SimplifyCFG.cpp revision 5622f07a21b799964dc172925b9ebc38191859f6
1//===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===// 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// 10// Peephole optimize the CFG. 11// 12//===----------------------------------------------------------------------===// 13 14#define DEBUG_TYPE "simplifycfg" 15#include "llvm/Transforms/Utils/Local.h" 16#include "llvm/Constants.h" 17#include "llvm/Instructions.h" 18#include "llvm/IntrinsicInst.h" 19#include "llvm/Type.h" 20#include "llvm/DerivedTypes.h" 21#include "llvm/Support/CFG.h" 22#include "llvm/Support/Debug.h" 23#include "llvm/Analysis/ConstantFolding.h" 24#include "llvm/Transforms/Utils/BasicBlockUtils.h" 25#include "llvm/ADT/SmallVector.h" 26#include "llvm/ADT/SmallPtrSet.h" 27#include "llvm/ADT/Statistic.h" 28#include <algorithm> 29#include <functional> 30#include <set> 31#include <map> 32using namespace llvm; 33 34STATISTIC(NumSpeculations, "Number of speculative executed instructions"); 35 36/// SafeToMergeTerminators - Return true if it is safe to merge these two 37/// terminator instructions together. 38/// 39static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) { 40 if (SI1 == SI2) return false; // Can't merge with self! 41 42 // It is not safe to merge these two switch instructions if they have a common 43 // successor, and if that successor has a PHI node, and if *that* PHI node has 44 // conflicting incoming values from the two switch blocks. 45 BasicBlock *SI1BB = SI1->getParent(); 46 BasicBlock *SI2BB = SI2->getParent(); 47 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB)); 48 49 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I) 50 if (SI1Succs.count(*I)) 51 for (BasicBlock::iterator BBI = (*I)->begin(); 52 isa<PHINode>(BBI); ++BBI) { 53 PHINode *PN = cast<PHINode>(BBI); 54 if (PN->getIncomingValueForBlock(SI1BB) != 55 PN->getIncomingValueForBlock(SI2BB)) 56 return false; 57 } 58 59 return true; 60} 61 62/// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will 63/// now be entries in it from the 'NewPred' block. The values that will be 64/// flowing into the PHI nodes will be the same as those coming in from 65/// ExistPred, an existing predecessor of Succ. 66static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred, 67 BasicBlock *ExistPred) { 68 assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) != 69 succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!"); 70 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do 71 72 PHINode *PN; 73 for (BasicBlock::iterator I = Succ->begin(); 74 (PN = dyn_cast<PHINode>(I)); ++I) 75 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred); 76} 77 78/// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an 79/// almost-empty BB ending in an unconditional branch to Succ, into succ. 80/// 81/// Assumption: Succ is the single successor for BB. 82/// 83static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) { 84 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!"); 85 86 DOUT << "Looking to fold " << BB->getNameStart() << " into " 87 << Succ->getNameStart() << "\n"; 88 // Shortcut, if there is only a single predecessor is must be BB and merging 89 // is always safe 90 if (Succ->getSinglePredecessor()) return true; 91 92 typedef SmallPtrSet<Instruction*, 16> InstrSet; 93 InstrSet BBPHIs; 94 95 // Make a list of all phi nodes in BB 96 BasicBlock::iterator BBI = BB->begin(); 97 while (isa<PHINode>(*BBI)) BBPHIs.insert(BBI++); 98 99 // Make a list of the predecessors of BB 100 typedef SmallPtrSet<BasicBlock*, 16> BlockSet; 101 BlockSet BBPreds(pred_begin(BB), pred_end(BB)); 102 103 // Use that list to make another list of common predecessors of BB and Succ 104 BlockSet CommonPreds; 105 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ); 106 PI != PE; ++PI) 107 if (BBPreds.count(*PI)) 108 CommonPreds.insert(*PI); 109 110 // Shortcut, if there are no common predecessors, merging is always safe 111 if (CommonPreds.empty()) 112 return true; 113 114 // Look at all the phi nodes in Succ, to see if they present a conflict when 115 // merging these blocks 116 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 117 PHINode *PN = cast<PHINode>(I); 118 119 // If the incoming value from BB is again a PHINode in 120 // BB which has the same incoming value for *PI as PN does, we can 121 // merge the phi nodes and then the blocks can still be merged 122 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB)); 123 if (BBPN && BBPN->getParent() == BB) { 124 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end(); 125 PI != PE; PI++) { 126 if (BBPN->getIncomingValueForBlock(*PI) 127 != PN->getIncomingValueForBlock(*PI)) { 128 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in " 129 << Succ->getNameStart() << " is conflicting with " 130 << BBPN->getNameStart() << " with regard to common predecessor " 131 << (*PI)->getNameStart() << "\n"; 132 return false; 133 } 134 } 135 // Remove this phinode from the list of phis in BB, since it has been 136 // handled. 137 BBPHIs.erase(BBPN); 138 } else { 139 Value* Val = PN->getIncomingValueForBlock(BB); 140 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end(); 141 PI != PE; PI++) { 142 // See if the incoming value for the common predecessor is equal to the 143 // one for BB, in which case this phi node will not prevent the merging 144 // of the block. 145 if (Val != PN->getIncomingValueForBlock(*PI)) { 146 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in " 147 << Succ->getNameStart() << " is conflicting with regard to common " 148 << "predecessor " << (*PI)->getNameStart() << "\n"; 149 return false; 150 } 151 } 152 } 153 } 154 155 // If there are any other phi nodes in BB that don't have a phi node in Succ 156 // to merge with, they must be moved to Succ completely. However, for any 157 // predecessors of Succ, branches will be added to the phi node that just 158 // point to itself. So, for any common predecessors, this must not cause 159 // conflicts. 160 for (InstrSet::iterator I = BBPHIs.begin(), E = BBPHIs.end(); 161 I != E; I++) { 162 PHINode *PN = cast<PHINode>(*I); 163 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end(); 164 PI != PE; PI++) 165 if (PN->getIncomingValueForBlock(*PI) != PN) { 166 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in " 167 << BB->getNameStart() << " is conflicting with regard to common " 168 << "predecessor " << (*PI)->getNameStart() << "\n"; 169 return false; 170 } 171 } 172 173 return true; 174} 175 176/// TryToSimplifyUncondBranchFromEmptyBlock - BB contains an unconditional 177/// branch to Succ, and contains no instructions other than PHI nodes and the 178/// branch. If possible, eliminate BB. 179static bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB, 180 BasicBlock *Succ) { 181 // Check to see if merging these blocks would cause conflicts for any of the 182 // phi nodes in BB or Succ. If not, we can safely merge. 183 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false; 184 185 DOUT << "Killing Trivial BB: \n" << *BB; 186 187 if (isa<PHINode>(Succ->begin())) { 188 // If there is more than one pred of succ, and there are PHI nodes in 189 // the successor, then we need to add incoming edges for the PHI nodes 190 // 191 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB)); 192 193 // Loop over all of the PHI nodes in the successor of BB. 194 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 195 PHINode *PN = cast<PHINode>(I); 196 Value *OldVal = PN->removeIncomingValue(BB, false); 197 assert(OldVal && "No entry in PHI for Pred BB!"); 198 199 // If this incoming value is one of the PHI nodes in BB, the new entries 200 // in the PHI node are the entries from the old PHI. 201 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) { 202 PHINode *OldValPN = cast<PHINode>(OldVal); 203 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) 204 // Note that, since we are merging phi nodes and BB and Succ might 205 // have common predecessors, we could end up with a phi node with 206 // identical incoming branches. This will be cleaned up later (and 207 // will trigger asserts if we try to clean it up now, without also 208 // simplifying the corresponding conditional branch). 209 PN->addIncoming(OldValPN->getIncomingValue(i), 210 OldValPN->getIncomingBlock(i)); 211 } else { 212 // Add an incoming value for each of the new incoming values. 213 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) 214 PN->addIncoming(OldVal, BBPreds[i]); 215 } 216 } 217 } 218 219 if (isa<PHINode>(&BB->front())) { 220 SmallVector<BasicBlock*, 16> 221 OldSuccPreds(pred_begin(Succ), pred_end(Succ)); 222 223 // Move all PHI nodes in BB to Succ if they are alive, otherwise 224 // delete them. 225 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { 226 if (PN->use_empty()) { 227 // Just remove the dead phi. This happens if Succ's PHIs were the only 228 // users of the PHI nodes. 229 PN->eraseFromParent(); 230 continue; 231 } 232 233 // The instruction is alive, so this means that BB must dominate all 234 // predecessors of Succ (Since all uses of the PN are after its 235 // definition, so in Succ or a block dominated by Succ. If a predecessor 236 // of Succ would not be dominated by BB, PN would violate the def before 237 // use SSA demand). Therefore, we can simply move the phi node to the 238 // next block. 239 Succ->getInstList().splice(Succ->begin(), 240 BB->getInstList(), BB->begin()); 241 242 // We need to add new entries for the PHI node to account for 243 // predecessors of Succ that the PHI node does not take into 244 // account. At this point, since we know that BB dominated succ and all 245 // of its predecessors, this means that we should any newly added 246 // incoming edges should use the PHI node itself as the value for these 247 // edges, because they are loop back edges. 248 for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i) 249 if (OldSuccPreds[i] != BB) 250 PN->addIncoming(PN, OldSuccPreds[i]); 251 } 252 } 253 254 // Everything that jumped to BB now goes to Succ. 255 BB->replaceAllUsesWith(Succ); 256 if (!Succ->hasName()) Succ->takeName(BB); 257 BB->eraseFromParent(); // Delete the old basic block. 258 return true; 259} 260 261/// GetIfCondition - Given a basic block (BB) with two predecessors (and 262/// presumably PHI nodes in it), check to see if the merge at this block is due 263/// to an "if condition". If so, return the boolean condition that determines 264/// which entry into BB will be taken. Also, return by references the block 265/// that will be entered from if the condition is true, and the block that will 266/// be entered if the condition is false. 