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 // If the trip count of a loop is computable, this pass also makes the following 15 // changes: 16 // 1. The exit condition for the loop is canonicalized to compare the 17 // induction value against the exit value. This turns loops like: 18 // 'for (i = 7; i*i < 1000; ++i)' into 'for (i = 0; i != 25; ++i)' 19 // 2. Any use outside of the loop of an expression derived from the indvar 20 // is changed to compute the derived value outside of the loop, eliminating 21 // the dependence on the exit value of the induction variable. If the only 22 // purpose of the loop is to compute the exit value of some derived 23 // expression, this transformation will make the loop dead. 24 // 25 //===----------------------------------------------------------------------===// 26 27 #define DEBUG_TYPE "indvars" 28 #include "llvm/Transforms/Scalar.h" 29 #include "llvm/BasicBlock.h" 30 #include "llvm/Constants.h" 31 #include "llvm/Instructions.h" 32 #include "llvm/IntrinsicInst.h" 33 #include "llvm/LLVMContext.h" 34 #include "llvm/Type.h" 35 #include "llvm/Analysis/Dominators.h" 36 #include "llvm/Analysis/ScalarEvolutionExpander.h" 37 #include "llvm/Analysis/LoopInfo.h" 38 #include "llvm/Analysis/LoopPass.h" 39 #include "llvm/Support/CFG.h" 40 #include "llvm/Support/CommandLine.h" 41 #include "llvm/Support/Debug.h" 42 #include "llvm/Support/raw_ostream.h" 43 #include "llvm/Transforms/Utils/Local.h" 44 #include "llvm/Transforms/Utils/BasicBlockUtils.h" 45 #include "llvm/Transforms/Utils/SimplifyIndVar.h" 46 #include "llvm/Target/TargetData.h" 47 #include "llvm/ADT/DenseMap.h" 48 #include "llvm/ADT/SmallVector.h" 49 #include "llvm/ADT/Statistic.h" 50 using namespace llvm; 51 52 STATISTIC(NumWidened , "Number of indvars widened"); 53 STATISTIC(NumReplaced , "Number of exit values replaced"); 54 STATISTIC(NumLFTR , "Number of loop exit tests replaced"); 55 STATISTIC(NumElimExt , "Number of IV sign/zero extends eliminated"); 56 STATISTIC(NumElimIV , "Number of congruent IVs eliminated"); 57 58 // Trip count verification can be enabled by default under NDEBUG if we 59 // implement a strong expression equivalence checker in SCEV. Until then, we 60 // use the verify-indvars flag, which may assert in some cases. 61 static cl::opt<bool> VerifyIndvars( 62 "verify-indvars", cl::Hidden, 63 cl::desc("Verify the ScalarEvolution result after running indvars")); 64 65 namespace { 66 class IndVarSimplify : public LoopPass { 67 LoopInfo *LI; 68 ScalarEvolution *SE; 69 DominatorTree *DT; 70 TargetData *TD; 71 72 SmallVector<WeakVH, 16> DeadInsts; 73 bool Changed; 74 public: 75 76 static char ID; // Pass identification, replacement for typeid 77 IndVarSimplify() : LoopPass(ID), LI(0), SE(0), DT(0), TD(0), 78 Changed(false) { 79 initializeIndVarSimplifyPass(*PassRegistry::getPassRegistry()); 80 } 81 82 virtual bool runOnLoop(Loop *L, LPPassManager &LPM); 83 84 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 85 AU.addRequired<DominatorTree>(); 86 AU.addRequired<LoopInfo>(); 87 AU.addRequired<ScalarEvolution>(); 88 AU.addRequiredID(LoopSimplifyID); 89 AU.addRequiredID(LCSSAID); 90 AU.addPreserved<ScalarEvolution>(); 91 AU.addPreservedID(LoopSimplifyID); 92 AU.addPreservedID(LCSSAID); 93 AU.setPreservesCFG(); 94 } 95 96 private: 97 virtual void releaseMemory() { 98 DeadInsts.clear(); 99 } 100 101 bool isValidRewrite(Value *FromVal, Value *ToVal); 102 103 void HandleFloatingPointIV(Loop *L, PHINode *PH); 104 void RewriteNonIntegerIVs(Loop *L); 105 106 void SimplifyAndExtend(Loop *L, SCEVExpander &Rewriter, LPPassManager &LPM); 107 108 void RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter); 109 110 Value *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount, 111 PHINode *IndVar, SCEVExpander &Rewriter); 112 113 void SinkUnusedInvariants(Loop *L); 114 }; 115 } 116 117 char IndVarSimplify::ID = 0; 118 INITIALIZE_PASS_BEGIN(IndVarSimplify, "indvars", 119 "Induction Variable Simplification", false, false) 120 INITIALIZE_PASS_DEPENDENCY(DominatorTree) 121 INITIALIZE_PASS_DEPENDENCY(LoopInfo) 122 INITIALIZE_PASS_DEPENDENCY(ScalarEvolution) 123 INITIALIZE_PASS_DEPENDENCY(LoopSimplify) 124 INITIALIZE_PASS_DEPENDENCY(LCSSA) 125 INITIALIZE_PASS_END(IndVarSimplify, "indvars", 126 "Induction Variable Simplification", false, false) 127 128 Pass *llvm::createIndVarSimplifyPass() { 129 return new IndVarSimplify(); 130 } 131 132 /// isValidRewrite - Return true if the SCEV expansion generated by the 133 /// rewriter can replace the original value. SCEV guarantees that it 134 /// produces the same value, but the way it is produced may be illegal IR. 135 /// Ideally, this function will only be called for verification. 136 bool IndVarSimplify::isValidRewrite(Value *FromVal, Value *ToVal) { 137 // If an SCEV expression subsumed multiple pointers, its expansion could 138 // reassociate the GEP changing the base pointer. This is illegal because the 139 // final address produced by a GEP chain must be inbounds relative to its 140 // underlying object. Otherwise basic alias analysis, among other things, 141 // could fail in a dangerous way. Ultimately, SCEV will be improved to avoid 142 // producing an expression involving multiple pointers. Until then, we must 143 // bail out here. 144 // 145 // Retrieve the pointer operand of the GEP. Don't use GetUnderlyingObject 146 // because it understands lcssa phis while SCEV does not. 147 Value *FromPtr = FromVal; 148 Value *ToPtr = ToVal; 149 if (GEPOperator *GEP = dyn_cast<GEPOperator>(FromVal)) { 150 FromPtr = GEP->getPointerOperand(); 151 } 152 if (GEPOperator *GEP = dyn_cast<GEPOperator>(ToVal)) { 153 ToPtr = GEP->getPointerOperand(); 154 } 155 if (FromPtr != FromVal || ToPtr != ToVal) { 156 // Quickly check the common case 157 if (FromPtr == ToPtr) 158 return true; 159 160 // SCEV may have rewritten an expression that produces the GEP's pointer 161 // operand. That's ok as long as the pointer operand has the same base 162 // pointer. Unlike GetUnderlyingObject(), getPointerBase() will find the 163 // base of a recurrence. This handles the case in which SCEV expansion 164 // converts a pointer type recurrence into a nonrecurrent pointer base 165 // indexed by an integer recurrence. 166 167 // If the GEP base pointer is a vector of pointers, abort. 168 if (!FromPtr->getType()->isPointerTy() || !ToPtr->getType()->isPointerTy()) 169 return false; 170 171 const SCEV *FromBase = SE->getPointerBase(SE->getSCEV(FromPtr)); 172 const SCEV *ToBase = SE->getPointerBase(SE->getSCEV(ToPtr)); 173 if (FromBase == ToBase) 174 return true; 175 176 DEBUG(dbgs() << "INDVARS: GEP rewrite bail out " 177 << *FromBase << " != " << *ToBase << "\n"); 178 179 return false; 180 } 181 return true; 182 } 183 184 /// Determine the insertion point for this user. By default, insert immediately 185 /// before the user. SCEVExpander or LICM will hoist loop invariants out of the 186 /// loop. For PHI nodes, there may be multiple uses, so compute the nearest 187 /// common dominator for the incoming blocks. 188 static Instruction *getInsertPointForUses(Instruction *User, Value *Def, 189 DominatorTree *DT) { 190 PHINode *PHI = dyn_cast<PHINode>(User); 191 if (!PHI) 192 return User; 193 194 Instruction *InsertPt = 0; 195 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) { 196 if (PHI->getIncomingValue(i) != Def) 197 continue; 198 199 BasicBlock *InsertBB = PHI->getIncomingBlock(i); 200 if (!InsertPt) { 201 InsertPt = InsertBB->getTerminator(); 202 continue; 203 } 204 InsertBB = DT->findNearestCommonDominator(InsertPt->getParent(), InsertBB); 205 InsertPt = InsertBB->getTerminator(); 206 } 207 assert(InsertPt && "Missing phi operand"); 208 assert((!isa<Instruction>(Def) || 209 DT->dominates(cast<Instruction>(Def), InsertPt)) && 210 "def does not dominate all uses"); 211 return InsertPt; 212 } 213 214 //===----------------------------------------------------------------------===// 215 // RewriteNonIntegerIVs and helpers. Prefer integer IVs. 216 //===----------------------------------------------------------------------===// 217 218 /// ConvertToSInt - Convert APF to an integer, if possible. 219 static bool ConvertToSInt(const APFloat &APF, int64_t &IntVal) { 220 bool isExact = false; 221 if (&APF.getSemantics() == &APFloat::PPCDoubleDouble) 222 return false; 223 // See if we can convert this to an int64_t 224 uint64_t UIntVal; 225 if (APF.convertToInteger(&UIntVal, 64, true, APFloat::rmTowardZero, 226 &isExact) != APFloat::opOK || !isExact) 227 return false; 228 IntVal = UIntVal; 229 return true; 230 } 231 232 /// HandleFloatingPointIV - If the loop has floating induction variable 233 /// then insert corresponding integer induction variable if possible. 