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/Type.h"
47 #include "llvm/Analysis/Dominators.h"
48 #include "llvm/Analysis/IVUsers.h"
49 #include "llvm/Analysis/ScalarEvolutionExpander.h"
50 #include "llvm/Analysis/LoopInfo.h"
51 #include "llvm/Analysis/LoopPass.h"
52 #include "llvm/Support/CFG.h"
53 #include "llvm/Support/Compiler.h"
54 #include "llvm/Support/Debug.h"
55 #include "llvm/Transforms/Utils/Local.h"
56 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
57 #include "llvm/Support/CommandLine.h"
58 #include "llvm/ADT/SmallVector.h"
59 #include "llvm/ADT/Statistic.h"
60 #include "llvm/ADT/STLExtras.h"
63 STATISTIC(NumRemoved , "Number of aux indvars removed");
64 STATISTIC(NumInserted, "Number of canonical indvars added");
65 STATISTIC(NumReplaced, "Number of exit values replaced");
66 STATISTIC(NumLFTR , "Number of loop exit tests replaced");
69 class VISIBILITY_HIDDEN IndVarSimplify : public LoopPass {
76 static char ID; // Pass identification, replacement for typeid
77 IndVarSimplify() : LoopPass(&ID) {}
79 virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
81 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
82 AU.addRequired<DominatorTree>();
83 AU.addRequired<ScalarEvolution>();
84 AU.addRequiredID(LCSSAID);
85 AU.addRequiredID(LoopSimplifyID);
86 AU.addRequired<LoopInfo>();
87 AU.addRequired<IVUsers>();
88 AU.addPreserved<ScalarEvolution>();
89 AU.addPreservedID(LoopSimplifyID);
90 AU.addPreserved<IVUsers>();
91 AU.addPreservedID(LCSSAID);
97 void RewriteNonIntegerIVs(Loop *L);
99 ICmpInst *LinearFunctionTestReplace(Loop *L, const SCEV* BackedgeTakenCount,
101 BasicBlock *ExitingBlock,
103 SCEVExpander &Rewriter);
104 void RewriteLoopExitValues(Loop *L, const SCEV *BackedgeTakenCount);
106 void RewriteIVExpressions(Loop *L, const Type *LargestType,
107 SCEVExpander &Rewriter);
109 void SinkUnusedInvariants(Loop *L, SCEVExpander &Rewriter);
111 void FixUsesBeforeDefs(Loop *L, SCEVExpander &Rewriter);
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 into the preheader of the loop.
173 BasicBlock *Preheader = L->getLoopPreheader();
174 Value *ExitCnt = Rewriter.expandCodeFor(RHS, IndVar->getType(),
175 Preheader->getTerminator());
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 DOUT << "INDVARS: Rewriting loop exit condition to:\n"
185 << " LHS:" << *CmpIndVar // includes a newline
187 << (Opcode == ICmpInst::ICMP_NE ? "!=" : "==") << "\n"
188 << " RHS:\t" << *RHS << "\n";
190 ICmpInst *Cond = new ICmpInst(Opcode, CmpIndVar, ExitCnt, "exitcond", BI);
192 Instruction *OrigCond = cast<Instruction>(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 const SCEV *BackedgeTakenCount) {
218 // Verify the input to the pass in already in LCSSA form.
219 assert(L->isLCSSAForm());
221 BasicBlock *Preheader = L->getLoopPreheader();
223 // Scan all of the instructions in the loop, looking at those that have
224 // extra-loop users and which are recurrences.
225 SCEVExpander Rewriter(*SE);
227 // We insert the code into the preheader of the loop if the loop contains
228 // multiple exit blocks, or in the exit block if there is exactly one.
229 BasicBlock *BlockToInsertInto;
230 SmallVector<BasicBlock*, 8> ExitBlocks;
231 L->getUniqueExitBlocks(ExitBlocks);
232 if (ExitBlocks.size() == 1)
233 BlockToInsertInto = ExitBlocks[0];
235 BlockToInsertInto = Preheader;
236 BasicBlock::iterator InsertPt = BlockToInsertInto->getFirstNonPHI();
238 std::map<Instruction*, Value*> ExitValues;
240 // Find all values that are computed inside the loop, but used outside of it.
241 // Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan
242 // the exit blocks of the loop to find them.
