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"
39 Statistic<> NumReduced ("loop-reduce", "Number of GEPs strength reduced");
40 Statistic<> NumInserted("loop-reduce", "Number of PHIs inserted");
41 Statistic<> NumVariable("loop-reduce","Number of PHIs with variable strides");
43 /// IVStrideUse - Keep track of one use of a strided induction variable, where
44 /// the stride is stored externally. The Offset member keeps track of the
45 /// offset from the IV, User is the actual user of the operand, and 'Operand'
46 /// is the operand # of the User that is the use.
50 Value *OperandValToReplace;
52 // isUseOfPostIncrementedValue - True if this should use the
53 // post-incremented version of this IV, not the preincremented version.
54 // This can only be set in special cases, such as the terminating setcc
55 // instruction for a loop or uses dominated by the loop.
56 bool isUseOfPostIncrementedValue;
58 IVStrideUse(const SCEVHandle &Offs, Instruction *U, Value *O)
59 : Offset(Offs), User(U), OperandValToReplace(O),
60 isUseOfPostIncrementedValue(false) {}
63 /// IVUsersOfOneStride - This structure keeps track of all instructions that
64 /// have an operand that is based on the trip count multiplied by some stride.
65 /// The stride for all of these users is common and kept external to this
67 struct IVUsersOfOneStride {
68 /// Users - Keep track of all of the users of this stride as well as the
69 /// initial value and the operand that uses the IV.
70 std::vector<IVStrideUse> Users;
72 void addUser(const SCEVHandle &Offset,Instruction *User, Value *Operand) {
73 Users.push_back(IVStrideUse(Offset, User, Operand));
78 class LoopStrengthReduce : public FunctionPass {
83 const Type *UIntPtrTy;
86 /// MaxTargetAMSize - This is the maximum power-of-two scale value that the
87 /// target can handle for free with its addressing modes.
88 unsigned MaxTargetAMSize;
90 /// IVUsesByStride - Keep track of all uses of induction variables that we
91 /// are interested in. The key of the map is the stride of the access.
92 std::map<SCEVHandle, IVUsersOfOneStride> IVUsesByStride;
94 /// StrideOrder - An ordering of the keys in IVUsesByStride that is stable:
95 /// We use this to iterate over the IVUsesByStride collection without being
96 /// dependent on random ordering of pointers in the process.
97 std::vector<SCEVHandle> StrideOrder;
99 /// CastedValues - As we need to cast values to uintptr_t, this keeps track
100 /// of the casted version of each value. This is accessed by
101 /// getCastedVersionOf.
102 std::map<Value*, Value*> CastedPointers;
104 /// DeadInsts - Keep track of instructions we may have made dead, so that
105 /// we can remove them after we are done working.
106 std::set<Instruction*> DeadInsts;
108 LoopStrengthReduce(unsigned MTAMS = 1)
109 : MaxTargetAMSize(MTAMS) {
112 virtual bool runOnFunction(Function &) {
113 LI = &getAnalysis<LoopInfo>();
114 DS = &getAnalysis<DominatorSet>();
115 SE = &getAnalysis<ScalarEvolution>();
116 TD = &getAnalysis<TargetData>();
117 UIntPtrTy = TD->getIntPtrType();
120 for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
126 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
127 // We split critical edges, so we change the CFG. However, we do update
128 // many analyses if they are around.
129 AU.addPreservedID(LoopSimplifyID);
130 AU.addPreserved<LoopInfo>();
131 AU.addPreserved<DominatorSet>();
132 AU.addPreserved<ImmediateDominators>();
133 AU.addPreserved<DominanceFrontier>();
134 AU.addPreserved<DominatorTree>();
136 AU.addRequiredID(LoopSimplifyID);
137 AU.addRequired<LoopInfo>();
138 AU.addRequired<DominatorSet>();
139 AU.addRequired<TargetData>();
140 AU.addRequired<ScalarEvolution>();
143 /// getCastedVersionOf - Return the specified value casted to uintptr_t.
145 Value *getCastedVersionOf(Value *V);
147 void runOnLoop(Loop *L);
148 bool AddUsersIfInteresting(Instruction *I, Loop *L,
149 std::set<Instruction*> &Processed);
150 SCEVHandle GetExpressionSCEV(Instruction *E, Loop *L);
152 void OptimizeIndvars(Loop *L);
154 void StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
155 IVUsersOfOneStride &Uses,
156 Loop *L, bool isOnlyStride);
157 void DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts);
159 RegisterOpt<LoopStrengthReduce> X("loop-reduce",
160 "Loop Strength Reduction");
163 FunctionPass *llvm::createLoopStrengthReducePass(unsigned MaxTargetAMSize) {
164 return new LoopStrengthReduce(MaxTargetAMSize);
167 /// getCastedVersionOf - Return the specified value casted to uintptr_t.
169 Value *LoopStrengthReduce::getCastedVersionOf(Value *V) {
170 if (V->getType() == UIntPtrTy) return V;
171 if (Constant *CB = dyn_cast<Constant>(V))
172 return ConstantExpr::getCast(CB, UIntPtrTy);
174 Value *&New = CastedPointers[V];
177 BasicBlock::iterator InsertPt;
178 if (Argument *Arg = dyn_cast<Argument>(V)) {
179 // Insert into the entry of the function, after any allocas.
180 InsertPt = Arg->getParent()->begin()->begin();
181 while (isa<AllocaInst>(InsertPt)) ++InsertPt;
183 if (InvokeInst *II = dyn_cast<InvokeInst>(V)) {
184 InsertPt = II->getNormalDest()->begin();
186 InsertPt = cast<Instruction>(V);
190 // Do not insert casts into the middle of PHI node blocks.
