IndVarSimplify.cpp revision 36a5bf8fd8b32fe749c207f8809ae7d4f66eeb03
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. Any pointer arithmetic recurrences are raised to use array subscripts. 21// 22// If the trip count of a loop is computable, this pass also makes the following 23// changes: 24// 1. The exit condition for the loop is canonicalized to compare the 25// induction value against the exit value. This turns loops like: 26// 'for (i = 7; i*i < 1000; ++i)' into 'for (i = 0; i != 25; ++i)' 27// 2. Any use outside of the loop of an expression derived from the indvar 28// is changed to compute the derived value outside of the loop, eliminating 29// the dependence on the exit value of the induction variable. If the only 30// purpose of the loop is to compute the exit value of some derived 31// expression, this transformation will make the loop dead. 32// 33// This transformation should be followed by strength reduction after all of the 34// desired loop transformations have been performed. Additionally, on targets 35// where it is profitable, the loop could be transformed to count down to zero 36// (the "do loop" optimization). 37// 38//===----------------------------------------------------------------------===// 39 40#define DEBUG_TYPE "indvars" 41#include "llvm/Transforms/Scalar.h" 42#include "llvm/BasicBlock.h" 43#include "llvm/Constants.h" 44#include "llvm/Instructions.h" 45#include "llvm/Type.h" 46#include "llvm/Analysis/ScalarEvolutionExpander.h" 47#include "llvm/Analysis/LoopInfo.h" 48#include "llvm/Analysis/LoopPass.h" 49#include "llvm/Support/CFG.h" 50#include "llvm/Support/Compiler.h" 51#include "llvm/Support/Debug.h" 52#include "llvm/Support/GetElementPtrTypeIterator.h" 53#include "llvm/Transforms/Utils/Local.h" 54#include "llvm/Support/CommandLine.h" 55#include "llvm/ADT/SmallVector.h" 56#include "llvm/ADT/Statistic.h" 57using namespace llvm; 58 59STATISTIC(NumRemoved , "Number of aux indvars removed"); 60STATISTIC(NumPointer , "Number of pointer indvars promoted"); 61STATISTIC(NumInserted, "Number of canonical indvars added"); 62STATISTIC(NumReplaced, "Number of exit values replaced"); 63STATISTIC(NumLFTR , "Number of loop exit tests replaced"); 64 65namespace { 66 class VISIBILITY_HIDDEN IndVarSimplify : public LoopPass { 67 LoopInfo *LI; 68 ScalarEvolution *SE; 69 bool Changed; 70 public: 71 72 static char ID; // Pass identification, replacement for typeid 73 IndVarSimplify() : LoopPass(&ID) {} 74 75 bool runOnLoop(Loop *L, LPPassManager &LPM); 76 bool doInitialization(Loop *L, LPPassManager &LPM); 77 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 78 AU.addRequired<ScalarEvolution>(); 79 AU.addRequiredID(LCSSAID); 80 AU.addRequiredID(LoopSimplifyID); 81 AU.addRequired<LoopInfo>(); 82 AU.addPreservedID(LoopSimplifyID); 83 AU.addPreservedID(LCSSAID); 84 AU.setPreservesCFG(); 85 } 86 87 private: 88 89 void EliminatePointerRecurrence(PHINode *PN, BasicBlock *Preheader, 90 std::set<Instruction*> &DeadInsts); 91 Instruction *LinearFunctionTestReplace(Loop *L, SCEV *IterationCount, 92 SCEVExpander &RW); 93 void RewriteLoopExitValues(Loop *L, SCEV *IterationCount); 94 95 void DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts); 96 97 void OptimizeCanonicalIVType(Loop *L); 98 }; 99} 100 101char IndVarSimplify::ID = 0; 102static RegisterPass<IndVarSimplify> 103X("indvars", "Canonicalize