267/// 268/// 269static Value *GetIfCondition(BasicBlock *BB, 270 BasicBlock *&IfTrue, BasicBlock *&IfFalse) { 271 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 && 272 "Function can only handle blocks with 2 predecessors!"); 273 BasicBlock *Pred1 = *pred_begin(BB); 274 BasicBlock *Pred2 = *++pred_begin(BB); 275 276 // We can only handle branches. Other control flow will be lowered to 277 // branches if possible anyway. 278 if (!isa<BranchInst>(Pred1->getTerminator()) || 279 !isa<BranchInst>(Pred2->getTerminator())) 280 return 0; 281 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator()); 282 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator()); 283 284 // Eliminate code duplication by ensuring that Pred1Br is conditional if 285 // either are. 286 if (Pred2Br->isConditional()) { 287 // If both branches are conditional, we don't have an "if statement". In 288 // reality, we could transform this case, but since the condition will be 289 // required anyway, we stand no chance of eliminating it, so the xform is 290 // probably not profitable. 291 if (Pred1Br->isConditional()) 292 return 0; 293 294 std::swap(Pred1, Pred2); 295 std::swap(Pred1Br, Pred2Br); 296 } 297 298 if (Pred1Br->isConditional()) { 299 // If we found a conditional branch predecessor, make sure that it branches 300 // to BB and Pred2Br. If it doesn't, this isn't an "if statement". 301 if (Pred1Br->getSuccessor(0) == BB && 302 Pred1Br->getSuccessor(1) == Pred2) { 303 IfTrue = Pred1; 304 IfFalse = Pred2; 305 } else if (Pred1Br->getSuccessor(0) == Pred2 && 306 Pred1Br->getSuccessor(1) == BB) { 307 IfTrue = Pred2; 308 IfFalse = Pred1; 309 } else { 310 // We know that one arm of the conditional goes to BB, so the other must 311 // go somewhere unrelated, and this must not be an "if statement". 312 return 0; 313 } 314 315 // The only thing we have to watch out for here is to make sure that Pred2 316 // doesn't have incoming edges from other blocks. If it does, the condition 317 // doesn't dominate BB. 318 if (++pred_begin(Pred2) != pred_end(Pred2)) 319 return 0; 320 321 return Pred1Br->getCondition(); 322 } 323 324 // Ok, if we got here, both predecessors end with an unconditional branch to 325 // BB. Don't panic! If both blocks only have a single (identical) 326 // predecessor, and THAT is a conditional branch, then we're all ok! 327 if (pred_begin(Pred1) == pred_end(Pred1) || 328 ++pred_begin(Pred1) != pred_end(Pred1) || 329 pred_begin(Pred2) == pred_end(Pred2) || 330 ++pred_begin(Pred2) != pred_end(Pred2) || 331 *pred_begin(Pred1) != *pred_begin(Pred2)) 332 return 0; 333 334 // Otherwise, if this is a conditional branch, then we can use it! 335 BasicBlock *CommonPred = *pred_begin(Pred1); 336 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) { 337 assert(BI->isConditional() && "Two successors but not conditional?"); 338 if (BI->getSuccessor(0) == Pred1) { 339 IfTrue = Pred1; 340 IfFalse = Pred2; 341 } else { 342 IfTrue = Pred2; 343 IfFalse = Pred1; 344 } 345 return BI->getCondition(); 346 } 347 return 0; 348} 349 350 351/// DominatesMergePoint - If we have a merge point of an "if condition" as 352/// accepted above, return true if the specified value dominates the block. We 353/// don't handle the true generality of domination here, just a special case 354/// which works well enough for us. 355/// 356/// If AggressiveInsts is non-null, and if V does not dominate BB, we check to 357/// see if V (which must be an instruction) is cheap to compute and is 358/// non-trapping. If both are true, the instruction is inserted into the set 359/// and true is returned. 360static bool DominatesMergePoint(Value *V, BasicBlock *BB, 361 std::set<Instruction*> *AggressiveInsts) { 362 Instruction *I = dyn_cast<Instruction>(V); 363 if (!I) { 364 // Non-instructions all dominate instructions, but not all constantexprs 365 // can be executed unconditionally. 366 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V)) 367 if (C->canTrap()) 368 return false; 369 return true; 370 } 371 BasicBlock *PBB = I->getParent(); 372 373 // We don't want to allow weird loops that might have the "if condition" in 374 // the bottom of this block. 375 if (PBB == BB) return false; 376 377 // If this instruction is defined in a block that contains an unconditional 378 // branch to BB, then it must be in the 'conditional' part of the "if 379 // statement". 380 if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator())) 381 if (BI->isUnconditional() && BI->getSuccessor(0) == BB) { 382 if (!AggressiveInsts) return false; 383 // Okay, it looks like the instruction IS in the "condition". Check to 384 // see if its a cheap instruction to unconditionally compute, and if it 385 // only uses stuff defined outside of the condition. If so, hoist it out. 386 switch (I->getOpcode()) { 387 default: return false; // Cannot hoist this out safely. 388 case Instruction::Load: 389 // We can hoist loads that are non-volatile and obviously cannot trap. 390 if (cast<LoadInst>(I)->isVolatile()) 391 return false; 392 // FIXME: A computation of a constant can trap! 393 if (!isa<AllocaInst>(I->getOperand(0)) && 394 !isa<Constant>(I->getOperand(0))) 395 return false; 396 397 // Finally, we have to check to make sure there are no instructions 398 // before the load in its basic block, as we are going to hoist the loop 399 // out to its predecessor. 400 if (PBB->begin() != BasicBlock::iterator(I)) 401 return false; 402 break; 403 case Instruction::Add: 404 case Instruction::Sub: 405 case Instruction::And: 406 case Instruction::Or: 407 case Instruction::Xor: 408 case Instruction::Shl: 409 case Instruction::LShr: 410 case Instruction::AShr: 411 case Instruction::ICmp: 412 case Instruction::FCmp: 413 if (I->getOperand(0)->getType()->isFPOrFPVector()) 414 return false; // FP arithmetic might trap. 415 break; // These are all cheap and non-trapping instructions. 416 } 417 418 // Okay, we can only really hoist these out if their operands are not 419 // defined in the conditional region. 420 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) 421 if (!DominatesMergePoint(*i, BB, 0)) 422 return false; 423 // Okay, it's safe to do this! Remember this instruction. 424 AggressiveInsts->insert(I); 425 } 426 427 return true; 428} 429 430/// GatherConstantSetEQs - Given a potentially 'or'd together collection of 431/// icmp_eq instructions that compare a value against a constant, return the 432/// value being compared, and stick the constant into the Values vector. 433static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){ 434 if (Instruction *Inst = dyn_cast<Instruction>(V)) { 435 if (Inst->getOpcode() == Instruction::ICmp && 436 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_EQ) { 437 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) { 438 Values.push_back(C); 439 return Inst->getOperand(0); 440 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) { 441 Values.push_back(C); 442 return Inst->getOperand(1); 443 } 444 } else if (Inst->getOpcode() == Instruction::Or) { 445 if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values)) 446 if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values)) 447 if (LHS == RHS) 448 return LHS; 449 } 450 } 451 return 0; 452} 453 454/// GatherConstantSetNEs - Given a potentially 'and'd together collection of 455/// setne instructions that compare a value against a constant, return the value 456/// being compared, and stick the constant into the Values vector. 457static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){ 458 if (Instruction *Inst = dyn_cast<Instruction>(V)) { 459 if (Inst->getOpcode() == Instruction::ICmp && 460 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_NE) { 461 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) { 462 Values.push_back(C); 463 return Inst->getOperand(0); 464 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) { 465 Values.push_back(C); 466 return Inst->getOperand(1); 467 } 468 } else if (Inst->getOpcode() == Instruction::And) { 469 if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values)) 470 if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values)) 471 if (LHS == RHS) 472 return LHS; 473 } 474 } 475 return 0; 476} 477 478/// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a 479/// bunch of comparisons of one value against constants, return the value and 480/// the constants being compared. 481static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal, 482 std::vector<ConstantInt*> &Values) { 483 if (Cond->getOpcode() == Instruction::Or) { 484 CompVal = GatherConstantSetEQs(Cond, Values); 485 486 // Return true to indicate that the condition is true if the CompVal is 487 // equal to one of the constants. 488 return true; 489 } else if (Cond->getOpcode() == Instruction::And) { 490 CompVal = GatherConstantSetNEs(Cond, Values); 491 492 // Return false to indicate that the condition is false if the CompVal is 493 // equal to one of the constants. 494 return false; 495 } 496 return false; 497} 498 499static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) { 500 Instruction* Cond = 0; 501 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 502 Cond = dyn_cast<Instruction>(SI->getCondition()); 503 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { 504 if (BI->isConditional()) 505 Cond = dyn_cast<Instruction>(BI->getCondition()); 506 } 507 508 TI->eraseFromParent(); 509 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond); 510} 511 512/// isValueEqualityComparison - Return true if the specified terminator checks 513/// to see if a value is equal to constant integer value. 514static Value *isValueEqualityComparison(TerminatorInst *TI) { 515 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 516 // Do not permit merging of large switch instructions into their 517 // predecessors unless there is only one predecessor. 518 if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()), 519 pred_end(SI->getParent())) > 128) 520 return 0; 521 522 return SI->getCondition(); 523 } 524 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) 525 if (BI->isConditional() && BI->getCondition()->hasOneUse()) 526 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition())) 527 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ || 528 ICI->getPredicate() == ICmpInst::ICMP_NE) && 529 isa<ConstantInt>(ICI->getOperand(1))) 530 return ICI->getOperand(0); 531 return 0; 532} 533 534/// GetValueEqualityComparisonCases - Given a value comparison instruction, 535/// decode all of the 'cases' that it represents and return the 'default' block. 