191 while (isa<PHINode>(InsertPt)) ++InsertPt;
194 New = new CastInst(V, UIntPtrTy, V->getName(), InsertPt);
195 DeadInsts.insert(cast<Instruction>(New));
200 /// DeleteTriviallyDeadInstructions - If any of the instructions is the
201 /// specified set are trivially dead, delete them and see if this makes any of
202 /// their operands subsequently dead.
203 void LoopStrengthReduce::
204 DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts) {
205 while (!Insts.empty()) {
206 Instruction *I = *Insts.begin();
207 Insts.erase(Insts.begin());
208 if (isInstructionTriviallyDead(I)) {
209 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
210 if (Instruction *U = dyn_cast<Instruction>(I->getOperand(i)))
212 SE->deleteInstructionFromRecords(I);
213 I->eraseFromParent();
220 /// GetExpressionSCEV - Compute and return the SCEV for the specified
222 SCEVHandle LoopStrengthReduce::GetExpressionSCEV(Instruction *Exp, Loop *L) {
223 // Scalar Evolutions doesn't know how to compute SCEV's for GEP instructions.
224 // If this is a GEP that SE doesn't know about, compute it now and insert it.
225 // If this is not a GEP, or if we have already done this computation, just let
227 GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Exp);
228 if (!GEP || SE->hasSCEV(GEP))
229 return SE->getSCEV(Exp);
231 // Analyze all of the subscripts of this getelementptr instruction, looking
232 // for uses that are determined by the trip count of L. First, skip all
233 // operands the are not dependent on the IV.
235 // Build up the base expression. Insert an LLVM cast of the pointer to
237 SCEVHandle GEPVal = SCEVUnknown::get(getCastedVersionOf(GEP->getOperand(0)));
239 gep_type_iterator GTI = gep_type_begin(GEP);
241 for (unsigned i = 1, e = GEP->getNumOperands(); i != e; ++i, ++GTI) {
242 // If this is a use of a recurrence that we can analyze, and it comes before
243 // Op does in the GEP operand list, we will handle this when we process this
245 if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
246 const StructLayout *SL = TD->getStructLayout(STy);
247 unsigned Idx = cast<ConstantUInt>(GEP->getOperand(i))->getValue();
248 uint64_t Offset = SL->MemberOffsets[Idx];
249 GEPVal = SCEVAddExpr::get(GEPVal,
250 SCEVUnknown::getIntegerSCEV(Offset, UIntPtrTy));
252 Value *OpVal = getCastedVersionOf(GEP->getOperand(i));
253 SCEVHandle Idx = SE->getSCEV(OpVal);
255 uint64_t TypeSize = TD->getTypeSize(GTI.getIndexedType());
257 Idx = SCEVMulExpr::get(Idx,
258 SCEVConstant::get(ConstantUInt::get(UIntPtrTy,
260 GEPVal = SCEVAddExpr::get(GEPVal, Idx);
264 SE->setSCEV(GEP, GEPVal);
268 /// getSCEVStartAndStride - Compute the start and stride of this expression,
269 /// returning false if the expression is not a start/stride pair, or true if it
270 /// is. The stride must be a loop invariant expression, but the start may be
271 /// a mix of loop invariant and loop variant expressions.
272 static bool getSCEVStartAndStride(const SCEVHandle &SH, Loop *L,
273 SCEVHandle &Start, SCEVHandle &Stride) {
274 SCEVHandle TheAddRec = Start; // Initialize to zero.
276 // If the outer level is an AddExpr, the operands are all start values except
277 // for a nested AddRecExpr.
278 if (SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(SH)) {
279 for (unsigned i = 0, e = AE->getNumOperands(); i != e; ++i)
280 if (SCEVAddRecExpr *AddRec =
281 dyn_cast<SCEVAddRecExpr>(AE->getOperand(i))) {
282 if (AddRec->getLoop() == L)
283 TheAddRec = SCEVAddExpr::get(AddRec, TheAddRec);
285 return false; // Nested IV of some sort?
287 Start = SCEVAddExpr::get(Start, AE->getOperand(i));
290 } else if (SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(SH)) {
293 return false; // not analyzable.
296 SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(TheAddRec);
297 if (!AddRec || AddRec->getLoop() != L) return false;
299 // FIXME: Generalize to non-affine IV's.
300 if (!AddRec->isAffine()) return false;
302 Start = SCEVAddExpr::get(Start, AddRec->getOperand(0));
304 if (!isa<SCEVConstant>(AddRec->getOperand(1)))
305 DEBUG(std::cerr << "[" << L->getHeader()->getName()
306 << "] Variable stride: " << *AddRec << "\n");
308 Stride = AddRec->getOperand(1);
309 // Check that all constant strides are the unsigned type, we don't want to
310 // have two IV's one of signed stride 4 and one of unsigned stride 4 to not be
312 assert((!isa<SCEVConstant>(Stride) || Stride->getType()->isUnsigned()) &&
313 "Constants should be canonicalized to unsigned!");
318 /// IVUseShouldUsePostIncValue - We have discovered a "User" of an IV expression
319 /// and now we need to decide whether the user should use the preinc or post-inc
320 /// value. If this user should use the post-inc version of the IV, return true.
322 /// Choosing wrong here can break dominance properties (if we choose to use the
323 /// post-inc value when we cannot) or it can end up adding extra live-ranges to
324 /// the loop, resulting in reg-reg copies (if we use the pre-inc value when we
325 /// should use the post-inc value).
