1 //===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // 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 makes 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. The canonical induction variable is guaranteed to be in a wide enough
21 // type so that IV expressions need not be (directly) zero-extended or
23 // 4. Any pointer arithmetic recurrences are raised to use array subscripts.
25 // If the trip count of a loop is computable, this pass also makes the following
27 // 1. The exit condition for the loop is canonicalized to compare the
28 // induction value against the exit value. This turns loops like:
29 // 'for (i = 7; i*i < 1000; ++i)' into 'for (i = 0; i != 25; ++i)'
30 // 2. Any use outside of the loop of an expression derived from the indvar
31 // is changed to compute the derived value outside of the loop, eliminating
32 // the dependence on the exit value of the induction variable. If the only
33 // purpose of the loop is to compute the exit value of some derived
34 // expression, this transformation will make the loop dead.
36 // This transformation should be followed by strength reduction after all of the
37 // desired loop transformations have been performed.
39 //===----------------------------------------------------------------------===//
41 #define DEBUG_TYPE "indvars"
42 #include "llvm/Transforms/Scalar.h"
43 #include "llvm/BasicBlock.h"
44 #include "llvm/Constants.h"
45 #include "llvm/Instructions.h"
46 #include "llvm/IntrinsicInst.h"
47 #include "llvm/LLVMContext.h"
48 #include "llvm/Type.h"
49 #include "llvm/Analysis/Dominators.h"
50 #include "llvm/Analysis/IVUsers.h"
51 #include "llvm/Analysis/ScalarEvolutionExpander.h"
52 #include "llvm/Analysis/LoopInfo.h"
53 #include "llvm/Analysis/LoopPass.h"
54 #include "llvm/Support/CFG.h"
55 #include "llvm/Support/CommandLine.h"
56 #include "llvm/Support/Debug.h"
57 #include "llvm/Support/raw_ostream.h"
58 #include "llvm/Transforms/Utils/Local.h"
59 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
60 #include "llvm/ADT/SmallVector.h"
61 #include "llvm/ADT/Statistic.h"
62 #include "llvm/ADT/STLExtras.h"
65 STATISTIC(NumRemoved , "Number of aux indvars removed");
66 STATISTIC(NumInserted, "Number of canonical indvars added");
67 STATISTIC(NumReplaced, "Number of exit values replaced");
68 STATISTIC(NumLFTR , "Number of loop exit tests replaced");
71 class IndVarSimplify : public LoopPass {
79 static char ID; // Pass identification, replacement for typeid
80 IndVarSimplify() : LoopPass(&ID) {}
82 virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
84 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
85 AU.addRequired<DominatorTree>();
86 AU.addRequired<LoopInfo>();
87 AU.addRequired<ScalarEvolution>();
88 AU.addRequiredID(LoopSimplifyID);
89 AU.addRequiredID(LCSSAID);
90 AU.addRequired<IVUsers>();
91 AU.addPreserved<ScalarEvolution>();
92 AU.addPreservedID(LoopSimplifyID);
93 AU.addPreservedID(LCSSAID);
94 AU.addPreserved<IVUsers>();
100 void RewriteNonIntegerIVs(Loop *L);
102 ICmpInst *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount,
104 BasicBlock *ExitingBlock,
106 SCEVExpander &Rewriter);
107 void RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter);
109 void RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter);
111 void SinkUnusedInvariants(Loop *L);
113 void HandleFloatingPointIV(Loop *L, PHINode *PH);
117 char IndVarSimplify::ID = 0;
118 static RegisterPass<IndVarSimplify>
119 X("indvars", "Canonicalize Induction Variables");
121 Pass *llvm::createIndVarSimplifyPass() {
122 return new IndVarSimplify();
125 /// LinearFunctionTestReplace - This method rewrites the exit condition of the
126 /// loop to be a canonical != comparison against the incremented loop induction
127 /// variable. This pass is able to rewrite the exit tests of any loop where the
128 /// SCEV analysis can determine a loop-invariant trip count of the loop, which
129 /// is actually a much broader range than just linear tests.
