IndVarSimplify.cpp revision 626f52d43df67c29b156f524551327d741ef80bf
1//===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===// 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// This transformation analyzes and transforms the induction variables (and 11// computations derived from them) into simpler forms suitable for subsequent 12// analysis and transformation. 13// 14// This transformation makes the following changes to each loop with an 15// identifiable induction variable: 16// 1. All loops are transformed to have a SINGLE canonical induction variable 17// which starts at zero and steps by one. 18// 2. The canonical induction variable is guaranteed to be the first PHI node 19// in the loop header block. 20// 3. The canonical induction variable is guaranteed to be in a wide enough 21// type so that IV expressions need not be (directly) zero-extended or 22// sign-extended. 23// 4. Any pointer arithmetic recurrences are raised to use array subscripts. 24// 25// If the trip count of a loop is computable, this pass also makes the following 26// changes: 27// 1. The exit condition for the loop is canonicalized to compare the 28// induction value against the exit value. This turns loops like: 29// 'for (i = 7; i*i < 1000; ++i)' into 'for (i = 0; i != 25; ++i)' 30// 2. Any use outside of the loop of an expression derived from the indvar 31// is changed to compute the derived value outside of the loop, eliminating 32// the dependence on the exit value of the induction variable. If the only 33// purpose of the loop is to compute the exit value of some derived 34// expression, this transformation will make the loop dead. 35// 36// This transformation should be followed by strength reduction after all of the 37// desired loop transformations have been performed. 38// 39//===----------------------------------------------------------------------===// 40 41#define DEBUG_TYPE "indvars" 42#include "llvm/Transforms/Scalar.h" 43#include "llvm/BasicBlock.h" 44#include "llvm/Constants.h" 45#include "llvm/Instructions.h" 46#include "llvm/IntrinsicInst.h" 47#include "llvm/LLVMContext.h" 48#include "llvm/Type.h" 49#include "llvm/Analysis/Dominators.h" 50#include "llvm/Analysis/IVUsers.h" 51#include "llvm/Analysis/ScalarEvolutionExpander.h" 52#include "llvm/Analysis/LoopInfo.h" 53#include "llvm/Analysis/LoopPass.h" 54#include "llvm/Support/CFG.h" 55#include "llvm/Support/CommandLine.h" 56#include "llvm/Support/Debug.h" 57#include "llvm/Support/raw_ostream.h" 58#include "llvm/Transforms/Utils/Local.h" 59#include "llvm/Transforms/Utils/BasicBlockUtils.h" 60#include "llvm/Target/TargetData.h" 61#include "llvm/ADT/DenseMap.h" 62#include "llvm/ADT/SmallVector.h" 63#include "llvm/ADT/Statistic.h" 64#include "llvm/ADT/STLExtras.h" 65using namespace llvm; 66 67STATISTIC(NumRemoved , "Number of aux indvars removed"); 68STATISTIC(NumWidened , "Number of indvars widened"); 69STATISTIC(NumInserted , "Number of canonical indvars added"); 70STATISTIC(NumReplaced , "Number of exit values replaced"); 71STATISTIC(NumLFTR , "Number of loop exit tests replaced"); 72STATISTIC(NumElimIdentity, "Number of IV identities eliminated"); 73STATISTIC(NumElimExt , "Number of IV sign/zero extends eliminated"); 74STATISTIC(NumElimRem , "Number of IV remainder operations eliminated"); 75STATISTIC(NumElimCmp , "Number of IV comparisons eliminated"); 76STATISTIC(NumElimIV , "Number of congruent IVs eliminated"); 77 78static cl::opt<bool> DisableIVRewrite( 79 "disable-iv-rewrite", cl::Hidden, 80 cl::desc("Disable canonical induction variable rewriting")); 81 82// Temporary flag for use with -disable-iv-rewrite to force a canonical IV for 83// LFTR purposes. 84static cl::opt<bool> ForceLFTR( 85 "force-lftr", cl::Hidden, 86 cl::desc("Enable forced linear function test replacement")); 87 88namespace { 89 class IndVarSimplify : public LoopPass { 90 IVUsers *IU; 91 LoopInfo *LI; 92 ScalarEvolution *SE; 93 DominatorTree *DT; 94 TargetData *TD; 95 96 SmallVector<WeakVH, 16> DeadInsts; 97 bool Changed; 98 public: 99 100 static char ID; // Pass identification, replacement for typeid 101 IndVarSimplify() : LoopPass(ID), IU(0), LI(0), SE(0), DT(0), TD(0), 102 Changed(false) { 103 initializeIndVarSimplifyPass(*PassRegistry::getPassRegistry()); 104 } 105 106 virtual bool runOnLoop(Loop *L, LPPassManager &LPM); 107 108 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 109 AU.addRequired<DominatorTree>(); 110 AU.addRequired<LoopInfo>(); 111 AU.addRequired<ScalarEvolution>(); 112 AU.addRequiredID(LoopSimplifyID); 113 AU.addRequiredID(LCSSAID); 114 if (!DisableIVRewrite) 115 AU.addRequired<IVUsers>(); 116 AU.addPreserved<ScalarEvolution>(); 117 AU.addPreservedID(LoopSimplifyID); 118 AU.addPreservedID(LCSSAID); 119 if (!DisableIVRewrite) 120 AU.addPreserved<IVUsers>(); 121 AU.setPreservesCFG(); 122 } 123 124 private: 125 virtual void releaseMemory() { 126 DeadInsts.clear(); 127 } 128 129 bool isValidRewrite(Value *FromVal, Value *ToVal); 130 131 void HandleFloatingPointIV(Loop *L, PHINode *PH); 132 void RewriteNonIntegerIVs(Loop *L); 133 134 void RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter); 135 136 void SimplifyIVUsers(SCEVExpander &Rewriter); 137 void SimplifyIVUsersNoRewrite(Loop *L, SCEVExpander &Rewriter); 138 139 bool EliminateIVUser(Instruction *UseInst, Instruction *IVOperand); 140 void EliminateIVComparison(ICmpInst *ICmp, Value *IVOperand); 141 void EliminateIVRemainder(BinaryOperator *Rem, 142 Value *IVOperand, 143 bool IsSigned); 144 145 void SimplifyCongruentIVs(Loop *L); 146 147 void RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter); 148 149 Value *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount, 150 PHINode *IndVar, SCEVExpander &Rewriter); 151 152 void SinkUnusedInvariants(Loop *L); 153 }; 154} 155 156char IndVarSimplify::ID = 0; 157INITIALIZE_PASS_BEGIN(IndVarSimplify, "indvars", 158 "Induction Variable Simplification", false, false) 159INITIALIZE_PASS_DEPENDENCY(DominatorTree) 160INITIALIZE_PASS_DEPENDENCY(LoopInfo) 161INITIALIZE_PASS_DEPENDENCY(ScalarEvolution) 162INITIALIZE_PASS_DEPENDENCY(LoopSimplify) 163INITIALIZE_PASS_DEPENDENCY(LCSSA) 164INITIALIZE_PASS_DEPENDENCY(IVUsers) 165INITIALIZE_PASS_END(IndVarSimplify, "indvars", 166 "Induction Variable Simplification", false, false) 167 168Pass *llvm::createIndVarSimplifyPass() { 169 return new IndVarSimplify(); 170} 171 172/// isValidRewrite - Return true if the SCEV expansion generated by the 173/// rewriter can replace the original value. SCEV guarantees that it 174/// produces the same value, but the way it is produced may be illegal IR. 175/// Ideally, this function will only be called for verification. 176bool IndVarSimplify::isValidRewrite(Value *FromVal, Value *ToVal) { 177 // If an SCEV expression subsumed multiple pointers, its expansion could 178 // reassociate the GEP changing the base pointer. This is illegal because the 179 // final address produced by a GEP chain must be inbounds relative to its 180 // underlying object. Otherwise basic alias analysis, among other things, 181 // could fail in a dangerous way. Ultimately, SCEV will be improved to avoid 182 // producing an expression involving multiple pointers. Until then, we must 183 // bail out here. 184 // 185 // Retrieve the pointer operand of the GEP. Don't use GetUnderlyingObject 186 // because it understands lcssa phis while SCEV does not. 187 Value *FromPtr = FromVal; 188 Value *ToPtr = ToVal; 189 if (GEPOperator *GEP = dyn_cast<GEPOperator>(FromVal)) { 190 FromPtr = GEP->getPointerOperand(); 191 } 192 if (GEPOperator *GEP = dyn_cast<GEPOperator>(ToVal)) { 193 ToPtr = GEP->getPointerOperand(); 194 } 195 if (FromPtr != FromVal || ToPtr != ToVal) { 196 // Quickly check the common case 197 if (FromPtr == ToPtr) 198 return true; 199 200 // SCEV may have rewritten an expression that produces the GEP's pointer 201 // operand. That's ok as long as the pointer operand has the same base 202 // pointer. Unlike GetUnderlyingObject(), getPointerBase() will find the 203 // base of a recurrence. This handles the case in which SCEV expansion 204 // converts a pointer type recurrence into a nonrecurrent pointer base 205 // indexed by an integer recurrence. 206 const SCEV *FromBase = SE->getPointerBase(SE->getSCEV(FromPtr)); 207 const SCEV *ToBase = SE->getPointerBase(SE->getSCEV(ToPtr)); 208 if (FromBase == ToBase) 209 return true; 210 211 DEBUG(dbgs() << "INDVARS: GEP rewrite bail out " 212 << *FromBase << " != " << *ToBase << "\n"); 213 214 return false; 215 } 216 return true; 217} 218 219/// Determine the insertion point for this user. By default, insert immediately 220/// before the user. SCEVExpander or LICM will hoist loop invariants out of the 221/// loop. For PHI nodes, there may be multiple uses, so compute the nearest 222/// common dominator for the incoming blocks. 223static Instruction *getInsertPointForUses(Instruction *User, Value *Def, 224 DominatorTree *DT) { 225 PHINode *PHI = dyn_cast<PHINode>(User); 226 if (!PHI) 227 return User; 228 229 Instruction *InsertPt = 0; 230 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) { 231 if (PHI->getIncomingValue(i) != Def) 232 continue; 233 234 BasicBlock *InsertBB = PHI->getIncomingBlock(i); 235 if (!InsertPt) { 236 InsertPt = InsertBB->getTerminator(); 237 continue; 238 } 239 InsertBB = DT->findNearestCommonDominator(InsertPt->getParent(), InsertBB); 240 InsertPt = InsertBB->getTerminator(); 241 } 242 assert(InsertPt && "Missing phi operand"); 243 assert((!isa<Instruction>(Def) || 244 DT->dominates(cast<Instruction>(Def), InsertPt)) && 245 "def does not dominate all uses"); 246 return InsertPt; 247} 248 249//===----------------------------------------------------------------------===// 250// RewriteNonIntegerIVs and helpers. Prefer integer IVs. 251//===----------------------------------------------------------------------===// 252 253/// ConvertToSInt - Convert APF to an integer, if possible. 254static bool ConvertToSInt(const APFloat &APF, int64_t &IntVal) { 255 bool isExact = false; 256 if (&APF.getSemantics() == &APFloat::PPCDoubleDouble) 257 return false; 258 // See if we can convert this to an int64_t 259 uint64_t UIntVal; 260 if (APF.convertToInteger(&UIntVal, 64, true, APFloat::rmTowardZero, 261 &isExact) != APFloat::opOK || !isExact) 262 return false; 263 IntVal = UIntVal; 264 return true; 265} 266 267/// HandleFloatingPointIV - If the loop has floating induction variable 268/// then insert corresponding integer induction variable if possible. 269/// For example, 270/// for(double i = 0; i < 10000; ++i) 271/// bar(i) 272/// is converted into 273/// for(int i = 0; i < 10000; ++i) 274/// bar((double)i); 275/// 276void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) { 277 unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0)); 278 unsigned BackEdge = IncomingEdge^1; 279 280 // Check incoming value. 