326 static bool IVUseShouldUsePostIncValue(Instruction *User, Instruction *IV,
327 Loop *L, DominatorSet *DS, Pass *P) {
328 // If the user is in the loop, use the preinc value.
329 if (L->contains(User->getParent())) return false;
331 BasicBlock *LatchBlock = L->getLoopLatch();
333 // Ok, the user is outside of the loop. If it is dominated by the latch
334 // block, use the post-inc value.
335 if (DS->dominates(LatchBlock, User->getParent()))
338 // There is one case we have to be careful of: PHI nodes. These little guys
339 // can live in blocks that do not dominate the latch block, but (since their
340 // uses occur in the predecessor block, not the block the PHI lives in) should
341 // still use the post-inc value. Check for this case now.
342 PHINode *PN = dyn_cast<PHINode>(User);
343 if (!PN) return false; // not a phi, not dominated by latch block.
345 // Look at all of the uses of IV by the PHI node. If any use corresponds to
346 // a block that is not dominated by the latch block, give up and use the
347 // preincremented value.
348 unsigned NumUses = 0;
349 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
350 if (PN->getIncomingValue(i) == IV) {
352 if (!DS->dominates(LatchBlock, PN->getIncomingBlock(i)))
356 // Okay, all uses of IV by PN are in predecessor blocks that really are
357 // dominated by the latch block. Split the critical edges and use the
358 // post-incremented value.
359 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
360 if (PN->getIncomingValue(i) == IV) {
361 SplitCriticalEdge(PN->getIncomingBlock(i), PN->getParent(), P);
362 if (--NumUses == 0) break;
370 /// AddUsersIfInteresting - Inspect the specified instruction. If it is a
371 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
372 /// return true. Otherwise, return false.
373 bool LoopStrengthReduce::AddUsersIfInteresting(Instruction *I, Loop *L,
374 std::set<Instruction*> &Processed) {
375 if (!I->getType()->isInteger() && !isa<PointerType>(I->getType()))
376 return false; // Void and FP expressions cannot be reduced.
377 if (!Processed.insert(I).second)
378 return true; // Instruction already handled.
380 // Get the symbolic expression for this instruction.
381 SCEVHandle ISE = GetExpressionSCEV(I, L);
382 if (isa<SCEVCouldNotCompute>(ISE)) return false;
384 // Get the start and stride for this expression.
385 SCEVHandle Start = SCEVUnknown::getIntegerSCEV(0, ISE->getType());
386 SCEVHandle Stride = Start;
387 if (!getSCEVStartAndStride(ISE, L, Start, Stride))
388 return false; // Non-reducible symbolic expression, bail out.
390 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;++UI){
391 Instruction *User = cast<Instruction>(*UI);
393 // Do not infinitely recurse on PHI nodes.
394 if (isa<PHINode>(User) && Processed.count(User))
397 // If this is an instruction defined in a nested loop, or outside this loop,
398 // don't recurse into it.
399 bool AddUserToIVUsers = false;
400 if (LI->getLoopFor(User->getParent()) != L) {
401 DEBUG(std::cerr << "FOUND USER in other loop: " << *User
402 << " OF SCEV: " << *ISE << "\n");
403 AddUserToIVUsers = true;
404 } else if (!AddUsersIfInteresting(User, L, Processed)) {
405 DEBUG(std::cerr << "FOUND USER: " << *User
406 << " OF SCEV: " << *ISE << "\n");
407 AddUserToIVUsers = true;
410 if (AddUserToIVUsers) {
411 IVUsersOfOneStride &StrideUses = IVUsesByStride[Stride];
412 if (StrideUses.Users.empty()) // First occurance of this stride?
413 StrideOrder.push_back(Stride);
415 // Okay, we found a user that we cannot reduce. Analyze the instruction
416 // and decide what to do with it. If we are a use inside of the loop, use
417 // the value before incrementation, otherwise use it after incrementation.
418 if (IVUseShouldUsePostIncValue(User, I, L, DS, this)) {
419 // The value used will be incremented by the stride more than we are
420 // expecting, so subtract this off.
421 SCEVHandle NewStart = SCEV::getMinusSCEV(Start, Stride);
422 StrideUses.addUser(NewStart, User, I);
423 StrideUses.Users.back().isUseOfPostIncrementedValue = true;
424 DEBUG(std::cerr << " USING POSTINC SCEV, START=" << *NewStart<< "\n");
426 StrideUses.addUser(Start, User, I);
434 /// BasedUser - For a particular base value, keep information about how we've
435 /// partitioned the expression so far.
437 /// Base - The Base value for the PHI node that needs to be inserted for
438 /// this use. As the use is processed, information gets moved from this
439 /// field to the Imm field (below). BasedUser values are sorted by this
443 /// Inst - The instruction using the induction variable.
446 /// OperandValToReplace - The operand value of Inst to replace with the
448 Value *OperandValToReplace;
450 /// Imm - The immediate value that should be added to the base immediately
451 /// before Inst, because it will be folded into the imm field of the
455 /// EmittedBase - The actual value* to use for the base value of this
456 /// operation. This is null if we should just use zero so far.
459 // isUseOfPostIncrementedValue - True if this should use the
460 // post-incremented version of this IV, not the preincremented version.
