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/ConstantFolding.h"
26 #include "llvm/Analysis/InstructionSimplify.h"
27 #include "llvm/Analysis/ProfileInfo.h"
28 #include "llvm/Analysis/ValueTracking.h"
29 #include "llvm/Target/TargetData.h"
30 #include "llvm/Support/CFG.h"
31 #include "llvm/Support/Debug.h"
32 #include "llvm/Support/GetElementPtrTypeIterator.h"
33 #include "llvm/Support/MathExtras.h"
34 #include "llvm/Support/ValueHandle.h"
35 #include "llvm/Support/raw_ostream.h"
38 //===----------------------------------------------------------------------===//
39 // Local constant propagation.
42 // ConstantFoldTerminator - If a terminator instruction is predicated on a
43 // constant value, convert it into an unconditional branch to the constant
46 bool llvm::ConstantFoldTerminator(BasicBlock *BB) {
47 TerminatorInst *T = BB->getTerminator();
49 // Branch - See if we are conditional jumping on constant
50 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
51 if (BI->isUnconditional()) return false; // Can't optimize uncond branch
52 BasicBlock *Dest1 = BI->getSuccessor(0);
53 BasicBlock *Dest2 = BI->getSuccessor(1);
55 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
56 // Are we branching on constant?
57 // YES. Change to unconditional branch...
58 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
59 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1;
61 //cerr << "Function: " << T->getParent()->getParent()
62 // << "\nRemoving branch from " << T->getParent()
63 // << "\n\nTo: " << OldDest << endl;
65 // Let the basic block know that we are letting go of it. Based on this,
66 // it will adjust it's PHI nodes.
67 assert(BI->getParent() && "Terminator not inserted in block!");
68 OldDest->removePredecessor(BI->getParent());
70 // Set the unconditional destination, and change the insn to be an
71 // unconditional branch.
72 BI->setUnconditionalDest(Destination);
76 if (Dest2 == Dest1) { // Conditional branch to same location?
77 // This branch matches something like this:
78 // br bool %cond, label %Dest, label %Dest
79 // and changes it into: br label %Dest
81 // Let the basic block know that we are letting go of one copy of it.
82 assert(BI->getParent() && "Terminator not inserted in block!");
83 Dest1->removePredecessor(BI->getParent());
85 // Change a conditional branch to unconditional.
86 BI->setUnconditionalDest(Dest1);
92 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
93 // If we are switching on a constant, we can convert the switch into a
94 // single branch instruction!
95 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
96 BasicBlock *TheOnlyDest = SI->getSuccessor(0); // The default dest
97 BasicBlock *DefaultDest = TheOnlyDest;
98 assert(TheOnlyDest == SI->getDefaultDest() &&
99 "Default destination is not successor #0?");
101 // Figure out which case it goes to.
102 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
103 // Found case matching a constant operand?
104 if (SI->getSuccessorValue(i) == CI) {
105 TheOnlyDest = SI->getSuccessor(i);
109 // Check to see if this branch is going to the same place as the default
110 // dest. If so, eliminate it as an explicit compare.
111 if (SI->getSuccessor(i) == DefaultDest) {
112 // Remove this entry.
113 DefaultDest->removePredecessor(SI->getParent());
115 --i; --e; // Don't skip an entry...
119 // Otherwise, check to see if the switch only branches to one destination.
120 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
122 if (SI->getSuccessor(i) != TheOnlyDest) TheOnlyDest = 0;
125 if (CI && !TheOnlyDest) {
126 // Branching on a constant, but not any of the cases, go to the default
128 TheOnlyDest = SI->getDefaultDest();
131 // If we found a single destination that we can fold the switch into, do so
134 // Insert the new branch.
135 BranchInst::Create(TheOnlyDest, SI);
136 BasicBlock *BB = SI->getParent();
138 // Remove entries from PHI nodes which we no longer branch to...
139 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
140 // Found case matching a constant operand?
141 BasicBlock *Succ = SI->getSuccessor(i);
142 if (Succ == TheOnlyDest)
143 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest
145 Succ->removePredecessor(BB);
148 // Delete the old switch.
149 BB->getInstList().erase(SI);
153 if (SI->getNumSuccessors() == 2) {
154 // Otherwise, we can fold this switch into a conditional branch
155 // instruction if it has only one non-default destination.
156 Value *Cond = new ICmpInst(SI, ICmpInst::ICMP_EQ, SI->getCondition(),
157 SI->getSuccessorValue(1), "cond");
158 // Insert the new branch.
