IndVarSimplify.cpp revision ae73dc1448d25b02cabc7c64c86c64371453dda8
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} 98 99char IndVarSimplify::ID = 0; 100static RegisterPass<IndVarSimplify> 101X("indvars", "Canonicalize Induction Variables"); 102 103LoopPass *llvm::createIndVarSimplifyPass() { 104 return new IndVarSimplify(); 105} 106 107/// DeleteTriviallyDeadInstructions - If any of the instructions is the 108/// specified set are trivially dead, delete them and see if this makes any of 109/// their operands subsequently dead. 110void IndVarSimplify:: 111DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts) { 112 while (!Insts.empty()) { 113 Instruction *I = *Insts.begin(); 114 Insts.erase(Insts.begin()); 115 if (isInstructionTriviallyDead(I)) { 116 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 117 if (Instruction *U = dyn_cast<Instruction>(I->getOperand(i))) 118 Insts.insert(U); 119 SE->deleteValueFromRecords(I); 120 DOUT << "INDVARS: Deleting: " << *I; 121 I->eraseFromParent(); 122 Changed = true; 123 } 124 } 125} 126 127 128/// EliminatePointerRecurrence - Check to see if this is a trivial GEP pointer 129/// recurrence. If so, change it into an integer recurrence, permitting 130/// analysis by the SCEV routines. 131void IndVarSimplify::EliminatePointerRecurrence(PHINode *PN, 132 BasicBlock *Preheader, 133 std::set<Instruction*> &DeadInsts) { 134 assert(PN->getNumIncomingValues() == 2 && "Noncanonicalized loop!"); 135 unsigned PreheaderIdx = PN->getBasicBlockIndex(Preheader); 136 unsigned BackedgeIdx = PreheaderIdx^1; 137 if (GetElementPtrInst *GEPI = 138 dyn_cast<GetElementPtrInst>(PN->getIncomingValue(BackedgeIdx))) 139 if (GEPI->getOperand(0) == PN) { 140 assert(GEPI->getNumOperands() == 2 && "GEP types must match!"); 141 DOUT << "INDVARS: Eliminating pointer recurrence: " << *GEPI; 142 143 // Okay, we found a pointer recurrence. Transform this pointer 144 // recurrence into an integer recurrence. Compute the value that gets 145 // added to the pointer at every iteration. 146 Value *AddedVal = GEPI->getOperand(1); 147 148 // Insert a new integer PHI node into the top of the block. 149 PHINode *NewPhi = PHINode::Create(AddedVal->getType(), 150 PN->getName()+".rec", PN); 151 NewPhi->addIncoming(Constant::getNullValue(NewPhi->getType()), Preheader); 152 153 // Create the new add instruction. 154 Value *NewAdd = BinaryOperator::CreateAdd(NewPhi, AddedVal, 155 GEPI->getName()+".rec", GEPI); 156 NewPhi->addIncoming(NewAdd, PN->getIncomingBlock(BackedgeIdx)); 157 158 // Update the existing GEP to use the recurrence. 159 GEPI->setOperand(0, PN->getIncomingValue(PreheaderIdx)); 160 161 // Update the GEP to use the new recurrence we just inserted. 162 GEPI->setOperand(1, NewAdd); 163 164 // If the incoming value is a constant expr GEP, try peeling out the array 165 // 0 index if possible to make things simpler. 166 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEPI->getOperand(0))) 167 if (CE->getOpcode() == Instruction::GetElementPtr) { 168 unsigned NumOps = CE->getNumOperands(); 169 assert(NumOps > 1 && "CE folding didn't work!"); 170 if (CE->getOperand(NumOps-1)->isNullValue()) { 171 // Check to make sure the last index really is an array index. 172 gep_type_iterator GTI = gep_type_begin(CE); 173 for (unsigned i = 1, e = CE->getNumOperands()-1; 174 i != e; ++i, ++GTI) 175 /*empty*/; 176 if (isa<SequentialType>(*GTI)) { 177 // Pull the last index out of the constant expr GEP. 178 SmallVector<Value*, 8> CEIdxs(CE->op_begin()+1, CE->op_end()-1); 179 Constant *NCE = ConstantExpr::getGetElementPtr(CE->getOperand(0), 180 &CEIdxs[0], 181 CEIdxs.size()); 182 Value *Idx[2]; 183 Idx[0] = Constant::getNullValue(Type::Int32Ty); 184 Idx[1] = NewAdd; 185 GetElementPtrInst *NGEPI = GetElementPtrInst::Create( 186 NCE, Idx, Idx + 2, 187 GEPI->getName(), GEPI); 188 SE->deleteValueFromRecords(GEPI); 189 GEPI->replaceAllUsesWith(NGEPI); 190 GEPI->eraseFromParent(); 191 GEPI = NGEPI; 192 } 193 } 194 } 195 196 197 // Finally, if there are any other users of the PHI node, we must 198 // insert a new GEP instruction that uses the pre-incremented version 199 // of the induction amount. 