LoopStrengthReduce.cpp revision 193574
1283625Sdim//===- LoopStrengthReduce.cpp - Strength Reduce IVs in Loops --------------===// 2283625Sdim// 3283625Sdim// The LLVM Compiler Infrastructure 4283625Sdim// 5283625Sdim// This file is distributed under the University of Illinois Open Source 6283625Sdim// License. See LICENSE.TXT for details. 7283625Sdim// 8283625Sdim//===----------------------------------------------------------------------===// 9283625Sdim// 10283625Sdim// This transformation analyzes and transforms the induction variables (and 11283625Sdim// computations derived from them) into forms suitable for efficient execution 12283625Sdim// on the target. 13283625Sdim// 14283625Sdim// This pass performs a strength reduction on array references inside loops that 15283625Sdim// have as one or more of their components the loop induction variable, it 16283625Sdim// rewrites expressions to take advantage of scaled-index addressing modes 17283625Sdim// available on the target, and it performs a variety of other optimizations 18283625Sdim// related to loop induction variables. 19283625Sdim// 20283625Sdim//===----------------------------------------------------------------------===// 21283625Sdim 22283625Sdim#define DEBUG_TYPE "loop-reduce" 23283625Sdim#include "llvm/Transforms/Scalar.h" 24283625Sdim#include "llvm/Constants.h" 25283625Sdim#include "llvm/Instructions.h" 26283625Sdim#include "llvm/IntrinsicInst.h" 27283625Sdim#include "llvm/Type.h" 28283625Sdim#include "llvm/DerivedTypes.h" 29283625Sdim#include "llvm/Analysis/Dominators.h" 30283625Sdim#include "llvm/Analysis/IVUsers.h" 31283625Sdim#include "llvm/Analysis/LoopInfo.h" 32283625Sdim#include "llvm/Analysis/LoopPass.h" 33283625Sdim#include "llvm/Analysis/ScalarEvolutionExpander.h" 34283625Sdim#include "llvm/Transforms/Utils/AddrModeMatcher.h" 35283625Sdim#include "llvm/Transforms/Utils/BasicBlockUtils.h" 36283625Sdim#include "llvm/Transforms/Utils/Local.h" 37283625Sdim#include "llvm/ADT/Statistic.h" 38283625Sdim#include "llvm/Support/CFG.h" 39283625Sdim#include "llvm/Support/Debug.h" 40283625Sdim#include "llvm/Support/Compiler.h" 41283625Sdim#include "llvm/Support/CommandLine.h" 42283625Sdim#include "llvm/Support/ValueHandle.h" 43283625Sdim#include "llvm/Target/TargetLowering.h" 44283625Sdim#include <algorithm> 45283625Sdimusing namespace llvm; 46283625Sdim 47283625SdimSTATISTIC(NumReduced , "Number of IV uses strength reduced"); 48283625SdimSTATISTIC(NumInserted, "Number of PHIs inserted"); 49283625SdimSTATISTIC(NumVariable, "Number of PHIs with variable strides"); 50283625SdimSTATISTIC(NumEliminated, "Number of strides eliminated"); 51283625SdimSTATISTIC(NumShadow, "Number of Shadow IVs optimized"); 52283625SdimSTATISTIC(NumImmSunk, "Number of common expr immediates sunk into uses"); 53283625SdimSTATISTIC(NumLoopCond, "Number of loop terminating conds optimized"); 54283625Sdim 55283625Sdimstatic cl::opt<bool> EnableFullLSRMode("enable-full-lsr", 56283625Sdim cl::init(false), 57283625Sdim cl::Hidden); 58283625Sdim 59283625Sdimnamespace { 60283625Sdim 61283625Sdim struct BasedUser; 62283625Sdim 63283625Sdim /// IVInfo - This structure keeps track of one IV expression inserted during 64283625Sdim /// StrengthReduceStridedIVUsers. It contains the stride, the common base, as 65283625Sdim /// well as the PHI node and increment value created for rewrite. 66283625Sdim struct VISIBILITY_HIDDEN IVExpr { 67283625Sdim SCEVHandle Stride; 68283625Sdim SCEVHandle Base; 69283625Sdim PHINode *PHI; 70283625Sdim 71283625Sdim IVExpr(const SCEVHandle &stride, const SCEVHandle &base, PHINode *phi) 72283625Sdim : Stride(stride), Base(base), PHI(phi) {} 73283625Sdim }; 74283625Sdim 75283625Sdim /// IVsOfOneStride - This structure keeps track of all IV expression inserted 76283625Sdim /// during StrengthReduceStridedIVUsers for a particular stride of the IV. 77283625Sdim struct VISIBILITY_HIDDEN IVsOfOneStride { 78283625Sdim std::vector<IVExpr> IVs; 79283625Sdim 80283625Sdim void addIV(const SCEVHandle &Stride, const SCEVHandle &Base, PHINode *PHI) { 81283625Sdim IVs.push_back(IVExpr(Stride, Base, PHI)); 82283625Sdim } 83283625Sdim }; 84283625Sdim 85283625Sdim class VISIBILITY_HIDDEN LoopStrengthReduce : public LoopPass { 86283625Sdim IVUsers *IU; 87283625Sdim LoopInfo *LI; 88283625Sdim DominatorTree *DT; 89283625Sdim ScalarEvolution *SE; 90283625Sdim bool Changed; 91283625Sdim 92283625Sdim /// IVsByStride - Keep track of all IVs that have been inserted for a 93283625Sdim /// particular stride. 94283625Sdim std::map<SCEVHandle, IVsOfOneStride> IVsByStride; 95283625Sdim 96283625Sdim /// StrideNoReuse - Keep track of all the strides whose ivs cannot be 97283625Sdim /// reused (nor should they be rewritten to reuse other strides). 98283625Sdim SmallSet<SCEVHandle, 4> StrideNoReuse; 99283625Sdim 100283625Sdim /// DeadInsts - Keep track of instructions we may have made dead, so that 101283625Sdim /// we can remove them after we are done working. 102283625Sdim SmallVector<WeakVH, 16> DeadInsts; 103283625Sdim 104283625Sdim /// TLI - Keep a pointer of a TargetLowering to consult for determining 105283625Sdim /// transformation profitability. 106283625Sdim const TargetLowering *TLI; 107283625Sdim 108283625Sdim public: 109283625Sdim static char ID; // Pass ID, replacement for typeid 110283625Sdim explicit LoopStrengthReduce(const TargetLowering *tli = NULL) : 111283625Sdim LoopPass(&ID), TLI(tli) { 112283625Sdim } 113283625Sdim 114283625Sdim bool runOnLoop(Loop *L, LPPassManager &LPM); 115283625Sdim 116283625Sdim virtual void getAnalysisUsage(AnalysisUsage &AU) const { 117283625Sdim // We split critical edges, so we change the CFG. However, we do update 118283625Sdim // many analyses if they are around. 119283625Sdim AU.addPreservedID(LoopSimplifyID); 120283625Sdim AU.addPreserved<LoopInfo>(); 121283625Sdim AU.addPreserved<DominanceFrontier>(); 122283625Sdim AU.addPreserved<DominatorTree>(); 123283625Sdim 124283625Sdim AU.addRequiredID(LoopSimplifyID); 125283625Sdim AU.addRequired<LoopInfo>(); 126283625Sdim AU.addRequired<DominatorTree>(); 127283625Sdim AU.addRequired<ScalarEvolution>(); 128283625Sdim AU.addPreserved<ScalarEvolution>(); 129283625Sdim AU.addRequired<IVUsers>(); 130283625Sdim AU.addPreserved<IVUsers>(); 131283625Sdim } 132283625Sdim 133283625Sdim private: 134283625Sdim ICmpInst *ChangeCompareStride(Loop *L, ICmpInst *Cond, 135283625Sdim IVStrideUse* &CondUse, 136283625Sdim const SCEVHandle* &CondStride); 137283625Sdim 138283625Sdim void OptimizeIndvars(Loop *L); 139283625Sdim void OptimizeLoopCountIV(Loop *L); 140283625Sdim void OptimizeLoopTermCond(Loop *L); 141283625Sdim 142296417Sdim /// OptimizeShadowIV - If IV is used in a int-to-float cast 143283625Sdim /// inside the loop then try to eliminate the cast opeation. 144283625Sdim void OptimizeShadowIV(Loop *L); 145283625Sdim 146283625Sdim /// OptimizeSMax - Rewrite the loop's terminating condition 147283625Sdim /// if it uses an smax computation. 148283625Sdim ICmpInst *OptimizeSMax(Loop *L, ICmpInst *Cond, 149283625Sdim IVStrideUse* &CondUse); 150283625Sdim 151283625Sdim bool FindIVUserForCond(ICmpInst *Cond, IVStrideUse *&CondUse, 152283625Sdim const SCEVHandle *&CondStride); 153283625Sdim bool RequiresTypeConversion(const Type *Ty, const Type *NewTy); 154283625Sdim SCEVHandle CheckForIVReuse(bool, bool, bool, const SCEVHandle&, 155283625Sdim IVExpr&, const Type*, 156283625Sdim const std::vector<BasedUser>& UsersToProcess); 157283625Sdim bool ValidScale(bool, int64_t, 158283625Sdim const std::vector<BasedUser>& UsersToProcess); 159283625Sdim bool ValidOffset(bool, int64_t, int64_t, 160283625Sdim const std::vector<BasedUser>& UsersToProcess); 161283625Sdim SCEVHandle CollectIVUsers(const SCEVHandle &Stride, 162283625Sdim IVUsersOfOneStride &Uses, 163283625Sdim Loop *L, 164283625Sdim bool &AllUsesAreAddresses, 165283625Sdim bool &AllUsesAreOutsideLoop, 166283625Sdim std::vector<BasedUser> &UsersToProcess); 167283625Sdim bool ShouldUseFullStrengthReductionMode( 168283625Sdim const std::vector<BasedUser> &UsersToProcess, 169283625Sdim const Loop *L, 170283625Sdim bool AllUsesAreAddresses, 171283625Sdim SCEVHandle Stride); 172283625Sdim void PrepareToStrengthReduceFully( 173283625Sdim std::vector<BasedUser> &UsersToProcess, 174283625Sdim SCEVHandle Stride, 175283625Sdim SCEVHandle CommonExprs, 176283625Sdim const Loop *L, 177283625Sdim SCEVExpander &PreheaderRewriter); 178283625Sdim void PrepareToStrengthReduceFromSmallerStride( 179283625Sdim std::vector<BasedUser> &UsersToProcess, 180283625Sdim Value *CommonBaseV, 181283625Sdim const IVExpr &ReuseIV, 182283625Sdim Instruction *PreInsertPt); 183283625Sdim void PrepareToStrengthReduceWithNewPhi( 184285181Sdim std::vector<BasedUser> &UsersToProcess, 185283625Sdim SCEVHandle Stride, 186283625Sdim SCEVHandle CommonExprs, 187283625Sdim Value *CommonBaseV, 188283625Sdim Instruction *IVIncInsertPt, 189283625Sdim const Loop *L, 190283625Sdim SCEVExpander &PreheaderRewriter); 191283625Sdim void StrengthReduceStridedIVUsers(const SCEVHandle &Stride, 192283625Sdim IVUsersOfOneStride &Uses, 193 Loop *L); 194 void DeleteTriviallyDeadInstructions(); 195 }; 196} 197 198char LoopStrengthReduce::ID = 0; 199static RegisterPass<LoopStrengthReduce> 200X("loop-reduce", "Loop Strength Reduction"); 201 202Pass *llvm::createLoopStrengthReducePass(const TargetLowering *TLI) { 203 return new LoopStrengthReduce(TLI); 204} 205 206/// DeleteTriviallyDeadInstructions - If any of the instructions is the 207/// specified set are trivially dead, delete them and see if this makes any of 208/// their operands subsequently dead. 209void LoopStrengthReduce::DeleteTriviallyDeadInstructions() { 210 if (DeadInsts.empty()) return; 211 212 while (!DeadInsts.empty()) { 213 Instruction *I = dyn_cast_or_null<Instruction>(DeadInsts.back()); 214 DeadInsts.pop_back(); 215 216 if (I == 0 || !isInstructionTriviallyDead(I)) 217 continue; 218 219 for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI) { 220 if (Instruction *U = dyn_cast<Instruction>(*OI)) { 221 *OI = 0; 222 if (U->use_empty()) 223 DeadInsts.push_back(U); 224 } 225 } 226 227 I->eraseFromParent(); 228 Changed = true; 229 } 230} 231 232/// containsAddRecFromDifferentLoop - Determine whether expression S involves a 233/// subexpression that is an AddRec from a loop other than L. An outer loop 234/// of L is OK, but not an inner loop nor a disjoint loop. 235static bool containsAddRecFromDifferentLoop(SCEVHandle S, Loop *L) { 236 // This is very common, put it first. 237 if (isa<SCEVConstant>(S)) 238 return false; 239 if (const SCEVCommutativeExpr *AE = dyn_cast<SCEVCommutativeExpr>(S)) { 240 for (unsigned int i=0; i< AE->getNumOperands(); i++) 241 if (containsAddRecFromDifferentLoop(AE->getOperand(i), L)) 242 return true; 243 return false; 244 } 245 if (const SCEVAddRecExpr *AE = dyn_cast<SCEVAddRecExpr>(S)) { 246 if (const Loop *newLoop = AE->getLoop()) { 247 if (newLoop == L) 248 return false; 249 // if newLoop is an outer loop of L, this is OK. 250 if (!LoopInfoBase<BasicBlock>::isNotAlreadyContainedIn(L, newLoop)) 251 return false; 252 } 253 return true; 254 } 255 if (const SCEVUDivExpr *DE = dyn_cast<SCEVUDivExpr>(S)) 256 return containsAddRecFromDifferentLoop(DE->getLHS(), L) || 257 containsAddRecFromDifferentLoop(DE->getRHS(), L); 258#if 0 259 // SCEVSDivExpr has been backed out temporarily, but will be back; we'll 260 // need this when it is. 261 if (const SCEVSDivExpr *DE = dyn_cast<SCEVSDivExpr>(S)) 262 return containsAddRecFromDifferentLoop(DE->getLHS(), L) || 263 containsAddRecFromDifferentLoop(DE->getRHS(), L); 264#endif 265 if (const SCEVCastExpr *CE = dyn_cast<SCEVCastExpr>(S)) 266 return containsAddRecFromDifferentLoop(CE->getOperand(), L); 267 return false; 268} 269 270/// isAddressUse - Returns true if the specified instruction is using the 271/// specified value as an address. 272static bool isAddressUse(Instruction *Inst, Value *OperandVal) { 273 bool isAddress = isa<LoadInst>(Inst); 274 if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 275 if (SI->getOperand(1) == OperandVal) 276 isAddress = true; 277 } else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) { 278 // Addressing modes can also be folded into prefetches and a variety 279 // of intrinsics. 280 switch (II->getIntrinsicID()) { 281 default: break; 282 case Intrinsic::prefetch: 283 case Intrinsic::x86_sse2_loadu_dq: 284 case Intrinsic::x86_sse2_loadu_pd: 285 case Intrinsic::x86_sse_loadu_ps: 286 case Intrinsic::x86_sse_storeu_ps: 287 case Intrinsic::x86_sse2_storeu_pd: 288 case Intrinsic::x86_sse2_storeu_dq: 289 case Intrinsic::x86_sse2_storel_dq: 290 if (II->getOperand(1) == OperandVal) 291 isAddress = true; 292 break; 293 } 294 } 295 return isAddress; 296} 297 298/// getAccessType - Return the type of the memory being accessed. 299static const Type *getAccessType(const Instruction *Inst) { 300 const Type *AccessTy = Inst->getType(); 301 if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) 302 AccessTy = SI->getOperand(0)->getType(); 303 else if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) { 304 // Addressing modes can also be folded into prefetches and a variety 305 // of intrinsics. 