281 ConstantFP *InitValueVal = 282 dyn_cast<ConstantFP>(PN->getIncomingValue(IncomingEdge)); 283 284 int64_t InitValue; 285 if (!InitValueVal || !ConvertToSInt(InitValueVal->getValueAPF(), InitValue)) 286 return; 287 288 // Check IV increment. Reject this PN if increment operation is not 289 // an add or increment value can not be represented by an integer. 290 BinaryOperator *Incr = 291 dyn_cast<BinaryOperator>(PN->getIncomingValue(BackEdge)); 292 if (Incr == 0 || Incr->getOpcode() != Instruction::FAdd) return; 293 294 // If this is not an add of the PHI with a constantfp, or if the constant fp 295 // is not an integer, bail out. 296 ConstantFP *IncValueVal = dyn_cast<ConstantFP>(Incr->getOperand(1)); 297 int64_t IncValue; 298 if (IncValueVal == 0 || Incr->getOperand(0) != PN || 299 !ConvertToSInt(IncValueVal->getValueAPF(), IncValue)) 300 return; 301 302 // Check Incr uses. One user is PN and the other user is an exit condition 303 // used by the conditional terminator. 304 Value::use_iterator IncrUse = Incr->use_begin(); 305 Instruction *U1 = cast<Instruction>(*IncrUse++); 306 if (IncrUse == Incr->use_end()) return; 307 Instruction *U2 = cast<Instruction>(*IncrUse++); 308 if (IncrUse != Incr->use_end()) return; 309 310 // Find exit condition, which is an fcmp. If it doesn't exist, or if it isn't 311 // only used by a branch, we can't transform it. 312 FCmpInst *Compare = dyn_cast<FCmpInst>(U1); 313 if (!Compare) 314 Compare = dyn_cast<FCmpInst>(U2); 315 if (Compare == 0 || !Compare->hasOneUse() || 316 !isa<BranchInst>(Compare->use_back())) 317 return; 318 319 BranchInst *TheBr = cast<BranchInst>(Compare->use_back()); 320 321 // We need to verify that the branch actually controls the iteration count 322 // of the loop. If not, the new IV can overflow and no one will notice. 323 // The branch block must be in the loop and one of the successors must be out 324 // of the loop. 325 assert(TheBr->isConditional() && "Can't use fcmp if not conditional"); 326 if (!L->contains(TheBr->getParent()) || 327 (L->contains(TheBr->getSuccessor(0)) && 328 L->contains(TheBr->getSuccessor(1)))) 329 return; 330 331 332 // If it isn't a comparison with an integer-as-fp (the exit value), we can't 333 // transform it. 334 ConstantFP *ExitValueVal = dyn_cast<ConstantFP>(Compare->getOperand(1)); 335 int64_t ExitValue; 336 if (ExitValueVal == 0 || 337 !ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue)) 338 return; 339 340 // Find new predicate for integer comparison. 341 CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE; 342 switch (Compare->getPredicate()) { 343 default: return; // Unknown comparison. 344 case CmpInst::FCMP_OEQ: 345 case CmpInst::FCMP_UEQ: NewPred = CmpInst::ICMP_EQ; break; 346 case CmpInst::FCMP_ONE: 347 case CmpInst::FCMP_UNE: NewPred = CmpInst::ICMP_NE; break; 348 case CmpInst::FCMP_OGT: 349 case CmpInst::FCMP_UGT: NewPred = CmpInst::ICMP_SGT; break; 350 case CmpInst::FCMP_OGE: 351 case CmpInst::FCMP_UGE: NewPred = CmpInst::ICMP_SGE; break; 352 case CmpInst::FCMP_OLT: 353 case CmpInst::FCMP_ULT: NewPred = CmpInst::ICMP_SLT; break; 354 case CmpInst::FCMP_OLE: 355 case CmpInst::FCMP_ULE: NewPred = CmpInst::ICMP_SLE; break; 356 } 357 358 // We convert the floating point induction variable to a signed i32 value if 359 // we can. This is only safe if the comparison will not overflow in a way 360 // that won't be trapped by the integer equivalent operations. Check for this 361 // now. 362 // TODO: We could use i64 if it is native and the range requires it. 363 364 // The start/stride/exit values must all fit in signed i32. 365 if (!isInt<32>(InitValue) || !isInt<32>(IncValue) || !isInt<32>(ExitValue)) 366 return; 367 368 // If not actually striding (add x, 0.0), avoid touching the code. 369 if (IncValue == 0) 370 return; 371 372 // Positive and negative strides have different safety conditions. 373 if (IncValue > 0) { 374 // If we have a positive stride, we require the init to be less than the 375 // exit value and an equality or less than comparison. 376 if (InitValue >= ExitValue || 377 NewPred == CmpInst::ICMP_SGT || NewPred == CmpInst::ICMP_SGE) 378 return; 379 380 uint32_t Range = uint32_t(ExitValue-InitValue); 381 if (NewPred == CmpInst::ICMP_SLE) { 382 // Normalize SLE -> SLT, check for infinite loop. 383 if (++Range == 0) return; // Range overflows. 384 } 385 386 unsigned Leftover = Range % uint32_t(IncValue); 387 388 // If this is an equality comparison, we require that the strided value 389 // exactly land on the exit value, otherwise the IV condition will wrap 390 // around and do things the fp IV wouldn't. 391 if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) && 392 Leftover != 0) 393 return; 394 395 // If the stride would wrap around the i32 before exiting, we can't 396 // transform the IV. 397 if (Leftover != 0 && int32_t(ExitValue+IncValue) < ExitValue) 398 return; 399 400 } else { 401 // If we have a negative stride, we require the init to be greater than the 402 // exit value and an equality or greater than comparison. 403 if (InitValue >= ExitValue || 404 NewPred == CmpInst::ICMP_SLT || NewPred == CmpInst::ICMP_SLE) 405 return; 406 407 uint32_t Range = uint32_t(InitValue-ExitValue); 408 if (NewPred == CmpInst::ICMP_SGE) { 409 // Normalize SGE -> SGT, check for infinite loop. 410 if (++Range == 0) return; // Range overflows. 411 } 412 413 unsigned Leftover = Range % uint32_t(-IncValue); 414 415 // If this is an equality comparison, we require that the strided value 416 // exactly land on the exit value, otherwise the IV condition will wrap 417 // around and do things the fp IV wouldn't. 418 if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) && 419 Leftover != 0) 420 return; 421 422 // If the stride would wrap around the i32 before exiting, we can't 423 // transform the IV. 424 if (Leftover != 0 && int32_t(ExitValue+IncValue) > ExitValue) 425 return; 426 } 427 428 IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext()); 429 430 // Insert new integer induction variable. 431 PHINode *NewPHI = PHINode::Create(Int32Ty, 2, PN->getName()+".int", PN); 432 NewPHI->addIncoming(ConstantInt::get(Int32Ty, InitValue), 433 PN->getIncomingBlock(IncomingEdge)); 434 435 Value *NewAdd = 436 BinaryOperator::CreateAdd(NewPHI, ConstantInt::get(Int32Ty, IncValue), 437 Incr->getName()+".int", Incr); 438 NewPHI->addIncoming(NewAdd, PN->getIncomingBlock(BackEdge)); 439 440 ICmpInst *NewCompare = new ICmpInst(TheBr, NewPred, NewAdd, 441 ConstantInt::get(Int32Ty, ExitValue), 442 Compare->getName()); 443 444 // In the following deletions, PN may become dead and may be deleted. 445 // Use a WeakVH to observe whether this happens. 446 WeakVH WeakPH = PN; 447 448 // Delete the old floating point exit comparison. The branch starts using the 449 // new comparison. 450 NewCompare->takeName(Compare); 451 Compare->replaceAllUsesWith(NewCompare); 452 RecursivelyDeleteTriviallyDeadInstructions(Compare); 453 454 // Delete the old floating point increment. 455 Incr->replaceAllUsesWith(UndefValue::get(Incr->getType())); 456 RecursivelyDeleteTriviallyDeadInstructions(Incr); 457 458 // If the FP induction variable still has uses, this is because something else 459 // in the loop uses its value. In order to canonicalize the induction 460 // variable, we chose to eliminate the IV and rewrite it in terms of an 461 // int->fp cast. 462 // 463 // We give preference to sitofp over uitofp because it is faster on most 464 // platforms. 465 if (WeakPH) { 466 Value *Conv = new SIToFPInst(NewPHI, PN->getType(), "indvar.conv", 467 PN->getParent()->getFirstNonPHI()); 468 PN->replaceAllUsesWith(Conv); 469 RecursivelyDeleteTriviallyDeadInstructions(PN); 470 } 471 472 // Add a new IVUsers entry for the newly-created integer PHI. 473 if (IU) 474 IU->AddUsersIfInteresting(NewPHI); 475} 476 477void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) { 478 // First step. Check to see if there are any floating-point recurrences. 479 // If there are, change them into integer recurrences, permitting analysis by 480 // the SCEV routines. 481 // 482 BasicBlock *Header = L->getHeader(); 483 484 SmallVector<WeakVH, 8> PHIs; 485 for (BasicBlock::iterator I = Header->begin(); 486 PHINode *PN = dyn_cast<PHINode>(I); ++I) 487 PHIs.push_back(PN); 488 489 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) 490 if (PHINode *PN = dyn_cast_or_null<PHINode>(&*PHIs[i])) 491 HandleFloatingPointIV(L, PN); 492 493 // If the loop previously had floating-point IV, ScalarEvolution 494 // may not have been able to compute a trip count. Now that we've done some 495 // re-writing, the trip count may be computable. 496 if (Changed) 497 SE->forgetLoop(L); 498} 499 500//===----------------------------------------------------------------------===// 501// RewriteLoopExitValues - Optimize IV users outside the loop. 502// As a side effect, reduces the amount of IV processing within the loop. 503//===----------------------------------------------------------------------===// 504 505/// RewriteLoopExitValues - Check to see if this loop has a computable 506/// loop-invariant execution count. If so, this means that we can compute the 507/// final value of any expressions that are recurrent in the loop, and 508/// substitute the exit values from the loop into any instructions outside of 509/// the loop that use the final values of the current expressions. 510/// 511/// This is mostly redundant with the regular IndVarSimplify activities that 512/// happen later, except that it's more powerful in some cases, because it's 513/// able to brute-force evaluate arbitrary instructions as long as they have 514/// constant operands at the beginning of the loop. 515void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) { 516 // Verify the input to the pass in already in LCSSA form. 517 assert(L->isLCSSAForm(*DT)); 518 519 SmallVector<BasicBlock*, 8> ExitBlocks; 520 L->getUniqueExitBlocks(ExitBlocks); 521 522 // Find all values that are computed inside the loop, but used outside of it. 523 // Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan 524 // the exit blocks of the loop to find them. 525 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { 526 BasicBlock *ExitBB = ExitBlocks[i]; 527 528 // If there are no PHI nodes in this exit block, then no values defined 529 // inside the loop are used on this path, skip it. 530 PHINode *PN = dyn_cast<PHINode>(ExitBB->begin()); 531 if (!PN) continue; 532 533 unsigned NumPreds = PN->getNumIncomingValues(); 534 535 // Iterate over all of the PHI nodes. 