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/ADT/DenseMap.h"
17 #include "llvm/ADT/STLExtras.h"
18 #include "llvm/ADT/SmallPtrSet.h"
19 #include "llvm/Analysis/Dominators.h"
20 #include "llvm/Analysis/InstructionSimplify.h"
21 #include "llvm/Analysis/MemoryBuiltins.h"
22 #include "llvm/Analysis/ProfileInfo.h"
23 #include "llvm/Analysis/ValueTracking.h"
24 #include "llvm/DIBuilder.h"
25 #include "llvm/DebugInfo.h"
26 #include "llvm/IR/Constants.h"
27 #include "llvm/IR/DataLayout.h"
28 #include "llvm/IR/DerivedTypes.h"
29 #include "llvm/IR/GlobalAlias.h"
30 #include "llvm/IR/GlobalVariable.h"
31 #include "llvm/IR/IRBuilder.h"
32 #include "llvm/IR/Instructions.h"
33 #include "llvm/IR/IntrinsicInst.h"
34 #include "llvm/IR/Intrinsics.h"
35 #include "llvm/IR/MDBuilder.h"
36 #include "llvm/IR/Metadata.h"
37 #include "llvm/IR/Operator.h"
38 #include "llvm/Support/CFG.h"
39 #include "llvm/Support/Debug.h"
40 #include "llvm/Support/GetElementPtrTypeIterator.h"
41 #include "llvm/Support/MathExtras.h"
42 #include "llvm/Support/ValueHandle.h"
43 #include "llvm/Support/raw_ostream.h"
46 //===----------------------------------------------------------------------===//
47 // Local constant propagation.
50 /// ConstantFoldTerminator - If a terminator instruction is predicated on a
51 /// constant value, convert it into an unconditional branch to the constant
52 /// destination. This is a nontrivial operation because the successors of this
53 /// basic block must have their PHI nodes updated.
54 /// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch
55 /// conditions and indirectbr addresses this might make dead if
56 /// DeleteDeadConditions is true.
57 bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions,
58 const TargetLibraryInfo *TLI) {
59 TerminatorInst *T = BB->getTerminator();
60 IRBuilder<> Builder(T);
62 // Branch - See if we are conditional jumping on constant
63 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
64 if (BI->isUnconditional()) return false; // Can't optimize uncond branch
65 BasicBlock *Dest1 = BI->getSuccessor(0);
66 BasicBlock *Dest2 = BI->getSuccessor(1);
68 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
69 // Are we branching on constant?
70 // YES. Change to unconditional branch...
71 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
72 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1;
74 //cerr << "Function: " << T->getParent()->getParent()
75 // << "\nRemoving branch from " << T->getParent()
76 // << "\n\nTo: " << OldDest << endl;
78 // Let the basic block know that we are letting go of it. Based on this,
79 // it will adjust it's PHI nodes.
80 OldDest->removePredecessor(BB);
82 // Replace the conditional branch with an unconditional one.
83 Builder.CreateBr(Destination);
84 BI->eraseFromParent();
88 if (Dest2 == Dest1) { // Conditional branch to same location?
89 // This branch matches something like this:
90 // br bool %cond, label %Dest, label %Dest
91 // and changes it into: br label %Dest
93 // Let the basic block know that we are letting go of one copy of it.
94 assert(BI->getParent() && "Terminator not inserted in block!");
95 Dest1->removePredecessor(BI->getParent());
97 // Replace the conditional branch with an unconditional one.
98 Builder.CreateBr(Dest1);
99 Value *Cond = BI->getCondition();
100 BI->eraseFromParent();
101 if (DeleteDeadConditions)
102 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
108 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
109 // If we are switching on a constant, we can convert the switch into a
110 // single branch instruction!
111 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
112 BasicBlock *TheOnlyDest = SI->getDefaultDest();
113 BasicBlock *DefaultDest = TheOnlyDest;
115 // Figure out which case it goes to.
116 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
118 // Found case matching a constant operand?
119 if (i.getCaseValue() == CI) {
120 TheOnlyDest = i.getCaseSuccessor();
124 // Check to see if this branch is going to the same place as the default
125 // dest. If so, eliminate it as an explicit compare.
126 if (i.getCaseSuccessor() == DefaultDest) {
127 MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
128 // MD should have 2 + NumCases operands.