536static BasicBlock * 537GetValueEqualityComparisonCases(TerminatorInst *TI, 538 std::vector<std::pair<ConstantInt*, 539 BasicBlock*> > &Cases) { 540 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 541 Cases.reserve(SI->getNumCases()); 542 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) 543 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i))); 544 return SI->getDefaultDest(); 545 } 546 547 BranchInst *BI = cast<BranchInst>(TI); 548 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition()); 549 Cases.push_back(std::make_pair(cast<ConstantInt>(ICI->getOperand(1)), 550 BI->getSuccessor(ICI->getPredicate() == 551 ICmpInst::ICMP_NE))); 552 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ); 553} 554 555 556/// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries 557/// in the list that match the specified block. 558static void EliminateBlockCases(BasicBlock *BB, 559 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) { 560 for (unsigned i = 0, e = Cases.size(); i != e; ++i) 561 if (Cases[i].second == BB) { 562 Cases.erase(Cases.begin()+i); 563 --i; --e; 564 } 565} 566 567/// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as 568/// well. 569static bool 570ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1, 571 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) { 572 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2; 573 574 // Make V1 be smaller than V2. 575 if (V1->size() > V2->size()) 576 std::swap(V1, V2); 577 578 if (V1->size() == 0) return false; 579 if (V1->size() == 1) { 580 // Just scan V2. 581 ConstantInt *TheVal = (*V1)[0].first; 582 for (unsigned i = 0, e = V2->size(); i != e; ++i) 583 if (TheVal == (*V2)[i].first) 584 return true; 585 } 586 587 // Otherwise, just sort both lists and compare element by element. 588 std::sort(V1->begin(), V1->end()); 589 std::sort(V2->begin(), V2->end()); 590 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size(); 591 while (i1 != e1 && i2 != e2) { 592 if ((*V1)[i1].first == (*V2)[i2].first) 593 return true; 594 if ((*V1)[i1].first < (*V2)[i2].first) 595 ++i1; 596 else 597 ++i2; 598 } 599 return false; 600} 601 602/// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a 603/// terminator instruction and its block is known to only have a single 604/// predecessor block, check to see if that predecessor is also a value 605/// comparison with the same value, and if that comparison determines the 606/// outcome of this comparison. If so, simplify TI. This does a very limited 607/// form of jump threading. 608static bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI, 609 BasicBlock *Pred) { 610 Value *PredVal = isValueEqualityComparison(Pred->getTerminator()); 611 if (!PredVal) return false; // Not a value comparison in predecessor. 612 613 Value *ThisVal = isValueEqualityComparison(TI); 614 assert(ThisVal && "This isn't a value comparison!!"); 615 if (ThisVal != PredVal) return false; // Different predicates. 616 617 // Find out information about when control will move from Pred to TI's block. 618 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases; 619 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(), 620 PredCases); 621 EliminateBlockCases(PredDef, PredCases); // Remove default from cases. 622 623 // Find information about how control leaves this block. 624 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases; 625 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases); 626 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases. 627 628 // If TI's block is the default block from Pred's comparison, potentially 629 // simplify TI based on this knowledge. 630 if (PredDef == TI->getParent()) { 631 // If we are here, we know that the value is none of those cases listed in 632 // PredCases. If there are any cases in ThisCases that are in PredCases, we 633 // can simplify TI. 634 if (ValuesOverlap(PredCases, ThisCases)) { 635 if (isa<BranchInst>(TI)) { 636 // Okay, one of the successors of this condbr is dead. Convert it to a 637 // uncond br. 638 assert(ThisCases.size() == 1 && "Branch can only have one case!"); 639 // Insert the new branch. 640 Instruction *NI = BranchInst::Create(ThisDef, TI); 641 642 // Remove PHI node entries for the dead edge. 643 ThisCases[0].second->removePredecessor(TI->getParent()); 644 645 DOUT << "Threading pred instr: " << *Pred->getTerminator() 646 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n"; 647 648 EraseTerminatorInstAndDCECond(TI); 649 return true; 650 651 } else { 652 SwitchInst *SI = cast<SwitchInst>(TI); 653 // Okay, TI has cases that are statically dead, prune them away. 654 SmallPtrSet<Constant*, 16> DeadCases; 655 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 656 DeadCases.insert(PredCases[i].first); 657 658 DOUT << "Threading pred instr: " << *Pred->getTerminator() 659 << "Through successor TI: " << *TI; 660 661 for (unsigned i = SI->getNumCases()-1; i != 0; --i) 662 if (DeadCases.count(SI->getCaseValue(i))) { 663 SI->getSuccessor(i)->removePredecessor(TI->getParent()); 664 SI->removeCase(i); 665 } 666 667 DOUT << "Leaving: " << *TI << "\n"; 668 return true; 669 } 670 } 671 672 } else { 673 // Otherwise, TI's block must correspond to some matched value. Find out 674 // which value (or set of values) this is. 675 ConstantInt *TIV = 0; 676 BasicBlock *TIBB = TI->getParent(); 677 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 678 if (PredCases[i].second == TIBB) { 679 if (TIV == 0) 680 TIV = PredCases[i].first; 681 else 682 return false; // Cannot handle multiple values coming to this block. 683 } 684 assert(TIV && "No edge from pred to succ?"); 685 686 // Okay, we found the one constant that our value can be if we get into TI's 687 // BB. Find out which successor will unconditionally be branched to. 688 BasicBlock *TheRealDest = 0; 689 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i) 690 if (ThisCases[i].first == TIV) { 691 TheRealDest = ThisCases[i].second; 692 break; 693 } 694 695 // If not handled by any explicit cases, it is handled by the default case. 696 if (TheRealDest == 0) TheRealDest = ThisDef; 697 698 // Remove PHI node entries for dead edges. 699 BasicBlock *CheckEdge = TheRealDest; 700 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI) 701 if (*SI != CheckEdge) 702 (*SI)->removePredecessor(TIBB); 703 else 704 CheckEdge = 0; 705 706 // Insert the new branch. 707 Instruction *NI = BranchInst::Create(TheRealDest, TI); 708 709 DOUT << "Threading pred instr: " << *Pred->getTerminator() 710 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n"; 711 712 EraseTerminatorInstAndDCECond(TI); 713 return true; 714 } 715 return false; 716} 717 718/// FoldValueComparisonIntoPredecessors - The specified terminator is a value 719/// equality comparison instruction (either a switch or a branch on "X == c"). 720/// See if any of the predecessors of the terminator block are value comparisons 721/// on the same value. If so, and if safe to do so, fold them together. 722static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) { 723 BasicBlock *BB = TI->getParent(); 724 Value *CV = isValueEqualityComparison(TI); // CondVal 725 assert(CV && "Not a comparison?"); 726 bool Changed = false; 727 728 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB)); 729 while (!Preds.empty()) { 730 BasicBlock *Pred = Preds.back(); 731 Preds.pop_back(); 732 733 // See if the predecessor is a comparison with the same value. 734 TerminatorInst *PTI = Pred->getTerminator(); 735 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal 736 737 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) { 738 // Figure out which 'cases' to copy from SI to PSI. 739 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases; 740 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases); 741 742 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases; 743 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases); 744 745 // Based on whether the default edge from PTI goes to BB or not, fill in 746 // PredCases and PredDefault with the new switch cases we would like to 747 // build. 748 SmallVector<BasicBlock*, 8> NewSuccessors; 749 750 if (PredDefault == BB) { 751 // If this is the default destination from PTI, only the edges in TI 752 // that don't occur in PTI, or that branch to BB will be activated. 753 std::set<ConstantInt*> PTIHandled; 754 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 755 if (PredCases[i].second != BB) 756 PTIHandled.insert(PredCases[i].first); 757 else { 758 // The default destination is BB, we don't need explicit targets. 759 std::swap(PredCases[i], PredCases.back()); 760 PredCases.pop_back(); 761 --i; --e; 762 } 763 764 // Reconstruct the new switch statement we will be building. 765 if (PredDefault != BBDefault) { 766 PredDefault->removePredecessor(Pred); 767 PredDefault = BBDefault; 768 NewSuccessors.push_back(BBDefault); 769 } 770 for (unsigned i = 0, e = BBCases.size(); i != e; ++i) 771 if (!PTIHandled.count(BBCases[i].first) && 772 BBCases[i].second != BBDefault) { 773 PredCases.push_back(BBCases[i]); 774 NewSuccessors.push_back(BBCases[i].second); 775 } 776 777 } else { 778 // If this is not the default destination from PSI, only the edges 779 // in SI that occur in PSI with a destination of BB will be 780 // activated. 781 std::set<ConstantInt*> PTIHandled; 782 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 783 if (PredCases[i].second == BB) { 784 PTIHandled.insert(PredCases[i].first); 785 std::swap(PredCases[i], PredCases.back()); 786 PredCases.pop_back(); 787 --i; --e; 788 } 789 790 // Okay, now we know which constants were sent to BB from the 791 // predecessor. Figure out where they will all go now. 792 for (unsigned i = 0, e = BBCases.size(); i != e; ++i) 793 if (PTIHandled.count(BBCases[i].first)) { 794 // If this is one we are capable of getting... 795 PredCases.push_back(BBCases[i]); 796 NewSuccessors.push_back(BBCases[i].second); 797 PTIHandled.erase(BBCases[i].first);// This constant is taken care of 798 } 799 800 // If there are any constants vectored to BB that TI doesn't handle, 801 // they must go to the default destination of TI. 802 for (std::set<ConstantInt*>::iterator I = PTIHandled.begin(), 803 E = PTIHandled.end(); I != E; ++I) { 804 PredCases.push_back(std::make_pair(*I, BBDefault)); 805 NewSuccessors.push_back(BBDefault); 806 } 807 } 808 809 // Okay, at this point, we know which new successor Pred will get. Make 810 // sure we update the number of entries in the PHI nodes for these 811 // successors. 