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/Transforms/Utils/Local.h"
49 #include "llvm/Support/CommandLine.h"
50 #include "llvm/ADT/Statistic.h"
54 /// SCEVExpander - This class uses information about analyze scalars to
55 /// rewrite expressions in canonical form.
57 /// Clients should create an instance of this class when rewriting is needed,
58 /// and destroying it when finished to allow the release of the associated
60 struct SCEVExpander : public SCEVVisitor<SCEVExpander, Value*> {
63 std::map<SCEVHandle, Value*> InsertedExpressions;
64 std::set<Instruction*> InsertedInstructions;
66 Instruction *InsertPt;
68 friend class SCEVVisitor<SCEVExpander, Value*>;
70 SCEVExpander(ScalarEvolution &se, LoopInfo &li) : SE(se), LI(li) {}
72 /// isInsertedInstruction - Return true if the specified instruction was
73 /// inserted by the code rewriter. If so, the client should not modify the
75 bool isInsertedInstruction(Instruction *I) const {
76 return InsertedInstructions.count(I);
79 /// getOrInsertCanonicalInductionVariable - This method returns the
80 /// canonical induction variable of the specified type for the specified
81 /// loop (inserting one if there is none). A canonical induction variable
82 /// starts at zero and steps by one on each iteration.
83 Value *getOrInsertCanonicalInductionVariable(const Loop *L, const Type *Ty){
84 assert((Ty->isInteger() || Ty->isFloatingPoint()) &&
85 "Can only insert integer or floating point induction variables!");
86 SCEVHandle H = SCEVAddRecExpr::get(SCEVUnknown::getIntegerSCEV(0, Ty),
87 SCEVUnknown::getIntegerSCEV(1, Ty), L);
91 /// addInsertedValue - Remember the specified instruction as being the
92 /// canonical form for the specified SCEV.
93 void addInsertedValue(Instruction *I, SCEV *S) {
94 InsertedExpressions[S] = (Value*)I;
95 InsertedInstructions.insert(I);
98 /// expandCodeFor - Insert code to directly compute the specified SCEV
99 /// expression into the program. The inserted code is inserted into the
102 /// If a particular value sign is required, a type may be specified for the
104 Value *expandCodeFor(SCEVHandle SH, Instruction *IP, const Type *Ty = 0) {
105 // Expand the code for this SCEV.
107 return expandInTy(SH, Ty);
111 Value *expand(SCEV *S) {
112 // Check to see if we already expanded this.
113 std::map<SCEVHandle, Value*>::iterator I = InsertedExpressions.find(S);
114 if (I != InsertedExpressions.end())
118 InsertedExpressions[S] = V;
122 Value *expandInTy(SCEV *S, const Type *Ty) {
123 Value *V = expand(S);
124 if (Ty && V->getType() != Ty) {
125 // FIXME: keep track of the cast instruction.
126 if (Constant *C = dyn_cast<Constant>(V))
127 return ConstantExpr::getCast(C, Ty);
128 else if (Instruction *I = dyn_cast<Instruction>(V)) {
129 // Check to see if there is already a cast. If there is, use it.
130 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
132 if ((*UI)->getType() == Ty)
133 if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI))) {
134 BasicBlock::iterator It = I; ++It;
135 while (isa<PHINode>(It)) ++It;
136 if (It != BasicBlock::iterator(CI)) {
137 // Splice the cast immediately after the operand in question.
138 I->getParent()->getInstList().splice(It,
139 CI->getParent()->getInstList(),
145 BasicBlock::iterator IP = I; ++IP;
146 if (InvokeInst *II = dyn_cast<InvokeInst>(I))
147 IP = II->getNormalDest()->begin();
148 while (isa<PHINode>(IP)) ++IP;
149 return new CastInst(V, Ty, V->getName(), IP);
151 // FIXME: check to see if there is already a cast!
