1 //===-- Local.cpp - Functions to perform local transformations ------------===//
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 family of functions perform various local transformations to the
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Transforms/Utils/Local.h"
16 #include "llvm/Constants.h"
17 #include "llvm/GlobalAlias.h"
18 #include "llvm/GlobalVariable.h"
19 #include "llvm/DerivedTypes.h"
20 #include "llvm/Instructions.h"
21 #include "llvm/Intrinsics.h"
22 #include "llvm/IntrinsicInst.h"
23 #include "llvm/ADT/DenseMap.h"
24 #include "llvm/ADT/SmallPtrSet.h"
25 #include "llvm/Analysis/Dominators.h"
26 #include "llvm/Analysis/ConstantFolding.h"
27 #include "llvm/Analysis/InstructionSimplify.h"
28 #include "llvm/Analysis/ProfileInfo.h"
29 #include "llvm/Analysis/ValueTracking.h"
30 #include "llvm/Target/TargetData.h"
31 #include "llvm/Support/CFG.h"
32 #include "llvm/Support/Debug.h"
33 #include "llvm/Support/GetElementPtrTypeIterator.h"
34 #include "llvm/Support/MathExtras.h"
35 #include "llvm/Support/ValueHandle.h"
36 #include "llvm/Support/raw_ostream.h"
39 //===----------------------------------------------------------------------===//
40 // Local constant propagation.
43 // ConstantFoldTerminator - If a terminator instruction is predicated on a
44 // constant value, convert it into an unconditional branch to the constant
47 bool llvm::ConstantFoldTerminator(BasicBlock *BB) {
48 TerminatorInst *T = BB->getTerminator();
50 // Branch - See if we are conditional jumping on constant
51 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
52 if (BI->isUnconditional()) return false; // Can't optimize uncond branch
53 BasicBlock *Dest1 = BI->getSuccessor(0);
54 BasicBlock *Dest2 = BI->getSuccessor(1);
56 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
57 // Are we branching on constant?
58 // YES. Change to unconditional branch...
59 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
60 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1;
62 //cerr << "Function: " << T->getParent()->getParent()
63 // << "\nRemoving branch from " << T->getParent()
64 // << "\n\nTo: " << OldDest << endl;
66 // Let the basic block know that we are letting go of it. Based on this,
67 // it will adjust it's PHI nodes.
68 assert(BI->getParent() && "Terminator not inserted in block!");
69 OldDest->removePredecessor(BI->getParent());
71 // Replace the conditional branch with an unconditional one.
72 BranchInst::Create(Destination, BI);
73 BI->eraseFromParent();
77 if (Dest2 == Dest1) { // Conditional branch to same location?
78 // This branch matches something like this:
79 // br bool %cond, label %Dest, label %Dest
80 // and changes it into: br label %Dest
82 // Let the basic block know that we are letting go of one copy of it.
83 assert(BI->getParent() && "Terminator not inserted in block!");
84 Dest1->removePredecessor(BI->getParent());
86 // Replace the conditional branch with an unconditional one.
87 BranchInst::Create(Dest1, BI);
88 BI->eraseFromParent();
94 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
95 // If we are switching on a constant, we can convert the switch into a
96 // single branch instruction!
97 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
98 BasicBlock *TheOnlyDest = SI->getSuccessor(0); // The default dest
99 BasicBlock *DefaultDest = TheOnlyDest;
100 assert(TheOnlyDest == SI->getDefaultDest() &&
101 "Default destination is not successor #0?");
103 // Figure out which case it goes to.
104 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
105 // Found case matching a constant operand?
106 if (SI->getSuccessorValue(i) == CI) {
107 TheOnlyDest = SI->getSuccessor(i);
111 // Check to see if this branch is going to the same place as the default
112 // dest. If so, eliminate it as an explicit compare.
113 if (SI->getSuccessor(i) == DefaultDest) {
114 // Remove this entry.
115 DefaultDest->removePredecessor(SI->getParent());
117 --i; --e; // Don't skip an entry...
121 // Otherwise, check to see if the switch only branches to one destination.
122 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
124 if (SI->getSuccessor(i) != TheOnlyDest) TheOnlyDest = 0;
127 if (CI && !TheOnlyDest) {
128 // Branching on a constant, but not any of the cases, go to the default
130 TheOnlyDest = SI->getDefaultDest();
133 // If we found a single destination that we can fold the switch into, do so
136 // Insert the new branch.
137 BranchInst::Create(TheOnlyDest, SI);
138 BasicBlock *BB = SI->getParent();
140 // Remove entries from PHI nodes which we no longer branch to...
