RegionInfo.cpp revision 1f74590e9d1b9cf0f1f81a156efea73f76546e05
1//===- RegionInfo.cpp - SESE region detection analysis --------------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// Detects single entry single exit regions in the control flow graph. 10//===----------------------------------------------------------------------===// 11 12#include "llvm/Analysis/RegionInfo.h" 13#include "llvm/Analysis/RegionIterator.h" 14 15#include "llvm/ADT/PostOrderIterator.h" 16#include "llvm/ADT/Statistic.h" 17#include "llvm/Support/CommandLine.h" 18#include "llvm/Support/ErrorHandling.h" 19#include "llvm/Support/raw_ostream.h" 20#include "llvm/Analysis/LoopInfo.h" 21 22#define DEBUG_TYPE "region" 23#include "llvm/Support/Debug.h" 24 25#include <set> 26#include <algorithm> 27 28using namespace llvm; 29 30// Always verify if expensive checking is enabled. 31#ifdef XDEBUG 32static bool VerifyRegionInfo = true; 33#else 34static bool VerifyRegionInfo = false; 35#endif 36 37static cl::opt<bool,true> 38VerifyRegionInfoX("verify-region-info", cl::location(VerifyRegionInfo), 39 cl::desc("Verify region info (time consuming)")); 40 41STATISTIC(numRegions, "The # of regions"); 42STATISTIC(numSimpleRegions, "The # of simple regions"); 43 44//===----------------------------------------------------------------------===// 45/// PrintStyle - Print region in difference ways. 46enum PrintStyle { PrintNone, PrintBB, PrintRN }; 47 48cl::opt<enum PrintStyle> printStyle("print-region-style", cl::Hidden, 49 cl::desc("style of printing regions"), 50 cl::values( 51 clEnumValN(PrintNone, "none", "print no details"), 52 clEnumValN(PrintBB, "bb", "print regions in detail with block_iterator"), 53 clEnumValN(PrintRN, "rn", "print regions in detail with element_iterator"), 54 clEnumValEnd)); 55//===----------------------------------------------------------------------===// 56/// Region Implementation 57Region::Region(BasicBlock *Entry, BasicBlock *Exit, RegionInfo* RInfo, 58 DominatorTree *dt, Region *Parent) 59 : RegionNode(Parent, Entry, 1), RI(RInfo), DT(dt), exit(Exit) {} 60 61Region::~Region() { 62 // Free the cached nodes. 63 for (BBNodeMapT::iterator it = BBNodeMap.begin(), 64 ie = BBNodeMap.end(); it != ie; ++it) 65 delete it->second; 66 67 // Only clean the cache for this Region. Caches of child Regions will be 68 // cleaned when the child Regions are deleted. 69 BBNodeMap.clear(); 70 71 for (iterator I = begin(), E = end(); I != E; ++I) 72 delete *I; 73} 74 75bool Region::contains(const BasicBlock *B) const { 76 BasicBlock *BB = const_cast<BasicBlock*>(B); 77 78 assert(DT->getNode(BB) && "BB not part of the dominance tree"); 79 80 BasicBlock *entry = getEntry(), *exit = getExit(); 81 82 // Toplevel region. 83 if (!exit) 84 return true; 85 86 return (DT->dominates(entry, BB) 87 && !(DT->dominates(exit, BB) && DT->dominates(entry, exit))); 88} 89 90bool Region::contains(const Loop *L) const { 91 // BBs that are not part of any loop are element of the Loop 92 // described by the NULL pointer. This loop is not part of any region, 93 // except if the region describes the whole function. 