152 return new CastInst(V, Ty, V->getName(), InsertPt);
158 Value *visitConstant(SCEVConstant *S) {
159 return S->getValue();
162 Value *visitTruncateExpr(SCEVTruncateExpr *S) {
163 Value *V = expand(S->getOperand());
164 return new CastInst(V, S->getType(), "tmp.", InsertPt);
167 Value *visitZeroExtendExpr(SCEVZeroExtendExpr *S) {
168 Value *V = expandInTy(S->getOperand(),S->getType()->getUnsignedVersion());
169 return new CastInst(V, S->getType(), "tmp.", InsertPt);
172 Value *visitAddExpr(SCEVAddExpr *S) {
173 const Type *Ty = S->getType();
174 Value *V = expandInTy(S->getOperand(S->getNumOperands()-1), Ty);
176 // Emit a bunch of add instructions
177 for (int i = S->getNumOperands()-2; i >= 0; --i)
178 V = BinaryOperator::createAdd(V, expandInTy(S->getOperand(i), Ty),
183 Value *visitMulExpr(SCEVMulExpr *S);
185 Value *visitUDivExpr(SCEVUDivExpr *S) {
186 const Type *Ty = S->getType();
187 Value *LHS = expandInTy(S->getLHS(), Ty);
188 Value *RHS = expandInTy(S->getRHS(), Ty);
189 return BinaryOperator::createDiv(LHS, RHS, "tmp.", InsertPt);
192 Value *visitAddRecExpr(SCEVAddRecExpr *S);
194 Value *visitUnknown(SCEVUnknown *S) {
195 return S->getValue();
200 Value *SCEVExpander::visitMulExpr(SCEVMulExpr *S) {
201 const Type *Ty = S->getType();
202 int FirstOp = 0; // Set if we should emit a subtract.
203 if (SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getOperand(0)))
204 if (SC->getValue()->isAllOnesValue())
207 int i = S->getNumOperands()-2;
208 Value *V = expandInTy(S->getOperand(i+1), Ty);
210 // Emit a bunch of multiply instructions
211 for (; i >= FirstOp; --i)
212 V = BinaryOperator::createMul(V, expandInTy(S->getOperand(i), Ty),
214 // -1 * ... ---> 0 - ...
216 V = BinaryOperator::createNeg(V, "tmp.", InsertPt);
220 Value *SCEVExpander::visitAddRecExpr(SCEVAddRecExpr *S) {
221 const Type *Ty = S->getType();
222 const Loop *L = S->getLoop();
223 // We cannot yet do fp recurrences, e.g. the xform of {X,+,F} --> X+{0,+,F}
224 assert(Ty->isIntegral() && "Cannot expand fp recurrences yet!");
226 // {X,+,F} --> X + {0,+,F}
227 if (!isa<SCEVConstant>(S->getStart()) ||
228 !cast<SCEVConstant>(S->getStart())->getValue()->isNullValue()) {
229 Value *Start = expandInTy(S->getStart(), Ty);
230 std::vector<SCEVHandle> NewOps(S->op_begin(), S->op_end());
231 NewOps[0] = SCEVUnknown::getIntegerSCEV(0, Ty);
232 Value *Rest = expandInTy(SCEVAddRecExpr::get(NewOps, L), Ty);
234 // FIXME: look for an existing add to use.
235 return BinaryOperator::createAdd(Rest, Start, "tmp.", InsertPt);
238 // {0,+,1} --> Insert a canonical induction variable into the loop!
239 if (S->getNumOperands() == 2 &&
240 S->getOperand(1) == SCEVUnknown::getIntegerSCEV(1, Ty)) {
241 // Create and insert the PHI node for the induction variable in the
243 BasicBlock *Header = L->getHeader();
244 PHINode *PN = new PHINode(Ty, "indvar", Header->begin());
245 PN->addIncoming(Constant::getNullValue(Ty), L->getLoopPreheader());
247 pred_iterator HPI = pred_begin(Header);
248 assert(HPI != pred_end(Header) && "Loop with zero preds???");
249 if (!L->contains(*HPI)) ++HPI;
250 assert(HPI != pred_end(Header) && L->contains(*HPI) &&
251 "No backedge in loop?");
253 // Insert a unit add instruction right before the terminator corresponding
255 Constant *One = Ty->isFloatingPoint() ? (Constant*)ConstantFP::get(Ty, 1.0)
256 : ConstantInt::get(Ty, 1);
257 Instruction *Add = BinaryOperator::createAdd(PN, One, "indvar.next",
258 (*HPI)->getTerminator());
260 pred_iterator PI = pred_begin(Header);
261 if (*PI == L->getLoopPreheader())
263 PN->addIncoming(Add, *PI);
267 // Get the canonical induction variable I for this loop.
