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/DebugInfo.h"
26 #include "llvm/Analysis/DIBuilder.h"
27 #include "llvm/Analysis/Dominators.h"
28 #include "llvm/Analysis/ConstantFolding.h"
29 #include "llvm/Analysis/InstructionSimplify.h"
30 #include "llvm/Analysis/ProfileInfo.h"
31 #include "llvm/Analysis/ValueTracking.h"
32 #include "llvm/Target/TargetData.h"
33 #include "llvm/Support/CFG.h"
34 #include "llvm/Support/Debug.h"
35 #include "llvm/Support/GetElementPtrTypeIterator.h"
36 #include "llvm/Support/MathExtras.h"
37 #include "llvm/Support/ValueHandle.h"
38 #include "llvm/Support/raw_ostream.h"
41 //===----------------------------------------------------------------------===//
42 // Local constant propagation.
45 // ConstantFoldTerminator - If a terminator instruction is predicated on a
46 // constant value, convert it into an unconditional branch to the constant
49 bool llvm::ConstantFoldTerminator(BasicBlock *BB) {
50 TerminatorInst *T = BB->getTerminator();
52 // Branch - See if we are conditional jumping on constant
53 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
54 if (BI->isUnconditional()) return false; // Can't optimize uncond branch
55 BasicBlock *Dest1 = BI->getSuccessor(0);
56 BasicBlock *Dest2 = BI->getSuccessor(1);
58 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
59 // Are we branching on constant?
60 // YES. Change to unconditional branch...
61 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
62 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1;
64 //cerr << "Function: " << T->getParent()->getParent()
65 // << "\nRemoving branch from " << T->getParent()
66 // << "\n\nTo: " << OldDest << endl;
68 // Let the basic block know that we are letting go of it. Based on this,
69 // it will adjust it's PHI nodes.
70 assert(BI->getParent() && "Terminator not inserted in block!");
71 OldDest->removePredecessor(BI->getParent());
73 // Replace the conditional branch with an unconditional one.
74 BranchInst::Create(Destination, BI);
75 BI->eraseFromParent();
79 if (Dest2 == Dest1) { // Conditional branch to same location?
80 // This branch matches something like this:
81 // br bool %cond, label %Dest, label %Dest
82 // and changes it into: br label %Dest
84 // Let the basic block know that we are letting go of one copy of it.
85 assert(BI->getParent() && "Terminator not inserted in block!");
86 Dest1->removePredecessor(BI->getParent());
88 // Replace the conditional branch with an unconditional one.
89 BranchInst::Create(Dest1, BI);
90 BI->eraseFromParent();
96 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
97 // If we are switching on a constant, we can convert the switch into a
98 // single branch instruction!
99 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
100 BasicBlock *TheOnlyDest = SI->getSuccessor(0); // The default dest
101 BasicBlock *DefaultDest = TheOnlyDest;
102 assert(TheOnlyDest == SI->getDefaultDest() &&
103 "Default destination is not successor #0?");
105 // Figure out which case it goes to.
106 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
107 // Found case matching a constant operand?
108 if (SI->getSuccessorValue(i) == CI) {
109 TheOnlyDest = SI->getSuccessor(i);
113 // Check to see if this branch is going to the same place as the default
114 // dest. If so, eliminate it as an explicit compare.
115 if (SI->getSuccessor(i) == DefaultDest) {
116 // Remove this entry.
117 DefaultDest->removePredecessor(SI->getParent());
119 --i; --e; // Don't skip an entry...
123 // Otherwise, check to see if the switch only branches to one destination.
124 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
126 if (SI->getSuccessor(i) != TheOnlyDest) TheOnlyDest = 0;
129 if (CI && !TheOnlyDest) {
130 // Branching on a constant, but not any of the cases, go to the default
132 TheOnlyDest = SI->getDefaultDest();
135 // If we found a single destination that we can fold the switch into, do so
138 // Insert the new branch.