130 ICmpInst *IndVarSimplify::LinearFunctionTestReplace(Loop *L,
131 const SCEV *BackedgeTakenCount,
133 BasicBlock *ExitingBlock,
135 SCEVExpander &Rewriter) {
136 // If the exiting block is not the same as the backedge block, we must compare
137 // against the preincremented value, otherwise we prefer to compare against
138 // the post-incremented value.
140 const SCEV *RHS = BackedgeTakenCount;
141 if (ExitingBlock == L->getLoopLatch()) {
142 // Add one to the "backedge-taken" count to get the trip count.
143 // If this addition may overflow, we have to be more pessimistic and
144 // cast the induction variable before doing the add.
145 const SCEV *Zero = SE->getIntegerSCEV(0, BackedgeTakenCount->getType());
147 SE->getAddExpr(BackedgeTakenCount,
148 SE->getIntegerSCEV(1, BackedgeTakenCount->getType()));
149 if ((isa<SCEVConstant>(N) && !N->isZero()) ||
150 SE->isLoopGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) {
151 // No overflow. Cast the sum.
152 RHS = SE->getTruncateOrZeroExtend(N, IndVar->getType());
154 // Potential overflow. Cast before doing the add.
155 RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
157 RHS = SE->getAddExpr(RHS,
158 SE->getIntegerSCEV(1, IndVar->getType()));
161 // The BackedgeTaken expression contains the number of times that the
162 // backedge branches to the loop header. This is one less than the
163 // number of times the loop executes, so use the incremented indvar.
164 CmpIndVar = L->getCanonicalInductionVariableIncrement();
166 // We have to use the preincremented value...
167 RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
172 // Expand the code for the iteration count.
173 assert(RHS->isLoopInvariant(L) &&
174 "Computed iteration count is not loop invariant!");
175 Value *ExitCnt = Rewriter.expandCodeFor(RHS, IndVar->getType(), BI);
177 // Insert a new icmp_ne or icmp_eq instruction before the branch.
178 ICmpInst::Predicate Opcode;
179 if (L->contains(BI->getSuccessor(0)))
180 Opcode = ICmpInst::ICMP_NE;
182 Opcode = ICmpInst::ICMP_EQ;
184 DEBUG(dbgs() << "INDVARS: Rewriting loop exit condition to:\n"
185 << " LHS:" << *CmpIndVar << '\n'
187 << (Opcode == ICmpInst::ICMP_NE ? "!=" : "==") << "\n"
188 << " RHS:\t" << *RHS << "\n");
190 ICmpInst *Cond = new ICmpInst(BI, Opcode, CmpIndVar, ExitCnt, "exitcond");
192 Value *OrigCond = BI->getCondition();
193 // It's tempting to use replaceAllUsesWith here to fully replace the old
194 // comparison, but that's not immediately safe, since users of the old
195 // comparison may not be dominated by the new comparison. Instead, just
196 // update the branch to use the new comparison; in the common case this
197 // will make old comparison dead.
198 BI->setCondition(Cond);
199 RecursivelyDeleteTriviallyDeadInstructions(OrigCond);
206 /// RewriteLoopExitValues - Check to see if this loop has a computable
207 /// loop-invariant execution count. If so, this means that we can compute the
208 /// final value of any expressions that are recurrent in the loop, and
209 /// substitute the exit values from the loop into any instructions outside of
210 /// the loop that use the final values of the current expressions.
212 /// This is mostly redundant with the regular IndVarSimplify activities that
213 /// happen later, except that it's more powerful in some cases, because it's
214 /// able to brute-force evaluate arbitrary instructions as long as they have
215 /// constant operands at the beginning of the loop.
216 void IndVarSimplify::RewriteLoopExitValues(Loop *L,
217 SCEVExpander &Rewriter) {
218 // Verify the input to the pass in already in LCSSA form.
219 assert(L->isLCSSAForm(*DT));
221 SmallVector<BasicBlock*, 8> ExitBlocks;
222 L->getUniqueExitBlocks(ExitBlocks);
224 // Find all values that are computed inside the loop, but used outside of it.
225 // Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan
226 // the exit blocks of the loop to find them.