Induction Variables"); 104 105LoopPass *llvm::createIndVarSimplifyPass() { 106 return new IndVarSimplify(); 107} 108 109/// DeleteTriviallyDeadInstructions - If any of the instructions is the 110/// specified set are trivially dead, delete them and see if this makes any of 111/// their operands subsequently dead. 112void IndVarSimplify:: 113DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts) { 114 while (!Insts.empty()) { 115 Instruction *I = *Insts.begin(); 116 Insts.erase(Insts.begin()); 117 if (isInstructionTriviallyDead(I)) { 118 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 119 if (Instruction *U = dyn_cast<Instruction>(I->getOperand(i))) 120 Insts.insert(U); 121 SE->deleteValueFromRecords(I); 122 DOUT << "INDVARS: Deleting: " << *I; 123 I->eraseFromParent(); 124 Changed = true; 125 } 126 } 127} 128 129 130/// EliminatePointerRecurrence - Check to see if this is a trivial GEP pointer 131/// recurrence. If so, change it into an integer recurrence, permitting 132/// analysis by the SCEV routines. 133void IndVarSimplify::EliminatePointerRecurrence(PHINode *PN, 134 BasicBlock *Preheader, 135 std::set<Instruction*> &DeadInsts) { 136 assert(PN->getNumIncomingValues() == 2 && "Noncanonicalized loop!"); 137 unsigned PreheaderIdx = PN->getBasicBlockIndex(Preheader); 138 unsigned BackedgeIdx = PreheaderIdx^1; 139 if (GetElementPtrInst *GEPI = 140 dyn_cast<GetElementPtrInst>(PN->getIncomingValue(BackedgeIdx))) 141 if (GEPI->getOperand(0) == PN) { 142 assert(GEPI->getNumOperands() == 2 && "GEP types must match!"); 143 DOUT << "INDVARS: Eliminating pointer recurrence: " << *GEPI; 144 145 // Okay, we found a pointer recurrence. Transform this pointer 146 // recurrence into an integer recurrence. Compute the value that gets 147 // added to the pointer at every iteration. 148 Value *AddedVal = GEPI->getOperand(1); 149 150 // Insert a new integer PHI node into the top of the block. 151 PHINode *NewPhi = PHINode::Create(AddedVal->getType(), 152 PN->getName()+".rec", PN); 153 NewPhi->addIncoming(Constant::getNullValue(NewPhi->getType()), Preheader); 154 155 // Create the new add instruction. 156 Value *NewAdd = BinaryOperator::CreateAdd(NewPhi, AddedVal, 157 GEPI->getName()+".rec", GEPI); 158 NewPhi->addIncoming(NewAdd, PN->getIncomingBlock(BackedgeIdx)); 159 160 // Update the existing GEP to use the recurrence. 161 GEPI->setOperand(0, PN->getIncomingValue(PreheaderIdx)); 162 163 // Update the GEP to use the new recurrence we just inserted. 164 GEPI->setOperand(1, NewAdd); 165 166 // If the incoming value is a constant expr GEP, try peeling out the array 167 // 0 index if possible to make things simpler. 168 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEPI->getOperand(0))) 169 if (CE->getOpcode() == Instruction::GetElementPtr) { 170 unsigned NumOps = CE->getNumOperands(); 171 assert(NumOps > 1 && "CE folding didn't work!"); 172 if (CE->getOperand(NumOps-1)->isNullValue()) { 173 // Check to make sure the last index really is an array index. 