306 switch (II->getIntrinsicID()) { 307 default: break; 308 case Intrinsic::x86_sse_storeu_ps: 309 case Intrinsic::x86_sse2_storeu_pd: 310 case Intrinsic::x86_sse2_storeu_dq: 311 case Intrinsic::x86_sse2_storel_dq: 312 AccessTy = II->getOperand(1)->getType(); 313 break; 314 } 315 } 316 return AccessTy; 317} 318 319namespace { 320 /// BasedUser - For a particular base value, keep information about how we've 321 /// partitioned the expression so far. 322 struct BasedUser { 323 /// SE - The current ScalarEvolution object. 324 ScalarEvolution *SE; 325 326 /// Base - The Base value for the PHI node that needs to be inserted for 327 /// this use. As the use is processed, information gets moved from this 328 /// field to the Imm field (below). BasedUser values are sorted by this 329 /// field. 330 SCEVHandle Base; 331 332 /// Inst - The instruction using the induction variable. 333 Instruction *Inst; 334 335 /// OperandValToReplace - The operand value of Inst to replace with the 336 /// EmittedBase. 337 Value *OperandValToReplace; 338 339 /// isSigned - The stride (and thus also the Base) of this use may be in 340 /// a narrower type than the use itself (OperandValToReplace->getType()). 341 /// When this is the case, the isSigned field indicates whether the 342 /// IV expression should be signed-extended instead of zero-extended to 343 /// fit the type of the use. 344 bool isSigned; 345 346 /// Imm - The immediate value that should be added to the base immediately 347 /// before Inst, because it will be folded into the imm field of the 348 /// instruction. This is also sometimes used for loop-variant values that 349 /// must be added inside the loop. 350 SCEVHandle Imm; 351 352 /// Phi - The induction variable that performs the striding that 353 /// should be used for this user. 354 PHINode *Phi; 355 356 // isUseOfPostIncrementedValue - True if this should use the 357 // post-incremented version of this IV, not the preincremented version. 358 // This can only be set in special cases, such as the terminating setcc 359 // instruction for a loop and uses outside the loop that are dominated by 360 // the loop. 361 bool isUseOfPostIncrementedValue; 362 363 BasedUser(IVStrideUse &IVSU, ScalarEvolution *se) 364 : SE(se), Base(IVSU.getOffset()), Inst(IVSU.getUser()), 365 OperandValToReplace(IVSU.getOperandValToReplace()), 366 isSigned(IVSU.isSigned()), 367 Imm(SE->getIntegerSCEV(0, Base->getType())), 368 isUseOfPostIncrementedValue(IVSU.isUseOfPostIncrementedValue()) {} 369 370 // Once we rewrite the code to insert the new IVs we want, update the 371 // operands of Inst to use the new expression 'NewBase', with 'Imm' added 372 // to it. 373 void RewriteInstructionToUseNewBase(const SCEVHandle &NewBase, 374 Instruction *InsertPt, 375 SCEVExpander &Rewriter, Loop *L, Pass *P, 376 LoopInfo &LI, 377 SmallVectorImpl<WeakVH> &DeadInsts); 378 379 Value *InsertCodeForBaseAtPosition(const SCEVHandle &NewBase, 380 const Type *Ty, 381 SCEVExpander &Rewriter, 382 Instruction *IP, Loop *L, 383 LoopInfo &LI); 384 void dump() const; 385 }; 386} 387 388void BasedUser::dump() const { 389 cerr << " Base=" << *Base; 390 cerr << " Imm=" << *Imm; 391 cerr << " Inst: " << *Inst; 392} 393 394Value *BasedUser::InsertCodeForBaseAtPosition(const SCEVHandle &NewBase, 395 const Type *Ty, 396 SCEVExpander &Rewriter, 397 Instruction *IP, Loop *L, 398 LoopInfo &LI) { 399 // Figure out where we *really* want to insert this code. In particular, if 400 // the user is inside of a loop that is nested inside of L, we really don't 401 // want to insert this expression before the user, we'd rather pull it out as 402 // many loops as possible. 403 Instruction *BaseInsertPt = IP; 404 405 // Figure out the most-nested loop that IP is in. 406 Loop *InsertLoop = LI.getLoopFor(IP->getParent()); 407 408 // If InsertLoop is not L, and InsertLoop is nested inside of L, figure out 409 // the preheader of the outer-most loop where NewBase is not loop invariant. 410 if (L->contains(IP->getParent())) 411 while (InsertLoop && NewBase->isLoopInvariant(InsertLoop)) { 412 BaseInsertPt = InsertLoop->getLoopPreheader()->getTerminator(); 413 InsertLoop = InsertLoop->getParentLoop(); 414 } 415 416 Value *Base = Rewriter.expandCodeFor(NewBase, 0, BaseInsertPt); 417 418 SCEVHandle NewValSCEV = SE->getUnknown(Base); 419 420 // If there is no immediate value, skip the next part. 421 if (!Imm->isZero()) { 422 // If we are inserting the base and imm values in the same block, make sure 423 // to adjust the IP position if insertion reused a result. 424 if (IP == BaseInsertPt) 425 IP = Rewriter.getInsertionPoint(); 426 427 // Always emit the immediate (if non-zero) into the same block as the user. 428 NewValSCEV = SE->getAddExpr(NewValSCEV, Imm); 429 } 430 431 if (isSigned) 432 NewValSCEV = SE->getTruncateOrSignExtend(NewValSCEV, Ty); 433 else 434 NewValSCEV = SE->getTruncateOrZeroExtend(NewValSCEV, Ty); 435 436 return Rewriter.expandCodeFor(NewValSCEV, Ty, IP); 437} 438 439 440// Once we rewrite the code to insert the new IVs we want, update the 441// operands of Inst to use the new expression 'NewBase', with 'Imm' added 442// to it. NewBasePt is the last instruction which contributes to the 443// value of NewBase in the case that it's a diffferent instruction from 444// the PHI that NewBase is computed from, or null otherwise. 445// 446void BasedUser::RewriteInstructionToUseNewBase(const SCEVHandle &NewBase, 447 Instruction *NewBasePt, 448 SCEVExpander &Rewriter, Loop *L, Pass *P, 449 LoopInfo &LI, 450 SmallVectorImpl<WeakVH> &DeadInsts) { 451 if (!isa<PHINode>(Inst)) { 452 // By default, insert code at the user instruction. 453 BasicBlock::iterator InsertPt = Inst; 454 455 // However, if the Operand is itself an instruction, the (potentially 456 // complex) inserted code may be shared by many users. Because of this, we 457 // want to emit code for the computation of the operand right before its old 458 // computation. This is usually safe, because we obviously used to use the 459 // computation when it was computed in its current block. However, in some 460 // cases (e.g. use of a post-incremented induction variable) the NewBase 461 // value will be pinned to live somewhere after the original computation. 462 // In this case, we have to back off. 463 // 464 // If this is a use outside the loop (which means after, since it is based 465 // on a loop indvar) we use the post-incremented value, so that we don't 466 // artificially make the preinc value live out the bottom of the loop. 467 if (!isUseOfPostIncrementedValue && L->contains(Inst->getParent())) { 468 if (NewBasePt && isa<PHINode>(OperandValToReplace)) { 469 InsertPt = NewBasePt; 470 ++InsertPt; 471 } else if (Instruction *OpInst 472 = dyn_cast<Instruction>(OperandValToReplace)) { 473 InsertPt = OpInst; 474 while (isa<PHINode>(InsertPt)) ++InsertPt; 475 } 476 } 477 Value *NewVal = InsertCodeForBaseAtPosition(NewBase, 478 OperandValToReplace->getType(), 479 Rewriter, InsertPt, L, LI); 480 // Replace the use of the operand Value with the new Phi we just created. 481 Inst->replaceUsesOfWith(OperandValToReplace, NewVal); 482 483 DOUT << " Replacing with "; 484 DEBUG(WriteAsOperand(*DOUT, NewVal, /*PrintType=*/false)); 485 DOUT << ", which has value " << *NewBase << " plus IMM " << *Imm << "\n"; 486 return; 487 } 488 489 // PHI nodes are more complex. We have to insert one copy of the NewBase+Imm 490 // expression into each operand block that uses it. Note that PHI nodes can 491 // have multiple entries for the same predecessor. We use a map to make sure 492 // that a PHI node only has a single Value* for each predecessor (which also 493 // prevents us from inserting duplicate code in some blocks). 494 DenseMap<BasicBlock*, Value*> InsertedCode; 495 PHINode *PN = cast<PHINode>(Inst); 496 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 497 if (PN->getIncomingValue(i) == OperandValToReplace) { 498 // If the original expression is outside the loop, put the replacement 499 // code in the same place as the original expression, 500 // which need not be an immediate predecessor of this PHI. This way we 501 // need only one copy of it even if it is referenced multiple times in 502 // the PHI. We don't do this when the original expression is inside the 503 // loop because multiple copies sometimes do useful sinking of code in 504 // that case(?). 505 Instruction *OldLoc = dyn_cast<Instruction>(OperandValToReplace); 506 if (L->contains(OldLoc->getParent())) { 507 // If this is a critical edge, split the edge so that we do not insert 508 // the code on all predecessor/successor paths. We do this unless this 509 // is the canonical backedge for this loop, as this can make some 510 // inserted code be in an illegal position. 511 BasicBlock *PHIPred = PN->getIncomingBlock(i); 512 if (e != 1 && PHIPred->getTerminator()->getNumSuccessors() > 1 && 513 (PN->getParent() != L->getHeader() || !L->contains(PHIPred))) { 514 515 // First step, split the critical edge. 516 SplitCriticalEdge(PHIPred, PN->getParent(), P, false); 517 518 // Next step: move the basic block. In particular, if the PHI node 519 // is outside of the loop, and PredTI is in the loop, we want to 520 // move the block to be immediately before the PHI block, not 521 // immediately after PredTI. 522 if (L->contains(PHIPred) && !L->contains(PN->getParent())) { 523 BasicBlock *NewBB = PN->getIncomingBlock(i); 524 NewBB->moveBefore(PN->getParent()); 525 } 526 527 // Splitting the edge can reduce the number of PHI entries we have. 528 e = PN->getNumIncomingValues(); 529 } 530 } 531 Value *&Code = InsertedCode[PN->getIncomingBlock(i)]; 532 if (!Code) { 533 // Insert the code into the end of the predecessor block. 534 Instruction *InsertPt = (L->contains(OldLoc->getParent())) ? 535 PN->getIncomingBlock(i)->getTerminator() : 536 OldLoc->getParent()->getTerminator(); 537 Code = InsertCodeForBaseAtPosition(NewBase, PN->getType(), 538 Rewriter, InsertPt, L, LI); 539 540 DOUT << " Changing PHI use to "; 541 DEBUG(WriteAsOperand(*DOUT, Code, /*PrintType=*/false)); 542 DOUT << ", which has value " << *NewBase << " plus IMM " << *Imm << "\n"; 543 } 544 545 // Replace the use of the operand Value with the new Phi we just created. 546 PN->setIncomingValue(i, Code); 547 Rewriter.clear(); 548 } 549 } 550 551 // PHI node might have become a constant value after SplitCriticalEdge. 552 DeadInsts.push_back(Inst); 553} 554 555 556/// fitsInAddressMode - Return true if V can be subsumed within an addressing 557/// mode, and does not need to be put in a register first. 558static bool fitsInAddressMode(const SCEVHandle &V, const Type *AccessTy, 559 const TargetLowering *TLI, bool HasBaseReg) { 560 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(V)) { 561 int64_t VC = SC->getValue()->getSExtValue(); 562 if (TLI) { 563 TargetLowering::AddrMode AM; 564 AM.BaseOffs = VC; 565 AM.HasBaseReg = HasBaseReg; 566 return TLI->isLegalAddressingMode(AM, AccessTy); 567 } else { 568 // Defaults to PPC. PPC allows a sign-extended 16-bit immediate field. 569 return (VC > -(1 << 16) && VC < (1 << 16)-1); 570 } 571 } 572 573 if (const SCEVUnknown *SU = dyn_cast<SCEVUnknown>(V)) 574 if (GlobalValue *GV = dyn_cast<GlobalValue>(SU->getValue())) { 575 if (TLI) { 576 TargetLowering::AddrMode AM; 577 AM.BaseGV = GV; 578 AM.HasBaseReg = HasBaseReg; 579 return TLI->isLegalAddressingMode(AM, AccessTy); 580 } else { 581 // Default: assume global addresses are not legal. 582 } 583 } 584 585 return false; 586} 587 588/// MoveLoopVariantsToImmediateField - Move any subexpressions from Val that are 589/// loop varying to the Imm operand. 590static void MoveLoopVariantsToImmediateField(SCEVHandle &Val, SCEVHandle &Imm, 591 Loop *L, ScalarEvolution *SE) { 592 if (Val->isLoopInvariant(L)) return; // Nothing to do. 593 594 if (const SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) { 595 std::vector<SCEVHandle> NewOps; 596 NewOps.reserve(SAE->getNumOperands()); 597 598 for (unsigned i = 0; i != SAE->getNumOperands(); ++i) 599 if (!SAE->getOperand(i)->isLoopInvariant(L)) { 600 // If this is a loop-variant expression, it must stay in the immediate 601 // field of the expression. 602 Imm = SE->getAddExpr(Imm, SAE->getOperand(i)); 603 } else { 604 NewOps.push_back(SAE->getOperand(i)); 605 } 606 607 if (NewOps.empty()) 608 Val = SE->getIntegerSCEV(0, Val->getType()); 609 else 610 Val = SE->getAddExpr(NewOps); 611 } else if (const SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Val)) { 612 // Try to pull immediates out of the start value of nested addrec's. 613 SCEVHandle Start = SARE->getStart(); 614 MoveLoopVariantsToImmediateField(Start, Imm, L, SE); 615 616 std::vector<SCEVHandle> Ops(SARE->op_begin(), SARE->op_end()); 617 Ops[0] = Start; 618 Val = SE->getAddRecExpr(Ops, SARE->getLoop()); 619 } else { 620 // Otherwise, all of Val is variant, move the whole thing over. 621 Imm = SE->getAddExpr(Imm, Val); 622 Val = SE->getIntegerSCEV(0, Val->getType()); 623 } 624} 625 626 627/// MoveImmediateValues - Look at Val, and pull out any additions of constants 628/// that can fit into the immediate field of instructions in the target. 629/// Accumulate these immediate values into the Imm value. 