536 BasicBlock::iterator BBI = ExitBB->begin(); 537 while ((PN = dyn_cast<PHINode>(BBI++))) { 538 if (PN->use_empty()) 539 continue; // dead use, don't replace it 540 541 // SCEV only supports integer expressions for now. 542 if (!PN->getType()->isIntegerTy() && !PN->getType()->isPointerTy()) 543 continue; 544 545 // It's necessary to tell ScalarEvolution about this explicitly so that 546 // it can walk the def-use list and forget all SCEVs, as it may not be 547 // watching the PHI itself. Once the new exit value is in place, there 548 // may not be a def-use connection between the loop and every instruction 549 // which got a SCEVAddRecExpr for that loop. 550 SE->forgetValue(PN); 551 552 // Iterate over all of the values in all the PHI nodes. 553 for (unsigned i = 0; i != NumPreds; ++i) { 554 // If the value being merged in is not integer or is not defined 555 // in the loop, skip it. 556 Value *InVal = PN->getIncomingValue(i); 557 if (!isa<Instruction>(InVal)) 558 continue; 559 560 // If this pred is for a subloop, not L itself, skip it. 561 if (LI->getLoopFor(PN->getIncomingBlock(i)) != L) 562 continue; // The Block is in a subloop, skip it. 563 564 // Check that InVal is defined in the loop. 565 Instruction *Inst = cast<Instruction>(InVal); 566 if (!L->contains(Inst)) 567 continue; 568 569 // Okay, this instruction has a user outside of the current loop 570 // and varies predictably *inside* the loop. Evaluate the value it 571 // contains when the loop exits, if possible. 572 const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop()); 573 if (!SE->isLoopInvariant(ExitValue, L)) 574 continue; 575 576 Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst); 577 578 DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n' 579 << " LoopVal = " << *Inst << "\n"); 580 581 if (!isValidRewrite(Inst, ExitVal)) { 582 DeadInsts.push_back(ExitVal); 583 continue; 584 } 585 Changed = true; 586 ++NumReplaced; 587 588 PN->setIncomingValue(i, ExitVal); 589 590 // If this instruction is dead now, delete it. 591 RecursivelyDeleteTriviallyDeadInstructions(Inst); 592 593 if (NumPreds == 1) { 594 // Completely replace a single-pred PHI. This is safe, because the 595 // NewVal won't be variant in the loop, so we don't need an LCSSA phi 596 // node anymore. 597 PN->replaceAllUsesWith(ExitVal); 598 RecursivelyDeleteTriviallyDeadInstructions(PN); 599 } 600 } 601 if (NumPreds != 1) { 602 // Clone the PHI and delete the original one. This lets IVUsers and 603 // any other maps purge the original user from their records. 604 PHINode *NewPN = cast<PHINode>(PN->clone()); 605 NewPN->takeName(PN); 606 NewPN->insertBefore(PN); 607 PN->replaceAllUsesWith(NewPN); 608 PN->eraseFromParent(); 609 } 610 } 611 } 612 613 // The insertion point instruction may have been deleted; clear it out 614 // so that the rewriter doesn't trip over it later. 615 Rewriter.clearInsertPoint(); 616} 617 618//===----------------------------------------------------------------------===// 619// Rewrite IV users based on a canonical IV. 620// To be replaced by -disable-iv-rewrite. 621//===----------------------------------------------------------------------===// 622 623/// SimplifyIVUsers - Iteratively perform simplification on IVUsers within this 624/// loop. IVUsers is treated as a worklist. Each successive simplification may 625/// push more users which may themselves be candidates for simplification. 626/// 627/// This is the old approach to IV simplification to be replaced by 628/// SimplifyIVUsersNoRewrite. 629/// 630void IndVarSimplify::SimplifyIVUsers(SCEVExpander &Rewriter) { 631 // Each round of simplification involves a round of eliminating operations 632 // followed by a round of widening IVs. A single IVUsers worklist is used 633 // across all rounds. The inner loop advances the user. If widening exposes 634 // more uses, then another pass through the outer loop is triggered. 635 for (IVUsers::iterator I = IU->begin(); I != IU->end(); ++I) { 636 Instruction *UseInst = I->getUser(); 637 Value *IVOperand = I->getOperandValToReplace(); 638 639 if (ICmpInst *ICmp = dyn_cast<ICmpInst>(UseInst)) { 640 EliminateIVComparison(ICmp, IVOperand); 641 continue; 642 } 643 if (BinaryOperator *Rem = dyn_cast<BinaryOperator>(UseInst)) { 644 bool IsSigned = Rem->getOpcode() == Instruction::SRem; 645 if (IsSigned || Rem->getOpcode() == Instruction::URem) { 646 EliminateIVRemainder(Rem, IVOperand, IsSigned); 647 continue; 648 } 649 } 650 } 651} 652 653// FIXME: It is an extremely bad idea to indvar substitute anything more 654// complex than affine induction variables. Doing so will put expensive 655// polynomial evaluations inside of the loop, and the str reduction pass 656// currently can only reduce affine polynomials. For now just disable 657// indvar subst on anything more complex than an affine addrec, unless 658// it can be expanded to a trivial value. 659static bool isSafe(const SCEV *S, const Loop *L, ScalarEvolution *SE) { 660 // Loop-invariant values are safe. 661 if (SE->isLoopInvariant(S, L)) return true; 662 663 // Affine addrecs are safe. Non-affine are not, because LSR doesn't know how 664 // to transform them into efficient code. 665 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) 666 return AR->isAffine(); 667 668 // An add is safe it all its operands are safe. 669 if (const SCEVCommutativeExpr *Commutative = dyn_cast<SCEVCommutativeExpr>(S)) { 670 for (SCEVCommutativeExpr::op_iterator I = Commutative->op_begin(), 671 E = Commutative->op_end(); I != E; ++I) 672 if (!isSafe(*I, L, SE)) return false; 673 return true; 674 } 675 676 // A cast is safe if its operand is. 677 if (const SCEVCastExpr *C = dyn_cast<SCEVCastExpr>(S)) 678 return isSafe(C->getOperand(), L, SE); 679 680 // A udiv is safe if its operands are. 681 if (const SCEVUDivExpr *UD = dyn_cast<SCEVUDivExpr>(S)) 682 return isSafe(UD->getLHS(), L, SE) && 683 isSafe(UD->getRHS(), L, SE); 684 685 // SCEVUnknown is always safe. 686 if (isa<SCEVUnknown>(S)) 687 return true; 688 689 // Nothing else is safe. 690 return false; 691} 692 693void IndVarSimplify::RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter) { 694 // Rewrite all induction variable expressions in terms of the canonical 695 // induction variable. 696 // 697 // If there were induction variables of other sizes or offsets, manually 698 // add the offsets to the primary induction variable and cast, avoiding 699 // the need for the code evaluation methods to insert induction variables 700 // of different sizes. 701 for (IVUsers::iterator UI = IU->begin(), E = IU->end(); UI != E; ++UI) { 702 Value *Op = UI->getOperandValToReplace(); 703 Type *UseTy = Op->getType(); 704 Instruction *User = UI->getUser(); 705 706 // Compute the final addrec to expand into code. 707 const SCEV *AR = IU->getReplacementExpr(*UI); 708 709 // Evaluate the expression out of the loop, if possible. 710 if (!L->contains(UI->getUser())) { 711 const SCEV *ExitVal = SE->getSCEVAtScope(AR, L->getParentLoop()); 712 if (SE->isLoopInvariant(ExitVal, L)) 713 AR = ExitVal; 714 } 715 716 // FIXME: It is an extremely bad idea to indvar substitute anything more 717 // complex than affine induction variables. Doing so will put expensive 718 // polynomial evaluations inside of the loop, and the str reduction pass 719 // currently can only reduce affine polynomials. For now just disable 720 // indvar subst on anything more complex than an affine addrec, unless 721 // it can be expanded to a trivial value. 722 if (!isSafe(AR, L, SE)) 723 continue; 724 725 // Determine the insertion point for this user. By default, insert 726 // immediately before the user. The SCEVExpander class will automatically 727 // hoist loop invariants out of the loop. For PHI nodes, there may be 728 // multiple uses, so compute the nearest common dominator for the 729 // incoming blocks. 730 Instruction *InsertPt = getInsertPointForUses(User, Op, DT); 731 732 // Now expand it into actual Instructions and patch it into place. 733 Value *NewVal = Rewriter.expandCodeFor(AR, UseTy, InsertPt); 734 735 DEBUG(dbgs() << "INDVARS: Rewrote IV '" << *AR << "' " << *Op << '\n' 736 << " into = " << *NewVal << "\n"); 737 738 if (!isValidRewrite(Op, NewVal)) { 739 DeadInsts.push_back(NewVal); 740 continue; 741 } 742 // Inform ScalarEvolution that this value is changing. The change doesn't 743 // affect its value, but it does potentially affect which use lists the 744 // value will be on after the replacement, which affects ScalarEvolution's 745 // ability to walk use lists and drop dangling pointers when a value is 746 // deleted. 747 SE->forgetValue(User); 748 749 // Patch the new value into place. 750 if (Op->hasName()) 751 NewVal->takeName(Op); 752 if (Instruction *NewValI = dyn_cast<Instruction>(NewVal)) 753 NewValI->setDebugLoc(User->getDebugLoc()); 754 User->replaceUsesOfWith(Op, NewVal); 755 UI->setOperandValToReplace(NewVal); 756 757 ++NumRemoved; 758 Changed = true; 759 760 // The old value may be dead now. 761 DeadInsts.push_back(Op); 762 } 763} 764 765//===----------------------------------------------------------------------===// 766// IV Widening - Extend the width of an IV to cover its widest uses. 767//===----------------------------------------------------------------------===// 768 769namespace { 770 // Collect information about induction variables that are used by sign/zero 771 // extend operations. This information is recorded by CollectExtend and 772 // provides the input to WidenIV. 773 struct WideIVInfo { 774 Type *WidestNativeType; // Widest integer type created [sz]ext 775 bool IsSigned; // Was an sext user seen before a zext? 776 777 WideIVInfo() : WidestNativeType(0), IsSigned(false) {} 778 }; 779} 780 781/// CollectExtend - Update information about the induction variable that is 782/// extended by this sign or zero extend operation. This is used to determine 783/// the final width of the IV before actually widening it. 784static void CollectExtend(CastInst *Cast, bool IsSigned, WideIVInfo &WI, 785 ScalarEvolution *SE, const TargetData *TD) { 786 Type *Ty = Cast->getType(); 787 uint64_t Width = SE->getTypeSizeInBits(Ty); 788 if (TD && !TD->isLegalInteger(Width)) 789 return; 790 791 if (!WI.WidestNativeType) { 792 WI.WidestNativeType = SE->getEffectiveSCEVType(Ty); 793 WI.IsSigned = IsSigned; 794 return; 795 } 796 797 // We extend the IV to satisfy the sign of its first user, arbitrarily. 798 if (WI.IsSigned != IsSigned) 799 return; 800 801 if (Width > SE->getTypeSizeInBits(WI.WidestNativeType)) 802 WI.WidestNativeType = SE->getEffectiveSCEVType(Ty); 803} 804 805namespace { 806 807/// NarrowIVDefUse - Record a link in the Narrow IV def-use chain along with the 808/// WideIV that computes the same value as the Narrow IV def. This avoids 809/// caching Use* pointers. 