268 Value *I = getOrInsertCanonicalInductionVariable(L, Ty);
270 if (S->getNumOperands() == 2) { // {0,+,F} --> i*F
271 Value *F = expandInTy(S->getOperand(1), Ty);
272 return BinaryOperator::createMul(I, F, "tmp.", InsertPt);
275 // If this is a chain of recurrences, turn it into a closed form, using the
276 // folders, then expandCodeFor the closed form. This allows the folders to
277 // simplify the expression without having to build a bunch of special code
279 SCEVHandle IH = SCEVUnknown::get(I); // Get I as a "symbolic" SCEV.
281 SCEVHandle V = S->evaluateAtIteration(IH);
282 //std::cerr << "Evaluated: " << *this << "\n to: " << *V << "\n";
284 return expandInTy(V, Ty);
289 Statistic<> NumRemoved ("indvars", "Number of aux indvars removed");
290 Statistic<> NumPointer ("indvars", "Number of pointer indvars promoted");
291 Statistic<> NumInserted("indvars", "Number of canonical indvars added");
292 Statistic<> NumReplaced("indvars", "Number of exit values replaced");
293 Statistic<> NumLFTR ("indvars", "Number of loop exit tests replaced");
295 class IndVarSimplify : public FunctionPass {
300 virtual bool runOnFunction(Function &) {
301 LI = &getAnalysis<LoopInfo>();
302 SE = &getAnalysis<ScalarEvolution>();
305 // Induction Variables live in the header nodes of loops
306 for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
311 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
312 AU.addRequiredID(LoopSimplifyID);
313 AU.addRequired<ScalarEvolution>();
314 AU.addRequired<LoopInfo>();
315 AU.addPreservedID(LoopSimplifyID);
316 AU.setPreservesCFG();
319 void runOnLoop(Loop *L);
320 void EliminatePointerRecurrence(PHINode *PN, BasicBlock *Preheader,
321 std::set<Instruction*> &DeadInsts);
322 void LinearFunctionTestReplace(Loop *L, SCEV *IterationCount,
324 void RewriteLoopExitValues(Loop *L);
326 void DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts);
328 RegisterOpt<IndVarSimplify> X("indvars", "Canonicalize Induction Variables");
331 Pass *llvm::createIndVarSimplifyPass() {
332 return new IndVarSimplify();
335 /// DeleteTriviallyDeadInstructions - If any of the instructions is the
336 /// specified set are trivially dead, delete them and see if this makes any of
337 /// their operands subsequently dead.
338 void IndVarSimplify::
339 DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts) {
340 while (!Insts.empty()) {
341 Instruction *I = *Insts.begin();
342 Insts.erase(Insts.begin());
343 if (isInstructionTriviallyDead(I)) {
344 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
345 if (Instruction *U = dyn_cast<Instruction>(I->getOperand(i)))
347 SE->deleteInstructionFromRecords(I);
348 I->getParent()->getInstList().erase(I);
355 /// EliminatePointerRecurrence - Check to see if this is a trivial GEP pointer
356 /// recurrence. If so, change it into an integer recurrence, permitting
357 /// analysis by the SCEV routines.
358 void IndVarSimplify::EliminatePointerRecurrence(PHINode *PN,
359 BasicBlock *Preheader,
360 std::set<Instruction*> &DeadInsts) {
361 assert(PN->getNumIncomingValues() == 2 && "Noncanonicalized loop!");
362 unsigned PreheaderIdx = PN->getBasicBlockIndex(Preheader);
363 unsigned BackedgeIdx = PreheaderIdx^1;
364 if (GetElementPtrInst *GEPI =
365 dyn_cast<GetElementPtrInst>(PN->getIncomingValue(BackedgeIdx)))
366 if (GEPI->getOperand(0) == PN) {
367 assert(GEPI->getNumOperands() == 2 && "GEP types must mismatch!");
369 // Okay, we found a pointer recurrence. Transform this pointer
370 // recurrence into an integer recurrence. Compute the value that gets
371 // added to the pointer at every iteration.
372 Value *AddedVal = GEPI->getOperand(1);
374 // Insert a new integer PHI node into the top of the block.
375 PHINode *NewPhi = new PHINode(AddedVal->getType(),
376 PN->getName()+".rec", PN);
377 NewPhi->addIncoming(Constant::getNullValue(NewPhi->getType()), Preheader);
379 // Create the new add instruction.
380 Value *NewAdd = BinaryOperator::createAdd(NewPhi, AddedVal,
381 GEPI->getName()+".rec", GEPI);
382 NewPhi->addIncoming(NewAdd, PN->getIncomingBlock(BackedgeIdx));
384 // Update the existing GEP to use the recurrence.
385 GEPI->setOperand(0, PN->getIncomingValue(PreheaderIdx));
387 // Update the GEP to use the new recurrence we just inserted.