243 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
244 BasicBlock *ExitBB = ExitBlocks[i];
246 // If there are no PHI nodes in this exit block, then no values defined
247 // inside the loop are used on this path, skip it.
248 PHINode *PN = dyn_cast<PHINode>(ExitBB->begin());
251 unsigned NumPreds = PN->getNumIncomingValues();
253 // Iterate over all of the PHI nodes.
254 BasicBlock::iterator BBI = ExitBB->begin();
255 while ((PN = dyn_cast<PHINode>(BBI++))) {
257 continue; // dead use, don't replace it
258 // Iterate over all of the values in all the PHI nodes.
259 for (unsigned i = 0; i != NumPreds; ++i) {
260 // If the value being merged in is not integer or is not defined
261 // in the loop, skip it.
262 Value *InVal = PN->getIncomingValue(i);
263 if (!isa<Instruction>(InVal) ||
264 // SCEV only supports integer expressions for now.
265 (!isa<IntegerType>(InVal->getType()) &&
266 !isa<PointerType>(InVal->getType())))
269 // If this pred is for a subloop, not L itself, skip it.
270 if (LI->getLoopFor(PN->getIncomingBlock(i)) != L)
271 continue; // The Block is in a subloop, skip it.
273 // Check that InVal is defined in the loop.
274 Instruction *Inst = cast<Instruction>(InVal);
275 if (!L->contains(Inst->getParent()))
278 // Okay, this instruction has a user outside of the current loop
279 // and varies predictably *inside* the loop. Evaluate the value it
280 // contains when the loop exits, if possible.
281 const SCEV* ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop());
282 if (!ExitValue->isLoopInvariant(L))
288 // See if we already computed the exit value for the instruction, if so,
290 Value *&ExitVal = ExitValues[Inst];
292 ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), InsertPt);
294 DOUT << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal
295 << " LoopVal = " << *Inst << "\n";
297 PN->setIncomingValue(i, ExitVal);
299 // If this instruction is dead now, delete it.
300 RecursivelyDeleteTriviallyDeadInstructions(Inst);
302 // If we're inserting code into the exit block rather than the
303 // preheader, we can (and have to) remove the PHI entirely.
304 // This is safe, because the NewVal won't be variant
305 // in the loop, so we don't need an LCSSA phi node anymore.
306 if (ExitBlocks.size() == 1) {
307 PN->replaceAllUsesWith(ExitVal);
308 RecursivelyDeleteTriviallyDeadInstructions(PN);
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.
336 SE->forgetLoopBackedgeTakenCount(L);
339 bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
340 IU = &getAnalysis<IVUsers>();
341 LI = &getAnalysis<LoopInfo>();
342 SE = &getAnalysis<ScalarEvolution>();
345 // If there are any floating-point recurrences, attempt to
346 // transform them to use integer recurrences.
347 RewriteNonIntegerIVs(L);
349 BasicBlock *Header = L->getHeader();
350 BasicBlock *ExitingBlock = L->getExitingBlock(); // may be null
351 const SCEV* BackedgeTakenCount = SE->getBackedgeTakenCount(L);
353 // Check to see if this loop has a computable loop-invariant execution count.
354 // If so, this means that we can compute the final value of any expressions
355 // that are recurrent in the loop, and substitute the exit values from the
356 // loop into any instructions outside of the loop that use the final values of
357 // the current expressions.
359 if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount))
360 RewriteLoopExitValues(L, BackedgeTakenCount);
362 // Compute the type of the largest recurrence expression, and decide whether
363 // a canonical induction variable should be inserted.
364 const Type *LargestType = 0;
365 bool NeedCannIV = false;
366 if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount)) {
367 LargestType = BackedgeTakenCount->getType();
368 LargestType = SE->getEffectiveSCEVType(LargestType);
369 // If we have a known trip count and a single exit block, we'll be
370 // rewriting the loop exit test condition below, which requires a
371 // canonical induction variable.
375 for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) {
376 const SCEV* Stride = IU->StrideOrder[i];
377 const Type *Ty = SE->getEffectiveSCEVType(Stride->getType());
379 SE->getTypeSizeInBits(Ty) >
380 SE->getTypeSizeInBits(LargestType))
383 std::map<const SCEV*, IVUsersOfOneStride *>::iterator SI =
384 IU->IVUsesByStride.find(IU->StrideOrder[i]);
385 assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
387 if (!SI->second->Users.empty())
391 // Create a rewriter object which we'll use to transform the code with.