630static void MoveImmediateValues(const TargetLowering *TLI, 631 const Type *AccessTy, 632 SCEVHandle &Val, SCEVHandle &Imm, 633 bool isAddress, Loop *L, 634 ScalarEvolution *SE) { 635 if (const SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) { 636 std::vector<SCEVHandle> NewOps; 637 NewOps.reserve(SAE->getNumOperands()); 638 639 for (unsigned i = 0; i != SAE->getNumOperands(); ++i) { 640 SCEVHandle NewOp = SAE->getOperand(i); 641 MoveImmediateValues(TLI, AccessTy, NewOp, Imm, isAddress, L, SE); 642 643 if (!NewOp->isLoopInvariant(L)) { 644 // If this is a loop-variant expression, it must stay in the immediate 645 // field of the expression. 646 Imm = SE->getAddExpr(Imm, NewOp); 647 } else { 648 NewOps.push_back(NewOp); 649 } 650 } 651 652 if (NewOps.empty()) 653 Val = SE->getIntegerSCEV(0, Val->getType()); 654 else 655 Val = SE->getAddExpr(NewOps); 656 return; 657 } else if (const SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Val)) { 658 // Try to pull immediates out of the start value of nested addrec's. 659 SCEVHandle Start = SARE->getStart(); 660 MoveImmediateValues(TLI, AccessTy, Start, Imm, isAddress, L, SE); 661 662 if (Start != SARE->getStart()) { 663 std::vector<SCEVHandle> Ops(SARE->op_begin(), SARE->op_end()); 664 Ops[0] = Start; 665 Val = SE->getAddRecExpr(Ops, SARE->getLoop()); 666 } 667 return; 668 } else if (const SCEVMulExpr *SME = dyn_cast<SCEVMulExpr>(Val)) { 669 // Transform "8 * (4 + v)" -> "32 + 8*V" if "32" fits in the immed field. 670 if (isAddress && 671 fitsInAddressMode(SME->getOperand(0), AccessTy, TLI, false) && 672 SME->getNumOperands() == 2 && SME->isLoopInvariant(L)) { 673 674 SCEVHandle SubImm = SE->getIntegerSCEV(0, Val->getType()); 675 SCEVHandle NewOp = SME->getOperand(1); 676 MoveImmediateValues(TLI, AccessTy, NewOp, SubImm, isAddress, L, SE); 677 678 // If we extracted something out of the subexpressions, see if we can 679 // simplify this! 680 if (NewOp != SME->getOperand(1)) { 681 // Scale SubImm up by "8". If the result is a target constant, we are 682 // good. 683 SubImm = SE->getMulExpr(SubImm, SME->getOperand(0)); 684 if (fitsInAddressMode(SubImm, AccessTy, TLI, false)) { 685 // Accumulate the immediate. 686 Imm = SE->getAddExpr(Imm, SubImm); 687 688 // Update what is left of 'Val'. 689 Val = SE->getMulExpr(SME->getOperand(0), NewOp); 690 return; 691 } 692 } 693 } 694 } 695 696 // Loop-variant expressions must stay in the immediate field of the 697 // expression. 698 if ((isAddress && fitsInAddressMode(Val, AccessTy, TLI, false)) || 699 !Val->isLoopInvariant(L)) { 700 Imm = SE->getAddExpr(Imm, Val); 701 Val = SE->getIntegerSCEV(0, Val->getType()); 702 return; 703 } 704 705 // Otherwise, no immediates to move. 706} 707 708static void MoveImmediateValues(const TargetLowering *TLI, 709 Instruction *User, 710 SCEVHandle &Val, SCEVHandle &Imm, 711 bool isAddress, Loop *L, 712 ScalarEvolution *SE) { 713 const Type *AccessTy = getAccessType(User); 714 MoveImmediateValues(TLI, AccessTy, Val, Imm, isAddress, L, SE); 715} 716 717/// SeparateSubExprs - Decompose Expr into all of the subexpressions that are 718/// added together. This is used to reassociate common addition subexprs 719/// together for maximal sharing when rewriting bases. 720static void SeparateSubExprs(std::vector<SCEVHandle> &SubExprs, 721 SCEVHandle Expr, 722 ScalarEvolution *SE) { 723 if (const SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(Expr)) { 724 for (unsigned j = 0, e = AE->getNumOperands(); j != e; ++j) 725 SeparateSubExprs(SubExprs, AE->getOperand(j), SE); 726 } else if (const SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Expr)) { 727 SCEVHandle Zero = SE->getIntegerSCEV(0, Expr->getType()); 728 if (SARE->getOperand(0) == Zero) { 729 SubExprs.push_back(Expr); 730 } else { 731 // Compute the addrec with zero as its base. 732 std::vector<SCEVHandle> Ops(SARE->op_begin(), SARE->op_end()); 733 Ops[0] = Zero; // Start with zero base. 734 SubExprs.push_back(SE->getAddRecExpr(Ops, SARE->getLoop())); 735 736 737 SeparateSubExprs(SubExprs, SARE->getOperand(0), SE); 738 } 739 } else if (!Expr->isZero()) { 740 // Do not add zero. 741 SubExprs.push_back(Expr); 742 } 743} 744 745// This is logically local to the following function, but C++ says we have 746// to make it file scope. 747struct SubExprUseData { unsigned Count; bool notAllUsesAreFree; }; 748 749/// RemoveCommonExpressionsFromUseBases - Look through all of the Bases of all 750/// the Uses, removing any common subexpressions, except that if all such 751/// subexpressions can be folded into an addressing mode for all uses inside 752/// the loop (this case is referred to as "free" in comments herein) we do 753/// not remove anything. This looks for things like (a+b+c) and 754/// (a+c+d) and computes the common (a+c) subexpression. The common expression 755/// is *removed* from the Bases and returned. 756static SCEVHandle 757RemoveCommonExpressionsFromUseBases(std::vector<BasedUser> &Uses, 758 ScalarEvolution *SE, Loop *L, 759 const TargetLowering *TLI) { 760 unsigned NumUses = Uses.size(); 761 762 // Only one use? This is a very common case, so we handle it specially and 763 // cheaply. 764 SCEVHandle Zero = SE->getIntegerSCEV(0, Uses[0].Base->getType()); 765 SCEVHandle Result = Zero; 766 SCEVHandle FreeResult = Zero; 767 if (NumUses == 1) { 768 // If the use is inside the loop, use its base, regardless of what it is: 769 // it is clearly shared across all the IV's. If the use is outside the loop 770 // (which means after it) we don't want to factor anything *into* the loop, 771 // so just use 0 as the base. 772 if (L->contains(Uses[0].Inst->getParent())) 773 std::swap(Result, Uses[0].Base); 774 return Result; 775 } 776 777 // To find common subexpressions, count how many of Uses use each expression. 778 // If any subexpressions are used Uses.size() times, they are common. 779 // Also track whether all uses of each expression can be moved into an 780 // an addressing mode "for free"; such expressions are left within the loop. 781 // struct SubExprUseData { unsigned Count; bool notAllUsesAreFree; }; 782 std::map<SCEVHandle, SubExprUseData> SubExpressionUseData; 783 784 // UniqueSubExprs - Keep track of all of the subexpressions we see in the 785 // order we see them. 786 std::vector<SCEVHandle> UniqueSubExprs; 787 788 std::vector<SCEVHandle> SubExprs; 789 unsigned NumUsesInsideLoop = 0; 790 for (unsigned i = 0; i != NumUses; ++i) { 791 // If the user is outside the loop, just ignore it for base computation. 792 // Since the user is outside the loop, it must be *after* the loop (if it 793 // were before, it could not be based on the loop IV). We don't want users 794 // after the loop to affect base computation of values *inside* the loop, 795 // because we can always add their offsets to the result IV after the loop 796 // is done, ensuring we get good code inside the loop. 797 if (!L->contains(Uses[i].Inst->getParent())) 798 continue; 799 NumUsesInsideLoop++; 800 801 // If the base is zero (which is common), return zero now, there are no 802 // CSEs we can find. 803 if (Uses[i].Base == Zero) return Zero; 804 805 // If this use is as an address we may be able to put CSEs in the addressing 806 // mode rather than hoisting them. 807 bool isAddrUse = isAddressUse(Uses[i].Inst, Uses[i].OperandValToReplace); 808 // We may need the AccessTy below, but only when isAddrUse, so compute it 809 // only in that case. 810 const Type *AccessTy = 0; 811 if (isAddrUse) 812 AccessTy = getAccessType(Uses[i].Inst); 813 814 // Split the expression into subexprs. 815 SeparateSubExprs(SubExprs, Uses[i].Base, SE); 816 // Add one to SubExpressionUseData.Count for each subexpr present, and 817 // if the subexpr is not a valid immediate within an addressing mode use, 818 // set SubExpressionUseData.notAllUsesAreFree. We definitely want to 819 // hoist these out of the loop (if they are common to all uses). 820 for (unsigned j = 0, e = SubExprs.size(); j != e; ++j) { 821 if (++SubExpressionUseData[SubExprs[j]].Count == 1) 822 UniqueSubExprs.push_back(SubExprs[j]); 823 if (!isAddrUse || !fitsInAddressMode(SubExprs[j], AccessTy, TLI, false)) 824 SubExpressionUseData[SubExprs[j]].notAllUsesAreFree = true; 825 } 826 SubExprs.clear(); 827 } 828 829 // Now that we know how many times each is used, build Result. Iterate over 830 // UniqueSubexprs so that we have a stable ordering. 831 for (unsigned i = 0, e = UniqueSubExprs.size(); i != e; ++i) { 832 std::map<SCEVHandle, SubExprUseData>::iterator I = 833 SubExpressionUseData.find(UniqueSubExprs[i]); 834 assert(I != SubExpressionUseData.end() && "Entry not found?"); 835 if (I->second.Count == NumUsesInsideLoop) { // Found CSE! 836 if (I->second.notAllUsesAreFree) 837 Result = SE->getAddExpr(Result, I->first); 838 else 839 FreeResult = SE->getAddExpr(FreeResult, I->first); 840 } else 841 // Remove non-cse's from SubExpressionUseData. 842 SubExpressionUseData.erase(I); 843 } 844 845 if (FreeResult != Zero) { 846 // We have some subexpressions that can be subsumed into addressing 847 // modes in every use inside the loop. However, it's possible that 848 // there are so many of them that the combined FreeResult cannot 849 // be subsumed, or that the target cannot handle both a FreeResult 850 // and a Result in the same instruction (for example because it would 851 // require too many registers). Check this. 852 for (unsigned i=0; i<NumUses; ++i) { 853 if (!L->contains(Uses[i].Inst->getParent())) 854 continue; 855 // We know this is an addressing mode use; if there are any uses that 856 // are not, FreeResult would be Zero. 857 const Type *AccessTy = getAccessType(Uses[i].Inst); 858 if (!fitsInAddressMode(FreeResult, AccessTy, TLI, Result!=Zero)) { 859 // FIXME: could split up FreeResult into pieces here, some hoisted 860 // and some not. There is no obvious advantage to this. 861 Result = SE->getAddExpr(Result, FreeResult); 862 FreeResult = Zero; 863 break; 864 } 865 } 866 } 867 868 // If we found no CSE's, return now. 869 if (Result == Zero) return Result; 870 871 // If we still have a FreeResult, remove its subexpressions from 872 // SubExpressionUseData. This means they will remain in the use Bases. 873 if (FreeResult != Zero) { 874 SeparateSubExprs(SubExprs, FreeResult, SE); 875 for (unsigned j = 0, e = SubExprs.size(); j != e; ++j) { 876 std::map<SCEVHandle, SubExprUseData>::iterator I = 877 SubExpressionUseData.find(SubExprs[j]); 878 SubExpressionUseData.erase(I); 879 } 880 SubExprs.clear(); 881 } 882 883 // Otherwise, remove all of the CSE's we found from each of the base values. 884 for (unsigned i = 0; i != NumUses; ++i) { 885 // Uses outside the loop don't necessarily include the common base, but 886 // the final IV value coming into those uses does. Instead of trying to 887 // remove the pieces of the common base, which might not be there, 888 // subtract off the base to compensate for this. 889 if (!L->contains(Uses[i].Inst->getParent())) { 890 Uses[i].Base = SE->getMinusSCEV(Uses[i].Base, Result); 891 continue; 892 } 893 894 // Split the expression into subexprs. 895 SeparateSubExprs(SubExprs, Uses[i].Base, SE); 896 897 // Remove any common subexpressions. 898 for (unsigned j = 0, e = SubExprs.size(); j != e; ++j) 899 if (SubExpressionUseData.count(SubExprs[j])) { 900 SubExprs.erase(SubExprs.begin()+j); 901 --j; --e; 902 } 903 904 // Finally, add the non-shared expressions together. 905 if (SubExprs.empty()) 906 Uses[i].Base = Zero; 907 else 908 Uses[i].Base = SE->getAddExpr(SubExprs); 909 SubExprs.clear(); 910 } 911 912 return Result; 913} 914 915/// ValidScale - Check whether the given Scale is valid for all loads and 916/// stores in UsersToProcess. 917/// 918bool LoopStrengthReduce::ValidScale(bool HasBaseReg, int64_t Scale, 919 const std::vector<BasedUser>& UsersToProcess) { 920 if (!TLI) 921 return true; 922 923 for (unsigned i = 0, e = UsersToProcess.size(); i!=e; ++i) { 924 // If this is a load or other access, pass the type of the access in. 925 const Type *AccessTy = Type::VoidTy; 926 if (isAddressUse(UsersToProcess[i].Inst, 927 UsersToProcess[i].OperandValToReplace)) 928 AccessTy = getAccessType(UsersToProcess[i].Inst); 929 else if (isa<PHINode>(UsersToProcess[i].Inst)) 930 continue; 931 932 TargetLowering::AddrMode AM; 933 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(UsersToProcess[i].Imm)) 934 AM.BaseOffs = SC->getValue()->getSExtValue(); 935 AM.HasBaseReg = HasBaseReg || !UsersToProcess[i].Base->isZero(); 936 AM.Scale = Scale; 937 938 // If load[imm+r*scale] is illegal, bail out. 939 if (!TLI->isLegalAddressingMode(AM, AccessTy)) 940 return false; 941 } 942 return true; 943} 944 945/// ValidOffset - Check whether the given Offset is valid for all loads and 946/// stores in UsersToProcess. 947/// 948bool LoopStrengthReduce::ValidOffset(bool HasBaseReg, 949 int64_t Offset, 950 int64_t Scale, 951 const std::vector<BasedUser>& UsersToProcess) { 952 if (!TLI) 953 return true; 954 955 for (unsigned i=0, e = UsersToProcess.size(); i!