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/Operator.h"
24 #include "llvm/ADT/DenseMap.h"
25 #include "llvm/ADT/SmallPtrSet.h"
26 #include "llvm/Analysis/DebugInfo.h"
27 #include "llvm/Analysis/DIBuilder.h"
28 #include "llvm/Analysis/Dominators.h"
29 #include "llvm/Analysis/ConstantFolding.h"
30 #include "llvm/Analysis/InstructionSimplify.h"
31 #include "llvm/Analysis/ProfileInfo.h"
32 #include "llvm/Analysis/ValueTracking.h"
33 #include "llvm/Target/TargetData.h"
34 #include "llvm/Support/CFG.h"
35 #include "llvm/Support/Debug.h"
36 #include "llvm/Support/GetElementPtrTypeIterator.h"
37 #include "llvm/SUpport/IRBuilder.h"
38 #include "llvm/Support/MathExtras.h"
39 #include "llvm/Support/ValueHandle.h"
40 #include "llvm/Support/raw_ostream.h"
43 //===----------------------------------------------------------------------===//
44 // Local constant propagation.
47 // ConstantFoldTerminator - If a terminator instruction is predicated on a
48 // constant value, convert it into an unconditional branch to the constant
51 bool llvm::ConstantFoldTerminator(BasicBlock *BB) {
52 TerminatorInst *T = BB->getTerminator();
53 IRBuilder<> Builder(T);
55 // Branch - See if we are conditional jumping on constant
56 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
57 if (BI->isUnconditional()) return false; // Can't optimize uncond branch
58 BasicBlock *Dest1 = BI->getSuccessor(0);
59 BasicBlock *Dest2 = BI->getSuccessor(1);
61 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
62 // Are we branching on constant?
63 // YES. Change to unconditional branch...
64 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
65 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1;
67 //cerr << "Function: " << T->getParent()->getParent()
68 // << "\nRemoving branch from " << T->getParent()
69 // << "\n\nTo: " << OldDest << endl;
71 // Let the basic block know that we are letting go of it. Based on this,
72 // it will adjust it's PHI nodes.
73 OldDest->removePredecessor(BB);
75 // Replace the conditional branch with an unconditional one.
76 Builder.CreateBr(Destination);
77 BI->eraseFromParent();
81 if (Dest2 == Dest1) { // Conditional branch to same location?
82 // This branch matches something like this:
83 // br bool %cond, label %Dest, label %Dest
84 // and changes it into: br label %Dest
86 // Let the basic block know that we are letting go of one copy of it.
87 assert(BI->getParent() && "Terminator not inserted in block!");
88 Dest1->removePredecessor(BI->getParent());
90 // Replace the conditional branch with an unconditional one.
91 Builder.CreateBr(Dest1);
92 BI->eraseFromParent();
98 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
99 // If we are switching on a constant, we can convert the switch into a
100 // single branch instruction!
101 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
102 BasicBlock *TheOnlyDest = SI->getSuccessor(0); // The default dest
103 BasicBlock *DefaultDest = TheOnlyDest;
104 assert(TheOnlyDest == SI->getDefaultDest() &&
105 "Default destination is not successor #0?");
107 // Figure out which case it goes to.
108 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
109 // Found case matching a constant operand?
110 if (SI->getSuccessorValue(i) == CI) {
111 TheOnlyDest = SI->getSuccessor(i);
115 // Check to see if this branch is going to the same place as the default
116 // dest. If so, eliminate it as an explicit compare.
117 if (SI->getSuccessor(i) == DefaultDest) {
118 // Remove this entry.
119 DefaultDest->removePredecessor(SI->getParent());
121 --i; --e; // Don't skip an entry...
125 // Otherwise, check to see if the switch only branches to one destination.
126 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
128 if (SI->getSuccessor(i) != TheOnlyDest) TheOnlyDest = 0;
131 if (CI && !TheOnlyDest) {
132 // Branching on a constant, but not any of the cases, go to the default
134 TheOnlyDest = SI->getDefaultDest();
137 // If we found a single destination that we can fold the switch into, do so
140 // Insert the new branch.
141 Builder.CreateBr(TheOnlyDest);
142 BasicBlock *BB = SI->getParent();
144 // Remove entries from PHI nodes which we no longer branch to...