234 /// For example, 235 /// for(double i = 0; i < 10000; ++i) 236 /// bar(i) 237 /// is converted into 238 /// for(int i = 0; i < 10000; ++i) 239 /// bar((double)i); 240 /// 241 void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) { 242 unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0)); 243 unsigned BackEdge = IncomingEdge^1; 244 245 // Check incoming value. 246 ConstantFP *InitValueVal = 247 dyn_cast<ConstantFP>(PN->getIncomingValue(IncomingEdge)); 248 249 int64_t InitValue; 250 if (!InitValueVal || !ConvertToSInt(InitValueVal->getValueAPF(), InitValue)) 251 return; 252 253 // Check IV increment. Reject this PN if increment operation is not 254 // an add or increment value can not be represented by an integer. 255 BinaryOperator *Incr = 256 dyn_cast<BinaryOperator>(PN->getIncomingValue(BackEdge)); 257 if (Incr == 0 || Incr->getOpcode() != Instruction::FAdd) return; 258 259 // If this is not an add of the PHI with a constantfp, or if the constant fp 260 // is not an integer, bail out. 261 ConstantFP *IncValueVal = dyn_cast<ConstantFP>(Incr->getOperand(1)); 262 int64_t IncValue; 263 if (IncValueVal == 0 || Incr->getOperand(0) != PN || 264 !ConvertToSInt(IncValueVal->getValueAPF(), IncValue)) 265 return; 266 267 // Check Incr uses. One user is PN and the other user is an exit condition 268 // used by the conditional terminator. 269 Value::use_iterator IncrUse = Incr->use_begin(); 270 Instruction *U1 = cast<Instruction>(*IncrUse++); 271 if (IncrUse == Incr->use_end()) return; 272 Instruction *U2 = cast<Instruction>(*IncrUse++); 273 if (IncrUse != Incr->use_end()) return; 274 275 // Find exit condition, which is an fcmp. If it doesn't exist, or if it isn't 276 // only used by a branch, we can't transform it. 277 FCmpInst *Compare = dyn_cast<FCmpInst>(U1); 278 if (!Compare) 279 Compare = dyn_cast<FCmpInst>(U2); 280 if (Compare == 0 || !Compare->hasOneUse() || 281 !isa<BranchInst>(Compare->use_back())) 282 return; 283 284 BranchInst *TheBr = cast<BranchInst>(Compare->use_back()); 285 286 // We need to verify that the branch actually controls the iteration count 287 // of the loop. If not, the new IV can overflow and no one will notice. 288 // The branch block must be in the loop and one of the successors must be out 289 // of the loop. 290 assert(TheBr->isConditional() && "Can't use fcmp if not conditional"); 291 if (!L->contains(TheBr->getParent()) || 292 (L->contains(TheBr->getSuccessor(0)) && 293 L->contains(TheBr->getSuccessor(1)))) 294 return; 295 296 297 // If it isn't a comparison with an integer-as-fp (the exit value), we can't 298 // transform it. 299 ConstantFP *ExitValueVal = dyn_cast<ConstantFP>(Compare->getOperand(1)); 300 int64_t ExitValue; 301 if (ExitValueVal == 0 || 302 !ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue)) 303 return; 304 305 // Find new predicate for integer comparison. 306 CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE; 307 switch (Compare->getPredicate()) { 308 default: return; // Unknown comparison. 309 case CmpInst::FCMP_OEQ: 310 case CmpInst::FCMP_UEQ: NewPred = CmpInst::ICMP_EQ; break; 311 case CmpInst::FCMP_ONE: 312 case CmpInst::FCMP_UNE: NewPred = CmpInst::ICMP_NE; break; 313 case CmpInst::FCMP_OGT: 314 case CmpInst::FCMP_UGT: NewPred = CmpInst::ICMP_SGT; break; 315 case CmpInst::FCMP_OGE: 316 case CmpInst::FCMP_UGE: NewPred = CmpInst::ICMP_SGE; break; 317 case CmpInst::FCMP_OLT: 318 case CmpInst::FCMP_ULT: NewPred = CmpInst::ICMP_SLT; break; 319 case CmpInst::FCMP_OLE: 320 case CmpInst::FCMP_ULE: NewPred = CmpInst::ICMP_SLE; break; 321 } 322 323 // We convert the floating point induction variable to a signed i32 value if 324 // we can. This is only safe if the comparison will not overflow in a way 325 // that won't be trapped by the integer equivalent operations. Check for this 326 // now. 327 // TODO: We could use i64 if it is native and the range requires it. 328 329 // The start/stride/exit values must all fit in signed i32. 330 if (!isInt<32>(InitValue) || !isInt<32>(IncValue) || !isInt<32>(ExitValue)) 331 return; 332 333 // If not actually striding (add x, 0.0), avoid touching the code. 334 if (IncValue == 0) 335 return; 336 337 // Positive and negative strides have different safety conditions. 338 if (IncValue > 0) { 339 // If we have a positive stride, we require the init to be less than the 340 // exit value. 341 if (InitValue >= ExitValue) 342 return; 343 344 uint32_t Range = uint32_t(ExitValue-InitValue); 345 // Check for infinite loop, either: 346 // while (i <= Exit) or until (i > Exit) 347 if (NewPred == CmpInst::ICMP_SLE || NewPred == CmpInst::ICMP_SGT) { 348 if (++Range == 0) return; // Range overflows. 349 } 350 351 unsigned Leftover = Range % uint32_t(IncValue); 352 353 // If this is an equality comparison, we require that the strided value 354 // exactly land on the exit value, otherwise the IV condition will wrap 355 // around and do things the fp IV wouldn't. 356 if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) && 357 Leftover != 0) 358 return; 359 360 // If the stride would wrap around the i32 before exiting, we can't 361 // transform the IV. 362 if (Leftover != 0 && int32_t(ExitValue+IncValue) < ExitValue) 363 return; 364 365 } else { 366 // If we have a negative stride, we require the init to be greater than the 367 // exit value. 368 if (InitValue <= ExitValue) 369 return; 370 371 uint32_t Range = uint32_t(InitValue-ExitValue); 372 // Check for infinite loop, either: 373 // while (i >= Exit) or until (i < Exit) 374 if (NewPred == CmpInst::ICMP_SGE || NewPred == CmpInst::ICMP_SLT) { 375 if (++Range == 0) return; // Range overflows. 376 } 377 378 unsigned Leftover = Range % uint32_t(-IncValue); 379 380 // If this is an equality comparison, we require that the strided value 381 // exactly land on the exit value, otherwise the IV condition will wrap 382 // around and do things the fp IV wouldn't. 383 if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) && 384 Leftover != 0) 385 return; 386 387 // If the stride would wrap around the i32 before exiting, we can't 388 // transform the IV. 389 if (Leftover != 0 && int32_t(ExitValue+IncValue) > ExitValue) 390 return; 391 } 392 393 IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext()); 394 395 // Insert new integer induction variable. 396 PHINode *NewPHI = PHINode::Create(Int32Ty, 2, PN->getName()+".int", PN); 397 NewPHI->addIncoming(ConstantInt::get(Int32Ty, InitValue), 398 PN->getIncomingBlock(IncomingEdge)); 399 400 Value *NewAdd = 401 BinaryOperator::CreateAdd(NewPHI, ConstantInt::get(Int32Ty, IncValue), 402 Incr->getName()+".int", Incr); 403 NewPHI->addIncoming(NewAdd, PN->getIncomingBlock(BackEdge)); 404 405 ICmpInst *NewCompare = new ICmpInst(TheBr, NewPred, NewAdd, 406 ConstantInt::get(Int32Ty, ExitValue), 407 Compare->getName()); 408 409 // In the following deletions, PN may become dead and may be deleted. 410 // Use a WeakVH to observe whether this happens. 411 WeakVH WeakPH = PN; 412 413 // Delete the old floating point exit comparison. The branch starts using the 414 // new comparison. 415 NewCompare->takeName(Compare); 416 Compare->replaceAllUsesWith(NewCompare); 417 RecursivelyDeleteTriviallyDeadInstructions(Compare); 418 419 // Delete the old floating point increment. 420 Incr->replaceAllUsesWith(UndefValue::get(Incr->getType())); 421 RecursivelyDeleteTriviallyDeadInstructions(Incr); 422 423 // If the FP induction variable still has uses, this is because something else 424 // in the loop uses its value. In order to canonicalize the induction 425 // variable, we chose to eliminate the IV and rewrite it in terms of an 426 // int->fp cast. 427 // 428 // We give preference to sitofp over uitofp because it is faster on most 429 // platforms. 430 if (WeakPH) { 431 Value *Conv = new SIToFPInst(NewPHI, PN->getType(), "indvar.conv", 432 PN->getParent()->getFirstInsertionPt()); 433 PN->replaceAllUsesWith(Conv); 434 RecursivelyDeleteTriviallyDeadInstructions(PN); 435 } 436 Changed = true; 437 } 438 439 void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) { 440 // First step. Check to see if there are any floating-point recurrences. 441 // If there are, change them into integer recurrences, permitting analysis by 442 // the SCEV routines. 443 // 444 BasicBlock *Header = L->getHeader(); 445 446 SmallVector<WeakVH, 8> PHIs; 447 for (BasicBlock::iterator I = Header->begin(); 448 PHINode *PN = dyn_cast<PHINode>(I); ++I) 449 PHIs.push_back(PN); 450 451 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) 452 if (PHINode *PN = dyn_cast_or_null<PHINode>(&*PHIs[i])) 453 HandleFloatingPointIV(L, PN); 454 455 // If the loop previously had floating-point IV, ScalarEvolution 456 // may not have been able to compute a trip count. Now that we've done some 457 // re-writing, the trip count may be computable. 