1 //===- LoopStrengthReduce.cpp - Strength Reduce GEPs in Loops -------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by Nate Begeman and is distributed under the
6 // University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass performs a strength reduction on array references inside loops that
11 // have as one or more of their components the loop induction variable. This is
12 // accomplished by creating a new Value to hold the initial value of the array
13 // access for the first iteration, and then creating a new GEP instruction in
14 // the loop to increment the value by the appropriate amount.
16 //===----------------------------------------------------------------------===//
18 #define DEBUG_TYPE "loop-reduce"
19 #include "llvm/Transforms/Scalar.h"
20 #include "llvm/Constants.h"
21 #include "llvm/Instructions.h"
22 #include "llvm/Type.h"
23 #include "llvm/DerivedTypes.h"
24 #include "llvm/Analysis/Dominators.h"
25 #include "llvm/Analysis/LoopInfo.h"
26 #include "llvm/Analysis/ScalarEvolutionExpander.h"
27 #include "llvm/Support/CFG.h"
28 #include "llvm/Support/GetElementPtrTypeIterator.h"
29 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
30 #include "llvm/Transforms/Utils/Local.h"
31 #include "llvm/Target/TargetData.h"
32 #include "llvm/ADT/Statistic.h"
33 #include "llvm/Support/Debug.h"
34 #include "llvm/Target/TargetLowering.h"
41 Statistic<> NumReduced ("loop-reduce", "Number of GEPs strength reduced");
42 Statistic<> NumInserted("loop-reduce", "Number of PHIs inserted");
43 Statistic<> NumVariable("loop-reduce","Number of PHIs with variable strides");
45 /// IVStrideUse - Keep track of one use of a strided induction variable, where
46 /// the stride is stored externally. The Offset member keeps track of the
47 /// offset from the IV, User is the actual user of the operand, and 'Operand'
48 /// is the operand # of the User that is the use.
52 Value *OperandValToReplace;
54 // isUseOfPostIncrementedValue - True if this should use the
55 // post-incremented version of this IV, not the preincremented version.
56 // This can only be set in special cases, such as the terminating setcc
57 // instruction for a loop or uses dominated by the loop.
58 bool isUseOfPostIncrementedValue;
60 IVStrideUse(const SCEVHandle &Offs, Instruction *U, Value *O)
61 : Offset(Offs), User(U), OperandValToReplace(O),
62 isUseOfPostIncrementedValue(false) {}
65 /// IVUsersOfOneStride - This structure keeps track of all instructions that
66 /// have an operand that is based on the trip count multiplied by some stride.
67 /// The stride for all of these users is common and kept external to this
69 struct IVUsersOfOneStride {
70 /// Users - Keep track of all of the users of this stride as well as the
71 /// initial value and the operand that uses the IV.
72 std::vector<IVStrideUse> Users;
74 void addUser(const SCEVHandle &Offset,Instruction *User, Value *Operand) {
75 Users.push_back(IVStrideUse(Offset, User, Operand));
79 /// IVInfo - This structure keeps track of one IV expression inserted during
80 /// StrengthReduceStridedIVUsers. It contains the base value, as well as the
81 /// PHI node and increment value created for rewrite.
87 IVExpr(const SCEVHandle &base, PHINode *phi, Value *incv)
88 : Base(base), PHI(phi), IncV(incv) {}
91 /// IVsOfOneStride - This structure keeps track of all IV expression inserted
92 /// during StrengthReduceStridedIVUsers for a particular stride of the IV.
93 struct IVsOfOneStride {
94 std::vector<IVExpr> IVs;
96 void addIV(const SCEVHandle &Base, PHINode *PHI, Value *IncV) {
97 IVs.push_back(IVExpr(Base, PHI, IncV));
101 class LoopStrengthReduce : public FunctionPass {
105 const TargetData *TD;
106 const Type *UIntPtrTy;
109 /// IVUsesByStride - Keep track of all uses of induction variables that we
110 /// are interested in. The key of the map is the stride of the access.
111 std::map<SCEVHandle, IVUsersOfOneStride> IVUsesByStride;
113 /// IVsByStride - Keep track of all IVs that have been inserted for a
114 /// particular stride.
115 std::map<SCEVHandle, IVsOfOneStride> IVsByStride;
117 /// StrideOrder - An ordering of the keys in IVUsesByStride that is stable:
118 /// We use this to iterate over the IVUsesByStride collection without being
119 /// dependent on random ordering of pointers in the process.
120 std::vector<SCEVHandle> StrideOrder;
122 /// CastedValues - As we need to cast values to uintptr_t, this keeps track
123 /// of the casted version of each value. This is accessed by
124 /// getCastedVersionOf.
125 std::map<Value*, Value*> CastedPointers;
127 /// DeadInsts - Keep track of instructions we may have made dead, so that
128 /// we can remove them after we are done working.
129 std::set<Instruction*> DeadInsts;
131 /// TLI - Keep a pointer of a TargetLowering to consult for determining
132 /// transformation profitability.
133 const TargetLowering *TLI;
136 LoopStrengthReduce(const TargetLowering *tli = NULL)
140 virtual bool runOnFunction(Function &) {
141 LI = &getAnalysis<LoopInfo>();
142 EF = &getAnalysis<ETForest>();
143 SE = &getAnalysis<ScalarEvolution>();
144 TD = &getAnalysis<TargetData>();
145 UIntPtrTy = TD->getIntPtrType();
148 for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
154 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
155 // We split critical edges, so we change the CFG. However, we do update
156 // many analyses if they are around.
157 AU.addPreservedID(LoopSimplifyID);
158 AU.addPreserved<LoopInfo>();
159 AU.addPreserved<DominatorSet>();
160 AU.addPreserved<ETForest>();
161 AU.addPreserved<ImmediateDominators>();
162 AU.addPreserved<DominanceFrontier>();
163 AU.addPreserved<DominatorTree>();
165 AU.addRequiredID(LoopSimplifyID);
166 AU.addRequired<LoopInfo>();
167 AU.addRequired<ETForest>();
168 AU.addRequired<TargetData>();
169 AU.addRequired<ScalarEvolution>();
172 /// getCastedVersionOf - Return the specified value casted to uintptr_t.