461 // This can only be set in special cases, such as the terminating setcc
462 // instruction for a loop and uses outside the loop that are dominated by
464 bool isUseOfPostIncrementedValue;
466 BasedUser(IVStrideUse &IVSU)
467 : Base(IVSU.Offset), Inst(IVSU.User),
468 OperandValToReplace(IVSU.OperandValToReplace),
469 Imm(SCEVUnknown::getIntegerSCEV(0, Base->getType())), EmittedBase(0),
470 isUseOfPostIncrementedValue(IVSU.isUseOfPostIncrementedValue) {}
472 // Once we rewrite the code to insert the new IVs we want, update the
473 // operands of Inst to use the new expression 'NewBase', with 'Imm' added
475 void RewriteInstructionToUseNewBase(const SCEVHandle &NewBase,
476 SCEVExpander &Rewriter, Loop *L,
482 void BasedUser::dump() const {
483 std::cerr << " Base=" << *Base;
484 std::cerr << " Imm=" << *Imm;
486 std::cerr << " EB=" << *EmittedBase;
488 std::cerr << " Inst: " << *Inst;
491 // Once we rewrite the code to insert the new IVs we want, update the
492 // operands of Inst to use the new expression 'NewBase', with 'Imm' added
494 void BasedUser::RewriteInstructionToUseNewBase(const SCEVHandle &NewBase,
495 SCEVExpander &Rewriter,
497 if (!isa<PHINode>(Inst)) {
498 SCEVHandle NewValSCEV = SCEVAddExpr::get(NewBase, Imm);
499 Value *NewVal = Rewriter.expandCodeFor(NewValSCEV, Inst,
500 OperandValToReplace->getType());
501 // Replace the use of the operand Value with the new Phi we just created.
502 Inst->replaceUsesOfWith(OperandValToReplace, NewVal);
503 DEBUG(std::cerr << " CHANGED: IMM =" << *Imm << " Inst = " << *Inst);
507 // PHI nodes are more complex. We have to insert one copy of the NewBase+Imm
508 // expression into each operand block that uses it. Note that PHI nodes can
509 // have multiple entries for the same predecessor. We use a map to make sure
510 // that a PHI node only has a single Value* for each predecessor (which also
511 // prevents us from inserting duplicate code in some blocks).
512 std::map<BasicBlock*, Value*> InsertedCode;
513 PHINode *PN = cast<PHINode>(Inst);
514 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
515 if (PN->getIncomingValue(i) == OperandValToReplace) {
516 // If this is a critical edge, split the edge so that we do not insert the
517 // code on all predecessor/successor paths. We do this unless this is the
518 // canonical backedge for this loop, as this can make some inserted code
519 // be in an illegal position.
520 BasicBlock *PHIPred = PN->getIncomingBlock(i);
521 if (e != 1 && PHIPred->getTerminator()->getNumSuccessors() > 1 &&
522 (PN->getParent() != L->getHeader() || !L->contains(PHIPred))) {
524 // First step, split the critical edge.
525 SplitCriticalEdge(PHIPred, PN->getParent(), P);
527 // Next step: move the basic block. In particular, if the PHI node
528 // is outside of the loop, and PredTI is in the loop, we want to
529 // move the block to be immediately before the PHI block, not
530 // immediately after PredTI.
531 if (L->contains(PHIPred) && !L->contains(PN->getParent())) {
532 BasicBlock *NewBB = PN->getIncomingBlock(i);
533 NewBB->moveBefore(PN->getParent());
537 Value *&Code = InsertedCode[PN->getIncomingBlock(i)];
539 // Insert the code into the end of the predecessor block.
540 BasicBlock::iterator InsertPt =PN->getIncomingBlock(i)->getTerminator();
542 SCEVHandle NewValSCEV = SCEVAddExpr::get(NewBase, Imm);
543 Code = Rewriter.expandCodeFor(NewValSCEV, InsertPt,
544 OperandValToReplace->getType());
547 // Replace the use of the operand Value with the new Phi we just created.
548 PN->setIncomingValue(i, Code);
552 DEBUG(std::cerr << " CHANGED: IMM =" << *Imm << " Inst = " << *Inst);
556 /// isTargetConstant - Return true if the following can be referenced by the
557 /// immediate field of a target instruction.
558 static bool isTargetConstant(const SCEVHandle &V) {
560 // FIXME: Look at the target to decide if &GV is a legal constant immediate.
561 if (SCEVConstant *SC = dyn_cast<SCEVConstant>(V)) {
562 // PPC allows a sign-extended 16-bit immediate field.
563 if ((int64_t)SC->getValue()->getRawValue() > -(1 << 16) &&
564 (int64_t)SC->getValue()->getRawValue() < (1 << 16)-1)
569 return false; // ENABLE this for x86
571 if (SCEVUnknown *SU = dyn_cast<SCEVUnknown>(V))
572 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(SU->getValue()))
573 if (CE->getOpcode() == Instruction::Cast)
574 if (isa<GlobalValue>(CE->getOperand(0)))
575 // FIXME: should check to see that the dest is uintptr_t!
580 /// MoveLoopVariantsToImediateField - Move any subexpressions from Val that are
581 /// loop varying to the Imm operand.
582 static void MoveLoopVariantsToImediateField(SCEVHandle &Val, SCEVHandle &Imm,
584 if (Val->isLoopInvariant(L)) return; // Nothing to do.
586 if (SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) {
587 std::vector<SCEVHandle> NewOps;
588 NewOps.reserve(SAE->getNumOperands());
590 for (unsigned i = 0; i != SAE->getNumOperands(); ++i)
591 if (!SAE->getOperand(i)->isLoopInvariant(L)) {
592 // If this is a loop-variant expression, it must stay in the immediate
593 // field of the expression.
594 Imm = SCEVAddExpr::get(Imm, SAE->getOperand(i));
596 NewOps.push_back(SAE->getOperand(i));
600 Val = SCEVUnknown::getIntegerSCEV(0, Val->getType());
602 Val = SCEVAddExpr::get(NewOps);
603 } else if (SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Val)) {
604 // Try to pull immediates out of the start value of nested addrec's.