458 if (Changed) 459 SE->forgetLoop(L); 460 } 461 462 //===----------------------------------------------------------------------===// 463 // RewriteLoopExitValues - Optimize IV users outside the loop. 464 // As a side effect, reduces the amount of IV processing within the loop. 465 //===----------------------------------------------------------------------===// 466 467 /// RewriteLoopExitValues - Check to see if this loop has a computable 468 /// loop-invariant execution count. If so, this means that we can compute the 469 /// final value of any expressions that are recurrent in the loop, and 470 /// substitute the exit values from the loop into any instructions outside of 471 /// the loop that use the final values of the current expressions. 472 /// 473 /// This is mostly redundant with the regular IndVarSimplify activities that 474 /// happen later, except that it's more powerful in some cases, because it's 475 /// able to brute-force evaluate arbitrary instructions as long as they have 476 /// constant operands at the beginning of the loop. 477 void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) { 478 // Verify the input to the pass in already in LCSSA form. 479 assert(L->isLCSSAForm(*DT)); 480 481 SmallVector<BasicBlock*, 8> ExitBlocks; 482 L->getUniqueExitBlocks(ExitBlocks); 483 484 // Find all values that are computed inside the loop, but used outside of it. 485 // Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan 486 // the exit blocks of the loop to find them. 487 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { 488 BasicBlock *ExitBB = ExitBlocks[i]; 489 490 // If there are no PHI nodes in this exit block, then no values defined 491 // inside the loop are used on this path, skip it. 492 PHINode *PN = dyn_cast<PHINode>(ExitBB->begin()); 493 if (!PN) continue; 494 495 unsigned NumPreds = PN->getNumIncomingValues(); 496 497 // Iterate over all of the PHI nodes. 498 BasicBlock::iterator BBI = ExitBB->begin(); 499 while ((PN = dyn_cast<PHINode>(BBI++))) { 500 if (PN->use_empty()) 501 continue; // dead use, don't replace it 502 503 // SCEV only supports integer expressions for now. 504 if (!PN->getType()->isIntegerTy() && !PN->getType()->isPointerTy()) 505 continue; 506 507 // It's necessary to tell ScalarEvolution about this explicitly so that 508 // it can walk the def-use list and forget all SCEVs, as it may not be 509 // watching the PHI itself. Once the new exit value is in place, there 510 // may not be a def-use connection between the loop and every instruction 511 // which got a SCEVAddRecExpr for that loop. 512 SE->forgetValue(PN); 513 514 // Iterate over all of the values in all the PHI nodes. 515 for (unsigned i = 0; i != NumPreds; ++i) { 516 // If the value being merged in is not integer or is not defined 517 // in the loop, skip it. 518 Value *InVal = PN->getIncomingValue(i); 519 if (!isa<Instruction>(InVal)) 520 continue; 521 522 // If this pred is for a subloop, not L itself, skip it. 523 if (LI->getLoopFor(PN->getIncomingBlock(i)) != L) 524 continue; // The Block is in a subloop, skip it. 525 526 // Check that InVal is defined in the loop. 527 Instruction *Inst = cast<Instruction>(InVal); 528 if (!L->contains(Inst)) 529 continue; 530 531 // Okay, this instruction has a user outside of the current loop 532 // and varies predictably *inside* the loop. Evaluate the value it 533 // contains when the loop exits, if possible. 534 const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop()); 535 if (!SE->isLoopInvariant(ExitValue, L)) 536 continue; 537 538 Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst); 539 540 DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n' 541 << " LoopVal = " << *Inst << "\n"); 542 543 if (!isValidRewrite(Inst, ExitVal)) { 544 DeadInsts.push_back(ExitVal); 545 continue; 546 } 547 Changed = true; 548 ++NumReplaced; 549 550 PN->setIncomingValue(i, ExitVal); 551 552 // If this instruction is dead now, delete it. 553 RecursivelyDeleteTriviallyDeadInstructions(Inst); 554 555 if (NumPreds == 1) { 556 // Completely replace a single-pred PHI. This is safe, because the 557 // NewVal won't be variant in the loop, so we don't need an LCSSA phi 558 // node anymore. 559 PN->replaceAllUsesWith(ExitVal); 560 RecursivelyDeleteTriviallyDeadInstructions(PN); 561 } 562 } 563 if (NumPreds != 1) { 564 // Clone the PHI and delete the original one. This lets IVUsers and 565 // any other maps purge the original user from their records. 566 PHINode *NewPN = cast<PHINode>(PN->clone()); 567 NewPN->takeName(PN); 568 NewPN->insertBefore(PN); 569 PN->replaceAllUsesWith(NewPN); 570 PN->eraseFromParent(); 571 } 572 } 573 } 574 575 // The insertion point instruction may have been deleted; clear it out 576 // so that the rewriter doesn't trip over it later. 577 Rewriter.clearInsertPoint(); 578 } 579 580 //===----------------------------------------------------------------------===// 581 // IV Widening - Extend the width of an IV to cover its widest uses. 582 //===----------------------------------------------------------------------===// 583 584 namespace { 585 // Collect information about induction variables that are used by sign/zero 586 // extend operations. This information is recorded by CollectExtend and 587 // provides the input to WidenIV. 588 struct WideIVInfo { 589 PHINode *NarrowIV; 590 Type *WidestNativeType; // Widest integer type created [sz]ext 591 bool IsSigned; // Was an sext user seen before a zext? 592 593 WideIVInfo() : NarrowIV(0), WidestNativeType(0), IsSigned(false) {} 594 }; 595 596 class WideIVVisitor : public IVVisitor { 597 ScalarEvolution *SE; 598 const TargetData *TD; 599 600 public: 601 WideIVInfo WI; 602 603 WideIVVisitor(PHINode *NarrowIV, ScalarEvolution *SCEV, 604 const TargetData *TData) : 605 SE(SCEV), TD(TData) { WI.NarrowIV = NarrowIV; } 606 607 // Implement the interface used by simplifyUsersOfIV. 608 virtual void visitCast(CastInst *Cast); 609 }; 610 } 611 612 /// visitCast - Update information about the induction variable that is 613 /// extended by this sign or zero extend operation. This is used to determine 614 /// the final width of the IV before actually widening it. 615 void WideIVVisitor::visitCast(CastInst *Cast) { 616 bool IsSigned = Cast->getOpcode() == Instruction::SExt; 617 if (!IsSigned && Cast->getOpcode() != Instruction::ZExt) 618 return; 619 620 Type *Ty = Cast->getType(); 621 uint64_t Width = SE->getTypeSizeInBits(Ty); 622 if (TD && !TD->isLegalInteger(Width)) 623 return; 624 625 if (!WI.WidestNativeType) { 626 WI.WidestNativeType = SE->getEffectiveSCEVType(Ty); 627 WI.IsSigned = IsSigned; 628 return; 629 } 630 631 // We extend the IV to satisfy the sign of its first user, arbitrarily. 632 if (WI.IsSigned != IsSigned) 633 return; 634 635 if (Width > SE->getTypeSizeInBits(WI.WidestNativeType)) 636 WI.WidestNativeType = SE->getEffectiveSCEVType(Ty); 637 } 638 639 namespace { 640 641 /// NarrowIVDefUse - Record a link in the Narrow IV def-use chain along with the 642 /// WideIV that computes the same value as the Narrow IV def. This avoids 643 /// caching Use* pointers. 644 struct NarrowIVDefUse { 645 Instruction *NarrowDef; 646 Instruction *NarrowUse; 647 Instruction *WideDef; 648 649 NarrowIVDefUse(): NarrowDef(0), NarrowUse(0), WideDef(0) {} 650 651 NarrowIVDefUse(Instruction *ND, Instruction *NU, Instruction *WD): 652 NarrowDef(ND), NarrowUse(NU), WideDef(WD) {} 653 }; 654 655 /// WidenIV - The goal of this transform is to remove sign and zero extends 656 /// without creating any new induction variables. To do this, it creates a new 657 /// phi of the wider type and redirects all users, either removing extends or 658 /// inserting truncs whenever we stop propagating the type. 659 /// 660 class WidenIV { 661 // Parameters 662 PHINode *OrigPhi; 663 Type *WideType; 664 bool IsSigned; 665 666 // Context 667 LoopInfo *LI; 668 Loop *L; 669 ScalarEvolution *SE; 670 DominatorTree *DT; 671 672 // Result 673 PHINode *WidePhi; 674 Instruction *WideInc; 675 const SCEV *WideIncExpr; 676 SmallVectorImpl<WeakVH> &DeadInsts; 677 678 SmallPtrSet<Instruction*,16> Widened; 679 SmallVector<NarrowIVDefUse, 8> NarrowIVUsers; 680 681 public: 682 WidenIV(const WideIVInfo &WI, LoopInfo *LInfo, 683 ScalarEvolution *SEv, DominatorTree *DTree, 684 SmallVectorImpl<WeakVH> &DI) : 685 OrigPhi(WI.NarrowIV), 686 WideType(WI.WidestNativeType), 687 IsSigned(WI.IsSigned), 688 LI(LInfo), 689 L(LI->getLoopFor(OrigPhi->getParent())), 690 SE(SEv), 691 DT(DTree), 692 WidePhi(0), 693 WideInc(0), 694 WideIncExpr(0), 695 DeadInsts(DI) { 696 assert(L->getHeader() == OrigPhi->getParent() && "Phi must be an IV"); 697 } 698 699 PHINode *CreateWideIV(SCEVExpander &Rewriter); 700 701 protected: 702 Value *getExtend(Value *NarrowOper, Type *WideType, bool IsSigned, 703 Instruction *Use); 704 705 Instruction *CloneIVUser(NarrowIVDefUse DU); 706 707 const SCEVAddRecExpr *GetWideRecurrence(Instruction *NarrowUse); 708 709 const SCEVAddRecExpr* GetExtendedOperandRecurrence(NarrowIVDefUse DU); 710 711 Instruction *WidenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter); 712 713 void pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef); 714 }; 715 } // anonymous namespace 716 717 /// isLoopInvariant - Perform a quick domtree based check for loop invariance 718 /// assuming that V is used within the loop. LoopInfo::isLoopInvariant() seems 719 /// gratuitous for this purpose. 