159 BranchInst::Create(SI->getSuccessor(1), SI->getSuccessor(0), Cond, SI);
161 // Delete the old switch.
162 SI->eraseFromParent();
168 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
169 // indirectbr blockaddress(@F, @BB) -> br label @BB
170 if (BlockAddress *BA =
171 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
172 BasicBlock *TheOnlyDest = BA->getBasicBlock();
173 // Insert the new branch.
174 BranchInst::Create(TheOnlyDest, IBI);
176 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
177 if (IBI->getDestination(i) == TheOnlyDest)
180 IBI->getDestination(i)->removePredecessor(IBI->getParent());
182 IBI->eraseFromParent();
184 // If we didn't find our destination in the IBI successor list, then we
185 // have undefined behavior. Replace the unconditional branch with an
186 // 'unreachable' instruction.
188 BB->getTerminator()->eraseFromParent();
189 new UnreachableInst(BB->getContext(), BB);
200 //===----------------------------------------------------------------------===//
201 // Local dead code elimination.
204 /// isInstructionTriviallyDead - Return true if the result produced by the
205 /// instruction is not used, and the instruction has no side effects.
207 bool llvm::isInstructionTriviallyDead(Instruction *I) {
208 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
210 // We don't want debug info removed by anything this general.
211 if (isa<DbgInfoIntrinsic>(I)) return false;
213 if (!I->mayHaveSideEffects()) return true;
215 // Special case intrinsics that "may have side effects" but can be deleted
217 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
218 // Safe to delete llvm.stacksave if dead.
219 if (II->getIntrinsicID() == Intrinsic::stacksave)
224 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
225 /// trivially dead instruction, delete it. If that makes any of its operands
226 /// trivially dead, delete them too, recursively. Return true if any
227 /// instructions were deleted.
228 bool llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V) {
229 Instruction *I = dyn_cast<Instruction>(V);
230 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I))
233 SmallVector<Instruction*, 16> DeadInsts;
234 DeadInsts.push_back(I);
237 I = DeadInsts.pop_back_val();
239 // Null out all of the instruction's operands to see if any operand becomes
241 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
242 Value *OpV = I->getOperand(i);
245 if (!OpV->use_empty()) continue;
247 // If the operand is an instruction that became dead as we nulled out the
248 // operand, and if it is 'trivially' dead, delete it in a future loop
250 if (Instruction *OpI = dyn_cast<Instruction>(OpV))
251 if (isInstructionTriviallyDead(OpI))
252 DeadInsts.push_back(OpI);
255 I->eraseFromParent();
256 } while (!DeadInsts.empty());
261 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
262 /// dead PHI node, due to being a def-use chain of single-use nodes that
263 /// either forms a cycle or is terminated by a trivially dead instruction,
264 /// delete it. If that makes any of its operands trivially dead, delete them
265 /// too, recursively. Return true if the PHI node is actually deleted.
267 llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) {
268 // We can remove a PHI if it is on a cycle in the def-use graph
269 // where each node in the cycle has degree one, i.e. only one use,
270 // and is an instruction with no side effects.
271 if (!PN->hasOneUse())
274 bool Changed = false;
275 SmallPtrSet<PHINode *, 4> PHIs;
277 for (Instruction *J = cast<Instruction>(*PN->use_begin());
278 J->hasOneUse() && !J->mayHaveSideEffects();
279 J = cast<Instruction>(*J->use_begin()))
280 // If we find a PHI more than once, we're on a cycle that
281 // won't prove fruitful.
282 if (PHINode *JP = dyn_cast<PHINode>(J))
283 if (!PHIs.insert(cast<PHINode>(JP))) {
284 // Break the cycle and delete the PHI and its operands.
285 JP->replaceAllUsesWith(UndefValue::get(JP->getType()));
286 (void)RecursivelyDeleteTriviallyDeadInstructions(JP);
293 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
294 /// simplify any instructions in it and recursively delete dead instructions.
296 /// This returns true if it changed the code, note that it can delete
297 /// instructions in other blocks as well in this block.
298 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD) {
299 bool MadeChange = false;
300 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
301 Instruction *Inst = BI++;
303 if (Value *V = SimplifyInstruction(Inst, TD)) {
305 ReplaceAndSimplifyAllUses(Inst, V, TD);
312 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst);
317 //===----------------------------------------------------------------------===//
318 // Control Flow Graph Restructuring.