174 Value *getCastedVersionOf(Value *V);
176 void runOnLoop(Loop *L);
177 bool AddUsersIfInteresting(Instruction *I, Loop *L,
178 std::set<Instruction*> &Processed);
179 SCEVHandle GetExpressionSCEV(Instruction *E, Loop *L);
181 void OptimizeIndvars(Loop *L);
183 void StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
184 IVUsersOfOneStride &Uses,
185 Loop *L, bool isOnlyStride);
186 void DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts);
188 RegisterOpt<LoopStrengthReduce> X("loop-reduce",
189 "Loop Strength Reduction");
192 FunctionPass *llvm::createLoopStrengthReducePass(const TargetLowering *TLI) {
193 return new LoopStrengthReduce(TLI);
196 /// getCastedVersionOf - Return the specified value casted to uintptr_t.
198 Value *LoopStrengthReduce::getCastedVersionOf(Value *V) {
199 if (V->getType() == UIntPtrTy) return V;
200 if (Constant *CB = dyn_cast<Constant>(V))
201 return ConstantExpr::getCast(CB, UIntPtrTy);
203 Value *&New = CastedPointers[V];
206 New = SCEVExpander::InsertCastOfTo(V, UIntPtrTy);
207 DeadInsts.insert(cast<Instruction>(New));
212 /// DeleteTriviallyDeadInstructions - If any of the instructions is the
213 /// specified set are trivially dead, delete them and see if this makes any of
214 /// their operands subsequently dead.
215 void LoopStrengthReduce::
216 DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts) {
217 while (!Insts.empty()) {
218 Instruction *I = *Insts.begin();
219 Insts.erase(Insts.begin());
220 if (isInstructionTriviallyDead(I)) {
221 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
222 if (Instruction *U = dyn_cast<Instruction>(I->getOperand(i)))
224 SE->deleteInstructionFromRecords(I);
225 I->eraseFromParent();
232 /// GetExpressionSCEV - Compute and return the SCEV for the specified
234 SCEVHandle LoopStrengthReduce::GetExpressionSCEV(Instruction *Exp, Loop *L) {
235 // Scalar Evolutions doesn't know how to compute SCEV's for GEP instructions.
236 // If this is a GEP that SE doesn't know about, compute it now and insert it.
237 // If this is not a GEP, or if we have already done this computation, just let
239 GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Exp);
240 if (!GEP || SE->hasSCEV(GEP))
241 return SE->getSCEV(Exp);
243 // Analyze all of the subscripts of this getelementptr instruction, looking
244 // for uses that are determined by the trip count of L. First, skip all
245 // operands the are not dependent on the IV.
247 // Build up the base expression. Insert an LLVM cast of the pointer to
249 SCEVHandle GEPVal = SCEVUnknown::get(getCastedVersionOf(GEP->getOperand(0)));
251 gep_type_iterator GTI = gep_type_begin(GEP);
253 for (unsigned i = 1, e = GEP->getNumOperands(); i != e; ++i, ++GTI) {
254 // If this is a use of a recurrence that we can analyze, and it comes before
255 // Op does in the GEP operand list, we will handle this when we process this
257 if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
258 const StructLayout *SL = TD->getStructLayout(STy);
259 unsigned Idx = cast<ConstantUInt>(GEP->getOperand(i))->getValue();
260 uint64_t Offset = SL->MemberOffsets[Idx];
261 GEPVal = SCEVAddExpr::get(GEPVal,
262 SCEVUnknown::getIntegerSCEV(Offset, UIntPtrTy));
264 Value *OpVal = getCastedVersionOf(GEP->getOperand(i));
265 SCEVHandle Idx = SE->getSCEV(OpVal);
267 uint64_t TypeSize = TD->getTypeSize(GTI.getIndexedType());
269 Idx = SCEVMulExpr::get(Idx,
270 SCEVConstant::get(ConstantUInt::get(UIntPtrTy,
272 GEPVal = SCEVAddExpr::get(GEPVal, Idx);
276 SE->setSCEV(GEP, GEPVal);
280 /// getSCEVStartAndStride - Compute the start and stride of this expression,
281 /// returning false if the expression is not a start/stride pair, or true if it
282 /// is. The stride must be a loop invariant expression, but the start may be
283 /// a mix of loop invariant and loop variant expressions.
284 static bool getSCEVStartAndStride(const SCEVHandle &SH, Loop *L,
285 SCEVHandle &Start, SCEVHandle &Stride) {
286 SCEVHandle TheAddRec = Start; // Initialize to zero.
288 // If the outer level is an AddExpr, the operands are all start values except
289 // for a nested AddRecExpr.
290 if (SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(SH)) {
291 for (unsigned i = 0, e = AE->getNumOperands(); i != e; ++i)
292 if (SCEVAddRecExpr *AddRec =
293 dyn_cast<SCEVAddRecExpr>(AE->getOperand(i))) {
294 if (AddRec->getLoop() == L)
295 TheAddRec = SCEVAddExpr::get(AddRec, TheAddRec);
297 return false; // Nested IV of some sort?
299 Start = SCEVAddExpr::get(Start, AE->getOperand(i));
302 } else if (SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(SH)) {
305 return false; // not analyzable.
308 SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(TheAddRec);
309 if (!AddRec || AddRec->getLoop() != L) return false;
311 // FIXME: Generalize to non-affine IV's.
312 if (!AddRec->isAffine()) return false;
314 Start = SCEVAddExpr::get(Start, AddRec->getOperand(0));
316 if (!isa<SCEVConstant>(AddRec->getOperand(1)))
317 DEBUG(std::cerr << "[" << L->getHeader()->getName()
318 << "] Variable stride: " << *AddRec << "\n");
320 Stride = AddRec->getOperand(1);
321 // Check that all constant strides are the unsigned type, we don't want to
322 // have two IV's one of signed stride 4 and one of unsigned stride 4 to not be
324 assert((!isa<SCEVConstant>(Stride) || Stride->getType()->isUnsigned()) &&
325 "Constants should be canonicalized to unsigned!");
330 /// IVUseShouldUsePostIncValue - We have discovered a "User" of an IV expression
331 /// and now we need to decide whether the user should use the preinc or post-inc
332 /// value. If this user should use the post-inc version of the IV, return true.
334 /// Choosing wrong here can break dominance properties (if we choose to use the
335 /// post-inc value when we cannot) or it can end up adding extra live-ranges to
336 /// the loop, resulting in reg-reg copies (if we use the pre-inc value when we
337 /// should use the post-inc value).