174 gep_type_iterator GTI = gep_type_begin(CE); 175 for (unsigned i = 1, e = CE->getNumOperands()-1; 176 i != e; ++i, ++GTI) 177 /*empty*/; 178 if (isa<SequentialType>(*GTI)) { 179 // Pull the last index out of the constant expr GEP. 180 SmallVector<Value*, 8> CEIdxs(CE->op_begin()+1, CE->op_end()-1); 181 Constant *NCE = ConstantExpr::getGetElementPtr(CE->getOperand(0), 182 &CEIdxs[0], 183 CEIdxs.size()); 184 Value *Idx[2]; 185 Idx[0] = Constant::getNullValue(Type::Int32Ty); 186 Idx[1] = NewAdd; 187 GetElementPtrInst *NGEPI = GetElementPtrInst::Create( 188 NCE, Idx, Idx + 2, 189 GEPI->getName(), GEPI); 190 SE->deleteValueFromRecords(GEPI); 191 GEPI->replaceAllUsesWith(NGEPI); 192 GEPI->eraseFromParent(); 193 GEPI = NGEPI; 194 } 195 } 196 } 197 198 199 // Finally, if there are any other users of the PHI node, we must 200 // insert a new GEP instruction that uses the pre-incremented version 201 // of the induction amount. 202 if (!PN->use_empty()) { 203 BasicBlock::iterator InsertPos = PN; ++InsertPos; 204 while (isa<PHINode>(InsertPos)) ++InsertPos; 205 Value *PreInc = 206 GetElementPtrInst::Create(PN->getIncomingValue(PreheaderIdx), 207 NewPhi, "", InsertPos); 208 PreInc->takeName(PN); 209 PN->replaceAllUsesWith(PreInc); 210 } 211 212 // Delete the old PHI for sure, and the GEP if its otherwise unused. 213 DeadInsts.insert(PN); 214 215 ++NumPointer; 216 Changed = true; 217 } 218} 219 220/// LinearFunctionTestReplace - This method rewrites the exit condition of the 221/// loop to be a canonical != comparison against the incremented loop induction 222/// variable. This pass is able to rewrite the exit tests of any loop where the 223/// SCEV analysis can determine a loop-invariant trip count of the loop, which 224/// is actually a much broader range than just linear tests. 225/// 226/// This method returns a "potentially dead" instruction whose computation chain 227/// should be deleted when convenient. 228Instruction *IndVarSimplify::LinearFunctionTestReplace(Loop *L, 229 SCEV *IterationCount, 230 SCEVExpander &RW) { 231 // Find the exit block for the loop. We can currently only handle loops with 232 // a single exit. 233 SmallVector<BasicBlock*, 8> ExitBlocks; 234 L->getExitBlocks(ExitBlocks); 235 if (ExitBlocks.size() != 1) return 0; 236 BasicBlock *ExitBlock = ExitBlocks[0]; 237 238 // Make sure there is only one predecessor block in the loop. 239 BasicBlock *ExitingBlock = 0; 240 for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock); 241 PI != PE; ++PI) 242 if (L->contains(*PI)) { 243 if (ExitingBlock == 0) 244 ExitingBlock = *PI; 245 else 246 return 0; // Multiple exits from loop to this block. 247 } 248 assert(ExitingBlock && "Loop info is broken"); 249 250 if (!isa<BranchInst>(ExitingBlock->getTerminator())) 251 return 0; // Can't rewrite non-branch yet 252 BranchInst *BI = cast<BranchInst>(ExitingBlock->getTerminator()); 253 assert(BI->isConditional() && "Must be conditional to be part of loop!"); 254 255 Instruction *PotentiallyDeadInst = dyn_cast<Instruction>(BI->getCondition()); 256 257 // If the exiting block is not the same as the backedge block, we must compare 258 // against the preincremented value, otherwise we prefer to compare against 259 // the post-incremented value. 260 BasicBlock *Header = L->getHeader(); 261 pred_iterator HPI = pred_begin(Header); 262 assert(HPI != pred_end(Header) && "Loop with zero preds???"); 263 if (!L->contains(*HPI)) ++HPI; 264 assert(HPI != pred_end(Header) && L->contains(*HPI) && 265 "No backedge in loop?"); 266 267 SCEVHandle TripCount = IterationCount; 268 Value *IndVar; 269 if (*HPI == ExitingBlock) { 270 // The IterationCount expression contains the number of times that the 271 // backedge actually branches to the loop header. This is one less than the 272 // number of times the loop executes, so add one to it. 273 ConstantInt *OneC = ConstantInt::get(IterationCount->getType(), 1); 274 TripCount = SE->getAddExpr(IterationCount, SE->getConstant(OneC)); 275 IndVar = L->getCanonicalInductionVariableIncrement(); 276 } else { 277 // We have to use the preincremented value... 