94 if (L == 0) 95 return getExit() == 0; 96 97 if (!contains(L->getHeader())) 98 return false; 99 100 SmallVector<BasicBlock *, 8> ExitingBlocks; 101 L->getExitingBlocks(ExitingBlocks); 102 103 for (SmallVectorImpl<BasicBlock*>::iterator BI = ExitingBlocks.begin(), 104 BE = ExitingBlocks.end(); BI != BE; ++BI) 105 if (!contains(*BI)) 106 return false; 107 108 return true; 109} 110 111Loop *Region::outermostLoopInRegion(Loop *L) const { 112 if (!contains(L)) 113 return 0; 114 115 while (L && contains(L->getParentLoop())) { 116 L = L->getParentLoop(); 117 } 118 119 return L; 120} 121 122Loop *Region::outermostLoopInRegion(LoopInfo *LI, BasicBlock* BB) const { 123 assert(LI && BB && "LI and BB cannot be null!"); 124 Loop *L = LI->getLoopFor(BB); 125 return outermostLoopInRegion(L); 126} 127 128bool Region::isSimple() const { 129 bool isSimple = true; 130 bool found = false; 131 132 BasicBlock *entry = getEntry(), *exit = getExit(); 133 134 // TopLevelRegion 135 if (!exit) 136 return false; 137 138 for (pred_iterator PI = pred_begin(entry), PE = pred_end(entry); PI != PE; 139 ++PI) 140 if (!contains(*PI)) { 141 if (found) { 142 isSimple = false; 143 break; 144 } 145 found = true; 146 } 147 148 found = false; 149 150 for (pred_iterator PI = pred_begin(exit), PE = pred_end(exit); PI != PE; 151 ++PI) 152 if (contains(*PI)) { 153 if (found) { 154 isSimple = false; 155 break; 156 } 157 found = true; 158 } 159 160 return isSimple; 161} 162 163std::string Region::getNameStr() const { 164 std::string exitName; 165 std::string entryName; 166 167 if (getEntry()->getName().empty()) { 168 raw_string_ostream OS(entryName); 169 170 WriteAsOperand(OS, getEntry(), false); 171 entryName = OS.str(); 172 } else 173 entryName = getEntry()->getNameStr(); 174 175 if (getExit()) { 176 if (getExit()->getName().empty()) { 177 raw_string_ostream OS(exitName); 178 179 WriteAsOperand(OS, getExit(), false); 180 exitName = OS.str(); 181 } else 182 exitName = getExit()->getNameStr(); 183 } else 184 exitName = "<Function Return>"; 185 186 return entryName + " => " + exitName; 187} 188 189void Region::verifyBBInRegion(BasicBlock *BB) const { 190 if (!contains(BB)) 191 llvm_unreachable("Broken region found!"); 192 193 BasicBlock *entry = getEntry(), *exit = getExit(); 194 195 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI) 196 if (!contains(*SI) && exit != *SI) 197 llvm_unreachable("Broken region found!"); 198 199 if (entry != BB) 200 for (pred_iterator SI = pred_begin(BB), SE = pred_end(BB); SI != SE; ++SI) 201 if (!contains(*SI)) 202 llvm_unreachable("Broken region found!"); 203} 204 205void Region::verifyWalk(BasicBlock *BB, std::set<BasicBlock*> *visited) const { 206 BasicBlock *exit = getExit(); 207 208 visited->insert(BB); 209 210 verifyBBInRegion(BB); 211 212 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI) 213 if (*SI != exit && visited->find(*SI) == visited->end()) 214 verifyWalk(*SI, visited); 215} 216 217void Region::verifyRegion() const { 218 // Only do verification when user wants to, otherwise this expensive 219 // check will be invoked by PassManager. 220 if (!VerifyRegionInfo) return; 221 222 std::set<BasicBlock*> visited; 223 verifyWalk(getEntry(), &visited); 224} 225 226void Region::verifyRegionNest() const { 227 for (Region::const_iterator RI = begin(), RE = end(); RI != RE; ++RI) 228 (*RI)->verifyRegionNest(); 229 230 verifyRegion(); 231} 232 233Region::block_iterator Region::block_begin() { 234 return GraphTraits<FlatIt<Region*> >::nodes_begin(this); 235} 236 237Region::block_iterator Region::block_end() { 238 return GraphTraits<FlatIt<Region*> >::nodes_end(this); 239} 240 241Region::const_block_iterator Region::block_begin() const { 242 return GraphTraits<FlatIt<const Region*> >::nodes_begin(this); 243} 244 245Region::const_block_iterator Region::block_end() const { 246 return GraphTraits<FlatIt<const Region*> >::nodes_end(this); 247} 248 249Region::element_iterator Region::element_begin() { 250 return