720 static bool isLoopInvariant(Value *V, const Loop *L, const DominatorTree *DT) { 721 Instruction *Inst = dyn_cast<Instruction>(V); 722 if (!Inst) 723 return true; 724 725 return DT->properlyDominates(Inst->getParent(), L->getHeader()); 726 } 727 728 Value *WidenIV::getExtend(Value *NarrowOper, Type *WideType, bool IsSigned, 729 Instruction *Use) { 730 // Set the debug location and conservative insertion point. 731 IRBuilder<> Builder(Use); 732 // Hoist the insertion point into loop preheaders as far as possible. 733 for (const Loop *L = LI->getLoopFor(Use->getParent()); 734 L && L->getLoopPreheader() && isLoopInvariant(NarrowOper, L, DT); 735 L = L->getParentLoop()) 736 Builder.SetInsertPoint(L->getLoopPreheader()->getTerminator()); 737 738 return IsSigned ? Builder.CreateSExt(NarrowOper, WideType) : 739 Builder.CreateZExt(NarrowOper, WideType); 740 } 741 742 /// CloneIVUser - Instantiate a wide operation to replace a narrow 743 /// operation. This only needs to handle operations that can evaluation to 744 /// SCEVAddRec. It can safely return 0 for any operation we decide not to clone. 745 Instruction *WidenIV::CloneIVUser(NarrowIVDefUse DU) { 746 unsigned Opcode = DU.NarrowUse->getOpcode(); 747 switch (Opcode) { 748 default: 749 return 0; 750 case Instruction::Add: 751 case Instruction::Mul: 752 case Instruction::UDiv: 753 case Instruction::Sub: 754 case Instruction::And: 755 case Instruction::Or: 756 case Instruction::Xor: 757 case Instruction::Shl: 758 case Instruction::LShr: 759 case Instruction::AShr: 760 DEBUG(dbgs() << "Cloning IVUser: " << *DU.NarrowUse << "\n"); 761 762 // Replace NarrowDef operands with WideDef. Otherwise, we don't know 763 // anything about the narrow operand yet so must insert a [sz]ext. It is 764 // probably loop invariant and will be folded or hoisted. If it actually 765 // comes from a widened IV, it should be removed during a future call to 766 // WidenIVUse. 767 Value *LHS = (DU.NarrowUse->getOperand(0) == DU.NarrowDef) ? DU.WideDef : 768 getExtend(DU.NarrowUse->getOperand(0), WideType, IsSigned, DU.NarrowUse); 769 Value *RHS = (DU.NarrowUse->getOperand(1) == DU.NarrowDef) ? DU.WideDef : 770 getExtend(DU.NarrowUse->getOperand(1), WideType, IsSigned, DU.NarrowUse); 771 772 BinaryOperator *NarrowBO = cast<BinaryOperator>(DU.NarrowUse); 773 BinaryOperator *WideBO = BinaryOperator::Create(NarrowBO->getOpcode(), 774 LHS, RHS, 775 NarrowBO->getName()); 776 IRBuilder<> Builder(DU.NarrowUse); 777 Builder.Insert(WideBO); 778 if (const OverflowingBinaryOperator *OBO = 779 dyn_cast<OverflowingBinaryOperator>(NarrowBO)) { 780 if (OBO->hasNoUnsignedWrap()) WideBO->setHasNoUnsignedWrap(); 781 if (OBO->hasNoSignedWrap()) WideBO->setHasNoSignedWrap(); 782 } 783 return WideBO; 784 } 785 } 786 787 /// No-wrap operations can transfer sign extension of their result to their 788 /// operands. Generate the SCEV value for the widened operation without 789 /// actually modifying the IR yet. If the expression after extending the 790 /// operands is an AddRec for this loop, return it. 791 const SCEVAddRecExpr* WidenIV::GetExtendedOperandRecurrence(NarrowIVDefUse DU) { 792 // Handle the common case of add<nsw/nuw> 793 if (DU.NarrowUse->getOpcode() != Instruction::Add) 794 return 0; 795 796 // One operand (NarrowDef) has already been extended to WideDef. Now determine 797 // if extending the other will lead to a recurrence. 798 unsigned ExtendOperIdx = DU.NarrowUse->getOperand(0) == DU.NarrowDef ? 1 : 0; 799 assert(DU.NarrowUse->getOperand(1-ExtendOperIdx) == DU.NarrowDef && "bad DU"); 800 801 const SCEV *ExtendOperExpr = 0; 802 const OverflowingBinaryOperator *OBO = 803 cast<OverflowingBinaryOperator>(DU.NarrowUse); 804 if (IsSigned && OBO->hasNoSignedWrap()) 805 ExtendOperExpr = SE->getSignExtendExpr( 806 SE->getSCEV(DU.NarrowUse->getOperand(ExtendOperIdx)), WideType); 807 else if(!IsSigned && OBO->hasNoUnsignedWrap()) 808 ExtendOperExpr = SE->getZeroExtendExpr( 809 SE->getSCEV(DU.NarrowUse->getOperand(ExtendOperIdx)), WideType); 810 else 811 return 0; 812 813 // When creating this AddExpr, don't apply the current operations NSW or NUW 814 // flags. This instruction may be guarded by control flow that the no-wrap 815 // behavior depends on. Non-control-equivalent instructions can be mapped to 816 // the same SCEV expression, and it would be incorrect to transfer NSW/NUW 817 // semantics to those operations. 818 const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>( 819 SE->getAddExpr(SE->getSCEV(DU.WideDef), ExtendOperExpr)); 820 821 if (!AddRec || AddRec->getLoop() != L) 822 return 0; 823 return AddRec; 824 } 825 826 /// GetWideRecurrence - Is this instruction potentially interesting from 827 /// IVUsers' perspective after widening it's type? In other words, can the 828 /// extend be safely hoisted out of the loop with SCEV reducing the value to a 829 /// recurrence on the same loop. If so, return the sign or zero extended 830 /// recurrence. Otherwise return NULL. 831 const SCEVAddRecExpr *WidenIV::GetWideRecurrence(Instruction *NarrowUse) { 832 if (!SE->isSCEVable(NarrowUse->getType())) 833 return 0; 834 835 const SCEV *NarrowExpr = SE->getSCEV(NarrowUse); 836 if (SE->getTypeSizeInBits(NarrowExpr->getType()) 837 >= SE->getTypeSizeInBits(WideType)) { 838 // NarrowUse implicitly widens its operand. e.g. a gep with a narrow 839 // index. So don't follow this use. 840 return 0; 841 } 842 843 const SCEV *WideExpr = IsSigned ? 844 SE->getSignExtendExpr(NarrowExpr, WideType) : 845 SE->getZeroExtendExpr(NarrowExpr, WideType); 846 const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(WideExpr); 847 if (!AddRec || AddRec->getLoop() != L) 848 return 0; 849 return AddRec; 850 } 851 852 /// WidenIVUse - Determine whether an individual user of the narrow IV can be 853 /// widened. If so, return the wide clone of the user. 854 Instruction *WidenIV::WidenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter) { 855 856 // Stop traversing the def-use chain at inner-loop phis or post-loop phis. 857 if (isa<PHINode>(DU.NarrowUse) && 858 LI->getLoopFor(DU.NarrowUse->getParent()) != L) 859 return 0; 860 861 // Our raison d'etre! Eliminate sign and zero extension. 862 if (IsSigned ? isa<SExtInst>(DU.NarrowUse) : isa<ZExtInst>(DU.NarrowUse)) { 863 Value *NewDef = DU.WideDef; 864 if (DU.NarrowUse->getType() != WideType) { 865 unsigned CastWidth = SE->getTypeSizeInBits(DU.NarrowUse->getType()); 866 unsigned IVWidth = SE->getTypeSizeInBits(WideType); 867 if (CastWidth < IVWidth) { 868 // The cast isn't as wide as the IV, so insert a Trunc. 869 IRBuilder<> Builder(DU.NarrowUse); 870 NewDef = Builder.CreateTrunc(DU.WideDef, DU.NarrowUse->getType()); 871 } 872 else { 873 // A wider extend was hidden behind a narrower one. This may induce 874 // another round of IV widening in which the intermediate IV becomes 875 // dead. It should be very rare. 876 DEBUG(dbgs() << "INDVARS: New IV " << *WidePhi 877 << " not wide enough to subsume " << *DU.NarrowUse << "\n"); 878 DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, DU.WideDef); 879 NewDef = DU.NarrowUse; 880 } 881 } 882 if (NewDef != DU.NarrowUse) { 883 DEBUG(dbgs() << "INDVARS: eliminating " << *DU.NarrowUse 884 << " replaced by " << *DU.WideDef << "\n"); 885 ++NumElimExt; 886 DU.NarrowUse->replaceAllUsesWith(NewDef); 887 DeadInsts.push_back(DU.NarrowUse); 888 } 889 // Now that the extend is gone, we want to expose it's uses for potential 890 // further simplification. We don't need to directly inform SimplifyIVUsers 891 // of the new users, because their parent IV will be processed later as a 892 // new loop phi. If we preserved IVUsers analysis, we would also want to 893 // push the uses of WideDef here. 894 895 // No further widening is needed. The deceased [sz]ext had done it for us. 896 return 0; 897 } 898 899 // Does this user itself evaluate to a recurrence after widening? 