145 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
146 // Found case matching a constant operand?
147 BasicBlock *Succ = SI->getSuccessor(i);
148 if (Succ == TheOnlyDest)
149 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest
151 Succ->removePredecessor(BB);
154 // Delete the old switch.
155 BB->getInstList().erase(SI);
159 if (SI->getNumSuccessors() == 2) {
160 // Otherwise, we can fold this switch into a conditional branch
161 // instruction if it has only one non-default destination.
162 Value *Cond = Builder.CreateICmpEQ(SI->getCondition(),
163 SI->getSuccessorValue(1), "cond");
165 // Insert the new branch.
166 Builder.CreateCondBr(Cond, SI->getSuccessor(1), SI->getSuccessor(0));
168 // Delete the old switch.
169 SI->eraseFromParent();
175 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
176 // indirectbr blockaddress(@F, @BB) -> br label @BB
177 if (BlockAddress *BA =
178 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
179 BasicBlock *TheOnlyDest = BA->getBasicBlock();
180 // Insert the new branch.
181 Builder.CreateBr(TheOnlyDest);
183 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
184 if (IBI->getDestination(i) == TheOnlyDest)
187 IBI->getDestination(i)->removePredecessor(IBI->getParent());
189 IBI->eraseFromParent();
191 // If we didn't find our destination in the IBI successor list, then we
192 // have undefined behavior. Replace the unconditional branch with an
193 // 'unreachable' instruction.
195 BB->getTerminator()->eraseFromParent();
196 new UnreachableInst(BB->getContext(), BB);
207 //===----------------------------------------------------------------------===//
208 // Local dead code elimination.
211 /// isInstructionTriviallyDead - Return true if the result produced by the
212 /// instruction is not used, and the instruction has no side effects.
214 bool llvm::isInstructionTriviallyDead(Instruction *I) {
215 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
217 // We don't want debug info removed by anything this general, unless
218 // debug info is empty.
219 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) {
220 if (DDI->getAddress())
224 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) {
230 if (!I->mayHaveSideEffects()) return true;
232 // Special case intrinsics that "may have side effects" but can be deleted
234 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
235 // Safe to delete llvm.stacksave if dead.
236 if (II->getIntrinsicID() == Intrinsic::stacksave)
241 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
242 /// trivially dead instruction, delete it. If that makes any of its operands
243 /// trivially dead, delete them too, recursively. Return true if any
244 /// instructions were deleted.
245 bool llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V) {
246 Instruction *I = dyn_cast<Instruction>(V);
247 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I))
250 SmallVector<Instruction*, 16> DeadInsts;
251 DeadInsts.push_back(I);
254 I = DeadInsts.pop_back_val();
256 // Null out all of the instruction's operands to see if any operand becomes
258 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
259 Value *OpV = I->getOperand(i);
262 if (!OpV->use_empty()) continue;
264 // If the operand is an instruction that became dead as we nulled out the
265 // operand, and if it is 'trivially' dead, delete it in a future loop
267 if (Instruction *OpI = dyn_cast<Instruction>(OpV))
268 if (isInstructionTriviallyDead(OpI))
269 DeadInsts.push_back(OpI);
272 I->eraseFromParent();
273 } while (!DeadInsts.empty());
278 /// areAllUsesEqual - Check whether the uses of a value are all the same.
279 /// This is similar to Instruction::hasOneUse() except this will also return
280 /// true when there are no uses or multiple uses that all refer to the same
282 static bool areAllUsesEqual(Instruction *I) {
283 Value::use_iterator UI = I->use_begin();
284 Value::use_iterator UE = I->use_end();
289 for (++UI; UI != UE; ++UI) {
296 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
297 /// dead PHI node, due to being a def-use chain of single-use nodes that
298 /// either forms a cycle or is terminated by a trivially dead instruction,
299 /// delete it. If that makes any of its operands trivially dead, delete them
300 /// too, recursively. Return true if a change was made.
301 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) {
302 SmallPtrSet<Instruction*, 4> Visited;
303 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
304 I = cast<Instruction>(*I->use_begin())) {
306 return RecursivelyDeleteTriviallyDeadInstructions(I);
308 // If we find an instruction more than once, we're on a cycle that
309 // won't prove fruitful.