139 BranchInst::Create(TheOnlyDest, SI);
140 BasicBlock *BB = SI->getParent();
142 // Remove entries from PHI nodes which we no longer branch to...
143 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
144 // Found case matching a constant operand?
145 BasicBlock *Succ = SI->getSuccessor(i);
146 if (Succ == TheOnlyDest)
147 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest
149 Succ->removePredecessor(BB);
152 // Delete the old switch.
153 BB->getInstList().erase(SI);
157 if (SI->getNumSuccessors() == 2) {
158 // Otherwise, we can fold this switch into a conditional branch
159 // instruction if it has only one non-default destination.
160 Value *Cond = new ICmpInst(SI, ICmpInst::ICMP_EQ, SI->getCondition(),
161 SI->getSuccessorValue(1), "cond");
162 // Insert the new branch.
163 BranchInst::Create(SI->getSuccessor(1), SI->getSuccessor(0), Cond, SI);
165 // Delete the old switch.
166 SI->eraseFromParent();
172 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
173 // indirectbr blockaddress(@F, @BB) -> br label @BB
174 if (BlockAddress *BA =
175 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
176 BasicBlock *TheOnlyDest = BA->getBasicBlock();
177 // Insert the new branch.
178 BranchInst::Create(TheOnlyDest, IBI);
180 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
181 if (IBI->getDestination(i) == TheOnlyDest)
184 IBI->getDestination(i)->removePredecessor(IBI->getParent());
186 IBI->eraseFromParent();
188 // If we didn't find our destination in the IBI successor list, then we
189 // have undefined behavior. Replace the unconditional branch with an
190 // 'unreachable' instruction.
192 BB->getTerminator()->eraseFromParent();
193 new UnreachableInst(BB->getContext(), BB);
204 //===----------------------------------------------------------------------===//
205 // Local dead code elimination.
208 /// isInstructionTriviallyDead - Return true if the result produced by the
209 /// instruction is not used, and the instruction has no side effects.
211 bool llvm::isInstructionTriviallyDead(Instruction *I) {
212 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
214 // We don't want debug info removed by anything this general.
215 if (isa<DbgInfoIntrinsic>(I)) return false;
217 if (!I->mayHaveSideEffects()) return true;
219 // Special case intrinsics that "may have side effects" but can be deleted
221 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
222 // Safe to delete llvm.stacksave if dead.
223 if (II->getIntrinsicID() == Intrinsic::stacksave)
228 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
229 /// trivially dead instruction, delete it. If that makes any of its operands
230 /// trivially dead, delete them too, recursively. Return true if any
231 /// instructions were deleted.
232 bool llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V) {
233 Instruction *I = dyn_cast<Instruction>(V);
234 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I))
237 SmallVector<Instruction*, 16> DeadInsts;
238 DeadInsts.push_back(I);
241 I = DeadInsts.pop_back_val();
243 // Null out all of the instruction's operands to see if any operand becomes
245 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
246 Value *OpV = I->getOperand(i);
249 if (!OpV->use_empty()) continue;
251 // If the operand is an instruction that became dead as we nulled out the
252 // operand, and if it is 'trivially' dead, delete it in a future loop
254 if (Instruction *OpI = dyn_cast<Instruction>(OpV))
255 if (isInstructionTriviallyDead(OpI))
256 DeadInsts.push_back(OpI);
259 I->eraseFromParent();
260 } while (!DeadInsts.empty());
265 /// areAllUsesEqual - Check whether the uses of a value are all the same.
266 /// This is similar to Instruction::hasOneUse() except this will also return
267 /// true when there are no uses or multiple uses that all refer to the same
269 static bool areAllUsesEqual(Instruction *I) {
270 Value::use_iterator UI = I->use_begin();
271 Value::use_iterator UE = I->use_end();
276 for (++UI; UI != UE; ++UI) {
283 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
284 /// dead PHI node, due to being a def-use chain of single-use nodes that
285 /// either forms a cycle or is terminated by a trivially dead instruction,
286 /// delete it. If that makes any of its operands trivially dead, delete them
287 /// too, recursively. Return true if a change was made.