810struct NarrowIVDefUse { 811 Instruction *NarrowDef; 812 Instruction *NarrowUse; 813 Instruction *WideDef; 814 815 NarrowIVDefUse(): NarrowDef(0), NarrowUse(0), WideDef(0) {} 816 817 NarrowIVDefUse(Instruction *ND, Instruction *NU, Instruction *WD): 818 NarrowDef(ND), NarrowUse(NU), WideDef(WD) {} 819}; 820 821/// WidenIV - The goal of this transform is to remove sign and zero extends 822/// without creating any new induction variables. To do this, it creates a new 823/// phi of the wider type and redirects all users, either removing extends or 824/// inserting truncs whenever we stop propagating the type. 825/// 826class WidenIV { 827 // Parameters 828 PHINode *OrigPhi; 829 Type *WideType; 830 bool IsSigned; 831 832 // Context 833 LoopInfo *LI; 834 Loop *L; 835 ScalarEvolution *SE; 836 DominatorTree *DT; 837 838 // Result 839 PHINode *WidePhi; 840 Instruction *WideInc; 841 const SCEV *WideIncExpr; 842 SmallVectorImpl<WeakVH> &DeadInsts; 843 844 SmallPtrSet<Instruction*,16> Widened; 845 SmallVector<NarrowIVDefUse, 8> NarrowIVUsers; 846 847public: 848 WidenIV(PHINode *PN, const WideIVInfo &WI, LoopInfo *LInfo, 849 ScalarEvolution *SEv, DominatorTree *DTree, 850 SmallVectorImpl<WeakVH> &DI) : 851 OrigPhi(PN), 852 WideType(WI.WidestNativeType), 853 IsSigned(WI.IsSigned), 854 LI(LInfo), 855 L(LI->getLoopFor(OrigPhi->getParent())), 856 SE(SEv), 857 DT(DTree), 858 WidePhi(0), 859 WideInc(0), 860 WideIncExpr(0), 861 DeadInsts(DI) { 862 assert(L->getHeader() == OrigPhi->getParent() && "Phi must be an IV"); 863 } 864 865 PHINode *CreateWideIV(SCEVExpander &Rewriter); 866 867protected: 868 Instruction *CloneIVUser(NarrowIVDefUse DU); 869 870 const SCEVAddRecExpr *GetWideRecurrence(Instruction *NarrowUse); 871 872 Instruction *WidenIVUse(NarrowIVDefUse DU); 873 874 void pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef); 875}; 876} // anonymous namespace 877 878static Value *getExtend( Value *NarrowOper, Type *WideType, 879 bool IsSigned, IRBuilder<> &Builder) { 880 return IsSigned ? Builder.CreateSExt(NarrowOper, WideType) : 881 Builder.CreateZExt(NarrowOper, WideType); 882} 883 884/// CloneIVUser - Instantiate a wide operation to replace a narrow 885/// operation. This only needs to handle operations that can evaluation to 886/// SCEVAddRec. It can safely return 0 for any operation we decide not to clone. 887Instruction *WidenIV::CloneIVUser(NarrowIVDefUse DU) { 888 unsigned Opcode = DU.NarrowUse->getOpcode(); 889 switch (Opcode) { 890 default: 891 return 0; 892 case Instruction::Add: 893 case Instruction::Mul: 894 case Instruction::UDiv: 895 case Instruction::Sub: 896 case Instruction::And: 897 case Instruction::Or: 898 case Instruction::Xor: 899 case Instruction::Shl: 900 case Instruction::LShr: 901 case Instruction::AShr: 902 DEBUG(dbgs() << "Cloning IVUser: " << *DU.NarrowUse << "\n"); 903 904 IRBuilder<> Builder(DU.NarrowUse); 905 906 // Replace NarrowDef operands with WideDef. Otherwise, we don't know 907 // anything about the narrow operand yet so must insert a [sz]ext. It is 908 // probably loop invariant and will be folded or hoisted. If it actually 909 // comes from a widened IV, it should be removed during a future call to 910 // WidenIVUse. 911 Value *LHS = (DU.NarrowUse->getOperand(0) == DU.NarrowDef) ? DU.WideDef : 912 getExtend(DU.NarrowUse->getOperand(0), WideType, IsSigned, Builder); 913 Value *RHS = (DU.NarrowUse->getOperand(1) == DU.NarrowDef) ? DU.WideDef : 914 getExtend(DU.NarrowUse->getOperand(1), WideType, IsSigned, Builder); 915 916 BinaryOperator *NarrowBO = cast<BinaryOperator>(DU.NarrowUse); 917 BinaryOperator *WideBO = BinaryOperator::Create(NarrowBO->getOpcode(), 918 LHS, RHS, 919 NarrowBO->getName()); 920 Builder.Insert(WideBO); 921 if (const OverflowingBinaryOperator *OBO = 922 dyn_cast<OverflowingBinaryOperator>(NarrowBO)) { 923 if (OBO->hasNoUnsignedWrap()) WideBO->setHasNoUnsignedWrap(); 924 if (OBO->hasNoSignedWrap()) WideBO->setHasNoSignedWrap(); 925 } 926 return WideBO; 927 } 928 llvm_unreachable(0); 929} 930 931/// HoistStep - Attempt to hoist an IV increment above a potential use. 932/// 933/// To successfully hoist, two criteria must be met: 934/// - IncV operands dominate InsertPos and 935/// - InsertPos dominates IncV 936/// 937/// Meeting the second condition means that we don't need to check all of IncV's 938/// existing uses (it's moving up in the domtree). 939/// 940/// This does not yet recursively hoist the operands, although that would 941/// not be difficult. 942static bool HoistStep(Instruction *IncV, Instruction *InsertPos, 943 const DominatorTree *DT) 944{ 945 if (DT->dominates(IncV, InsertPos)) 946 return true; 947 948 if (!DT->dominates(InsertPos->getParent(), IncV->getParent())) 949 return false; 950 951 if (IncV->mayHaveSideEffects()) 952 return false; 953 954 // Attempt to hoist IncV 955 for (User::op_iterator OI = IncV->op_begin(), OE = IncV->op_end(); 956 OI != OE; ++OI) { 957 Instruction *OInst = dyn_cast<Instruction>(OI); 958 if (OInst && !DT->dominates(OInst, InsertPos)) 959 return false; 960 } 961 IncV->moveBefore(InsertPos); 962 return true; 963} 964 965// GetWideRecurrence - Is this instruction potentially interesting from IVUsers' 966// perspective after widening it's type? In other words, can the extend be 967// safely hoisted out of the loop with SCEV reducing the value to a recurrence 968// on the same loop. If so, return the sign or zero extended 969// recurrence. Otherwise return NULL. 970const SCEVAddRecExpr *WidenIV::GetWideRecurrence(Instruction *NarrowUse) { 971 if (!SE->isSCEVable(NarrowUse->getType())) 972 return 0; 973 974 const SCEV *NarrowExpr = SE->getSCEV(NarrowUse); 975 if (SE->getTypeSizeInBits(NarrowExpr->getType()) 976 >= SE->getTypeSizeInBits(WideType)) { 977 // NarrowUse implicitly widens its operand. e.g. a gep with a narrow 978 // index. So don't follow this use. 979 return 0; 980 } 981 982 const SCEV *WideExpr = IsSigned ? 983 SE->getSignExtendExpr(NarrowExpr, WideType) : 984 SE->getZeroExtendExpr(NarrowExpr, WideType); 985 const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(WideExpr); 986 if (!AddRec || AddRec->getLoop() != L) 987 return 0; 988 989 return AddRec; 990} 991 992/// WidenIVUse - Determine whether an individual user of the narrow IV can be 993/// widened. If so, return the wide clone of the user. 994Instruction *WidenIV::WidenIVUse(NarrowIVDefUse DU) { 995 996 // Stop traversing the def-use chain at inner-loop phis or post-loop phis. 997 if (isa<PHINode>(DU.NarrowUse) && 998 LI->getLoopFor(DU.NarrowUse->getParent()) != L) 999 return 0; 1000 1001 // Our raison d'etre! Eliminate sign and zero extension. 1002 if (IsSigned ? isa<SExtInst>(DU.NarrowUse) : isa<ZExtInst>(DU.NarrowUse)) { 1003 Value *NewDef = DU.WideDef; 1004 if (DU.NarrowUse->getType() != WideType) { 1005 unsigned CastWidth = SE->getTypeSizeInBits(DU.NarrowUse->getType()); 1006 unsigned IVWidth = SE->getTypeSizeInBits(WideType); 1007 if (CastWidth < IVWidth) { 1008 // The cast isn't as wide as the IV, so insert a Trunc. 1009 IRBuilder<> Builder(DU.NarrowUse); 1010 NewDef = Builder.CreateTrunc(DU.WideDef, DU.NarrowUse->getType()); 1011 } 1012 else { 1013 // A wider extend was hidden behind a narrower one. This may induce 1014 // another round of IV widening in which the intermediate IV becomes 1015 // dead. It should be very rare. 1016 DEBUG(dbgs() << "INDVARS: New IV " << *WidePhi 1017 << " not wide enough to subsume " << *DU.NarrowUse << "\n"); 1018 DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, DU.WideDef); 1019 NewDef = DU.NarrowUse; 1020 } 1021 } 1022 if (NewDef != DU.NarrowUse) { 1023 DEBUG(dbgs() << "INDVARS: eliminating " << *DU.NarrowUse 1024 << " replaced by " << *DU.WideDef << "\n"); 1025 ++NumElimExt; 1026 DU.NarrowUse->replaceAllUsesWith(NewDef); 1027 DeadInsts.push_back(DU.NarrowUse); 1028 } 1029 // Now that the extend is gone, we want to expose it's uses for potential 1030 // further simplification. We don't need to directly inform SimplifyIVUsers 1031 // of the new users, because their parent IV will be processed later as a 1032 // new loop phi. If we preserved IVUsers analysis, we would also want to 1033 // push the uses of WideDef here. 1034 1035 // No further widening is needed. The deceased [sz]ext had done it for us. 1036 return 0; 1037 } 1038 1039 // Does this user itself evaluate to a recurrence after widening? 1040 const SCEVAddRecExpr *WideAddRec = GetWideRecurrence(DU.NarrowUse); 1041 if (!WideAddRec) { 1042 // This user does not evaluate to a recurence after widening, so don't 1043 // follow it. Instead insert a Trunc to kill off the original use, 1044 // eventually isolating the original narrow IV so it can be removed. 1045 IRBuilder<> Builder(getInsertPointForUses(DU.NarrowUse, DU.NarrowDef, DT)); 1046 Value *Trunc = Builder.CreateTrunc(DU.WideDef, DU.NarrowDef->getType()); 1047 DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, Trunc); 1048 return 0; 1049 } 1050 // Assume block terminators cannot evaluate to a recurrence. We can't to 1051 // insert a Trunc after a terminator if there happens to be a critical edge. 1052 assert(DU.NarrowUse != DU.NarrowUse->getParent()->getTerminator() && 1053 "SCEV is not expected to evaluate a block terminator"); 1054 1055 // Reuse the IV increment that SCEVExpander created as long as it dominates 1056 // NarrowUse. 1057 Instruction *WideUse = 0; 1058 if (WideAddRec == WideIncExpr && HoistStep(WideInc, DU.NarrowUse, DT)) { 1059 WideUse = WideInc; 1060 } 1061 else { 1062 WideUse = CloneIVUser(DU); 1063 if (!WideUse) 1064 return 0; 1065 } 1066 // Evaluation of WideAddRec ensured that the narrow expression could be 1067 // extended outside the loop without overflow. This suggests that the wide use 1068 // evaluates to the same expression as the extended narrow use, but doesn't 1069 // absolutely guarantee it. Hence the following failsafe check. In rare cases 1070 // where it fails, we simply throw away the newly created wide use. 1071 if (WideAddRec != SE->getSCEV(WideUse)) { 1072 DEBUG(dbgs() << "Wide use expression mismatch: " << *WideUse 1073 << ": " << *SE->getSCEV(WideUse) << " != " << *WideAddRec << "\n"); 1074 DeadInsts.push_back(WideUse); 1075 return 0; 1076 } 1077 1078 // Returning WideUse pushes it on the worklist. 1079 return WideUse; 1080} 1081 1082/// pushNarrowIVUsers - Add eligible users of NarrowDef to NarrowIVUsers. 1083/// 1084void WidenIV::pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef) { 1085 for (Value::use_iterator UI = NarrowDef->use_begin(), 1086 UE = NarrowDef->use_end(); UI != UE; ++UI) { 1087 Instruction *NarrowUse = cast<Instruction>(*UI); 1088 1089 // Handle data flow merges and bizarre phi cycles. 1090 if (!Widened.insert(NarrowUse)) 1091 continue; 1092 1093 NarrowIVUsers.push_back(NarrowIVDefUse(NarrowDef, NarrowUse, WideDef)); 1094 } 1095} 1096 1097/// CreateWideIV - Process a single induction variable. First use the 1098/// SCEVExpander to create a wide induction variable that evaluates to the same 1099/// recurrence as the original narrow IV. Then use a worklist to forward 1100/// traverse the narrow IV's def-use chain. After WidenIVUse has processed all 1101/// interesting IV users, the narrow IV will be isolated for removal by 1102/// DeleteDeadPHIs. 