278 IndVar = L->getCanonicalInductionVariable(); 279 } 280 281 DOUT << "INDVARS: LFTR: TripCount = " << *TripCount 282 << " IndVar = " << *IndVar << "\n"; 283 284 // Expand the code for the iteration count into the preheader of the loop. 285 BasicBlock *Preheader = L->getLoopPreheader(); 286 Value *ExitCnt = RW.expandCodeFor(TripCount, Preheader->getTerminator()); 287 288 // Insert a new icmp_ne or icmp_eq instruction before the branch. 289 ICmpInst::Predicate Opcode; 290 if (L->contains(BI->getSuccessor(0))) 291 Opcode = ICmpInst::ICMP_NE; 292 else 293 Opcode = ICmpInst::ICMP_EQ; 294 295 Value *Cond = new ICmpInst(Opcode, IndVar, ExitCnt, "exitcond", BI); 296 BI->setCondition(Cond); 297 ++NumLFTR; 298 Changed = true; 299 return PotentiallyDeadInst; 300} 301 302 303/// RewriteLoopExitValues - Check to see if this loop has a computable 304/// loop-invariant execution count. If so, this means that we can compute the 305/// final value of any expressions that are recurrent in the loop, and 306/// substitute the exit values from the loop into any instructions outside of 307/// the loop that use the final values of the current expressions. 308void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEV *IterationCount) { 309 BasicBlock *Preheader = L->getLoopPreheader(); 310 311 // Scan all of the instructions in the loop, looking at those that have 312 // extra-loop users and which are recurrences. 313 SCEVExpander Rewriter(*SE, *LI); 314 315 // We insert the code into the preheader of the loop if the loop contains 316 // multiple exit blocks, or in the exit block if there is exactly one. 317 BasicBlock *BlockToInsertInto; 318 SmallVector<BasicBlock*, 8> ExitBlocks; 319 L->getUniqueExitBlocks(ExitBlocks); 320 if (ExitBlocks.size() == 1) 321 BlockToInsertInto = ExitBlocks[0]; 322 else 323 BlockToInsertInto = Preheader; 324 BasicBlock::iterator InsertPt = BlockToInsertInto->getFirstNonPHI(); 325 326 bool HasConstantItCount = isa<SCEVConstant>(IterationCount); 327 328 std::set<Instruction*> InstructionsToDelete; 329 std::map<Instruction*, Value*> ExitValues; 330 331 // Find all values that are computed inside the loop, but used outside of it. 332 // Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan 333 // the exit blocks of the loop to find them. 334 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { 335 BasicBlock *ExitBB = ExitBlocks[i]; 336 337 // If there are no PHI nodes in this exit block, then no values defined 338 // inside the loop are used on this path, skip it. 339 PHINode *PN = dyn_cast<PHINode>(ExitBB->begin()); 340 if (!PN) continue; 341 342 unsigned NumPreds = PN->getNumIncomingValues(); 343 344 // Iterate over all of the PHI nodes. 345 BasicBlock::iterator BBI = ExitBB->begin(); 346 while ((PN = dyn_cast<PHINode>(BBI++))) { 347 348 // Iterate over all of the values in all the PHI nodes. 