1 //===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This transformation analyzes and transforms the induction variables (and
11 // computations derived from them) into simpler forms suitable for subsequent
12 // analysis and transformation.
14 // This transformation make the following changes to each loop with an
15 // identifiable induction variable:
16 // 1. All loops are transformed to have a SINGLE canonical induction variable
17 // which starts at zero and steps by one.
18 // 2. The canonical induction variable is guaranteed to be the first PHI node
19 // in the loop header block.
20 // 3. Any pointer arithmetic recurrences are raised to use array subscripts.
22 // If the trip count of a loop is computable, this pass also makes the following
24 // 1. The exit condition for the loop is canonicalized to compare the
25 // induction value against the exit value. This turns loops like:
26 // 'for (i = 7; i*i < 1000; ++i)' into 'for (i = 0; i != 25; ++i)'
27 // 2. Any use outside of the loop of an expression derived from the indvar
28 // is changed to compute the derived value outside of the loop, eliminating
29 // the dependence on the exit value of the induction variable. If the only
30 // purpose of the loop is to compute the exit value of some derived
31 // expression, this transformation will make the loop dead.
33 // This transformation should be followed by strength reduction after all of the
34 // desired loop transformations have been performed. Additionally, on targets
35 // where it is profitable, the loop could be transformed to count down to zero
36 // (the "do loop" optimization).
38 //===----------------------------------------------------------------------===//
40 #include "llvm/Transforms/Scalar.h"
41 #include "llvm/BasicBlock.h"
42 #include "llvm/Constants.h"
43 #include "llvm/Instructions.h"
44 #include "llvm/Type.h"
45 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
46 #include "llvm/Analysis/LoopInfo.h"
47 #include "llvm/Support/CFG.h"
48 #include "llvm/Support/GetElementPtrTypeIterator.h"
49 #include "llvm/Transforms/Utils/Local.h"
50 #include "llvm/Support/CommandLine.h"
51 #include "llvm/ADT/Statistic.h"
55 /// SCEVExpander - This class uses information about analyze scalars to
56 /// rewrite expressions in canonical form.
58 /// Clients should create an instance of this class when rewriting is needed,
59 /// and destroying it when finished to allow the release of the associated
61 struct SCEVExpander : public SCEVVisitor<SCEVExpander, Value*> {
64 std::map<SCEVHandle, Value*> InsertedExpressions;
65 std::set<Instruction*> InsertedInstructions;
67 Instruction *InsertPt;
69 friend struct SCEVVisitor<SCEVExpander, Value*>;
71 SCEVExpander(ScalarEvolution &se, LoopInfo &li) : SE(se), LI(li) {}
73 /// isInsertedInstruction - Return true if the specified instruction was
74 /// inserted by the code rewriter. If so, the client should not modify the
76 bool isInsertedInstruction(Instruction *I) const {
77 return InsertedInstructions.count(I);
80 /// getOrInsertCanonicalInductionVariable - This method returns the
81 /// canonical induction variable of the specified type for the specified
82 /// loop (inserting one if there is none). A canonical induction variable
83 /// starts at zero and steps by one on each iteration.
84 Value *getOrInsertCanonicalInductionVariable(const Loop *L, const Type *Ty){
85 assert((Ty->isInteger() || Ty->isFloatingPoint()) &&
86 "Can only insert integer or floating point induction variables!");
87 SCEVHandle H = SCEVAddRecExpr::get(SCEVUnknown::getIntegerSCEV(0, Ty),
88 SCEVUnknown::getIntegerSCEV(1, Ty), L);
92 /// addInsertedValue - Remember the specified instruction as being the
93 /// canonical form for the specified SCEV.
94 void addInsertedValue(Instruction *I, SCEV *S) {
95 InsertedExpressions[S] = (Value*)I;
96 InsertedInstructions.insert(I);
99 /// expandCodeFor - Insert code to directly compute the specified SCEV
100 /// expression into the program. The inserted code is inserted into the
103 /// If a particular value sign is required, a type may be specified for the
105 Value *expandCodeFor(SCEVHandle SH, Instruction *IP, const Type *Ty = 0) {
106 // Expand the code for this SCEV.
108 return expandInTy(SH, Ty);
112 Value *expand(SCEV *S) {
113 // Check to see if we already expanded this.