310 if (!Visited.insert(I)) {
311 // Break the cycle and delete the instruction and its operands.
312 I->replaceAllUsesWith(UndefValue::get(I->getType()));
313 (void)RecursivelyDeleteTriviallyDeadInstructions(I);
320 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
321 /// simplify any instructions in it and recursively delete dead instructions.
323 /// This returns true if it changed the code, note that it can delete
324 /// instructions in other blocks as well in this block.
325 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD) {
326 bool MadeChange = false;
327 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
328 Instruction *Inst = BI++;
330 if (Value *V = SimplifyInstruction(Inst, TD)) {
332 ReplaceAndSimplifyAllUses(Inst, V, TD);
339 if (Inst->isTerminator())
343 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst);
350 //===----------------------------------------------------------------------===//
351 // Control Flow Graph Restructuring.
355 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
356 /// method is called when we're about to delete Pred as a predecessor of BB. If
357 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
359 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
360 /// nodes that collapse into identity values. For example, if we have:
361 /// x = phi(1, 0, 0, 0)
364 /// .. and delete the predecessor corresponding to the '1', this will attempt to
365 /// recursively fold the and to 0.
366 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
368 // This only adjusts blocks with PHI nodes.
369 if (!isa<PHINode>(BB->begin()))
372 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
373 // them down. This will leave us with single entry phi nodes and other phis
374 // that can be removed.
375 BB->removePredecessor(Pred, true);
377 WeakVH PhiIt = &BB->front();
378 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
379 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
381 Value *PNV = SimplifyInstruction(PN, TD);
382 if (PNV == 0) continue;
384 // If we're able to simplify the phi to a single value, substitute the new
385 // value into all of its uses.
386 assert(PNV != PN && "SimplifyInstruction broken!");
388 Value *OldPhiIt = PhiIt;
389 ReplaceAndSimplifyAllUses(PN, PNV, TD);
391 // If recursive simplification ended up deleting the next PHI node we would
392 // iterate to, then our iterator is invalid, restart scanning from the top
394 if (PhiIt != OldPhiIt) PhiIt = &BB->front();
399 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
400 /// predecessor is known to have one successor (DestBB!). Eliminate the edge
401 /// between them, moving the instructions in the predecessor into DestBB and
402 /// deleting the predecessor block.
404 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) {
405 // If BB has single-entry PHI nodes, fold them.
406 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
407 Value *NewVal = PN->getIncomingValue(0);
408 // Replace self referencing PHI with undef, it must be dead.
409 if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
410 PN->replaceAllUsesWith(NewVal);
411 PN->eraseFromParent();
414 BasicBlock *PredBB = DestBB->getSinglePredecessor();
415 assert(PredBB && "Block doesn't have a single predecessor!");
417 // Splice all the instructions from PredBB to DestBB.
418 PredBB->getTerminator()->eraseFromParent();
419 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
421 // Zap anything that took the address of DestBB. Not doing this will give the
422 // address an invalid value.
423 if (DestBB->hasAddressTaken()) {
424 BlockAddress *BA = BlockAddress::get(DestBB);
425 Constant *Replacement =
426 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1);
427 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
429 BA->destroyConstant();
432 // Anything that branched to PredBB now branches to DestBB.
433 PredBB->replaceAllUsesWith(DestBB);
436 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>();
438 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock();
439 DT->changeImmediateDominator(DestBB, PredBBIDom);
440 DT->eraseNode(PredBB);
442 ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>();
444 PI->replaceAllUses(PredBB, DestBB);
445 PI->removeEdge(ProfileInfo::getEdge(PredBB, DestBB));
449 PredBB->eraseFromParent();
452 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
453 /// almost-empty BB ending in an unconditional branch to Succ, into succ.
455 /// Assumption: Succ is the single successor for BB.