227 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
228 BasicBlock *ExitBB = ExitBlocks[i];
230 // If there are no PHI nodes in this exit block, then no values defined
231 // inside the loop are used on this path, skip it.
232 PHINode *PN = dyn_cast<PHINode>(ExitBB->begin());
235 unsigned NumPreds = PN->getNumIncomingValues();
237 // Iterate over all of the PHI nodes.
238 BasicBlock::iterator BBI = ExitBB->begin();
239 while ((PN = dyn_cast<PHINode>(BBI++))) {
241 continue; // dead use, don't replace it
243 // SCEV only supports integer expressions for now.
244 if (!PN->getType()->isIntegerTy() && !PN->getType()->isPointerTy())
247 // It's necessary to tell ScalarEvolution about this explicitly so that
248 // it can walk the def-use list and forget all SCEVs, as it may not be
249 // watching the PHI itself. Once the new exit value is in place, there
250 // may not be a def-use connection between the loop and every instruction
251 // which got a SCEVAddRecExpr for that loop.
254 // Iterate over all of the values in all the PHI nodes.
255 for (unsigned i = 0; i != NumPreds; ++i) {
256 // If the value being merged in is not integer or is not defined
257 // in the loop, skip it.
258 Value *InVal = PN->getIncomingValue(i);
259 if (!isa<Instruction>(InVal))
262 // If this pred is for a subloop, not L itself, skip it.
263 if (LI->getLoopFor(PN->getIncomingBlock(i)) != L)
264 continue; // The Block is in a subloop, skip it.
266 // Check that InVal is defined in the loop.
267 Instruction *Inst = cast<Instruction>(InVal);
268 if (!L->contains(Inst))
271 // Okay, this instruction has a user outside of the current loop
272 // and varies predictably *inside* the loop. Evaluate the value it
273 // contains when the loop exits, if possible.
274 const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop());
275 if (!ExitValue->isLoopInvariant(L))
281 Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst);
283 DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n'
284 << " LoopVal = " << *Inst << "\n");
286 PN->setIncomingValue(i, ExitVal);
288 // If this instruction is dead now, delete it.
289 RecursivelyDeleteTriviallyDeadInstructions(Inst);
292 // Completely replace a single-pred PHI. This is safe, because the
293 // NewVal won't be variant in the loop, so we don't need an LCSSA phi
295 PN->replaceAllUsesWith(ExitVal);
296 RecursivelyDeleteTriviallyDeadInstructions(PN);
300 // Clone the PHI and delete the original one. This lets IVUsers and
301 // any other maps purge the original user from their records.
302 PHINode *NewPN = cast<PHINode>(PN->clone());
304 NewPN->insertBefore(PN);
305 PN->replaceAllUsesWith(NewPN);
306 PN->eraseFromParent();
311 // The insertion point instruction may have been deleted; clear it out
312 // so that the rewriter doesn't trip over it later.
313 Rewriter.clearInsertPoint();
316 void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) {
317 // First step. Check to see if there are any floating-point recurrences.
318 // If there are, change them into integer recurrences, permitting analysis by
319 // the SCEV routines.
321 BasicBlock *Header = L->getHeader();
323 SmallVector<WeakVH, 8> PHIs;
324 for (BasicBlock::iterator I = Header->begin();
325 PHINode *PN = dyn_cast<PHINode>(I); ++I)
328 for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
329 if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i]))
330 HandleFloatingPointIV(L, PN);
332 // If the loop previously had floating-point IV, ScalarEvolution
333 // may not have been able to compute a trip count. Now that we've done some
334 // re-writing, the trip count may be computable.
339 bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
340 IU = &getAnalysis<IVUsers>();
341 LI = &getAnalysis<LoopInfo>();
342 SE = &getAnalysis<ScalarEvolution>();
343 DT = &getAnalysis<DominatorTree>();
346 // If there are any floating-point recurrences, attempt to
347 // transform them to use integer recurrences.
348 RewriteNonIntegerIVs(L);
350 BasicBlock *ExitingBlock = L->getExitingBlock(); // may be null
351 const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
353 // Create a rewriter object which we'll use to transform the code with.