200 if (!PN->use_empty()) { 201 BasicBlock::iterator InsertPos = PN; ++InsertPos; 202 while (isa<PHINode>(InsertPos)) ++InsertPos; 203 Value *PreInc = 204 GetElementPtrInst::Create(PN->getIncomingValue(PreheaderIdx), 205 NewPhi, "", InsertPos); 206 PreInc->takeName(PN); 207 PN->replaceAllUsesWith(PreInc); 208 } 209 210 // Delete the old PHI for sure, and the GEP if its otherwise unused. 211 DeadInsts.insert(PN); 212 213 ++NumPointer; 214 Changed = true; 215 } 216} 217 218/// LinearFunctionTestReplace - This method rewrites the exit condition of the 219/// loop to be a canonical != comparison against the incremented loop induction 220/// variable. This pass is able to rewrite the exit tests of any loop where the 221/// SCEV analysis can determine a loop-invariant trip count of the loop, which 222/// is actually a much broader range than just linear tests. 223/// 224/// This method returns a "potentially dead" instruction whose computation chain 225/// should be deleted when convenient. 226Instruction *IndVarSimplify::LinearFunctionTestReplace(Loop *L, 227 SCEV *IterationCount, 228 SCEVExpander &RW) { 229 // Find the exit block for the loop. We can currently only handle loops with 230 // a single exit. 231 SmallVector<BasicBlock*, 8> ExitBlocks; 232 L->getExitBlocks(ExitBlocks); 233 if (ExitBlocks.size() != 1) return 0; 234 BasicBlock *ExitBlock = ExitBlocks[0]; 235 236 // Make sure there is only one predecessor block in the loop. 237 BasicBlock *ExitingBlock = 0; 238 for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock); 239 PI != PE; ++PI) 240 if (L->contains(*PI)) { 241 if (ExitingBlock == 0) 242 ExitingBlock = *PI; 243 else 244 return 0; // Multiple exits from loop to this block. 245 } 246 assert(ExitingBlock && "Loop info is broken"); 247 248 if (!isa<BranchInst>(ExitingBlock->getTerminator())) 249 return 0; // Can't rewrite non-branch yet 250 BranchInst *BI = cast<BranchInst>(ExitingBlock->getTerminator()); 251 assert(BI->isConditional() && "Must be conditional to be part of loop!"); 252 253 Instruction *PotentiallyDeadInst = dyn_cast<Instruction>(BI->getCondition()); 254 255 // If the exiting block is not the same as the backedge block, we must compare 256 // against the preincremented value, otherwise we prefer to compare against 257 // the post-incremented value. 258 BasicBlock *Header = L->getHeader(); 259 pred_iterator HPI = pred_begin(Header); 260 assert(HPI != pred_end(Header) && "Loop with zero preds???"); 261 if (!L->contains(*HPI)) ++HPI; 262 assert(HPI != pred_end(Header) && L->contains(*HPI) && 263 "No backedge in loop?"); 264 265 SCEVHandle TripCount = IterationCount; 266 Value *IndVar; 267 if (*HPI == ExitingBlock) { 268 // The IterationCount expression contains the number of times that the 269 // backedge actually branches to the loop header. This is one less than the 270 // number of times the loop executes, so add one to it. 271 ConstantInt *OneC = ConstantInt::get(IterationCount->getType(), 1); 272 TripCount = SE->getAddExpr(IterationCount, SE->getConstant(OneC)); 273 IndVar = L->getCanonicalInductionVariableIncrement(); 274 } else { 275 // We have to use the preincremented value... 276 IndVar = L->getCanonicalInductionVariable(); 277 } 278 279 DOUT << "INDVARS: LFTR: TripCount = " << *TripCount 280 << " IndVar = " << *IndVar << "\n"; 281 282 // Expand the code for the iteration count into the preheader of the loop. 283 BasicBlock *Preheader = L->getLoopPreheader(); 284 Value *ExitCnt = RW.expandCodeFor(TripCount, Preheader->getTerminator()); 285 286 // Insert a new icmp_ne or icmp_eq instruction before the branch. 