388 GEPI->setOperand(1, NewAdd);
390 // Finally, if there are any other users of the PHI node, we must
391 // insert a new GEP instruction that uses the pre-incremented version
392 // of the induction amount.
393 if (!PN->use_empty()) {
394 BasicBlock::iterator InsertPos = PN; ++InsertPos;
395 while (isa<PHINode>(InsertPos)) ++InsertPos;
396 std::string Name = PN->getName(); PN->setName("");
398 new GetElementPtrInst(PN->getIncomingValue(PreheaderIdx),
399 std::vector<Value*>(1, NewPhi), Name,
401 PN->replaceAllUsesWith(PreInc);
404 // Delete the old PHI for sure, and the GEP if its otherwise unused.
405 DeadInsts.insert(PN);
412 /// LinearFunctionTestReplace - This method rewrites the exit condition of the
413 /// loop to be a canonical != comparison against the incremented loop induction
414 /// variable. This pass is able to rewrite the exit tests of any loop where the
415 /// SCEV analysis can determine a loop-invariant trip count of the loop, which
416 /// is actually a much broader range than just linear tests.
417 void IndVarSimplify::LinearFunctionTestReplace(Loop *L, SCEV *IterationCount,
419 // Find the exit block for the loop. We can currently only handle loops with
421 std::vector<BasicBlock*> ExitBlocks;
422 L->getExitBlocks(ExitBlocks);
423 if (ExitBlocks.size() != 1) return;
424 BasicBlock *ExitBlock = ExitBlocks[0];
426 // Make sure there is only one predecessor block in the loop.
427 BasicBlock *ExitingBlock = 0;
428 for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
430 if (L->contains(*PI)) {
431 if (ExitingBlock == 0)
434 return; // Multiple exits from loop to this block.
436 assert(ExitingBlock && "Loop info is broken");
438 if (!isa<BranchInst>(ExitingBlock->getTerminator()))
439 return; // Can't rewrite non-branch yet
440 BranchInst *BI = cast<BranchInst>(ExitingBlock->getTerminator());
441 assert(BI->isConditional() && "Must be conditional to be part of loop!");
443 std::set<Instruction*> InstructionsToDelete;
444 if (Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()))
445 InstructionsToDelete.insert(Cond);
447 // If the exiting block is not the same as the backedge block, we must compare
448 // against the preincremented value, otherwise we prefer to compare against
449 // the post-incremented value.
450 BasicBlock *Header = L->getHeader();
451 pred_iterator HPI = pred_begin(Header);
452 assert(HPI != pred_end(Header) && "Loop with zero preds???");
453 if (!L->contains(*HPI)) ++HPI;
454 assert(HPI != pred_end(Header) && L->contains(*HPI) &&
455 "No backedge in loop?");
457 SCEVHandle TripCount = IterationCount;
459 if (*HPI == ExitingBlock) {
460 // The IterationCount expression contains the number of times that the
461 // backedge actually branches to the loop header. This is one less than the
462 // number of times the loop executes, so add one to it.
463 Constant *OneC = ConstantInt::get(IterationCount->getType(), 1);
464 TripCount = SCEVAddExpr::get(IterationCount, SCEVUnknown::get(OneC));
465 IndVar = L->getCanonicalInductionVariableIncrement();
467 // We have to use the preincremented value...
468 IndVar = L->getCanonicalInductionVariable();
471 // Expand the code for the iteration count into the preheader of the loop.
472 BasicBlock *Preheader = L->getLoopPreheader();
473 Value *ExitCnt = RW.expandCodeFor(TripCount, Preheader->getTerminator(),
476 // Insert a new setne or seteq instruction before the branch.
477 Instruction::BinaryOps Opcode;
478 if (L->contains(BI->getSuccessor(0)))
479 Opcode = Instruction::SetNE;
481 Opcode = Instruction::SetEQ;
483 Value *Cond = new SetCondInst(Opcode, IndVar, ExitCnt, "exitcond", BI);
484 BI->setCondition(Cond);
488 DeleteTriviallyDeadInstructions(InstructionsToDelete);
492 /// RewriteLoopExitValues - Check to see if this loop has a computable
493 /// loop-invariant execution count. If so, this means that we can compute the
494 /// final value of any expressions that are recurrent in the loop, and
495 /// substitute the exit values from the loop into any instructions outside of
496 /// the loop that use the final values of the current expressions.
497 void IndVarSimplify::RewriteLoopExitValues(Loop *L) {
498 BasicBlock *Preheader = L->getLoopPreheader();
500 // Scan all of the instructions in the loop, looking at those that have
501 // extra-loop users and which are recurrences.