322 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
323 /// method is called when we're about to delete Pred as a predecessor of BB. If
324 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
326 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
327 /// nodes that collapse into identity values. For example, if we have:
328 /// x = phi(1, 0, 0, 0)
331 /// .. and delete the predecessor corresponding to the '1', this will attempt to
332 /// recursively fold the and to 0.
333 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
335 // This only adjusts blocks with PHI nodes.
336 if (!isa<PHINode>(BB->begin()))
339 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
340 // them down. This will leave us with single entry phi nodes and other phis
341 // that can be removed.
342 BB->removePredecessor(Pred, true);
344 WeakVH PhiIt = &BB->front();
345 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
346 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
348 Value *PNV = SimplifyInstruction(PN, TD);
349 if (PNV == 0) continue;
351 // If we're able to simplify the phi to a single value, substitute the new
352 // value into all of its uses.
353 assert(PNV != PN && "SimplifyInstruction broken!");
355 Value *OldPhiIt = PhiIt;
356 ReplaceAndSimplifyAllUses(PN, PNV, TD);
358 // If recursive simplification ended up deleting the next PHI node we would
359 // iterate to, then our iterator is invalid, restart scanning from the top
361 if (PhiIt != OldPhiIt) PhiIt = &BB->front();
366 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
367 /// predecessor is known to have one successor (DestBB!). Eliminate the edge
368 /// between them, moving the instructions in the predecessor into DestBB and
369 /// deleting the predecessor block.
371 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) {
372 // If BB has single-entry PHI nodes, fold them.
373 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
374 Value *NewVal = PN->getIncomingValue(0);
375 // Replace self referencing PHI with undef, it must be dead.
376 if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
377 PN->replaceAllUsesWith(NewVal);
378 PN->eraseFromParent();
381 BasicBlock *PredBB = DestBB->getSinglePredecessor();
382 assert(PredBB && "Block doesn't have a single predecessor!");
384 // Splice all the instructions from PredBB to DestBB.
385 PredBB->getTerminator()->eraseFromParent();
386 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
388 // Zap anything that took the address of DestBB. Not doing this will give the
389 // address an invalid value.
390 if (DestBB->hasAddressTaken()) {
391 BlockAddress *BA = BlockAddress::get(DestBB);
392 Constant *Replacement =
393 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1);
394 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
396 BA->destroyConstant();
399 // Anything that branched to PredBB now branches to DestBB.
400 PredBB->replaceAllUsesWith(DestBB);
403 ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>();
405 PI->replaceAllUses(PredBB, DestBB);
406 PI->removeEdge(ProfileInfo::getEdge(PredBB, DestBB));
410 PredBB->eraseFromParent();
413 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
414 /// almost-empty BB ending in an unconditional branch to Succ, into succ.
416 /// Assumption: Succ is the single successor for BB.
418 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
419 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
421 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
422 << Succ->getName() << "\n");
423 // Shortcut, if there is only a single predecessor it must be BB and merging
425 if (Succ->getSinglePredecessor()) return true;
427 // Make a list of the predecessors of BB
428 typedef SmallPtrSet<BasicBlock*, 16> BlockSet;
429 BlockSet BBPreds(pred_begin(BB), pred_end(BB));
431 // Use that list to make another list of common predecessors of BB and Succ
432 BlockSet CommonPreds;
433 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
436 if (BBPreds.count(P))
437 CommonPreds.insert(P);
440 // Shortcut, if there are no common predecessors, merging is always safe
441 if (CommonPreds.empty())
444 // Look at all the phi nodes in Succ, to see if they present a conflict when
445 // merging these blocks
446 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
447 PHINode *PN = cast<PHINode>(I);
449 // If the incoming value from BB is again a PHINode in
450 // BB which has the same incoming value for *PI as PN does, we can
451 // merge the phi nodes and then the blocks can still be merged
452 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
453 if (BBPN && BBPN->getParent() == BB) {
454 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
456 if (BBPN->getIncomingValueForBlock(*PI)
457 != PN->getIncomingValueForBlock(*PI)) {
458 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
459 << Succ->getName() << " is conflicting with "
460 << BBPN->getName() << " with regard to common predecessor "
461 << (*PI)->getName() << "\n");
466 Value* Val = PN->getIncomingValueForBlock(BB);
467 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
469 // See if the incoming value for the common predecessor is equal to the
470 // one for BB, in which case this phi node will not prevent the merging
472 if (Val != PN->getIncomingValueForBlock(*PI)) {
473 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
474 << Succ->getName() << " is conflicting with regard to common "
475 << "predecessor " << (*PI)->getName() << "\n");
485 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
486 /// unconditional branch, and contains no instructions other than PHI nodes,
487 /// potential debug intrinsics and the branch. If possible, eliminate BB by
488 /// rewriting all the predecessors to branch to the successor block and return
489 /// true. If we can't transform, return false.