114 std::map<SCEVHandle, Value*>::iterator I = InsertedExpressions.find(S);
115 if (I != InsertedExpressions.end())
119 InsertedExpressions[S] = V;
123 Value *expandInTy(SCEV *S, const Type *Ty) {
124 Value *V = expand(S);
125 if (Ty && V->getType() != Ty) {
126 // FIXME: keep track of the cast instruction.
127 if (Constant *C = dyn_cast<Constant>(V))
128 return ConstantExpr::getCast(C, Ty);
129 else if (Instruction *I = dyn_cast<Instruction>(V)) {
130 // Check to see if there is already a cast. If there is, use it.
131 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
133 if ((*UI)->getType() == Ty)
134 if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI))) {
135 BasicBlock::iterator It = I; ++It;
136 if (isa<InvokeInst>(I))
137 It = cast<InvokeInst>(I)->getNormalDest()->begin();
138 while (isa<PHINode>(It)) ++It;
139 if (It != BasicBlock::iterator(CI)) {
140 // Splice the cast immediately after the operand in question.
141 BasicBlock::InstListType &InstList =
142 It->getParent()->getInstList();
143 InstList.splice(It, CI->getParent()->getInstList(), CI);
148 BasicBlock::iterator IP = I; ++IP;
149 if (InvokeInst *II = dyn_cast<InvokeInst>(I))
150 IP = II->getNormalDest()->begin();
151 while (isa<PHINode>(IP)) ++IP;
152 return new CastInst(V, Ty, V->getName(), IP);
154 // FIXME: check to see if there is already a cast!
155 return new CastInst(V, Ty, V->getName(), InsertPt);
161 Value *visitConstant(SCEVConstant *S) {
162 return S->getValue();
165 Value *visitTruncateExpr(SCEVTruncateExpr *S) {
166 Value *V = expand(S->getOperand());
167 return new CastInst(V, S->getType(), "tmp.", InsertPt);
170 Value *visitZeroExtendExpr(SCEVZeroExtendExpr *S) {
171 Value *V = expandInTy(S->getOperand(),S->getType()->getUnsignedVersion());
172 return new CastInst(V, S->getType(), "tmp.", InsertPt);
175 Value *visitAddExpr(SCEVAddExpr *S) {
176 const Type *Ty = S->getType();
177 Value *V = expandInTy(S->getOperand(S->getNumOperands()-1), Ty);
179 // Emit a bunch of add instructions
180 for (int i = S->getNumOperands()-2; i >= 0; --i)
181 V = BinaryOperator::createAdd(V, expandInTy(S->getOperand(i), Ty),
186 Value *visitMulExpr(SCEVMulExpr *S);
188 Value *visitUDivExpr(SCEVUDivExpr *S) {
189 const Type *Ty = S->getType();
190 Value *LHS = expandInTy(S->getLHS(), Ty);
191 Value *RHS = expandInTy(S->getRHS(), Ty);
192 return BinaryOperator::createDiv(LHS, RHS, "tmp.", InsertPt);
195 Value *visitAddRecExpr(SCEVAddRecExpr *S);
197 Value *visitUnknown(SCEVUnknown *S) {
198 return S->getValue();
203 Value *SCEVExpander::visitMulExpr(SCEVMulExpr *S) {
204 const Type *Ty = S->getType();
205 int FirstOp = 0; // Set if we should emit a subtract.
206 if (SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getOperand(0)))
207 if (SC->getValue()->isAllOnesValue())
210 int i = S->getNumOperands()-2;
211 Value *V = expandInTy(S->getOperand(i+1), Ty);
213 // Emit a bunch of multiply instructions
214 for (; i >= FirstOp; --i)
215 V = BinaryOperator::createMul(V, expandInTy(S->getOperand(i), Ty),
217 // -1 * ... ---> 0 - ...