338 static bool IVUseShouldUsePostIncValue(Instruction *User, Instruction *IV,
339 Loop *L, ETForest *EF, Pass *P) {
340 // If the user is in the loop, use the preinc value.
341 if (L->contains(User->getParent())) return false;
343 BasicBlock *LatchBlock = L->getLoopLatch();
345 // Ok, the user is outside of the loop. If it is dominated by the latch
346 // block, use the post-inc value.
347 if (EF->dominates(LatchBlock, User->getParent()))
350 // There is one case we have to be careful of: PHI nodes. These little guys
351 // can live in blocks that do not dominate the latch block, but (since their
352 // uses occur in the predecessor block, not the block the PHI lives in) should
353 // still use the post-inc value. Check for this case now.
354 PHINode *PN = dyn_cast<PHINode>(User);
355 if (!PN) return false; // not a phi, not dominated by latch block.
357 // Look at all of the uses of IV by the PHI node. If any use corresponds to
358 // a block that is not dominated by the latch block, give up and use the
359 // preincremented value.
360 unsigned NumUses = 0;
361 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
362 if (PN->getIncomingValue(i) == IV) {
364 if (!EF->dominates(LatchBlock, PN->getIncomingBlock(i)))
368 // Okay, all uses of IV by PN are in predecessor blocks that really are
369 // dominated by the latch block. Split the critical edges and use the
370 // post-incremented value.
371 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
372 if (PN->getIncomingValue(i) == IV) {
373 SplitCriticalEdge(PN->getIncomingBlock(i), PN->getParent(), P);
374 if (--NumUses == 0) break;
382 /// AddUsersIfInteresting - Inspect the specified instruction. If it is a
383 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
384 /// return true. Otherwise, return false.
385 bool LoopStrengthReduce::AddUsersIfInteresting(Instruction *I, Loop *L,
386 std::set<Instruction*> &Processed) {
387 if (!I->getType()->isInteger() && !isa<PointerType>(I->getType()))
388 return false; // Void and FP expressions cannot be reduced.
389 if (!Processed.insert(I).second)
390 return true; // Instruction already handled.
392 // Get the symbolic expression for this instruction.
393 SCEVHandle ISE = GetExpressionSCEV(I, L);
394 if (isa<SCEVCouldNotCompute>(ISE)) return false;
396 // Get the start and stride for this expression.
397 SCEVHandle Start = SCEVUnknown::getIntegerSCEV(0, ISE->getType());
398 SCEVHandle Stride = Start;
399 if (!getSCEVStartAndStride(ISE, L, Start, Stride))
400 return false; // Non-reducible symbolic expression, bail out.
402 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;++UI){
403 Instruction *User = cast<Instruction>(*UI);
405 // Do not infinitely recurse on PHI nodes.
406 if (isa<PHINode>(User) && Processed.count(User))
409 // If this is an instruction defined in a nested loop, or outside this loop,
410 // don't recurse into it.
411 bool AddUserToIVUsers = false;
412 if (LI->getLoopFor(User->getParent()) != L) {
413 DEBUG(std::cerr << "FOUND USER in other loop: " << *User
414 << " OF SCEV: " << *ISE << "\n");
415 AddUserToIVUsers = true;
416 } else if (!AddUsersIfInteresting(User, L, Processed)) {
417 DEBUG(std::cerr << "FOUND USER: " << *User
418 << " OF SCEV: " << *ISE << "\n");
419 AddUserToIVUsers = true;
422 if (AddUserToIVUsers) {
423 IVUsersOfOneStride &StrideUses = IVUsesByStride[Stride];
424 if (StrideUses.Users.empty()) // First occurance of this stride?
425 StrideOrder.push_back(Stride);
427 // Okay, we found a user that we cannot reduce. Analyze the instruction
428 // and decide what to do with it. If we are a use inside of the loop, use
429 // the value before incrementation, otherwise use it after incrementation.
430 if (IVUseShouldUsePostIncValue(User, I, L, EF, this)) {
431 // The value used will be incremented by the stride more than we are
432 // expecting, so subtract this off.
433 SCEVHandle NewStart = SCEV::getMinusSCEV(Start, Stride);
434 StrideUses.addUser(NewStart, User, I);
435 StrideUses.Users.back().isUseOfPostIncrementedValue = true;
436 DEBUG(std::cerr << " USING POSTINC SCEV, START=" << *NewStart<< "\n");
438 StrideUses.addUser(Start, User, I);
446 /// BasedUser - For a particular base value, keep information about how we've
447 /// partitioned the expression so far.
449 /// Base - The Base value for the PHI node that needs to be inserted for
450 /// this use. As the use is processed, information gets moved from this
451 /// field to the Imm field (below). BasedUser values are sorted by this
455 /// Inst - The instruction using the induction variable.
458 /// OperandValToReplace - The operand value of Inst to replace with the
460 Value *OperandValToReplace;
462 /// Imm - The immediate value that should be added to the base immediately
463 /// before Inst, because it will be folded into the imm field of the
467 /// EmittedBase - The actual value* to use for the base value of this
468 /// operation. This is null if we should just use zero so far.
471 // isUseOfPostIncrementedValue - True if this should use the
472 // post-incremented version of this IV, not the preincremented version.
473 // This can only be set in special cases, such as the terminating setcc
474 // instruction for a loop and uses outside the loop that are dominated by
476 bool isUseOfPostIncrementedValue;
478 BasedUser(IVStrideUse &IVSU)
479 : Base(IVSU.Offset), Inst(IVSU.User),
480 OperandValToReplace(IVSU.OperandValToReplace),
481 Imm(SCEVUnknown::getIntegerSCEV(0, Base->getType())), EmittedBase(0),
482 isUseOfPostIncrementedValue(IVSU.isUseOfPostIncrementedValue) {}
484 // Once we rewrite the code to insert the new IVs we want, update the
485 // operands of Inst to use the new expression 'NewBase', with 'Imm' added
487 void RewriteInstructionToUseNewBase(const SCEVHandle &NewBase,
488 SCEVExpander &Rewriter, Loop *L,
491 Value *InsertCodeForBaseAtPosition(const SCEVHandle &NewBase,
492 SCEVExpander &Rewriter,
493 Instruction *IP, Loop *L);
498 void BasedUser::dump() const {
499 std::cerr << " Base=" << *Base;
500 std::cerr << " Imm=" << *Imm;
502 std::cerr << " EB=" << *EmittedBase;
504 std::cerr << " Inst: " << *Inst;
507 Value *BasedUser::InsertCodeForBaseAtPosition(const SCEVHandle &NewBase,
508 SCEVExpander &Rewriter,
509 Instruction *IP, Loop *L) {
510 // Figure out where we *really* want to insert this code. In particular, if
511 // the user is inside of a loop that is nested inside of L, we really don't
512 // want to insert this expression before the user, we'd rather pull it out as
513 // many loops as possible.