141 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
142 // Found case matching a constant operand?
143 BasicBlock *Succ = SI->getSuccessor(i);
144 if (Succ == TheOnlyDest)
145 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest
147 Succ->removePredecessor(BB);
150 // Delete the old switch.
151 BB->getInstList().erase(SI);
155 if (SI->getNumSuccessors() == 2) {
156 // Otherwise, we can fold this switch into a conditional branch
157 // instruction if it has only one non-default destination.
158 Value *Cond = new ICmpInst(SI, ICmpInst::ICMP_EQ, SI->getCondition(),
159 SI->getSuccessorValue(1), "cond");
160 // Insert the new branch.
161 BranchInst::Create(SI->getSuccessor(1), SI->getSuccessor(0), Cond, SI);
163 // Delete the old switch.
164 SI->eraseFromParent();
170 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
171 // indirectbr blockaddress(@F, @BB) -> br label @BB
172 if (BlockAddress *BA =
173 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
174 BasicBlock *TheOnlyDest = BA->getBasicBlock();
175 // Insert the new branch.
176 BranchInst::Create(TheOnlyDest, IBI);
178 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
179 if (IBI->getDestination(i) == TheOnlyDest)
182 IBI->getDestination(i)->removePredecessor(IBI->getParent());
184 IBI->eraseFromParent();
186 // If we didn't find our destination in the IBI successor list, then we
187 // have undefined behavior. Replace the unconditional branch with an
188 // 'unreachable' instruction.
190 BB->getTerminator()->eraseFromParent();
191 new UnreachableInst(BB->getContext(), BB);
202 //===----------------------------------------------------------------------===//
203 // Local dead code elimination.
206 /// isInstructionTriviallyDead - Return true if the result produced by the
207 /// instruction is not used, and the instruction has no side effects.
209 bool llvm::isInstructionTriviallyDead(Instruction *I) {
210 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
212 // We don't want debug info removed by anything this general.
213 if (isa<DbgInfoIntrinsic>(I)) return false;
215 if (!I->mayHaveSideEffects()) return true;
217 // Special case intrinsics that "may have side effects" but can be deleted
219 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
220 // Safe to delete llvm.stacksave if dead.
221 if (II->getIntrinsicID() == Intrinsic::stacksave)
226 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
227 /// trivially dead instruction, delete it. If that makes any of its operands
228 /// trivially dead, delete them too, recursively. Return true if any
229 /// instructions were deleted.
230 bool llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V) {
231 Instruction *I = dyn_cast<Instruction>(V);
232 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I))
235 SmallVector<Instruction*, 16> DeadInsts;
236 DeadInsts.push_back(I);
239 I = DeadInsts.pop_back_val();
241 // Null out all of the instruction's operands to see if any operand becomes
243 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
244 Value *OpV = I->getOperand(i);
247 if (!OpV->use_empty()) continue;
249 // If the operand is an instruction that became dead as we nulled out the
250 // operand, and if it is 'trivially' dead, delete it in a future loop
252 if (Instruction *OpI = dyn_cast<Instruction>(OpV))
253 if (isInstructionTriviallyDead(OpI))
254 DeadInsts.push_back(OpI);
257 I->eraseFromParent();
258 } while (!DeadInsts.empty());
263 /// areAllUsesEqual - Check whether the uses of a value are all the same.
264 /// This is similar to Instruction::hasOneUse() except this will also return
265 /// true when there are no uses or multiple uses that all refer to the same
267 static bool areAllUsesEqual(Instruction *I) {
268 Value::use_iterator UI = I->use_begin();
269 Value::use_iterator UE = I->use_end();
274 for (++UI; UI != UE; ++UI) {
281 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
282 /// dead PHI node, due to being a def-use chain of single-use nodes that
283 /// either forms a cycle or is terminated by a trivially dead instruction,
284 /// delete it. If that makes any of its operands trivially dead, delete them
285 /// too, recursively. Return true if a change was made.
286 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) {
287 SmallPtrSet<Instruction*, 4> Visited;
288 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
289 I = cast<Instruction>(*I->use_begin())) {
291 return RecursivelyDeleteTriviallyDeadInstructions(I);
293 // If we find an instruction more than once, we're on a cycle that
294 // won't prove fruitful.
295 if (!Visited.insert(I)) {
296 // Break the cycle and delete the instruction and its operands.
297 I->replaceAllUsesWith(UndefValue::get(I->getType()));
298 (void)RecursivelyDeleteTriviallyDeadInstructions(I);
305 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
306 /// simplify any instructions in it and recursively delete dead instructions.