1103/// 1104/// It would be simpler to delete uses as they are processed, but we must avoid 1105/// invalidating SCEV expressions. 1106/// 1107PHINode *WidenIV::CreateWideIV(SCEVExpander &Rewriter) { 1108 // Is this phi an induction variable? 1109 const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(OrigPhi)); 1110 if (!AddRec) 1111 return NULL; 1112 1113 // Widen the induction variable expression. 1114 const SCEV *WideIVExpr = IsSigned ? 1115 SE->getSignExtendExpr(AddRec, WideType) : 1116 SE->getZeroExtendExpr(AddRec, WideType); 1117 1118 assert(SE->getEffectiveSCEVType(WideIVExpr->getType()) == WideType && 1119 "Expect the new IV expression to preserve its type"); 1120 1121 // Can the IV be extended outside the loop without overflow? 1122 AddRec = dyn_cast<SCEVAddRecExpr>(WideIVExpr); 1123 if (!AddRec || AddRec->getLoop() != L) 1124 return NULL; 1125 1126 // An AddRec must have loop-invariant operands. Since this AddRec is 1127 // materialized by a loop header phi, the expression cannot have any post-loop 1128 // operands, so they must dominate the loop header. 1129 assert(SE->properlyDominates(AddRec->getStart(), L->getHeader()) && 1130 SE->properlyDominates(AddRec->getStepRecurrence(*SE), L->getHeader()) 1131 && "Loop header phi recurrence inputs do not dominate the loop"); 1132 1133 // The rewriter provides a value for the desired IV expression. This may 1134 // either find an existing phi or materialize a new one. Either way, we 1135 // expect a well-formed cyclic phi-with-increments. i.e. any operand not part 1136 // of the phi-SCC dominates the loop entry. 1137 Instruction *InsertPt = L->getHeader()->begin(); 1138 WidePhi = cast<PHINode>(Rewriter.expandCodeFor(AddRec, WideType, InsertPt)); 1139 1140 // Remembering the WideIV increment generated by SCEVExpander allows 1141 // WidenIVUse to reuse it when widening the narrow IV's increment. We don't 1142 // employ a general reuse mechanism because the call above is the only call to 1143 // SCEVExpander. Henceforth, we produce 1-to-1 narrow to wide uses. 1144 if (BasicBlock *LatchBlock = L->getLoopLatch()) { 1145 WideInc = 1146 cast<Instruction>(WidePhi->getIncomingValueForBlock(LatchBlock)); 1147 WideIncExpr = SE->getSCEV(WideInc); 1148 } 1149 1150 DEBUG(dbgs() << "Wide IV: " << *WidePhi << "\n"); 1151 ++NumWidened; 1152 1153 // Traverse the def-use chain using a worklist starting at the original IV. 1154 assert(Widened.empty() && NarrowIVUsers.empty() && "expect initial state" ); 1155 1156 Widened.insert(OrigPhi); 1157 pushNarrowIVUsers(OrigPhi, WidePhi); 1158 1159 while (!NarrowIVUsers.empty()) { 1160 NarrowIVDefUse DU = NarrowIVUsers.pop_back_val(); 1161 1162 // Process a def-use edge. This may replace the use, so don't hold a 1163 // use_iterator across it. 1164 Instruction *WideUse = WidenIVUse(DU); 1165 1166 // Follow all def-use edges from the previous narrow use. 1167 if (WideUse) 1168 pushNarrowIVUsers(DU.NarrowUse, WideUse); 1169 1170 // WidenIVUse may have removed the def-use edge. 1171 if (DU.NarrowDef->use_empty()) 1172 DeadInsts.push_back(DU.NarrowDef); 1173 } 1174 return WidePhi; 1175} 1176 1177//===----------------------------------------------------------------------===// 1178// Simplification of IV users based on SCEV evaluation. 1179//===----------------------------------------------------------------------===// 1180 1181void IndVarSimplify::EliminateIVComparison(ICmpInst *ICmp, Value *IVOperand) { 1182 unsigned IVOperIdx = 0; 1183 ICmpInst::Predicate Pred = ICmp->getPredicate(); 1184 if (IVOperand != ICmp->getOperand(0)) { 1185 // Swapped 1186 assert(IVOperand == ICmp->getOperand(1) && "Can't find IVOperand"); 1187 IVOperIdx = 1; 1188 Pred = ICmpInst::getSwappedPredicate(Pred); 1189 } 1190 1191 // Get the SCEVs for the ICmp operands. 1192 const SCEV *S = SE->getSCEV(ICmp->getOperand(IVOperIdx)); 1193 const SCEV *X = SE->getSCEV(ICmp->getOperand(1 - IVOperIdx)); 1194 1195 // Simplify unnecessary loops away. 1196 const Loop *ICmpLoop = LI->getLoopFor(ICmp->getParent()); 1197 S = SE->getSCEVAtScope(S, ICmpLoop); 1198 X = SE->getSCEVAtScope(X, ICmpLoop); 1199 1200 // If the condition is always true or always false, replace it with 1201 // a constant value. 1202 if (SE->isKnownPredicate(Pred, S, X)) 1203 ICmp->replaceAllUsesWith(ConstantInt::getTrue(ICmp->getContext())); 1204 else if (SE->isKnownPredicate(ICmpInst::getInversePredicate(Pred), S, X)) 1205 ICmp->replaceAllUsesWith(ConstantInt::getFalse(ICmp->getContext())); 1206 else 1207 return; 1208 1209 DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n'); 1210 ++NumElimCmp; 1211 Changed = true; 1212 DeadInsts.push_back(ICmp); 1213} 1214 1215void IndVarSimplify::EliminateIVRemainder(BinaryOperator *Rem, 1216 Value *IVOperand, 1217 bool IsSigned) { 1218 // We're only interested in the case where we know something about 1219 // the numerator. 1220 if (IVOperand != Rem->getOperand(0)) 1221 return; 1222 1223 // Get the SCEVs for the ICmp operands. 1224 const SCEV *S = SE->getSCEV(Rem->getOperand(0)); 1225 const SCEV *X = SE->getSCEV(Rem->getOperand(1)); 1226 1227 // Simplify unnecessary loops away. 1228 const Loop *ICmpLoop = LI->getLoopFor(Rem->getParent()); 1229 S = SE->getSCEVAtScope(S, ICmpLoop); 1230 X = SE->getSCEVAtScope(X, ICmpLoop); 1231 1232 // i % n --> i if i is in [0,n). 1233 if ((!IsSigned || SE->isKnownNonNegative(S)) && 1234 SE->isKnownPredicate(IsSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, 1235 S, X)) 1236 Rem->replaceAllUsesWith(Rem->getOperand(0)); 1237 else { 1238 // (i+1) % n --> (i+1)==n?0:(i+1) if i is in [0,n). 1239 const SCEV *LessOne = 1240 SE->getMinusSCEV(S, SE->getConstant(S->getType(), 1)); 1241 if (IsSigned && !SE->isKnownNonNegative(LessOne)) 1242 return; 1243 1244 if (!SE->isKnownPredicate(IsSigned ? 1245 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, 1246 LessOne, X)) 1247 return; 1248 1249 ICmpInst *ICmp = new ICmpInst(Rem, ICmpInst::ICMP_EQ, 1250 Rem->getOperand(0), Rem->getOperand(1), 1251 "tmp"); 1252 SelectInst *Sel = 1253 SelectInst::Create(ICmp, 1254 ConstantInt::get(Rem->getType(), 0), 1255 Rem->getOperand(0), "tmp", Rem); 1256 Rem->replaceAllUsesWith(Sel); 1257 } 1258 1259 // Inform IVUsers about the new users. 1260 if (IU) { 1261 if (Instruction *I = dyn_cast<Instruction>(Rem->getOperand(0))) 1262 IU->AddUsersIfInteresting(I); 1263 } 1264 DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n'); 1265 ++NumElimRem; 1266 Changed = true; 1267 DeadInsts.push_back(Rem); 1268} 1269 1270/// EliminateIVUser - Eliminate an operation that consumes a simple IV and has 1271/// no observable side-effect given the range of IV values. 1272bool IndVarSimplify::EliminateIVUser(Instruction *UseInst, 1273 Instruction *IVOperand) { 1274 if (ICmpInst *ICmp = dyn_cast<ICmpInst>(UseInst)) { 1275 EliminateIVComparison(ICmp, IVOperand); 1276 return true; 1277 } 1278 if (BinaryOperator *Rem = dyn_cast<BinaryOperator>(UseInst)) { 1279 bool IsSigned = Rem->getOpcode() == Instruction::SRem; 1280 if (IsSigned || Rem->getOpcode() == Instruction::URem) { 1281 EliminateIVRemainder(Rem, IVOperand, IsSigned); 1282 return true; 1283 } 1284 } 1285 1286 // Eliminate any operation that SCEV can prove is an identity function. 1287 if (!SE->isSCEVable(UseInst->getType()) || 1288 (UseInst->getType() != IVOperand->getType()) || 1289 (SE->getSCEV(UseInst) != SE->getSCEV(IVOperand))) 1290 return false; 1291 1292 DEBUG(dbgs() << "INDVARS: Eliminated identity: " << *UseInst << '\n'); 1293 1294 UseInst->replaceAllUsesWith(IVOperand); 1295 ++NumElimIdentity; 1296 Changed = true; 1297 DeadInsts.push_back(UseInst); 1298 return true; 1299} 1300 1301/// pushIVUsers - Add all uses of Def to the current IV's worklist. 1302/// 1303static void pushIVUsers( 1304 Instruction *Def, 1305 SmallPtrSet<Instruction*,16> &Simplified, 1306 SmallVectorImpl< std::pair<Instruction*,Instruction*> > &SimpleIVUsers) { 1307 1308 for (Value::use_iterator UI = Def->use_begin(), E = Def->use_end(); 1309 UI != E; ++UI) { 1310 Instruction *User = cast<Instruction>(*UI); 1311 1312 // Avoid infinite or exponential worklist processing. 1313 // Also ensure unique worklist users. 1314 // If Def is a LoopPhi, it may not be in the Simplified set, so check for 1315 // self edges first. 1316 if (User != Def && Simplified.insert(User)) 1317 SimpleIVUsers.push_back(std::make_pair(User, Def)); 1318 } 1319} 1320 1321/// isSimpleIVUser - Return true if this instruction generates a simple SCEV 1322/// expression in terms of that IV. 1323/// 1324/// This is similar to IVUsers' isInsteresting() but processes each instruction 1325/// non-recursively when the operand is already known to be a simpleIVUser. 1326/// 1327static bool isSimpleIVUser(Instruction *I, const Loop *L, ScalarEvolution *SE) { 1328 if (!SE->isSCEVable(I->getType())) 1329 return false; 1330 1331 // Get the symbolic expression for this instruction. 1332 const SCEV *S = SE->getSCEV(I); 1333 1334 // Only consider affine recurrences. 1335 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S); 1336 if (AR && AR->getLoop() == L) 1337 return true; 1338 1339 return false; 1340} 1341 1342/// SimplifyIVUsersNoRewrite - Iteratively perform simplification on a worklist 1343/// of IV users. Each successive simplification may push more users which may 1344/// themselves be candidates for simplification. 1345/// 1346/// The "NoRewrite" algorithm does not require IVUsers analysis. Instead, it 1347/// simplifies instructions in-place during analysis. Rather than rewriting 1348/// induction variables bottom-up from their users, it transforms a chain of 1349/// IVUsers top-down, updating the IR only when it encouters a clear 1350/// optimization opportunitiy. A SCEVExpander "Rewriter" instance is still 1351/// needed, but only used to generate a new IV (phi) of wider type for sign/zero 1352/// extend elimination. 1353/// 1354/// Once DisableIVRewrite is default, LSR will be the only client of IVUsers. 1355/// 1356void IndVarSimplify::SimplifyIVUsersNoRewrite(Loop *L, SCEVExpander &Rewriter) { 1357 std::map<PHINode *, WideIVInfo> WideIVMap; 1358 1359 SmallVector<PHINode*, 8> LoopPhis; 1360 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) { 1361 LoopPhis.push_back(cast<PHINode>(I)); 1362 } 1363 // Each round of simplification iterates through the SimplifyIVUsers worklist 1364 // for all current phis, then determines whether any IVs can be 1365 // widened. Widening adds new phis to LoopPhis, inducing another round of 1366 // simplification on the wide IVs. 1367 while (!LoopPhis.empty()) { 1368 // Evaluate as many IV expressions as possible before widening any IVs. This 1369 // forces SCEV to set no-wrap flags before evaluating sign/zero 1370 // extension. The first time SCEV attempts to normalize sign/zero extension, 1371 // the result becomes final. So for the most predictable results, we delay 1372 // evaluation of sign/zero extend evaluation until needed, and avoid running 1373 // other SCEV based analysis prior to SimplifyIVUsersNoRewrite. 