349 for (unsigned i = 0; i != NumPreds; ++i) { 350 // If the value being merged in is not integer or is not defined 351 // in the loop, skip it. 352 Value *InVal = PN->getIncomingValue(i); 353 if (!isa<Instruction>(InVal) || 354 // SCEV only supports integer expressions for now. 355 !isa<IntegerType>(InVal->getType())) 356 continue; 357 358 // If this pred is for a subloop, not L itself, skip it. 359 if (LI->getLoopFor(PN->getIncomingBlock(i)) != L) 360 continue; // The Block is in a subloop, skip it. 361 362 // Check that InVal is defined in the loop. 363 Instruction *Inst = cast<Instruction>(InVal); 364 if (!L->contains(Inst->getParent())) 365 continue; 366 367 // We require that this value either have a computable evolution or that 368 // the loop have a constant iteration count. In the case where the loop 369 // has a constant iteration count, we can sometimes force evaluation of 370 // the exit value through brute force. 371 SCEVHandle SH = SE->getSCEV(Inst); 372 if (!SH->hasComputableLoopEvolution(L) && !HasConstantItCount) 373 continue; // Cannot get exit evolution for the loop value. 374 375 // Okay, this instruction has a user outside of the current loop 376 // and varies predictably *inside* the loop. Evaluate the value it 377 // contains when the loop exits, if possible. 378 SCEVHandle ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop()); 379 if (isa<SCEVCouldNotCompute>(ExitValue) || 380 !ExitValue->isLoopInvariant(L)) 381 continue; 382 383 Changed = true; 384 ++NumReplaced; 385 386 // See if we already computed the exit value for the instruction, if so, 387 // just reuse it. 388 Value *&ExitVal = ExitValues[Inst]; 389 if (!ExitVal) 390 ExitVal = Rewriter.expandCodeFor(ExitValue, InsertPt); 391 392 DOUT << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal 393 << " LoopVal = " << *Inst << "\n"; 394 395 PN->setIncomingValue(i, ExitVal); 396 397 // If this instruction is dead now, schedule it to be removed. 398 if (Inst->use_empty()) 399 InstructionsToDelete.insert(Inst); 400 401 // See if this is a single-entry LCSSA PHI node. If so, we can (and 402 // have to) remove 403 // the PHI entirely. This is safe, because the NewVal won't be variant 404 // in the loop, so we don't need an LCSSA phi node anymore. 405 if (NumPreds == 1) { 406 SE->deleteValueFromRecords(PN); 407 PN->replaceAllUsesWith(ExitVal); 408 PN->eraseFromParent(); 409 break; 410 } 411 } 412 } 413 } 414 415 DeleteTriviallyDeadInstructions(InstructionsToDelete); 416} 417 418bool IndVarSimplify::doInitialization(Loop *L, LPPassManager &LPM) { 419 420 Changed = false; 421 // First step. Check to see if there are any trivial GEP pointer recurrences. 422 // If there are, change them into integer recurrences, permitting analysis by 423 // the SCEV routines. 424 // 425 BasicBlock *Header = L->getHeader(); 426 BasicBlock *Preheader = L->getLoopPreheader(); 427 SE = &LPM.getAnalysis<ScalarEvolution>(); 428 429 std::set<Instruction*> DeadInsts; 430 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) { 431 PHINode *PN = cast<PHINode>(I); 432 if (isa<PointerType>(PN->getType())) 433 EliminatePointerRecurrence(PN, Preheader, DeadInsts); 434 } 435 436 if (!DeadInsts.empty()) 437 DeleteTriviallyDeadInstructions(DeadInsts); 438 439 return Changed; 440} 441 442bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) { 443 444 445 LI = &getAnalysis<LoopInfo>(); 446 SE = &getAnalysis<ScalarEvolution>(); 447 448 Changed = false; 449 BasicBlock *Header = L->getHeader(); 450 std::set<Instruction*> DeadInsts; 451 452 // Verify the input to the pass in already in LCSSA form. 453 assert(L->isLCSSAForm()); 454 455 // Check to see if this loop has a computable loop-invariant execution count. 