287 ICmpInst::Predicate Opcode; 288 if (L->contains(BI->getSuccessor(0))) 289 Opcode = ICmpInst::ICMP_NE; 290 else 291 Opcode = ICmpInst::ICMP_EQ; 292 293 Value *Cond = new ICmpInst(Opcode, IndVar, ExitCnt, "exitcond", BI); 294 BI->setCondition(Cond); 295 ++NumLFTR; 296 Changed = true; 297 return PotentiallyDeadInst; 298} 299 300 301/// RewriteLoopExitValues - Check to see if this loop has a computable 302/// loop-invariant execution count. If so, this means that we can compute the 303/// final value of any expressions that are recurrent in the loop, and 304/// substitute the exit values from the loop into any instructions outside of 305/// the loop that use the final values of the current expressions. 306void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEV *IterationCount) { 307 BasicBlock *Preheader = L->getLoopPreheader(); 308 309 // Scan all of the instructions in the loop, looking at those that have 310 // extra-loop users and which are recurrences. 311 SCEVExpander Rewriter(*SE, *LI); 312 313 // We insert the code into the preheader of the loop if the loop contains 314 // multiple exit blocks, or in the exit block if there is exactly one. 315 BasicBlock *BlockToInsertInto; 316 SmallVector<BasicBlock*, 8> ExitBlocks; 317 L->getUniqueExitBlocks(ExitBlocks); 318 if (ExitBlocks.size() == 1) 319 BlockToInsertInto = ExitBlocks[0]; 320 else 321 BlockToInsertInto = Preheader; 322 BasicBlock::iterator InsertPt = BlockToInsertInto->getFirstNonPHI(); 323 324 bool HasConstantItCount = isa<SCEVConstant>(IterationCount); 325 326 std::set<Instruction*> InstructionsToDelete; 327 std::map<Instruction*, Value*> ExitValues; 328 329 // Find all values that are computed inside the loop, but used outside of it. 330 // Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan 331 // the exit blocks of the loop to find them. 332 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { 333 BasicBlock *ExitBB = ExitBlocks[i]; 334 335 // If there are no PHI nodes in this exit block, then no values defined 336 // inside the loop are used on this path, skip it. 337 PHINode *PN = dyn_cast<PHINode>(ExitBB->begin()); 338 if (!PN) continue; 339 340 unsigned NumPreds = PN->getNumIncomingValues(); 341 342 // Iterate over all of the PHI nodes. 343 BasicBlock::iterator BBI = ExitBB->begin(); 344 while ((PN = dyn_cast<PHINode>(BBI++))) { 345 346 // Iterate over all of the values in all the PHI nodes. 347 for (unsigned i = 0; i != NumPreds; ++i) { 348 // If the value being merged in is not integer or is not defined 349 // in the loop, skip it. 350 Value *InVal = PN->getIncomingValue(i); 351 if (!isa<Instruction>(InVal) || 352 // SCEV only supports integer expressions for now. 353 !isa<IntegerType>(InVal->getType())) 354 continue; 355 356 // If this pred is for a subloop, not L itself, skip it. 357 if (LI->getLoopFor(PN->getIncomingBlock(i)) != L) 358 continue; // The Block is in a subloop, skip it. 359 360 // Check that InVal is defined in the loop. 361 Instruction *Inst = cast<Instruction>(InVal); 362 if (!L->contains(Inst->getParent())) 363 continue; 364 365 // We require that this value either have a computable evolution or that 366 // the loop have a constant iteration count. In the case where the loop 367 // has a constant iteration count, we can sometimes force evaluation of 368 // the exit value through brute force. 369 SCEVHandle SH = SE->getSCEV(Inst); 370 if (!SH->hasComputableLoopEvolution(L) && !HasConstantItCount) 371 continue; // Cannot get exit evolution for the loop value. 372 373 // Okay, this instruction has a user outside of the current loop 374 // and varies predictably *inside* the loop. Evaluate the value it 375 // contains when the loop exits, if possible. 376 SCEVHandle ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop()); 377 if (isa<SCEVCouldNotCompute>(ExitValue) || 378 !ExitValue->isLoopInvariant(L)) 379 continue; 380 381 Changed = true; 382 ++NumReplaced; 383 384 // See if we already computed the exit value for the instruction, if so, 385 // just reuse it. 386 Value *&ExitVal = ExitValues[Inst]; 387 if (!ExitVal) 388 ExitVal = Rewriter.expandCodeFor(ExitValue, InsertPt); 389 390 DOUT << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal 391 << " LoopVal = " << *Inst << "\n"; 392 393 PN->setIncomingValue(i, ExitVal); 394 395 // If this instruction is dead now, schedule it to be removed. 