605 SCEVHandle Start = SARE->getStart();
606 MoveLoopVariantsToImediateField(Start, Imm, L);
608 std::vector<SCEVHandle> Ops(SARE->op_begin(), SARE->op_end());
610 Val = SCEVAddRecExpr::get(Ops, SARE->getLoop());
612 // Otherwise, all of Val is variant, move the whole thing over.
613 Imm = SCEVAddExpr::get(Imm, Val);
614 Val = SCEVUnknown::getIntegerSCEV(0, Val->getType());
619 /// MoveImmediateValues - Look at Val, and pull out any additions of constants
620 /// that can fit into the immediate field of instructions in the target.
621 /// Accumulate these immediate values into the Imm value.
622 static void MoveImmediateValues(SCEVHandle &Val, SCEVHandle &Imm,
623 bool isAddress, Loop *L) {
624 if (SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) {
625 std::vector<SCEVHandle> NewOps;
626 NewOps.reserve(SAE->getNumOperands());
628 for (unsigned i = 0; i != SAE->getNumOperands(); ++i)
629 if (isAddress && isTargetConstant(SAE->getOperand(i))) {
630 Imm = SCEVAddExpr::get(Imm, SAE->getOperand(i));
631 } else if (!SAE->getOperand(i)->isLoopInvariant(L)) {
632 // If this is a loop-variant expression, it must stay in the immediate
633 // field of the expression.
634 Imm = SCEVAddExpr::get(Imm, SAE->getOperand(i));
636 NewOps.push_back(SAE->getOperand(i));
640 Val = SCEVUnknown::getIntegerSCEV(0, Val->getType());
642 Val = SCEVAddExpr::get(NewOps);
644 } else if (SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Val)) {
645 // Try to pull immediates out of the start value of nested addrec's.
646 SCEVHandle Start = SARE->getStart();
647 MoveImmediateValues(Start, Imm, isAddress, L);
649 if (Start != SARE->getStart()) {
650 std::vector<SCEVHandle> Ops(SARE->op_begin(), SARE->op_end());
652 Val = SCEVAddRecExpr::get(Ops, SARE->getLoop());
657 // Loop-variant expressions must stay in the immediate field of the
659 if ((isAddress && isTargetConstant(Val)) ||
660 !Val->isLoopInvariant(L)) {
661 Imm = SCEVAddExpr::get(Imm, Val);
662 Val = SCEVUnknown::getIntegerSCEV(0, Val->getType());
666 // Otherwise, no immediates to move.
670 /// IncrementAddExprUses - Decompose the specified expression into its added
671 /// subexpressions, and increment SubExpressionUseCounts for each of these
672 /// decomposed parts.
673 static void SeparateSubExprs(std::vector<SCEVHandle> &SubExprs,
675 if (SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(Expr)) {
676 for (unsigned j = 0, e = AE->getNumOperands(); j != e; ++j)
677 SeparateSubExprs(SubExprs, AE->getOperand(j));
678 } else if (SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Expr)) {
679 SCEVHandle Zero = SCEVUnknown::getIntegerSCEV(0, Expr->getType());
680 if (SARE->getOperand(0) == Zero) {
681 SubExprs.push_back(Expr);
683 // Compute the addrec with zero as its base.
684 std::vector<SCEVHandle> Ops(SARE->op_begin(), SARE->op_end());
685 Ops[0] = Zero; // Start with zero base.
686 SubExprs.push_back(SCEVAddRecExpr::get(Ops, SARE->getLoop()));
689 SeparateSubExprs(SubExprs, SARE->getOperand(0));
691 } else if (!isa<SCEVConstant>(Expr) ||
692 !cast<SCEVConstant>(Expr)->getValue()->isNullValue()) {
694 SubExprs.push_back(Expr);
699 /// RemoveCommonExpressionsFromUseBases - Look through all of the uses in Bases,
700 /// removing any common subexpressions from it. Anything truly common is
701 /// removed, accumulated, and returned. This looks for things like (a+b+c) and
702 /// (a+c+d) -> (a+c). The common expression is *removed* from the Bases.
704 RemoveCommonExpressionsFromUseBases(std::vector<BasedUser> &Uses) {
705 unsigned NumUses = Uses.size();
707 // Only one use? Use its base, regardless of what it is!
708 SCEVHandle Zero = SCEVUnknown::getIntegerSCEV(0, Uses[0].Base->getType());
709 SCEVHandle Result = Zero;
711 std::swap(Result, Uses[0].Base);
715 // To find common subexpressions, count how many of Uses use each expression.
716 // If any subexpressions are used Uses.size() times, they are common.
717 std::map<SCEVHandle, unsigned> SubExpressionUseCounts;
719 // UniqueSubExprs - Keep track of all of the subexpressions we see in the
720 // order we see them.
721 std::vector<SCEVHandle> UniqueSubExprs;
723 std::vector<SCEVHandle> SubExprs;
724 for (unsigned i = 0; i != NumUses; ++i) {
725 // If the base is zero (which is common), return zero now, there are no
727 if (Uses[i].Base == Zero) return Zero;
729 // Split the expression into subexprs.
730 SeparateSubExprs(SubExprs, Uses[i].Base);
731 // Add one to SubExpressionUseCounts for each subexpr present.
732 for (unsigned j = 0, e = SubExprs.size(); j != e; ++j)
733 if (++SubExpressionUseCounts[SubExprs[j]] == 1)
734 UniqueSubExprs.push_back(SubExprs[j]);
738 // Now that we know how many times each is used, build Result. Iterate over
739 // UniqueSubexprs so that we have a stable ordering.