129 if (MD && MD->getNumOperands() == 2 + SI->getNumCases()) {
130 // Collect branch weights into a vector.
131 SmallVector<uint32_t, 8> Weights;
132 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
134 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(MD_i));
136 Weights.push_back(CI->getValue().getZExtValue());
138 // Merge weight of this case to the default weight.
139 unsigned idx = i.getCaseIndex();
140 Weights[0] += Weights[idx+1];
141 // Remove weight for this case.
142 std::swap(Weights[idx+1], Weights.back());
144 SI->setMetadata(LLVMContext::MD_prof,
145 MDBuilder(BB->getContext()).
146 createBranchWeights(Weights));
148 // Remove this entry.
149 DefaultDest->removePredecessor(SI->getParent());
155 // Otherwise, check to see if the switch only branches to one destination.
156 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
158 if (i.getCaseSuccessor() != TheOnlyDest) TheOnlyDest = 0;
161 if (CI && !TheOnlyDest) {
162 // Branching on a constant, but not any of the cases, go to the default
164 TheOnlyDest = SI->getDefaultDest();
167 // If we found a single destination that we can fold the switch into, do so
170 // Insert the new branch.
171 Builder.CreateBr(TheOnlyDest);
172 BasicBlock *BB = SI->getParent();
174 // Remove entries from PHI nodes which we no longer branch to...
175 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
176 // Found case matching a constant operand?
177 BasicBlock *Succ = SI->getSuccessor(i);
178 if (Succ == TheOnlyDest)
179 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest
181 Succ->removePredecessor(BB);
184 // Delete the old switch.
185 Value *Cond = SI->getCondition();
186 SI->eraseFromParent();
187 if (DeleteDeadConditions)
188 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
192 if (SI->getNumCases() == 1) {
193 // Otherwise, we can fold this switch into a conditional branch
194 // instruction if it has only one non-default destination.
195 SwitchInst::CaseIt FirstCase = SI->case_begin();
196 IntegersSubset& Case = FirstCase.getCaseValueEx();
197 if (Case.isSingleNumber()) {
198 // FIXME: Currently work with ConstantInt based numbers.
199 Value *Cond = Builder.CreateICmpEQ(SI->getCondition(),
200 Case.getSingleNumber(0).toConstantInt(),
203 // Insert the new branch.
204 BranchInst *NewBr = Builder.CreateCondBr(Cond,
205 FirstCase.getCaseSuccessor(),
206 SI->getDefaultDest());
207 MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
208 if (MD && MD->getNumOperands() == 3) {
209 ConstantInt *SICase = dyn_cast<ConstantInt>(MD->getOperand(2));
210 ConstantInt *SIDef = dyn_cast<ConstantInt>(MD->getOperand(1));
211 assert(SICase && SIDef);
212 // The TrueWeight should be the weight for the single case of SI.
213 NewBr->setMetadata(LLVMContext::MD_prof,
214 MDBuilder(BB->getContext()).
215 createBranchWeights(SICase->getValue().getZExtValue(),
216 SIDef->getValue().getZExtValue()));
219 // Delete the old switch.
220 SI->eraseFromParent();
227 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
228 // indirectbr blockaddress(@F, @BB) -> br label @BB
229 if (BlockAddress *BA =
230 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
231 BasicBlock *TheOnlyDest = BA->getBasicBlock();
232 // Insert the new branch.
233 Builder.CreateBr(TheOnlyDest);
235 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
236 if (IBI->getDestination(i) == TheOnlyDest)
239 IBI->getDestination(i)->removePredecessor(IBI->getParent());
241 Value *Address = IBI->getAddress();
242 IBI->eraseFromParent();
243 if (DeleteDeadConditions)
244 RecursivelyDeleteTriviallyDeadInstructions(Address, TLI);
246 // If we didn't find our destination in the IBI successor list, then we
247 // have undefined behavior. Replace the unconditional branch with an
248 // 'unreachable' instruction.
250 BB->getTerminator()->eraseFromParent();
251 new UnreachableInst(BB->getContext(), BB);
262 //===----------------------------------------------------------------------===//
263 // Local dead code elimination.
266 /// isInstructionTriviallyDead - Return true if the result produced by the
267 /// instruction is not used, and the instruction has no side effects.