=e; ++i) { 956 // If this is a load or other access, pass the type of the access in. 957 const Type *AccessTy = Type::VoidTy; 958 if (isAddressUse(UsersToProcess[i].Inst, 959 UsersToProcess[i].OperandValToReplace)) 960 AccessTy = getAccessType(UsersToProcess[i].Inst); 961 else if (isa<PHINode>(UsersToProcess[i].Inst)) 962 continue; 963 964 TargetLowering::AddrMode AM; 965 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(UsersToProcess[i].Imm)) 966 AM.BaseOffs = SC->getValue()->getSExtValue(); 967 AM.BaseOffs = (uint64_t)AM.BaseOffs + (uint64_t)Offset; 968 AM.HasBaseReg = HasBaseReg || !UsersToProcess[i].Base->isZero(); 969 AM.Scale = Scale; 970 971 // If load[imm+r*scale] is illegal, bail out. 972 if (!TLI->isLegalAddressingMode(AM, AccessTy)) 973 return false; 974 } 975 return true; 976} 977 978/// RequiresTypeConversion - Returns true if converting Ty1 to Ty2 is not 979/// a nop. 980bool LoopStrengthReduce::RequiresTypeConversion(const Type *Ty1, 981 const Type *Ty2) { 982 if (Ty1 == Ty2) 983 return false; 984 Ty1 = SE->getEffectiveSCEVType(Ty1); 985 Ty2 = SE->getEffectiveSCEVType(Ty2); 986 if (Ty1 == Ty2) 987 return false; 988 if (Ty1->canLosslesslyBitCastTo(Ty2)) 989 return false; 990 if (TLI && TLI->isTruncateFree(Ty1, Ty2)) 991 return false; 992 return true; 993} 994 995/// CheckForIVReuse - Returns the multiple if the stride is the multiple 996/// of a previous stride and it is a legal value for the target addressing 997/// mode scale component and optional base reg. This allows the users of 998/// this stride to be rewritten as prev iv * factor. It returns 0 if no 999/// reuse is possible. Factors can be negative on same targets, e.g. ARM. 1000/// 1001/// If all uses are outside the loop, we don't require that all multiplies 1002/// be folded into the addressing mode, nor even that the factor be constant; 1003/// a multiply (executed once) outside the loop is better than another IV 1004/// within. Well, usually. 1005SCEVHandle LoopStrengthReduce::CheckForIVReuse(bool HasBaseReg, 1006 bool AllUsesAreAddresses, 1007 bool AllUsesAreOutsideLoop, 1008 const SCEVHandle &Stride, 1009 IVExpr &IV, const Type *Ty, 1010 const std::vector<BasedUser>& UsersToProcess) { 1011 if (StrideNoReuse.count(Stride)) 1012 return SE->getIntegerSCEV(0, Stride->getType()); 1013 1014 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Stride)) { 1015 int64_t SInt = SC->getValue()->getSExtValue(); 1016 for (unsigned NewStride = 0, e = IU->StrideOrder.size(); 1017 NewStride != e; ++NewStride) { 1018 std::map<SCEVHandle, IVsOfOneStride>::iterator SI = 1019 IVsByStride.find(IU->StrideOrder[NewStride]); 1020 if (SI == IVsByStride.end() || !isa<SCEVConstant>(SI->first) || 1021 StrideNoReuse.count(SI->first)) 1022 continue; 1023 int64_t SSInt = cast<SCEVConstant>(SI->first)->getValue()->getSExtValue(); 1024 if (SI->first != Stride && 1025 (unsigned(abs64(SInt)) < SSInt || (SInt % SSInt) != 0)) 1026 continue; 1027 int64_t Scale = SInt / SSInt; 1028 // Check that this stride is valid for all the types used for loads and 1029 // stores; if it can be used for some and not others, we might as well use 1030 // the original stride everywhere, since we have to create the IV for it 1031 // anyway. If the scale is 1, then we don't need to worry about folding 1032 // multiplications. 1033 if (Scale == 1 || 1034 (AllUsesAreAddresses && 1035 ValidScale(HasBaseReg, Scale, UsersToProcess))) { 1036 // Prefer to reuse an IV with a base of zero. 1037 for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(), 1038 IE = SI->second.IVs.end(); II != IE; ++II) 1039 // Only reuse previous IV if it would not require a type conversion 1040 // and if the base difference can be folded. 1041 if (II->Base->isZero() && 1042 !RequiresTypeConversion(II->Base->getType(), Ty)) { 1043 IV = *II; 1044 return SE->getIntegerSCEV(Scale, Stride->getType()); 1045 } 1046 // Otherwise, settle for an IV with a foldable base. 1047 if (AllUsesAreAddresses) 1048 for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(), 1049 IE = SI->second.IVs.end(); II != IE; ++II) 1050 // Only reuse previous IV if it would not require a type conversion 1051 // and if the base difference can be folded. 1052 if (SE->getEffectiveSCEVType(II->Base->getType()) == 1053 SE->getEffectiveSCEVType(Ty) && 1054 isa<SCEVConstant>(II->Base)) { 1055 int64_t Base = 1056 cast<SCEVConstant>(II->Base)->getValue()->getSExtValue(); 1057 if (Base > INT32_MIN && Base <= INT32_MAX && 1058 ValidOffset(HasBaseReg, -Base * Scale, 1059 Scale, UsersToProcess)) { 1060 IV = *II; 1061 return SE->getIntegerSCEV(Scale, Stride->getType()); 1062 } 1063 } 1064 } 1065 } 1066 } else if (AllUsesAreOutsideLoop) { 1067 // Accept nonconstant strides here; it is really really right to substitute 1068 // an existing IV if we can. 1069 for (unsigned NewStride = 0, e = IU->StrideOrder.size(); 1070 NewStride != e; ++NewStride) { 1071 std::map<SCEVHandle, IVsOfOneStride>::iterator SI = 1072 IVsByStride.find(IU->StrideOrder[NewStride]); 1073 if (SI == IVsByStride.end() || !isa<SCEVConstant>(SI->first)) 1074 continue; 1075 int64_t SSInt = cast<SCEVConstant>(SI->first)->getValue()->getSExtValue(); 1076 if (SI->first != Stride && SSInt != 1) 1077 continue; 1078 for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(), 1079 IE = SI->second.IVs.end(); II != IE; ++II) 1080 // Accept nonzero base here. 1081 // Only reuse previous IV if it would not require a type conversion. 1082 if (!RequiresTypeConversion(II->Base->getType(), Ty)) { 1083 IV = *II; 1084 return Stride; 1085 } 1086 } 1087 // Special case, old IV is -1*x and this one is x. Can treat this one as 1088 // -1*old. 1089 for (unsigned NewStride = 0, e = IU->StrideOrder.size(); 1090 NewStride != e; ++NewStride) { 1091 std::map<SCEVHandle, IVsOfOneStride>::iterator SI = 1092 IVsByStride.find(IU->StrideOrder[NewStride]); 1093 if (SI == IVsByStride.end()) 1094 continue; 1095 if (const SCEVMulExpr *ME = dyn_cast<SCEVMulExpr>(SI->first)) 1096 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(ME->getOperand(0))) 1097 if (Stride == ME->getOperand(1) && 1098 SC->getValue()->getSExtValue() == -1LL) 1099 for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(), 1100 IE = SI->second.IVs.end(); II != IE; ++II) 1101 // Accept nonzero base here. 1102 // Only reuse previous IV if it would not require type conversion. 1103 if (!RequiresTypeConversion(II->Base->getType(), Ty)) { 1104 IV = *II; 1105 return SE->getIntegerSCEV(-1LL, Stride->getType()); 1106 } 1107 } 1108 } 1109 return SE->getIntegerSCEV(0, Stride->getType()); 1110} 1111 1112/// PartitionByIsUseOfPostIncrementedValue - Simple boolean predicate that 1113/// returns true if Val's isUseOfPostIncrementedValue is true. 1114static bool PartitionByIsUseOfPostIncrementedValue(const BasedUser &Val) { 1115 return Val.isUseOfPostIncrementedValue; 1116} 1117 1118/// isNonConstantNegative - Return true if the specified scev is negated, but 1119/// not a constant. 1120static bool isNonConstantNegative(const SCEVHandle &Expr) { 1121 const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(Expr); 1122 if (!Mul) return false; 1123 1124 // If there is a constant factor, it will be first. 1125 const SCEVConstant *SC = dyn_cast<SCEVConstant>(Mul->getOperand(0)); 1126 if (!SC) return false; 1127 1128 // Return true if the value is negative, this matches things like (-42 * V). 1129 return SC->getValue()->getValue().isNegative(); 1130} 1131 1132// CollectIVUsers - Transform our list of users and offsets to a bit more 1133// complex table. In this new vector, each 'BasedUser' contains 'Base', the base 1134// of the strided accesses, as well as the old information from Uses. We 1135// progressively move information from the Base field to the Imm field, until 1136// we eventually have the full access expression to rewrite the use. 1137SCEVHandle LoopStrengthReduce::CollectIVUsers(const SCEVHandle &Stride, 1138 IVUsersOfOneStride &Uses, 1139 Loop *L, 1140 bool &AllUsesAreAddresses, 1141 bool &AllUsesAreOutsideLoop, 1142 std::vector<BasedUser> &UsersToProcess) { 1143 // FIXME: Generalize to non-affine IV's. 1144 if (!Stride->isLoopInvariant(L)) 1145 return SE->getIntegerSCEV(0, Stride->getType()); 1146 1147 UsersToProcess.reserve(Uses.Users.size()); 1148 for (ilist<IVStrideUse>::iterator I = Uses.Users.begin(), 1149 E = Uses.Users.end(); I != E; ++I) { 1150 UsersToProcess.push_back(BasedUser(*I, SE)); 1151 1152 // Move any loop variant operands from the offset field to the immediate 1153 // field of the use, so that we don't try to use something before it is 1154 // computed. 1155 MoveLoopVariantsToImmediateField(UsersToProcess.back().Base, 1156 UsersToProcess.back().Imm, L, SE); 1157 assert(UsersToProcess.back().Base->isLoopInvariant(L) && 1158 "Base value is not loop invariant!"); 1159 } 1160 1161 // We now have a whole bunch of uses of like-strided induction variables, but 1162 // they might all have different bases. We want to emit one PHI node for this 1163 // stride which we fold as many common expressions (between the IVs) into as 1164 // possible. Start by identifying the common expressions in the base values 1165 // for the strides (e.g. if we have "A+C+B" and "A+B+D" as our bases, find 1166 // "A+B"), emit it to the preheader, then remove the expression from the 1167 // UsersToProcess base values. 1168 SCEVHandle CommonExprs = 1169 RemoveCommonExpressionsFromUseBases(UsersToProcess, SE, L, TLI); 1170 1171 // Next, figure out what we can represent in the immediate fields of 1172 // instructions. If we can represent anything there, move it to the imm 1173 // fields of the BasedUsers. We do this so that it increases the commonality 1174 // of the remaining uses. 1175 unsigned NumPHI = 0; 1176 bool HasAddress = false; 1177 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) { 1178 // If the user is not in the current loop, this means it is using the exit 1179 // value of the IV. Do not put anything in the base, make sure it's all in 1180 // the immediate field to allow as much factoring as possible. 1181 if (!L->contains(UsersToProcess[i].Inst->getParent())) { 1182 UsersToProcess[i].Imm = SE->getAddExpr(UsersToProcess[i].Imm, 1183 UsersToProcess[i].Base); 1184 UsersToProcess[i].Base = 1185 SE->getIntegerSCEV(0, UsersToProcess[i].Base->getType()); 1186 } else { 1187 // Not all uses are outside the loop. 1188 AllUsesAreOutsideLoop = false; 1189 1190 // Addressing modes can be folded into loads and stores. Be careful that 1191 // the store is through the expression, not of the expression though. 1192 bool isPHI = false; 1193 bool isAddress = isAddressUse(UsersToProcess[i].Inst, 1194 UsersToProcess[i].OperandValToReplace); 1195 if (isa<PHINode>(UsersToProcess[i].Inst)) { 1196 isPHI = true; 1197 ++NumPHI; 1198 } 1199 1200 if (isAddress) 1201 HasAddress = true; 1202 1203 // If this use isn't an address, then not all uses are addresses. 1204 if (!isAddress && !isPHI) 1205 AllUsesAreAddresses = false; 1206 1207 MoveImmediateValues(TLI, UsersToProcess[i].Inst, UsersToProcess[i].Base, 1208 UsersToProcess[i].Imm, isAddress, L, SE); 1209 } 1210 } 1211 1212 // If one of the use is a PHI node and all other uses are addresses, still 1213 // allow iv reuse. Essentially we are trading one constant multiplication 1214 // for one fewer iv. 1215 if (NumPHI > 1) 1216 AllUsesAreAddresses = false; 1217 1218 // There are no in-loop address uses. 1219 if (AllUsesAreAddresses && (!HasAddress && !AllUsesAreOutsideLoop)) 1220 AllUsesAreAddresses = false; 1221 1222 return CommonExprs; 1223} 1224 1225/// ShouldUseFullStrengthReductionMode - Test whether full strength-reduction 1226/// is valid and profitable for the given set of users of a stride. In 1227/// full strength-reduction mode, all addresses at the current stride are 1228/// strength-reduced all the way down to pointer arithmetic. 1229/// 1230bool LoopStrengthReduce::ShouldUseFullStrengthReductionMode( 1231 const std::vector<BasedUser> &UsersToProcess, 1232 const Loop *L, 1233 bool AllUsesAreAddresses, 1234 SCEVHandle Stride) { 1235 if (!EnableFullLSRMode) 1236 return false; 1237 1238 // The heuristics below aim to avoid increasing register pressure, but 1239 // fully strength-reducing all the addresses increases the number of 1240 // add instructions, so don't do this when optimizing for size. 1241 // TODO: If the loop is large, the savings due to simpler addresses 1242 // may oughtweight the costs of the extra increment instructions. 1243 if (L->getHeader()->getParent()->hasFnAttr(Attribute::OptimizeForSize)) 1244 return false; 1245 1246 // TODO: For now, don't do full strength reduction if there could 1247 // potentially be greater-stride multiples of the current stride 1248 // which could reuse the current stride IV. 1249 if (IU->StrideOrder.back() != Stride) 1250 return false; 1251 1252 // Iterate through the uses to find conditions that automatically rule out 1253 // full-lsr mode. 1254 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ) { 1255 const SCEV *Base = UsersToProcess[i].Base; 1256 const SCEV *Imm = UsersToProcess[i].Imm; 1257 // If any users have a loop-variant component, they can't be fully 1258 // strength-reduced. 1259 if (Imm && !Imm->isLoopInvariant(L)) 1260 return false; 1261 // If there are to users with the same base and the difference between 1262 // the two Imm values can't be folded into the address, full 1263 // strength reduction would increase register pressure. 