308 /// This returns true if it changed the code, note that it can delete
309 /// instructions in other blocks as well in this block.
310 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD) {
311 bool MadeChange = false;
312 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
313 Instruction *Inst = BI++;
315 if (Value *V = SimplifyInstruction(Inst, TD)) {
317 ReplaceAndSimplifyAllUses(Inst, V, TD);
324 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst);
329 //===----------------------------------------------------------------------===//
330 // Control Flow Graph Restructuring.
334 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
335 /// method is called when we're about to delete Pred as a predecessor of BB. If
336 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
338 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
339 /// nodes that collapse into identity values. For example, if we have:
340 /// x = phi(1, 0, 0, 0)
343 /// .. and delete the predecessor corresponding to the '1', this will attempt to
344 /// recursively fold the and to 0.
345 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
347 // This only adjusts blocks with PHI nodes.
348 if (!isa<PHINode>(BB->begin()))
351 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
352 // them down. This will leave us with single entry phi nodes and other phis
353 // that can be removed.
354 BB->removePredecessor(Pred, true);
356 WeakVH PhiIt = &BB->front();
357 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
358 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
360 Value *PNV = SimplifyInstruction(PN, TD);
361 if (PNV == 0) continue;
363 // If we're able to simplify the phi to a single value, substitute the new
364 // value into all of its uses.
365 assert(PNV != PN && "SimplifyInstruction broken!");
367 Value *OldPhiIt = PhiIt;
368 ReplaceAndSimplifyAllUses(PN, PNV, TD);
370 // If recursive simplification ended up deleting the next PHI node we would
371 // iterate to, then our iterator is invalid, restart scanning from the top
373 if (PhiIt != OldPhiIt) PhiIt = &BB->front();
378 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
379 /// predecessor is known to have one successor (DestBB!). Eliminate the edge
380 /// between them, moving the instructions in the predecessor into DestBB and
381 /// deleting the predecessor block.
383 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) {
384 // If BB has single-entry PHI nodes, fold them.
385 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
386 Value *NewVal = PN->getIncomingValue(0);
387 // Replace self referencing PHI with undef, it must be dead.
388 if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
389 PN->replaceAllUsesWith(NewVal);
390 PN->eraseFromParent();
393 BasicBlock *PredBB = DestBB->getSinglePredecessor();
394 assert(PredBB && "Block doesn't have a single predecessor!");
396 // Splice all the instructions from PredBB to DestBB.
397 PredBB->getTerminator()->eraseFromParent();
398 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
400 // Zap anything that took the address of DestBB. Not doing this will give the
401 // address an invalid value.
402 if (DestBB->hasAddressTaken()) {
403 BlockAddress *BA = BlockAddress::get(DestBB);
404 Constant *Replacement =
405 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1);
406 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
408 BA->destroyConstant();
411 // Anything that branched to PredBB now branches to DestBB.
412 PredBB->replaceAllUsesWith(DestBB);
415 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>();
417 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock();
418 DT->changeImmediateDominator(DestBB, PredBBIDom);
419 DT->eraseNode(PredBB);
421 ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>();
423 PI->replaceAllUses(PredBB, DestBB);
424 PI->removeEdge(ProfileInfo::getEdge(PredBB, DestBB));
428 PredBB->eraseFromParent();
431 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
432 /// almost-empty BB ending in an unconditional branch to Succ, into succ.
434 /// Assumption: Succ is the single successor for BB.
436 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
437 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
439 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
440 << Succ->getName() << "\n");
441 // Shortcut, if there is only a single predecessor it must be BB and merging
443 if (Succ->getSinglePredecessor()) return true;
445 // Make a list of the predecessors of BB
446 typedef SmallPtrSet<BasicBlock*, 16> BlockSet;
447 BlockSet BBPreds(pred_begin(BB), pred_end(BB));
449 // Use that list to make another list of common predecessors of BB and Succ
450 BlockSet CommonPreds;
451 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
454 if (BBPreds.count(P))
455 CommonPreds.insert(P);
458 // Shortcut, if there are no common predecessors, merging is always safe
459 if (CommonPreds.empty())
462 // Look at all the phi nodes in Succ, to see if they present a conflict when
463 // merging these blocks
464 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
465 PHINode *PN = cast<PHINode>(I);
467 // If the incoming value from BB is again a PHINode in
468 // BB which has the same incoming value for *PI as PN does, we can
469 // merge the phi nodes and then the blocks can still be merged
470 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
471 if (BBPN && BBPN->getParent() == BB) {
472 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
474 if (BBPN->getIncomingValueForBlock(*PI)
475 != PN->getIncomingValueForBlock(*PI)) {
476 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
477 << Succ->getName() << " is conflicting with "
478 << BBPN->getName() << " with regard to common predecessor "
479 << (*PI)->getName() << "\n");
484 Value* Val = PN->getIncomingValueForBlock(BB);
485 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
487 // See if the incoming value for the common predecessor is equal to the
488 // one for BB, in which case this phi node will not prevent the merging
490 if (Val != PN->getIncomingValueForBlock(*PI)) {
491 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
492 << Succ->getName() << " is conflicting with regard to common "
493 << "predecessor " << (*PI)->getName() << "\n");
503 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
504 /// unconditional branch, and contains no instructions other than PHI nodes,
505 /// potential debug intrinsics and the branch. If possible, eliminate BB by
506 /// rewriting all the predecessors to branch to the successor block and return
507 /// true. If we can't transform, return false.