219 V = BinaryOperator::createNeg(V, "tmp.", InsertPt);
223 Value *SCEVExpander::visitAddRecExpr(SCEVAddRecExpr *S) {
224 const Type *Ty = S->getType();
225 const Loop *L = S->getLoop();
226 // We cannot yet do fp recurrences, e.g. the xform of {X,+,F} --> X+{0,+,F}
227 assert(Ty->isIntegral() && "Cannot expand fp recurrences yet!");
229 // {X,+,F} --> X + {0,+,F}
230 if (!isa<SCEVConstant>(S->getStart()) ||
231 !cast<SCEVConstant>(S->getStart())->getValue()->isNullValue()) {
232 Value *Start = expandInTy(S->getStart(), Ty);
233 std::vector<SCEVHandle> NewOps(S->op_begin(), S->op_end());
234 NewOps[0] = SCEVUnknown::getIntegerSCEV(0, Ty);
235 Value *Rest = expandInTy(SCEVAddRecExpr::get(NewOps, L), Ty);
237 // FIXME: look for an existing add to use.
238 return BinaryOperator::createAdd(Rest, Start, "tmp.", InsertPt);
241 // {0,+,1} --> Insert a canonical induction variable into the loop!
242 if (S->getNumOperands() == 2 &&
243 S->getOperand(1) == SCEVUnknown::getIntegerSCEV(1, Ty)) {
244 // Create and insert the PHI node for the induction variable in the
246 BasicBlock *Header = L->getHeader();
247 PHINode *PN = new PHINode(Ty, "indvar", Header->begin());
248 PN->addIncoming(Constant::getNullValue(Ty), L->getLoopPreheader());
250 pred_iterator HPI = pred_begin(Header);
251 assert(HPI != pred_end(Header) && "Loop with zero preds???");
252 if (!L->contains(*HPI)) ++HPI;
253 assert(HPI != pred_end(Header) && L->contains(*HPI) &&
254 "No backedge in loop?");
256 // Insert a unit add instruction right before the terminator corresponding
258 Constant *One = Ty->isFloatingPoint() ? (Constant*)ConstantFP::get(Ty, 1.0)
259 : ConstantInt::get(Ty, 1);
260 Instruction *Add = BinaryOperator::createAdd(PN, One, "indvar.next",
261 (*HPI)->getTerminator());
263 pred_iterator PI = pred_begin(Header);
264 if (*PI == L->getLoopPreheader())
266 PN->addIncoming(Add, *PI);
270 // Get the canonical induction variable I for this loop.
271 Value *I = getOrInsertCanonicalInductionVariable(L, Ty);
273 if (S->getNumOperands() == 2) { // {0,+,F} --> i*F
274 Value *F = expandInTy(S->getOperand(1), Ty);
275 return BinaryOperator::createMul(I, F, "tmp.", InsertPt);
278 // If this is a chain of recurrences, turn it into a closed form, using the
279 // folders, then expandCodeFor the closed form. This allows the folders to
280 // simplify the expression without having to build a bunch of special code
282 SCEVHandle IH = SCEVUnknown::get(I); // Get I as a "symbolic" SCEV.
284 SCEVHandle V = S->evaluateAtIteration(IH);
285 //std::cerr << "Evaluated: " << *this << "\n to: " << *V << "\n";
287 return expandInTy(V, Ty);
292 Statistic<> NumRemoved ("indvars", "Number of aux indvars removed");
293 Statistic<> NumPointer ("indvars", "Number of pointer indvars promoted");
294 Statistic<> NumInserted("indvars", "Number of canonical indvars added");
295 Statistic<> NumReplaced("indvars", "Number of exit values replaced");
296 Statistic<> NumLFTR ("indvars", "Number of loop exit tests replaced");
298 class IndVarSimplify : public FunctionPass {
303 virtual bool runOnFunction(Function &) {
304 LI = &getAnalysis<LoopInfo>();
305 SE = &getAnalysis<ScalarEvolution>();
308 // Induction Variables live in the header nodes of loops
309 for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
314 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
315 AU.addRequiredID(LoopSimplifyID);
316 AU.addRequired<ScalarEvolution>();
317 AU.addRequired<LoopInfo>();
318 AU.addPreservedID(LoopSimplifyID);
319 AU.setPreservesCFG();
322 void runOnLoop(Loop *L);
323 void EliminatePointerRecurrence(PHINode *PN, BasicBlock *Preheader,
324 std::set<Instruction*> &DeadInsts);
325 void LinearFunctionTestReplace(Loop *L, SCEV *IterationCount,
327 void RewriteLoopExitValues(Loop *L);
329 void DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts);
331 RegisterOpt<IndVarSimplify> X("indvars", "Canonicalize Induction Variables");
334 FunctionPass *llvm::createIndVarSimplifyPass() {
335 return new IndVarSimplify();
338 /// DeleteTriviallyDeadInstructions - If any of the instructions is the
339 /// specified set are trivially dead, delete them and see if this makes any of
340 /// their operands subsequently dead.