1264 do { 1265 const SCEV *CurImm = UsersToProcess[i].Imm; 1266 if ((CurImm || Imm) && CurImm != Imm) { 1267 if (!CurImm) CurImm = SE->getIntegerSCEV(0, Stride->getType()); 1268 if (!Imm) Imm = SE->getIntegerSCEV(0, Stride->getType()); 1269 const Instruction *Inst = UsersToProcess[i].Inst; 1270 const Type *AccessTy = getAccessType(Inst); 1271 SCEVHandle Diff = SE->getMinusSCEV(UsersToProcess[i].Imm, Imm); 1272 if (!Diff->isZero() && 1273 (!AllUsesAreAddresses || 1274 !fitsInAddressMode(Diff, AccessTy, TLI, /*HasBaseReg=*/true))) 1275 return false; 1276 } 1277 } while (++i != e && Base == UsersToProcess[i].Base); 1278 } 1279 1280 // If there's exactly one user in this stride, fully strength-reducing it 1281 // won't increase register pressure. If it's starting from a non-zero base, 1282 // it'll be simpler this way. 1283 if (UsersToProcess.size() == 1 && !UsersToProcess[0].Base->isZero()) 1284 return true; 1285 1286 // Otherwise, if there are any users in this stride that don't require 1287 // a register for their base, full strength-reduction will increase 1288 // register pressure. 1289 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) 1290 if (UsersToProcess[i].Base->isZero()) 1291 return false; 1292 1293 // Otherwise, go for it. 1294 return true; 1295} 1296 1297/// InsertAffinePhi Create and insert a PHI node for an induction variable 1298/// with the specified start and step values in the specified loop. 1299/// 1300/// If NegateStride is true, the stride should be negated by using a 1301/// subtract instead of an add. 1302/// 1303/// Return the created phi node. 1304/// 1305static PHINode *InsertAffinePhi(SCEVHandle Start, SCEVHandle Step, 1306 Instruction *IVIncInsertPt, 1307 const Loop *L, 1308 SCEVExpander &Rewriter) { 1309 assert(Start->isLoopInvariant(L) && "New PHI start is not loop invariant!"); 1310 assert(Step->isLoopInvariant(L) && "New PHI stride is not loop invariant!"); 1311 1312 BasicBlock *Header = L->getHeader(); 1313 BasicBlock *Preheader = L->getLoopPreheader(); 1314 BasicBlock *LatchBlock = L->getLoopLatch(); 1315 const Type *Ty = Start->getType(); 1316 Ty = Rewriter.SE.getEffectiveSCEVType(Ty); 1317 1318 PHINode *PN = PHINode::Create(Ty, "lsr.iv", Header->begin()); 1319 PN->addIncoming(Rewriter.expandCodeFor(Start, Ty, Preheader->getTerminator()), 1320 Preheader); 1321 1322 // If the stride is negative, insert a sub instead of an add for the 1323 // increment. 1324 bool isNegative = isNonConstantNegative(Step); 1325 SCEVHandle IncAmount = Step; 1326 if (isNegative) 1327 IncAmount = Rewriter.SE.getNegativeSCEV(Step); 1328 1329 // Insert an add instruction right before the terminator corresponding 1330 // to the back-edge or just before the only use. The location is determined 1331 // by the caller and passed in as IVIncInsertPt. 1332 Value *StepV = Rewriter.expandCodeFor(IncAmount, Ty, 1333 Preheader->getTerminator()); 1334 Instruction *IncV; 1335 if (isNegative) { 1336 IncV = BinaryOperator::CreateSub(PN, StepV, "lsr.iv.next", 1337 IVIncInsertPt); 1338 } else { 1339 IncV = BinaryOperator::CreateAdd(PN, StepV, "lsr.iv.next", 1340 IVIncInsertPt); 1341 } 1342 if (!isa<ConstantInt>(StepV)) ++NumVariable; 1343 1344 PN->addIncoming(IncV, LatchBlock); 1345 1346 ++NumInserted; 1347 return PN; 1348} 1349 1350static void SortUsersToProcess(std::vector<BasedUser> &UsersToProcess) { 1351 // We want to emit code for users inside the loop first. To do this, we 1352 // rearrange BasedUser so that the entries at the end have 1353 // isUseOfPostIncrementedValue = false, because we pop off the end of the 1354 // vector (so we handle them first). 1355 std::partition(UsersToProcess.begin(), UsersToProcess.end(), 1356 PartitionByIsUseOfPostIncrementedValue); 1357 1358 // Sort this by base, so that things with the same base are handled 1359 // together. By partitioning first and stable-sorting later, we are 1360 // guaranteed that within each base we will pop off users from within the 1361 // loop before users outside of the loop with a particular base. 1362 // 1363 // We would like to use stable_sort here, but we can't. The problem is that 1364 // SCEVHandle's don't have a deterministic ordering w.r.t to each other, so 1365 // we don't have anything to do a '<' comparison on. Because we think the 1366 // number of uses is small, do a horrible bubble sort which just relies on 1367 // ==. 1368 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) { 1369 // Get a base value. 1370 SCEVHandle Base = UsersToProcess[i].Base; 1371 1372 // Compact everything with this base to be consecutive with this one. 1373 for (unsigned j = i+1; j != e; ++j) { 1374 if (UsersToProcess[j].Base == Base) { 1375 std::swap(UsersToProcess[i+1], UsersToProcess[j]); 1376 ++i; 1377 } 1378 } 1379 } 1380} 1381 1382/// PrepareToStrengthReduceFully - Prepare to fully strength-reduce 1383/// UsersToProcess, meaning lowering addresses all the way down to direct 1384/// pointer arithmetic. 1385/// 1386void 1387LoopStrengthReduce::PrepareToStrengthReduceFully( 1388 std::vector<BasedUser> &UsersToProcess, 1389 SCEVHandle Stride, 1390 SCEVHandle CommonExprs, 1391 const Loop *L, 1392 SCEVExpander &PreheaderRewriter) { 1393 DOUT << " Fully reducing all users\n"; 1394 1395 // Rewrite the UsersToProcess records, creating a separate PHI for each 1396 // unique Base value. 1397 Instruction *IVIncInsertPt = L->getLoopLatch()->getTerminator(); 1398 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ) { 1399 // TODO: The uses are grouped by base, but not sorted. We arbitrarily 1400 // pick the first Imm value here to start with, and adjust it for the 1401 // other uses. 1402 SCEVHandle Imm = UsersToProcess[i].Imm; 1403 SCEVHandle Base = UsersToProcess[i].Base; 1404 SCEVHandle Start = SE->getAddExpr(CommonExprs, Base, Imm); 1405 PHINode *Phi = InsertAffinePhi(Start, Stride, IVIncInsertPt, L, 1406 PreheaderRewriter); 1407 // Loop over all the users with the same base. 1408 do { 1409 UsersToProcess[i].Base = SE->getIntegerSCEV(0, Stride->getType()); 1410 UsersToProcess[i].Imm = SE->getMinusSCEV(UsersToProcess[i].Imm, Imm); 1411 UsersToProcess[i].Phi = Phi; 1412 assert(UsersToProcess[i].Imm->isLoopInvariant(L) && 1413 "ShouldUseFullStrengthReductionMode should reject this!"); 1414 } while (++i != e && Base == UsersToProcess[i].Base); 1415 } 1416} 1417 1418/// FindIVIncInsertPt - Return the location to insert the increment instruction. 1419/// If the only use if a use of postinc value, (must be the loop termination 1420/// condition), then insert it just before the use. 1421static Instruction *FindIVIncInsertPt(std::vector<BasedUser> &UsersToProcess, 1422 const Loop *L) { 1423 if (UsersToProcess.size() == 1 && 1424 UsersToProcess[0].isUseOfPostIncrementedValue && 1425 L->contains(UsersToProcess[0].Inst->getParent())) 1426 return UsersToProcess[0].Inst; 1427 return L->getLoopLatch()->getTerminator(); 1428} 1429 1430/// PrepareToStrengthReduceWithNewPhi - Insert a new induction variable for the 1431/// given users to share. 1432/// 1433void 1434LoopStrengthReduce::PrepareToStrengthReduceWithNewPhi( 1435 std::vector<BasedUser> &UsersToProcess, 1436 SCEVHandle Stride, 1437 SCEVHandle CommonExprs, 1438 Value *CommonBaseV, 1439 Instruction *IVIncInsertPt, 1440 const Loop *L, 1441 SCEVExpander &PreheaderRewriter) { 1442 DOUT << " Inserting new PHI:\n"; 1443 1444 PHINode *Phi = InsertAffinePhi(SE->getUnknown(CommonBaseV), 1445 Stride, IVIncInsertPt, L, 1446 PreheaderRewriter); 1447 1448 // Remember this in case a later stride is multiple of this. 1449 IVsByStride[Stride].addIV(Stride, CommonExprs, Phi); 1450 1451 // All the users will share this new IV. 1452 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) 1453 UsersToProcess[i].Phi = Phi; 1454 1455 DOUT << " IV="; 1456 DEBUG(WriteAsOperand(*DOUT, Phi, /*PrintType=*/false)); 1457 DOUT << "\n"; 1458} 1459 1460/// PrepareToStrengthReduceFromSmallerStride - Prepare for the given users to 1461/// reuse an induction variable with a stride that is a factor of the current 1462/// induction variable. 1463/// 1464void 1465LoopStrengthReduce::PrepareToStrengthReduceFromSmallerStride( 1466 std::vector<BasedUser> &UsersToProcess, 1467 Value *CommonBaseV, 1468 const IVExpr &ReuseIV, 1469 Instruction *PreInsertPt) { 1470 DOUT << " Rewriting in terms of existing IV of STRIDE " << *ReuseIV.Stride 1471 << " and BASE " << *ReuseIV.Base << "\n"; 1472 1473 // All the users will share the reused IV. 1474 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) 1475 UsersToProcess[i].Phi = ReuseIV.PHI; 1476 1477 Constant *C = dyn_cast<Constant>(CommonBaseV); 1478 if (C && 1479 (!C->isNullValue() && 1480 !fitsInAddressMode(SE->getUnknown(CommonBaseV), CommonBaseV->getType(), 1481 TLI, false))) 1482 // We want the common base emitted into the preheader! This is just 1483 // using cast as a copy so BitCast (no-op cast) is appropriate 1484 CommonBaseV = new BitCastInst(CommonBaseV, CommonBaseV->getType(), 1485 "commonbase", PreInsertPt); 1486} 1487 1488static bool IsImmFoldedIntoAddrMode(GlobalValue *GV, int64_t Offset, 1489 const Type *AccessTy, 1490 std::vector<BasedUser> &UsersToProcess, 1491 const TargetLowering *TLI) { 1492 SmallVector<Instruction*, 16> AddrModeInsts; 1493 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) { 1494 if (UsersToProcess[i].isUseOfPostIncrementedValue) 1495 continue; 1496 ExtAddrMode AddrMode = 1497 AddressingModeMatcher::Match(UsersToProcess[i].OperandValToReplace, 1498 AccessTy, UsersToProcess[i].Inst, 1499 AddrModeInsts, *TLI); 1500 if (GV && GV != AddrMode.BaseGV) 1501 return false; 1502 if (Offset && !AddrMode.BaseOffs) 1503 // FIXME: How to accurate check it's immediate offset is folded. 1504 return false; 1505 AddrModeInsts.clear(); 1506 } 1507 return true; 1508} 1509 1510/// StrengthReduceStridedIVUsers - Strength reduce all of the users of a single 1511/// stride of IV. All of the users may have different starting values, and this 1512/// may not be the only stride. 1513void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride, 1514 IVUsersOfOneStride &Uses, 1515 Loop *L) { 1516 // If all the users are moved to another stride, then there is nothing to do. 1517 if (Uses.Users.empty()) 1518 return; 1519 1520 // Keep track if every use in UsersToProcess is an address. If they all are, 1521 // we may be able to rewrite the entire collection of them in terms of a 1522 // smaller-stride IV. 1523 bool AllUsesAreAddresses = true; 1524 1525 // Keep track if every use of a single stride is outside the loop. If so, 1526 // we want to be more aggressive about reusing a smaller-stride IV; a 1527 // multiply outside the loop is better than another IV inside. Well, usually. 1528 bool AllUsesAreOutsideLoop = true; 1529 1530 // Transform our list of users and offsets to a bit more complex table. In 1531 // this new vector, each 'BasedUser' contains 'Base' the base of the 1532 // strided accessas well as the old information from Uses. We progressively 1533 // move information from the Base field to the Imm field, until we eventually 1534 // have the full access expression to rewrite the use. 1535 std::vector<BasedUser> UsersToProcess; 1536 SCEVHandle CommonExprs = CollectIVUsers(Stride, Uses, L, AllUsesAreAddresses, 1537 AllUsesAreOutsideLoop, 1538 UsersToProcess); 1539 1540 // Sort the UsersToProcess array so that users with common bases are 1541 // next to each other. 1542 SortUsersToProcess(UsersToProcess); 1543 1544 // If we managed to find some expressions in common, we'll need to carry 1545 // their value in a register and add it in for each use. This will take up 1546 // a register operand, which potentially restricts what stride values are 1547 // valid. 1548 bool HaveCommonExprs = !CommonExprs->isZero(); 1549 const Type *ReplacedTy = CommonExprs->getType(); 1550 1551 // If all uses are addresses, consider sinking the immediate part of the 1552 // common expression back into uses if they can fit in the immediate fields. 1553 if (TLI && HaveCommonExprs && AllUsesAreAddresses) { 1554 SCEVHandle NewCommon = CommonExprs; 1555 SCEVHandle Imm = SE->getIntegerSCEV(0, ReplacedTy); 1556 MoveImmediateValues(TLI, Type::VoidTy, NewCommon, Imm, true, L, SE); 1557 if (!Imm->isZero()) { 1558 bool DoSink = true; 1559 1560 // If the immediate part of the common expression is a GV, check if it's 1561 // possible to fold it into the target addressing mode. 1562 GlobalValue *GV = 0; 1563 if (const SCEVUnknown *SU = dyn_cast<SCEVUnknown>(Imm)) 1564 GV = dyn_cast<GlobalValue>(SU->getValue()); 1565 int64_t Offset = 0; 1566 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Imm)) 1567 Offset = SC->getValue()->getSExtValue(); 1568 if (GV || Offset) 1569 // Pass VoidTy as the AccessTy to be conservative, because 1570 // there could be multiple access types among all the uses. 1571 DoSink = IsImmFoldedIntoAddrMode(GV, Offset, Type::VoidTy, 1572 UsersToProcess, TLI); 1573 1574 if (DoSink) { 1575 DOUT << " Sinking " << *Imm << " back down into uses\n"; 1576 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) 1577 UsersToProcess[i].Imm = SE->getAddExpr(UsersToProcess[i].Imm, Imm); 1578 CommonExprs = NewCommon; 1579 HaveCommonExprs = !CommonExprs->isZero(); 1580 ++NumImmSunk; 1581 } 1582 } 1583 } 1584 1585 // Now that we know what we need to do, insert the PHI node itself. 1586 // 1587 DOUT << "LSR: Examining IVs of TYPE " << *ReplacedTy << " of STRIDE " 1588 << *Stride << ":\n" 1589 << " Common base: " << *CommonExprs << "\n"; 1590 1591 SCEVExpander Rewriter(*SE); 1592 SCEVExpander PreheaderRewriter(*SE); 1593 1594 BasicBlock *Preheader = L->getLoopPreheader(); 1595 Instruction *PreInsertPt = Preheader->getTerminator(); 1596 BasicBlock *LatchBlock = L->getLoopLatch(); 1597 Instruction *IVIncInsertPt = LatchBlock->getTerminator(); 1598 1599 Value *CommonBaseV = Constant::getNullValue(ReplacedTy); 1600 1601 SCEVHandle RewriteFactor = SE->getIntegerSCEV(0, ReplacedTy); 1602 IVExpr ReuseIV(SE->getIntegerSCEV(0, Type::Int32Ty), 1603 SE->getIntegerSCEV(0, Type::Int32Ty), 1604 0); 1605 1606 /// Choose a strength-reduction strategy and prepare for it by creating 1607 /// the necessary PHIs and adjusting the bookkeeping. 