392 SCEVExpander Rewriter(*SE);
394 // Now that we know the largest of of the induction variable expressions
395 // in this loop, insert a canonical induction variable of the largest size.
398 // Check to see if the loop already has a canonical-looking induction
399 // variable. If one is present and it's wider than the planned canonical
400 // induction variable, temporarily remove it, so that the Rewriter
401 // doesn't attempt to reuse it.
402 PHINode *OldCannIV = L->getCanonicalInductionVariable();
404 if (SE->getTypeSizeInBits(OldCannIV->getType()) >
405 SE->getTypeSizeInBits(LargestType))
406 OldCannIV->removeFromParent();
411 IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L,LargestType);
415 DOUT << "INDVARS: New CanIV: " << *IndVar;
417 // Now that the official induction variable is established, reinsert
418 // the old canonical-looking variable after it so that the IR remains
419 // consistent. It will be deleted as part of the dead-PHI deletion at
420 // the end of the pass.
422 OldCannIV->insertAfter(cast<Instruction>(IndVar));
425 // If we have a trip count expression, rewrite the loop's exit condition
426 // using it. We can currently only handle loops with a single exit.
427 ICmpInst *NewICmp = 0;
428 if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount) && ExitingBlock) {
430 "LinearFunctionTestReplace requires a canonical induction variable");
431 // Can't rewrite non-branch yet.
432 if (BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator()))
433 NewICmp = LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar,
434 ExitingBlock, BI, Rewriter);
437 Rewriter.setInsertionPoint(Header->getFirstNonPHI());
439 // Rewrite IV-derived expressions. Clears the rewriter cache.
440 RewriteIVExpressions(L, LargestType, Rewriter);
442 // The Rewriter may only be used for isInsertedInstruction queries from this
445 // Loop-invariant instructions in the preheader that aren't used in the
446 // loop may be sunk below the loop to reduce register pressure.
447 SinkUnusedInvariants(L, Rewriter);
449 // Reorder instructions to avoid use-before-def conditions.
450 FixUsesBeforeDefs(L, Rewriter);
452 // For completeness, inform IVUsers of the IV use in the newly-created
453 // loop exit test instruction.
455 IU->AddUsersIfInteresting(cast<Instruction>(NewICmp->getOperand(0)));
457 // Clean up dead instructions.
458 DeleteDeadPHIs(L->getHeader());
459 // Check a post-condition.
460 assert(L->isLCSSAForm() && "Indvars did not leave the loop in lcssa form!");
464 void IndVarSimplify::RewriteIVExpressions(Loop *L, const Type *LargestType,
465 SCEVExpander &Rewriter) {
466 SmallVector<WeakVH, 16> DeadInsts;
468 // Rewrite all induction variable expressions in terms of the canonical
469 // induction variable.
471 // If there were induction variables of other sizes or offsets, manually
472 // add the offsets to the primary induction variable and cast, avoiding
473 // the need for the code evaluation methods to insert induction variables
474 // of different sizes.
475 for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) {
476 const SCEV* Stride = IU->StrideOrder[i];
478 std::map<const SCEV*, IVUsersOfOneStride *>::iterator SI =
479 IU->IVUsesByStride.find(IU->StrideOrder[i]);
480 assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
481 ilist<IVStrideUse> &List = SI->second->Users;
482 for (ilist<IVStrideUse>::iterator UI = List.begin(),
483 E = List.end(); UI != E; ++UI) {
484 Value *Op = UI->getOperandValToReplace();
485 const Type *UseTy = Op->getType();
486 Instruction *User = UI->getUser();
488 // Compute the final addrec to expand into code.
489 const SCEV* AR = IU->getReplacementExpr(*UI);
492 if (AR->isLoopInvariant(L)) {
493 BasicBlock::iterator I = Rewriter.getInsertionPoint();
494 // Expand loop-invariant values in the loop preheader. They will
495 // be sunk to the exit block later, if possible.
497 Rewriter.expandCodeFor(AR, UseTy,
498 L->getLoopPreheader()->getTerminator());
499 Rewriter.setInsertionPoint(I);
502 // FIXME: It is an extremely bad idea to indvar substitute anything more
503 // complex than affine induction variables. Doing so will put expensive
504 // polynomial evaluations inside of the loop, and the str reduction pass
505 // currently can only reduce affine polynomials. For now just disable
506 // indvar subst on anything more complex than an affine addrec, unless
507 // it can be expanded to a trivial value.