514 LoopInfo &LI = Rewriter.getLoopInfo();
515 Instruction *BaseInsertPt = IP;
517 // Figure out the most-nested loop that IP is in.
518 Loop *InsertLoop = LI.getLoopFor(IP->getParent());
520 // If InsertLoop is not L, and InsertLoop is nested inside of L, figure out
521 // the preheader of the outer-most loop where NewBase is not loop invariant.
522 while (InsertLoop && NewBase->isLoopInvariant(InsertLoop)) {
523 BaseInsertPt = InsertLoop->getLoopPreheader()->getTerminator();
524 InsertLoop = InsertLoop->getParentLoop();
527 // If there is no immediate value, skip the next part.
528 if (SCEVConstant *SC = dyn_cast<SCEVConstant>(Imm))
529 if (SC->getValue()->isNullValue())
530 return Rewriter.expandCodeFor(NewBase, BaseInsertPt,
531 OperandValToReplace->getType());
533 Value *Base = Rewriter.expandCodeFor(NewBase, BaseInsertPt);
535 // Always emit the immediate (if non-zero) into the same block as the user.
536 SCEVHandle NewValSCEV = SCEVAddExpr::get(SCEVUnknown::get(Base), Imm);
537 return Rewriter.expandCodeFor(NewValSCEV, IP,
538 OperandValToReplace->getType());
542 // Once we rewrite the code to insert the new IVs we want, update the
543 // operands of Inst to use the new expression 'NewBase', with 'Imm' added
545 void BasedUser::RewriteInstructionToUseNewBase(const SCEVHandle &NewBase,
546 SCEVExpander &Rewriter,
548 if (!isa<PHINode>(Inst)) {
549 Value *NewVal = InsertCodeForBaseAtPosition(NewBase, Rewriter, Inst, L);
550 // Replace the use of the operand Value with the new Phi we just created.
551 Inst->replaceUsesOfWith(OperandValToReplace, NewVal);
552 DEBUG(std::cerr << " CHANGED: IMM =" << *Imm << " Inst = " << *Inst);
556 // PHI nodes are more complex. We have to insert one copy of the NewBase+Imm
557 // expression into each operand block that uses it. Note that PHI nodes can
558 // have multiple entries for the same predecessor. We use a map to make sure
559 // that a PHI node only has a single Value* for each predecessor (which also
560 // prevents us from inserting duplicate code in some blocks).
561 std::map<BasicBlock*, Value*> InsertedCode;
562 PHINode *PN = cast<PHINode>(Inst);
563 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
564 if (PN->getIncomingValue(i) == OperandValToReplace) {
565 // If this is a critical edge, split the edge so that we do not insert the
566 // code on all predecessor/successor paths. We do this unless this is the
567 // canonical backedge for this loop, as this can make some inserted code
568 // be in an illegal position.
569 BasicBlock *PHIPred = PN->getIncomingBlock(i);
570 if (e != 1 && PHIPred->getTerminator()->getNumSuccessors() > 1 &&
571 (PN->getParent() != L->getHeader() || !L->contains(PHIPred))) {
573 // First step, split the critical edge.
574 SplitCriticalEdge(PHIPred, PN->getParent(), P);
576 // Next step: move the basic block. In particular, if the PHI node
577 // is outside of the loop, and PredTI is in the loop, we want to
578 // move the block to be immediately before the PHI block, not
579 // immediately after PredTI.
580 if (L->contains(PHIPred) && !L->contains(PN->getParent())) {
581 BasicBlock *NewBB = PN->getIncomingBlock(i);
582 NewBB->moveBefore(PN->getParent());
586 Value *&Code = InsertedCode[PN->getIncomingBlock(i)];
588 // Insert the code into the end of the predecessor block.
589 Instruction *InsertPt = PN->getIncomingBlock(i)->getTerminator();
590 Code = InsertCodeForBaseAtPosition(NewBase, Rewriter, InsertPt, L);
593 // Replace the use of the operand Value with the new Phi we just created.
594 PN->setIncomingValue(i, Code);
598 DEBUG(std::cerr << " CHANGED: IMM =" << *Imm << " Inst = " << *Inst);
602 /// isTargetConstant - Return true if the following can be referenced by the
603 /// immediate field of a target instruction.
604 static bool isTargetConstant(const SCEVHandle &V, const TargetLowering *TLI) {
605 if (SCEVConstant *SC = dyn_cast<SCEVConstant>(V)) {
606 int64_t V = SC->getValue()->getSExtValue();
608 return TLI->isLegalAddressImmediate(V);
610 // Defaults to PPC. PPC allows a sign-extended 16-bit immediate field.
611 return (V > -(1 << 16) && V < (1 << 16)-1);
614 if (SCEVUnknown *SU = dyn_cast<SCEVUnknown>(V))
615 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(SU->getValue()))
616 if (CE->getOpcode() == Instruction::Cast) {
617 Constant *Op0 = CE->getOperand(0);
618 if (isa<GlobalValue>(Op0) &&
620 TLI->isLegalAddressImmediate(cast<GlobalValue>(Op0)))
626 /// MoveLoopVariantsToImediateField - Move any subexpressions from Val that are
627 /// loop varying to the Imm operand.
628 static void MoveLoopVariantsToImediateField(SCEVHandle &Val, SCEVHandle &Imm,
630 if (Val->isLoopInvariant(L)) return; // Nothing to do.
632 if (SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) {
633 std::vector<SCEVHandle> NewOps;
634 NewOps.reserve(SAE->getNumOperands());
636 for (unsigned i = 0; i != SAE->getNumOperands(); ++i)
637 if (!SAE->getOperand(i)->isLoopInvariant(L)) {
638 // If this is a loop-variant expression, it must stay in the immediate
639 // field of the expression.
640 Imm = SCEVAddExpr::get(Imm, SAE->getOperand(i));
642 NewOps.push_back(SAE->getOperand(i));
646 Val = SCEVUnknown::getIntegerSCEV(0, Val->getType());
648 Val = SCEVAddExpr::get(NewOps);
649 } else if (SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Val)) {
650 // Try to pull immediates out of the start value of nested addrec's.