341 void IndVarSimplify::
342 DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts) {
343 while (!Insts.empty()) {
344 Instruction *I = *Insts.begin();
345 Insts.erase(Insts.begin());
346 if (isInstructionTriviallyDead(I)) {
347 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
348 if (Instruction *U = dyn_cast<Instruction>(I->getOperand(i)))
350 SE->deleteInstructionFromRecords(I);
351 I->eraseFromParent();
358 /// EliminatePointerRecurrence - Check to see if this is a trivial GEP pointer
359 /// recurrence. If so, change it into an integer recurrence, permitting
360 /// analysis by the SCEV routines.
361 void IndVarSimplify::EliminatePointerRecurrence(PHINode *PN,
362 BasicBlock *Preheader,
363 std::set<Instruction*> &DeadInsts) {
364 assert(PN->getNumIncomingValues() == 2 && "Noncanonicalized loop!");
365 unsigned PreheaderIdx = PN->getBasicBlockIndex(Preheader);
366 unsigned BackedgeIdx = PreheaderIdx^1;
367 if (GetElementPtrInst *GEPI =
368 dyn_cast<GetElementPtrInst>(PN->getIncomingValue(BackedgeIdx)))
369 if (GEPI->getOperand(0) == PN) {
370 assert(GEPI->getNumOperands() == 2 && "GEP types must mismatch!");
372 // Okay, we found a pointer recurrence. Transform this pointer
373 // recurrence into an integer recurrence. Compute the value that gets
374 // added to the pointer at every iteration.
375 Value *AddedVal = GEPI->getOperand(1);
377 // Insert a new integer PHI node into the top of the block.
378 PHINode *NewPhi = new PHINode(AddedVal->getType(),
379 PN->getName()+".rec", PN);
380 NewPhi->addIncoming(Constant::getNullValue(NewPhi->getType()), Preheader);
382 // Create the new add instruction.
383 Value *NewAdd = BinaryOperator::createAdd(NewPhi, AddedVal,
384 GEPI->getName()+".rec", GEPI);
385 NewPhi->addIncoming(NewAdd, PN->getIncomingBlock(BackedgeIdx));
387 // Update the existing GEP to use the recurrence.
388 GEPI->setOperand(0, PN->getIncomingValue(PreheaderIdx));
390 // Update the GEP to use the new recurrence we just inserted.
391 GEPI->setOperand(1, NewAdd);
393 // If the incoming value is a constant expr GEP, try peeling out the array
394 // 0 index if possible to make things simpler.
395 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEPI->getOperand(0)))
396 if (CE->getOpcode() == Instruction::GetElementPtr) {
397 unsigned NumOps = CE->getNumOperands();
398 assert(NumOps > 1 && "CE folding didn't work!");
399 if (CE->getOperand(NumOps-1)->isNullValue()) {
400 // Check to make sure the last index really is an array index.
401 gep_type_iterator GTI = gep_type_begin(GEPI);
402 for (unsigned i = 1, e = GEPI->getNumOperands()-1;
405 if (isa<SequentialType>(*GTI)) {
406 // Pull the last index out of the constant expr GEP.
407 std::vector<Value*> CEIdxs(CE->op_begin()+1, CE->op_end()-1);
408 Constant *NCE = ConstantExpr::getGetElementPtr(CE->getOperand(0),
410 GetElementPtrInst *NGEPI =
411 new GetElementPtrInst(NCE, Constant::getNullValue(Type::IntTy),
412 NewAdd, GEPI->getName(), GEPI);
413 GEPI->replaceAllUsesWith(NGEPI);
414 GEPI->eraseFromParent();
421 // Finally, if there are any other users of the PHI node, we must
422 // insert a new GEP instruction that uses the pre-incremented version
423 // of the induction amount.
424 if (!PN->use_empty()) {
425 BasicBlock::iterator InsertPos = PN; ++InsertPos;
426 while (isa<PHINode>(InsertPos)) ++InsertPos;
427 std::string Name = PN->getName(); PN->setName("");
429 new GetElementPtrInst(PN->getIncomingValue(PreheaderIdx),
430 std::vector<Value*>(1, NewPhi), Name,
432 PN->replaceAllUsesWith(PreInc);
435 // Delete the old PHI for sure, and the GEP if its otherwise unused.