288 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) {
289 SmallPtrSet<Instruction*, 4> Visited;
290 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
291 I = cast<Instruction>(*I->use_begin())) {
293 return RecursivelyDeleteTriviallyDeadInstructions(I);
295 // If we find an instruction more than once, we're on a cycle that
296 // won't prove fruitful.
297 if (!Visited.insert(I)) {
298 // Break the cycle and delete the instruction and its operands.
299 I->replaceAllUsesWith(UndefValue::get(I->getType()));
300 (void)RecursivelyDeleteTriviallyDeadInstructions(I);
307 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
308 /// simplify any instructions in it and recursively delete dead instructions.
310 /// This returns true if it changed the code, note that it can delete
311 /// instructions in other blocks as well in this block.
312 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD) {
313 bool MadeChange = false;
314 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
315 Instruction *Inst = BI++;
317 if (Value *V = SimplifyInstruction(Inst, TD)) {
319 ReplaceAndSimplifyAllUses(Inst, V, TD);
326 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst);
331 //===----------------------------------------------------------------------===//
332 // Control Flow Graph Restructuring.
336 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
337 /// method is called when we're about to delete Pred as a predecessor of BB. If
338 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
340 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
341 /// nodes that collapse into identity values. For example, if we have:
342 /// x = phi(1, 0, 0, 0)
345 /// .. and delete the predecessor corresponding to the '1', this will attempt to
346 /// recursively fold the and to 0.
347 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
349 // This only adjusts blocks with PHI nodes.
350 if (!isa<PHINode>(BB->begin()))
353 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
354 // them down. This will leave us with single entry phi nodes and other phis
355 // that can be removed.
356 BB->removePredecessor(Pred, true);
358 WeakVH PhiIt = &BB->front();
359 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
360 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
362 Value *PNV = SimplifyInstruction(PN, TD);
363 if (PNV == 0) continue;
365 // If we're able to simplify the phi to a single value, substitute the new
366 // value into all of its uses.
367 assert(PNV != PN && "SimplifyInstruction broken!");
369 Value *OldPhiIt = PhiIt;
370 ReplaceAndSimplifyAllUses(PN, PNV, TD);
372 // If recursive simplification ended up deleting the next PHI node we would
373 // iterate to, then our iterator is invalid, restart scanning from the top
375 if (PhiIt != OldPhiIt) PhiIt = &BB->front();
380 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
381 /// predecessor is known to have one successor (DestBB!). Eliminate the edge
382 /// between them, moving the instructions in the predecessor into DestBB and
383 /// deleting the predecessor block.
385 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) {
386 // If BB has single-entry PHI nodes, fold them.
387 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
388 Value *NewVal = PN->getIncomingValue(0);
389 // Replace self referencing PHI with undef, it must be dead.
390 if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
391 PN->replaceAllUsesWith(NewVal);
392 PN->eraseFromParent();
395 BasicBlock *PredBB = DestBB->getSinglePredecessor();
396 assert(PredBB && "Block doesn't have a single predecessor!");
398 // Splice all the instructions from PredBB to DestBB.
399 PredBB->getTerminator()->eraseFromParent();
400 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
402 // Zap anything that took the address of DestBB. Not doing this will give the
403 // address an invalid value.
404 if (DestBB->hasAddressTaken()) {
405 BlockAddress *BA = BlockAddress::get(DestBB);
406 Constant *Replacement =
407 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1);
408 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
410 BA->destroyConstant();
413 // Anything that branched to PredBB now branches to DestBB.
414 PredBB->replaceAllUsesWith(DestBB);
417 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>();
419 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock();
420 DT->changeImmediateDominator(DestBB, PredBBIDom);
421 DT->eraseNode(PredBB);
423 ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>();
425 PI->replaceAllUses(PredBB, DestBB);
426 PI->removeEdge(ProfileInfo::getEdge(PredBB, DestBB));
430 PredBB->eraseFromParent();
433 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
434 /// almost-empty BB ending in an unconditional branch to Succ, into succ.