GraphTraits<Region*>::nodes_begin(this); 251} 252 253Region::element_iterator Region::element_end() { 254 return GraphTraits<Region*>::nodes_end(this); 255} 256 257Region::const_element_iterator Region::element_begin() const { 258 return GraphTraits<const Region*>::nodes_begin(this); 259} 260 261Region::const_element_iterator Region::element_end() const { 262 return GraphTraits<const Region*>::nodes_end(this); 263} 264 265Region* Region::getSubRegionNode(BasicBlock *BB) const { 266 Region *R = RI->getRegionFor(BB); 267 268 if (!R || R == this) 269 return 0; 270 271 // If we pass the BB out of this region, that means our code is broken. 272 assert(contains(R) && "BB not in current region!"); 273 274 while (contains(R->getParent()) && R->getParent() != this) 275 R = R->getParent(); 276 277 if (R->getEntry() != BB) 278 return 0; 279 280 return R; 281} 282 283RegionNode* Region::getBBNode(BasicBlock *BB) const { 284 assert(contains(BB) && "Can get BB node out of this region!"); 285 286 BBNodeMapT::const_iterator at = BBNodeMap.find(BB); 287 288 if (at != BBNodeMap.end()) 289 return at->second; 290 291 RegionNode *NewNode = new RegionNode(const_cast<Region*>(this), BB); 292 BBNodeMap.insert(std::make_pair(BB, NewNode)); 293 return NewNode; 294} 295 296RegionNode* Region::getNode(BasicBlock *BB) const { 297 assert(contains(BB) && "Can get BB node out of this region!"); 298 if (Region* Child = getSubRegionNode(BB)) 299 return Child->getNode(); 300 301 return getBBNode(BB); 302} 303 304void Region::transferChildrenTo(Region *To) { 305 for (iterator I = begin(), E = end(); I != E; ++I) { 306 (*I)->parent = To; 307 To->children.push_back(*I); 308 } 309 children.clear(); 310} 311 312void Region::addSubRegion(Region *SubRegion) { 313 assert(SubRegion->parent == 0 && "SubRegion already has a parent!"); 314 SubRegion->parent = this; 315 // Set up the region node. 316 assert(std::find(children.begin(), children.end(), SubRegion) == children.end() 317 && "Node already exist!"); 318 children.push_back(SubRegion); 319} 320 321 322Region *Region::removeSubRegion(Region *Child) { 323 assert(Child->parent == this && "Child is not a child of this region!"); 324 Child->parent = 0; 325 RegionSet::iterator I = std::find(children.begin(), children.end(), Child); 326 assert(I != children.end() && "Region does not exit. Unable to remove."); 327 children.erase(children.begin()+(I-begin())); 328 return Child; 329} 330 331unsigned Region::getDepth() const { 332 unsigned Depth = 0; 333 334 for (Region *R = parent; R != 0; R = R->parent) 335 ++Depth; 336 337 return Depth; 338} 339 340void Region::print(raw_ostream &OS, bool print_tree, unsigned level) const { 341 if (print_tree) 342 OS.indent(level*2) << "[" << level << "] " << getNameStr(); 343 else 344 OS.indent(level*2) << getNameStr(); 345 346 OS << "\n"; 347 348 349 if (printStyle != PrintNone) { 350 OS.indent(level*2) << "{\n"; 351 OS.indent(level*2 + 2); 352 353 if (printStyle == PrintBB) { 354 for (const_block_iterator I = block_begin(), E = block_end(); I!=E; ++I) 355 OS << **I << ", "; // TODO: remove the last "," 356 } else if (printStyle == PrintRN) { 357 for (const_element_iterator I = element_begin(), E = element_end(); I!