354 SCEVExpander Rewriter(*SE);
356 // Check to see if this loop has a computable loop-invariant execution count.
357 // If so, this means that we can compute the final value of any expressions
358 // that are recurrent in the loop, and substitute the exit values from the
359 // loop into any instructions outside of the loop that use the final values of
360 // the current expressions.
362 if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount))
363 RewriteLoopExitValues(L, Rewriter);
365 // Compute the type of the largest recurrence expression, and decide whether
366 // a canonical induction variable should be inserted.
367 const Type *LargestType = 0;
368 bool NeedCannIV = false;
369 if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount)) {
370 LargestType = BackedgeTakenCount->getType();
371 LargestType = SE->getEffectiveSCEVType(LargestType);
372 // If we have a known trip count and a single exit block, we'll be
373 // rewriting the loop exit test condition below, which requires a
374 // canonical induction variable.
378 for (IVUsers::const_iterator I = IU->begin(), E = IU->end(); I != E; ++I) {
380 SE->getEffectiveSCEVType(I->getOperandValToReplace()->getType());
382 SE->getTypeSizeInBits(Ty) >
383 SE->getTypeSizeInBits(LargestType))
388 // Now that we know the largest of the induction variable expressions
389 // in this loop, insert a canonical induction variable of the largest size.
392 // Check to see if the loop already has any canonical-looking induction
393 // variables. If any are present and wider than the planned canonical
394 // induction variable, temporarily remove them, so that the Rewriter
395 // doesn't attempt to reuse them.
396 SmallVector<PHINode *, 2> OldCannIVs;
397 while (PHINode *OldCannIV = L->getCanonicalInductionVariable()) {
398 if (SE->getTypeSizeInBits(OldCannIV->getType()) >
399 SE->getTypeSizeInBits(LargestType))
400 OldCannIV->removeFromParent();
403 OldCannIVs.push_back(OldCannIV);
406 IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L, LargestType);
410 DEBUG(dbgs() << "INDVARS: New CanIV: " << *IndVar << '\n');
412 // Now that the official induction variable is established, reinsert
413 // any old canonical-looking variables after it so that the IR remains
414 // consistent. They will be deleted as part of the dead-PHI deletion at
415 // the end of the pass.
416 while (!OldCannIVs.empty()) {
417 PHINode *OldCannIV = OldCannIVs.pop_back_val();
418 OldCannIV->insertBefore(L->getHeader()->getFirstNonPHI());
422 // If we have a trip count expression, rewrite the loop's exit condition
423 // using it. We can currently only handle loops with a single exit.
424 ICmpInst *NewICmp = 0;
425 if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount) &&
426 !BackedgeTakenCount->isZero() &&
429 "LinearFunctionTestReplace requires a canonical induction variable");
430 // Can't rewrite non-branch yet.
431 if (BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator()))
432 NewICmp = LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar,
433 ExitingBlock, BI, Rewriter);
436 // Rewrite IV-derived expressions. Clears the rewriter cache.
437 RewriteIVExpressions(L, Rewriter);
439 // The Rewriter may not be used from this point on.
441 // Loop-invariant instructions in the preheader that aren't used in the
442 // loop may be sunk below the loop to reduce register pressure.
443 SinkUnusedInvariants(L);
445 // For completeness, inform IVUsers of the IV use in the newly-created
446 // loop exit test instruction.
448 IU->AddUsersIfInteresting(cast<Instruction>(NewICmp->getOperand(0)));
450 // Clean up dead instructions.
451 Changed |= DeleteDeadPHIs(L->getHeader());
452 // Check a post-condition.
453 assert(L->isLCSSAForm(*DT) && "Indvars did not leave the loop in lcssa form!");
457 void IndVarSimplify::RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter) {
458 SmallVector<WeakVH, 16> DeadInsts;
460 // Rewrite all induction variable expressions in terms of the canonical
461 // induction variable.
463 // If there were induction variables of other sizes or offsets, manually
464 // add the offsets to the primary induction variable and cast, avoiding
465 // the need for the code evaluation methods to insert induction variables
466 // of different sizes.