457 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
458 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
460 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
461 << Succ->getName() << "\n");
462 // Shortcut, if there is only a single predecessor it must be BB and merging
464 if (Succ->getSinglePredecessor()) return true;
466 // Make a list of the predecessors of BB
467 typedef SmallPtrSet<BasicBlock*, 16> BlockSet;
468 BlockSet BBPreds(pred_begin(BB), pred_end(BB));
470 // Use that list to make another list of common predecessors of BB and Succ
471 BlockSet CommonPreds;
472 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
475 if (BBPreds.count(P))
476 CommonPreds.insert(P);
479 // Shortcut, if there are no common predecessors, merging is always safe
480 if (CommonPreds.empty())
483 // Look at all the phi nodes in Succ, to see if they present a conflict when
484 // merging these blocks
485 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
486 PHINode *PN = cast<PHINode>(I);
488 // If the incoming value from BB is again a PHINode in
489 // BB which has the same incoming value for *PI as PN does, we can
490 // merge the phi nodes and then the blocks can still be merged
491 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
492 if (BBPN && BBPN->getParent() == BB) {
493 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
495 if (BBPN->getIncomingValueForBlock(*PI)
496 != PN->getIncomingValueForBlock(*PI)) {
497 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
498 << Succ->getName() << " is conflicting with "
499 << BBPN->getName() << " with regard to common predecessor "
500 << (*PI)->getName() << "\n");
505 Value* Val = PN->getIncomingValueForBlock(BB);
506 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
508 // See if the incoming value for the common predecessor is equal to the
509 // one for BB, in which case this phi node will not prevent the merging
511 if (Val != PN->getIncomingValueForBlock(*PI)) {
512 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
513 << Succ->getName() << " is conflicting with regard to common "
514 << "predecessor " << (*PI)->getName() << "\n");
524 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
525 /// unconditional branch, and contains no instructions other than PHI nodes,
526 /// potential debug intrinsics and the branch. If possible, eliminate BB by
527 /// rewriting all the predecessors to branch to the successor block and return
528 /// true. If we can't transform, return false.
529 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
530 assert(BB != &BB->getParent()->getEntryBlock() &&
531 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
533 // We can't eliminate infinite loops.
534 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
535 if (BB == Succ) return false;
537 // Check to see if merging these blocks would cause conflicts for any of the
538 // phi nodes in BB or Succ. If not, we can safely merge.
539 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
541 // Check for cases where Succ has multiple predecessors and a PHI node in BB
542 // has uses which will not disappear when the PHI nodes are merged. It is
543 // possible to handle such cases, but difficult: it requires checking whether
544 // BB dominates Succ, which is non-trivial to calculate in the case where
545 // Succ has multiple predecessors. Also, it requires checking whether
546 // constructing the necessary self-referential PHI node doesn't intoduce any
547 // conflicts; this isn't too difficult, but the previous code for doing this
550 // Note that if this check finds a live use, BB dominates Succ, so BB is
551 // something like a loop pre-header (or rarely, a part of an irreducible CFG);
552 // folding the branch isn't profitable in that case anyway.
553 if (!Succ->getSinglePredecessor()) {
554 BasicBlock::iterator BBI = BB->begin();
555 while (isa<PHINode>(*BBI)) {
556 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
558 if (PHINode* PN = dyn_cast<PHINode>(*UI)) {
559 if (PN->getIncomingBlock(UI) != BB)
569 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
571 if (isa<PHINode>(Succ->begin())) {
572 // If there is more than one pred of succ, and there are PHI nodes in
573 // the successor, then we need to add incoming edges for the PHI nodes
575 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
577 // Loop over all of the PHI nodes in the successor of BB.
578 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
579 PHINode *PN = cast<PHINode>(I);
580 Value *OldVal = PN->removeIncomingValue(BB, false);
581 assert(OldVal && "No entry in PHI for Pred BB!");
583 // If this incoming value is one of the PHI nodes in BB, the new entries
584 // in the PHI node are the entries from the old PHI.
585 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
586 PHINode *OldValPN = cast<PHINode>(OldVal);
587 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
588 // Note that, since we are merging phi nodes and BB and Succ might
589 // have common predecessors, we could end up with a phi node with
590 // identical incoming branches. This will be cleaned up later (and
591 // will trigger asserts if we try to clean it up now, without also
592 // simplifying the corresponding conditional branch).
593 PN->addIncoming(OldValPN->getIncomingValue(i),
594 OldValPN->getIncomingBlock(i));
596 // Add an incoming value for each of the new incoming values.