900 const SCEVAddRecExpr *WideAddRec = GetWideRecurrence(DU.NarrowUse); 901 if (!WideAddRec) { 902 WideAddRec = GetExtendedOperandRecurrence(DU); 903 } 904 if (!WideAddRec) { 905 // This user does not evaluate to a recurence after widening, so don't 906 // follow it. Instead insert a Trunc to kill off the original use, 907 // eventually isolating the original narrow IV so it can be removed. 908 IRBuilder<> Builder(getInsertPointForUses(DU.NarrowUse, DU.NarrowDef, DT)); 909 Value *Trunc = Builder.CreateTrunc(DU.WideDef, DU.NarrowDef->getType()); 910 DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, Trunc); 911 return 0; 912 } 913 // Assume block terminators cannot evaluate to a recurrence. We can't to 914 // insert a Trunc after a terminator if there happens to be a critical edge. 915 assert(DU.NarrowUse != DU.NarrowUse->getParent()->getTerminator() && 916 "SCEV is not expected to evaluate a block terminator"); 917 918 // Reuse the IV increment that SCEVExpander created as long as it dominates 919 // NarrowUse. 920 Instruction *WideUse = 0; 921 if (WideAddRec == WideIncExpr 922 && Rewriter.hoistIVInc(WideInc, DU.NarrowUse)) 923 WideUse = WideInc; 924 else { 925 WideUse = CloneIVUser(DU); 926 if (!WideUse) 927 return 0; 928 } 929 // Evaluation of WideAddRec ensured that the narrow expression could be 930 // extended outside the loop without overflow. This suggests that the wide use 931 // evaluates to the same expression as the extended narrow use, but doesn't 932 // absolutely guarantee it. Hence the following failsafe check. In rare cases 933 // where it fails, we simply throw away the newly created wide use. 934 if (WideAddRec != SE->getSCEV(WideUse)) { 935 DEBUG(dbgs() << "Wide use expression mismatch: " << *WideUse 936 << ": " << *SE->getSCEV(WideUse) << " != " << *WideAddRec << "\n"); 937 DeadInsts.push_back(WideUse); 938 return 0; 939 } 940 941 // Returning WideUse pushes it on the worklist. 942 return WideUse; 943 } 944 945 /// pushNarrowIVUsers - Add eligible users of NarrowDef to NarrowIVUsers. 946 /// 947 void WidenIV::pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef) { 948 for (Value::use_iterator UI = NarrowDef->use_begin(), 949 UE = NarrowDef->use_end(); UI != UE; ++UI) { 950 Instruction *NarrowUse = cast<Instruction>(*UI); 951 952 // Handle data flow merges and bizarre phi cycles. 953 if (!Widened.insert(NarrowUse)) 954 continue; 955 956 NarrowIVUsers.push_back(NarrowIVDefUse(NarrowDef, NarrowUse, WideDef)); 957 } 958 } 959 960 /// CreateWideIV - Process a single induction variable. First use the 961 /// SCEVExpander to create a wide induction variable that evaluates to the same 962 /// recurrence as the original narrow IV. Then use a worklist to forward 963 /// traverse the narrow IV's def-use chain. After WidenIVUse has processed all 964 /// interesting IV users, the narrow IV will be isolated for removal by 965 /// DeleteDeadPHIs. 966 /// 967 /// It would be simpler to delete uses as they are processed, but we must avoid 968 /// invalidating SCEV expressions. 969 /// 970 PHINode *WidenIV::CreateWideIV(SCEVExpander &Rewriter) { 971 // Is this phi an induction variable? 972 const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(OrigPhi)); 973 if (!AddRec) 974 return NULL; 975 976 // Widen the induction variable expression. 977 const SCEV *WideIVExpr = IsSigned ? 978 SE->getSignExtendExpr(AddRec, WideType) : 979 SE->getZeroExtendExpr(AddRec, WideType); 980 981 assert(SE->getEffectiveSCEVType(WideIVExpr->getType()) == WideType && 982 "Expect the new IV expression to preserve its type"); 983 984 // Can the IV be extended outside the loop without overflow? 985 AddRec = dyn_cast<SCEVAddRecExpr>(WideIVExpr); 986 if (!AddRec || AddRec->getLoop() != L) 987 return NULL; 988 989 // An AddRec must have loop-invariant operands. Since this AddRec is 990 // materialized by a loop header phi, the expression cannot have any post-loop 991 // operands, so they must dominate the loop header. 992 assert(SE->properlyDominates(AddRec->getStart(), L->getHeader()) && 993 SE->properlyDominates(AddRec->getStepRecurrence(*SE), L->getHeader()) 994 && "Loop header phi recurrence inputs do not dominate the loop"); 995 996 // The rewriter provides a value for the desired IV expression. This may 997 // either find an existing phi or materialize a new one. Either way, we 998 // expect a well-formed cyclic phi-with-increments. i.e. any operand not part 999 // of the phi-SCC dominates the loop entry. 1000 Instruction *InsertPt = L->getHeader()->begin(); 1001 WidePhi = cast<PHINode>(Rewriter.expandCodeFor(AddRec, WideType, InsertPt)); 1002 1003 // Remembering the WideIV increment generated by SCEVExpander allows 1004 // WidenIVUse to reuse it when widening the narrow IV's increment. We don't 1005 // employ a general reuse mechanism because the call above is the only call to 1006 // SCEVExpander. Henceforth, we produce 1-to-1 narrow to wide uses. 1007 if (BasicBlock *LatchBlock = L->getLoopLatch()) { 1008 WideInc = 1009 cast<Instruction>(WidePhi->getIncomingValueForBlock(LatchBlock)); 1010 WideIncExpr = SE->getSCEV(WideInc); 1011 } 1012 1013 DEBUG(dbgs() << "Wide IV: " << *WidePhi << "\n"); 1014 ++NumWidened; 1015 1016 // Traverse the def-use chain using a worklist starting at the original IV. 1017 assert(Widened.empty() && NarrowIVUsers.empty() && "expect initial state" ); 1018 1019 Widened.insert(OrigPhi); 1020 pushNarrowIVUsers(OrigPhi, WidePhi); 1021 1022 while (!NarrowIVUsers.empty()) { 1023 NarrowIVDefUse DU = NarrowIVUsers.pop_back_val(); 1024 1025 // Process a def-use edge. This may replace the use, so don't hold a 1026 // use_iterator across it. 1027 Instruction *WideUse = WidenIVUse(DU, Rewriter); 1028 1029 // Follow all def-use edges from the previous narrow use. 1030 if (WideUse) 1031 pushNarrowIVUsers(DU.NarrowUse, WideUse); 1032 1033 // WidenIVUse may have removed the def-use edge. 1034 if (DU.NarrowDef->use_empty()) 1035 DeadInsts.push_back(DU.NarrowDef); 1036 } 1037 return WidePhi; 1038 } 1039 1040 //===----------------------------------------------------------------------===// 1041 // Simplification of IV users based on SCEV evaluation. 1042 //===----------------------------------------------------------------------===// 1043 1044 1045 /// SimplifyAndExtend - Iteratively perform simplification on a worklist of IV 1046 /// users. Each successive simplification may push more users which may 1047 /// themselves be candidates for simplification. 1048 /// 1049 /// Sign/Zero extend elimination is interleaved with IV simplification. 1050 /// 1051 void IndVarSimplify::SimplifyAndExtend(Loop *L, 1052 SCEVExpander &Rewriter, 1053 LPPassManager &LPM) { 1054 SmallVector<WideIVInfo, 8> WideIVs; 1055 1056 SmallVector<PHINode*, 8> LoopPhis; 1057 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) { 1058 LoopPhis.push_back(cast<PHINode>(I)); 1059 } 1060 // Each round of simplification iterates through the SimplifyIVUsers worklist 1061 // for all current phis, then determines whether any IVs can be 1062 // widened. Widening adds new phis to LoopPhis, inducing another round of 1063 // simplification on the wide IVs. 1064 while (!LoopPhis.empty()) { 1065 // Evaluate as many IV expressions as possible before widening any IVs. This 1066 // forces SCEV to set no-wrap flags before evaluating sign/zero 1067 // extension. The first time SCEV attempts to normalize sign/zero extension, 1068 // the result becomes final. So for the most predictable results, we delay 1069 // evaluation of sign/zero extend evaluation until needed, and avoid running 1070 // other SCEV based analysis prior to SimplifyAndExtend. 1071 do { 1072 PHINode *CurrIV = LoopPhis.pop_back_val(); 1073 1074 // Information about sign/zero extensions of CurrIV. 1075 WideIVVisitor WIV(CurrIV, SE, TD); 1076 1077 Changed |= simplifyUsersOfIV(CurrIV, SE, &LPM, DeadInsts, &WIV); 1078 1079 if (WIV.WI.WidestNativeType) { 1080 WideIVs.push_back(WIV.WI); 1081 } 1082 } while(!LoopPhis.empty()); 1083 1084 for (; !WideIVs.empty(); WideIVs.pop_back()) { 1085 WidenIV Widener(WideIVs.back(), LI, SE, DT, DeadInsts); 1086 if (PHINode *WidePhi = Widener.CreateWideIV(Rewriter)) { 1087 Changed = true; 1088 LoopPhis.push_back(WidePhi); 1089 } 1090 } 1091 } 1092 } 1093 1094 //===----------------------------------------------------------------------===// 1095 // LinearFunctionTestReplace and its kin. Rewrite the loop exit condition. 1096 //===----------------------------------------------------------------------===// 1097 1098 /// Check for expressions that ScalarEvolution generates to compute 1099 /// BackedgeTakenInfo. If these expressions have not been reduced, then 1100 /// expanding them may incur additional cost (albeit in the loop preheader). 