396 if (Inst->use_empty()) 397 InstructionsToDelete.insert(Inst); 398 399 // See if this is a single-entry LCSSA PHI node. If so, we can (and 400 // have to) remove 401 // the PHI entirely. This is safe, because the NewVal won't be variant 402 // in the loop, so we don't need an LCSSA phi node anymore. 403 if (NumPreds == 1) { 404 SE->deleteValueFromRecords(PN); 405 PN->replaceAllUsesWith(ExitVal); 406 PN->eraseFromParent(); 407 break; 408 } 409 } 410 } 411 } 412 413 DeleteTriviallyDeadInstructions(InstructionsToDelete); 414} 415 416bool IndVarSimplify::doInitialization(Loop *L, LPPassManager &LPM) { 417 418 Changed = false; 419 // First step. Check to see if there are any trivial GEP pointer recurrences. 420 // If there are, change them into integer recurrences, permitting analysis by 421 // the SCEV routines. 422 // 423 BasicBlock *Header = L->getHeader(); 424 BasicBlock *Preheader = L->getLoopPreheader(); 425 SE = &LPM.getAnalysis<ScalarEvolution>(); 426 427 std::set<Instruction*> DeadInsts; 428 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) { 429 PHINode *PN = cast<PHINode>(I); 430 if (isa<PointerType>(PN->getType())) 431 EliminatePointerRecurrence(PN, Preheader, DeadInsts); 432 } 433 434 if (!DeadInsts.empty()) 435 DeleteTriviallyDeadInstructions(DeadInsts); 436 437 return Changed; 438} 439 440bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) { 441 442 443 LI = &getAnalysis<LoopInfo>(); 444 SE = &getAnalysis<ScalarEvolution>(); 445 446 Changed = false; 447 BasicBlock *Header = L->getHeader(); 448 std::set<Instruction*> DeadInsts; 449 450 // Verify the input to the pass in already in LCSSA form. 451 assert(L->isLCSSAForm()); 452 453 // Check to see if this loop has a computable loop-invariant execution count. 454 // If so, this means that we can compute the final value of any expressions 455 // that are recurrent in the loop, and substitute the exit values from the 456 // loop into any instructions outside of the loop that use the final values of 457 // the current expressions. 458 // 459 SCEVHandle IterationCount = SE->getIterationCount(L); 460 if (!isa<SCEVCouldNotCompute>(IterationCount)) 461 RewriteLoopExitValues(L, IterationCount); 462 463 // Next, analyze all of the induction variables in the loop, canonicalizing 464 // auxillary induction variables. 465 std::vector<std::pair<PHINode*, SCEVHandle> > IndVars; 466 467 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) { 468 PHINode *PN = cast<PHINode>(I); 469 if (PN->getType()->isInteger()) { // FIXME: when we have fast-math, enable! 470 SCEVHandle SCEV = SE->getSCEV(PN); 471 if (SCEV->hasComputableLoopEvolution(L)) 472 // FIXME: It is an extremely bad idea to indvar substitute anything more 473 // complex than affine induction variables. Doing so will put expensive 474 // polynomial evaluations inside of the loop, and the str reduction pass 475 // currently can only reduce affine polynomials. For now just disable 476 // indvar subst on anything more complex than an affine addrec. 477 if (SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SCEV)) 478 if (AR->isAffine()) 479 IndVars.push_back(std::make_pair(PN, SCEV)); 480 } 481 } 482 483 // If there are no induction variables in the loop, there is nothing more to 484 // do. 485 if (IndVars.empty()) { 486 // Actually, if we know how many times the loop iterates, lets insert a 487 // canonical induction variable to help subsequent passes. 488 if (!isa<SCEVCouldNotCompute>(IterationCount)) { 489 SCEVExpander Rewriter(*SE, *LI); 490 Rewriter.getOrInsertCanonicalInductionVariable(L, 491 IterationCount->getType()); 492 if (Instruction *I = LinearFunctionTestReplace(L, IterationCount, 493 Rewriter)) { 494 std::set<Instruction*> InstructionsToDelete; 495 InstructionsToDelete.insert(I); 496 DeleteTriviallyDeadInstructions(InstructionsToDelete); 497 } 498 } 499 return Changed; 500 } 501 502 // Compute the type of the largest recurrence expression. 