436 /// Assumption: Succ is the single successor for BB.
438 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
439 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
441 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
442 << Succ->getName() << "\n");
443 // Shortcut, if there is only a single predecessor it must be BB and merging
445 if (Succ->getSinglePredecessor()) return true;
447 // Make a list of the predecessors of BB
448 typedef SmallPtrSet<BasicBlock*, 16> BlockSet;
449 BlockSet BBPreds(pred_begin(BB), pred_end(BB));
451 // Use that list to make another list of common predecessors of BB and Succ
452 BlockSet CommonPreds;
453 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
456 if (BBPreds.count(P))
457 CommonPreds.insert(P);
460 // Shortcut, if there are no common predecessors, merging is always safe
461 if (CommonPreds.empty())
464 // Look at all the phi nodes in Succ, to see if they present a conflict when
465 // merging these blocks
466 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
467 PHINode *PN = cast<PHINode>(I);
469 // If the incoming value from BB is again a PHINode in
470 // BB which has the same incoming value for *PI as PN does, we can
471 // merge the phi nodes and then the blocks can still be merged
472 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
473 if (BBPN && BBPN->getParent() == BB) {
474 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
476 if (BBPN->getIncomingValueForBlock(*PI)
477 != PN->getIncomingValueForBlock(*PI)) {
478 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
479 << Succ->getName() << " is conflicting with "
480 << BBPN->getName() << " with regard to common predecessor "
481 << (*PI)->getName() << "\n");
486 Value* Val = PN->getIncomingValueForBlock(BB);
487 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
489 // See if the incoming value for the common predecessor is equal to the
490 // one for BB, in which case this phi node will not prevent the merging
492 if (Val != PN->getIncomingValueForBlock(*PI)) {
493 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
494 << Succ->getName() << " is conflicting with regard to common "
495 << "predecessor " << (*PI)->getName() << "\n");
505 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
506 /// unconditional branch, and contains no instructions other than PHI nodes,
507 /// potential debug intrinsics and the branch. If possible, eliminate BB by
508 /// rewriting all the predecessors to branch to the successor block and return
509 /// true. If we can't transform, return false.
510 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
511 assert(BB != &BB->getParent()->getEntryBlock() &&
512 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
514 // We can't eliminate infinite loops.
515 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
516 if (BB == Succ) return false;
518 // Check to see if merging these blocks would cause conflicts for any of the
519 // phi nodes in BB or Succ. If not, we can safely merge.
520 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
522 // Check for cases where Succ has multiple predecessors and a PHI node in BB
523 // has uses which will not disappear when the PHI nodes are merged. It is
524 // possible to handle such cases, but difficult: it requires checking whether
525 // BB dominates Succ, which is non-trivial to calculate in the case where
526 // Succ has multiple predecessors. Also, it requires checking whether
527 // constructing the necessary self-referential PHI node doesn't intoduce any
528 // conflicts; this isn't too difficult, but the previous code for doing this
531 // Note that if this check finds a live use, BB dominates Succ, so BB is
532 // something like a loop pre-header (or rarely, a part of an irreducible CFG);
533 // folding the branch isn't profitable in that case anyway.
534 if (!Succ->getSinglePredecessor()) {
535 BasicBlock::iterator BBI = BB->begin();
536 while (isa<PHINode>(*BBI)) {
537 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
539 if (PHINode* PN = dyn_cast<PHINode>(*UI)) {
540 if (PN->getIncomingBlock(UI) != BB)
550 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
552 if (isa<PHINode>(Succ->begin())) {
553 // If there is more than one pred of succ, and there are PHI nodes in
554 // the successor, then we need to add incoming edges for the PHI nodes
556 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
558 // Loop over all of the PHI nodes in the successor of BB.
559 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
560 PHINode *PN = cast<PHINode>(I);
561 Value *OldVal = PN->removeIncomingValue(BB, false);
562 assert(OldVal && "No entry in PHI for Pred BB!");
564 // If this incoming value is one of the PHI nodes in BB, the new entries
565 // in the PHI node are the entries from the old PHI.