1101 static bool isHighCostExpansion(const SCEV *S, BranchInst *BI, 1102 SmallPtrSet<const SCEV*, 8> &Processed, 1103 ScalarEvolution *SE) { 1104 if (!Processed.insert(S)) 1105 return false; 1106 1107 // If the backedge-taken count is a UDiv, it's very likely a UDiv that 1108 // ScalarEvolution's HowFarToZero or HowManyLessThans produced to compute a 1109 // precise expression, rather than a UDiv from the user's code. If we can't 1110 // find a UDiv in the code with some simple searching, assume the former and 1111 // forego rewriting the loop. 1112 if (isa<SCEVUDivExpr>(S)) { 1113 ICmpInst *OrigCond = dyn_cast<ICmpInst>(BI->getCondition()); 1114 if (!OrigCond) return true; 1115 const SCEV *R = SE->getSCEV(OrigCond->getOperand(1)); 1116 R = SE->getMinusSCEV(R, SE->getConstant(R->getType(), 1)); 1117 if (R != S) { 1118 const SCEV *L = SE->getSCEV(OrigCond->getOperand(0)); 1119 L = SE->getMinusSCEV(L, SE->getConstant(L->getType(), 1)); 1120 if (L != S) 1121 return true; 1122 } 1123 } 1124 1125 // Recurse past add expressions, which commonly occur in the 1126 // BackedgeTakenCount. They may already exist in program code, and if not, 1127 // they are not too expensive rematerialize. 1128 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) { 1129 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end(); 1130 I != E; ++I) { 1131 if (isHighCostExpansion(*I, BI, Processed, SE)) 1132 return true; 1133 } 1134 return false; 1135 } 1136 1137 // HowManyLessThans uses a Max expression whenever the loop is not guarded by 1138 // the exit condition. 1139 if (isa<SCEVSMaxExpr>(S) || isa<SCEVUMaxExpr>(S)) 1140 return true; 1141 1142 // If we haven't recognized an expensive SCEV pattern, assume it's an 1143 // expression produced by program code. 1144 return false; 1145 } 1146 1147 /// canExpandBackedgeTakenCount - Return true if this loop's backedge taken 1148 /// count expression can be safely and cheaply expanded into an instruction 1149 /// sequence that can be used by LinearFunctionTestReplace. 1150 /// 1151 /// TODO: This fails for pointer-type loop counters with greater than one byte 1152 /// strides, consequently preventing LFTR from running. For the purpose of LFTR 1153 /// we could skip this check in the case that the LFTR loop counter (chosen by 1154 /// FindLoopCounter) is also pointer type. Instead, we could directly convert 1155 /// the loop test to an inequality test by checking the target data's alignment 1156 /// of element types (given that the initial pointer value originates from or is 1157 /// used by ABI constrained operation, as opposed to inttoptr/ptrtoint). 1158 /// However, we don't yet have a strong motivation for converting loop tests 1159 /// into inequality tests. 1160 static bool canExpandBackedgeTakenCount(Loop *L, ScalarEvolution *SE) { 1161 const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L); 1162 if (isa<SCEVCouldNotCompute>(BackedgeTakenCount) || 1163 BackedgeTakenCount->isZero()) 1164 return false; 1165 1166 if (!L->getExitingBlock()) 1167 return false; 1168 1169 // Can't rewrite non-branch yet. 1170 BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator()); 1171 if (!BI) 1172 return false; 1173 1174 SmallPtrSet<const SCEV*, 8> Processed; 1175 if (isHighCostExpansion(BackedgeTakenCount, BI, Processed, SE)) 1176 return false; 1177 1178 return true; 1179 } 1180 1181 /// getLoopPhiForCounter - Return the loop header phi IFF IncV adds a loop 1182 /// invariant value to the phi. 1183 static PHINode *getLoopPhiForCounter(Value *IncV, Loop *L, DominatorTree *DT) { 1184 Instruction *IncI = dyn_cast<Instruction>(IncV); 1185 if (!IncI) 1186 return 0; 1187 1188 switch (IncI->getOpcode()) { 1189 case Instruction::Add: 1190 case Instruction::Sub: 1191 break; 1192 case Instruction::GetElementPtr: 1193 // An IV counter must preserve its type. 1194 if (IncI->getNumOperands() == 2) 1195 break; 1196 default: 1197 return 0; 1198 } 1199 1200 PHINode *Phi = dyn_cast<PHINode>(IncI->getOperand(0)); 1201 if (Phi && Phi->getParent() == L->getHeader()) { 1202 if (isLoopInvariant(IncI->getOperand(1), L, DT)) 1203 return Phi; 1204 return 0; 1205 } 1206 if (IncI->getOpcode() == Instruction::GetElementPtr) 1207 return 0; 1208 1209 // Allow add/sub to be commuted. 1210 Phi = dyn_cast<PHINode>(IncI->getOperand(1)); 1211 if (Phi && Phi->getParent() == L->getHeader()) { 1212 if (isLoopInvariant(IncI->getOperand(0), L, DT)) 1213 return Phi; 1214 } 1215 return 0; 1216 } 1217 1218 /// needsLFTR - LinearFunctionTestReplace policy. Return true unless we can show 1219 /// that the current exit test is already sufficiently canonical. 1220 static bool needsLFTR(Loop *L, DominatorTree *DT) { 1221 assert(L->getExitingBlock() && "expected loop exit"); 1222 1223 BasicBlock *LatchBlock = L->getLoopLatch(); 1224 // Don't bother with LFTR if the loop is not properly simplified. 1225 if (!LatchBlock) 1226 return false; 1227 1228 BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator()); 1229 assert(BI && "expected exit branch"); 1230 1231 // Do LFTR to simplify the exit condition to an ICMP. 1232 ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition()); 1233 if (!Cond) 1234 return true; 1235 1236 // Do LFTR to simplify the exit ICMP to EQ/NE 1237 ICmpInst::Predicate Pred = Cond->getPredicate(); 1238 if (Pred != ICmpInst::ICMP_NE && Pred != ICmpInst::ICMP_EQ) 1239 return true; 1240 1241 // Look for a loop invariant RHS 1242 Value *LHS = Cond->getOperand(0); 1243 Value *RHS = Cond->getOperand(1); 1244 if (!isLoopInvariant(RHS, L, DT)) { 1245 if (!isLoopInvariant(LHS, L, DT)) 1246 return true; 1247 std::swap(LHS, RHS); 1248 } 1249 // Look for a simple IV counter LHS 1250 PHINode *Phi = dyn_cast<PHINode>(LHS); 1251 if (!Phi) 1252 Phi = getLoopPhiForCounter(LHS, L, DT); 1253 1254 if (!Phi) 1255 return true; 1256 1257 // Do LFTR if the exit condition's IV is *not* a simple counter. 1258 Value *IncV = Phi->getIncomingValueForBlock(L->getLoopLatch()); 1259 return Phi != getLoopPhiForCounter(IncV, L, DT); 1260 } 1261 1262 /// AlmostDeadIV - Return true if this IV has any uses other than the (soon to 1263 /// be rewritten) loop exit test. 1264 static bool AlmostDeadIV(PHINode *Phi, BasicBlock *LatchBlock, Value *Cond) { 1265 int LatchIdx = Phi->getBasicBlockIndex(LatchBlock); 1266 Value *IncV = Phi->getIncomingValue(LatchIdx); 1267 1268 for (Value::use_iterator UI = Phi->use_begin(), UE = Phi->use_end(); 1269 UI != UE; ++UI) { 1270 if (*UI != Cond && *UI != IncV) return false; 1271 } 1272 1273 for (Value::use_iterator UI = IncV->use_begin(), UE = IncV->use_end(); 1274 UI != UE; ++UI) { 1275 if (*UI != Cond && *UI != Phi) return false; 1276 } 1277 return true; 1278 } 1279 1280 /// FindLoopCounter - Find an affine IV in canonical form. 1281 /// 1282 /// BECount may be an i8* pointer type. The pointer difference is already 1283 /// valid count without scaling the address stride, so it remains a pointer 1284 /// expression as far as SCEV is concerned. 1285 /// 1286 /// FIXME: Accept -1 stride and set IVLimit = IVInit - BECount 1287 /// 1288 /// FIXME: Accept non-unit stride as long as SCEV can reduce BECount * Stride. 1289 /// This is difficult in general for SCEV because of potential overflow. But we 1290 /// could at least handle constant BECounts. 1291 static PHINode * 1292 FindLoopCounter(Loop *L, const SCEV *BECount, 1293 ScalarEvolution *SE, DominatorTree *DT, const TargetData *TD) { 1294 uint64_t BCWidth = SE->getTypeSizeInBits(BECount->getType()); 1295 1296 Value *Cond = 1297 cast<BranchInst>(L->getExitingBlock()->getTerminator())->getCondition(); 1298 1299 // Loop over all of the PHI nodes, looking for a simple counter. 1300 PHINode *BestPhi = 0; 1301 const SCEV *BestInit = 0; 1302 BasicBlock *LatchBlock = L->getLoopLatch(); 1303 assert(LatchBlock && "needsLFTR should guarantee a loop latch"); 1304 1305 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) { 1306 PHINode *Phi = cast<PHINode>(I); 1307 if (!SE->isSCEVable(Phi->getType())) 1308 continue; 1309 1310 // Avoid comparing an integer IV against a pointer Limit. 1311 if (BECount->getType()->isPointerTy() && !Phi->getType()->isPointerTy()) 1312 continue; 1313 1314 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Phi)); 1315 if (!AR || AR->getLoop() != L || !AR->isAffine()) 1316 continue; 1317 1318 // AR may be a pointer type, while BECount is an integer type. 1319 // AR may be wider than BECount. With eq/ne tests overflow is immaterial. 