467 for (IVUsers::iterator UI = IU->begin(), E = IU->end(); UI != E; ++UI) {
468 const SCEV *Stride = UI->getStride();
469 Value *Op = UI->getOperandValToReplace();
470 const Type *UseTy = Op->getType();
471 Instruction *User = UI->getUser();
473 // Compute the final addrec to expand into code.
474 const SCEV *AR = IU->getReplacementExpr(*UI);
476 // Evaluate the expression out of the loop, if possible.
477 if (!L->contains(UI->getUser())) {
478 const SCEV *ExitVal = SE->getSCEVAtScope(AR, L->getParentLoop());
479 if (ExitVal->isLoopInvariant(L))
483 // FIXME: It is an extremely bad idea to indvar substitute anything more
484 // complex than affine induction variables. Doing so will put expensive
485 // polynomial evaluations inside of the loop, and the str reduction pass
486 // currently can only reduce affine polynomials. For now just disable
487 // indvar subst on anything more complex than an affine addrec, unless
488 // it can be expanded to a trivial value.
489 if (!AR->isLoopInvariant(L) && !Stride->isLoopInvariant(L))
492 // Determine the insertion point for this user. By default, insert
493 // immediately before the user. The SCEVExpander class will automatically
494 // hoist loop invariants out of the loop. For PHI nodes, there may be
495 // multiple uses, so compute the nearest common dominator for the
497 Instruction *InsertPt = User;
498 if (PHINode *PHI = dyn_cast<PHINode>(InsertPt))
499 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
500 if (PHI->getIncomingValue(i) == Op) {
501 if (InsertPt == User)
502 InsertPt = PHI->getIncomingBlock(i)->getTerminator();
505 DT->findNearestCommonDominator(InsertPt->getParent(),
506 PHI->getIncomingBlock(i))
510 // Now expand it into actual Instructions and patch it into place.
511 Value *NewVal = Rewriter.expandCodeFor(AR, UseTy, InsertPt);
513 // Inform ScalarEvolution that this value is changing. The change doesn't
514 // affect its value, but it does potentially affect which use lists the
515 // value will be on after the replacement, which affects ScalarEvolution's
516 // ability to walk use lists and drop dangling pointers when a value is
518 SE->forgetValue(User);
520 // Patch the new value into place.
522 NewVal->takeName(Op);
523 User->replaceUsesOfWith(Op, NewVal);
524 UI->setOperandValToReplace(NewVal);
525 DEBUG(dbgs() << "INDVARS: Rewrote IV '" << *AR << "' " << *Op << '\n'
526 << " into = " << *NewVal << "\n");
530 // The old value may be dead now.
531 DeadInsts.push_back(Op);
534 // Clear the rewriter cache, because values that are in the rewriter's cache
535 // can be deleted in the loop below, causing the AssertingVH in the cache to
538 // Now that we're done iterating through lists, clean up any instructions
539 // which are now dead.
540 while (!DeadInsts.empty())
541 if (Instruction *Inst =
542 dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val()))
543 RecursivelyDeleteTriviallyDeadInstructions(Inst);
546 /// If there's a single exit block, sink any loop-invariant values that
547 /// were defined in the preheader but not used inside the loop into the
548 /// exit block to reduce register pressure in the loop.
549 void IndVarSimplify::SinkUnusedInvariants(Loop *L) {
550 BasicBlock *ExitBlock = L->getExitBlock();
551 if (!ExitBlock) return;
553 BasicBlock *Preheader = L->getLoopPreheader();
554 if (!Preheader) return;
556 Instruction *InsertPt = ExitBlock->getFirstNonPHI();
557 BasicBlock::iterator I = Preheader->getTerminator();
558 while (I != Preheader->begin()) {
560 // New instructions were inserted at the end of the preheader.
564 // Don't move instructions which might have side effects, since the side
565 // effects need to complete before instructions inside the loop. Also don't
566 // move instructions which might read memory, since the loop may modify
567 // memory. Note that it's okay if the instruction might have undefined
568 // behavior: LoopSimplify guarantees that the preheader dominates the exit
570 if (I->mayHaveSideEffects() || I->mayReadFromMemory())
573 // Skip debug info intrinsics.