=E; ++I) 358 OS << **I << ", "; // TODO: remove the last ", 359 } 360 361 OS << "\n"; 362 } 363 364 if (print_tree) 365 for (const_iterator RI = begin(), RE = end(); RI != RE; ++RI) 366 (*RI)->print(OS, print_tree, level+1); 367 368 if (printStyle != PrintNone) 369 OS.indent(level*2) << "} \n"; 370} 371 372void Region::dump() const { 373 print(dbgs(), true, getDepth()); 374} 375 376void Region::clearNodeCache() { 377 BBNodeMap.clear(); 378 for (Region::iterator RI = begin(), RE = end(); RI != RE; ++RI) 379 (*RI)->clearNodeCache(); 380} 381 382//===----------------------------------------------------------------------===// 383// RegionInfo implementation 384// 385 386bool RegionInfo::isCommonDomFrontier(BasicBlock *BB, BasicBlock *entry, 387 BasicBlock *exit) const { 388 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE; ++PI) { 389 BasicBlock *P = *PI; 390 if (DT->dominates(entry, P) && !DT->dominates(exit, P)) 391 return false; 392 } 393 return true; 394} 395 396bool RegionInfo::isRegion(BasicBlock *entry, BasicBlock *exit) const { 397 assert(entry && exit && "entry and exit must not be null!"); 398 typedef DominanceFrontier::DomSetType DST; 399 400 DST *entrySuccs = &DF->find(entry)->second; 401 402 // Exit is the header of a loop that contains the entry. In this case, 403 // the dominance frontier must only contain the exit. 404 if (!DT->dominates(entry, exit)) { 405 for (DST::iterator SI = entrySuccs->begin(), SE = entrySuccs->end(); 406 SI != SE; ++SI) 407 if (*SI != exit && *SI != entry) 408 return false; 409 410 return true; 411 } 412 413 DST *exitSuccs = &DF->find(exit)->second; 414 415 // Do not allow edges leaving the region. 416 for (DST::iterator SI = entrySuccs->begin(), SE = entrySuccs->end(); 417 SI != SE; ++SI) { 418 if (*SI == exit || *SI == entry) 419 continue; 420 if (exitSuccs->find(*SI) == exitSuccs->end()) 421 return false; 422 if (!isCommonDomFrontier(*SI, entry, exit)) 423 return false; 424 } 425 426 // Do not allow edges pointing into the region. 427 for (DST::iterator SI = exitSuccs->begin(), SE = exitSuccs->end(); 428 SI != SE; ++SI) 429 if (DT->properlyDominates(entry, *SI) && *SI != exit) 430 return false; 431 432 433 return true; 434} 435 436void RegionInfo::insertShortCut(BasicBlock *entry, BasicBlock *exit, 437 BBtoBBMap *ShortCut) const { 438 assert(entry && exit && "entry and exit must not be null!"); 439 440 BBtoBBMap::iterator e = ShortCut->find(exit); 441 442 if (e == ShortCut->end()) 443 // No further region at exit available. 444 (*ShortCut)[entry] = exit; 445 else { 446 // We found a region e that starts at exit. Therefore (entry, e->second) 447 // is also a region, that is larger than (entry, exit). Insert the 448 // larger one. 449 BasicBlock *BB = e->second; 450 (*ShortCut)[entry] = BB; 451 } 452} 453 454DomTreeNode* RegionInfo::getNextPostDom(DomTreeNode* N, 455 BBtoBBMap *ShortCut) const { 456 BBtoBBMap::iterator e = ShortCut->find(N->getBlock()); 457 458 if (e == ShortCut->end()) 459 return N->getIDom(); 460 461 return PDT->getNode(e->second)->getIDom(); 462} 463 464bool RegionInfo::isTrivialRegion(BasicBlock *entry, BasicBlock *exit) const { 465 assert(entry && exit && "entry and exit must not be null!"); 466 467 unsigned num_successors = succ_end(entry) - succ_begin(entry); 468 469 if (num_successors <= 1 && exit == *(succ_begin(entry))) 470 return true; 471 472 return false; 473} 474 475void RegionInfo::updateStatistics(Region *R) { 476 ++numRegions; 477 478 // TODO: Slow. Should only be enabled if -stats is used. 479 if (R->isSimple()) ++numSimpleRegions; 480} 481 482Region *RegionInfo::createRegion(BasicBlock *entry, BasicBlock *exit) { 483 assert(entry && exit && "entry and exit must not be null!"); 484 485 if (isTrivialRegion(entry, exit)) 486 return 0; 487 488 Region *region = new Region(entry, exit, this, DT); 489 BBtoRegion.insert(std::make_pair(entry, region)); 490 491 #ifdef XDEBUG 492 region->verifyRegion(); 493 #else 494 DEBUG(region->verifyRegion()); 495 #endif 496 497 updateStatistics(region); 498 return region; 499} 500 501void RegionInfo::findRegionsWithEntry(BasicBlock *entry, BBtoBBMap *ShortCut) { 502 assert(entry); 503 504 DomTreeNode *N = PDT->getNode(entry); 505 506 if (!N) 507 return; 508 509 Region *lastRegion= 0; 510 BasicBlock *lastExit = entry; 511 512 // As only a BasicBlock that postdominates entry can finish a region, walk the 513 // post dominance tree upwards. 