269 bool llvm::isInstructionTriviallyDead(Instruction *I,
270 const TargetLibraryInfo *TLI) {
271 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
273 // We don't want the landingpad instruction removed by anything this general.
274 if (isa<LandingPadInst>(I))
277 // We don't want debug info removed by anything this general, unless
278 // debug info is empty.
279 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) {
280 if (DDI->getAddress())
284 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) {
290 if (!I->mayHaveSideEffects()) return true;
292 // Special case intrinsics that "may have side effects" but can be deleted
294 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
295 // Safe to delete llvm.stacksave if dead.
296 if (II->getIntrinsicID() == Intrinsic::stacksave)
299 // Lifetime intrinsics are dead when their right-hand is undef.
300 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
301 II->getIntrinsicID() == Intrinsic::lifetime_end)
302 return isa<UndefValue>(II->getArgOperand(1));
305 if (isAllocLikeFn(I, TLI)) return true;
307 if (CallInst *CI = isFreeCall(I, TLI))
308 if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
309 return C->isNullValue() || isa<UndefValue>(C);
314 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
315 /// trivially dead instruction, delete it. If that makes any of its operands
316 /// trivially dead, delete them too, recursively. Return true if any
317 /// instructions were deleted.
319 llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V,
320 const TargetLibraryInfo *TLI) {
321 Instruction *I = dyn_cast<Instruction>(V);
322 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I, TLI))
325 SmallVector<Instruction*, 16> DeadInsts;
326 DeadInsts.push_back(I);
329 I = DeadInsts.pop_back_val();
331 // Null out all of the instruction's operands to see if any operand becomes
333 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
334 Value *OpV = I->getOperand(i);
337 if (!OpV->use_empty()) continue;
339 // If the operand is an instruction that became dead as we nulled out the
340 // operand, and if it is 'trivially' dead, delete it in a future loop
342 if (Instruction *OpI = dyn_cast<Instruction>(OpV))
343 if (isInstructionTriviallyDead(OpI, TLI))
344 DeadInsts.push_back(OpI);
347 I->eraseFromParent();
348 } while (!DeadInsts.empty());
353 /// areAllUsesEqual - Check whether the uses of a value are all the same.
354 /// This is similar to Instruction::hasOneUse() except this will also return
355 /// true when there are no uses or multiple uses that all refer to the same
357 static bool areAllUsesEqual(Instruction *I) {
358 Value::use_iterator UI = I->use_begin();
359 Value::use_iterator UE = I->use_end();
364 for (++UI; UI != UE; ++UI) {
371 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
372 /// dead PHI node, due to being a def-use chain of single-use nodes that
373 /// either forms a cycle or is terminated by a trivially dead instruction,
374 /// delete it. If that makes any of its operands trivially dead, delete them
375 /// too, recursively. Return true if a change was made.
376 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN,
377 const TargetLibraryInfo *TLI) {
378 SmallPtrSet<Instruction*, 4> Visited;
379 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
380 I = cast<Instruction>(*I->use_begin())) {
382 return RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
384 // If we find an instruction more than once, we're on a cycle that
385 // won't prove fruitful.
386 if (!Visited.insert(I)) {
387 // Break the cycle and delete the instruction and its operands.
388 I->replaceAllUsesWith(UndefValue::get(I->getType()));
389 (void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
396 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
397 /// simplify any instructions in it and recursively delete dead instructions.
399 /// This returns true if it changed the code, note that it can delete
400 /// instructions in other blocks as well in this block.
401 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const DataLayout *TD,
402 const TargetLibraryInfo *TLI) {
403 bool MadeChange = false;
406 // In debug builds, ensure that the terminator of the block is never replaced
407 // or deleted by these simplifications. The idea of simplification is that it
408 // cannot introduce new instructions, and there is no way to replace the
409 // terminator of a block without introducing a new instruction.
410 AssertingVH<Instruction> TerminatorVH(--BB->end());
413 for (BasicBlock::iterator BI = BB->begin(), E = --BB->end(); BI != E; ) {
414 assert(!BI->isTerminator());
415 Instruction *Inst = BI++;
418 if (recursivelySimplifyInstruction(Inst, TD)) {
425 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI);
432 //===----------------------------------------------------------------------===//
433 // Control Flow Graph Restructuring.