1608 if (ShouldUseFullStrengthReductionMode(UsersToProcess, L, 1609 AllUsesAreAddresses, Stride)) { 1610 PrepareToStrengthReduceFully(UsersToProcess, Stride, CommonExprs, L, 1611 PreheaderRewriter); 1612 } else { 1613 // Emit the initial base value into the loop preheader. 1614 CommonBaseV = PreheaderRewriter.expandCodeFor(CommonExprs, ReplacedTy, 1615 PreInsertPt); 1616 1617 // If all uses are addresses, check if it is possible to reuse an IV. The 1618 // new IV must have a stride that is a multiple of the old stride; the 1619 // multiple must be a number that can be encoded in the scale field of the 1620 // target addressing mode; and we must have a valid instruction after this 1621 // substitution, including the immediate field, if any. 1622 RewriteFactor = CheckForIVReuse(HaveCommonExprs, AllUsesAreAddresses, 1623 AllUsesAreOutsideLoop, 1624 Stride, ReuseIV, ReplacedTy, 1625 UsersToProcess); 1626 if (!RewriteFactor->isZero()) 1627 PrepareToStrengthReduceFromSmallerStride(UsersToProcess, CommonBaseV, 1628 ReuseIV, PreInsertPt); 1629 else { 1630 IVIncInsertPt = FindIVIncInsertPt(UsersToProcess, L); 1631 PrepareToStrengthReduceWithNewPhi(UsersToProcess, Stride, CommonExprs, 1632 CommonBaseV, IVIncInsertPt, 1633 L, PreheaderRewriter); 1634 } 1635 } 1636 1637 // Process all the users now, replacing their strided uses with 1638 // strength-reduced forms. This outer loop handles all bases, the inner 1639 // loop handles all users of a particular base. 1640 while (!UsersToProcess.empty()) { 1641 SCEVHandle Base = UsersToProcess.back().Base; 1642 Instruction *Inst = UsersToProcess.back().Inst; 1643 1644 // Emit the code for Base into the preheader. 1645 Value *BaseV = 0; 1646 if (!Base->isZero()) { 1647 BaseV = PreheaderRewriter.expandCodeFor(Base, 0, PreInsertPt); 1648 1649 DOUT << " INSERTING code for BASE = " << *Base << ":"; 1650 if (BaseV->hasName()) 1651 DOUT << " Result value name = %" << BaseV->getNameStr(); 1652 DOUT << "\n"; 1653 1654 // If BaseV is a non-zero constant, make sure that it gets inserted into 1655 // the preheader, instead of being forward substituted into the uses. We 1656 // do this by forcing a BitCast (noop cast) to be inserted into the 1657 // preheader in this case. 1658 if (!fitsInAddressMode(Base, getAccessType(Inst), TLI, false)) { 1659 // We want this constant emitted into the preheader! This is just 1660 // using cast as a copy so BitCast (no-op cast) is appropriate 1661 BaseV = new BitCastInst(BaseV, BaseV->getType(), "preheaderinsert", 1662 PreInsertPt); 1663 } 1664 } 1665 1666 // Emit the code to add the immediate offset to the Phi value, just before 1667 // the instructions that we identified as using this stride and base. 1668 do { 1669 // FIXME: Use emitted users to emit other users. 1670 BasedUser &User = UsersToProcess.back(); 1671 1672 DOUT << " Examining "; 1673 if (User.isUseOfPostIncrementedValue) 1674 DOUT << "postinc"; 1675 else 1676 DOUT << "preinc"; 1677 DOUT << " use "; 1678 DEBUG(WriteAsOperand(*DOUT, UsersToProcess.back().OperandValToReplace, 1679 /*PrintType=*/false)); 1680 DOUT << " in Inst: " << *(User.Inst); 1681 1682 // If this instruction wants to use the post-incremented value, move it 1683 // after the post-inc and use its value instead of the PHI. 1684 Value *RewriteOp = User.Phi; 1685 if (User.isUseOfPostIncrementedValue) { 1686 RewriteOp = User.Phi->getIncomingValueForBlock(LatchBlock); 1687 // If this user is in the loop, make sure it is the last thing in the 1688 // loop to ensure it is dominated by the increment. In case it's the 1689 // only use of the iv, the increment instruction is already before the 1690 // use. 1691 if (L->contains(User.Inst->getParent()) && User.Inst != IVIncInsertPt) 1692 User.Inst->moveBefore(IVIncInsertPt); 1693 } 1694 1695 SCEVHandle RewriteExpr = SE->getUnknown(RewriteOp); 1696 1697 if (SE->getEffectiveSCEVType(RewriteOp->getType()) != 1698 SE->getEffectiveSCEVType(ReplacedTy)) { 1699 assert(SE->getTypeSizeInBits(RewriteOp->getType()) > 1700 SE->getTypeSizeInBits(ReplacedTy) && 1701 "Unexpected widening cast!"); 1702 RewriteExpr = SE->getTruncateExpr(RewriteExpr, ReplacedTy); 1703 } 1704 1705 // If we had to insert new instructions for RewriteOp, we have to 1706 // consider that they may not have been able to end up immediately 1707 // next to RewriteOp, because non-PHI instructions may never precede 1708 // PHI instructions in a block. In this case, remember where the last 1709 // instruction was inserted so that if we're replacing a different 1710 // PHI node, we can use the later point to expand the final 1711 // RewriteExpr. 1712 Instruction *NewBasePt = dyn_cast<Instruction>(RewriteOp); 1713 if (RewriteOp == User.Phi) NewBasePt = 0; 1714 1715 // Clear the SCEVExpander's expression map so that we are guaranteed 1716 // to have the code emitted where we expect it. 1717 Rewriter.clear(); 1718 1719 // If we are reusing the iv, then it must be multiplied by a constant 1720 // factor to take advantage of the addressing mode scale component. 1721 if (!RewriteFactor->isZero()) { 1722 // If we're reusing an IV with a nonzero base (currently this happens 1723 // only when all reuses are outside the loop) subtract that base here. 1724 // The base has been used to initialize the PHI node but we don't want 1725 // it here. 1726 if (!ReuseIV.Base->isZero()) { 1727 SCEVHandle typedBase = ReuseIV.Base; 1728 if (SE->getEffectiveSCEVType(RewriteExpr->getType()) != 1729 SE->getEffectiveSCEVType(ReuseIV.Base->getType())) { 1730 // It's possible the original IV is a larger type than the new IV, 1731 // in which case we have to truncate the Base. We checked in 1732 // RequiresTypeConversion that this is valid. 1733 assert(SE->getTypeSizeInBits(RewriteExpr->getType()) < 1734 SE->getTypeSizeInBits(ReuseIV.Base->getType()) && 1735 "Unexpected lengthening conversion!"); 1736 typedBase = SE->getTruncateExpr(ReuseIV.Base, 1737 RewriteExpr->getType()); 1738 } 1739 RewriteExpr = SE->getMinusSCEV(RewriteExpr, typedBase); 1740 } 1741 1742 // Multiply old variable, with base removed, by new scale factor. 1743 RewriteExpr = SE->getMulExpr(RewriteFactor, 1744 RewriteExpr); 1745 1746 // The common base is emitted in the loop preheader. But since we 1747 // are reusing an IV, it has not been used to initialize the PHI node. 1748 // Add it to the expression used to rewrite the uses. 1749 // When this use is outside the loop, we earlier subtracted the 1750 // common base, and are adding it back here. Use the same expression 1751 // as before, rather than CommonBaseV, so DAGCombiner will zap it. 1752 if (!CommonExprs->isZero()) { 1753 if (L->contains(User.Inst->getParent())) 1754 RewriteExpr = SE->getAddExpr(RewriteExpr, 1755 SE->getUnknown(CommonBaseV)); 1756 else 1757 RewriteExpr = SE->getAddExpr(RewriteExpr, CommonExprs); 1758 } 1759 } 1760 1761 // Now that we know what we need to do, insert code before User for the 1762 // immediate and any loop-variant expressions. 1763 if (BaseV) 1764 // Add BaseV to the PHI value if needed. 1765 RewriteExpr = SE->getAddExpr(RewriteExpr, SE->getUnknown(BaseV)); 1766 1767 User.RewriteInstructionToUseNewBase(RewriteExpr, NewBasePt, 1768 Rewriter, L, this, *LI, 1769 DeadInsts); 1770 1771 // Mark old value we replaced as possibly dead, so that it is eliminated 1772 // if we just replaced the last use of that value. 1773 DeadInsts.push_back(User.OperandValToReplace); 1774 1775 UsersToProcess.pop_back(); 1776 ++NumReduced; 1777 1778 // If there are any more users to process with the same base, process them 1779 // now. We sorted by base above, so we just have to check the last elt. 1780 } while (!UsersToProcess.empty() && UsersToProcess.back().Base == Base); 1781 // TODO: Next, find out which base index is the most common, pull it out. 1782 } 1783 1784 // IMPORTANT TODO: Figure out how to partition the IV's with this stride, but 1785 // different starting values, into different PHIs. 1786} 1787 1788/// FindIVUserForCond - If Cond has an operand that is an expression of an IV, 1789/// set the IV user and stride information and return true, otherwise return 1790/// false. 1791bool LoopStrengthReduce::FindIVUserForCond(ICmpInst *Cond, IVStrideUse *&CondUse, 1792 const SCEVHandle *&CondStride) { 1793 for (unsigned Stride = 0, e = IU->StrideOrder.size(); 1794 Stride != e && !CondUse; ++Stride) { 1795 std::map<SCEVHandle, IVUsersOfOneStride *>::iterator SI = 1796 IU->IVUsesByStride.find(IU->StrideOrder[Stride]); 1797 assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!"); 1798 1799 for (ilist<IVStrideUse>::iterator UI = SI->second->Users.begin(), 1800 E = SI->second->Users.end(); UI != E; ++UI) 1801 if (UI->getUser() == Cond) { 1802 // NOTE: we could handle setcc instructions with multiple uses here, but 1803 // InstCombine does it as well for simple uses, it's not clear that it 1804 // occurs enough in real life to handle. 1805 CondUse = UI; 1806 CondStride = &SI->first; 1807 return true; 1808 } 1809 } 1810 return false; 1811} 1812 1813namespace { 1814 // Constant strides come first which in turns are sorted by their absolute 1815 // values. If absolute values are the same, then positive strides comes first. 1816 // e.g. 1817 // 4, -1, X, 1, 2 ==> 1, -1, 2, 4, X 1818 struct StrideCompare { 1819 const ScalarEvolution *SE; 1820 explicit StrideCompare(const ScalarEvolution *se) : SE(se) {} 1821 1822 bool operator()(const SCEVHandle &LHS, const SCEVHandle &RHS) { 1823 const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS); 1824 const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS); 1825 if (LHSC && RHSC) { 1826 int64_t LV = LHSC->getValue()->getSExtValue(); 1827 int64_t RV = RHSC->getValue()->getSExtValue(); 1828 uint64_t ALV = (LV < 0) ? -LV : LV; 1829 uint64_t ARV = (RV < 0) ? -RV : RV; 1830 if (ALV == ARV) { 1831 if (LV != RV) 1832 return LV > RV; 1833 } else { 1834 return ALV < ARV; 1835 } 1836 1837 // If it's the same value but different type, sort by bit width so 1838 // that we emit larger induction variables before smaller 1839 // ones, letting the smaller be re-written in terms of larger ones. 1840 return SE->getTypeSizeInBits(RHS->getType()) < 1841 SE->getTypeSizeInBits(LHS->getType()); 1842 } 1843 return LHSC && !RHSC; 1844 } 1845 }; 1846} 1847 1848/// ChangeCompareStride - If a loop termination compare instruction is the 1849/// only use of its stride, and the compaison is against a constant value, 1850/// try eliminate the stride by moving the compare instruction to another 1851/// stride and change its constant operand accordingly. e.g. 1852/// 1853/// loop: 1854/// ... 1855/// v1 = v1 + 3 1856/// v2 = v2 + 1 1857/// if (v2 < 10) goto loop 1858/// => 1859/// loop: 1860/// ... 1861/// v1 = v1 + 3 1862/// if (v1 < 30) goto loop 1863ICmpInst *LoopStrengthReduce::ChangeCompareStride(Loop *L, ICmpInst *Cond, 1864 IVStrideUse* &CondUse, 1865 const SCEVHandle* &CondStride) { 1866 // If there's only one stride in the loop, there's nothing to do here. 1867 if (IU->StrideOrder.size() < 2) 1868 return Cond; 1869 // If there are other users of the condition's stride, don't bother 1870 // trying to change the condition because the stride will still 1871 // remain. 1872 std::map<SCEVHandle, IVUsersOfOneStride *>::iterator I = 1873 IU->IVUsesByStride.find(*CondStride); 1874 if (I == IU->IVUsesByStride.end() || 1875 I->second->Users.size() != 1) 1876 return Cond; 1877 // Only handle constant strides for now. 1878 const SCEVConstant *SC = dyn_cast<SCEVConstant>(*CondStride); 1879 if (!SC) return Cond; 1880 1881 ICmpInst::Predicate Predicate = Cond->getPredicate(); 1882 int64_t CmpSSInt = SC->getValue()->getSExtValue(); 1883 unsigned BitWidth = SE->getTypeSizeInBits((*CondStride)->getType()); 1884 uint64_t SignBit = 1ULL << (BitWidth-1); 1885 const Type *CmpTy = Cond->getOperand(0)->getType(); 1886 const Type *NewCmpTy = NULL; 1887 unsigned TyBits = SE->getTypeSizeInBits(CmpTy); 1888 unsigned NewTyBits = 0; 1889 SCEVHandle *NewStride = NULL; 1890 Value *NewCmpLHS = NULL; 1891 Value *NewCmpRHS = NULL; 1892 int64_t Scale = 1; 1893 SCEVHandle NewOffset = SE->getIntegerSCEV(0, CmpTy); 1894 1895 if (ConstantInt *C = dyn_cast<ConstantInt>(Cond->getOperand(1))) { 1896 int64_t CmpVal = C->getValue().getSExtValue(); 1897 1898 // Check stride constant and the comparision constant signs to detect 1899 // overflow. 1900 if ((CmpVal & SignBit) != (CmpSSInt & SignBit)) 1901 return Cond; 1902 1903 // Look for a suitable stride / iv as replacement. 1904 for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) { 1905 std::map<SCEVHandle, IVUsersOfOneStride *>::iterator SI = 1906 IU->IVUsesByStride.find(IU->StrideOrder[i]); 1907 if (!isa<SCEVConstant>(SI->first)) 1908 continue; 1909 int64_t SSInt = cast<SCEVConstant>(SI->first)->getValue()->getSExtValue(); 1910 if (SSInt == CmpSSInt || 1911 abs64(SSInt) < abs64(CmpSSInt) || 1912 (SSInt % CmpSSInt) != 0) 1913 continue; 1914 1915 Scale = SSInt / CmpSSInt; 1916 int64_t NewCmpVal = CmpVal * Scale; 1917 APInt Mul = APInt(BitWidth*2, CmpVal, true); 1918 Mul = Mul * APInt(BitWidth*2, Scale, true); 1919 // Check for overflow. 