502 SCEVExpander Rewriter(*SE, *LI);
504 // We insert the code into the preheader of the loop if the loop contains
505 // multiple exit blocks, or in the exit block if there is exactly one.
506 BasicBlock *BlockToInsertInto;
507 std::vector<BasicBlock*> ExitBlocks;
508 L->getExitBlocks(ExitBlocks);
509 if (ExitBlocks.size() == 1)
510 BlockToInsertInto = ExitBlocks[0];
512 BlockToInsertInto = Preheader;
513 BasicBlock::iterator InsertPt = BlockToInsertInto->begin();
514 while (isa<PHINode>(InsertPt)) ++InsertPt;
516 bool HasConstantItCount = isa<SCEVConstant>(SE->getIterationCount(L));
518 std::set<Instruction*> InstructionsToDelete;
520 for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i)
521 if (LI->getLoopFor(L->getBlocks()[i]) == L) { // Not in a subloop...
522 BasicBlock *BB = L->getBlocks()[i];
523 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
524 if (I->getType()->isInteger()) { // Is an integer instruction
525 SCEVHandle SH = SE->getSCEV(I);
526 if (SH->hasComputableLoopEvolution(L) || // Varies predictably
527 HasConstantItCount) {
528 // Find out if this predictably varying value is actually used
529 // outside of the loop. "extra" as opposed to "intra".
530 std::vector<User*> ExtraLoopUsers;
531 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
533 if (!L->contains(cast<Instruction>(*UI)->getParent()))
534 ExtraLoopUsers.push_back(*UI);
535 if (!ExtraLoopUsers.empty()) {
536 // Okay, this instruction has a user outside of the current loop
537 // and varies predictably in this loop. Evaluate the value it
538 // contains when the loop exits, and insert code for it.
539 SCEVHandle ExitValue = SE->getSCEVAtScope(I, L->getParentLoop());
540 if (!isa<SCEVCouldNotCompute>(ExitValue)) {
543 Value *NewVal = Rewriter.expandCodeFor(ExitValue, InsertPt,
546 // Rewrite any users of the computed value outside of the loop
547 // with the newly computed value.
548 for (unsigned i = 0, e = ExtraLoopUsers.size(); i != e; ++i)
549 ExtraLoopUsers[i]->replaceUsesOfWith(I, NewVal);
551 // If this instruction is dead now, schedule it to be removed.
553 InstructionsToDelete.insert(I);
560 DeleteTriviallyDeadInstructions(InstructionsToDelete);
564 void IndVarSimplify::runOnLoop(Loop *L) {
565 // First step. Check to see if there are any trivial GEP pointer recurrences.
566 // If there are, change them into integer recurrences, permitting analysis by
567 // the SCEV routines.
569 BasicBlock *Header = L->getHeader();
570 BasicBlock *Preheader = L->getLoopPreheader();
572 std::set<Instruction*> DeadInsts;
573 for (BasicBlock::iterator I = Header->begin();
574 PHINode *PN = dyn_cast<PHINode>(I); ++I)
575 if (isa<PointerType>(PN->getType()))
576 EliminatePointerRecurrence(PN, Preheader, DeadInsts);
578 if (!DeadInsts.empty())
579 DeleteTriviallyDeadInstructions(DeadInsts);
582 // Next, transform all loops nesting inside of this loop.
583 for (LoopInfo::iterator I = L->begin(), E = L->end(); I != E; ++I)
586 // Check to see if this loop has a computable loop-invariant execution count.
587 // If so, this means that we can compute the final value of any expressions
588 // that are recurrent in the loop, and substitute the exit values from the
589 // loop into any instructions outside of the loop that use the final values of
590 // the current expressions.
592 SCEVHandle IterationCount = SE->getIterationCount(L);
593 if (!isa<SCEVCouldNotCompute>(IterationCount))
594 RewriteLoopExitValues(L);
596 // Next, analyze all of the induction variables in the loop, canonicalizing
597 // auxillary induction variables.
598 std::vector<std::pair<PHINode*, SCEVHandle> > IndVars;
600 for (BasicBlock::iterator I = Header->begin();
601 PHINode *PN = dyn_cast<PHINode>(I); ++I)
602 if (PN->getType()->isInteger()) { // FIXME: when we have fast-math, enable!