437 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
438 /// method is called when we're about to delete Pred as a predecessor of BB. If
439 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
441 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
442 /// nodes that collapse into identity values. For example, if we have:
443 /// x = phi(1, 0, 0, 0)
446 /// .. and delete the predecessor corresponding to the '1', this will attempt to
447 /// recursively fold the and to 0.
448 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
450 // This only adjusts blocks with PHI nodes.
451 if (!isa<PHINode>(BB->begin()))
454 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
455 // them down. This will leave us with single entry phi nodes and other phis
456 // that can be removed.
457 BB->removePredecessor(Pred, true);
459 WeakVH PhiIt = &BB->front();
460 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
461 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
462 Value *OldPhiIt = PhiIt;
464 if (!recursivelySimplifyInstruction(PN, TD))
467 // If recursive simplification ended up deleting the next PHI node we would
468 // iterate to, then our iterator is invalid, restart scanning from the top
470 if (PhiIt != OldPhiIt) PhiIt = &BB->front();
475 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
476 /// predecessor is known to have one successor (DestBB!). Eliminate the edge
477 /// between them, moving the instructions in the predecessor into DestBB and
478 /// deleting the predecessor block.
480 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) {
481 // If BB has single-entry PHI nodes, fold them.
482 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
483 Value *NewVal = PN->getIncomingValue(0);
484 // Replace self referencing PHI with undef, it must be dead.
485 if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
486 PN->replaceAllUsesWith(NewVal);
487 PN->eraseFromParent();
490 BasicBlock *PredBB = DestBB->getSinglePredecessor();
491 assert(PredBB && "Block doesn't have a single predecessor!");
493 // Zap anything that took the address of DestBB. Not doing this will give the
494 // address an invalid value.
495 if (DestBB->hasAddressTaken()) {
496 BlockAddress *BA = BlockAddress::get(DestBB);
497 Constant *Replacement =
498 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1);
499 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
501 BA->destroyConstant();
504 // Anything that branched to PredBB now branches to DestBB.
505 PredBB->replaceAllUsesWith(DestBB);
507 // Splice all the instructions from PredBB to DestBB.
508 PredBB->getTerminator()->eraseFromParent();
509 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
512 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>();
514 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock();
515 DT->changeImmediateDominator(DestBB, PredBBIDom);
516 DT->eraseNode(PredBB);
518 ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>();
520 PI->replaceAllUses(PredBB, DestBB);
521 PI->removeEdge(ProfileInfo::getEdge(PredBB, DestBB));
525 PredBB->eraseFromParent();
528 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
529 /// almost-empty BB ending in an unconditional branch to Succ, into succ.
531 /// Assumption: Succ is the single successor for BB.
533 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
534 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
536 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
537 << Succ->getName() << "\n");
538 // Shortcut, if there is only a single predecessor it must be BB and merging
540 if (Succ->getSinglePredecessor()) return true;
542 // Make a list of the predecessors of BB
543 SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
545 // Look at all the phi nodes in Succ, to see if they present a conflict when
546 // merging these blocks
547 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
548 PHINode *PN = cast<PHINode>(I);
550 // If the incoming value from BB is again a PHINode in
551 // BB which has the same incoming value for *PI as PN does, we can
552 // merge the phi nodes and then the blocks can still be merged
553 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
554 if (BBPN && BBPN->getParent() == BB) {
555 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
556 BasicBlock *IBB = PN->getIncomingBlock(PI);
557 if (BBPreds.count(IBB) &&
558 BBPN->getIncomingValueForBlock(IBB) != PN->getIncomingValue(PI)) {
559 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
560 << Succ->getName() << " is conflicting with "
561 << BBPN->getName() << " with regard to common predecessor "
562 << IBB->getName() << "\n");
567 Value* Val = PN->getIncomingValueForBlock(BB);
568 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
569 // See if the incoming value for the common predecessor is equal to the
570 // one for BB, in which case this phi node will not prevent the merging
572 BasicBlock *IBB = PN->getIncomingBlock(PI);
573 if (BBPreds.count(IBB) && Val != PN->getIncomingValue(PI)) {
574 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
575 << Succ->getName() << " is conflicting with regard to common "
576 << "predecessor " << IBB->getName() << "\n");
586 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
587 /// unconditional branch, and contains no instructions other than PHI nodes,
588 /// potential side-effect free intrinsics and the branch. If possible,
589 /// eliminate BB by rewriting all the predecessors to branch to the successor
590 /// block and return true. If we can't transform, return false.