514 while ((N = getNextPostDom(N, ShortCut))) { 515 BasicBlock *exit = N->getBlock(); 516 517 if (!exit) 518 break; 519 520 if (isRegion(entry, exit)) { 521 Region *newRegion = createRegion(entry, exit); 522 523 if (lastRegion) 524 newRegion->addSubRegion(lastRegion); 525 526 lastRegion = newRegion; 527 lastExit = exit; 528 } 529 530 // This can never be a region, so stop the search. 531 if (!DT->dominates(entry, exit)) 532 break; 533 } 534 535 // Tried to create regions from entry to lastExit. Next time take a 536 // shortcut from entry to lastExit. 537 if (lastExit != entry) 538 insertShortCut(entry, lastExit, ShortCut); 539} 540 541void RegionInfo::scanForRegions(Function &F, BBtoBBMap *ShortCut) { 542 BasicBlock *entry = &(F.getEntryBlock()); 543 DomTreeNode *N = DT->getNode(entry); 544 545 // Iterate over the dominance tree in post order to start with the small 546 // regions from the bottom of the dominance tree. If the small regions are 547 // detected first, detection of bigger regions is faster, as we can jump 548 // over the small regions. 549 for (po_iterator<DomTreeNode*> FI = po_begin(N), FE = po_end(N); FI != FE; 550 ++FI) { 551 findRegionsWithEntry(FI->getBlock(), ShortCut); 552 } 553} 554 555Region *RegionInfo::getTopMostParent(Region *region) { 556 while (region->parent) 557 region = region->getParent(); 558 559 return region; 560} 561 562void RegionInfo::buildRegionsTree(DomTreeNode *N, Region *region) { 563 BasicBlock *BB = N->getBlock(); 564 565 // Passed region exit 566 while (BB == region->getExit()) 567 region = region->getParent(); 568 569 BBtoRegionMap::iterator it = BBtoRegion.find(BB); 570 571 // This basic block is a start block of a region. It is already in the 572 // BBtoRegion relation. Only the child basic blocks have to be updated. 573 if (it != BBtoRegion.end()) { 574 Region *newRegion = it->second;; 575 region->addSubRegion(getTopMostParent(newRegion)); 576 region = newRegion; 577 } else { 578 BBtoRegion[BB] = region; 579 } 580 581 for (DomTreeNode::iterator CI = N->begin(), CE = N->end(); CI != CE; ++CI) 582 buildRegionsTree(*CI, region); 583} 584 585void RegionInfo::releaseMemory() { 586 BBtoRegion.clear(); 587 if (TopLevelRegion) 588 delete TopLevelRegion; 589 TopLevelRegion = 0; 590} 591 592RegionInfo::RegionInfo() : FunctionPass(&ID) { 593 TopLevelRegion = 0; 594} 595 596RegionInfo::~RegionInfo() { 597 releaseMemory(); 598} 599 600void RegionInfo::Calculate(Function &F) { 601 // ShortCut a function where for every BB the exit of the largest region 602 // starting with BB is stored. These regions can be threated as single BBS. 603 // This improves performance on linear CFGs. 604 BBtoBBMap ShortCut; 605 606 scanForRegions(F, &ShortCut); 607 BasicBlock *BB = &F.getEntryBlock(); 608 buildRegionsTree(DT->getNode(BB), TopLevelRegion); 609} 610 611bool RegionInfo::runOnFunction(Function &F) { 612 releaseMemory(); 613 614 DT = &getAnalysis<DominatorTree>(); 615 PDT = &getAnalysis<PostDominatorTree>(); 616 DF = &getAnalysis<DominanceFrontier>(); 617 