566 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
567 PHINode *OldValPN = cast<PHINode>(OldVal);
568 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
569 // Note that, since we are merging phi nodes and BB and Succ might
570 // have common predecessors, we could end up with a phi node with
571 // identical incoming branches. This will be cleaned up later (and
572 // will trigger asserts if we try to clean it up now, without also
573 // simplifying the corresponding conditional branch).
574 PN->addIncoming(OldValPN->getIncomingValue(i),
575 OldValPN->getIncomingBlock(i));
577 // Add an incoming value for each of the new incoming values.
578 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
579 PN->addIncoming(OldVal, BBPreds[i]);
584 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
585 if (Succ->getSinglePredecessor()) {
586 // BB is the only predecessor of Succ, so Succ will end up with exactly
587 // the same predecessors BB had.
588 Succ->getInstList().splice(Succ->begin(),
589 BB->getInstList(), BB->begin());
591 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
592 assert(PN->use_empty() && "There shouldn't be any uses here!");
593 PN->eraseFromParent();
597 // Everything that jumped to BB now goes to Succ.
598 BB->replaceAllUsesWith(Succ);
599 if (!Succ->hasName()) Succ->takeName(BB);
600 BB->eraseFromParent(); // Delete the old basic block.
604 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
605 /// nodes in this block. This doesn't try to be clever about PHI nodes
606 /// which differ only in the order of the incoming values, but instcombine
607 /// orders them so it usually won't matter.
609 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
610 bool Changed = false;
612 // This implementation doesn't currently consider undef operands
613 // specially. Theroetically, two phis which are identical except for
614 // one having an undef where the other doesn't could be collapsed.
616 // Map from PHI hash values to PHI nodes. If multiple PHIs have
617 // the same hash value, the element is the first PHI in the
618 // linked list in CollisionMap.
619 DenseMap<uintptr_t, PHINode *> HashMap;
621 // Maintain linked lists of PHI nodes with common hash values.
622 DenseMap<PHINode *, PHINode *> CollisionMap;
625 for (BasicBlock::iterator I = BB->begin();
626 PHINode *PN = dyn_cast<PHINode>(I++); ) {
627 // Compute a hash value on the operands. Instcombine will likely have sorted
628 // them, which helps expose duplicates, but we have to check all the
629 // operands to be safe in case instcombine hasn't run.
631 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
632 // This hash algorithm is quite weak as hash functions go, but it seems
633 // to do a good enough job for this particular purpose, and is very quick.
634 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
635 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
637 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1.
639 // If we've never seen this hash value before, it's a unique PHI.
640 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
641 HashMap.insert(std::make_pair(Hash, PN));
642 if (Pair.second) continue;
643 // Otherwise it's either a duplicate or a hash collision.
644 for (PHINode *OtherPN = Pair.first->second; ; ) {
645 if (OtherPN->isIdenticalTo(PN)) {
646 // A duplicate. Replace this PHI with its duplicate.
647 PN->replaceAllUsesWith(OtherPN);
648 PN->eraseFromParent();
652 // A non-duplicate hash collision.
653 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
654 if (I == CollisionMap.end()) {
655 // Set this PHI to be the head of the linked list of colliding PHIs.
656 PHINode *Old = Pair.first->second;
657 Pair.first->second = PN;
658 CollisionMap[PN] = Old;
661 // Procede to the next PHI in the list.
669 /// enforceKnownAlignment - If the specified pointer points to an object that
670 /// we control, modify the object's alignment to PrefAlign. This isn't
671 /// often possible though. If alignment is important, a more reliable approach
672 /// is to simply align all global variables and allocation instructions to
673 /// their preferred alignment from the beginning.