591 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
592 assert(BB != &BB->getParent()->getEntryBlock() &&
593 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
595 // We can't eliminate infinite loops.
596 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
597 if (BB == Succ) return false;
599 // Check to see if merging these blocks would cause conflicts for any of the
600 // phi nodes in BB or Succ. If not, we can safely merge.
601 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
603 // Check for cases where Succ has multiple predecessors and a PHI node in BB
604 // has uses which will not disappear when the PHI nodes are merged. It is
605 // possible to handle such cases, but difficult: it requires checking whether
606 // BB dominates Succ, which is non-trivial to calculate in the case where
607 // Succ has multiple predecessors. Also, it requires checking whether
608 // constructing the necessary self-referential PHI node doesn't introduce any
609 // conflicts; this isn't too difficult, but the previous code for doing this
612 // Note that if this check finds a live use, BB dominates Succ, so BB is
613 // something like a loop pre-header (or rarely, a part of an irreducible CFG);
614 // folding the branch isn't profitable in that case anyway.
615 if (!Succ->getSinglePredecessor()) {
616 BasicBlock::iterator BBI = BB->begin();
617 while (isa<PHINode>(*BBI)) {
618 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
620 if (PHINode* PN = dyn_cast<PHINode>(*UI)) {
621 if (PN->getIncomingBlock(UI) != BB)
631 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
633 if (isa<PHINode>(Succ->begin())) {
634 // If there is more than one pred of succ, and there are PHI nodes in
635 // the successor, then we need to add incoming edges for the PHI nodes
637 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
639 // Loop over all of the PHI nodes in the successor of BB.
640 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
641 PHINode *PN = cast<PHINode>(I);
642 Value *OldVal = PN->removeIncomingValue(BB, false);
643 assert(OldVal && "No entry in PHI for Pred BB!");
645 // If this incoming value is one of the PHI nodes in BB, the new entries
646 // in the PHI node are the entries from the old PHI.
647 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
648 PHINode *OldValPN = cast<PHINode>(OldVal);
649 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
650 // Note that, since we are merging phi nodes and BB and Succ might
651 // have common predecessors, we could end up with a phi node with
652 // identical incoming branches. This will be cleaned up later (and
653 // will trigger asserts if we try to clean it up now, without also
654 // simplifying the corresponding conditional branch).
655 PN->addIncoming(OldValPN->getIncomingValue(i),
656 OldValPN->getIncomingBlock(i));
658 // Add an incoming value for each of the new incoming values.
659 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
660 PN->addIncoming(OldVal, BBPreds[i]);
665 if (Succ->getSinglePredecessor()) {
666 // BB is the only predecessor of Succ, so Succ will end up with exactly
667 // the same predecessors BB had.
669 // Copy over any phi, debug or lifetime instruction.
670 BB->getTerminator()->eraseFromParent();
671 Succ->getInstList().splice(Succ->getFirstNonPHI(), BB->getInstList());
673 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
674 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
675 assert(PN->use_empty() && "There shouldn't be any uses here!");
676 PN->eraseFromParent();
680 // Everything that jumped to BB now goes to Succ.
681 BB->replaceAllUsesWith(Succ);
682 if (!Succ->hasName()) Succ->takeName(BB);
683 BB->eraseFromParent(); // Delete the old basic block.
687 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
688 /// nodes in this block. This doesn't try to be clever about PHI nodes
689 /// which differ only in the order of the incoming values, but instcombine
690 /// orders them so it usually won't matter.
692 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
693 bool Changed = false;
695 // This implementation doesn't currently consider undef operands
696 // specially. Theoretically, two phis which are identical except for
697 // one having an undef where the other doesn't could be collapsed.
699 // Map from PHI hash values to PHI nodes. If multiple PHIs have
700 // the same hash value, the element is the first PHI in the
701 // linked list in CollisionMap.
702 DenseMap<uintptr_t, PHINode *> HashMap;
704 // Maintain linked lists of PHI nodes with common hash values.
