl->is_normal_loop() ) // Convert to 'pre/main/post' loops 1667 phase->insert_pre_post_loops(this,old_new, !may_rce_align); 1668 1669 // Adjust the pre- and main-loop limits to let the pre and post loops run 1670 // with full checks, but the main-loop with no checks. Remove said 1671 // checks from the main body. 1672 if( should_rce ) 1673 phase->do_range_check(this,old_new); 1674 1675 // Double loop body for unrolling. Adjust the minimum-trip test (will do 1676 // twice as many iterations as before) and the main body limit (only do 1677 // an even number of trips). If we are peeling, we might enable some RCE 1678 // and we'd rather unroll the post-RCE'd loop SO... do not unroll if 1679 // peeling. 1680 if( should_unroll && !should_peel ) 1681 phase->do_unroll(this,old_new, true); 1682 1683 // Adjust the pre-loop limits to align the main body 1684 // iterations. 1685 if( should_align ) 1686 Unimplemented(); 1687 1688 } else { // Else we have an unchanged counted loop 1689 if( should_peel ) // Might want to peel but do nothing else 1690 phase->do_peeling(this,old_new); 1691 } 1692} 1693 1694 1695//============================================================================= 1696//------------------------------iteration_split-------------------------------- 1697void IdealLoopTree::iteration_split( PhaseIdealLoop *phase, Node_List &old_new ) { 1698 // Recursively iteration split nested loops 1699 if( _child ) _child->iteration_split( phase, old_new ); 1700 1701 // Clean out prior deadwood 1702 DCE_loop_body(); 1703 1704 1705 // Look for loop-exit tests with my 50/50 guesses from the Parsing stage. 1706 // Replace with a 1-in-10 exit guess. 1707 if( _parent /*not the root loop*/ && 1708 !_irreducible && 1709 // Also ignore the occasional dead backedge 1710 !tail()->is_top() ) { 1711 adjust_loop_exit_prob(phase); 1712 } 1713 1714 1715 // Gate unrolling, RCE and peeling efforts. 1716 if( !_child && // If not an inner loop, do not split 1717 !_irreducible && 1718 _allow_optimizations && 1719 !tail()->is_top() ) { // Also ignore the occasional dead backedge 1720 if (!_has_call) { 1721 iteration_split_impl( phase, old_new ); 1722 } else if (policy_unswitching(phase)) { 1723 phase->do_unswitching(this, old_new); 1724 } 1725 } 1726 1727 // Minor offset re-organization to remove loop-fallout uses of 1728 // trip counter. 1729 if( _head->is_CountedLoop() ) phase->reorg_offsets( this ); 1730 if( _next ) _next->iteration_split( phase, old_new ); 1731} 1732