597 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
598 PN->addIncoming(OldVal, BBPreds[i]);
603 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
604 if (Succ->getSinglePredecessor()) {
605 // BB is the only predecessor of Succ, so Succ will end up with exactly
606 // the same predecessors BB had.
607 Succ->getInstList().splice(Succ->begin(),
608 BB->getInstList(), BB->begin());
610 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
611 assert(PN->use_empty() && "There shouldn't be any uses here!");
612 PN->eraseFromParent();
616 // Everything that jumped to BB now goes to Succ.
617 BB->replaceAllUsesWith(Succ);
618 if (!Succ->hasName()) Succ->takeName(BB);
619 BB->eraseFromParent(); // Delete the old basic block.
623 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
624 /// nodes in this block. This doesn't try to be clever about PHI nodes
625 /// which differ only in the order of the incoming values, but instcombine
626 /// orders them so it usually won't matter.
628 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
629 bool Changed = false;
631 // This implementation doesn't currently consider undef operands
632 // specially. Theroetically, two phis which are identical except for
633 // one having an undef where the other doesn't could be collapsed.
635 // Map from PHI hash values to PHI nodes. If multiple PHIs have
636 // the same hash value, the element is the first PHI in the
637 // linked list in CollisionMap.
638 DenseMap<uintptr_t, PHINode *> HashMap;
640 // Maintain linked lists of PHI nodes with common hash values.
641 DenseMap<PHINode *, PHINode *> CollisionMap;
644 for (BasicBlock::iterator I = BB->begin();
645 PHINode *PN = dyn_cast<PHINode>(I++); ) {
646 // Compute a hash value on the operands. Instcombine will likely have sorted
647 // them, which helps expose duplicates, but we have to check all the
648 // operands to be safe in case instcombine hasn't run.
650 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
651 // This hash algorithm is quite weak as hash functions go, but it seems
652 // to do a good enough job for this particular purpose, and is very quick.
653 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
654 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
656 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1.
658 // If we've never seen this hash value before, it's a unique PHI.
659 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
660 HashMap.insert(std::make_pair(Hash, PN));
661 if (Pair.second) continue;
662 // Otherwise it's either a duplicate or a hash collision.
663 for (PHINode *OtherPN = Pair.first->second; ; ) {
664 if (OtherPN->isIdenticalTo(PN)) {
665 // A duplicate. Replace this PHI with its duplicate.
666 PN->replaceAllUsesWith(OtherPN);
667 PN->eraseFromParent();
671 // A non-duplicate hash collision.
672 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
673 if (I == CollisionMap.end()) {
674 // Set this PHI to be the head of the linked list of colliding PHIs.
675 PHINode *Old = Pair.first->second;
676 Pair.first->second = PN;
677 CollisionMap[PN] = Old;
680 // Procede to the next PHI in the list.
688 /// enforceKnownAlignment - If the specified pointer points to an object that
689 /// we control, modify the object's alignment to PrefAlign. This isn't
690 /// often possible though. If alignment is important, a more reliable approach
691 /// is to simply align all global variables and allocation instructions to
692 /// their preferred alignment from the beginning.
694 static unsigned enforceKnownAlignment(Value *V, unsigned Align,
695 unsigned PrefAlign) {
697 User *U = dyn_cast<User>(V);
698 if (!U) return Align;
700 switch (Operator::getOpcode(U)) {
702 case Instruction::BitCast:
703 return enforceKnownAlignment(U->getOperand(0), Align, PrefAlign);
704 case Instruction::GetElementPtr: {
705 // If all indexes are zero, it is just the alignment of the base pointer.
706 bool AllZeroOperands = true;
707 for (User::op_iterator i = U->op_begin() + 1, e = U->op_end(); i != e; ++i)
708 if (!isa<Constant>(*i) ||
709 !cast<Constant>(*i)->isNullValue()) {
710 AllZeroOperands = false;
714 if (AllZeroOperands) {
715 // Treat this like a bitcast.
716 return enforceKnownAlignment(U->getOperand(0), Align, PrefAlign);
720 case Instruction::Alloca: {
721 AllocaInst *AI = cast<AllocaInst>(V);
722 // If there is a requested alignment and if this is an alloca, round up.