508 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
509 assert(BB != &BB->getParent()->getEntryBlock() &&
510 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
512 // We can't eliminate infinite loops.
513 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
514 if (BB == Succ) return false;
516 // Check to see if merging these blocks would cause conflicts for any of the
517 // phi nodes in BB or Succ. If not, we can safely merge.
518 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
520 // Check for cases where Succ has multiple predecessors and a PHI node in BB
521 // has uses which will not disappear when the PHI nodes are merged. It is
522 // possible to handle such cases, but difficult: it requires checking whether
523 // BB dominates Succ, which is non-trivial to calculate in the case where
524 // Succ has multiple predecessors. Also, it requires checking whether
525 // constructing the necessary self-referential PHI node doesn't intoduce any
526 // conflicts; this isn't too difficult, but the previous code for doing this
529 // Note that if this check finds a live use, BB dominates Succ, so BB is
530 // something like a loop pre-header (or rarely, a part of an irreducible CFG);
531 // folding the branch isn't profitable in that case anyway.
532 if (!Succ->getSinglePredecessor()) {
533 BasicBlock::iterator BBI = BB->begin();
534 while (isa<PHINode>(*BBI)) {
535 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
537 if (PHINode* PN = dyn_cast<PHINode>(*UI)) {
538 if (PN->getIncomingBlock(UI) != BB)
548 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
550 if (isa<PHINode>(Succ->begin())) {
551 // If there is more than one pred of succ, and there are PHI nodes in
552 // the successor, then we need to add incoming edges for the PHI nodes
554 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
556 // Loop over all of the PHI nodes in the successor of BB.
557 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
558 PHINode *PN = cast<PHINode>(I);
559 Value *OldVal = PN->removeIncomingValue(BB, false);
560 assert(OldVal && "No entry in PHI for Pred BB!");
562 // If this incoming value is one of the PHI nodes in BB, the new entries
563 // in the PHI node are the entries from the old PHI.
564 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
565 PHINode *OldValPN = cast<PHINode>(OldVal);
566 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
567 // Note that, since we are merging phi nodes and BB and Succ might
568 // have common predecessors, we could end up with a phi node with
569 // identical incoming branches. This will be cleaned up later (and
570 // will trigger asserts if we try to clean it up now, without also
571 // simplifying the corresponding conditional branch).
572 PN->addIncoming(OldValPN->getIncomingValue(i),
573 OldValPN->getIncomingBlock(i));
575 // Add an incoming value for each of the new incoming values.
576 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
577 PN->addIncoming(OldVal, BBPreds[i]);
582 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
583 if (Succ->getSinglePredecessor()) {
584 // BB is the only predecessor of Succ, so Succ will end up with exactly
585 // the same predecessors BB had.
586 Succ->getInstList().splice(Succ->begin(),
587 BB->getInstList(), BB->begin());
589 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
590 assert(PN->use_empty() && "There shouldn't be any uses here!");
591 PN->eraseFromParent();
595 // Everything that jumped to BB now goes to Succ.
596 BB->replaceAllUsesWith(Succ);
597 if (!Succ->hasName()) Succ->takeName(BB);
598 BB->eraseFromParent(); // Delete the old basic block.
602 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
603 /// nodes in this block. This doesn't try to be clever about PHI nodes
604 /// which differ only in the order of the incoming values, but instcombine
605 /// orders them so it usually won't matter.
607 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
608 bool Changed = false;
610 // This implementation doesn't currently consider undef operands
611 // specially. Theroetically, two phis which are identical except for
612 // one having an undef where the other doesn't could be collapsed.
614 // Map from PHI hash values to PHI nodes. If multiple PHIs have
615 // the same hash value, the element is the first PHI in the
616 // linked list in CollisionMap.