508 if (!Stride->isLoopInvariant(L))
511 // Now expand it into actual Instructions and patch it into place.
512 NewVal = Rewriter.expandCodeFor(AR, UseTy);
515 // Patch the new value into place.
517 NewVal->takeName(Op);
518 User->replaceUsesOfWith(Op, NewVal);
519 UI->setOperandValToReplace(NewVal);
520 DOUT << "INDVARS: Rewrote IV '" << *AR << "' " << *Op
521 << " into = " << *NewVal << "\n";
525 // The old value may be dead now.
526 DeadInsts.push_back(Op);
530 // Clear the rewriter cache, because values that are in the rewriter's cache
531 // can be deleted in the loop below, causing the AssertingVH in the cache to
534 // Now that we're done iterating through lists, clean up any instructions
535 // which are now dead.
536 while (!DeadInsts.empty()) {
537 Instruction *Inst = dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val());
539 RecursivelyDeleteTriviallyDeadInstructions(Inst);
543 /// If there's a single exit block, sink any loop-invariant values that
544 /// were defined in the preheader but not used inside the loop into the
545 /// exit block to reduce register pressure in the loop.
546 void IndVarSimplify::SinkUnusedInvariants(Loop *L, SCEVExpander &Rewriter) {
547 BasicBlock *ExitBlock = L->getExitBlock();
548 if (!ExitBlock) return;
550 Instruction *NonPHI = ExitBlock->getFirstNonPHI();
551 BasicBlock *Preheader = L->getLoopPreheader();
552 BasicBlock::iterator I = Preheader->getTerminator();
553 while (I != Preheader->begin()) {
555 // New instructions were inserted at the end of the preheader. Only
556 // consider those new instructions.
557 if (!Rewriter.isInsertedInstruction(I))
559 // Determine if there is a use in or before the loop (direct or
561 bool UsedInLoop = false;
562 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
564 BasicBlock *UseBB = cast<Instruction>(UI)->getParent();
565 if (PHINode *P = dyn_cast<PHINode>(UI)) {
567 PHINode::getIncomingValueNumForOperand(UI.getOperandNo());
568 UseBB = P->getIncomingBlock(i);
570 if (UseBB == Preheader || L->contains(UseBB)) {
575 // If there is, the def must remain in the preheader.
578 // Otherwise, sink it to the exit block.
579 Instruction *ToMove = I;
581 if (I != Preheader->begin())
585 ToMove->moveBefore(NonPHI);
591 /// Re-schedule the inserted instructions to put defs before uses. This
592 /// fixes problems that arrise when SCEV expressions contain loop-variant
593 /// values unrelated to the induction variable which are defined inside the
594 /// loop. FIXME: It would be better to insert instructions in the right
595 /// place so that this step isn't needed.
596 void IndVarSimplify::FixUsesBeforeDefs(Loop *L, SCEVExpander &Rewriter) {
597 // Visit all the blocks in the loop in pre-order dom-tree dfs order.
598 DominatorTree *DT = &getAnalysis<DominatorTree>();
599 std::map<Instruction *, unsigned> NumPredsLeft;
600 SmallVector<DomTreeNode *, 16> Worklist;
601 Worklist.push_back(DT->getNode(L->getHeader()));
603 DomTreeNode *Node = Worklist.pop_back_val();
604 for (DomTreeNode::iterator I = Node->begin(), E = Node->end(); I != E; ++I)
605 if (L->contains((*I)->getBlock()))
606 Worklist.push_back(*I);
607 BasicBlock *BB = Node->getBlock();
608 // Visit all the instructions in the block top down.
609 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
610 // Count the number of operands that aren't properly dominating.
611 unsigned NumPreds = 0;
612 if (Rewriter.isInsertedInstruction(I) && !isa<PHINode>(I))
613 for (User::op_iterator OI = I->op_begin(), OE = I->op_end();
615 if (Instruction *Inst = dyn_cast<Instruction>(OI))
616 if (L->contains(Inst->getParent()) && !NumPredsLeft.count(Inst))
618 NumPredsLeft[I] = NumPreds;
619 // Notify uses of the position of this instruction, and move the
620 // users (and their dependents, recursively) into place after this
621 // instruction if it is their last outstanding operand.