723 if (AI->getAlignment() >= PrefAlign)
724 return AI->getAlignment();
725 AI->setAlignment(PrefAlign);
730 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
731 // If there is a large requested alignment and we can, bump up the alignment
733 if (GV->isDeclaration()) return Align;
735 if (GV->getAlignment() >= PrefAlign)
736 return GV->getAlignment();
737 // We can only increase the alignment of the global if it has no alignment
738 // specified or if it is not assigned a section. If it is assigned a
739 // section, the global could be densely packed with other objects in the
740 // section, increasing the alignment could cause padding issues.
741 if (!GV->hasSection() || GV->getAlignment() == 0)
742 GV->setAlignment(PrefAlign);
743 return GV->getAlignment();
749 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
750 /// we can determine, return it, otherwise return 0. If PrefAlign is specified,
751 /// and it is more than the alignment of the ultimate object, see if we can
752 /// increase the alignment of the ultimate object, making this check succeed.
753 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
754 const TargetData *TD) {
755 assert(V->getType()->isPointerTy() &&
756 "getOrEnforceKnownAlignment expects a pointer!");
757 unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64;
758 APInt Mask = APInt::getAllOnesValue(BitWidth);
759 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
760 ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD);
761 unsigned TrailZ = KnownZero.countTrailingOnes();
763 // Avoid trouble with rediculously large TrailZ values, such as
764 // those computed from a null pointer.
765 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
767 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
769 // LLVM doesn't support alignments larger than this currently.
770 Align = std::min(Align, +Value::MaximumAlignment);
772 if (PrefAlign > Align)
773 Align = enforceKnownAlignment(V, Align, PrefAlign);
775 // We don't need to make any adjustment.
779 ///===---------------------------------------------------------------------===//
780 /// Dbg Intrinsic utilities
783 /// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value
784 /// that has an associated llvm.dbg.decl intrinsic.
785 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
786 StoreInst *SI, DIBuilder &Builder) {
787 DIVariable DIVar(DDI->getVariable());
791 Instruction *DbgVal = NULL;
792 // If an argument is zero extended then use argument directly. The ZExt
793 // may be zapped by an optimization pass in future.
794 Argument *ExtendedArg = NULL;
795 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
796 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0));
797 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
798 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0));
800 DbgVal = Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, SI);
802 DbgVal = Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, SI);
804 // Propagate any debug metadata from the store onto the dbg.value.
805 DebugLoc SIDL = SI->getDebugLoc();
806 if (!SIDL.isUnknown())
807 DbgVal->setDebugLoc(SIDL);
808 // Otherwise propagate debug metadata from dbg.declare.
810 DbgVal->setDebugLoc(DDI->getDebugLoc());
814 /// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value
815 /// that has an associated llvm.dbg.decl intrinsic.
816 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
817 LoadInst *LI, DIBuilder &Builder) {
818 DIVariable DIVar(DDI->getVariable());
822 Instruction *DbgVal =
823 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0,
826 // Propagate any debug metadata from the store onto the dbg.value.
827 DebugLoc LIDL = LI->getDebugLoc();
828 if (!LIDL.isUnknown())
829 DbgVal->setDebugLoc(LIDL);
830 // Otherwise propagate debug metadata from dbg.declare.
832 DbgVal->setDebugLoc(DDI->getDebugLoc());
836 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
837 /// of llvm.dbg.value intrinsics.
838 bool llvm::LowerDbgDeclare(Function &F) {
839 DIBuilder DIB(*F.getParent());
840 SmallVector<DbgDeclareInst *, 4> Dbgs;
841 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
842 for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ++BI) {
843 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(BI))
849 for (SmallVector<DbgDeclareInst *, 4>::iterator I = Dbgs.begin(),
850 E = Dbgs.end(); I != E; ++I) {
851 DbgDeclareInst *DDI = *I;
852 if (AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress())) {
853 bool RemoveDDI = true;
854 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
856 if (StoreInst *SI = dyn_cast<StoreInst>(*UI))
857 ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
858 else if (LoadInst *LI = dyn_cast<LoadInst>(*UI))
859 ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
863 DDI->eraseFromParent();