1374 do { 1375 PHINode *CurrIV = LoopPhis.pop_back_val(); 1376 1377 // Information about sign/zero extensions of CurrIV. 1378 WideIVInfo WI; 1379 1380 // Instructions processed by SimplifyIVUsers for CurrIV. 1381 SmallPtrSet<Instruction*,16> Simplified; 1382 1383 // Use-def pairs if IV users waiting to be processed for CurrIV. 1384 SmallVector<std::pair<Instruction*, Instruction*>, 8> SimpleIVUsers; 1385 1386 // Push users of the current LoopPhi. In rare cases, pushIVUsers may be 1387 // called multiple times for the same LoopPhi. This is the proper thing to 1388 // do for loop header phis that use each other. 1389 pushIVUsers(CurrIV, Simplified, SimpleIVUsers); 1390 1391 while (!SimpleIVUsers.empty()) { 1392 Instruction *UseInst, *Operand; 1393 tie(UseInst, Operand) = SimpleIVUsers.pop_back_val(); 1394 // Bypass back edges to avoid extra work. 1395 if (UseInst == CurrIV) continue; 1396 1397 if (EliminateIVUser(UseInst, Operand)) { 1398 pushIVUsers(Operand, Simplified, SimpleIVUsers); 1399 continue; 1400 } 1401 if (CastInst *Cast = dyn_cast<CastInst>(UseInst)) { 1402 bool IsSigned = Cast->getOpcode() == Instruction::SExt; 1403 if (IsSigned || Cast->getOpcode() == Instruction::ZExt) { 1404 CollectExtend(Cast, IsSigned, WI, SE, TD); 1405 } 1406 continue; 1407 } 1408 if (isSimpleIVUser(UseInst, L, SE)) { 1409 pushIVUsers(UseInst, Simplified, SimpleIVUsers); 1410 } 1411 } 1412 if (WI.WidestNativeType) { 1413 WideIVMap[CurrIV] = WI; 1414 } 1415 } while(!LoopPhis.empty()); 1416 1417 for (std::map<PHINode *, WideIVInfo>::const_iterator I = WideIVMap.begin(), 1418 E = WideIVMap.end(); I != E; ++I) { 1419 WidenIV Widener(I->first, I->second, LI, SE, DT, DeadInsts); 1420 if (PHINode *WidePhi = Widener.CreateWideIV(Rewriter)) { 1421 Changed = true; 1422 LoopPhis.push_back(WidePhi); 1423 } 1424 } 1425 WideIVMap.clear(); 1426 } 1427} 1428 1429/// SimplifyCongruentIVs - Check for congruent phis in this loop header and 1430/// populate ExprToIVMap for use later. 1431/// 1432void IndVarSimplify::SimplifyCongruentIVs(Loop *L) { 1433 DenseMap<const SCEV *, PHINode *> ExprToIVMap; 1434 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) { 1435 PHINode *Phi = cast<PHINode>(I); 1436 if (!SE->isSCEVable(Phi->getType())) 1437 continue; 1438 1439 const SCEV *S = SE->getSCEV(Phi); 1440 DenseMap<const SCEV *, PHINode *>::const_iterator Pos; 1441 bool Inserted; 1442 tie(Pos, Inserted) = ExprToIVMap.insert(std::make_pair(S, Phi)); 1443 if (Inserted) 1444 continue; 1445 PHINode *OrigPhi = Pos->second; 1446 1447 // If one phi derives from the other via GEPs, types may differ. 1448 if (OrigPhi->getType() != Phi->getType()) 1449 continue; 1450 1451 // Replacing the congruent phi is sufficient because acyclic redundancy 1452 // elimination, CSE/GVN, should handle the rest. However, once SCEV proves 1453 // that a phi is congruent, it's almost certain to be the head of an IV 1454 // user cycle that is isomorphic with the original phi. So it's worth 1455 // eagerly cleaning up the common case of a single IV increment. 1456 if (BasicBlock *LatchBlock = L->getLoopLatch()) { 1457 Instruction *OrigInc = 1458 cast<Instruction>(OrigPhi->getIncomingValueForBlock(LatchBlock)); 1459 Instruction *IsomorphicInc = 1460 cast<Instruction>(Phi->getIncomingValueForBlock(LatchBlock)); 1461 if (OrigInc != IsomorphicInc && 1462 OrigInc->getType() == IsomorphicInc->getType() && 1463 SE->getSCEV(OrigInc) == SE->getSCEV(IsomorphicInc) && 1464 HoistStep(OrigInc, IsomorphicInc, DT)) { 1465 DEBUG(dbgs() << "INDVARS: Eliminated congruent iv.inc: " 1466 << *IsomorphicInc << '\n'); 1467 IsomorphicInc->replaceAllUsesWith(OrigInc); 1468 DeadInsts.push_back(IsomorphicInc); 1469 } 1470 } 1471 DEBUG(dbgs() << "INDVARS: Eliminated congruent iv: " << *Phi << '\n'); 1472 ++NumElimIV; 1473 Phi->replaceAllUsesWith(OrigPhi); 1474 DeadInsts.push_back(Phi); 1475 } 1476} 1477 1478//===----------------------------------------------------------------------===// 1479// LinearFunctionTestReplace and its kin. Rewrite the loop exit condition. 1480//===----------------------------------------------------------------------===// 1481 1482// Check for expressions that ScalarEvolution generates to compute 1483// BackedgeTakenInfo. If these expressions have not been reduced, then expanding 1484// them may incur additional cost (albeit in the loop preheader). 1485static bool isHighCostExpansion(const SCEV *S, BranchInst *BI, 1486 ScalarEvolution *SE) { 1487 // If the backedge-taken count is a UDiv, it's very likely a UDiv that 1488 // ScalarEvolution's HowFarToZero or HowManyLessThans produced to compute a 1489 // precise expression, rather than a UDiv from the user's code. If we can't 1490 // find a UDiv in the code with some simple searching, assume the former and 1491 // forego rewriting the loop. 1492 if (isa<SCEVUDivExpr>(S)) { 1493 ICmpInst *OrigCond = dyn_cast<ICmpInst>(BI->getCondition()); 1494 if (!OrigCond) return true; 1495 const SCEV *R = SE->getSCEV(OrigCond->getOperand(1)); 1496 R = SE->getMinusSCEV(R, SE->getConstant(R->getType(), 1)); 1497 if (R != S) { 1498 const SCEV *L = SE->getSCEV(OrigCond->getOperand(0)); 1499 L = SE->getMinusSCEV(L, SE->getConstant(L->getType(), 1)); 1500 if (L != S) 1501 return true; 1502 } 1503 } 1504 1505 if (!DisableIVRewrite || ForceLFTR) 1506 return false; 1507 1508 // Recurse past add expressions, which commonly occur in the 1509 // BackedgeTakenCount. They may already exist in program code, and if not, 1510 // they are not too expensive rematerialize. 1511 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) { 1512 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end(); 1513 I != E; ++I) { 1514 if (isHighCostExpansion(*I, BI, SE)) 1515 return true; 1516 } 1517 return false; 1518 } 1519 1520 // HowManyLessThans uses a Max expression whenever the loop is not guarded by 1521 // the exit condition. 1522 if (isa<SCEVSMaxExpr>(S) || isa<SCEVUMaxExpr>(S)) 1523 return true; 1524 1525 // If we haven't recognized an expensive SCEV patter, assume its an expression 1526 // produced by program code. 1527 return false; 1528} 1529 1530/// canExpandBackedgeTakenCount - Return true if this loop's backedge taken 1531/// count expression can be safely and cheaply expanded into an instruction 1532/// sequence that can be used by LinearFunctionTestReplace. 1533static bool canExpandBackedgeTakenCount(Loop *L, ScalarEvolution *SE) { 1534 const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L); 1535 if (isa<SCEVCouldNotCompute>(BackedgeTakenCount) || 1536 BackedgeTakenCount->isZero()) 1537 return false; 1538 1539 if (!L->getExitingBlock()) 1540 return false; 1541 1542 // Can't rewrite non-branch yet. 1543 BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator()); 1544 if (!BI) 1545 return false; 1546 1547 if (isHighCostExpansion(BackedgeTakenCount, BI, SE)) 1548 return false; 1549 1550 return true; 1551} 1552 1553/// getBackedgeIVType - Get the widest type used by the loop test after peeking 1554/// through Truncs. 1555/// 1556/// TODO: Unnecessary when ForceLFTR is removed. 1557static Type *getBackedgeIVType(Loop *L) { 1558 if (!L->getExitingBlock()) 1559 return 0; 1560 1561 // Can't rewrite non-branch yet. 1562 BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator()); 1563 if (!BI) 1564 return 0; 1565 1566 ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition()); 1567 if (!Cond) 1568 return 0; 1569 1570 Type *Ty = 0; 1571 for(User::op_iterator OI = Cond->op_begin(), OE = Cond->op_end(); 1572 OI != OE; ++OI) { 1573 assert((!Ty || Ty == (*OI)->getType()) && "bad icmp operand types"); 1574 TruncInst *Trunc = dyn_cast<TruncInst>(*OI); 1575 if (!Trunc) 1576 continue; 1577 1578 return Trunc->getSrcTy(); 1579 } 1580 return Ty; 1581} 1582 1583/// isLoopInvariant - Perform a quick domtree based check for loop invariance 1584/// assuming that V is used within the loop. LoopInfo::isLoopInvariant() seems 1585/// gratuitous for this purpose. 1586static bool isLoopInvariant(Value *V, Loop *L, DominatorTree *DT) { 1587 Instruction *Inst = dyn_cast<Instruction>(V); 1588 if (!Inst) 1589 return true; 1590 1591 return DT->properlyDominates(Inst->getParent(), L->getHeader()); 1592} 1593 1594/// getLoopPhiForCounter - Return the loop header phi IFF IncV adds a loop 1595/// invariant value to the phi. 1596static PHINode *getLoopPhiForCounter(Value *IncV, Loop *L, DominatorTree *DT) { 1597 Instruction *IncI = dyn_cast<Instruction>(IncV); 1598 if (!IncI) 1599 return 0; 1600 1601 switch (IncI->getOpcode()) { 1602 case Instruction::Add: 1603 case Instruction::Sub: 1604 break; 1605 case Instruction::GetElementPtr: 1606 // An IV counter must preserve its type. 1607 if (IncI->getNumOperands() == 2) 1608 break; 1609 default: 1610 return 0; 1611 } 1612 1613 PHINode *Phi = dyn_cast<PHINode>(IncI->getOperand(0)); 1614 if (Phi && Phi->getParent() == L->getHeader()) { 1615 if (isLoopInvariant(IncI->getOperand(1), L, DT)) 1616 return Phi; 1617 return 0; 1618 } 1619 if (IncI->getOpcode() == Instruction::GetElementPtr) 1620 return 0; 1621 1622 // Allow add/sub to be commuted. 1623 Phi = dyn_cast<PHINode>(IncI->getOperand(1)); 1624 if (Phi && Phi->getParent() == L->getHeader()) { 1625 if (isLoopInvariant(IncI->getOperand(0), L, DT)) 1626 return Phi; 1627 } 1628 return 0; 1629} 1630 1631/// needsLFTR - LinearFunctionTestReplace policy. Return true unless we can show 1632/// that the current exit test is already sufficiently canonical. 1633static bool needsLFTR(Loop *L, DominatorTree *DT) { 1634 assert(L->getExitingBlock() && "expected loop exit"); 1635 1636 BasicBlock *LatchBlock = L->getLoopLatch(); 1637 // Don't bother with LFTR if the loop is not properly simplified. 1638 if (!LatchBlock) 1639 return false; 1640 1641 BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator()); 1642 assert(BI && "expected exit branch"); 1643 1644 // Do LFTR to simplify the exit condition to an ICMP. 1645 ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition()); 1646 if (!Cond) 1647 return true; 1648 1649 // Do LFTR to simplify the exit ICMP to EQ/NE 1650 ICmpInst::Predicate Pred = Cond->getPredicate(); 1651 if (Pred != ICmpInst::ICMP_NE && Pred != ICmpInst::ICMP_EQ) 1652 return true; 1653 1654 // Look for a loop invariant RHS 1655 Value *LHS = Cond->getOperand(0); 1656 Value *RHS = Cond->getOperand(1); 1657 if (!isLoopInvariant(RHS, L, DT)) { 1658 if (!isLoopInvariant(LHS, L, DT)) 1659 return true; 1660 std::swap(LHS, RHS); 1661 } 1662 // Look for a simple IV counter LHS 1663 PHINode *Phi = dyn_cast<PHINode>(LHS); 1664 if (!Phi) 1665 Phi = getLoopPhiForCounter(LHS, L, DT); 1666 1667 if (!Phi) 1668 return true; 1669 1670 // Do LFTR if the exit condition's IV is *not* a simple counter. 