622 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
624 Instruction *Inst = cast<Instruction>(UI);
625 std::map<Instruction *, unsigned>::iterator Z = NumPredsLeft.find(Inst);
626 if (Z != NumPredsLeft.end() && Z->second != 0 && --Z->second == 0) {
627 SmallVector<Instruction *, 4> UseWorkList;
628 UseWorkList.push_back(Inst);
629 BasicBlock::iterator InsertPt = I;
630 if (InvokeInst *II = dyn_cast<InvokeInst>(InsertPt))
631 InsertPt = II->getNormalDest()->begin();
634 while (isa<PHINode>(InsertPt)) ++InsertPt;
636 Instruction *Use = UseWorkList.pop_back_val();
637 Use->moveBefore(InsertPt);
638 NumPredsLeft.erase(Use);
639 for (Value::use_iterator IUI = Use->use_begin(),
640 IUE = Use->use_end(); IUI != IUE; ++IUI) {
641 Instruction *IUIInst = cast<Instruction>(IUI);
642 if (L->contains(IUIInst->getParent()) &&
643 Rewriter.isInsertedInstruction(IUIInst) &&
644 !isa<PHINode>(IUIInst))
645 UseWorkList.push_back(IUIInst);
647 } while (!UseWorkList.empty());
651 } while (!Worklist.empty());
654 /// Return true if it is OK to use SIToFPInst for an inducation variable
655 /// with given inital and exit values.
656 static bool useSIToFPInst(ConstantFP &InitV, ConstantFP &ExitV,
657 uint64_t intIV, uint64_t intEV) {
659 if (InitV.getValueAPF().isNegative() || ExitV.getValueAPF().isNegative())
662 // If the iteration range can be handled by SIToFPInst then use it.
663 APInt Max = APInt::getSignedMaxValue(32);
664 if (Max.getZExtValue() > static_cast<uint64_t>(abs64(intEV - intIV)))
670 /// convertToInt - Convert APF to an integer, if possible.
671 static bool convertToInt(const APFloat &APF, uint64_t *intVal) {
673 bool isExact = false;
674 if (&APF.getSemantics() == &APFloat::PPCDoubleDouble)
676 if (APF.convertToInteger(intVal, 32, APF.isNegative(),
677 APFloat::rmTowardZero, &isExact)
686 /// HandleFloatingPointIV - If the loop has floating induction variable
687 /// then insert corresponding integer induction variable if possible.
689 /// for(double i = 0; i < 10000; ++i)
691 /// is converted into
692 /// for(int i = 0; i < 10000; ++i)
695 void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PH) {
697 unsigned IncomingEdge = L->contains(PH->getIncomingBlock(0));
698 unsigned BackEdge = IncomingEdge^1;
700 // Check incoming value.
701 ConstantFP *InitValue = dyn_cast<ConstantFP>(PH->getIncomingValue(IncomingEdge));
702 if (!InitValue) return;
703 uint64_t newInitValue = Type::Int32Ty->getPrimitiveSizeInBits();
704 if (!convertToInt(InitValue->getValueAPF(), &newInitValue))
707 // Check IV increment. Reject this PH if increement operation is not
708 // an add or increment value can not be represented by an integer.
709 BinaryOperator *Incr =
710 dyn_cast<BinaryOperator>(PH->getIncomingValue(BackEdge));
712 if (Incr->getOpcode() != Instruction::FAdd) return;
713 ConstantFP *IncrValue = NULL;
714 unsigned IncrVIndex = 1;
715 if (Incr->getOperand(1) == PH)
717 IncrValue = dyn_cast<ConstantFP>(Incr->getOperand(IncrVIndex));
718 if (!IncrValue) return;
719 uint64_t newIncrValue = Type::Int32Ty->getPrimitiveSizeInBits();
720 if (!convertToInt(IncrValue->getValueAPF(), &newIncrValue))
723 // Check Incr uses. One user is PH and the other users is exit condition used
724 // by the conditional terminator.
725 Value::use_iterator IncrUse = Incr->use_begin();
726 Instruction *U1 = cast<Instruction>(IncrUse++);
727 if (IncrUse == Incr->use_end()) return;
728 Instruction *U2 = cast<Instruction>(IncrUse++);
729 if (IncrUse != Incr->use_end()) return;
731 // Find exit condition.