1920 if (!Mul.isSignedIntN(BitWidth)) 1921 continue; 1922 // Check for overflow in the stride's type too. 1923 if (!Mul.isSignedIntN(SE->getTypeSizeInBits(SI->first->getType()))) 1924 continue; 1925 1926 // Watch out for overflow. 1927 if (ICmpInst::isSignedPredicate(Predicate) && 1928 (CmpVal & SignBit) != (NewCmpVal & SignBit)) 1929 continue; 1930 1931 if (NewCmpVal == CmpVal) 1932 continue; 1933 // Pick the best iv to use trying to avoid a cast. 1934 NewCmpLHS = NULL; 1935 for (ilist<IVStrideUse>::iterator UI = SI->second->Users.begin(), 1936 E = SI->second->Users.end(); UI != E; ++UI) { 1937 Value *Op = UI->getOperandValToReplace(); 1938 1939 // If the IVStrideUse implies a cast, check for an actual cast which 1940 // can be used to find the original IV expression. 1941 if (SE->getEffectiveSCEVType(Op->getType()) != 1942 SE->getEffectiveSCEVType(SI->first->getType())) { 1943 CastInst *CI = dyn_cast<CastInst>(Op); 1944 // If it's not a simple cast, it's complicated. 1945 if (!CI) 1946 continue; 1947 // If it's a cast from a type other than the stride type, 1948 // it's complicated. 1949 if (CI->getOperand(0)->getType() != SI->first->getType()) 1950 continue; 1951 // Ok, we found the IV expression in the stride's type. 1952 Op = CI->getOperand(0); 1953 } 1954 1955 NewCmpLHS = Op; 1956 if (NewCmpLHS->getType() == CmpTy) 1957 break; 1958 } 1959 if (!NewCmpLHS) 1960 continue; 1961 1962 NewCmpTy = NewCmpLHS->getType(); 1963 NewTyBits = SE->getTypeSizeInBits(NewCmpTy); 1964 const Type *NewCmpIntTy = IntegerType::get(NewTyBits); 1965 if (RequiresTypeConversion(NewCmpTy, CmpTy)) { 1966 // Check if it is possible to rewrite it using 1967 // an iv / stride of a smaller integer type. 1968 unsigned Bits = NewTyBits; 1969 if (ICmpInst::isSignedPredicate(Predicate)) 1970 --Bits; 1971 uint64_t Mask = (1ULL << Bits) - 1; 1972 if (((uint64_t)NewCmpVal & Mask) != (uint64_t)NewCmpVal) 1973 continue; 1974 } 1975 1976 // Don't rewrite if use offset is non-constant and the new type is 1977 // of a different type. 1978 // FIXME: too conservative? 1979 if (NewTyBits != TyBits && !isa<SCEVConstant>(CondUse->getOffset())) 1980 continue; 1981 1982 bool AllUsesAreAddresses = true; 1983 bool AllUsesAreOutsideLoop = true; 1984 std::vector<BasedUser> UsersToProcess; 1985 SCEVHandle CommonExprs = CollectIVUsers(SI->first, *SI->second, L, 1986 AllUsesAreAddresses, 1987 AllUsesAreOutsideLoop, 1988 UsersToProcess); 1989 // Avoid rewriting the compare instruction with an iv of new stride 1990 // if it's likely the new stride uses will be rewritten using the 1991 // stride of the compare instruction. 1992 if (AllUsesAreAddresses && 1993 ValidScale(!CommonExprs->isZero(), Scale, UsersToProcess)) 1994 continue; 1995 1996 // Avoid rewriting the compare instruction with an iv which has 1997 // implicit extension or truncation built into it. 1998 // TODO: This is over-conservative. 1999 if (SE->getTypeSizeInBits(CondUse->getOffset()->getType()) != TyBits) 2000 continue; 2001 2002 // If scale is negative, use swapped predicate unless it's testing 2003 // for equality. 2004 if (Scale < 0 && !Cond->isEquality()) 2005 Predicate = ICmpInst::getSwappedPredicate(Predicate); 2006 2007 NewStride = &IU->StrideOrder[i]; 2008 if (!isa<PointerType>(NewCmpTy)) 2009 NewCmpRHS = ConstantInt::get(NewCmpTy, NewCmpVal); 2010 else { 2011 ConstantInt *CI = ConstantInt::get(NewCmpIntTy, NewCmpVal); 2012 NewCmpRHS = ConstantExpr::getIntToPtr(CI, NewCmpTy); 2013 } 2014 NewOffset = TyBits == NewTyBits 2015 ? SE->getMulExpr(CondUse->getOffset(), 2016 SE->getConstant(ConstantInt::get(CmpTy, Scale))) 2017 : SE->getConstant(ConstantInt::get(NewCmpIntTy, 2018 cast<SCEVConstant>(CondUse->getOffset())->getValue() 2019 ->getSExtValue()*Scale)); 2020 break; 2021 } 2022 } 2023 2024 // Forgo this transformation if it the increment happens to be 2025 // unfortunately positioned after the condition, and the condition 2026 // has multiple uses which prevent it from being moved immediately 2027 // before the branch. See 2028 // test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness-*.ll 2029 // for an example of this situation. 2030 if (!Cond->hasOneUse()) { 2031 for (BasicBlock::iterator I = Cond, E = Cond->getParent()->end(); 2032 I != E; ++I) 2033 if (I == NewCmpLHS) 2034 return Cond; 2035 } 2036 2037 if (NewCmpRHS) { 2038 // Create a new compare instruction using new stride / iv. 2039 ICmpInst *OldCond = Cond; 2040 // Insert new compare instruction. 2041 Cond = new ICmpInst(Predicate, NewCmpLHS, NewCmpRHS, 2042 L->getHeader()->getName() + ".termcond", 2043 OldCond); 2044 2045 // Remove the old compare instruction. The old indvar is probably dead too. 2046 DeadInsts.push_back(CondUse->getOperandValToReplace()); 2047 OldCond->replaceAllUsesWith(Cond); 2048 OldCond->eraseFromParent(); 2049 2050 IU->IVUsesByStride[*NewStride]->addUser(NewOffset, Cond, NewCmpLHS, false); 2051 CondUse = &IU->IVUsesByStride[*NewStride]->Users.back(); 2052 CondStride = NewStride; 2053 ++NumEliminated; 2054 Changed = true; 2055 } 2056 2057 return Cond; 2058} 2059 2060/// OptimizeSMax - Rewrite the loop's terminating condition if it uses 2061/// an smax computation. 2062/// 2063/// This is a narrow solution to a specific, but acute, problem. For loops 2064/// like this: 2065/// 2066/// i = 0; 2067/// do { 2068/// p[i] = 0.0; 2069/// } while (++i < n); 2070/// 2071/// where the comparison is signed, the trip count isn't just 'n', because 2072/// 'n' could be negative. And unfortunately this can come up even for loops 2073/// where the user didn't use a C do-while loop. For example, seemingly 2074/// well-behaved top-test loops will commonly be lowered like this: 2075// 2076/// if (n > 0) { 2077/// i = 0; 2078/// do { 2079/// p[i] = 0.0; 2080/// } while (++i < n); 2081/// } 2082/// 2083/// and then it's possible for subsequent optimization to obscure the if 2084/// test in such a way that indvars can't find it. 2085/// 2086/// When indvars can't find the if test in loops like this, it creates a 2087/// signed-max expression, which allows it to give the loop a canonical 2088/// induction variable: 2089/// 2090/// i = 0; 2091/// smax = n < 1 ? 1 : n; 2092/// do { 2093/// p[i] = 0.0; 2094/// } while (++i != smax); 2095/// 2096/// Canonical induction variables are necessary because the loop passes 2097/// are designed around them. The most obvious example of this is the 2098/// LoopInfo analysis, which doesn't remember trip count values. It 2099/// expects to be able to rediscover the trip count each time it is 2100/// needed, and it does this using a simple analyis that only succeeds if 2101/// the loop has a canonical induction variable. 2102/// 2103/// However, when it comes time to generate code, the maximum operation 2104/// can be quite costly, especially if it's inside of an outer loop. 2105/// 2106/// This function solves this problem by detecting this type of loop and 2107/// rewriting their conditions from ICMP_NE back to ICMP_SLT, and deleting 2108/// the instructions for the maximum computation. 2109/// 2110ICmpInst *LoopStrengthReduce::OptimizeSMax(Loop *L, ICmpInst *Cond, 2111 IVStrideUse* &CondUse) { 2112 // Check that the loop matches the pattern we're looking for. 2113 if (Cond->getPredicate() != CmpInst::ICMP_EQ && 2114 Cond->getPredicate() != CmpInst::ICMP_NE) 2115 return Cond; 2116 2117 SelectInst *Sel = dyn_cast<SelectInst>(Cond->getOperand(1)); 2118 if (!Sel || !Sel->hasOneUse()) return Cond; 2119 2120 SCEVHandle BackedgeTakenCount = SE->getBackedgeTakenCount(L); 2121 if (isa<SCEVCouldNotCompute>(BackedgeTakenCount)) 2122 return Cond; 2123 SCEVHandle One = SE->getIntegerSCEV(1, BackedgeTakenCount->getType()); 2124 2125 // Add one to the backedge-taken count to get the trip count. 2126 SCEVHandle IterationCount = SE->getAddExpr(BackedgeTakenCount, One); 2127 2128 // Check for a max calculation that matches the pattern. 2129 const SCEVSMaxExpr *SMax = dyn_cast<SCEVSMaxExpr>(IterationCount); 2130 if (!SMax || SMax != SE->getSCEV(Sel)) return Cond; 2131 2132 SCEVHandle SMaxLHS = SMax->getOperand(0); 2133 SCEVHandle SMaxRHS = SMax->getOperand(1); 2134 if (!SMaxLHS || SMaxLHS != One) return Cond; 2135 2136 // Check the relevant induction variable for conformance to 2137 // the pattern. 2138 SCEVHandle IV = SE->getSCEV(Cond->getOperand(0)); 2139 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV); 2140 if (!AR || !AR->isAffine() || 2141 AR->getStart() != One || 2142 AR->getStepRecurrence(*SE) != One) 2143 return Cond; 2144 2145 assert(AR->getLoop() == L && 2146 "Loop condition operand is an addrec in a different loop!"); 2147 2148 // Check the right operand of the select, and remember it, as it will 2149 // be used in the new comparison instruction. 2150 Value *NewRHS = 0; 2151 if (SE->getSCEV(Sel->getOperand(1)) == SMaxRHS) 2152 NewRHS = Sel->getOperand(1); 2153 else if (SE->getSCEV(Sel->getOperand(2)) == SMaxRHS) 2154 NewRHS = Sel->getOperand(2); 2155 if (!NewRHS) return Cond; 2156 2157 // Ok, everything looks ok to change the condition into an SLT or SGE and 2158 // delete the max calculation. 2159 ICmpInst *NewCond = 2160 new ICmpInst(Cond->getPredicate() == CmpInst::ICMP_NE ? 2161 CmpInst::ICMP_SLT : 2162 CmpInst::ICMP_SGE, 2163 Cond->getOperand(0), NewRHS, "scmp", Cond); 2164 2165 // Delete the max calculation instructions. 2166 Cond->replaceAllUsesWith(NewCond); 2167 CondUse->setUser(NewCond); 2168 Instruction *Cmp = cast<Instruction>(Sel->getOperand(0)); 2169 Cond->eraseFromParent(); 2170 Sel->eraseFromParent(); 2171 if (Cmp->use_empty()) 2172 Cmp->eraseFromParent(); 2173 return NewCond; 2174} 2175 2176/// OptimizeShadowIV - If IV is used in a int-to-float cast 2177/// inside the loop then try to eliminate the cast opeation. 2178void LoopStrengthReduce::OptimizeShadowIV(Loop *L) { 2179 2180 SCEVHandle BackedgeTakenCount = SE->getBackedgeTakenCount(L); 2181 if (isa<SCEVCouldNotCompute>(BackedgeTakenCount)) 2182 return; 2183 2184 for (unsigned Stride = 0, e = IU->StrideOrder.size(); Stride != e; 2185 ++Stride) { 2186 std::map<SCEVHandle, IVUsersOfOneStride *>::iterator SI = 2187 IU->IVUsesByStride.find(IU->StrideOrder[Stride]); 2188 assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!"); 2189 if (!isa<SCEVConstant>(SI->first)) 2190 continue; 2191 2192 for (ilist<IVStrideUse>::iterator UI = SI->second->Users.begin(), 2193 E = SI->second->Users.end(); UI != E; /* empty */) { 2194 ilist<IVStrideUse>::iterator CandidateUI = UI; 2195 ++UI; 2196 Instruction *ShadowUse = CandidateUI->getUser(); 2197 const Type *DestTy = NULL; 2198 2199 /* If shadow use is a int->float cast then insert a second IV 2200 to eliminate this cast. 2201 2202 for (unsigned i = 0; i < n; ++i) 2203 foo((double)i); 2204 2205 is transformed into 2206 2207 double d = 0.0; 2208 for (unsigned i = 0; i < n; ++i, ++d) 2209 foo(d); 2210 */ 2211 if (UIToFPInst *UCast = dyn_cast<UIToFPInst>(CandidateUI->getUser())) 2212 DestTy = UCast->getDestTy(); 2213 else if (SIToFPInst *SCast = dyn_cast<SIToFPInst>(CandidateUI->getUser())) 2214 DestTy = SCast->getDestTy(); 2215 if (!DestTy) continue; 2216 2217 if (TLI) { 2218 // If target does not support DestTy natively then do not apply 2219 // this transformation. 2220 MVT DVT = TLI->getValueType(DestTy); 2221 if (!TLI->isTypeLegal(DVT)) continue; 2222 } 2223 2224 PHINode *PH = dyn_cast<PHINode>(ShadowUse->getOperand(0)); 2225 if (!PH) continue; 2226 if (PH->getNumIncomingValues() != 2) continue; 2227 2228 const Type *SrcTy = PH->getType(); 2229 int Mantissa = DestTy->getFPMantissaWidth(); 2230 if (Mantissa == -1) continue; 2231 if ((int)SE->getTypeSizeInBits(SrcTy) > Mantissa) 2232 continue; 2233 2234 unsigned Entry, Latch; 2235 if (PH->getIncomingBlock(0) == L->getLoopPreheader()) { 2236 Entry = 0; 2237 Latch = 1; 2238 } else { 2239 Entry = 1; 2240 Latch = 0; 2241 } 2242 2243 ConstantInt *Init = dyn_cast<ConstantInt>(PH->getIncomingValue(Entry)); 2244 if (!Init) continue; 2245 ConstantFP *NewInit = ConstantFP::get(DestTy, Init->getZExtValue()); 2246 2247 BinaryOperator *Incr = 2248 dyn_cast<BinaryOperator>(PH->getIncomingValue(Latch)); 2249 if (!Incr) continue; 2250 if (Incr->getOpcode() != Instruction::Add 2251 && Incr->getOpcode() != Instruction::Sub) 2252 continue; 2253 2254 /* Initialize new IV, double d = 0.0 in above example. */ 2255 ConstantInt *C = NULL; 2256 if (Incr->getOperand(0) == PH) 2257 C = dyn_cast<ConstantInt>(Incr->getOperand(1)); 2258 else if (Incr->getOperand(1) == PH) 2259 C = dyn_cast<ConstantInt>(Incr->getOperand(0)); 2260 else 2261 continue; 2262 2263 if (!C) continue; 2264 2265 /* Add new PHINode. */ 2266 PHINode *NewPH = PHINode::Create(DestTy, "IV.S.", PH); 2267 2268 /* create new increment. '++d' in above example. */ 2269 ConstantFP *CFP = ConstantFP::get(DestTy, C->getZExtValue()); 2270 BinaryOperator *NewIncr = 2271 BinaryOperator::Create(Incr->getOpcode() == Instruction::Add ? 