651 SCEVHandle Start = SARE->getStart();
652 MoveLoopVariantsToImediateField(Start, Imm, L);
654 std::vector<SCEVHandle> Ops(SARE->op_begin(), SARE->op_end());
656 Val = SCEVAddRecExpr::get(Ops, SARE->getLoop());
658 // Otherwise, all of Val is variant, move the whole thing over.
659 Imm = SCEVAddExpr::get(Imm, Val);
660 Val = SCEVUnknown::getIntegerSCEV(0, Val->getType());
665 /// MoveImmediateValues - Look at Val, and pull out any additions of constants
666 /// that can fit into the immediate field of instructions in the target.
667 /// Accumulate these immediate values into the Imm value.
668 static void MoveImmediateValues(const TargetLowering *TLI,
669 SCEVHandle &Val, SCEVHandle &Imm,
670 bool isAddress, Loop *L) {
671 if (SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) {
672 std::vector<SCEVHandle> NewOps;
673 NewOps.reserve(SAE->getNumOperands());
675 for (unsigned i = 0; i != SAE->getNumOperands(); ++i) {
676 SCEVHandle NewOp = SAE->getOperand(i);
677 MoveImmediateValues(TLI, NewOp, Imm, isAddress, L);
679 if (!NewOp->isLoopInvariant(L)) {
680 // If this is a loop-variant expression, it must stay in the immediate
681 // field of the expression.
682 Imm = SCEVAddExpr::get(Imm, NewOp);
684 NewOps.push_back(NewOp);
689 Val = SCEVUnknown::getIntegerSCEV(0, Val->getType());
691 Val = SCEVAddExpr::get(NewOps);
693 } else if (SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Val)) {
694 // Try to pull immediates out of the start value of nested addrec's.
695 SCEVHandle Start = SARE->getStart();
696 MoveImmediateValues(TLI, Start, Imm, isAddress, L);
698 if (Start != SARE->getStart()) {
699 std::vector<SCEVHandle> Ops(SARE->op_begin(), SARE->op_end());
701 Val = SCEVAddRecExpr::get(Ops, SARE->getLoop());
704 } else if (SCEVMulExpr *SME = dyn_cast<SCEVMulExpr>(Val)) {
705 // Transform "8 * (4 + v)" -> "32 + 8*V" if "32" fits in the immed field.
706 if (isAddress && isTargetConstant(SME->getOperand(0), TLI) &&
707 SME->getNumOperands() == 2 && SME->isLoopInvariant(L)) {
709 SCEVHandle SubImm = SCEVUnknown::getIntegerSCEV(0, Val->getType());
710 SCEVHandle NewOp = SME->getOperand(1);
711 MoveImmediateValues(TLI, NewOp, SubImm, isAddress, L);
713 // If we extracted something out of the subexpressions, see if we can
715 if (NewOp != SME->getOperand(1)) {
716 // Scale SubImm up by "8". If the result is a target constant, we are
718 SubImm = SCEVMulExpr::get(SubImm, SME->getOperand(0));
719 if (isTargetConstant(SubImm, TLI)) {
720 // Accumulate the immediate.
721 Imm = SCEVAddExpr::get(Imm, SubImm);
723 // Update what is left of 'Val'.
724 Val = SCEVMulExpr::get(SME->getOperand(0), NewOp);
731 // Loop-variant expressions must stay in the immediate field of the
733 if ((isAddress && isTargetConstant(Val, TLI)) ||
734 !Val->isLoopInvariant(L)) {
735 Imm = SCEVAddExpr::get(Imm, Val);
736 Val = SCEVUnknown::getIntegerSCEV(0, Val->getType());
740 // Otherwise, no immediates to move.
744 /// IncrementAddExprUses - Decompose the specified expression into its added
745 /// subexpressions, and increment SubExpressionUseCounts for each of these
746 /// decomposed parts.
747 static void SeparateSubExprs(std::vector<SCEVHandle> &SubExprs,
749 if (SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(Expr)) {
750 for (unsigned j = 0, e = AE->getNumOperands(); j != e; ++j)
751 SeparateSubExprs(SubExprs, AE->getOperand(j));
752 } else if (SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Expr)) {
753 SCEVHandle Zero = SCEVUnknown::getIntegerSCEV(0, Expr->getType());
754 if (SARE->getOperand(0) == Zero) {
755 SubExprs.push_back(Expr);
757 // Compute the addrec with zero as its base.
758 std::vector<SCEVHandle> Ops(SARE->op_begin(), SARE->op_end());
759 Ops[0] = Zero; // Start with zero base.
760 SubExprs.push_back(SCEVAddRecExpr::get(Ops, SARE->getLoop()));
763 SeparateSubExprs(SubExprs, SARE->getOperand(0));
765 } else if (!isa<SCEVConstant>(Expr) ||
766 !cast<SCEVConstant>(Expr)->getValue()->isNullValue()) {
768 SubExprs.push_back(Expr);
773 /// RemoveCommonExpressionsFromUseBases - Look through all of the uses in Bases,
774 /// removing any common subexpressions from it. Anything truly common is
775 /// removed, accumulated, and returned. This looks for things like (a+b+c) and
776 /// (a+c+d) -> (a+c). The common expression is *removed* from the Bases.
778 RemoveCommonExpressionsFromUseBases(std::vector<BasedUser> &Uses) {
779 unsigned NumUses = Uses.size();
781 // Only one use? Use its base, regardless of what it is!
782 SCEVHandle Zero = SCEVUnknown::getIntegerSCEV(0, Uses[0].Base->getType());
783 SCEVHandle Result = Zero;
785 std::swap(Result, Uses[0].Base);
789 // To find common subexpressions, count how many of Uses use each expression.
790 // If any subexpressions are used Uses.size() times, they are common.
791 std::map<SCEVHandle, unsigned> SubExpressionUseCounts;
793 // UniqueSubExprs - Keep track of all of the subexpressions we see in the
794 // order we see them.
795 std::vector<SCEVHandle> UniqueSubExprs;
797 std::vector<SCEVHandle> SubExprs;
798 for (unsigned i = 0; i != NumUses; ++i) {
799 // If the base is zero (which is common), return zero now, there are no
801 if (Uses[i].Base == Zero) return Zero;
803 // Split the expression into subexprs.