812 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i) 813 AddPredecessorToBlock(NewSuccessors[i], Pred, BB); 814 815 // Now that the successors are updated, create the new Switch instruction. 816 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault, 817 PredCases.size(), PTI); 818 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 819 NewSI->addCase(PredCases[i].first, PredCases[i].second); 820 821 EraseTerminatorInstAndDCECond(PTI); 822 823 // Okay, last check. If BB is still a successor of PSI, then we must 824 // have an infinite loop case. If so, add an infinitely looping block 825 // to handle the case to preserve the behavior of the code. 826 BasicBlock *InfLoopBlock = 0; 827 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i) 828 if (NewSI->getSuccessor(i) == BB) { 829 if (InfLoopBlock == 0) { 830 // Insert it at the end of the function, because it's either code, 831 // or it won't matter if it's hot. :) 832 InfLoopBlock = BasicBlock::Create("infloop", BB->getParent()); 833 BranchInst::Create(InfLoopBlock, InfLoopBlock); 834 } 835 NewSI->setSuccessor(i, InfLoopBlock); 836 } 837 838 Changed = true; 839 } 840 } 841 return Changed; 842} 843 844/// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and 845/// BB2, hoist any common code in the two blocks up into the branch block. The 846/// caller of this function guarantees that BI's block dominates BB1 and BB2. 847static bool HoistThenElseCodeToIf(BranchInst *BI) { 848 // This does very trivial matching, with limited scanning, to find identical 849 // instructions in the two blocks. In particular, we don't want to get into 850 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As 851 // such, we currently just scan for obviously identical instructions in an 852 // identical order. 853 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination. 854 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination 855 856 BasicBlock::iterator BB1_Itr = BB1->begin(); 857 BasicBlock::iterator BB2_Itr = BB2->begin(); 858 859 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++; 860 while (isa<DbgInfoIntrinsic>(I1)) 861 I1 = BB1_Itr++; 862 while (isa<DbgInfoIntrinsic>(I2)) 863 I2 = BB2_Itr++; 864 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) || 865 isa<InvokeInst>(I1) || !I1->isIdenticalTo(I2)) 866 return false; 867 868 // If we get here, we can hoist at least one instruction. 869 BasicBlock *BIParent = BI->getParent(); 870 871 do { 872 // If we are hoisting the terminator instruction, don't move one (making a 873 // broken BB), instead clone it, and remove BI. 874 if (isa<TerminatorInst>(I1)) 875 goto HoistTerminator; 876 877 // For a normal instruction, we just move one to right before the branch, 878 // then replace all uses of the other with the first. Finally, we remove 879 // the now redundant second instruction. 880 BIParent->getInstList().splice(BI, BB1->getInstList(), I1); 881 if (!I2->use_empty()) 882 I2->replaceAllUsesWith(I1); 883 BB2->getInstList().erase(I2); 884 885 I1 = BB1_Itr++; 886 while (isa<DbgInfoIntrinsic>(I1)) 887 I1 = BB1_Itr++; 888 I2 = BB2_Itr++; 889 while (isa<DbgInfoIntrinsic>(I2)) 890 I2 = BB2_Itr++; 891 } while (I1->getOpcode() == I2->getOpcode() && I1->isIdenticalTo(I2)); 892 893 return true; 894 895HoistTerminator: 896 // Okay, it is safe to hoist the terminator. 897 Instruction *NT = I1->clone(); 898 BIParent->getInstList().insert(BI, NT); 899 if (NT->getType() != Type::VoidTy) { 900 I1->replaceAllUsesWith(NT); 901 I2->replaceAllUsesWith(NT); 902 NT->takeName(I1); 903 } 904 905 // Hoisting one of the terminators from our successor is a great thing. 906 // Unfortunately, the successors of the if/else blocks may have PHI nodes in 907 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI 908 // nodes, so we insert select instruction to compute the final result. 909 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects; 910 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) { 911 PHINode *PN; 912 for (BasicBlock::iterator BBI = SI->begin(); 913 (PN = dyn_cast<PHINode>(BBI)); ++BBI) { 914 Value *BB1V = PN->getIncomingValueForBlock(BB1); 915 Value *BB2V = PN->getIncomingValueForBlock(BB2); 916 if (BB1V != BB2V) { 917 // These values do not agree. Insert a select instruction before NT 918 // that determines the right value. 919 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)]; 920 if (SI == 0) 921 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V, 922 BB1V->getName()+"."+BB2V->getName(), NT); 923 // Make the PHI node use the select for all incoming values for BB1/BB2 924 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 925 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2) 926 PN->setIncomingValue(i, SI); 927 } 928 } 929 } 930 931 // Update any PHI nodes in our new successors. 932 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) 933 AddPredecessorToBlock(*SI, BIParent, BB1); 934 935 EraseTerminatorInstAndDCECond(BI); 936 return true; 937} 938 939/// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1 940/// and an BB2 and the only successor of BB1 is BB2, hoist simple code 941/// (for now, restricted to a single instruction that's side effect free) from 942/// the BB1 into the branch block to speculatively execute it. 943static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) { 944 // Only speculatively execution a single instruction (not counting the 945 // terminator) for now. 946 BasicBlock::iterator BBI = BB1->begin(); 947 ++BBI; // must have at least a terminator 948 if (BBI == BB1->end()) return false; // only one inst 949 ++BBI; 950 if (BBI != BB1->end()) return false; // more than 2 insts. 951 952 // Be conservative for now. FP select instruction can often be expensive. 953 Value *BrCond = BI->getCondition(); 954 if (isa<Instruction>(BrCond) && 955 cast<Instruction>(BrCond)->getOpcode() == Instruction::FCmp) 956 return false; 957 958 // If BB1 is actually on the false edge of the conditional branch, remember 959 // to swap the select operands later. 960 bool Invert = false; 961 if (BB1 != BI->getSuccessor(0)) { 962 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?"); 963 Invert = true; 964 } 965 966 // Turn 967 // BB: 968 // %t1 = icmp 969 // br i1 %t1, label %BB1, label %BB2 970 // BB1: 971 // %t3 = add %t2, c 972 // br label BB2 973 // BB2: 974 // => 975 // BB: 976 // %t1 = icmp 977 // %t4 = add %t2, c 978 // %t3 = select i1 %t1, %t2, %t3 979 Instruction *I = BB1->begin(); 980 switch (I->getOpcode()) { 981 default: return false; // Not safe / profitable to hoist. 982 case Instruction::Add: 983 case Instruction::Sub: 984 // FP arithmetic might trap. Not worth doing for vector ops. 985 if (I->getType()->isFloatingPoint() || isa<VectorType>(I->getType())) 986 return false; 987 break; 988 case Instruction::And: 989 case Instruction::Or: 990 case Instruction::Xor: 991 case Instruction::Shl: 992 case Instruction::LShr: 993 case Instruction::AShr: 994 // Don't mess with vector operations. 995 if (isa<VectorType>(I->getType())) 996 return false; 997 break; // These are all cheap and non-trapping instructions. 998 } 999 1000 // If the instruction is obviously dead, don't try to predicate it. 1001 if (I->use_empty()) { 1002 I->eraseFromParent(); 1003 return true; 1004 } 1005 1006 // Can we speculatively execute the instruction? And what is the value 1007 // if the condition is false? Consider the phi uses, if the incoming value 1008 // from the "if" block are all the same V, then V is the value of the 1009 // select if the condition is false. 1010 BasicBlock *BIParent = BI->getParent(); 1011 SmallVector<PHINode*, 4> PHIUses; 1012 Value *FalseV = NULL; 1013 1014 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0); 1015 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); 1016 UI != E; ++UI) { 1017 // Ignore any user that is not a PHI node in BB2. These can only occur in 1018 // unreachable blocks, because they would not be dominated by the instr. 1019 PHINode *PN = dyn_cast<PHINode>(UI); 1020 if (!PN || PN->getParent() != BB2) 1021 return false; 1022 PHIUses.push_back(PN); 1023 1024 Value *PHIV = PN->getIncomingValueForBlock(BIParent); 1025 if (!FalseV) 1026 FalseV = PHIV; 1027 else if (FalseV != PHIV) 1028 return false; // Inconsistent value when condition is false. 1029 } 1030 1031 assert(FalseV && "Must have at least one user, and it must be a PHI"); 1032 1033 // Do not hoist the instruction if any of its operands are defined but not 1034 // used in this BB. The transformation will prevent the operand from 1035 // being sunk into the use block. 1036 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) { 1037 Instruction *OpI = dyn_cast<Instruction>(*i); 1038 if (OpI && OpI->getParent() == BIParent && 1039 !OpI->isUsedInBasicBlock(BIParent)) 1040 return false; 1041 } 1042 1043 // If we get here, we can hoist the instruction. Try to place it 1044 // before the icmp instruction preceeding the conditional branch. 1045 BasicBlock::iterator InsertPos = BI; 1046 if (InsertPos != BIParent->begin()) 1047 --InsertPos; 1048 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) { 1049 SmallPtrSet<Instruction *, 4> BB1Insns; 1050 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end(); 1051 BB1I != BB1E; ++BB1I) 1052 BB1Insns.insert(BB1I); 1053 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end(); 1054 UI != UE; ++UI) { 1055 Instruction *Use = cast<Instruction>(*UI); 1056 if (BB1Insns.count(Use)) { 1057 // If BrCond uses the instruction that place it just before 1058 // branch instruction. 1059 InsertPos = BI; 1060 break; 1061 } 1062 } 1063 } else 1064 InsertPos = BI; 1065 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), I); 1066 1067 // Create a select whose true value is the speculatively executed value and 1068 // false value is the previously determined FalseV. 1069 SelectInst *SI; 1070 if (Invert) 1071 SI = SelectInst::Create(BrCond, FalseV, I, 1072 FalseV->getName() + "." + I->getName(), BI); 1073 else 1074 SI = SelectInst::Create(BrCond, I, FalseV, 1075 I->getName() + "." + FalseV->getName(), BI); 1076 1077 // Make the PHI node use the select for all incoming values for "then" and 1078 // "if" blocks. 1079 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) { 1080 PHINode *PN = PHIUses[i]; 1081 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j) 1082 if (PN->getIncomingBlock(j) == BB1 || 1083 PN->getIncomingBlock(j) == BIParent) 1084 PN->setIncomingValue(j, SI); 1085 } 1086 1087 ++NumSpeculations; 1088 return true; 1089} 1090 1091/// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch 1092/// across this block. 