1671 Value *IncV = Phi->getIncomingValueForBlock(L->getLoopLatch()); 1672 return Phi != getLoopPhiForCounter(IncV, L, DT); 1673} 1674 1675/// AlmostDeadIV - Return true if this IV has any uses other than the (soon to 1676/// be rewritten) loop exit test. 1677static bool AlmostDeadIV(PHINode *Phi, BasicBlock *LatchBlock, Value *Cond) { 1678 int LatchIdx = Phi->getBasicBlockIndex(LatchBlock); 1679 Value *IncV = Phi->getIncomingValue(LatchIdx); 1680 1681 for (Value::use_iterator UI = Phi->use_begin(), UE = Phi->use_end(); 1682 UI != UE; ++UI) { 1683 if (*UI != Cond && *UI != IncV) return false; 1684 } 1685 1686 for (Value::use_iterator UI = IncV->use_begin(), UE = IncV->use_end(); 1687 UI != UE; ++UI) { 1688 if (*UI != Cond && *UI != Phi) return false; 1689 } 1690 return true; 1691} 1692 1693/// FindLoopCounter - Find an affine IV in canonical form. 1694/// 1695/// FIXME: Accept -1 stride and set IVLimit = IVInit - BECount 1696/// 1697/// FIXME: Accept non-unit stride as long as SCEV can reduce BECount * Stride. 1698/// This is difficult in general for SCEV because of potential overflow. But we 1699/// could at least handle constant BECounts. 1700static PHINode * 1701FindLoopCounter(Loop *L, const SCEV *BECount, 1702 ScalarEvolution *SE, DominatorTree *DT, const TargetData *TD) { 1703 // I'm not sure how BECount could be a pointer type, but we definitely don't 1704 // want to LFTR that. 1705 if (BECount->getType()->isPointerTy()) 1706 return 0; 1707 1708 uint64_t BCWidth = SE->getTypeSizeInBits(BECount->getType()); 1709 1710 Value *Cond = 1711 cast<BranchInst>(L->getExitingBlock()->getTerminator())->getCondition(); 1712 1713 // Loop over all of the PHI nodes, looking for a simple counter. 1714 PHINode *BestPhi = 0; 1715 const SCEV *BestInit = 0; 1716 BasicBlock *LatchBlock = L->getLoopLatch(); 1717 assert(LatchBlock && "needsLFTR should guarantee a loop latch"); 1718 1719 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) { 1720 PHINode *Phi = cast<PHINode>(I); 1721 if (!SE->isSCEVable(Phi->getType())) 1722 continue; 1723 1724 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Phi)); 1725 if (!AR || AR->getLoop() != L || !AR->isAffine()) 1726 continue; 1727 1728 // AR may be a pointer type, while BECount is an integer type. 1729 // AR may be wider than BECount. With eq/ne tests overflow is immaterial. 1730 // AR may not be a narrower type, or we may never exit. 1731 uint64_t PhiWidth = SE->getTypeSizeInBits(AR->getType()); 1732 if (PhiWidth < BCWidth || (TD && !TD->isLegalInteger(PhiWidth))) 1733 continue; 1734 1735 const SCEV *Step = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*SE)); 1736 if (!Step || !Step->isOne()) 1737 continue; 1738 1739 int LatchIdx = Phi->getBasicBlockIndex(LatchBlock); 1740 Value *IncV = Phi->getIncomingValue(LatchIdx); 1741 if (getLoopPhiForCounter(IncV, L, DT) != Phi) 1742 continue; 1743 1744 const SCEV *Init = AR->getStart(); 1745 1746 if (BestPhi && !AlmostDeadIV(BestPhi, LatchBlock, Cond)) { 1747 // Don't force a live loop counter if another IV can be used. 1748 if (AlmostDeadIV(Phi, LatchBlock, Cond)) 1749 continue; 1750 1751 // Prefer to count-from-zero. This is a more "canonical" counter form. It 1752 // also prefers integer to pointer IVs. 1753 if (BestInit->isZero() != Init->isZero()) { 1754 if (BestInit->isZero()) 1755 continue; 1756 } 1757 // If two IVs both count from zero or both count from nonzero then the 1758 // narrower is likely a dead phi that has been widened. Use the wider phi 1759 // to allow the other to be eliminated. 1760 if (PhiWidth <= SE->getTypeSizeInBits(BestPhi->getType())) 1761 continue; 1762 } 1763 BestPhi = Phi; 1764 BestInit = Init; 1765 } 1766 return BestPhi; 1767} 1768 1769/// LinearFunctionTestReplace - This method rewrites the exit condition of the 1770/// loop to be a canonical != comparison against the incremented loop induction 1771/// variable. This pass is able to rewrite the exit tests of any loop where the 1772/// SCEV analysis can determine a loop-invariant trip count of the loop, which 1773/// is actually a much broader range than just linear tests. 1774Value *IndVarSimplify:: 1775LinearFunctionTestReplace(Loop *L, 1776 const SCEV *BackedgeTakenCount, 1777 PHINode *IndVar, 1778 SCEVExpander &Rewriter) { 1779 assert(canExpandBackedgeTakenCount(L, SE) && "precondition"); 1780 BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator()); 1781 1782 // In DisableIVRewrite mode, IndVar is not necessarily a canonical IV. In this 1783 // mode, LFTR can ignore IV overflow and truncate to the width of 1784 // BECount. This avoids materializing the add(zext(add)) expression. 1785 Type *CntTy = DisableIVRewrite ? 1786 BackedgeTakenCount->getType() : IndVar->getType(); 1787 1788 const SCEV *IVLimit = BackedgeTakenCount; 1789 1790 // If the exiting block is not the same as the backedge block, we must compare 1791 // against the preincremented value, otherwise we prefer to compare against 1792 // the post-incremented value. 1793 Value *CmpIndVar; 1794 if (L->getExitingBlock() == L->getLoopLatch()) { 1795 // Add one to the "backedge-taken" count to get the trip count. 1796 // If this addition may overflow, we have to be more pessimistic and 1797 // cast the induction variable before doing the add. 1798 const SCEV *N = 1799 SE->getAddExpr(IVLimit, SE->getConstant(IVLimit->getType(), 1)); 1800 if (CntTy == IVLimit->getType()) 1801 IVLimit = N; 1802 else { 1803 const SCEV *Zero = SE->getConstant(IVLimit->getType(), 0); 1804 if ((isa<SCEVConstant>(N) && !N->isZero()) || 1805 SE->isLoopEntryGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) { 1806 // No overflow. Cast the sum. 1807 IVLimit = SE->getTruncateOrZeroExtend(N, CntTy); 1808 } else { 1809 // Potential overflow. Cast before doing the add. 1810 IVLimit = SE->getTruncateOrZeroExtend(IVLimit, CntTy); 1811 IVLimit = SE->getAddExpr(IVLimit, SE->getConstant(CntTy, 1)); 1812 } 1813 } 1814 // The BackedgeTaken expression contains the number of times that the 1815 // backedge branches to the loop header. This is one less than the 1816 // number of times the loop executes, so use the incremented indvar. 1817 CmpIndVar = IndVar->getIncomingValueForBlock(L->getExitingBlock()); 1818 } else { 1819 // We have to use the preincremented value... 1820 IVLimit = SE->getTruncateOrZeroExtend(IVLimit, CntTy); 1821 CmpIndVar = IndVar; 1822 } 1823 1824 // For unit stride, IVLimit = Start + BECount with 2's complement overflow. 1825 // So for, non-zero start compute the IVLimit here. 1826 bool isPtrIV = false; 1827 Type *CmpTy = CntTy; 1828 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(IndVar)); 1829 assert(AR && AR->getLoop() == L && AR->isAffine() && "bad loop counter"); 1830 if (!AR->getStart()->isZero()) { 1831 assert(AR->getStepRecurrence(*SE)->isOne() && "only handles unit stride"); 1832 const SCEV *IVInit = AR->getStart(); 1833 1834 // For pointer types, sign extend BECount in order to materialize a GEP. 1835 // Note that for DisableIVRewrite, we never run SCEVExpander on a 1836 // pointer type, because we must preserve the existing GEPs. Instead we 1837 // directly generate a GEP later. 1838 if (IVInit->getType()->isPointerTy()) { 1839 isPtrIV = true; 1840 CmpTy = SE->getEffectiveSCEVType(IVInit->getType()); 1841 IVLimit = SE->getTruncateOrSignExtend(IVLimit, CmpTy); 1842 } 1843 // For integer types, truncate the IV before computing IVInit + BECount. 1844 else { 1845 if (SE->getTypeSizeInBits(IVInit->getType()) 1846 > SE->getTypeSizeInBits(CmpTy)) 1847 IVInit = SE->getTruncateExpr(IVInit, CmpTy); 1848 1849 IVLimit = SE->getAddExpr(IVInit, IVLimit); 1850 } 1851 } 1852 // Expand the code for the iteration count. 1853 IRBuilder<> Builder(BI); 1854 1855 assert(SE->isLoopInvariant(IVLimit, L) && 1856 "Computed iteration count is not loop invariant!"); 1857 Value *ExitCnt = Rewriter.expandCodeFor(IVLimit, CmpTy, BI); 1858 1859 // Create a gep for IVInit + IVLimit from on an existing pointer base. 1860 assert(isPtrIV == IndVar->getType()->isPointerTy() && 1861 "IndVar type must match IVInit type"); 1862 if (isPtrIV) { 1863 Value *IVStart = IndVar->getIncomingValueForBlock(L->getLoopPreheader()); 1864 assert(AR->getStart() == SE->getSCEV(IVStart) && "bad loop counter"); 1865 assert(SE->getSizeOfExpr( 1866 cast<PointerType>(IVStart->getType())->getElementType())->isOne() 1867 && "unit stride pointer IV must be i8*"); 1868 1869 Builder.SetInsertPoint(L->getLoopPreheader()->getTerminator()); 1870 ExitCnt = Builder.CreateGEP(IVStart, ExitCnt, "lftr.limit"); 1871 Builder.SetInsertPoint(BI); 1872 } 1873 1874 // Insert a new icmp_ne or icmp_eq instruction before the branch. 1875 ICmpInst::Predicate P; 1876 if (L->contains(BI->getSuccessor(0))) 1877 P = ICmpInst::ICMP_NE; 1878 else 1879 P = ICmpInst::ICMP_EQ; 1880 1881 DEBUG(dbgs() << "INDVARS: Rewriting loop exit condition to:\n" 1882 << " LHS:" << *CmpIndVar << '\n' 1883 << " op:\t" 1884 << (P == ICmpInst::ICMP_NE ? "!=" : "==") << "\n" 1885 << " RHS:\t" << *ExitCnt << "\n" 1886 << " Expr:\t" << *IVLimit << "\n"); 1887 1888 if (SE->getTypeSizeInBits(CmpIndVar->getType()) 1889 > SE->getTypeSizeInBits(CmpTy)) { 1890 CmpIndVar = Builder.CreateTrunc(CmpIndVar, CmpTy, "lftr.wideiv"); 1891 } 1892 1893 Value *Cond = Builder.CreateICmp(P, CmpIndVar, ExitCnt, "exitcond"); 1894 Value *OrigCond = BI->getCondition(); 1895 // It's tempting to use replaceAllUsesWith here to fully replace the old 1896 // comparison, but that's not immediately safe, since users of the old 1897 // comparison may not be dominated by the new comparison. Instead, just 1898 // update the branch to use the new comparison; in the common case this 1899 // will make old comparison dead. 1900 BI->setCondition(Cond); 1901 DeadInsts.push_back(OrigCond); 1902 1903 ++NumLFTR; 1904 Changed = true; 1905 return Cond; 1906} 1907 1908//===----------------------------------------------------------------------===// 1909// SinkUnusedInvariants. A late subpass to cleanup loop preheaders. 1910//===----------------------------------------------------------------------===// 1911 1912/// If there's a single exit block, sink any loop-invariant values that 1913/// were defined in the preheader but not used inside the loop into the 1914/// exit block to reduce register pressure in the loop. 1915void IndVarSimplify::SinkUnusedInvariants(Loop *L) { 1916 BasicBlock *ExitBlock = L->getExitBlock(); 1917 if (!ExitBlock) return; 1918 1919 BasicBlock *Preheader = L->getLoopPreheader(); 1920 if (!Preheader) return; 1921 1922 Instruction *InsertPt = ExitBlock->getFirstNonPHI(); 1923 BasicBlock::iterator I = Preheader->getTerminator(); 1924 while (I != Preheader->begin()) { 1925 --I; 1926 // New instructions were inserted at the end of the preheader. 