804 SeparateSubExprs(SubExprs, Uses[i].Base);
805 // Add one to SubExpressionUseCounts for each subexpr present.
806 for (unsigned j = 0, e = SubExprs.size(); j != e; ++j)
807 if (++SubExpressionUseCounts[SubExprs[j]] == 1)
808 UniqueSubExprs.push_back(SubExprs[j]);
812 // Now that we know how many times each is used, build Result. Iterate over
813 // UniqueSubexprs so that we have a stable ordering.
814 for (unsigned i = 0, e = UniqueSubExprs.size(); i != e; ++i) {
815 std::map<SCEVHandle, unsigned>::iterator I =
816 SubExpressionUseCounts.find(UniqueSubExprs[i]);
817 assert(I != SubExpressionUseCounts.end() && "Entry not found?");
818 if (I->second == NumUses) { // Found CSE!
819 Result = SCEVAddExpr::get(Result, I->first);
821 // Remove non-cse's from SubExpressionUseCounts.
822 SubExpressionUseCounts.erase(I);
826 // If we found no CSE's, return now.
827 if (Result == Zero) return Result;
829 // Otherwise, remove all of the CSE's we found from each of the base values.
830 for (unsigned i = 0; i != NumUses; ++i) {
831 // Split the expression into subexprs.
832 SeparateSubExprs(SubExprs, Uses[i].Base);
834 // Remove any common subexpressions.
835 for (unsigned j = 0, e = SubExprs.size(); j != e; ++j)
836 if (SubExpressionUseCounts.count(SubExprs[j])) {
837 SubExprs.erase(SubExprs.begin()+j);
841 // Finally, the non-shared expressions together.
842 if (SubExprs.empty())
845 Uses[i].Base = SCEVAddExpr::get(SubExprs);
852 /// isZero - returns true if the scalar evolution expression is zero.
854 static bool isZero(SCEVHandle &V) {
855 if (SCEVConstant *SC = dyn_cast<SCEVConstant>(V))
856 return SC->getValue()->getRawValue() == 0;
861 /// StrengthReduceStridedIVUsers - Strength reduce all of the users of a single
862 /// stride of IV. All of the users may have different starting values, and this
863 /// may not be the only stride (we know it is if isOnlyStride is true).
864 void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
865 IVUsersOfOneStride &Uses,
868 // Transform our list of users and offsets to a bit more complex table. In
869 // this new vector, each 'BasedUser' contains 'Base' the base of the
870 // strided accessas well as the old information from Uses. We progressively
871 // move information from the Base field to the Imm field, until we eventually
872 // have the full access expression to rewrite the use.
873 std::vector<BasedUser> UsersToProcess;
874 UsersToProcess.reserve(Uses.Users.size());
875 for (unsigned i = 0, e = Uses.Users.size(); i != e; ++i) {
876 UsersToProcess.push_back(Uses.Users[i]);
878 // Move any loop invariant operands from the offset field to the immediate
879 // field of the use, so that we don't try to use something before it is
881 MoveLoopVariantsToImediateField(UsersToProcess.back().Base,
882 UsersToProcess.back().Imm, L);
883 assert(UsersToProcess.back().Base->isLoopInvariant(L) &&
884 "Base value is not loop invariant!");
887 // We now have a whole bunch of uses of like-strided induction variables, but
888 // they might all have different bases. We want to emit one PHI node for this
889 // stride which we fold as many common expressions (between the IVs) into as
890 // possible. Start by identifying the common expressions in the base values
891 // for the strides (e.g. if we have "A+C+B" and "A+B+D" as our bases, find
892 // "A+B"), emit it to the preheader, then remove the expression from the
893 // UsersToProcess base values.
894 SCEVHandle CommonExprs =
895 RemoveCommonExpressionsFromUseBases(UsersToProcess);
897 // Next, figure out what we can represent in the immediate fields of
898 // instructions. If we can represent anything there, move it to the imm
899 // fields of the BasedUsers. We do this so that it increases the commonality
900 // of the remaining uses.
901 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) {
902 // If the user is not in the current loop, this means it is using the exit
903 // value of the IV. Do not put anything in the base, make sure it's all in
904 // the immediate field to allow as much factoring as possible.
905 if (!L->contains(UsersToProcess[i].Inst->getParent())) {
906 UsersToProcess[i].Imm = SCEVAddExpr::get(UsersToProcess[i].Imm,
907 UsersToProcess[i].Base);
908 UsersToProcess[i].Base =
909 SCEVUnknown::getIntegerSCEV(0, UsersToProcess[i].Base->getType());
912 // Addressing modes can be folded into loads and stores. Be careful that
913 // the store is through the expression, not of the expression though.
914 bool isAddress = isa<LoadInst>(UsersToProcess[i].Inst);
915 if (StoreInst *SI = dyn_cast<StoreInst>(UsersToProcess[i].Inst))
916 if (SI->getOperand(1) == UsersToProcess[i].OperandValToReplace)
919 MoveImmediateValues(TLI, UsersToProcess[i].Base, UsersToProcess[i].Imm,
924 // Now that we know what we need to do, insert the PHI node itself.
926 DEBUG(std::cerr << "INSERTING IV of STRIDE " << *Stride << " and BASE "
927 << *CommonExprs << " :\n");
929 SCEVExpander Rewriter(*SE, *LI);
930 SCEVExpander PreheaderRewriter(*SE, *LI);
932 BasicBlock *Preheader = L->getLoopPreheader();
933 Instruction *PreInsertPt = Preheader->getTerminator();
934 Instruction *PhiInsertBefore = L->getHeader()->begin();
936 BasicBlock *LatchBlock = L->getLoopLatch();
938 unsigned RewriteFactor = 1;
939 PHINode *NewPHI = NULL;
941 // FIXME: Only handle base == 0 for now.
942 if (TLI && isZero(CommonExprs)) {
943 if (SCEVConstant *SC = dyn_cast<SCEVConstant>(Stride)) {
944 unsigned SInt = SC->getValue()->getRawValue();
945 for (TargetLowering::legal_am_scale_iterator
946 I = TLI->legal_am_scale_begin(), E = TLI->legal_am_scale_end();
949 if ((SInt % Scale) != 0)
951 std::map<SCEVHandle, IVsOfOneStride>::iterator SI =
952 IVsByStride.find(SCEVUnknown::getIntegerSCEV(SInt/Scale, Type::UIntTy));
953 if (SI == IVsByStride.end())
955 for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(),
956 IE = SI->second.IVs.end(); II != IE; ++II)
957 if (isZero(II->Base)) {
958 RewriteFactor = Scale;
963 if (RewriteFactor != 1)
969 const Type *ReplacedTy = CommonExprs->getType();
970 if (RewriteFactor == 1) {
971 // Create a new Phi for this base, and stick it in the loop header.