1093static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) { 1094 BranchInst *BI = cast<BranchInst>(BB->getTerminator()); 1095 unsigned Size = 0; 1096 1097 // If this basic block contains anything other than a PHI (which controls the 1098 // branch) and branch itself, bail out. FIXME: improve this in the future. 1099 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI, ++Size) { 1100 if (Size > 10) return false; // Don't clone large BB's. 1101 1102 // We can only support instructions that are do not define values that are 1103 // live outside of the current basic block. 1104 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end(); 1105 UI != E; ++UI) { 1106 Instruction *U = cast<Instruction>(*UI); 1107 if (U->getParent() != BB || isa<PHINode>(U)) return false; 1108 } 1109 1110 // Looks ok, continue checking. 1111 } 1112 1113 return true; 1114} 1115 1116/// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value 1117/// that is defined in the same block as the branch and if any PHI entries are 1118/// constants, thread edges corresponding to that entry to be branches to their 1119/// ultimate destination. 1120static bool FoldCondBranchOnPHI(BranchInst *BI) { 1121 BasicBlock *BB = BI->getParent(); 1122 PHINode *PN = dyn_cast<PHINode>(BI->getCondition()); 1123 // NOTE: we currently cannot transform this case if the PHI node is used 1124 // outside of the block. 1125 if (!PN || PN->getParent() != BB || !PN->hasOneUse()) 1126 return false; 1127 1128 // Degenerate case of a single entry PHI. 1129 if (PN->getNumIncomingValues() == 1) { 1130 FoldSingleEntryPHINodes(PN->getParent()); 1131 return true; 1132 } 1133 1134 // Now we know that this block has multiple preds and two succs. 1135 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false; 1136 1137 // Okay, this is a simple enough basic block. See if any phi values are 1138 // constants. 1139 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 1140 ConstantInt *CB; 1141 if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) && 1142 CB->getType() == Type::Int1Ty) { 1143 // Okay, we now know that all edges from PredBB should be revectored to 1144 // branch to RealDest. 1145 BasicBlock *PredBB = PN->getIncomingBlock(i); 1146 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue()); 1147 1148 if (RealDest == BB) continue; // Skip self loops. 1149 1150 // The dest block might have PHI nodes, other predecessors and other 1151 // difficult cases. Instead of being smart about this, just insert a new 1152 // block that jumps to the destination block, effectively splitting 1153 // the edge we are about to create. 1154 BasicBlock *EdgeBB = BasicBlock::Create(RealDest->getName()+".critedge", 1155 RealDest->getParent(), RealDest); 1156 BranchInst::Create(RealDest, EdgeBB); 1157 PHINode *PN; 1158 for (BasicBlock::iterator BBI = RealDest->begin(); 1159 (PN = dyn_cast<PHINode>(BBI)); ++BBI) { 1160 Value *V = PN->getIncomingValueForBlock(BB); 1161 PN->addIncoming(V, EdgeBB); 1162 } 1163 1164 // BB may have instructions that are being threaded over. Clone these 1165 // instructions into EdgeBB. We know that there will be no uses of the 1166 // cloned instructions outside of EdgeBB. 1167 BasicBlock::iterator InsertPt = EdgeBB->begin(); 1168 std::map<Value*, Value*> TranslateMap; // Track translated values. 1169 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) { 1170 if (PHINode *PN = dyn_cast<PHINode>(BBI)) { 1171 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB); 1172 } else { 1173 // Clone the instruction. 1174 Instruction *N = BBI->clone(); 1175 if (BBI->hasName()) N->setName(BBI->getName()+".c"); 1176 1177 // Update operands due to translation. 1178 for (User::op_iterator i = N->op_begin(), e = N->op_end(); 1179 i != e; ++i) { 1180 std::map<Value*, Value*>::iterator PI = 1181 TranslateMap.find(*i); 1182 if (PI != TranslateMap.end()) 1183 *i = PI->second; 1184 } 1185 1186 // Check for trivial simplification. 1187 if (Constant *C = ConstantFoldInstruction(N)) { 1188 TranslateMap[BBI] = C; 1189 delete N; // Constant folded away, don't need actual inst 1190 } else { 1191 // Insert the new instruction into its new home. 1192 EdgeBB->getInstList().insert(InsertPt, N); 1193 if (!BBI->use_empty()) 1194 TranslateMap[BBI] = N; 1195 } 1196 } 1197 } 1198 1199 // Loop over all of the edges from PredBB to BB, changing them to branch 1200 // to EdgeBB instead. 1201 TerminatorInst *PredBBTI = PredBB->getTerminator(); 1202 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i) 1203 if (PredBBTI->getSuccessor(i) == BB) { 1204 BB->removePredecessor(PredBB); 1205 PredBBTI->setSuccessor(i, EdgeBB); 1206 } 1207 1208 // Recurse, simplifying any other constants. 1209 return FoldCondBranchOnPHI(BI) | true; 1210 } 1211 } 1212 1213 return false; 1214} 1215 1216/// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry 1217/// PHI node, see if we can eliminate it. 1218static bool FoldTwoEntryPHINode(PHINode *PN) { 1219 // Ok, this is a two entry PHI node. Check to see if this is a simple "if 1220 // statement", which has a very simple dominance structure. Basically, we 1221 // are trying to find the condition that is being branched on, which 1222 // subsequently causes this merge to happen. We really want control 1223 // dependence information for this check, but simplifycfg can't keep it up 1224 // to date, and this catches most of the cases we care about anyway. 1225 // 1226 BasicBlock *BB = PN->getParent(); 1227 BasicBlock *IfTrue, *IfFalse; 1228 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse); 1229 if (!IfCond) return false; 1230 1231 // Okay, we found that we can merge this two-entry phi node into a select. 1232 // Doing so would require us to fold *all* two entry phi nodes in this block. 1233 // At some point this becomes non-profitable (particularly if the target 1234 // doesn't support cmov's). Only do this transformation if there are two or 1235 // fewer PHI nodes in this block. 1236 unsigned NumPhis = 0; 1237 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I) 1238 if (NumPhis > 2) 1239 return false; 1240 1241 DOUT << "FOUND IF CONDITION! " << *IfCond << " T: " 1242 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n"; 1243 1244 // Loop over the PHI's seeing if we can promote them all to select 1245 // instructions. While we are at it, keep track of the instructions 1246 // that need to be moved to the dominating block. 1247 std::set<Instruction*> AggressiveInsts; 1248 1249 BasicBlock::iterator AfterPHIIt = BB->begin(); 1250 while (isa<PHINode>(AfterPHIIt)) { 1251 PHINode *PN = cast<PHINode>(AfterPHIIt++); 1252 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) { 1253 if (PN->getIncomingValue(0) != PN) 1254 PN->replaceAllUsesWith(PN->getIncomingValue(0)); 1255 else 1256 PN->replaceAllUsesWith(UndefValue::get(PN->getType())); 1257 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB, 1258 &AggressiveInsts) || 1259 !DominatesMergePoint(PN->getIncomingValue(1), BB, 1260 &AggressiveInsts)) { 1261 return false; 1262 } 1263 } 1264 1265 // If we all PHI nodes are promotable, check to make sure that all 1266 // instructions in the predecessor blocks can be promoted as well. If 1267 // not, we won't be able to get rid of the control flow, so it's not 1268 // worth promoting to select instructions. 1269 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0; 1270 PN = cast<PHINode>(BB->begin()); 1271 BasicBlock *Pred = PN->getIncomingBlock(0); 1272 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) { 1273 IfBlock1 = Pred; 1274 DomBlock = *pred_begin(Pred); 1275 for (BasicBlock::iterator I = Pred->begin(); 1276 !isa<TerminatorInst>(I); ++I) 1277 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) { 1278 // This is not an aggressive instruction that we can promote. 1279 // Because of this, we won't be able to get rid of the control 1280 // flow, so the xform is not worth it. 1281 return false; 1282 } 1283 } 1284 1285 Pred = PN->getIncomingBlock(1); 1286 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) { 1287 IfBlock2 = Pred; 1288 DomBlock = *pred_begin(Pred); 1289 for (BasicBlock::iterator I = Pred->begin(); 1290 !isa<TerminatorInst>(I); ++I) 1291 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) { 1292 // This is not an aggressive instruction that we can promote. 1293 // Because of this, we won't be able to get rid of the control 1294 // flow, so the xform is not worth it. 1295 return false; 1296 } 1297 } 1298 1299 // If we can still promote the PHI nodes after this gauntlet of tests, 1300 // do all of the PHI's now. 1301 1302 // Move all 'aggressive' instructions, which are defined in the 1303 // conditional parts of the if's up to the dominating block. 1304 if (IfBlock1) { 1305 DomBlock->getInstList().splice(DomBlock->getTerminator(), 1306 IfBlock1->getInstList(), 1307 IfBlock1->begin(), 1308 IfBlock1->getTerminator()); 1309 } 1310 if (IfBlock2) { 1311 DomBlock->getInstList().splice(DomBlock->getTerminator(), 1312 IfBlock2->getInstList(), 1313 IfBlock2->begin(), 1314 IfBlock2->getTerminator()); 1315 } 1316 1317 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) { 1318 // Change the PHI node into a select instruction. 1319 Value *TrueVal = 1320 PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse); 1321 Value *FalseVal = 1322 PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue); 1323 1324 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt); 1325 PN->replaceAllUsesWith(NV); 1326 NV->takeName(PN); 1327 1328 BB->getInstList().erase(PN); 1329 } 1330 return true; 1331} 1332 1333/// isTerminatorFirstRelevantInsn - Return true if Term is very first 1334/// instruction ignoring Phi nodes and dbg intrinsics. 1335static bool isTerminatorFirstRelevantInsn(BasicBlock *BB, Instruction *Term) { 1336 BasicBlock::iterator BBI = Term; 1337 while (BBI != BB->begin()) { 1338 --BBI; 1339 if (!isa<DbgInfoIntrinsic>(BBI)) 1340 break; 1341 } 1342 1343 if (isa<PHINode>(BBI) || &*BBI == Term || isa<DbgInfoIntrinsic>(BBI)) 1344 return true; 1345 return false; 1346} 1347 1348/// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes 1349/// to two returning blocks, try to merge them together into one return, 1350/// introducing a select if the return values disagree. 1351static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) { 1352 assert(BI->isConditional() && "Must be a conditional branch"); 1353 BasicBlock *TrueSucc = BI->getSuccessor(0); 1354 BasicBlock *FalseSucc = BI->getSuccessor(1); 1355 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator()); 1356 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator()); 1357 1358 // Check to ensure both blocks are empty (just a return) or optionally empty 1359 // with PHI nodes. If there are other instructions, merging would cause extra 1360 // computation on one path or the other. 