456 // If so, this means that we can compute the final value of any expressions 457 // that are recurrent in the loop, and substitute the exit values from the 458 // loop into any instructions outside of the loop that use the final values of 459 // the current expressions. 460 // 461 SCEVHandle IterationCount = SE->getIterationCount(L); 462 if (!isa<SCEVCouldNotCompute>(IterationCount)) 463 RewriteLoopExitValues(L, IterationCount); 464 465 // Next, analyze all of the induction variables in the loop, canonicalizing 466 // auxillary induction variables. 467 std::vector<std::pair<PHINode*, SCEVHandle> > IndVars; 468 469 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) { 470 PHINode *PN = cast<PHINode>(I); 471 if (PN->getType()->isInteger()) { // FIXME: when we have fast-math, enable! 472 SCEVHandle SCEV = SE->getSCEV(PN); 473 if (SCEV->hasComputableLoopEvolution(L)) 474 // FIXME: It is an extremely bad idea to indvar substitute anything more 475 // complex than affine induction variables. Doing so will put expensive 476 // polynomial evaluations inside of the loop, and the str reduction pass 477 // currently can only reduce affine polynomials. For now just disable 478 // indvar subst on anything more complex than an affine addrec. 479 if (SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SCEV)) 480 if (AR->isAffine()) 481 IndVars.push_back(std::make_pair(PN, SCEV)); 482 } 483 } 484 485 // If there are no induction variables in the loop, there is nothing more to 486 // do. 487 if (IndVars.empty()) { 488 // Actually, if we know how many times the loop iterates, lets insert a 489 // canonical induction variable to help subsequent passes. 490 if (!isa<SCEVCouldNotCompute>(IterationCount)) { 491 SCEVExpander Rewriter(*SE, *LI); 492 Rewriter.getOrInsertCanonicalInductionVariable(L, 493 IterationCount->getType()); 494 if (Instruction *I = LinearFunctionTestReplace(L, IterationCount, 495 Rewriter)) { 496 std::set<Instruction*> InstructionsToDelete; 497 InstructionsToDelete.insert(I); 498 DeleteTriviallyDeadInstructions(InstructionsToDelete); 499 } 500 } 501 return Changed; 502 } 503 504 // Compute the type of the largest recurrence expression. 505 // 506 const Type *LargestType = IndVars[0].first->getType(); 507 bool DifferingSizes = false; 508 for (unsigned i = 1, e = IndVars.size(); i != e; ++i) { 509 const Type *Ty = IndVars[i].first->getType(); 510 DifferingSizes |= 511 Ty->getPrimitiveSizeInBits() != LargestType->getPrimitiveSizeInBits(); 512 if (Ty->getPrimitiveSizeInBits() > LargestType->getPrimitiveSizeInBits()) 513 LargestType = Ty; 514 } 515 516 // Create a rewriter object which we'll use to transform the code with. 517 SCEVExpander Rewriter(*SE, *LI); 518 519 // Now that we know the largest of of the induction variables in this loop, 520 // insert a canonical induction variable of the largest size. 521 Value *IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L,LargestType); 522 ++NumInserted; 523 Changed = true; 524 DOUT << "INDVARS: New CanIV: " << *IndVar; 525 526 if (!isa<SCEVCouldNotCompute>(IterationCount)) { 527 IterationCount = SE->getTruncateOrZeroExtend(IterationCount, LargestType); 