740 for (unsigned i = 0, e = UniqueSubExprs.size(); i != e; ++i) {
741 std::map<SCEVHandle, unsigned>::iterator I =
742 SubExpressionUseCounts.find(UniqueSubExprs[i]);
743 assert(I != SubExpressionUseCounts.end() && "Entry not found?");
744 if (I->second == NumUses) { // Found CSE!
745 Result = SCEVAddExpr::get(Result, I->first);
747 // Remove non-cse's from SubExpressionUseCounts.
748 SubExpressionUseCounts.erase(I);
752 // If we found no CSE's, return now.
753 if (Result == Zero) return Result;
755 // Otherwise, remove all of the CSE's we found from each of the base values.
756 for (unsigned i = 0; i != NumUses; ++i) {
757 // Split the expression into subexprs.
758 SeparateSubExprs(SubExprs, Uses[i].Base);
760 // Remove any common subexpressions.
761 for (unsigned j = 0, e = SubExprs.size(); j != e; ++j)
762 if (SubExpressionUseCounts.count(SubExprs[j])) {
763 SubExprs.erase(SubExprs.begin()+j);
767 // Finally, the non-shared expressions together.
768 if (SubExprs.empty())
771 Uses[i].Base = SCEVAddExpr::get(SubExprs);
779 /// StrengthReduceStridedIVUsers - Strength reduce all of the users of a single
780 /// stride of IV. All of the users may have different starting values, and this
781 /// may not be the only stride (we know it is if isOnlyStride is true).
782 void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
783 IVUsersOfOneStride &Uses,
786 // Transform our list of users and offsets to a bit more complex table. In
787 // this new vector, each 'BasedUser' contains 'Base' the base of the
788 // strided accessas well as the old information from Uses. We progressively
789 // move information from the Base field to the Imm field, until we eventually
790 // have the full access expression to rewrite the use.
791 std::vector<BasedUser> UsersToProcess;
792 UsersToProcess.reserve(Uses.Users.size());
793 for (unsigned i = 0, e = Uses.Users.size(); i != e; ++i) {
794 UsersToProcess.push_back(Uses.Users[i]);
796 // Move any loop invariant operands from the offset field to the immediate
797 // field of the use, so that we don't try to use something before it is
799 MoveLoopVariantsToImediateField(UsersToProcess.back().Base,
800 UsersToProcess.back().Imm, L);
801 assert(UsersToProcess.back().Base->isLoopInvariant(L) &&
802 "Base value is not loop invariant!");
805 // We now have a whole bunch of uses of like-strided induction variables, but
806 // they might all have different bases. We want to emit one PHI node for this
807 // stride which we fold as many common expressions (between the IVs) into as
808 // possible. Start by identifying the common expressions in the base values
809 // for the strides (e.g. if we have "A+C+B" and "A+B+D" as our bases, find
810 // "A+B"), emit it to the preheader, then remove the expression from the
811 // UsersToProcess base values.
812 SCEVHandle CommonExprs = RemoveCommonExpressionsFromUseBases(UsersToProcess);
814 // Next, figure out what we can represent in the immediate fields of
815 // instructions. If we can represent anything there, move it to the imm
816 // fields of the BasedUsers. We do this so that it increases the commonality
817 // of the remaining uses.
818 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) {
819 // If the user is not in the current loop, this means it is using the exit
820 // value of the IV. Do not put anything in the base, make sure it's all in
821 // the immediate field to allow as much factoring as possible.
822 if (!L->contains(UsersToProcess[i].Inst->getParent())) {
823 UsersToProcess[i].Imm = SCEVAddExpr::get(UsersToProcess[i].Imm,
824 UsersToProcess[i].Base);
825 UsersToProcess[i].Base =
826 SCEVUnknown::getIntegerSCEV(0, UsersToProcess[i].Base->getType());
829 // Addressing modes can be folded into loads and stores. Be careful that
830 // the store is through the expression, not of the expression though.
831 bool isAddress = isa<LoadInst>(UsersToProcess[i].Inst);
832 if (StoreInst *SI = dyn_cast<StoreInst>(UsersToProcess[i].Inst))
833 if (SI->getOperand(1) == UsersToProcess[i].OperandValToReplace)
836 MoveImmediateValues(UsersToProcess[i].Base, UsersToProcess[i].Imm,
841 // Now that we know what we need to do, insert the PHI node itself.
843 DEBUG(std::cerr << "INSERTING IV of STRIDE " << *Stride << " and BASE "
844 << *CommonExprs << " :\n");
846 SCEVExpander Rewriter(*SE, *LI);
847 SCEVExpander PreheaderRewriter(*SE, *LI);
849 BasicBlock *Preheader = L->getLoopPreheader();
850 Instruction *PreInsertPt = Preheader->getTerminator();
851 Instruction *PhiInsertBefore = L->getHeader()->begin();
853 BasicBlock *LatchBlock = L->getLoopLatch();
855 // Create a new Phi for this base, and stick it in the loop header.
856 const Type *ReplacedTy = CommonExprs->getType();
857 PHINode *NewPHI = new PHINode(ReplacedTy, "iv.", PhiInsertBefore);
860 // Insert the stride into the preheader.
861 Value *StrideV = PreheaderRewriter.expandCodeFor(Stride, PreInsertPt,
863 if (!isa<ConstantInt>(StrideV)) ++NumVariable;
866 // Emit the initial base value into the loop preheader, and add it to the
868 Value *PHIBaseV = PreheaderRewriter.expandCodeFor(CommonExprs, PreInsertPt,
870 NewPHI->addIncoming(PHIBaseV, Preheader);
872 // Emit the increment of the base value before the terminator of the loop
873 // latch block, and add it to the Phi node.