617 DenseMap<uintptr_t, PHINode *> HashMap;
619 // Maintain linked lists of PHI nodes with common hash values.
620 DenseMap<PHINode *, PHINode *> CollisionMap;
623 for (BasicBlock::iterator I = BB->begin();
624 PHINode *PN = dyn_cast<PHINode>(I++); ) {
625 // Compute a hash value on the operands. Instcombine will likely have sorted
626 // them, which helps expose duplicates, but we have to check all the
627 // operands to be safe in case instcombine hasn't run.
629 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
630 // This hash algorithm is quite weak as hash functions go, but it seems
631 // to do a good enough job for this particular purpose, and is very quick.
632 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
633 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
635 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1.
637 // If we've never seen this hash value before, it's a unique PHI.
638 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
639 HashMap.insert(std::make_pair(Hash, PN));
640 if (Pair.second) continue;
641 // Otherwise it's either a duplicate or a hash collision.
642 for (PHINode *OtherPN = Pair.first->second; ; ) {
643 if (OtherPN->isIdenticalTo(PN)) {
644 // A duplicate. Replace this PHI with its duplicate.
645 PN->replaceAllUsesWith(OtherPN);
646 PN->eraseFromParent();
650 // A non-duplicate hash collision.
651 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
652 if (I == CollisionMap.end()) {
653 // Set this PHI to be the head of the linked list of colliding PHIs.
654 PHINode *Old = Pair.first->second;
655 Pair.first->second = PN;
656 CollisionMap[PN] = Old;
659 // Procede to the next PHI in the list.
667 /// enforceKnownAlignment - If the specified pointer points to an object that
668 /// we control, modify the object's alignment to PrefAlign. This isn't
669 /// often possible though. If alignment is important, a more reliable approach
670 /// is to simply align all global variables and allocation instructions to
671 /// their preferred alignment from the beginning.
673 static unsigned enforceKnownAlignment(Value *V, unsigned Align,
674 unsigned PrefAlign) {
676 User *U = dyn_cast<User>(V);
677 if (!U) return Align;
679 switch (Operator::getOpcode(U)) {
681 case Instruction::BitCast:
682 return enforceKnownAlignment(U->getOperand(0), Align, PrefAlign);
683 case Instruction::GetElementPtr: {
684 // If all indexes are zero, it is just the alignment of the base pointer.
685 bool AllZeroOperands = true;
686 for (User::op_iterator i = U->op_begin() + 1, e = U->op_end(); i != e; ++i)
687 if (!isa<Constant>(*i) ||
688 !cast<Constant>(*i)->isNullValue()) {
689 AllZeroOperands = false;
693 if (AllZeroOperands) {
694 // Treat this like a bitcast.
695 return enforceKnownAlignment(U->getOperand(0), Align, PrefAlign);
699 case Instruction::Alloca: {
700 AllocaInst *AI = cast<AllocaInst>(V);
701 // If there is a requested alignment and if this is an alloca, round up.
702 if (AI->getAlignment() >= PrefAlign)
703 return AI->getAlignment();
704 AI->setAlignment(PrefAlign);
709 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
710 // If there is a large requested alignment and we can, bump up the alignment
712 if (GV->isDeclaration()) return Align;
714 if (GV->getAlignment() >= PrefAlign)
715 return GV->getAlignment();
716 // We can only increase the alignment of the global if it has no alignment
717 // specified or if it is not assigned a section. If it is assigned a
718 // section, the global could be densely packed with other objects in the
719 // section, increasing the alignment could cause padding issues.
720 if (!GV->hasSection() || GV->getAlignment() == 0)
721 GV->setAlignment(PrefAlign);
722 return GV->getAlignment();
728 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
729 /// we can determine, return it, otherwise return 0. If PrefAlign is specified,
730 /// and it is more than the alignment of the ultimate object, see if we can
731 /// increase the alignment of the ultimate object, making this check succeed.
732 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
733 const TargetData *TD) {
734 assert(V->getType()->isPointerTy() &&
735 "getOrEnforceKnownAlignment expects a pointer!");
736 unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64;
737 APInt Mask = APInt::getAllOnesValue(BitWidth);
738 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
739 ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD);
740 unsigned TrailZ = KnownZero.countTrailingOnes();
742 // Avoid trouble with rediculously large TrailZ values, such as
743 // those computed from a null pointer.
744 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
746 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
748 // LLVM doesn't support alignments larger than this currently.
749 Align = std::min(Align, +Value::MaximumAlignment);
751 if (PrefAlign > Align)
752 Align = enforceKnownAlignment(V, Align, PrefAlign);
754 // We don't need to make any adjustment.