528 if (Instruction *DI = LinearFunctionTestReplace(L, IterationCount,Rewriter)) 529 DeadInsts.insert(DI); 530 } 531 532 // Now that we have a canonical induction variable, we can rewrite any 533 // recurrences in terms of the induction variable. Start with the auxillary 534 // induction variables, and recursively rewrite any of their uses. 535 BasicBlock::iterator InsertPt = Header->getFirstNonPHI(); 536 537 // If there were induction variables of other sizes, cast the primary 538 // induction variable to the right size for them, avoiding the need for the 539 // code evaluation methods to insert induction variables of different sizes. 540 if (DifferingSizes) { 541 SmallVector<unsigned,4> InsertedSizes; 542 InsertedSizes.push_back(LargestType->getPrimitiveSizeInBits()); 543 for (unsigned i = 0, e = IndVars.size(); i != e; ++i) { 544 unsigned ithSize = IndVars[i].first->getType()->getPrimitiveSizeInBits(); 545 if (std::find(InsertedSizes.begin(), InsertedSizes.end(), ithSize) 546 == InsertedSizes.end()) { 547 PHINode *PN = IndVars[i].first; 548 InsertedSizes.push_back(ithSize); 549 Instruction *New = new TruncInst(IndVar, PN->getType(), "indvar", 550 InsertPt); 551 Rewriter.addInsertedValue(New, SE->getSCEV(New)); 552 DOUT << "INDVARS: Made trunc IV for " << *PN 553 << " NewVal = " << *New << "\n"; 554 } 555 } 556 } 557 558 // Rewrite all induction variables in terms of the canonical induction 559 // variable. 560 while (!IndVars.empty()) { 561 PHINode *PN = IndVars.back().first; 562 Value *NewVal = Rewriter.expandCodeFor(IndVars.back().second, InsertPt); 563 DOUT << "INDVARS: Rewrote IV '" << *IndVars.back().second << "' " << *PN 564 << " into = " << *NewVal << "\n"; 565 NewVal->takeName(PN); 566 567 // Replace the old PHI Node with the inserted computation. 568 PN->replaceAllUsesWith(NewVal); 569 DeadInsts.insert(PN); 570 IndVars.pop_back(); 571 ++NumRemoved; 572 Changed = true; 573 } 574 575#if 0 576 // Now replace all derived expressions in the loop body with simpler 577 // expressions. 578 for (LoopInfo::block_iterator I = L->block_begin(), E = L->block_end(); 579 I != E; ++I) { 580 BasicBlock *BB = *I; 581 if (LI->getLoopFor(BB) == L) { // Not in a subloop... 582 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 583 if (I->getType()->isInteger() && // Is an integer instruction 584 !I->use_empty() && 585 !Rewriter.isInsertedInstruction(I)) { 586 SCEVHandle SH = SE->getSCEV(I); 587 Value *V = Rewriter.expandCodeFor(SH, I, I->getType()); 588 if (V != I) { 589 if (isa<Instruction>(V)) 590 V->takeName(I); 591 I->replaceAllUsesWith(V); 592 DeadInsts.insert(I); 593 ++NumRemoved; 594 Changed = true; 595 } 596 } 597 } 598 } 599#endif 600 601 DeleteTriviallyDeadInstructions(DeadInsts); 602 OptimizeCanonicalIVType(L); 603 assert(L->isLCSSAForm()); 604 return Changed; 605} 606 607/// OptimizeCanonicalIVType - If loop induction variable is always 608/// sign or zero extended then extend the type of the induction 609/// variable. 610void IndVarSimplify::OptimizeCanonicalIVType(Loop *L) { 611 PHINode *PH = L->getCanonicalInductionVariable(); 612 if (!PH) return; 613 614 // Check loop iteration count. 