1320 // AR may not be a narrower type, or we may never exit. 1321 uint64_t PhiWidth = SE->getTypeSizeInBits(AR->getType()); 1322 if (PhiWidth < BCWidth || (TD && !TD->isLegalInteger(PhiWidth))) 1323 continue; 1324 1325 const SCEV *Step = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*SE)); 1326 if (!Step || !Step->isOne()) 1327 continue; 1328 1329 int LatchIdx = Phi->getBasicBlockIndex(LatchBlock); 1330 Value *IncV = Phi->getIncomingValue(LatchIdx); 1331 if (getLoopPhiForCounter(IncV, L, DT) != Phi) 1332 continue; 1333 1334 const SCEV *Init = AR->getStart(); 1335 1336 if (BestPhi && !AlmostDeadIV(BestPhi, LatchBlock, Cond)) { 1337 // Don't force a live loop counter if another IV can be used. 1338 if (AlmostDeadIV(Phi, LatchBlock, Cond)) 1339 continue; 1340 1341 // Prefer to count-from-zero. This is a more "canonical" counter form. It 1342 // also prefers integer to pointer IVs. 1343 if (BestInit->isZero() != Init->isZero()) { 1344 if (BestInit->isZero()) 1345 continue; 1346 } 1347 // If two IVs both count from zero or both count from nonzero then the 1348 // narrower is likely a dead phi that has been widened. Use the wider phi 1349 // to allow the other to be eliminated. 1350 if (PhiWidth <= SE->getTypeSizeInBits(BestPhi->getType())) 1351 continue; 1352 } 1353 BestPhi = Phi; 1354 BestInit = Init; 1355 } 1356 return BestPhi; 1357 } 1358 1359 /// genLoopLimit - Help LinearFunctionTestReplace by generating a value that 1360 /// holds the RHS of the new loop test. 1361 static Value *genLoopLimit(PHINode *IndVar, const SCEV *IVCount, Loop *L, 1362 SCEVExpander &Rewriter, ScalarEvolution *SE) { 1363 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(IndVar)); 1364 assert(AR && AR->getLoop() == L && AR->isAffine() && "bad loop counter"); 1365 const SCEV *IVInit = AR->getStart(); 1366 1367 // IVInit may be a pointer while IVCount is an integer when FindLoopCounter 1368 // finds a valid pointer IV. Sign extend BECount in order to materialize a 1369 // GEP. Avoid running SCEVExpander on a new pointer value, instead reusing 1370 // the existing GEPs whenever possible. 1371 if (IndVar->getType()->isPointerTy() 1372 && !IVCount->getType()->isPointerTy()) { 1373 1374 Type *OfsTy = SE->getEffectiveSCEVType(IVInit->getType()); 1375 const SCEV *IVOffset = SE->getTruncateOrSignExtend(IVCount, OfsTy); 1376 1377 // Expand the code for the iteration count. 1378 assert(SE->isLoopInvariant(IVOffset, L) && 1379 "Computed iteration count is not loop invariant!"); 1380 BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator()); 1381 Value *GEPOffset = Rewriter.expandCodeFor(IVOffset, OfsTy, BI); 1382 1383 Value *GEPBase = IndVar->getIncomingValueForBlock(L->getLoopPreheader()); 1384 assert(AR->getStart() == SE->getSCEV(GEPBase) && "bad loop counter"); 1385 // We could handle pointer IVs other than i8*, but we need to compensate for 1386 // gep index scaling. See canExpandBackedgeTakenCount comments. 1387 assert(SE->getSizeOfExpr( 1388 cast<PointerType>(GEPBase->getType())->getElementType())->isOne() 1389 && "unit stride pointer IV must be i8*"); 1390 1391 IRBuilder<> Builder(L->getLoopPreheader()->getTerminator()); 1392 return Builder.CreateGEP(GEPBase, GEPOffset, "lftr.limit"); 1393 } 1394 else { 1395 // In any other case, convert both IVInit and IVCount to integers before 1396 // comparing. This may result in SCEV expension of pointers, but in practice 1397 // SCEV will fold the pointer arithmetic away as such: 1398 // BECount = (IVEnd - IVInit - 1) => IVLimit = IVInit (postinc). 1399 // 1400 // Valid Cases: (1) both integers is most common; (2) both may be pointers 1401 // for simple memset-style loops; (3) IVInit is an integer and IVCount is a 1402 // pointer may occur when enable-iv-rewrite generates a canonical IV on top 1403 // of case #2. 1404 1405 const SCEV *IVLimit = 0; 1406 // For unit stride, IVCount = Start + BECount with 2's complement overflow. 1407 // For non-zero Start, compute IVCount here. 1408 if (AR->getStart()->isZero()) 1409 IVLimit = IVCount; 1410 else { 1411 assert(AR->getStepRecurrence(*SE)->isOne() && "only handles unit stride"); 1412 const SCEV *IVInit = AR->getStart(); 1413 1414 // For integer IVs, truncate the IV before computing IVInit + BECount. 1415 if (SE->getTypeSizeInBits(IVInit->getType()) 1416 > SE->getTypeSizeInBits(IVCount->getType())) 1417 IVInit = SE->getTruncateExpr(IVInit, IVCount->getType()); 1418 1419 IVLimit = SE->getAddExpr(IVInit, IVCount); 1420 } 1421 // Expand the code for the iteration count. 1422 BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator()); 1423 IRBuilder<> Builder(BI); 1424 assert(SE->isLoopInvariant(IVLimit, L) && 1425 "Computed iteration count is not loop invariant!"); 1426 // Ensure that we generate the same type as IndVar, or a smaller integer 1427 // type. In the presence of null pointer values, we have an integer type 1428 // SCEV expression (IVInit) for a pointer type IV value (IndVar). 1429 Type *LimitTy = IVCount->getType()->isPointerTy() ? 1430 IndVar->getType() : IVCount->getType(); 1431 return Rewriter.expandCodeFor(IVLimit, LimitTy, BI); 1432 } 1433 } 1434 1435 /// LinearFunctionTestReplace - This method rewrites the exit condition of the 1436 /// loop to be a canonical != comparison against the incremented loop induction 1437 /// variable. This pass is able to rewrite the exit tests of any loop where the 1438 /// SCEV analysis can determine a loop-invariant trip count of the loop, which 1439 /// is actually a much broader range than just linear tests. 1440 Value *IndVarSimplify:: 1441 LinearFunctionTestReplace(Loop *L, 1442 const SCEV *BackedgeTakenCount, 1443 PHINode *IndVar, 1444 SCEVExpander &Rewriter) { 1445 assert(canExpandBackedgeTakenCount(L, SE) && "precondition"); 1446 1447 // LFTR can ignore IV overflow and truncate to the width of 1448 // BECount. This avoids materializing the add(zext(add)) expression. 1449 Type *CntTy = BackedgeTakenCount->getType(); 1450 1451 const SCEV *IVCount = BackedgeTakenCount; 1452 1453 // If the exiting block is the same as the backedge block, we prefer to 1454 // compare against the post-incremented value, otherwise we must compare 1455 // against the preincremented value. 1456 Value *CmpIndVar; 1457 if (L->getExitingBlock() == L->getLoopLatch()) { 1458 // Add one to the "backedge-taken" count to get the trip count. 1459 // If this addition may overflow, we have to be more pessimistic and 1460 // cast the induction variable before doing the add. 1461 const SCEV *N = 1462 SE->getAddExpr(IVCount, SE->getConstant(IVCount->getType(), 1)); 1463 if (CntTy == IVCount->getType()) 1464 IVCount = N; 1465 else { 1466 const SCEV *Zero = SE->getConstant(IVCount->getType(), 0); 1467 if ((isa<SCEVConstant>(N) && !N->isZero()) || 1468 SE->isLoopEntryGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) { 1469 // No overflow. Cast the sum. 1470 IVCount = SE->getTruncateOrZeroExtend(N, CntTy); 1471 } else { 1472 // Potential overflow. Cast before doing the add. 1473 IVCount = SE->getTruncateOrZeroExtend(IVCount, CntTy); 1474 IVCount = SE->getAddExpr(IVCount, SE->getConstant(CntTy, 1)); 1475 } 1476 } 1477 // The BackedgeTaken expression contains the number of times that the 1478 // backedge branches to the loop header. This is one less than the 1479 // number of times the loop executes, so use the incremented indvar. 1480 CmpIndVar = IndVar->getIncomingValueForBlock(L->getExitingBlock()); 1481 } else { 1482 // We must use the preincremented value... 1483 IVCount = SE->getTruncateOrZeroExtend(IVCount, CntTy); 1484 CmpIndVar = IndVar; 1485 } 1486 1487 Value *ExitCnt = genLoopLimit(IndVar, IVCount, L, Rewriter, SE); 1488 assert(ExitCnt->getType()->isPointerTy() == IndVar->getType()->isPointerTy() 1489 && "genLoopLimit missed a cast"); 1490 1491 // Insert a new icmp_ne or icmp_eq instruction before the branch. 1492 BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator()); 1493 ICmpInst::Predicate P; 1494 if (L->contains(BI->getSuccessor(0))) 1495 P = ICmpInst::ICMP_NE; 1496 else 1497 P = ICmpInst::ICMP_EQ; 1498 1499 DEBUG(dbgs() << "INDVARS: Rewriting loop exit condition to:\n" 1500 << " LHS:" << *CmpIndVar << '\n' 1501 << " op:\t" 1502 << (P == ICmpInst::ICMP_NE ? "!=" : "==") << "\n" 1503 << " RHS:\t" << *ExitCnt << "\n" 1504 << " IVCount:\t" << *IVCount << "\n"); 1505 1506 IRBuilder<> Builder(BI); 1507 if (SE->getTypeSizeInBits(CmpIndVar->getType()) 1508 > SE->getTypeSizeInBits(ExitCnt->getType())) { 1509 CmpIndVar = Builder.CreateTrunc(CmpIndVar, ExitCnt->getType(), 1510 "lftr.wideiv"); 1511 } 1512 1513 Value *Cond = Builder.CreateICmp(P, CmpIndVar, ExitCnt, "exitcond"); 1514 Value *OrigCond = BI->getCondition(); 1515 // It's tempting to use replaceAllUsesWith here to fully replace the old 1516 // comparison, but that's not immediately safe, since users of the old 1517 // comparison may not be dominated by the new comparison. Instead, just 1518 // update the branch to use the new comparison; in the common case this 1519 // will make old comparison dead. 1520 BI->setCondition(Cond); 1521 DeadInsts.push_back(OrigCond); 1522 1523 ++NumLFTR; 1524 Changed = true; 1525 return Cond; 1526 } 1527 1528 //===----------------------------------------------------------------------===// 1529 // SinkUnusedInvariants. A late subpass to cleanup loop preheaders. 