503 // 504 const Type *LargestType = IndVars[0].first->getType(); 505 bool DifferingSizes = false; 506 for (unsigned i = 1, e = IndVars.size(); i != e; ++i) { 507 const Type *Ty = IndVars[i].first->getType(); 508 DifferingSizes |= 509 Ty->getPrimitiveSizeInBits() != LargestType->getPrimitiveSizeInBits(); 510 if (Ty->getPrimitiveSizeInBits() > LargestType->getPrimitiveSizeInBits()) 511 LargestType = Ty; 512 } 513 514 // Create a rewriter object which we'll use to transform the code with. 515 SCEVExpander Rewriter(*SE, *LI); 516 517 // Now that we know the largest of of the induction variables in this loop, 518 // insert a canonical induction variable of the largest size. 519 Value *IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L,LargestType); 520 ++NumInserted; 521 Changed = true; 522 DOUT << "INDVARS: New CanIV: " << *IndVar; 523 524 if (!isa<SCEVCouldNotCompute>(IterationCount)) { 525 IterationCount = SE->getTruncateOrZeroExtend(IterationCount, LargestType); 526 if (Instruction *DI = LinearFunctionTestReplace(L, IterationCount,Rewriter)) 527 DeadInsts.insert(DI); 528 } 529 530 // Now that we have a canonical induction variable, we can rewrite any 531 // recurrences in terms of the induction variable. Start with the auxillary 532 // induction variables, and recursively rewrite any of their uses. 533 BasicBlock::iterator InsertPt = Header->getFirstNonPHI(); 534 535 // If there were induction variables of other sizes, cast the primary 536 // induction variable to the right size for them, avoiding the need for the 537 // code evaluation methods to insert induction variables of different sizes. 538 if (DifferingSizes) { 539 SmallVector<unsigned,4> InsertedSizes; 540 InsertedSizes.push_back(LargestType->getPrimitiveSizeInBits()); 541 for (unsigned i = 0, e = IndVars.size(); i != e; ++i) { 542 unsigned ithSize = IndVars[i].first->getType()->getPrimitiveSizeInBits(); 543 if (std::find(InsertedSizes.begin(), InsertedSizes.end(), ithSize) 544 == InsertedSizes.end()) { 545 PHINode *PN = IndVars[i].first; 546 InsertedSizes.push_back(ithSize); 547 Instruction *New = new TruncInst(IndVar, PN->getType(), "indvar", 548 InsertPt); 549 Rewriter.addInsertedValue(New, SE->getSCEV(New)); 550 DOUT << "INDVARS: Made trunc IV for " << *PN 551 << " NewVal = " << *New << "\n"; 552 } 553 } 554 } 555 556 // Rewrite all induction variables in terms of the canonical induction 557 // variable. 558 std::map<unsigned, Value*> InsertedSizes; 559 while (!IndVars.empty()) { 560 PHINode *PN = IndVars.back().first; 561 Value *NewVal = Rewriter.expandCodeFor(IndVars.back().second, InsertPt); 562 DOUT << "INDVARS: Rewrote IV '" << *IndVars.back().second << "' " << *PN 563 << " into = " << *NewVal << "\n"; 564 NewVal->takeName(PN); 565 566 // Replace the old PHI Node with the inserted computation. 567 PN->replaceAllUsesWith(NewVal); 568 DeadInsts.insert(PN); 569 IndVars.pop_back(); 570 ++NumRemoved; 571 Changed = true; 572 } 573 574#if 0 575 // Now replace all derived expressions in the loop body with simpler 576 // expressions. 577 for (LoopInfo::block_iterator I = L->block_begin(), E = L->block_end(); 578 I != E; ++I) { 579 BasicBlock *BB = *I; 580 if (LI->getLoopFor(BB) == L) { // Not in a subloop... 581 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 582 if (I->getType()->isInteger() && // Is an integer instruction 583 !I->use_empty() && 584 !Rewriter.isInsertedInstruction(I)) { 585 SCEVHandle SH = SE->getSCEV(I); 586 Value *V = Rewriter.expandCodeFor(SH, I, I->getType()); 587 if (V != I) { 588 if (isa<Instruction>(V)) 589 V->takeName(I); 590 I->replaceAllUsesWith(V); 591 DeadInsts.insert(I); 592 ++NumRemoved; 593 Changed = true; 594 } 595 } 596 } 597 } 598#endif 599 600 DeleteTriviallyDeadInstructions(DeadInsts); 601 602 assert(L->isLCSSAForm()); 603 return Changed; 604} 605