732 FCmpInst *EC = dyn_cast<FCmpInst>(U1);
734 EC = dyn_cast<FCmpInst>(U2);
737 if (BranchInst *BI = dyn_cast<BranchInst>(EC->getParent()->getTerminator())) {
738 if (!BI->isConditional()) return;
739 if (BI->getCondition() != EC) return;
742 // Find exit value. If exit value can not be represented as an interger then
743 // do not handle this floating point PH.
744 ConstantFP *EV = NULL;
745 unsigned EVIndex = 1;
746 if (EC->getOperand(1) == Incr)
748 EV = dyn_cast<ConstantFP>(EC->getOperand(EVIndex));
750 uint64_t intEV = Type::Int32Ty->getPrimitiveSizeInBits();
751 if (!convertToInt(EV->getValueAPF(), &intEV))
754 // Find new predicate for integer comparison.
755 CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE;
756 switch (EC->getPredicate()) {
757 case CmpInst::FCMP_OEQ:
758 case CmpInst::FCMP_UEQ:
759 NewPred = CmpInst::ICMP_EQ;
761 case CmpInst::FCMP_OGT:
762 case CmpInst::FCMP_UGT:
763 NewPred = CmpInst::ICMP_UGT;
765 case CmpInst::FCMP_OGE:
766 case CmpInst::FCMP_UGE:
767 NewPred = CmpInst::ICMP_UGE;
769 case CmpInst::FCMP_OLT:
770 case CmpInst::FCMP_ULT:
771 NewPred = CmpInst::ICMP_ULT;
773 case CmpInst::FCMP_OLE:
774 case CmpInst::FCMP_ULE:
775 NewPred = CmpInst::ICMP_ULE;
780 if (NewPred == CmpInst::BAD_ICMP_PREDICATE) return;
782 // Insert new integer induction variable.
783 PHINode *NewPHI = PHINode::Create(Type::Int32Ty,
784 PH->getName()+".int", PH);
785 NewPHI->addIncoming(ConstantInt::get(Type::Int32Ty, newInitValue),
786 PH->getIncomingBlock(IncomingEdge));
788 Value *NewAdd = BinaryOperator::CreateAdd(NewPHI,
789 ConstantInt::get(Type::Int32Ty,
791 Incr->getName()+".int", Incr);
792 NewPHI->addIncoming(NewAdd, PH->getIncomingBlock(BackEdge));
794 // The back edge is edge 1 of newPHI, whatever it may have been in the
796 ConstantInt *NewEV = ConstantInt::get(Type::Int32Ty, intEV);
797 Value *LHS = (EVIndex == 1 ? NewPHI->getIncomingValue(1) : NewEV);
798 Value *RHS = (EVIndex == 1 ? NewEV : NewPHI->getIncomingValue(1));
799 ICmpInst *NewEC = new ICmpInst(NewPred, LHS, RHS, EC->getNameStart(),
800 EC->getParent()->getTerminator());
802 // In the following deltions, PH may become dead and may be deleted.
803 // Use a WeakVH to observe whether this happens.
806 // Delete old, floating point, exit comparision instruction.
808 EC->replaceAllUsesWith(NewEC);
809 RecursivelyDeleteTriviallyDeadInstructions(EC);
811 // Delete old, floating point, increment instruction.
812 Incr->replaceAllUsesWith(UndefValue::get(Incr->getType()));
813 RecursivelyDeleteTriviallyDeadInstructions(Incr);
815 // Replace floating induction variable, if it isn't already deleted.
816 // Give SIToFPInst preference over UIToFPInst because it is faster on
817 // platforms that are widely used.
818 if (WeakPH && !PH->use_empty()) {
819 if (useSIToFPInst(*InitValue, *EV, newInitValue, intEV)) {
820 SIToFPInst *Conv = new SIToFPInst(NewPHI, PH->getType(), "indvar.conv",
821 PH->getParent()->getFirstNonPHI());
822 PH->replaceAllUsesWith(Conv);
824 UIToFPInst *Conv = new UIToFPInst(NewPHI, PH->getType(), "indvar.conv",
825 PH->getParent()->getFirstNonPHI());
826 PH->replaceAllUsesWith(Conv);
828 RecursivelyDeleteTriviallyDeadInstructions(PH);
831 // Add a new IVUsers entry for the newly-created integer PHI.
832 IU->AddUsersIfInteresting(NewPHI);