618 TopLevelRegion = new Region(&F.getEntryBlock(), 0, this, DT, 0); 619 updateStatistics(TopLevelRegion); 620 621 Calculate(F); 622 623 return false; 624} 625 626void RegionInfo::getAnalysisUsage(AnalysisUsage &AU) const { 627 AU.setPreservesAll(); 628 AU.addRequiredTransitive<DominatorTree>(); 629 AU.addRequired<PostDominatorTree>(); 630 AU.addRequired<DominanceFrontier>(); 631} 632 633void RegionInfo::print(raw_ostream &OS, const Module *) const { 634 OS << "Region tree:\n"; 635 TopLevelRegion->print(OS, true, 0); 636 OS << "End region tree\n"; 637} 638 639void RegionInfo::verifyAnalysis() const { 640 // Only do verification when user wants to, otherwise this expensive check 641 // will be invoked by PMDataManager::verifyPreservedAnalysis when 642 // a regionpass (marked PreservedAll) finish. 643 if (!VerifyRegionInfo) return; 644 645 TopLevelRegion->verifyRegionNest(); 646} 647 648// Region pass manager support. 649Region *RegionInfo::getRegionFor(BasicBlock *BB) const { 650 BBtoRegionMap::const_iterator I= 651 BBtoRegion.find(BB); 652 return I != BBtoRegion.end() ? I->second : 0; 653} 654 655Region *RegionInfo::operator[](BasicBlock *BB) const { 656 return getRegionFor(BB); 657} 658 659 660BasicBlock *RegionInfo::getMaxRegionExit(BasicBlock *BB) const { 661 BasicBlock *Exit = NULL; 662 663 while (true) { 664 // Get largest region that starts at BB. 665 Region *R = getRegionFor(BB); 666 while (R && R->getParent() && R->getParent()->getEntry() == BB) 667 R = R->getParent(); 668 669 // Get the single exit of BB. 670 if (R && R->getEntry() == BB) 671 Exit = R->getExit(); 672 else if (++succ_begin(BB) == succ_end(BB)) 673 Exit = *succ_begin(BB); 674 else // No single exit exists. 675 return Exit; 676 677 // Get largest region that starts at Exit. 678 Region *ExitR = getRegionFor(Exit); 679 while (ExitR && ExitR->getParent() 680 && ExitR->getParent()->getEntry() == Exit) 681 ExitR = ExitR->getParent(); 682 683 for (pred_iterator PI = pred_begin(Exit), PE = pred_end(Exit); PI != PE; 684 ++PI) 685 if (!R->contains(*PI) && !ExitR->contains(*PI)) 686 break; 687 688 // This stops infinite cycles. 689 if (DT->dominates(Exit, BB)) 690 break; 691 692 BB = Exit; 693 } 694 695 return Exit; 696} 697 698Region* 699RegionInfo::getCommonRegion(Region *A, Region *B) const { 700 assert (A && B && "One of the Regions is NULL"); 701 702 if (A->contains(B)) return A; 703 704 while (!B->contains(A)) 705 B = B->getParent(); 706 707 return B; 708} 709 710Region* 711RegionInfo::getCommonRegion(SmallVectorImpl<Region*> &Regions) const { 712 Region* ret = Regions.back(); 713 Regions.pop_back(); 714 715 for (SmallVectorImpl<Region*>::const_iterator I = Regions.begin(), 716 E = Regions.end(); I != E; ++I) 717 ret = getCommonRegion(ret, *I); 718 719 return ret; 720} 721 722Region* 723RegionInfo::getCommonRegion(SmallVectorImpl<BasicBlock*> &BBs) const { 724 Region* ret = getRegionFor(BBs.back()); 725 BBs.pop_back(); 726 727 for (SmallVectorImpl<BasicBlock*>::const_iterator I = BBs.begin(), 728 E = BBs.end(); I != E; ++I) 729 ret = getCommonRegion(ret, getRegionFor(*I)); 730 731 return ret; 732} 733 734char RegionInfo::ID = 0; 735INITIALIZE_PASS(RegionInfo, "regions", 736 "Detect single entry single exit regions", true, true); 737 738// Create methods available outside of this file, to use them 739// "include/llvm/LinkAllPasses.h". Otherwise the pass would be deleted by 740// the link time optimization. 741 742namespace llvm { 743 FunctionPass *createRegionInfoPass() { 744 return new RegionInfo(); 745 } 746} 747 748