490 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
491 assert(BB != &BB->getParent()->getEntryBlock() &&
492 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
494 // We can't eliminate infinite loops.
495 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
496 if (BB == Succ) return false;
498 // Check to see if merging these blocks would cause conflicts for any of the
499 // phi nodes in BB or Succ. If not, we can safely merge.
500 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
502 // Check for cases where Succ has multiple predecessors and a PHI node in BB
503 // has uses which will not disappear when the PHI nodes are merged. It is
504 // possible to handle such cases, but difficult: it requires checking whether
505 // BB dominates Succ, which is non-trivial to calculate in the case where
506 // Succ has multiple predecessors. Also, it requires checking whether
507 // constructing the necessary self-referential PHI node doesn't intoduce any
508 // conflicts; this isn't too difficult, but the previous code for doing this
511 // Note that if this check finds a live use, BB dominates Succ, so BB is
512 // something like a loop pre-header (or rarely, a part of an irreducible CFG);
513 // folding the branch isn't profitable in that case anyway.
514 if (!Succ->getSinglePredecessor()) {
515 BasicBlock::iterator BBI = BB->begin();
516 while (isa<PHINode>(*BBI)) {
517 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
519 if (PHINode* PN = dyn_cast<PHINode>(*UI)) {
520 if (PN->getIncomingBlock(UI) != BB)
530 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
532 if (isa<PHINode>(Succ->begin())) {
533 // If there is more than one pred of succ, and there are PHI nodes in
534 // the successor, then we need to add incoming edges for the PHI nodes
536 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
538 // Loop over all of the PHI nodes in the successor of BB.
539 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
540 PHINode *PN = cast<PHINode>(I);
541 Value *OldVal = PN->removeIncomingValue(BB, false);
542 assert(OldVal && "No entry in PHI for Pred BB!");
544 // If this incoming value is one of the PHI nodes in BB, the new entries
545 // in the PHI node are the entries from the old PHI.
546 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
547 PHINode *OldValPN = cast<PHINode>(OldVal);
548 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
549 // Note that, since we are merging phi nodes and BB and Succ might
550 // have common predecessors, we could end up with a phi node with
551 // identical incoming branches. This will be cleaned up later (and
552 // will trigger asserts if we try to clean it up now, without also
553 // simplifying the corresponding conditional branch).
554 PN->addIncoming(OldValPN->getIncomingValue(i),
555 OldValPN->getIncomingBlock(i));
557 // Add an incoming value for each of the new incoming values.
558 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
559 PN->addIncoming(OldVal, BBPreds[i]);
564 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
565 if (Succ->getSinglePredecessor()) {
566 // BB is the only predecessor of Succ, so Succ will end up with exactly
567 // the same predecessors BB had.
568 Succ->getInstList().splice(Succ->begin(),
569 BB->getInstList(), BB->begin());
571 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
572 assert(PN->use_empty() && "There shouldn't be any uses here!");
573 PN->eraseFromParent();
577 // Everything that jumped to BB now goes to Succ.
578 BB->replaceAllUsesWith(Succ);
579 if (!Succ->hasName()) Succ->takeName(BB);
580 BB->eraseFromParent(); // Delete the old basic block.
584 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
585 /// nodes in this block. This doesn't try to be clever about PHI nodes
586 /// which differ only in the order of the incoming values, but instcombine
587 /// orders them so it usually won't matter.
589 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
590 bool Changed = false;
592 // This implementation doesn't currently consider undef operands
593 // specially. Theroetically, two phis which are identical except for
594 // one having an undef where the other doesn't could be collapsed.
596 // Map from PHI hash values to PHI nodes. If multiple PHIs have
597 // the same hash value, the element is the first PHI in the
598 // linked list in CollisionMap.
599 DenseMap<uintptr_t, PHINode *> HashMap;
601 // Maintain linked lists of PHI nodes with common hash values.