1530 //===----------------------------------------------------------------------===// 1531 1532 /// If there's a single exit block, sink any loop-invariant values that 1533 /// were defined in the preheader but not used inside the loop into the 1534 /// exit block to reduce register pressure in the loop. 1535 void IndVarSimplify::SinkUnusedInvariants(Loop *L) { 1536 BasicBlock *ExitBlock = L->getExitBlock(); 1537 if (!ExitBlock) return; 1538 1539 BasicBlock *Preheader = L->getLoopPreheader(); 1540 if (!Preheader) return; 1541 1542 Instruction *InsertPt = ExitBlock->getFirstInsertionPt(); 1543 BasicBlock::iterator I = Preheader->getTerminator(); 1544 while (I != Preheader->begin()) { 1545 --I; 1546 // New instructions were inserted at the end of the preheader. 1547 if (isa<PHINode>(I)) 1548 break; 1549 1550 // Don't move instructions which might have side effects, since the side 1551 // effects need to complete before instructions inside the loop. Also don't 1552 // move instructions which might read memory, since the loop may modify 1553 // memory. Note that it's okay if the instruction might have undefined 1554 // behavior: LoopSimplify guarantees that the preheader dominates the exit 1555 // block. 1556 if (I->mayHaveSideEffects() || I->mayReadFromMemory()) 1557 continue; 1558 1559 // Skip debug info intrinsics. 1560 if (isa<DbgInfoIntrinsic>(I)) 1561 continue; 1562 1563 // Skip landingpad instructions. 1564 if (isa<LandingPadInst>(I)) 1565 continue; 1566 1567 // Don't sink alloca: we never want to sink static alloca's out of the 1568 // entry block, and correctly sinking dynamic alloca's requires 1569 // checks for stacksave/stackrestore intrinsics. 1570 // FIXME: Refactor this check somehow? 1571 if (isa<AllocaInst>(I)) 1572 continue; 1573 1574 // Determine if there is a use in or before the loop (direct or 1575 // otherwise). 1576 bool UsedInLoop = false; 1577 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end(); 1578 UI != UE; ++UI) { 1579 User *U = *UI; 1580 BasicBlock *UseBB = cast<Instruction>(U)->getParent(); 1581 if (PHINode *P = dyn_cast<PHINode>(U)) { 1582 unsigned i = 1583 PHINode::getIncomingValueNumForOperand(UI.getOperandNo()); 1584 UseBB = P->getIncomingBlock(i); 1585 } 1586 if (UseBB == Preheader || L->contains(UseBB)) { 1587 UsedInLoop = true; 1588 break; 1589 } 1590 } 1591 1592 // If there is, the def must remain in the preheader. 1593 if (UsedInLoop) 1594 continue; 1595 1596 // Otherwise, sink it to the exit block. 1597 Instruction *ToMove = I; 1598 bool Done = false; 1599 1600 if (I != Preheader->begin()) { 1601 // Skip debug info intrinsics. 1602 do { 1603 --I; 1604 } while (isa<DbgInfoIntrinsic>(I) && I != Preheader->begin()); 1605 1606 if (isa<DbgInfoIntrinsic>(I) && I == Preheader->begin()) 1607 Done = true; 1608 } else { 1609 Done = true; 1610 } 1611 1612 ToMove->moveBefore(InsertPt); 1613 if (Done) break; 1614 InsertPt = ToMove; 1615 } 1616 } 1617 1618 //===----------------------------------------------------------------------===// 1619 // IndVarSimplify driver. Manage several subpasses of IV simplification. 1620 //===----------------------------------------------------------------------===// 1621 1622 bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) { 1623 // If LoopSimplify form is not available, stay out of trouble. Some notes: 1624 // - LSR currently only supports LoopSimplify-form loops. Indvars' 1625 // canonicalization can be a pessimization without LSR to "clean up" 1626 // afterwards. 1627 // - We depend on having a preheader; in particular, 1628 // Loop::getCanonicalInductionVariable only supports loops with preheaders, 1629 // and we're in trouble if we can't find the induction variable even when 1630 // we've manually inserted one. 1631 if (!L->isLoopSimplifyForm()) 1632 return false; 1633 1634 LI = &getAnalysis<LoopInfo>(); 1635 SE = &getAnalysis<ScalarEvolution>(); 1636 DT = &getAnalysis<DominatorTree>(); 1637 TD = getAnalysisIfAvailable<TargetData>(); 1638 1639 DeadInsts.clear(); 1640 Changed = false; 1641 1642 // If there are any floating-point recurrences, attempt to 1643 // transform them to use integer recurrences. 1644 RewriteNonIntegerIVs(L); 1645 1646 const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L); 1647 1648 // Create a rewriter object which we'll use to transform the code with. 1649 SCEVExpander Rewriter(*SE, "indvars"); 1650 #ifndef NDEBUG 1651 Rewriter.setDebugType(DEBUG_TYPE); 1652 #endif 1653 1654 // Eliminate redundant IV users. 1655 // 1656 // Simplification works best when run before other consumers of SCEV. We 1657 // attempt to avoid evaluating SCEVs for sign/zero extend operations until 1658 // other expressions involving loop IVs have been evaluated. This helps SCEV 1659 // set no-wrap flags before normalizing sign/zero extension. 1660 Rewriter.disableCanonicalMode(); 1661 SimplifyAndExtend(L, Rewriter, LPM); 1662 1663 // Check to see if this loop has a computable loop-invariant execution count. 1664 // If so, this means that we can compute the final value of any expressions 1665 // that are recurrent in the loop, and substitute the exit values from the 1666 // loop into any instructions outside of the loop that use the final values of 1667 // the current expressions. 1668 // 1669 if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount)) 1670 RewriteLoopExitValues(L, Rewriter); 1671 1672 // Eliminate redundant IV cycles. 1673 NumElimIV += Rewriter.replaceCongruentIVs(L, DT, DeadInsts); 1674 1675 // If we have a trip count expression, rewrite the loop's exit condition 1676 // using it. We can currently only handle loops with a single exit. 1677 if (canExpandBackedgeTakenCount(L, SE) && needsLFTR(L, DT)) { 1678 PHINode *IndVar = FindLoopCounter(L, BackedgeTakenCount, SE, DT, TD); 1679 if (IndVar) { 1680 // Check preconditions for proper SCEVExpander operation. SCEV does not 1681 // express SCEVExpander's dependencies, such as LoopSimplify. Instead any 1682 // pass that uses the SCEVExpander must do it. This does not work well for 1683 // loop passes because SCEVExpander makes assumptions about all loops, while 1684 // LoopPassManager only forces the current loop to be simplified. 1685 // 1686 // FIXME: SCEV expansion has no way to bail out, so the caller must 1687 // explicitly check any assumptions made by SCEV. Brittle. 1688 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(BackedgeTakenCount); 1689 if (!AR || AR->getLoop()->getLoopPreheader()) 1690 (void)LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar, 1691 Rewriter); 1692 } 1693 } 1694 // Clear the rewriter cache, because values that are in the rewriter's cache 1695 // can be deleted in the loop below, causing the AssertingVH in the cache to 1696 // trigger. 1697 Rewriter.clear(); 1698 1699 // Now that we're done iterating through lists, clean up any instructions 1700 // which are now dead. 1701 while (!DeadInsts.empty()) 1702 if (Instruction *Inst = 1703 dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val())) 1704 RecursivelyDeleteTriviallyDeadInstructions(Inst); 1705 1706 // The Rewriter may not be used from this point on. 1707 1708 // Loop-invariant instructions in the preheader that aren't used in the 1709 // loop may be sunk below the loop to reduce register pressure. 1710 SinkUnusedInvariants(L); 1711 1712 // Clean up dead instructions. 1713 Changed |= DeleteDeadPHIs(L->getHeader()); 1714 // Check a post-condition. 1715 assert(L->isLCSSAForm(*DT) && 1716 "Indvars did not leave the loop in lcssa form!"); 1717 1718 // Verify that LFTR, and any other change have not interfered with SCEV's 1719 // ability to compute trip count. 1720 #ifndef NDEBUG 1721 if (VerifyIndvars && !isa<SCEVCouldNotCompute>(BackedgeTakenCount)) { 1722 SE->forgetLoop(L); 1723 const SCEV *NewBECount = SE->getBackedgeTakenCount(L); 1724 if (SE->getTypeSizeInBits(BackedgeTakenCount->getType()) < 1725 SE->getTypeSizeInBits(NewBECount->getType())) 1726 NewBECount = SE->getTruncateOrNoop(NewBECount, 1727 BackedgeTakenCount->getType()); 1728 else 1729 BackedgeTakenCount = SE->getTruncateOrNoop(BackedgeTakenCount, 1730 NewBECount->getType()); 1731 assert(BackedgeTakenCount == NewBECount && "indvars must preserve SCEV"); 1732 } 1733 #endif 1734 1735 return Changed; 1736 } 1737