1927 if (isa<PHINode>(I)) 1928 break; 1929 1930 // Don't move instructions which might have side effects, since the side 1931 // effects need to complete before instructions inside the loop. Also don't 1932 // move instructions which might read memory, since the loop may modify 1933 // memory. Note that it's okay if the instruction might have undefined 1934 // behavior: LoopSimplify guarantees that the preheader dominates the exit 1935 // block. 1936 if (I->mayHaveSideEffects() || I->mayReadFromMemory()) 1937 continue; 1938 1939 // Skip debug info intrinsics. 1940 if (isa<DbgInfoIntrinsic>(I)) 1941 continue; 1942 1943 // Don't sink static AllocaInsts out of the entry block, which would 1944 // turn them into dynamic allocas! 1945 if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) 1946 if (AI->isStaticAlloca()) 1947 continue; 1948 1949 // Determine if there is a use in or before the loop (direct or 1950 // otherwise). 1951 bool UsedInLoop = false; 1952 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end(); 1953 UI != UE; ++UI) { 1954 User *U = *UI; 1955 BasicBlock *UseBB = cast<Instruction>(U)->getParent(); 1956 if (PHINode *P = dyn_cast<PHINode>(U)) { 1957 unsigned i = 1958 PHINode::getIncomingValueNumForOperand(UI.getOperandNo()); 1959 UseBB = P->getIncomingBlock(i); 1960 } 1961 if (UseBB == Preheader || L->contains(UseBB)) { 1962 UsedInLoop = true; 1963 break; 1964 } 1965 } 1966 1967 // If there is, the def must remain in the preheader. 1968 if (UsedInLoop) 1969 continue; 1970 1971 // Otherwise, sink it to the exit block. 1972 Instruction *ToMove = I; 1973 bool Done = false; 1974 1975 if (I != Preheader->begin()) { 1976 // Skip debug info intrinsics. 1977 do { 1978 --I; 1979 } while (isa<DbgInfoIntrinsic>(I) && I != Preheader->begin()); 1980 1981 if (isa<DbgInfoIntrinsic>(I) && I == Preheader->begin()) 1982 Done = true; 1983 } else { 1984 Done = true; 1985 } 1986 1987 ToMove->moveBefore(InsertPt); 1988 if (Done) break; 1989 InsertPt = ToMove; 1990 } 1991} 1992 1993//===----------------------------------------------------------------------===// 1994// IndVarSimplify driver. Manage several subpasses of IV simplification. 1995//===----------------------------------------------------------------------===// 1996 1997bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) { 1998 // If LoopSimplify form is not available, stay out of trouble. Some notes: 1999 // - LSR currently only supports LoopSimplify-form loops. Indvars' 2000 // canonicalization can be a pessimization without LSR to "clean up" 2001 // afterwards. 2002 // - We depend on having a preheader; in particular, 2003 // Loop::getCanonicalInductionVariable only supports loops with preheaders, 2004 // and we're in trouble if we can't find the induction variable even when 2005 // we've manually inserted one. 2006 if (!L->isLoopSimplifyForm()) 2007 return false; 2008 2009 if (!DisableIVRewrite) 2010 IU = &getAnalysis<IVUsers>(); 2011 LI = &getAnalysis<LoopInfo>(); 2012 SE = &getAnalysis<ScalarEvolution>(); 2013 DT = &getAnalysis<DominatorTree>(); 2014 TD = getAnalysisIfAvailable<TargetData>(); 2015 2016 DeadInsts.clear(); 2017 Changed = false; 2018 2019 // If there are any floating-point recurrences, attempt to 2020 // transform them to use integer recurrences. 2021 RewriteNonIntegerIVs(L); 2022 2023 const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L); 2024 2025 // Create a rewriter object which we'll use to transform the code with. 2026 SCEVExpander Rewriter(*SE, "indvars"); 2027 2028 // Eliminate redundant IV users. 2029 // 2030 // Simplification works best when run before other consumers of SCEV. We 2031 // attempt to avoid evaluating SCEVs for sign/zero extend operations until 2032 // other expressions involving loop IVs have been evaluated. This helps SCEV 2033 // set no-wrap flags before normalizing sign/zero extension. 2034 if (DisableIVRewrite) { 2035 Rewriter.disableCanonicalMode(); 2036 SimplifyIVUsersNoRewrite(L, Rewriter); 2037 } 2038 2039 // Check to see if this loop has a computable loop-invariant execution count. 2040 // If so, this means that we can compute the final value of any expressions 2041 // that are recurrent in the loop, and substitute the exit values from the 2042 // loop into any instructions outside of the loop that use the final values of 2043 // the current expressions. 2044 // 2045 if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount)) 2046 RewriteLoopExitValues(L, Rewriter); 2047 2048 // Eliminate redundant IV users. 2049 if (!DisableIVRewrite) 2050 SimplifyIVUsers(Rewriter); 2051 2052 // Eliminate redundant IV cycles. 2053 if (DisableIVRewrite) 2054 SimplifyCongruentIVs(L); 2055 2056 // Compute the type of the largest recurrence expression, and decide whether 2057 // a canonical induction variable should be inserted. 2058 Type *LargestType = 0; 2059 bool NeedCannIV = false; 2060 bool ReuseIVForExit = DisableIVRewrite && !ForceLFTR; 2061 bool ExpandBECount = canExpandBackedgeTakenCount(L, SE); 2062 if (ExpandBECount && !ReuseIVForExit) { 2063 // If we have a known trip count and a single exit block, we'll be 2064 // rewriting the loop exit test condition below, which requires a 2065 // canonical induction variable. 2066 NeedCannIV = true; 2067 Type *Ty = BackedgeTakenCount->getType(); 2068 if (DisableIVRewrite) { 2069 // In this mode, SimplifyIVUsers may have already widened the IV used by 2070 // the backedge test and inserted a Trunc on the compare's operand. Get 2071 // the wider type to avoid creating a redundant narrow IV only used by the 2072 // loop test. 2073 LargestType = getBackedgeIVType(L); 2074 } 2075 if (!LargestType || 2076 SE->getTypeSizeInBits(Ty) > 2077 SE->getTypeSizeInBits(LargestType)) 2078 LargestType = SE->getEffectiveSCEVType(Ty); 2079 } 2080 if (!DisableIVRewrite) { 2081 for (IVUsers::const_iterator I = IU->begin(), E = IU->end(); I != E; ++I) { 2082 NeedCannIV = true; 2083 Type *Ty = 2084 SE->getEffectiveSCEVType(I->getOperandValToReplace()->getType()); 2085 if (!LargestType || 2086 SE->getTypeSizeInBits(Ty) > 2087 SE->getTypeSizeInBits(LargestType)) 2088 LargestType = Ty; 2089 } 2090 } 2091 2092 // Now that we know the largest of the induction variable expressions 2093 // in this loop, insert a canonical induction variable of the largest size. 2094 PHINode *IndVar = 0; 2095 if (NeedCannIV) { 2096 // Check to see if the loop already has any canonical-looking induction 2097 // variables. If any are present and wider than the planned canonical 2098 // induction variable, temporarily remove them, so that the Rewriter 2099 // doesn't attempt to reuse them. 2100 SmallVector<PHINode *, 2> OldCannIVs; 2101 while (PHINode *OldCannIV = L->getCanonicalInductionVariable()) { 2102 if (SE->getTypeSizeInBits(OldCannIV->getType()) > 2103 SE->getTypeSizeInBits(LargestType)) 2104 OldCannIV->removeFromParent(); 2105 else 2106 break; 2107 OldCannIVs.push_back(OldCannIV); 2108 } 2109 2110 IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L, LargestType); 2111 2112 ++NumInserted; 2113 Changed = true; 2114 DEBUG(dbgs() << "INDVARS: New CanIV: " << *IndVar << '\n'); 2115 2116 // Now that the official induction variable is established, reinsert 2117 // any old canonical-looking variables after it so that the IR remains 2118 // consistent. They will be deleted as part of the dead-PHI deletion at 2119 // the end of the pass. 2120 while (!OldCannIVs.empty()) { 2121 PHINode *OldCannIV = OldCannIVs.pop_back_val(); 2122 OldCannIV->insertBefore(L->getHeader()->getFirstNonPHI()); 2123 } 2124 } 2125 else if (ExpandBECount && ReuseIVForExit && needsLFTR(L, DT)) { 2126 IndVar = FindLoopCounter(L, BackedgeTakenCount, SE, DT, TD); 2127 } 2128 // If we have a trip count expression, rewrite the loop's exit condition 2129 // using it. We can currently only handle loops with a single exit. 2130 Value *NewICmp = 0; 2131 if (ExpandBECount && IndVar) { 2132 // Check preconditions for proper SCEVExpander operation. SCEV does not 2133 // express SCEVExpander's dependencies, such as LoopSimplify. Instead any 2134 // pass that uses the SCEVExpander must do it. This does not work well for 2135 // loop passes because SCEVExpander makes assumptions about all loops, while 2136 // LoopPassManager only forces the current loop to be simplified. 2137 // 2138 // FIXME: SCEV expansion has no way to bail out, so the caller must 2139 // explicitly check any assumptions made by SCEV. Brittle. 2140 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(BackedgeTakenCount); 2141 if (!AR || AR->getLoop()->getLoopPreheader()) 2142 NewICmp = 2143 LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar, Rewriter); 2144 } 2145 // Rewrite IV-derived expressions. 2146 if (!DisableIVRewrite) 2147 RewriteIVExpressions(L, Rewriter); 2148 2149 // Clear the rewriter cache, because values that are in the rewriter's cache 2150 // can be deleted in the loop below, causing the AssertingVH in the cache to 2151 // trigger. 2152 Rewriter.clear(); 2153 2154 // Now that we're done iterating through lists, clean up any instructions 2155 // which are now dead. 2156 while (!DeadInsts.empty()) 2157 if (Instruction *Inst = 2158 dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val())) 2159 RecursivelyDeleteTriviallyDeadInstructions(Inst); 2160 2161 // The Rewriter may not be used from this point on. 2162 2163 // Loop-invariant instructions in the preheader that aren't used in the 2164 // loop may be sunk below the loop to reduce register pressure. 2165 SinkUnusedInvariants(L); 2166 2167 // For completeness, inform IVUsers of the IV use in the newly-created 2168 // loop exit test instruction. 2169 if (IU && NewICmp) { 2170 ICmpInst *NewICmpInst = dyn_cast<ICmpInst>(NewICmp); 2171 if (NewICmpInst) 2172 IU->AddUsersIfInteresting(cast<Instruction>(NewICmpInst->getOperand(0))); 2173 } 2174 // Clean up dead instructions. 2175 Changed |= DeleteDeadPHIs(L->getHeader()); 2176 // Check a post-condition. 2177 assert(L->isLCSSAForm(*DT) && 2178 "Indvars did not leave the loop in lcssa form!"); 2179 2180 // Verify that LFTR, and any other change have not interfered with SCEV's 2181 // ability to compute trip count. 2182#ifndef NDEBUG 2183 if (DisableIVRewrite && !isa<SCEVCouldNotCompute>(BackedgeTakenCount)) { 2184 SE->forgetLoop(L); 2185 const SCEV *NewBECount = SE->getBackedgeTakenCount(L); 2186 if (SE->getTypeSizeInBits(BackedgeTakenCount->getType()) < 2187 SE->getTypeSizeInBits(NewBECount->getType())) 2188 NewBECount = SE->getTruncateOrNoop(NewBECount, 2189 BackedgeTakenCount->getType()); 2190 else 2191 BackedgeTakenCount = SE->getTruncateOrNoop(BackedgeTakenCount, 2192 NewBECount->getType()); 2193 assert(BackedgeTakenCount == NewBECount && "indvars must preserve SCEV"); 2194 } 2195#endif 2196 2197 return Changed; 2198} 2199