436 DeadInsts.insert(PN);
443 /// LinearFunctionTestReplace - This method rewrites the exit condition of the
444 /// loop to be a canonical != comparison against the incremented loop induction
445 /// variable. This pass is able to rewrite the exit tests of any loop where the
446 /// SCEV analysis can determine a loop-invariant trip count of the loop, which
447 /// is actually a much broader range than just linear tests.
448 void IndVarSimplify::LinearFunctionTestReplace(Loop *L, SCEV *IterationCount,
450 // Find the exit block for the loop. We can currently only handle loops with
452 std::vector<BasicBlock*> ExitBlocks;
453 L->getExitBlocks(ExitBlocks);
454 if (ExitBlocks.size() != 1) return;
455 BasicBlock *ExitBlock = ExitBlocks[0];
457 // Make sure there is only one predecessor block in the loop.
458 BasicBlock *ExitingBlock = 0;
459 for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
461 if (L->contains(*PI)) {
462 if (ExitingBlock == 0)
465 return; // Multiple exits from loop to this block.
467 assert(ExitingBlock && "Loop info is broken");
469 if (!isa<BranchInst>(ExitingBlock->getTerminator()))
470 return; // Can't rewrite non-branch yet
471 BranchInst *BI = cast<BranchInst>(ExitingBlock->getTerminator());
472 assert(BI->isConditional() && "Must be conditional to be part of loop!");
474 std::set<Instruction*> InstructionsToDelete;
475 if (Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()))
476 InstructionsToDelete.insert(Cond);
478 // If the exiting block is not the same as the backedge block, we must compare
479 // against the preincremented value, otherwise we prefer to compare against
480 // the post-incremented value.
481 BasicBlock *Header = L->getHeader();
482 pred_iterator HPI = pred_begin(Header);
483 assert(HPI != pred_end(Header) && "Loop with zero preds???");
484 if (!L->contains(*HPI)) ++HPI;
485 assert(HPI != pred_end(Header) && L->contains(*HPI) &&
486 "No backedge in loop?");
488 SCEVHandle TripCount = IterationCount;
490 if (*HPI == ExitingBlock) {
491 // The IterationCount expression contains the number of times that the
492 // backedge actually branches to the loop header. This is one less than the
493 // number of times the loop executes, so add one to it.
494 Constant *OneC = ConstantInt::get(IterationCount->getType(), 1);
495 TripCount = SCEVAddExpr::get(IterationCount, SCEVUnknown::get(OneC));
496 IndVar = L->getCanonicalInductionVariableIncrement();
498 // We have to use the preincremented value...
499 IndVar = L->getCanonicalInductionVariable();
502 // Expand the code for the iteration count into the preheader of the loop.
503 BasicBlock *Preheader = L->getLoopPreheader();
504 Value *ExitCnt = RW.expandCodeFor(TripCount, Preheader->getTerminator(),
507 // Insert a new setne or seteq instruction before the branch.
508 Instruction::BinaryOps Opcode;
509 if (L->contains(BI->getSuccessor(0)))
510 Opcode = Instruction::SetNE;
512 Opcode = Instruction::SetEQ;
514 Value *Cond = new SetCondInst(Opcode, IndVar, ExitCnt, "exitcond", BI);
515 BI->setCondition(Cond);
519 DeleteTriviallyDeadInstructions(InstructionsToDelete);
523 /// RewriteLoopExitValues - Check to see if this loop has a computable
524 /// loop-invariant execution count. If so, this means that we can compute the
525 /// final value of any expressions that are recurrent in the loop, and
526 /// substitute the exit values from the loop into any instructions outside of
527 /// the loop that use the final values of the current expressions.
528 void IndVarSimplify::RewriteLoopExitValues(Loop *L) {
529 BasicBlock *Preheader = L->getLoopPreheader();
531 // Scan all of the instructions in the loop, looking at those that have
532 // extra-loop users and which are recurrences.
533 SCEVExpander Rewriter(*SE, *LI);
535 // We insert the code into the preheader of the loop if the loop contains
536 // multiple exit blocks, or in the exit block if there is exactly one.