2272 Instruction::FAdd : Instruction::FSub, 2273 NewPH, CFP, "IV.S.next.", Incr); 2274 2275 NewPH->addIncoming(NewInit, PH->getIncomingBlock(Entry)); 2276 NewPH->addIncoming(NewIncr, PH->getIncomingBlock(Latch)); 2277 2278 /* Remove cast operation */ 2279 ShadowUse->replaceAllUsesWith(NewPH); 2280 ShadowUse->eraseFromParent(); 2281 NumShadow++; 2282 break; 2283 } 2284 } 2285} 2286 2287// OptimizeIndvars - Now that IVUsesByStride is set up with all of the indvar 2288// uses in the loop, look to see if we can eliminate some, in favor of using 2289// common indvars for the different uses. 2290void LoopStrengthReduce::OptimizeIndvars(Loop *L) { 2291 // TODO: implement optzns here. 2292 2293 OptimizeShadowIV(L); 2294} 2295 2296/// OptimizeLoopTermCond - Change loop terminating condition to use the 2297/// postinc iv when possible. 2298void LoopStrengthReduce::OptimizeLoopTermCond(Loop *L) { 2299 // Finally, get the terminating condition for the loop if possible. If we 2300 // can, we want to change it to use a post-incremented version of its 2301 // induction variable, to allow coalescing the live ranges for the IV into 2302 // one register value. 2303 BasicBlock *LatchBlock = L->getLoopLatch(); 2304 BasicBlock *ExitBlock = L->getExitingBlock(); 2305 if (!ExitBlock) 2306 // Multiple exits, just look at the exit in the latch block if there is one. 2307 ExitBlock = LatchBlock; 2308 BranchInst *TermBr = dyn_cast<BranchInst>(ExitBlock->getTerminator()); 2309 if (!TermBr) 2310 return; 2311 if (TermBr->isUnconditional() || !isa<ICmpInst>(TermBr->getCondition())) 2312 return; 2313 2314 // Search IVUsesByStride to find Cond's IVUse if there is one. 2315 IVStrideUse *CondUse = 0; 2316 const SCEVHandle *CondStride = 0; 2317 ICmpInst *Cond = cast<ICmpInst>(TermBr->getCondition()); 2318 if (!FindIVUserForCond(Cond, CondUse, CondStride)) 2319 return; // setcc doesn't use the IV. 2320 2321 if (ExitBlock != LatchBlock) { 2322 if (!Cond->hasOneUse()) 2323 // See below, we don't want the condition to be cloned. 2324 return; 2325 2326 // If exiting block is the latch block, we know it's safe and profitable to 2327 // transform the icmp to use post-inc iv. Otherwise do so only if it would 2328 // not reuse another iv and its iv would be reused by other uses. We are 2329 // optimizing for the case where the icmp is the only use of the iv. 2330 IVUsersOfOneStride &StrideUses = *IU->IVUsesByStride[*CondStride]; 2331 for (ilist<IVStrideUse>::iterator I = StrideUses.Users.begin(), 2332 E = StrideUses.Users.end(); I != E; ++I) { 2333 if (I->getUser() == Cond) 2334 continue; 2335 if (!I->isUseOfPostIncrementedValue()) 2336 return; 2337 } 2338 2339 // FIXME: This is expensive, and worse still ChangeCompareStride does a 2340 // similar check. Can we perform all the icmp related transformations after 2341 // StrengthReduceStridedIVUsers? 2342 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(*CondStride)) { 2343 int64_t SInt = SC->getValue()->getSExtValue(); 2344 for (unsigned NewStride = 0, ee = IU->StrideOrder.size(); NewStride != ee; 2345 ++NewStride) { 2346 std::map<SCEVHandle, IVUsersOfOneStride *>::iterator SI = 2347 IU->IVUsesByStride.find(IU->StrideOrder[NewStride]); 2348 if (!isa<SCEVConstant>(SI->first) || SI->first == *CondStride) 2349 continue; 2350 int64_t SSInt = 2351 cast<SCEVConstant>(SI->first)->getValue()->getSExtValue(); 2352 if (SSInt == SInt) 2353 return; // This can definitely be reused. 2354 if (unsigned(abs64(SSInt)) < SInt || (SSInt % SInt) != 0) 2355 continue; 2356 int64_t Scale = SSInt / SInt; 2357 bool AllUsesAreAddresses = true; 2358 bool AllUsesAreOutsideLoop = true; 2359 std::vector<BasedUser> UsersToProcess; 2360 SCEVHandle CommonExprs = CollectIVUsers(SI->first, *SI->second, L, 2361 AllUsesAreAddresses, 2362 AllUsesAreOutsideLoop, 2363 UsersToProcess); 2364 // Avoid rewriting the compare instruction with an iv of new stride 2365 // if it's likely the new stride uses will be rewritten using the 2366 // stride of the compare instruction. 2367 if (AllUsesAreAddresses && 2368 ValidScale(!CommonExprs->isZero(), Scale, UsersToProcess)) 2369 return; 2370 } 2371 } 2372 2373 StrideNoReuse.insert(*CondStride); 2374 } 2375 2376 // If the trip count is computed in terms of an smax (due to ScalarEvolution 2377 // being unable to find a sufficient guard, for example), change the loop 2378 // comparison to use SLT instead of NE. 2379 Cond = OptimizeSMax(L, Cond, CondUse); 2380 2381 // If possible, change stride and operands of the compare instruction to 2382 // eliminate one stride. 2383 if (ExitBlock == LatchBlock) 2384 Cond = ChangeCompareStride(L, Cond, CondUse, CondStride); 2385 2386 // It's possible for the setcc instruction to be anywhere in the loop, and 2387 // possible for it to have multiple users. If it is not immediately before 2388 // the latch block branch, move it. 2389 if (&*++BasicBlock::iterator(Cond) != (Instruction*)TermBr) { 2390 if (Cond->hasOneUse()) { // Condition has a single use, just move it. 2391 Cond->moveBefore(TermBr); 2392 } else { 2393 // Otherwise, clone the terminating condition and insert into the loopend. 2394 Cond = cast<ICmpInst>(Cond->clone()); 2395 Cond->setName(L->getHeader()->getName() + ".termcond"); 2396 LatchBlock->getInstList().insert(TermBr, Cond); 2397 2398 // Clone the IVUse, as the old use still exists! 2399 IU->IVUsesByStride[*CondStride]->addUser(CondUse->getOffset(), Cond, 2400 CondUse->getOperandValToReplace(), 2401 false); 2402 CondUse = &IU->IVUsesByStride[*CondStride]->Users.back(); 2403 } 2404 } 2405 2406 // If we get to here, we know that we can transform the setcc instruction to 2407 // use the post-incremented version of the IV, allowing us to coalesce the 2408 // live ranges for the IV correctly. 2409 CondUse->setOffset(SE->getMinusSCEV(CondUse->getOffset(), *CondStride)); 2410 CondUse->setIsUseOfPostIncrementedValue(true); 2411 Changed = true; 2412 2413 ++NumLoopCond; 2414} 2415 2416// OptimizeLoopCountIV - If, after all sharing of IVs, the IV used for deciding 2417// when to exit the loop is used only for that purpose, try to rearrange things 2418// so it counts down to a test against zero. 2419void LoopStrengthReduce::OptimizeLoopCountIV(Loop *L) { 2420 2421 // If the number of times the loop is executed isn't computable, give up. 2422 SCEVHandle BackedgeTakenCount = SE->getBackedgeTakenCount(L); 2423 if (isa<SCEVCouldNotCompute>(BackedgeTakenCount)) 2424 return; 2425 2426 // Get the terminating condition for the loop if possible (this isn't 2427 // necessarily in the latch, or a block that's a predecessor of the header). 2428 if (!L->getExitBlock()) 2429 return; // More than one loop exit blocks. 2430 2431 // Okay, there is one exit block. Try to find the condition that causes the 2432 // loop to be exited. 2433 BasicBlock *ExitingBlock = L->getExitingBlock(); 2434 if (!ExitingBlock) 2435 return; // More than one block exiting! 2436 2437 // Okay, we've computed the exiting block. See what condition causes us to 2438 // exit. 2439 // 2440 // FIXME: we should be able to handle switch instructions (with a single exit) 2441 BranchInst *TermBr = dyn_cast<BranchInst>(ExitingBlock->getTerminator()); 2442 if (TermBr == 0) return; 2443 assert(TermBr->isConditional() && "If unconditional, it can't be in loop!"); 2444 if (!isa<ICmpInst>(TermBr->getCondition())) 2445 return; 2446 ICmpInst *Cond = cast<ICmpInst>(TermBr->getCondition()); 2447 2448 // Handle only tests for equality for the moment, and only stride 1. 2449 if (Cond->getPredicate() != CmpInst::ICMP_EQ) 2450 return; 2451 SCEVHandle IV = SE->getSCEV(Cond->getOperand(0)); 2452 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV); 2453 SCEVHandle One = SE->getIntegerSCEV(1, BackedgeTakenCount->getType()); 2454 if (!AR || !AR->isAffine() || AR->getStepRecurrence(*SE) != One) 2455 return; 2456 // If the RHS of the comparison is defined inside the loop, the rewrite 2457 // cannot be done. 2458 if (Instruction *CR = dyn_cast<Instruction>(Cond->getOperand(1))) 2459 if (L->contains(CR->getParent())) 2460 return; 2461 2462 // Make sure the IV is only used for counting. Value may be preinc or 2463 // postinc; 2 uses in either case. 2464 if (!Cond->getOperand(0)->hasNUses(2)) 2465 return; 2466 PHINode *phi = dyn_cast<PHINode>(Cond->getOperand(0)); 2467 Instruction *incr; 2468 if (phi && phi->getParent()==L->getHeader()) { 2469 // value tested is preinc. Find the increment. 2470 // A CmpInst is not a BinaryOperator; we depend on this. 2471 Instruction::use_iterator UI = phi->use_begin(); 2472 incr = dyn_cast<BinaryOperator>(UI); 2473 if (!incr) 2474 incr = dyn_cast<BinaryOperator>(++UI); 2475 // 1 use for postinc value, the phi. Unnecessarily conservative? 2476 if (!incr || !incr->hasOneUse() || incr->getOpcode()!=Instruction::Add) 2477 return; 2478 } else { 2479 // Value tested is postinc. Find the phi node. 2480 incr = dyn_cast<BinaryOperator>(Cond->getOperand(0)); 2481 if (!incr || incr->getOpcode()!=Instruction::Add) 2482 return; 2483 2484 Instruction::use_iterator UI = Cond->getOperand(0)->use_begin(); 2485 phi = dyn_cast<PHINode>(UI); 2486 if (!phi) 2487 phi = dyn_cast<PHINode>(++UI); 2488 // 1 use for preinc value, the increment. 2489 if (!phi || phi->getParent()!=L->getHeader() || !phi->hasOneUse()) 2490 return; 2491 } 2492 2493 // Replace the increment with a decrement. 2494 BinaryOperator *decr = 2495 BinaryOperator::Create(Instruction::Sub, incr->getOperand(0), 2496 incr->getOperand(1), "tmp", incr); 2497 incr->replaceAllUsesWith(decr); 2498 incr->eraseFromParent(); 2499 2500 // Substitute endval-startval for the original startval, and 0 for the 2501 // original endval. Since we're only testing for equality this is OK even 2502 // if the computation wraps around. 2503 BasicBlock *Preheader = L->getLoopPreheader(); 2504 Instruction *PreInsertPt = Preheader->getTerminator(); 2505 int inBlock = L->contains(phi->getIncomingBlock(0)) ? 1 : 0; 2506 Value *startVal = phi->getIncomingValue(inBlock); 2507 Value *endVal = Cond->getOperand(1); 2508 // FIXME check for case where both are constant 2509 ConstantInt* Zero = ConstantInt::get(Cond->getOperand(1)->getType(), 0); 2510 BinaryOperator *NewStartVal = 2511 BinaryOperator::Create(Instruction::Sub, endVal, startVal, 2512 "tmp", PreInsertPt); 2513 phi->setIncomingValue(inBlock, NewStartVal); 2514 Cond->setOperand(1, Zero); 2515 2516 Changed = true; 2517} 2518 2519bool LoopStrengthReduce::runOnLoop(Loop *L, LPPassManager &LPM) { 2520 2521 IU = &getAnalysis<IVUsers>(); 2522 LI = &getAnalysis<LoopInfo>(); 2523 DT = &getAnalysis<DominatorTree>(); 2524 SE = &getAnalysis<ScalarEvolution>(); 2525 Changed = false; 2526 2527 if (!IU->IVUsesByStride.empty()) { 2528#ifndef NDEBUG 2529 DOUT << "\nLSR on \"" << L->getHeader()->getParent()->getNameStart() 2530 << "\" "; 2531 DEBUG(L->dump()); 2532#endif 2533 2534 // Sort the StrideOrder so we process larger strides first. 2535 std::stable_sort(IU->StrideOrder.begin(), IU->StrideOrder.end(), 2536 StrideCompare(SE)); 2537 2538 // Optimize induction variables. Some indvar uses can be transformed to use 2539 // strides that will be needed for other purposes. A common example of this 2540 // is the exit test for the loop, which can often be rewritten to use the 2541 // computation of some other indvar to decide when to terminate the loop. 2542 OptimizeIndvars(L); 2543 2544 // Change loop terminating condition to use the postinc iv when possible 2545 // and optimize loop terminating compare. FIXME: Move this after 2546 // StrengthReduceStridedIVUsers? 2547 OptimizeLoopTermCond(L); 2548 2549 // FIXME: We can shrink overlarge IV's here. e.g. if the code has 2550 // computation in i64 values and the target doesn't support i64, demote 2551 // the computation to 32-bit if safe. 2552 2553 // FIXME: Attempt to reuse values across multiple IV's. In particular, we 2554 // could have something like "for(i) { foo(i*8); bar(i*16) }", which should 2555 // be codegened as "for (j = 0;; j+=8) { foo(j); bar(j+j); }" on X86/PPC. 2556 // Need to be careful that IV's are all the same type. Only works for 2557 // intptr_t indvars. 2558 2559 // IVsByStride keeps IVs for one particular loop. 2560 assert(IVsByStride.empty() && "Stale entries in IVsByStride?"); 2561 2562 // Note: this processes each stride/type pair individually. All users 2563 // passed into StrengthReduceStridedIVUsers have the same type AND stride. 2564 // Also, note that we iterate over IVUsesByStride indirectly by using 2565 // StrideOrder. This extra layer of indirection makes the ordering of 2566 // strides deterministic - not dependent on map order. 2567 for (unsigned Stride = 0, e = IU->StrideOrder.size(); 2568 Stride != e; ++Stride) { 2569 std::map<SCEVHandle, IVUsersOfOneStride *>::iterator SI = 2570 IU->IVUsesByStride.find(IU->StrideOrder[Stride]); 2571 assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!"); 2572 // FIXME: Generalize to non-affine IV's. 2573 if (!SI->first->isLoopInvariant(L)) 2574 continue; 2575 StrengthReduceStridedIVUsers(SI->first, *SI->second, L); 2576 } 2577 } 2578 2579 // After all sharing is done, see if we can adjust the loop to test against 2580 // zero instead of counting up to a maximum. This is usually faster. 2581 OptimizeLoopCountIV(L); 2582 2583 // We're done analyzing this loop; release all the state we built up for it. 2584 IVsByStride.clear(); 2585 StrideNoReuse.clear(); 2586 2587 // Clean up after ourselves 2588 if (!DeadInsts.empty()) 2589 DeleteTriviallyDeadInstructions(); 2590 2591 // At this point, it is worth checking to see if any recurrence PHIs are also 2592 // dead, so that we can remove them as well. 2593 DeleteDeadPHIs(L->getHeader()); 2594 2595 return Changed; 2596} 2597