874 SCEVHandle IncExp = SCEVAddExpr::get(SCEVUnknown::get(NewPHI),
875 SCEVUnknown::get(StrideV));
877 Value *IncV = Rewriter.expandCodeFor(IncExp, LatchBlock->getTerminator(),
879 IncV->setName(NewPHI->getName()+".inc");
880 NewPHI->addIncoming(IncV, LatchBlock);
882 // Sort by the base value, so that all IVs with identical bases are next to
884 while (!UsersToProcess.empty()) {
885 SCEVHandle Base = UsersToProcess.back().Base;
887 DEBUG(std::cerr << " INSERTING code for BASE = " << *Base << ":\n");
889 // Emit the code for Base into the preheader.
890 Value *BaseV = PreheaderRewriter.expandCodeFor(Base, PreInsertPt,
893 // If BaseV is a constant other than 0, make sure that it gets inserted into
894 // the preheader, instead of being forward substituted into the uses. We do
895 // this by forcing a noop cast to be inserted into the preheader in this
897 if (Constant *C = dyn_cast<Constant>(BaseV))
898 if (!C->isNullValue() && !isTargetConstant(Base)) {
899 // We want this constant emitted into the preheader!
900 BaseV = new CastInst(BaseV, BaseV->getType(), "preheaderinsert",
904 // Emit the code to add the immediate offset to the Phi value, just before
905 // the instructions that we identified as using this stride and base.
906 unsigned ScanPos = 0;
908 BasedUser &User = UsersToProcess.back();
910 // If this instruction wants to use the post-incremented value, move it
911 // after the post-inc and use its value instead of the PHI.
912 Value *RewriteOp = NewPHI;
913 if (User.isUseOfPostIncrementedValue) {
916 // If this user is in the loop, make sure it is the last thing in the
917 // loop to ensure it is dominated by the increment.
918 if (L->contains(User.Inst->getParent()))
919 User.Inst->moveBefore(LatchBlock->getTerminator());
921 SCEVHandle RewriteExpr = SCEVUnknown::get(RewriteOp);
923 // Clear the SCEVExpander's expression map so that we are guaranteed
924 // to have the code emitted where we expect it.
927 // Now that we know what we need to do, insert code before User for the
928 // immediate and any loop-variant expressions.
929 if (!isa<ConstantInt>(BaseV) || !cast<ConstantInt>(BaseV)->isNullValue())
930 // Add BaseV to the PHI value if needed.
931 RewriteExpr = SCEVAddExpr::get(RewriteExpr, SCEVUnknown::get(BaseV));
933 User.RewriteInstructionToUseNewBase(RewriteExpr, Rewriter, L, this);
935 // Mark old value we replaced as possibly dead, so that it is elminated
936 // if we just replaced the last use of that value.
937 DeadInsts.insert(cast<Instruction>(User.OperandValToReplace));
939 UsersToProcess.pop_back();
942 // If there are any more users to process with the same base, move one of
943 // them to the end of the list so that we will process it.
944 if (!UsersToProcess.empty()) {
945 for (unsigned e = UsersToProcess.size(); ScanPos != e; ++ScanPos)
946 if (UsersToProcess[ScanPos].Base == Base) {
947 std::swap(UsersToProcess[ScanPos], UsersToProcess.back());
951 } while (!UsersToProcess.empty() && UsersToProcess.back().Base == Base);
952 // TODO: Next, find out which base index is the most common, pull it out.
955 // IMPORTANT TODO: Figure out how to partition the IV's with this stride, but
956 // different starting values, into different PHIs.
959 // OptimizeIndvars - Now that IVUsesByStride is set up with all of the indvar
960 // uses in the loop, look to see if we can eliminate some, in favor of using
961 // common indvars for the different uses.
962 void LoopStrengthReduce::OptimizeIndvars(Loop *L) {
963 // TODO: implement optzns here.
968 // Finally, get the terminating condition for the loop if possible. If we
969 // can, we want to change it to use a post-incremented version of its
970 // induction variable, to allow coallescing the live ranges for the IV into
971 // one register value.
972 PHINode *SomePHI = cast<PHINode>(L->getHeader()->begin());
973 BasicBlock *Preheader = L->getLoopPreheader();
974 BasicBlock *LatchBlock =
975 SomePHI->getIncomingBlock(SomePHI->getIncomingBlock(0) == Preheader);
976 BranchInst *TermBr = dyn_cast<BranchInst>(LatchBlock->getTerminator());
977 if (!TermBr || TermBr->isUnconditional() ||
978 !isa<SetCondInst>(TermBr->getCondition()))
980 SetCondInst *Cond = cast<SetCondInst>(TermBr->getCondition());
982 // Search IVUsesByStride to find Cond's IVUse if there is one.
983 IVStrideUse *CondUse = 0;
984 const SCEVHandle *CondStride = 0;
986 for (unsigned Stride = 0, e = StrideOrder.size(); Stride != e && !CondUse;
988 std::map<SCEVHandle, IVUsersOfOneStride>::iterator SI =
989 IVUsesByStride.find(StrideOrder[Stride]);
990 assert(SI != IVUsesByStride.end() && "Stride doesn't exist!");
992 for (std::vector<IVStrideUse>::iterator UI = SI->second.Users.begin(),
993 E = SI->second.Users.end(); UI != E; ++UI)
994 if (UI->User == Cond) {
996 CondStride = &SI->first;
997 // NOTE: we could handle setcc instructions with multiple uses here, but
998 // InstCombine does it as well for simple uses, it's not clear that it
999 // occurs enough in real life to handle.