675 static unsigned enforceKnownAlignment(Value *V, unsigned Align,
676 unsigned PrefAlign) {
678 User *U = dyn_cast<User>(V);
679 if (!U) return Align;
681 switch (Operator::getOpcode(U)) {
683 case Instruction::BitCast:
684 return enforceKnownAlignment(U->getOperand(0), Align, PrefAlign);
685 case Instruction::GetElementPtr: {
686 // If all indexes are zero, it is just the alignment of the base pointer.
687 bool AllZeroOperands = true;
688 for (User::op_iterator i = U->op_begin() + 1, e = U->op_end(); i != e; ++i)
689 if (!isa<Constant>(*i) ||
690 !cast<Constant>(*i)->isNullValue()) {
691 AllZeroOperands = false;
695 if (AllZeroOperands) {
696 // Treat this like a bitcast.
697 return enforceKnownAlignment(U->getOperand(0), Align, PrefAlign);
701 case Instruction::Alloca: {
702 AllocaInst *AI = cast<AllocaInst>(V);
703 // If there is a requested alignment and if this is an alloca, round up.
704 if (AI->getAlignment() >= PrefAlign)
705 return AI->getAlignment();
706 AI->setAlignment(PrefAlign);
711 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
712 // If there is a large requested alignment and we can, bump up the alignment
714 if (GV->isDeclaration()) return Align;
716 if (GV->getAlignment() >= PrefAlign)
717 return GV->getAlignment();
718 // We can only increase the alignment of the global if it has no alignment
719 // specified or if it is not assigned a section. If it is assigned a
720 // section, the global could be densely packed with other objects in the
721 // section, increasing the alignment could cause padding issues.
722 if (!GV->hasSection() || GV->getAlignment() == 0)
723 GV->setAlignment(PrefAlign);
724 return GV->getAlignment();
730 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
731 /// we can determine, return it, otherwise return 0. If PrefAlign is specified,
732 /// and it is more than the alignment of the ultimate object, see if we can
733 /// increase the alignment of the ultimate object, making this check succeed.
734 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
735 const TargetData *TD) {
736 assert(V->getType()->isPointerTy() &&
737 "getOrEnforceKnownAlignment expects a pointer!");
738 unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64;
739 APInt Mask = APInt::getAllOnesValue(BitWidth);
740 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
741 ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD);
742 unsigned TrailZ = KnownZero.countTrailingOnes();
744 // Avoid trouble with rediculously large TrailZ values, such as
745 // those computed from a null pointer.
746 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
748 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
750 // LLVM doesn't support alignments larger than this currently.
751 Align = std::min(Align, +Value::MaximumAlignment);
753 if (PrefAlign > Align)
754 Align = enforceKnownAlignment(V, Align, PrefAlign);
756 // We don't need to make any adjustment.
760 ///===---------------------------------------------------------------------===//
761 /// Dbg Intrinsic utilities
764 /// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value
765 /// that has an associated llvm.dbg.decl intrinsic.
766 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
767 StoreInst *SI, DIBuilder &Builder) {
768 DIVariable DIVar(DDI->getVariable());
772 Instruction *DbgVal =
773 Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0,
776 // Propagate any debug metadata from the store onto the dbg.value.
777 DebugLoc SIDL = SI->getDebugLoc();
778 if (!SIDL.isUnknown())
779 DbgVal->setDebugLoc(SIDL);
780 // Otherwise propagate debug metadata from dbg.declare.
782 DbgVal->setDebugLoc(DDI->getDebugLoc());
786 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
787 /// of llvm.dbg.value intrinsics.
788 bool llvm::LowerDbgDeclare(Function &F) {
789 DIBuilder DIB(*F.getParent());
790 SmallVector<DbgDeclareInst *, 4> Dbgs;
791 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
792 for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ++BI) {
793 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(BI))
799 for (SmallVector<DbgDeclareInst *, 4>::iterator I = Dbgs.begin(),
800 E = Dbgs.end(); I != E; ++I) {
801 DbgDeclareInst *DDI = *I;
802 if (AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress())) {
803 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
805 if (StoreInst *SI = dyn_cast<StoreInst>(*UI))
806 ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
808 DDI->eraseFromParent();