615 SCEVHandle IC = SE->getIterationCount(L); 616 if (isa<SCEVCouldNotCompute>(IC)) return; 617 SCEVConstant *IterationCount = dyn_cast<SCEVConstant>(IC); 618 if (!IterationCount) return; 619 620 unsigned IncomingEdge = L->contains(PH->getIncomingBlock(0)); 621 unsigned BackEdge = IncomingEdge^1; 622 623 // Check IV uses. If all IV uses are either SEXT or ZEXT (except 624 // IV increment instruction) then this IV is suitable for this 625 // transformation. 626 bool isSEXT = false; 627 BinaryOperator *Incr = NULL; 628 const Type *NewType = NULL; 629 for(Value::use_iterator UI = PH->use_begin(), UE = PH->use_end(); 630 UI != UE; ++UI) { 631 const Type *CandidateType = NULL; 632 if (ZExtInst *ZI = dyn_cast<ZExtInst>(UI)) 633 CandidateType = ZI->getDestTy(); 634 else if (SExtInst *SI = dyn_cast<SExtInst>(UI)) { 635 CandidateType = SI->getDestTy(); 636 isSEXT = true; 637 } 638 else if ((Incr = dyn_cast<BinaryOperator>(UI))) { 639 // Validate IV increment instruction. 640 if (PH->getIncomingValue(BackEdge) == Incr) 641 continue; 642 } 643 if (!CandidateType) { 644 NewType = NULL; 645 break; 646 } 647 if (!NewType) 648 NewType = CandidateType; 649 else if (NewType != CandidateType) { 650 NewType = NULL; 651 break; 652 } 653 } 654 655 // IV uses are not suitable then avoid this transformation. 656 if (!NewType || !Incr) 657 return; 658 659 // IV increment instruction has two uses, one is loop exit condition 660 // and second is the IV (phi node) itself. 661 ICmpInst *Exit = NULL; 662 for(Value::use_iterator II = Incr->use_begin(), IE = Incr->use_end(); 663 II != IE; ++II) { 664 if (PH == *II) continue; 665 Exit = dyn_cast<ICmpInst>(*II); 666 break; 667 } 668 if (!Exit) return; 669 ConstantInt *EV = dyn_cast<ConstantInt>(Exit->getOperand(0)); 670 if (!EV) 671 EV = dyn_cast<ConstantInt>(Exit->getOperand(1)); 672 if (!EV) return; 673 674 // Check iteration count max value to avoid loops that wrap around IV. 675 APInt ICount = IterationCount->getValue()->getValue(); 676 if (ICount.isNegative()) return; 677 uint32_t BW = PH->getType()->getPrimitiveSizeInBits(); 678 APInt Max = (isSEXT ? APInt::getSignedMaxValue(BW) : APInt::getMaxValue(BW)); 679 if (ICount.getZExtValue() > Max.getZExtValue()) return; 680 681 // Extend IV type. 682 683 SCEVExpander Rewriter(*SE, *LI); 684 Value *NewIV = Rewriter.getOrInsertCanonicalInductionVariable(L,NewType); 685 PHINode *NewPH = cast<PHINode>(NewIV); 686 Instruction *NewIncr = cast<Instruction>(NewPH->getIncomingValue(BackEdge)); 687 688 // Replace all SEXT or ZEXT uses. 689 SmallVector<Instruction *, 4> PHUses; 690 for(Value::use_iterator UI = PH->use_begin(), UE = PH->use_end(); 691 UI != UE; ++UI) { 692 Instruction *I = cast<Instruction>(UI); 693 PHUses.push_back(I); 694 } 695 while (!PHUses.empty()){ 696 Instruction *Use = PHUses.back(); PHUses.pop_back(); 697 if (Incr == Use) continue; 698 699 SE->deleteValueFromRecords(Use); 700 Use->replaceAllUsesWith(NewIV); 701 Use->eraseFromParent(); 702 } 703 704 // Replace exit condition. 705 ConstantInt *NEV = ConstantInt::get(NewType, EV->getZExtValue()); 706 Instruction *NE = new ICmpInst(Exit->getPredicate(), 707 NewIncr, NEV, "new.exit", 708 Exit->getParent()->getTerminator()); 709 SE->deleteValueFromRecords(Exit); 710 Exit->replaceAllUsesWith(NE); 711 Exit->eraseFromParent(); 712 713 // Remove old IV and increment instructions. 714 SE->deleteValueFromRecords(PH); 715 PH->removeIncomingValue((unsigned)0); 716 PH->removeIncomingValue((unsigned)0); 717 SE->deleteValueFromRecords(Incr); 718 Incr->eraseFromParent(); 719} 720 721