1361 if (!isTerminatorFirstRelevantInsn(TrueSucc, TrueRet)) 1362 return false; 1363 if (!isTerminatorFirstRelevantInsn(FalseSucc, FalseRet)) 1364 return false; 1365 1366 // Okay, we found a branch that is going to two return nodes. If 1367 // there is no return value for this function, just change the 1368 // branch into a return. 1369 if (FalseRet->getNumOperands() == 0) { 1370 TrueSucc->removePredecessor(BI->getParent()); 1371 FalseSucc->removePredecessor(BI->getParent()); 1372 ReturnInst::Create(0, BI); 1373 EraseTerminatorInstAndDCECond(BI); 1374 return true; 1375 } 1376 1377 // Otherwise, figure out what the true and false return values are 1378 // so we can insert a new select instruction. 1379 Value *TrueValue = TrueRet->getReturnValue(); 1380 Value *FalseValue = FalseRet->getReturnValue(); 1381 1382 // Unwrap any PHI nodes in the return blocks. 1383 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue)) 1384 if (TVPN->getParent() == TrueSucc) 1385 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent()); 1386 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue)) 1387 if (FVPN->getParent() == FalseSucc) 1388 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent()); 1389 1390 // In order for this transformation to be safe, we must be able to 1391 // unconditionally execute both operands to the return. This is 1392 // normally the case, but we could have a potentially-trapping 1393 // constant expression that prevents this transformation from being 1394 // safe. 1395 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue)) 1396 if (TCV->canTrap()) 1397 return false; 1398 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue)) 1399 if (FCV->canTrap()) 1400 return false; 1401 1402 // Okay, we collected all the mapped values and checked them for sanity, and 1403 // defined to really do this transformation. First, update the CFG. 1404 TrueSucc->removePredecessor(BI->getParent()); 1405 FalseSucc->removePredecessor(BI->getParent()); 1406 1407 // Insert select instructions where needed. 1408 Value *BrCond = BI->getCondition(); 1409 if (TrueValue) { 1410 // Insert a select if the results differ. 1411 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) { 1412 } else if (isa<UndefValue>(TrueValue)) { 1413 TrueValue = FalseValue; 1414 } else { 1415 TrueValue = SelectInst::Create(BrCond, TrueValue, 1416 FalseValue, "retval", BI); 1417 } 1418 } 1419 1420 Value *RI = !TrueValue ? 1421 ReturnInst::Create(BI) : 1422 ReturnInst::Create(TrueValue, BI); 1423 1424 DOUT << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:" 1425 << "\n " << *BI << "NewRet = " << *RI 1426 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc; 1427 1428 EraseTerminatorInstAndDCECond(BI); 1429 1430 return true; 1431} 1432 1433/// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch, 1434/// and if a predecessor branches to us and one of our successors, fold the 1435/// setcc into the predecessor and use logical operations to pick the right 1436/// destination. 1437static bool FoldBranchToCommonDest(BranchInst *BI) { 1438 BasicBlock *BB = BI->getParent(); 1439 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()); 1440 if (Cond == 0) return false; 1441 1442 1443 // Only allow this if the condition is a simple instruction that can be 1444 // executed unconditionally. It must be in the same block as the branch, and 1445 // must be at the front of the block. 1446 BasicBlock::iterator FrontIt = BB->front(); 1447 // Ignore dbg intrinsics. 1448 while(isa<DbgInfoIntrinsic>(FrontIt)) 1449 ++FrontIt; 1450 if ((!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) || 1451 Cond->getParent() != BB || &*FrontIt != Cond || !Cond->hasOneUse()) { 1452 return false; 1453 } 1454 1455 // Make sure the instruction after the condition is the cond branch. 1456 BasicBlock::iterator CondIt = Cond; ++CondIt; 1457 // Ingore dbg intrinsics. 1458 while(isa<DbgInfoIntrinsic>(CondIt)) 1459 ++CondIt; 1460 if (&*CondIt != BI) { 1461 assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!"); 1462 return false; 1463 } 1464 1465 // Cond is known to be a compare or binary operator. Check to make sure that 1466 // neither operand is a potentially-trapping constant expression. 1467 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0))) 1468 if (CE->canTrap()) 1469 return false; 1470 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1))) 1471 if (CE->canTrap()) 1472 return false; 1473 1474 1475 // Finally, don't infinitely unroll conditional loops. 1476 BasicBlock *TrueDest = BI->getSuccessor(0); 1477 BasicBlock *FalseDest = BI->getSuccessor(1); 1478 if (TrueDest == BB || FalseDest == BB) 1479 return false; 1480 1481 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 1482 BasicBlock *PredBlock = *PI; 1483 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator()); 1484 1485 // Check that we have two conditional branches. If there is a PHI node in 1486 // the common successor, verify that the same value flows in from both 1487 // blocks. 1488 if (PBI == 0 || PBI->isUnconditional() || 1489 !SafeToMergeTerminators(BI, PBI)) 1490 continue; 1491 1492 Instruction::BinaryOps Opc; 1493 bool InvertPredCond = false; 1494 1495 if (PBI->getSuccessor(0) == TrueDest) 1496 Opc = Instruction::Or; 1497 else if (PBI->getSuccessor(1) == FalseDest) 1498 Opc = Instruction::And; 1499 else if (PBI->getSuccessor(0) == FalseDest) 1500 Opc = Instruction::And, InvertPredCond = true; 1501 else if (PBI->getSuccessor(1) == TrueDest) 1502 Opc = Instruction::Or, InvertPredCond = true; 1503 else 1504 continue; 1505 1506 DOUT << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB; 1507 1508 // If we need to invert the condition in the pred block to match, do so now. 1509 if (InvertPredCond) { 1510 Value *NewCond = 1511 BinaryOperator::CreateNot(PBI->getCondition(), 1512 PBI->getCondition()->getName()+".not", PBI); 1513 PBI->setCondition(NewCond); 1514 BasicBlock *OldTrue = PBI->getSuccessor(0); 1515 BasicBlock *OldFalse = PBI->getSuccessor(1); 1516 PBI->setSuccessor(0, OldFalse); 1517 PBI->setSuccessor(1, OldTrue); 1518 } 1519 1520 // Clone Cond into the predecessor basic block, and or/and the 1521 // two conditions together. 1522 Instruction *New = Cond->clone(); 1523 PredBlock->getInstList().insert(PBI, New); 1524 New->takeName(Cond); 1525 Cond->setName(New->getName()+".old"); 1526 1527 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(), 1528 New, "or.cond", PBI); 1529 PBI->setCondition(NewCond); 1530 if (PBI->getSuccessor(0) == BB) { 1531 AddPredecessorToBlock(TrueDest, PredBlock, BB); 1532 PBI->setSuccessor(0, TrueDest); 1533 } 1534 if (PBI->getSuccessor(1) == BB) { 1535 AddPredecessorToBlock(FalseDest, PredBlock, BB); 1536 PBI->setSuccessor(1, FalseDest); 1537 } 1538 return true; 1539 } 1540 return false; 1541} 1542 1543/// SimplifyCondBranchToCondBranch - If we have a conditional branch as a 1544/// predecessor of another block, this function tries to simplify it. We know 1545/// that PBI and BI are both conditional branches, and BI is in one of the 1546/// successor blocks of PBI - PBI branches to BI. 1547static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) { 1548 assert(PBI->isConditional() && BI->isConditional()); 1549 BasicBlock *BB = BI->getParent(); 1550 1551 // If this block ends with a branch instruction, and if there is a 1552 // predecessor that ends on a branch of the same condition, make 1553 // this conditional branch redundant. 1554 if (PBI->getCondition() == BI->getCondition() && 1555 PBI->getSuccessor(0) != PBI->getSuccessor(1)) { 1556 // Okay, the outcome of this conditional branch is statically 1557 // knowable. If this block had a single pred, handle specially. 1558 if (BB->getSinglePredecessor()) { 1559 // Turn this into a branch on constant. 1560 bool CondIsTrue = PBI->getSuccessor(0) == BB; 1561 BI->setCondition(ConstantInt::get(Type::Int1Ty, CondIsTrue)); 1562 return true; // Nuke the branch on constant. 1563 } 1564 1565 // Otherwise, if there are multiple predecessors, insert a PHI that merges 1566 // in the constant and simplify the block result. Subsequent passes of 1567 // simplifycfg will thread the block. 1568 if (BlockIsSimpleEnoughToThreadThrough(BB)) { 1569 PHINode *NewPN = PHINode::Create(Type::Int1Ty, 1570 BI->getCondition()->getName() + ".pr", 1571 BB->begin()); 1572 // Okay, we're going to insert the PHI node. Since PBI is not the only 1573 // predecessor, compute the PHI'd conditional value for all of the preds. 1574 // Any predecessor where the condition is not computable we keep symbolic. 1575 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) 1576 if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) && 1577 PBI != BI && PBI->isConditional() && 1578 PBI->getCondition() == BI->getCondition() && 1579 PBI->getSuccessor(0) != PBI->getSuccessor(1)) { 1580 bool CondIsTrue = PBI->getSuccessor(0) == BB; 1581 NewPN->addIncoming(ConstantInt::get(Type::Int1Ty, 1582 CondIsTrue), *PI); 1583 } else { 1584 NewPN->addIncoming(BI->getCondition(), *PI); 1585 } 1586 1587 BI->setCondition(NewPN); 1588 return true; 1589 } 1590 } 1591 1592 // If this is a conditional branch in an empty block, and if any 1593 // predecessors is a conditional branch to one of our destinations, 1594 // fold the conditions into logical ops and one cond br. 1595 if (&BB->front() != BI) 1596 return false; 1597 1598 1599 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition())) 1600 if (CE->canTrap()) 1601 return false; 1602 1603 int PBIOp, BIOp; 1604 if (PBI->getSuccessor(0) == BI->getSuccessor(0)) 1605 PBIOp = BIOp = 0; 1606 else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) 1607 PBIOp = 0, BIOp = 1; 1608 else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) 1609 PBIOp = 1, BIOp = 0; 1610 else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) 1611 PBIOp = BIOp = 1; 1612 else 1613 return false; 1614 1615 // Check to make sure that the other destination of this branch 1616 // isn't BB itself. If so, this is an infinite loop that will 1617 // keep getting unwound. 1618 if (PBI->getSuccessor(PBIOp) == BB) 1619 return false; 1620 1621 // Do not perform this transformation if it would require 1622 // insertion of a large number of select instructions. For targets 1623 // without predication/cmovs, this is a big pessimization. 1624 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp); 1625 1626 unsigned NumPhis = 0; 1627 for (BasicBlock::iterator II = CommonDest->begin(); 1628 isa<PHINode>(II); ++II, ++NumPhis) 1629 if (NumPhis > 2) // Disable this xform. 