603 SCEVHandle SCEV = SE->getSCEV(PN);
604 if (SCEV->hasComputableLoopEvolution(L))
605 // FIXME: Without a strength reduction pass, it is an extremely bad idea
606 // to indvar substitute anything more complex than a linear induction
607 // variable. Doing so will put expensive multiply instructions inside
608 // of the loop. For now just disable indvar subst on anything more
609 // complex than a linear addrec.
610 if (SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SCEV))
611 if (AR->getNumOperands() == 2 && isa<SCEVConstant>(AR->getOperand(1)))
612 IndVars.push_back(std::make_pair(PN, SCEV));
615 // If there are no induction variables in the loop, there is nothing more to
617 if (IndVars.empty()) {
618 // Actually, if we know how many times the loop iterates, lets insert a
619 // canonical induction variable to help subsequent passes.
620 if (!isa<SCEVCouldNotCompute>(IterationCount)) {
621 SCEVExpander Rewriter(*SE, *LI);
622 Rewriter.getOrInsertCanonicalInductionVariable(L,
623 IterationCount->getType());
624 LinearFunctionTestReplace(L, IterationCount, Rewriter);
629 // Compute the type of the largest recurrence expression.
631 const Type *LargestType = IndVars[0].first->getType();
632 bool DifferingSizes = false;
633 for (unsigned i = 1, e = IndVars.size(); i != e; ++i) {
634 const Type *Ty = IndVars[i].first->getType();
635 DifferingSizes |= Ty->getPrimitiveSize() != LargestType->getPrimitiveSize();
636 if (Ty->getPrimitiveSize() > LargestType->getPrimitiveSize())
640 // Create a rewriter object which we'll use to transform the code with.
641 SCEVExpander Rewriter(*SE, *LI);
643 // Now that we know the largest of of the induction variables in this loop,
644 // insert a canonical induction variable of the largest size.
645 LargestType = LargestType->getUnsignedVersion();
646 Value *IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L,LargestType);
650 if (!isa<SCEVCouldNotCompute>(IterationCount))
651 LinearFunctionTestReplace(L, IterationCount, Rewriter);
653 // Now that we have a canonical induction variable, we can rewrite any
654 // recurrences in terms of the induction variable. Start with the auxillary
655 // induction variables, and recursively rewrite any of their uses.
656 BasicBlock::iterator InsertPt = Header->begin();
657 while (isa<PHINode>(InsertPt)) ++InsertPt;
659 // If there were induction variables of other sizes, cast the primary
660 // induction variable to the right size for them, avoiding the need for the
661 // code evaluation methods to insert induction variables of different sizes.
662 if (DifferingSizes) {
663 bool InsertedSizes[17] = { false };
664 InsertedSizes[LargestType->getPrimitiveSize()] = true;
665 for (unsigned i = 0, e = IndVars.size(); i != e; ++i)
666 if (!InsertedSizes[IndVars[i].first->getType()->getPrimitiveSize()]) {
667 PHINode *PN = IndVars[i].first;
668 InsertedSizes[PN->getType()->getPrimitiveSize()] = true;
669 Instruction *New = new CastInst(IndVar,
670 PN->getType()->getUnsignedVersion(),
672 Rewriter.addInsertedValue(New, SE->getSCEV(New));
676 // If there were induction variables of other sizes, cast the primary
677 // induction variable to the right size for them, avoiding the need for the
678 // code evaluation methods to insert induction variables of different sizes.
679 std::map<unsigned, Value*> InsertedSizes;
680 while (!IndVars.empty()) {
681 PHINode *PN = IndVars.back().first;
682 Value *NewVal = Rewriter.expandCodeFor(IndVars.back().second, InsertPt,
684 std::string Name = PN->getName();
686 NewVal->setName(Name);
688 // Replace the old PHI Node with the inserted computation.
689 PN->replaceAllUsesWith(NewVal);
690 DeadInsts.insert(PN);
697 // Now replace all derived expressions in the loop body with simpler
699 for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i)
700 if (LI->getLoopFor(L->getBlocks()[i]) == L) { // Not in a subloop...
701 BasicBlock *BB = L->getBlocks()[i];
702 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
703 if (I->getType()->isInteger() && // Is an integer instruction
705 !Rewriter.isInsertedInstruction(I)) {
706 SCEVHandle SH = SE->getSCEV(I);
707 Value *V = Rewriter.expandCodeFor(SH, I, I->getType());
709 if (isa<Instruction>(V)) {
710 std::string Name = I->getName();
714 I->replaceAllUsesWith(V);
723 DeleteTriviallyDeadInstructions(DeadInsts);