972 NewPHI = new PHINode(ReplacedTy, "iv.", PhiInsertBefore);
975 // Insert the stride into the preheader.
976 Value *StrideV = PreheaderRewriter.expandCodeFor(Stride, PreInsertPt,
978 if (!isa<ConstantInt>(StrideV)) ++NumVariable;
981 // Emit the initial base value into the loop preheader, and add it to the
983 Value *PHIBaseV = PreheaderRewriter.expandCodeFor(CommonExprs, PreInsertPt,
985 NewPHI->addIncoming(PHIBaseV, Preheader);
987 // Emit the increment of the base value before the terminator of the loop
988 // latch block, and add it to the Phi node.
989 SCEVHandle IncExp = SCEVAddExpr::get(SCEVUnknown::get(NewPHI),
990 SCEVUnknown::get(StrideV));
992 IncV = Rewriter.expandCodeFor(IncExp, LatchBlock->getTerminator(),
994 IncV->setName(NewPHI->getName()+".inc");
995 NewPHI->addIncoming(IncV, LatchBlock);
997 IVsByStride[Stride].addIV(CommonExprs, NewPHI, IncV);
1000 // Sort by the base value, so that all IVs with identical bases are next to
1002 while (!UsersToProcess.empty()) {
1003 SCEVHandle Base = UsersToProcess.back().Base;
1005 DEBUG(std::cerr << " INSERTING code for BASE = " << *Base << ":\n");
1007 // Emit the code for Base into the preheader.
1008 Value *BaseV = PreheaderRewriter.expandCodeFor(Base, PreInsertPt,
1011 // If BaseV is a constant other than 0, make sure that it gets inserted into
1012 // the preheader, instead of being forward substituted into the uses. We do
1013 // this by forcing a noop cast to be inserted into the preheader in this
1015 if (Constant *C = dyn_cast<Constant>(BaseV))
1016 if (!C->isNullValue() && !isTargetConstant(Base, TLI)) {
1017 // We want this constant emitted into the preheader!
1018 BaseV = new CastInst(BaseV, BaseV->getType(), "preheaderinsert",
1022 // Emit the code to add the immediate offset to the Phi value, just before
1023 // the instructions that we identified as using this stride and base.
1024 unsigned ScanPos = 0;
1026 BasedUser &User = UsersToProcess.back();
1028 // If this instruction wants to use the post-incremented value, move it
1029 // after the post-inc and use its value instead of the PHI.
1030 Value *RewriteOp = NewPHI;
1031 if (User.isUseOfPostIncrementedValue) {
1034 // If this user is in the loop, make sure it is the last thing in the
1035 // loop to ensure it is dominated by the increment.
1036 if (L->contains(User.Inst->getParent()))
1037 User.Inst->moveBefore(LatchBlock->getTerminator());
1039 SCEVHandle RewriteExpr = SCEVUnknown::get(RewriteOp);
1041 // Clear the SCEVExpander's expression map so that we are guaranteed
1042 // to have the code emitted where we expect it.
1045 // If we are reusing the iv, then it must be multiplied by a constant
1046 // factor take advantage of addressing mode scale component.
1047 if (RewriteFactor != 1)
1049 SCEVMulExpr::get(SCEVUnknown::getIntegerSCEV(RewriteFactor,
1050 RewriteExpr->getType()), RewriteExpr);
1052 // Now that we know what we need to do, insert code before User for the
1053 // immediate and any loop-variant expressions.
1054 if (!isa<ConstantInt>(BaseV) || !cast<ConstantInt>(BaseV)->isNullValue())
1055 // Add BaseV to the PHI value if needed.
1056 RewriteExpr = SCEVAddExpr::get(RewriteExpr, SCEVUnknown::get(BaseV));
1058 User.RewriteInstructionToUseNewBase(RewriteExpr, Rewriter, L, this);
1060 // Mark old value we replaced as possibly dead, so that it is elminated
1061 // if we just replaced the last use of that value.
1062 DeadInsts.insert(cast<Instruction>(User.OperandValToReplace));
1064 UsersToProcess.pop_back();
1067 // If there are any more users to process with the same base, move one of
1068 // them to the end of the list so that we will process it.
1069 if (!UsersToProcess.empty()) {
1070 for (unsigned e = UsersToProcess.size(); ScanPos != e; ++ScanPos)
1071 if (UsersToProcess[ScanPos].Base == Base) {
1072 std::swap(UsersToProcess[ScanPos], UsersToProcess.back());
1076 } while (!UsersToProcess.empty() && UsersToProcess.back().Base == Base);
1077 // TODO: Next, find out which base index is the most common, pull it out.
1080 // IMPORTANT TODO: Figure out how to partition the IV's with this stride, but
1081 // different starting values, into different PHIs.
1084 // OptimizeIndvars - Now that IVUsesByStride is set up with all of the indvar
1085 // uses in the loop, look to see if we can eliminate some, in favor of using
1086 // common indvars for the different uses.
1087 void LoopStrengthReduce::OptimizeIndvars(Loop *L) {
1088 // TODO: implement optzns here.
1093 // Finally, get the terminating condition for the loop if possible. If we
1094 // can, we want to change it to use a post-incremented version of its
1095 // induction variable, to allow coallescing the live ranges for the IV into
1096 // one register value.
1097 PHINode *SomePHI = cast<PHINode>(L->getHeader()->begin());
1098 BasicBlock *Preheader = L->getLoopPreheader();
1099 BasicBlock *LatchBlock =
1100 SomePHI->getIncomingBlock(SomePHI->getIncomingBlock(0) == Preheader);
1101 BranchInst *TermBr = dyn_cast<BranchInst>(LatchBlock->getTerminator());
1102 if (!TermBr || TermBr->isUnconditional() ||
1103 !isa<SetCondInst>(TermBr->getCondition()))
1105 SetCondInst *Cond = cast<SetCondInst>(TermBr->getCondition());
1107 // Search IVUsesByStride to find Cond's IVUse if there is one.