1630 return false; 1631 1632 // Finally, if everything is ok, fold the branches to logical ops. 1633 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1); 1634 1635 DOUT << "FOLDING BRs:" << *PBI->getParent() 1636 << "AND: " << *BI->getParent(); 1637 1638 1639 // If OtherDest *is* BB, then BB is a basic block with a single conditional 1640 // branch in it, where one edge (OtherDest) goes back to itself but the other 1641 // exits. We don't *know* that the program avoids the infinite loop 1642 // (even though that seems likely). If we do this xform naively, we'll end up 1643 // recursively unpeeling the loop. Since we know that (after the xform is 1644 // done) that the block *is* infinite if reached, we just make it an obviously 1645 // infinite loop with no cond branch. 1646 if (OtherDest == BB) { 1647 // Insert it at the end of the function, because it's either code, 1648 // or it won't matter if it's hot. :) 1649 BasicBlock *InfLoopBlock = BasicBlock::Create("infloop", BB->getParent()); 1650 BranchInst::Create(InfLoopBlock, InfLoopBlock); 1651 OtherDest = InfLoopBlock; 1652 } 1653 1654 DOUT << *PBI->getParent()->getParent(); 1655 1656 // BI may have other predecessors. Because of this, we leave 1657 // it alone, but modify PBI. 1658 1659 // Make sure we get to CommonDest on True&True directions. 1660 Value *PBICond = PBI->getCondition(); 1661 if (PBIOp) 1662 PBICond = BinaryOperator::CreateNot(PBICond, 1663 PBICond->getName()+".not", 1664 PBI); 1665 Value *BICond = BI->getCondition(); 1666 if (BIOp) 1667 BICond = BinaryOperator::CreateNot(BICond, 1668 BICond->getName()+".not", 1669 PBI); 1670 // Merge the conditions. 1671 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI); 1672 1673 // Modify PBI to branch on the new condition to the new dests. 1674 PBI->setCondition(Cond); 1675 PBI->setSuccessor(0, CommonDest); 1676 PBI->setSuccessor(1, OtherDest); 1677 1678 // OtherDest may have phi nodes. If so, add an entry from PBI's 1679 // block that are identical to the entries for BI's block. 1680 PHINode *PN; 1681 for (BasicBlock::iterator II = OtherDest->begin(); 1682 (PN = dyn_cast<PHINode>(II)); ++II) { 1683 Value *V = PN->getIncomingValueForBlock(BB); 1684 PN->addIncoming(V, PBI->getParent()); 1685 } 1686 1687 // We know that the CommonDest already had an edge from PBI to 1688 // it. If it has PHIs though, the PHIs may have different 1689 // entries for BB and PBI's BB. If so, insert a select to make 1690 // them agree. 1691 for (BasicBlock::iterator II = CommonDest->begin(); 1692 (PN = dyn_cast<PHINode>(II)); ++II) { 1693 Value *BIV = PN->getIncomingValueForBlock(BB); 1694 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent()); 1695 Value *PBIV = PN->getIncomingValue(PBBIdx); 1696 if (BIV != PBIV) { 1697 // Insert a select in PBI to pick the right value. 1698 Value *NV = SelectInst::Create(PBICond, PBIV, BIV, 1699 PBIV->getName()+".mux", PBI); 1700 PN->setIncomingValue(PBBIdx, NV); 1701 } 1702 } 1703 1704 DOUT << "INTO: " << *PBI->getParent(); 1705 1706 DOUT << *PBI->getParent()->getParent(); 1707 1708 // This basic block is probably dead. We know it has at least 1709 // one fewer predecessor. 1710 return true; 1711} 1712 1713 1714namespace { 1715 /// ConstantIntOrdering - This class implements a stable ordering of constant 1716 /// integers that does not depend on their address. This is important for 1717 /// applications that sort ConstantInt's to ensure uniqueness. 1718 struct ConstantIntOrdering { 1719 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const { 1720 return LHS->getValue().ult(RHS->getValue()); 1721 } 1722 }; 1723} 1724 1725/// SimplifyCFG - This function is used to do simplification of a CFG. For 1726/// example, it adjusts branches to branches to eliminate the extra hop, it 1727/// eliminates unreachable basic blocks, and does other "peephole" optimization 1728/// of the CFG. It returns true if a modification was made. 1729/// 1730/// WARNING: The entry node of a function may not be simplified. 1731/// 1732bool llvm::SimplifyCFG(BasicBlock *BB) { 1733 bool Changed = false; 1734 Function *M = BB->getParent(); 1735 1736 assert(BB && BB->getParent() && "Block not embedded in function!"); 1737 assert(BB->getTerminator() && "Degenerate basic block encountered!"); 1738 assert(&BB->getParent()->getEntryBlock() != BB && 1739 "Can't Simplify entry block!"); 1740 1741 // Remove basic blocks that have no predecessors... or that just have themself 1742 // as a predecessor. These are unreachable. 1743 if (pred_begin(BB) == pred_end(BB) || BB->getSinglePredecessor() == BB) { 1744 DOUT << "Removing BB: \n" << *BB; 1745 DeleteDeadBlock(BB); 1746 return true; 1747 } 1748 1749 // Check to see if we can constant propagate this terminator instruction 1750 // away... 1751 Changed |= ConstantFoldTerminator(BB); 1752 1753 // If there is a trivial two-entry PHI node in this basic block, and we can 1754 // eliminate it, do so now. 1755 if (PHINode *PN = dyn_cast<PHINode>(BB->begin())) 1756 if (PN->getNumIncomingValues() == 2) 1757 Changed |= FoldTwoEntryPHINode(PN); 1758 1759 // If this is a returning block with only PHI nodes in it, fold the return 1760 // instruction into any unconditional branch predecessors. 1761 // 1762 // If any predecessor is a conditional branch that just selects among 1763 // different return values, fold the replace the branch/return with a select 1764 // and return. 1765 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 1766 if (isTerminatorFirstRelevantInsn(BB, BB->getTerminator())) { 1767 // Find predecessors that end with branches. 1768 SmallVector<BasicBlock*, 8> UncondBranchPreds; 1769 SmallVector<BranchInst*, 8> CondBranchPreds; 1770 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 1771 TerminatorInst *PTI = (*PI)->getTerminator(); 1772 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) { 1773 if (BI->isUnconditional()) 1774 UncondBranchPreds.push_back(*PI); 1775 else 1776 CondBranchPreds.push_back(BI); 1777 } 1778 } 1779 1780 // If we found some, do the transformation! 1781 if (!UncondBranchPreds.empty()) { 1782 while (!UncondBranchPreds.empty()) { 1783 BasicBlock *Pred = UncondBranchPreds.back(); 1784 DOUT << "FOLDING: " << *BB 1785 << "INTO UNCOND BRANCH PRED: " << *Pred; 1786 UncondBranchPreds.pop_back(); 1787 Instruction *UncondBranch = Pred->getTerminator(); 1788 // Clone the return and add it to the end of the predecessor. 1789 Instruction *NewRet = RI->clone(); 1790 Pred->getInstList().push_back(NewRet); 1791 1792 BasicBlock::iterator BBI = RI; 1793 if (BBI != BB->begin()) { 1794 // Move region end info into the predecessor. 1795 if (DbgRegionEndInst *DREI = dyn_cast<DbgRegionEndInst>(--BBI)) 1796 DREI->moveBefore(NewRet); 1797 } 1798 1799 // If the return instruction returns a value, and if the value was a 1800 // PHI node in "BB", propagate the right value into the return. 1801 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end(); 1802 i != e; ++i) 1803 if (PHINode *PN = dyn_cast<PHINode>(*i)) 1804 if (PN->getParent() == BB) 1805 *i = PN->getIncomingValueForBlock(Pred); 1806 1807 // Update any PHI nodes in the returning block to realize that we no 1808 // longer branch to them. 1809 BB->removePredecessor(Pred); 1810 Pred->getInstList().erase(UncondBranch); 1811 } 1812 1813 // If we eliminated all predecessors of the block, delete the block now. 1814 if (pred_begin(BB) == pred_end(BB)) 1815 // We know there are no successors, so just nuke the block. 1816 M->getBasicBlockList().erase(BB); 1817 1818 return true; 1819 } 1820 1821 // Check out all of the conditional branches going to this return 1822 // instruction. If any of them just select between returns, change the 1823 // branch itself into a select/return pair. 1824 while (!CondBranchPreds.empty()) { 1825 BranchInst *BI = CondBranchPreds.back(); 1826 CondBranchPreds.pop_back(); 1827 1828 // Check to see if the non-BB successor is also a return block. 1829 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) && 1830 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) && 1831 SimplifyCondBranchToTwoReturns(BI)) 1832 return true; 1833 } 1834 } 1835 } else if (isa<UnwindInst>(BB->begin())) { 1836 // Check to see if the first instruction in this block is just an unwind. 1837 // If so, replace any invoke instructions which use this as an exception 1838 // destination with call instructions, and any unconditional branch 1839 // predecessor with an unwind. 1840 // 1841 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB)); 1842 while (!Preds.empty()) { 1843 BasicBlock *Pred = Preds.back(); 1844 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) { 1845 if (BI->isUnconditional()) { 1846 Pred->getInstList().pop_back(); // nuke uncond branch 1847 new UnwindInst(Pred); // Use unwind. 1848 Changed = true; 1849 } 1850 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator())) 1851 if (II->getUnwindDest() == BB) { 1852 // Insert a new branch instruction before the invoke, because this 1853 // is now a fall through... 1854 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II); 1855 Pred->getInstList().remove(II); // Take out of symbol table 1856 1857 // Insert the call now... 1858 SmallVector<Value*,8> Args(II->op_begin()+3, II->op_end()); 1859 CallInst *CI = CallInst::Create(II->getCalledValue(), 1860 Args.begin(), Args.end(), 1861 II->getName(), BI); 1862 CI->setCallingConv(II->getCallingConv()); 1863 CI->setAttributes(II->getAttributes()); 1864 // If the invoke produced a value, the Call now does instead 1865 II->replaceAllUsesWith(CI); 1866 delete II; 1867 Changed = true; 1868 } 1869 1870 Preds.pop_back(); 1871 } 1872 1873 // If this block is now dead, remove it. 1874 if (pred_begin(BB) == pred_end(BB)) { 1875 // We know there are no successors, so just nuke the block. 1876 M->getBasicBlockList().erase(BB); 1877 return true; 1878 } 1879 1880 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) { 1881 if (isValueEqualityComparison(SI)) { 1882 // If we only have one predecessor, and if it is a branch on this value, 1883 // see if that predecessor totally determines the outcome of this switch. 1884 if (BasicBlock *OnlyPred = BB->getSinglePredecessor()) 1885 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred)) 1886 return SimplifyCFG(BB) || 1; 1887 1888 // If the block only contains the switch, see if we can fold the block 1889 // away into any preds. 1890 if (SI == &BB->front()) 1891 if (FoldValueComparisonIntoPredecessors(SI)) 1892 return SimplifyCFG(BB) || 1; 1893 } 1894 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) { 1895 if (BI->isUnconditional()) { 1896 BasicBlock::iterator BBI = BB->getFirstNonPHI(); 1897 1898 BasicBlock *Succ = BI->getSuccessor(0); 1899 // Ignore dbg intrinsics. 