602 DenseMap<PHINode *, PHINode *> CollisionMap;
605 for (BasicBlock::iterator I = BB->begin();
606 PHINode *PN = dyn_cast<PHINode>(I++); ) {
607 // Compute a hash value on the operands. Instcombine will likely have sorted
608 // them, which helps expose duplicates, but we have to check all the
609 // operands to be safe in case instcombine hasn't run.
611 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
612 // This hash algorithm is quite weak as hash functions go, but it seems
613 // to do a good enough job for this particular purpose, and is very quick.
614 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
615 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
617 // If we've never seen this hash value before, it's a unique PHI.
618 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
619 HashMap.insert(std::make_pair(Hash, PN));
620 if (Pair.second) continue;
621 // Otherwise it's either a duplicate or a hash collision.
622 for (PHINode *OtherPN = Pair.first->second; ; ) {
623 if (OtherPN->isIdenticalTo(PN)) {
624 // A duplicate. Replace this PHI with its duplicate.
625 PN->replaceAllUsesWith(OtherPN);
626 PN->eraseFromParent();
630 // A non-duplicate hash collision.
631 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
632 if (I == CollisionMap.end()) {
633 // Set this PHI to be the head of the linked list of colliding PHIs.
634 PHINode *Old = Pair.first->second;
635 Pair.first->second = PN;
636 CollisionMap[PN] = Old;
639 // Procede to the next PHI in the list.
647 /// enforceKnownAlignment - If the specified pointer points to an object that
648 /// we control, modify the object's alignment to PrefAlign. This isn't
649 /// often possible though. If alignment is important, a more reliable approach
650 /// is to simply align all global variables and allocation instructions to
651 /// their preferred alignment from the beginning.
653 static unsigned enforceKnownAlignment(Value *V, unsigned Align,
654 unsigned PrefAlign) {
656 User *U = dyn_cast<User>(V);
657 if (!U) return Align;
659 switch (Operator::getOpcode(U)) {
661 case Instruction::BitCast:
662 return enforceKnownAlignment(U->getOperand(0), Align, PrefAlign);
663 case Instruction::GetElementPtr: {
664 // If all indexes are zero, it is just the alignment of the base pointer.
665 bool AllZeroOperands = true;
666 for (User::op_iterator i = U->op_begin() + 1, e = U->op_end(); i != e; ++i)
667 if (!isa<Constant>(*i) ||
668 !cast<Constant>(*i)->isNullValue()) {
669 AllZeroOperands = false;
673 if (AllZeroOperands) {
674 // Treat this like a bitcast.
675 return enforceKnownAlignment(U->getOperand(0), Align, PrefAlign);
679 case Instruction::Alloca: {
680 AllocaInst *AI = cast<AllocaInst>(V);
681 // If there is a requested alignment and if this is an alloca, round up.
682 if (AI->getAlignment() >= PrefAlign)
683 return AI->getAlignment();
684 AI->setAlignment(PrefAlign);
689 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
690 // If there is a large requested alignment and we can, bump up the alignment
692 if (GV->isDeclaration()) return Align;
694 if (GV->getAlignment() >= PrefAlign)
695 return GV->getAlignment();
696 // We can only increase the alignment of the global if it has no alignment
697 // specified or if it is not assigned a section. If it is assigned a
698 // section, the global could be densely packed with other objects in the
699 // section, increasing the alignment could cause padding issues.
700 if (!GV->hasSection() || GV->getAlignment() == 0)
701 GV->setAlignment(PrefAlign);
702 return GV->getAlignment();
708 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
709 /// we can determine, return it, otherwise return 0. If PrefAlign is specified,
710 /// and it is more than the alignment of the ultimate object, see if we can
711 /// increase the alignment of the ultimate object, making this check succeed.
712 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
713 const TargetData *TD) {
714 assert(V->getType()->isPointerTy() &&
715 "getOrEnforceKnownAlignment expects a pointer!");
716 unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64;
717 APInt Mask = APInt::getAllOnesValue(BitWidth);
718 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
719 ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD);
720 unsigned TrailZ = KnownZero.countTrailingOnes();
722 // Avoid trouble with rediculously large TrailZ values, such as
723 // those computed from a null pointer.
724 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
726 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
728 // LLVM doesn't support alignments larger than this currently.
729 Align = std::min(Align, +Value::MaximumAlignment);
731 if (PrefAlign > Align)
732 Align = enforceKnownAlignment(V, Align, PrefAlign);
734 // We don't need to make any adjustment.