1108 IVStrideUse *CondUse = 0;
1109 const SCEVHandle *CondStride = 0;
1111 for (unsigned Stride = 0, e = StrideOrder.size(); Stride != e && !CondUse;
1113 std::map<SCEVHandle, IVUsersOfOneStride>::iterator SI =
1114 IVUsesByStride.find(StrideOrder[Stride]);
1115 assert(SI != IVUsesByStride.end() && "Stride doesn't exist!");
1117 for (std::vector<IVStrideUse>::iterator UI = SI->second.Users.begin(),
1118 E = SI->second.Users.end(); UI != E; ++UI)
1119 if (UI->User == Cond) {
1121 CondStride = &SI->first;
1122 // NOTE: we could handle setcc instructions with multiple uses here, but
1123 // InstCombine does it as well for simple uses, it's not clear that it
1124 // occurs enough in real life to handle.
1128 if (!CondUse) return; // setcc doesn't use the IV.
1130 // setcc stride is complex, don't mess with users.
1131 // FIXME: Evaluate whether this is a good idea or not.
1132 if (!isa<SCEVConstant>(*CondStride)) return;
1134 // It's possible for the setcc instruction to be anywhere in the loop, and
1135 // possible for it to have multiple users. If it is not immediately before
1136 // the latch block branch, move it.
1137 if (&*++BasicBlock::iterator(Cond) != (Instruction*)TermBr) {
1138 if (Cond->hasOneUse()) { // Condition has a single use, just move it.
1139 Cond->moveBefore(TermBr);
1141 // Otherwise, clone the terminating condition and insert into the loopend.
1142 Cond = cast<SetCondInst>(Cond->clone());
1143 Cond->setName(L->getHeader()->getName() + ".termcond");
1144 LatchBlock->getInstList().insert(TermBr, Cond);
1146 // Clone the IVUse, as the old use still exists!
1147 IVUsesByStride[*CondStride].addUser(CondUse->Offset, Cond,
1148 CondUse->OperandValToReplace);
1149 CondUse = &IVUsesByStride[*CondStride].Users.back();
1153 // If we get to here, we know that we can transform the setcc instruction to
1154 // use the post-incremented version of the IV, allowing us to coallesce the
1155 // live ranges for the IV correctly.
1156 CondUse->Offset = SCEV::getMinusSCEV(CondUse->Offset, *CondStride);
1157 CondUse->isUseOfPostIncrementedValue = true;
1160 void LoopStrengthReduce::runOnLoop(Loop *L) {
1161 // First step, transform all loops nesting inside of this loop.
1162 for (LoopInfo::iterator I = L->begin(), E = L->end(); I != E; ++I)
1165 // Next, find all uses of induction variables in this loop, and catagorize
1166 // them by stride. Start by finding all of the PHI nodes in the header for
1167 // this loop. If they are induction variables, inspect their uses.
1168 std::set<Instruction*> Processed; // Don't reprocess instructions.
1169 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
1170 AddUsersIfInteresting(I, L, Processed);
1172 // If we have nothing to do, return.
1173 if (IVUsesByStride.empty()) return;
1175 // Optimize induction variables. Some indvar uses can be transformed to use
1176 // strides that will be needed for other purposes. A common example of this
1177 // is the exit test for the loop, which can often be rewritten to use the
1178 // computation of some other indvar to decide when to terminate the loop.
1182 // FIXME: We can widen subreg IV's here for RISC targets. e.g. instead of
1183 // doing computation in byte values, promote to 32-bit values if safe.
1185 // FIXME: Attempt to reuse values across multiple IV's. In particular, we
1186 // could have something like "for(i) { foo(i*8); bar(i*16) }", which should be
1187 // codegened as "for (j = 0;; j+=8) { foo(j); bar(j+j); }" on X86/PPC. Need
1188 // to be careful that IV's are all the same type. Only works for intptr_t
1191 // If we only have one stride, we can more aggressively eliminate some things.
1192 bool HasOneStride = IVUsesByStride.size() == 1;
1195 DEBUG(std::cerr << "\nLSR on ");
1199 // IVsByStride keeps IVs for one particular loop.
1200 IVsByStride.clear();
1202 // Note: this processes each stride/type pair individually. All users passed
1203 // into StrengthReduceStridedIVUsers have the same type AND stride. Also,
1204 // node that we iterate over IVUsesByStride indirectly by using StrideOrder.
1205 // This extra layer of indirection makes the ordering of strides deterministic
1206 // - not dependent on map order.
1207 for (unsigned Stride = 0, e = StrideOrder.size(); Stride != e; ++Stride) {
1208 std::map<SCEVHandle, IVUsersOfOneStride>::iterator SI =
1209 IVUsesByStride.find(StrideOrder[Stride]);
1210 assert(SI != IVUsesByStride.end() && "Stride doesn't exist!");
1211 StrengthReduceStridedIVUsers(SI->first, SI->second, L, HasOneStride);
1214 // Clean up after ourselves
1215 if (!DeadInsts.empty()) {
1216 DeleteTriviallyDeadInstructions(DeadInsts);
1218 BasicBlock::iterator I = L->getHeader()->begin();
1220 while ((PN = dyn_cast<PHINode>(I))) {
1221 ++I; // Preincrement iterator to avoid invalidating it when deleting PN.
1223 // At this point, we know that we have killed one or more GEP
1224 // instructions. It is worth checking to see if the cann indvar is also
1225 // dead, so that we can remove it as well. The requirements for the cann
1226 // indvar to be considered dead are:
1227 // 1. the cann indvar has one use
1228 // 2. the use is an add instruction
1229 // 3. the add has one use
1230 // 4. the add is used by the cann indvar
1231 // If all four cases above are true, then we can remove both the add and
1233 // FIXME: this needs to eliminate an induction variable even if it's being
1234 // compared against some value to decide loop termination.
1235 if (PN->hasOneUse()) {
1236 BinaryOperator *BO = dyn_cast<BinaryOperator>(*(PN->use_begin()));
1237 if (BO && BO->hasOneUse()) {
1238 if (PN == *(BO->use_begin())) {
1239 DeadInsts.insert(BO);
1240 // Break the cycle, then delete the PHI.
1241 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1242 SE->deleteInstructionFromRecords(PN);
1243 PN->eraseFromParent();
1248 DeleteTriviallyDeadInstructions(DeadInsts);
1251 CastedPointers.clear();
1252 IVUsesByStride.clear();
1253 StrideOrder.clear();