574 if (isa<DbgInfoIntrinsic>(I))
577 // Don't sink static AllocaInsts out of the entry block, which would
578 // turn them into dynamic allocas!
579 if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
580 if (AI->isStaticAlloca())
583 // Determine if there is a use in or before the loop (direct or
585 bool UsedInLoop = false;
586 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
588 BasicBlock *UseBB = cast<Instruction>(UI)->getParent();
589 if (PHINode *P = dyn_cast<PHINode>(UI)) {
591 PHINode::getIncomingValueNumForOperand(UI.getOperandNo());
592 UseBB = P->getIncomingBlock(i);
594 if (UseBB == Preheader || L->contains(UseBB)) {
600 // If there is, the def must remain in the preheader.
604 // Otherwise, sink it to the exit block.
605 Instruction *ToMove = I;
608 if (I != Preheader->begin()) {
609 // Skip debug info intrinsics.
612 } while (isa<DbgInfoIntrinsic>(I) && I != Preheader->begin());
614 if (isa<DbgInfoIntrinsic>(I) && I == Preheader->begin())
620 ToMove->moveBefore(InsertPt);
626 /// Return true if it is OK to use SIToFPInst for an induction variable
627 /// with given initial and exit values.
628 static bool useSIToFPInst(ConstantFP *InitV, ConstantFP *ExitV,
629 uint64_t intIV, uint64_t intEV) {
631 if (InitV->getValueAPF().isNegative() || ExitV->getValueAPF().isNegative())
634 // If the iteration range can be handled by SIToFPInst then use it.
635 APInt Max = APInt::getSignedMaxValue(32);
636 if (Max.getZExtValue() > static_cast<uint64_t>(abs64(intEV - intIV)))
642 /// convertToInt - Convert APF to an integer, if possible.
643 static bool convertToInt(const APFloat &APF, uint64_t &intVal) {
644 bool isExact = false;
645 if (&APF.getSemantics() == &APFloat::PPCDoubleDouble)
647 if (APF.convertToInteger(&intVal, 32, APF.isNegative(),
648 APFloat::rmTowardZero, &isExact) != APFloat::opOK)
655 /// HandleFloatingPointIV - If the loop has floating induction variable
656 /// then insert corresponding integer induction variable if possible.
658 /// for(double i = 0; i < 10000; ++i)
660 /// is converted into
661 /// for(int i = 0; i < 10000; ++i)
664 void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PH) {
665 unsigned IncomingEdge = L->contains(PH->getIncomingBlock(0));
666 unsigned BackEdge = IncomingEdge^1;
668 // Check incoming value.
669 ConstantFP *InitValueVal =
670 dyn_cast<ConstantFP>(PH->getIncomingValue(IncomingEdge));
671 if (!InitValueVal) return;
674 if (!convertToInt(InitValueVal->getValueAPF(), InitValue))
677 // Check IV increment. Reject this PH if increment operation is not
678 // an add or increment value can not be represented by an integer.
679 BinaryOperator *Incr =
680 dyn_cast<BinaryOperator>(PH->getIncomingValue(BackEdge));
681 if (Incr == 0 || Incr->getOpcode() != Instruction::FAdd) return;
683 // If this is not an add of the PHI with a constantfp, or if the constant fp
684 // is not an integer, bail out.
685 ConstantFP *IncValueVal = dyn_cast<ConstantFP>(Incr->getOperand(1));
687 if (IncValueVal == 0 || Incr->getOperand(0) != PH ||
688 !convertToInt(IncValueVal->getValueAPF(), IntValue))
691 // Check Incr uses. One user is PH and the other user is an exit condition
692 // used by the conditional terminator.
693 Value::use_iterator IncrUse = Incr->use_begin();
694 Instruction *U1 = cast<Instruction>(IncrUse++);
695 if (IncrUse == Incr->use_end()) return;
696 Instruction *U2 = cast<Instruction>(IncrUse++);
697 if (IncrUse != Incr->use_end()) return;
699 // Find exit condition, which is an fcmp. If it doesn't exist, or if it isn't
700 // only used by a branch, we can't transform it.