537 BasicBlock *BlockToInsertInto;
538 std::vector<BasicBlock*> ExitBlocks;
539 L->getExitBlocks(ExitBlocks);
540 if (ExitBlocks.size() == 1)
541 BlockToInsertInto = ExitBlocks[0];
543 BlockToInsertInto = Preheader;
544 BasicBlock::iterator InsertPt = BlockToInsertInto->begin();
545 while (isa<PHINode>(InsertPt)) ++InsertPt;
547 bool HasConstantItCount = isa<SCEVConstant>(SE->getIterationCount(L));
549 std::set<Instruction*> InstructionsToDelete;
551 for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i)
552 if (LI->getLoopFor(L->getBlocks()[i]) == L) { // Not in a subloop...
553 BasicBlock *BB = L->getBlocks()[i];
554 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
555 if (I->getType()->isInteger()) { // Is an integer instruction
556 SCEVHandle SH = SE->getSCEV(I);
557 if (SH->hasComputableLoopEvolution(L) || // Varies predictably
558 HasConstantItCount) {
559 // Find out if this predictably varying value is actually used
560 // outside of the loop. "extra" as opposed to "intra".
561 std::vector<User*> ExtraLoopUsers;
562 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
564 if (!L->contains(cast<Instruction>(*UI)->getParent()))
565 ExtraLoopUsers.push_back(*UI);
566 if (!ExtraLoopUsers.empty()) {
567 // Okay, this instruction has a user outside of the current loop
568 // and varies predictably in this loop. Evaluate the value it
569 // contains when the loop exits, and insert code for it.
570 SCEVHandle ExitValue = SE->getSCEVAtScope(I, L->getParentLoop());
571 if (!isa<SCEVCouldNotCompute>(ExitValue)) {
574 Value *NewVal = Rewriter.expandCodeFor(ExitValue, InsertPt,
577 // Rewrite any users of the computed value outside of the loop
578 // with the newly computed value.
579 for (unsigned i = 0, e = ExtraLoopUsers.size(); i != e; ++i)
580 ExtraLoopUsers[i]->replaceUsesOfWith(I, NewVal);
582 // If this instruction is dead now, schedule it to be removed.
584 InstructionsToDelete.insert(I);
591 DeleteTriviallyDeadInstructions(InstructionsToDelete);
595 void IndVarSimplify::runOnLoop(Loop *L) {
596 // First step. Check to see if there are any trivial GEP pointer recurrences.
597 // If there are, change them into integer recurrences, permitting analysis by
598 // the SCEV routines.
600 BasicBlock *Header = L->getHeader();
601 BasicBlock *Preheader = L->getLoopPreheader();
603 std::set<Instruction*> DeadInsts;
604 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
605 PHINode *PN = cast<PHINode>(I);
606 if (isa<PointerType>(PN->getType()))
607 EliminatePointerRecurrence(PN, Preheader, DeadInsts);
610 if (!DeadInsts.empty())
611 DeleteTriviallyDeadInstructions(DeadInsts);
614 // Next, transform all loops nesting inside of this loop.
615 for (LoopInfo::iterator I = L->begin(), E = L->end(); I != E; ++I)
618 // Check to see if this loop has a computable loop-invariant execution count.
619 // If so, this means that we can compute the final value of any expressions
620 // that are recurrent in the loop, and substitute the exit values from the
621 // loop into any instructions outside of the loop that use the final values of
622 // the current expressions.
624 SCEVHandle IterationCount = SE->getIterationCount(L);
625 if (!isa<SCEVCouldNotCompute>(IterationCount))
626 RewriteLoopExitValues(L);
628 // Next, analyze all of the induction variables in the loop, canonicalizing
629 // auxillary induction variables.
630 std::vector<std::pair<PHINode*, SCEVHandle> > IndVars;
632 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
633 PHINode *PN = cast<PHINode>(I);
634 if (PN->getType()->isInteger()) { // FIXME: when we have fast-math, enable!
635 SCEVHandle SCEV = SE->getSCEV(PN);
636 if (SCEV->hasComputableLoopEvolution(L))
637 // FIXME: Without a strength reduction pass, it is an extremely bad idea
638 // to indvar substitute anything more complex than a linear induction
639 // variable. Doing so will put expensive multiply instructions inside
640 // of the loop. For now just disable indvar subst on anything more
641 // complex than a linear addrec.