1003 if (!CondUse) return; // setcc doesn't use the IV.
1005 // setcc stride is complex, don't mess with users.
1006 // FIXME: Evaluate whether this is a good idea or not.
1007 if (!isa<SCEVConstant>(*CondStride)) return;
1009 // It's possible for the setcc instruction to be anywhere in the loop, and
1010 // possible for it to have multiple users. If it is not immediately before
1011 // the latch block branch, move it.
1012 if (&*++BasicBlock::iterator(Cond) != (Instruction*)TermBr) {
1013 if (Cond->hasOneUse()) { // Condition has a single use, just move it.
1014 Cond->moveBefore(TermBr);
1016 // Otherwise, clone the terminating condition and insert into the loopend.
1017 Cond = cast<SetCondInst>(Cond->clone());
1018 Cond->setName(L->getHeader()->getName() + ".termcond");
1019 LatchBlock->getInstList().insert(TermBr, Cond);
1021 // Clone the IVUse, as the old use still exists!
1022 IVUsesByStride[*CondStride].addUser(CondUse->Offset, Cond,
1023 CondUse->OperandValToReplace);
1024 CondUse = &IVUsesByStride[*CondStride].Users.back();
1028 // If we get to here, we know that we can transform the setcc instruction to
1029 // use the post-incremented version of the IV, allowing us to coallesce the
1030 // live ranges for the IV correctly.
1031 CondUse->Offset = SCEV::getMinusSCEV(CondUse->Offset, *CondStride);
1032 CondUse->isUseOfPostIncrementedValue = true;
1035 void LoopStrengthReduce::runOnLoop(Loop *L) {
1036 // First step, transform all loops nesting inside of this loop.
1037 for (LoopInfo::iterator I = L->begin(), E = L->end(); I != E; ++I)
1040 // Next, find all uses of induction variables in this loop, and catagorize
1041 // them by stride. Start by finding all of the PHI nodes in the header for
1042 // this loop. If they are induction variables, inspect their uses.
1043 std::set<Instruction*> Processed; // Don't reprocess instructions.
1044 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
1045 AddUsersIfInteresting(I, L, Processed);
1047 // If we have nothing to do, return.
1048 if (IVUsesByStride.empty()) return;
1050 // Optimize induction variables. Some indvar uses can be transformed to use
1051 // strides that will be needed for other purposes. A common example of this
1052 // is the exit test for the loop, which can often be rewritten to use the
1053 // computation of some other indvar to decide when to terminate the loop.
1057 // FIXME: We can widen subreg IV's here for RISC targets. e.g. instead of
1058 // doing computation in byte values, promote to 32-bit values if safe.
1060 // FIXME: Attempt to reuse values across multiple IV's. In particular, we
1061 // could have something like "for(i) { foo(i*8); bar(i*16) }", which should be
1062 // codegened as "for (j = 0;; j+=8) { foo(j); bar(j+j); }" on X86/PPC. Need
1063 // to be careful that IV's are all the same type. Only works for intptr_t
1066 // If we only have one stride, we can more aggressively eliminate some things.
1067 bool HasOneStride = IVUsesByStride.size() == 1;
1069 // Note: this processes each stride/type pair individually. All users passed
1070 // into StrengthReduceStridedIVUsers have the same type AND stride. Also,
1071 // node that we iterate over IVUsesByStride indirectly by using StrideOrder.
1072 // This extra layer of indirection makes the ordering of strides deterministic
1073 // - not dependent on map order.
1074 for (unsigned Stride = 0, e = StrideOrder.size(); Stride != e; ++Stride) {
1075 std::map<SCEVHandle, IVUsersOfOneStride>::iterator SI =
1076 IVUsesByStride.find(StrideOrder[Stride]);
1077 assert(SI != IVUsesByStride.end() && "Stride doesn't exist!");
1078 StrengthReduceStridedIVUsers(SI->first, SI->second, L, HasOneStride);
1081 // Clean up after ourselves
1082 if (!DeadInsts.empty()) {
1083 DeleteTriviallyDeadInstructions(DeadInsts);
1085 BasicBlock::iterator I = L->getHeader()->begin();
1087 while ((PN = dyn_cast<PHINode>(I))) {
1088 ++I; // Preincrement iterator to avoid invalidating it when deleting PN.
1090 // At this point, we know that we have killed one or more GEP
1091 // instructions. It is worth checking to see if the cann indvar is also
1092 // dead, so that we can remove it as well. The requirements for the cann
1093 // indvar to be considered dead are:
1094 // 1. the cann indvar has one use
1095 // 2. the use is an add instruction
1096 // 3. the add has one use
1097 // 4. the add is used by the cann indvar
1098 // If all four cases above are true, then we can remove both the add and
1100 // FIXME: this needs to eliminate an induction variable even if it's being
1101 // compared against some value to decide loop termination.
1102 if (PN->hasOneUse()) {
1103 BinaryOperator *BO = dyn_cast<BinaryOperator>(*(PN->use_begin()));
1104 if (BO && BO->hasOneUse()) {
1105 if (PN == *(BO->use_begin())) {
1106 DeadInsts.insert(BO);
1107 // Break the cycle, then delete the PHI.
1108 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1109 SE->deleteInstructionFromRecords(PN);
1110 PN->eraseFromParent();
1115 DeleteTriviallyDeadInstructions(DeadInsts);
1118 CastedPointers.clear();
1119 IVUsesByStride.clear();
1120 StrideOrder.clear();