701 FCmpInst *EC = dyn_cast<FCmpInst>(U1);
703 EC = dyn_cast<FCmpInst>(U2);
704 if (EC == 0 || !EC->hasOneUse() || !isa<BranchInst>(EC->use_back()))
707 BranchInst *TheBr = cast<BranchInst>(EC->use_back());
709 // If it isn't a comparison with an integer-as-fp (the exit value), we can't
711 ConstantFP *ExitValueVal = dyn_cast<ConstantFP>(EC->getOperand(1));
713 if (ExitValueVal == 0 || !convertToInt(ExitValueVal->getValueAPF(),ExitValue))
716 // Find new predicate for integer comparison.
717 CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE;
718 switch (EC->getPredicate()) {
719 default: return; // Unknown comparison.
720 case CmpInst::FCMP_OEQ:
721 case CmpInst::FCMP_UEQ: NewPred = CmpInst::ICMP_EQ; break;
722 case CmpInst::FCMP_OGT:
723 case CmpInst::FCMP_UGT: NewPred = CmpInst::ICMP_UGT; break;
724 case CmpInst::FCMP_OGE:
725 case CmpInst::FCMP_UGE: NewPred = CmpInst::ICMP_UGE; break;
726 case CmpInst::FCMP_OLT:
727 case CmpInst::FCMP_ULT: NewPred = CmpInst::ICMP_ULT; break;
728 case CmpInst::FCMP_OLE:
729 case CmpInst::FCMP_ULE: NewPred = CmpInst::ICMP_ULE; break;
732 const IntegerType *Int32Ty = Type::getInt32Ty(PH->getContext());
734 // Insert new integer induction variable.
735 PHINode *NewPHI = PHINode::Create(Int32Ty, PH->getName()+".int", PH);
736 NewPHI->addIncoming(ConstantInt::get(Int32Ty, InitValue),
737 PH->getIncomingBlock(IncomingEdge));
740 BinaryOperator::CreateAdd(NewPHI, ConstantInt::get(Int32Ty, IntValue),
741 Incr->getName()+".int", Incr);
742 NewPHI->addIncoming(NewAdd, PH->getIncomingBlock(BackEdge));
744 // The back edge is edge 1 of newPHI, whatever it may have been in the
746 ConstantInt *NewEV = ConstantInt::get(Int32Ty, ExitValue);
748 ICmpInst *NewCompare = new ICmpInst(TheBr, NewPred, NewAdd, NewEV,
751 // In the following deletions, PH may become dead and may be deleted.
752 // Use a WeakVH to observe whether this happens.
755 // Delete old, floating point, exit comparison instruction.
756 NewCompare->takeName(EC);
757 EC->replaceAllUsesWith(NewCompare);
758 RecursivelyDeleteTriviallyDeadInstructions(EC);
760 // Delete old, floating point, increment instruction.
761 Incr->replaceAllUsesWith(UndefValue::get(Incr->getType()));
762 RecursivelyDeleteTriviallyDeadInstructions(Incr);
764 // Replace floating induction variable, if it isn't already deleted.
765 // Give SIToFPInst preference over UIToFPInst because it is faster on
766 // platforms that are widely used.
767 if (WeakPH && !PH->use_empty()) {
768 if (useSIToFPInst(InitValueVal, ExitValueVal, InitValue, ExitValue)) {
769 SIToFPInst *Conv = new SIToFPInst(NewPHI, PH->getType(), "indvar.conv",
770 PH->getParent()->getFirstNonPHI());
771 PH->replaceAllUsesWith(Conv);
773 UIToFPInst *Conv = new UIToFPInst(NewPHI, PH->getType(), "indvar.conv",
774 PH->getParent()->getFirstNonPHI());
775 PH->replaceAllUsesWith(Conv);
777 RecursivelyDeleteTriviallyDeadInstructions(PH);
780 // Add a new IVUsers entry for the newly-created integer PHI.
781 IU->AddUsersIfInteresting(NewPHI);