642 if (SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SCEV))
643 if (AR->getNumOperands() == 2 && isa<SCEVConstant>(AR->getOperand(1)))
644 IndVars.push_back(std::make_pair(PN, SCEV));
648 // If there are no induction variables in the loop, there is nothing more to
650 if (IndVars.empty()) {
651 // Actually, if we know how many times the loop iterates, lets insert a
652 // canonical induction variable to help subsequent passes.
653 if (!isa<SCEVCouldNotCompute>(IterationCount)) {
654 SCEVExpander Rewriter(*SE, *LI);
655 Rewriter.getOrInsertCanonicalInductionVariable(L,
656 IterationCount->getType());
657 LinearFunctionTestReplace(L, IterationCount, Rewriter);
662 // Compute the type of the largest recurrence expression.
664 const Type *LargestType = IndVars[0].first->getType();
665 bool DifferingSizes = false;
666 for (unsigned i = 1, e = IndVars.size(); i != e; ++i) {
667 const Type *Ty = IndVars[i].first->getType();
668 DifferingSizes |= Ty->getPrimitiveSize() != LargestType->getPrimitiveSize();
669 if (Ty->getPrimitiveSize() > LargestType->getPrimitiveSize())
673 // Create a rewriter object which we'll use to transform the code with.
674 SCEVExpander Rewriter(*SE, *LI);
676 // Now that we know the largest of of the induction variables in this loop,
677 // insert a canonical induction variable of the largest size.
678 LargestType = LargestType->getUnsignedVersion();
679 Value *IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L,LargestType);
683 if (!isa<SCEVCouldNotCompute>(IterationCount))
684 LinearFunctionTestReplace(L, IterationCount, Rewriter);
686 // Now that we have a canonical induction variable, we can rewrite any
687 // recurrences in terms of the induction variable. Start with the auxillary
688 // induction variables, and recursively rewrite any of their uses.
689 BasicBlock::iterator InsertPt = Header->begin();
690 while (isa<PHINode>(InsertPt)) ++InsertPt;
692 // If there were induction variables of other sizes, cast the primary
693 // induction variable to the right size for them, avoiding the need for the
694 // code evaluation methods to insert induction variables of different sizes.
695 if (DifferingSizes) {
696 bool InsertedSizes[17] = { false };
697 InsertedSizes[LargestType->getPrimitiveSize()] = true;
698 for (unsigned i = 0, e = IndVars.size(); i != e; ++i)
699 if (!InsertedSizes[IndVars[i].first->getType()->getPrimitiveSize()]) {
700 PHINode *PN = IndVars[i].first;
701 InsertedSizes[PN->getType()->getPrimitiveSize()] = true;
702 Instruction *New = new CastInst(IndVar,
703 PN->getType()->getUnsignedVersion(),
705 Rewriter.addInsertedValue(New, SE->getSCEV(New));
709 // If there were induction variables of other sizes, cast the primary
710 // induction variable to the right size for them, avoiding the need for the
711 // code evaluation methods to insert induction variables of different sizes.
712 std::map<unsigned, Value*> InsertedSizes;
713 while (!IndVars.empty()) {
714 PHINode *PN = IndVars.back().first;
715 Value *NewVal = Rewriter.expandCodeFor(IndVars.back().second, InsertPt,
717 std::string Name = PN->getName();
719 NewVal->setName(Name);
721 // Replace the old PHI Node with the inserted computation.
722 PN->replaceAllUsesWith(NewVal);
723 DeadInsts.insert(PN);
730 // Now replace all derived expressions in the loop body with simpler
732 for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i)
733 if (LI->getLoopFor(L->getBlocks()[i]) == L) { // Not in a subloop...
734 BasicBlock *BB = L->getBlocks()[i];
735 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
736 if (I->getType()->isInteger() && // Is an integer instruction
738 !Rewriter.isInsertedInstruction(I)) {
739 SCEVHandle SH = SE->getSCEV(I);
740 Value *V = Rewriter.expandCodeFor(SH, I, I->getType());
742 if (isa<Instruction>(V)) {
743 std::string Name = I->getName();
747 I->replaceAllUsesWith(V);
756 DeleteTriviallyDeadInstructions(DeadInsts);