1900 while (isa<DbgInfoIntrinsic>(BBI)) 1901 ++BBI; 1902 if (BBI->isTerminator() && // Terminator is the only non-phi instruction! 1903 Succ != BB) // Don't hurt infinite loops! 1904 if (TryToSimplifyUncondBranchFromEmptyBlock(BB, Succ)) 1905 return true; 1906 1907 } else { // Conditional branch 1908 if (isValueEqualityComparison(BI)) { 1909 // If we only have one predecessor, and if it is a branch on this value, 1910 // see if that predecessor totally determines the outcome of this 1911 // switch. 1912 if (BasicBlock *OnlyPred = BB->getSinglePredecessor()) 1913 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred)) 1914 return SimplifyCFG(BB) || 1; 1915 1916 // This block must be empty, except for the setcond inst, if it exists. 1917 // Ignore dbg intrinsics. 1918 BasicBlock::iterator I = BB->begin(); 1919 // Ignore dbg intrinsics. 1920 while (isa<DbgInfoIntrinsic>(I)) 1921 ++I; 1922 if (&*I == BI) { 1923 if (FoldValueComparisonIntoPredecessors(BI)) 1924 return SimplifyCFG(BB) | true; 1925 } else if (&*I == cast<Instruction>(BI->getCondition())){ 1926 ++I; 1927 // Ignore dbg intrinsics. 1928 while (isa<DbgInfoIntrinsic>(I)) 1929 ++I; 1930 if(&*I == BI) { 1931 if (FoldValueComparisonIntoPredecessors(BI)) 1932 return SimplifyCFG(BB) | true; 1933 } 1934 } 1935 } 1936 1937 // If this is a branch on a phi node in the current block, thread control 1938 // through this block if any PHI node entries are constants. 1939 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition())) 1940 if (PN->getParent() == BI->getParent()) 1941 if (FoldCondBranchOnPHI(BI)) 1942 return SimplifyCFG(BB) | true; 1943 1944 // If this basic block is ONLY a setcc and a branch, and if a predecessor 1945 // branches to us and one of our successors, fold the setcc into the 1946 // predecessor and use logical operations to pick the right destination. 1947 if (FoldBranchToCommonDest(BI)) 1948 return SimplifyCFG(BB) | 1; 1949 1950 1951 // Scan predecessor blocks for conditional branches. 1952 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) 1953 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) 1954 if (PBI != BI && PBI->isConditional()) 1955 if (SimplifyCondBranchToCondBranch(PBI, BI)) 1956 return SimplifyCFG(BB) | true; 1957 } 1958 } else if (isa<UnreachableInst>(BB->getTerminator())) { 1959 // If there are any instructions immediately before the unreachable that can 1960 // be removed, do so. 1961 Instruction *Unreachable = BB->getTerminator(); 1962 while (Unreachable != BB->begin()) { 1963 BasicBlock::iterator BBI = Unreachable; 1964 --BBI; 1965 // Do not delete instructions that can have side effects, like calls 1966 // (which may never return) and volatile loads and stores. 1967 if (isa<CallInst>(BBI)) break; 1968 1969 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) 1970 if (SI->isVolatile()) 1971 break; 1972 1973 if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) 1974 if (LI->isVolatile()) 1975 break; 1976 1977 // Delete this instruction 1978 BB->getInstList().erase(BBI); 1979 Changed = true; 1980 } 1981 1982 // If the unreachable instruction is the first in the block, take a gander 1983 // at all of the predecessors of this instruction, and simplify them. 1984 if (&BB->front() == Unreachable) { 1985 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB)); 1986 for (unsigned i = 0, e = Preds.size(); i != e; ++i) { 1987 TerminatorInst *TI = Preds[i]->getTerminator(); 1988 1989 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { 1990 if (BI->isUnconditional()) { 1991 if (BI->getSuccessor(0) == BB) { 1992 new UnreachableInst(TI); 1993 TI->eraseFromParent(); 1994 Changed = true; 1995 } 1996 } else { 1997 if (BI->getSuccessor(0) == BB) { 1998 BranchInst::Create(BI->getSuccessor(1), BI); 1999 EraseTerminatorInstAndDCECond(BI); 2000 } else if (BI->getSuccessor(1) == BB) { 2001 BranchInst::Create(BI->getSuccessor(0), BI); 2002 EraseTerminatorInstAndDCECond(BI); 2003 Changed = true; 2004 } 2005 } 2006 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 2007 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) 2008 if (SI->getSuccessor(i) == BB) { 2009 BB->removePredecessor(SI->getParent()); 2010 SI->removeCase(i); 2011 --i; --e; 2012 Changed = true; 2013 } 2014 // If the default value is unreachable, figure out the most popular 2015 // destination and make it the default. 2016 if (SI->getSuccessor(0) == BB) { 2017 std::map<BasicBlock*, unsigned> Popularity; 2018 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) 2019 Popularity[SI->getSuccessor(i)]++; 2020 2021 // Find the most popular block. 2022 unsigned MaxPop = 0; 2023 BasicBlock *MaxBlock = 0; 2024 for (std::map<BasicBlock*, unsigned>::iterator 2025 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) { 2026 if (I->second > MaxPop) { 2027 MaxPop = I->second; 2028 MaxBlock = I->first; 2029 } 2030 } 2031 if (MaxBlock) { 2032 // Make this the new default, allowing us to delete any explicit 2033 // edges to it. 2034 SI->setSuccessor(0, MaxBlock); 2035 Changed = true; 2036 2037 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from 2038 // it. 2039 if (isa<PHINode>(MaxBlock->begin())) 2040 for (unsigned i = 0; i != MaxPop-1; ++i) 2041 MaxBlock->removePredecessor(SI->getParent()); 2042 2043 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) 2044 if (SI->getSuccessor(i) == MaxBlock) { 2045 SI->removeCase(i); 2046 --i; --e; 2047 } 2048 } 2049 } 2050 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) { 2051 if (II->getUnwindDest() == BB) { 2052 // Convert the invoke to a call instruction. This would be a good 2053 // place to note that the call does not throw though. 2054 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II); 2055 II->removeFromParent(); // Take out of symbol table 2056 2057 // Insert the call now... 2058 SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end()); 2059 CallInst *CI = CallInst::Create(II->getCalledValue(), 2060 Args.begin(), Args.end(), 2061 II->getName(), BI); 2062 CI->setCallingConv(II->getCallingConv()); 2063 CI->setAttributes(II->getAttributes()); 2064 // If the invoke produced a value, the Call does now instead. 2065 II->replaceAllUsesWith(CI); 2066 delete II; 2067 Changed = true; 2068 } 2069 } 2070 } 2071 2072 // If this block is now dead, remove it. 2073 if (pred_begin(BB) == pred_end(BB)) { 2074 // We know there are no successors, so just nuke the block. 2075 M->getBasicBlockList().erase(BB); 2076 return true; 2077 } 2078 } 2079 } 2080 2081 // Merge basic blocks into their predecessor if there is only one distinct 2082 // pred, and if there is only one distinct successor of the predecessor, and 2083 // if there are no PHI nodes. 2084 // 2085 if (MergeBlockIntoPredecessor(BB)) 2086 return true; 2087 2088 // Otherwise, if this block only has a single predecessor, and if that block 2089 // is a conditional branch, see if we can hoist any code from this block up 2090 // into our predecessor. 2091 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB)); 2092 BasicBlock *OnlyPred = *PI++; 2093 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same 2094 if (*PI != OnlyPred) { 2095 OnlyPred = 0; // There are multiple different predecessors... 2096 break; 2097 } 2098 2099 if (OnlyPred) 2100 if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator())) 2101 if (BI->isConditional()) { 2102 // Get the other block. 2103 BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB); 2104 PI = pred_begin(OtherBB); 2105 ++PI; 2106 2107 if (PI == pred_end(OtherBB)) { 2108 // We have a conditional branch to two blocks that are only reachable 2109 // from the condbr. We know that the condbr dominates the two blocks, 2110 // so see if there is any identical code in the "then" and "else" 2111 // blocks. If so, we can hoist it up to the branching block. 2112 Changed |= HoistThenElseCodeToIf(BI); 2113 } else { 2114 BasicBlock* OnlySucc = NULL; 2115 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); 2116 SI != SE; ++SI) { 2117 if (!OnlySucc) 2118 OnlySucc = *SI; 2119 else if (*SI != OnlySucc) { 2120 OnlySucc = 0; // There are multiple distinct successors! 2121 break; 2122 } 2123 } 2124 2125 if (OnlySucc == OtherBB) { 2126 // If BB's only successor is the other successor of the predecessor, 2127 // i.e. a triangle, see if we can hoist any code from this block up 2128 // to the "if" block. 2129 Changed |= SpeculativelyExecuteBB(BI, BB); 2130 } 2131 } 2132 } 2133 2134 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) 2135 if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator())) 2136 // Change br (X == 0 | X == 1), T, F into a switch instruction. 2137 if (BI->isConditional() && isa<Instruction>(BI->getCondition())) { 2138 Instruction *Cond = cast<Instruction>(BI->getCondition()); 2139 // If this is a bunch of seteq's or'd together, or if it's a bunch of 2140 // 'setne's and'ed together, collect them. 2141 Value *CompVal = 0; 2142 std::vector<ConstantInt*> Values; 2143 bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values); 2144 if (CompVal && CompVal->getType()->isInteger()) { 2145 // There might be duplicate constants in the list, which the switch 2146 // instruction can't handle, remove them now. 2147 std::sort(Values.begin(), Values.end(), ConstantIntOrdering()); 2148 Values.erase(std::unique(Values.begin(), Values.end()), Values.end()); 2149 2150 // Figure out which block is which destination. 2151 BasicBlock *DefaultBB = BI->getSuccessor(1); 2152 BasicBlock *EdgeBB = BI->getSuccessor(0); 2153 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB); 2154 2155 // Create the new switch instruction now. 2156 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB, 2157 Values.size(), BI); 2158 2159 // Add all of the 'cases' to the switch instruction. 2160 for (unsigned i = 0, e = Values.size(); i != e; ++i) 2161 New->addCase(Values[i], EdgeBB); 2162 2163 // We added edges from PI to the EdgeBB. As such, if there were any 2164 // PHI nodes in EdgeBB, they need entries to be added corresponding to 2165 // the number of edges added. 2166 for (BasicBlock::iterator BBI = EdgeBB->begin(); 2167 isa<PHINode>(BBI); ++BBI) { 2168 PHINode *PN = cast<PHINode>(BBI); 2169 Value *InVal = PN->getIncomingValueForBlock(*PI); 2170 for (unsigned i = 0, e = Values.size()-1; i != e; ++i) 2171 PN->addIncoming(InVal, *PI); 2172 } 2173 2174 // Erase the old branch instruction. 2175 EraseTerminatorInstAndDCECond(BI); 2176 return true; 2177 } 2178 } 2179 2180 return Changed; 2181} 2182