705 DenseMap<PHINode *, PHINode *> CollisionMap;
708 for (BasicBlock::iterator I = BB->begin();
709 PHINode *PN = dyn_cast<PHINode>(I++); ) {
710 // Compute a hash value on the operands. Instcombine will likely have sorted
711 // them, which helps expose duplicates, but we have to check all the
712 // operands to be safe in case instcombine hasn't run.
714 // This hash algorithm is quite weak as hash functions go, but it seems
715 // to do a good enough job for this particular purpose, and is very quick.
716 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
717 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
718 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
720 for (PHINode::block_iterator I = PN->block_begin(), E = PN->block_end();
722 Hash ^= reinterpret_cast<uintptr_t>(static_cast<BasicBlock *>(*I));
723 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
725 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1.
727 // If we've never seen this hash value before, it's a unique PHI.
728 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
729 HashMap.insert(std::make_pair(Hash, PN));
730 if (Pair.second) continue;
731 // Otherwise it's either a duplicate or a hash collision.
732 for (PHINode *OtherPN = Pair.first->second; ; ) {
733 if (OtherPN->isIdenticalTo(PN)) {
734 // A duplicate. Replace this PHI with its duplicate.
735 PN->replaceAllUsesWith(OtherPN);
736 PN->eraseFromParent();
740 // A non-duplicate hash collision.
741 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
742 if (I == CollisionMap.end()) {
743 // Set this PHI to be the head of the linked list of colliding PHIs.
744 PHINode *Old = Pair.first->second;
745 Pair.first->second = PN;
746 CollisionMap[PN] = Old;
749 // Proceed to the next PHI in the list.
757 /// enforceKnownAlignment - If the specified pointer points to an object that
758 /// we control, modify the object's alignment to PrefAlign. This isn't
759 /// often possible though. If alignment is important, a more reliable approach
760 /// is to simply align all global variables and allocation instructions to
761 /// their preferred alignment from the beginning.
763 static unsigned enforceKnownAlignment(Value *V, unsigned Align,
764 unsigned PrefAlign, const DataLayout *TD) {
765 V = V->stripPointerCasts();
767 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
768 // If the preferred alignment is greater than the natural stack alignment
769 // then don't round up. This avoids dynamic stack realignment.
770 if (TD && TD->exceedsNaturalStackAlignment(PrefAlign))
772 // If there is a requested alignment and if this is an alloca, round up.
773 if (AI->getAlignment() >= PrefAlign)
774 return AI->getAlignment();
775 AI->setAlignment(PrefAlign);
779 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
780 // If there is a large requested alignment and we can, bump up the alignment
782 if (GV->isDeclaration()) return Align;
783 // If the memory we set aside for the global may not be the memory used by
784 // the final program then it is impossible for us to reliably enforce the
785 // preferred alignment.
786 if (GV->isWeakForLinker()) return Align;
788 if (GV->getAlignment() >= PrefAlign)
789 return GV->getAlignment();
790 // We can only increase the alignment of the global if it has no alignment
791 // specified or if it is not assigned a section. If it is assigned a
792 // section, the global could be densely packed with other objects in the
793 // section, increasing the alignment could cause padding issues.
794 if (!GV->hasSection() || GV->getAlignment() == 0)
795 GV->setAlignment(PrefAlign);
796 return GV->getAlignment();
802 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
803 /// we can determine, return it, otherwise return 0. If PrefAlign is specified,
804 /// and it is more than the alignment of the ultimate object, see if we can
805 /// increase the alignment of the ultimate object, making this check succeed.
806 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
807 const DataLayout *TD) {
808 assert(V->getType()->isPointerTy() &&
809 "getOrEnforceKnownAlignment expects a pointer!");
810 unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64;
811 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
812 ComputeMaskedBits(V, KnownZero, KnownOne, TD);
813 unsigned TrailZ = KnownZero.countTrailingOnes();
815 // Avoid trouble with rediculously large TrailZ values, such as
816 // those computed from a null pointer.
817 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
819 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
821 // LLVM doesn't support alignments larger than this currently.
822 Align = std::min(Align, +Value::MaximumAlignment);
824 if (PrefAlign > Align)
825 Align = enforceKnownAlignment(V, Align, PrefAlign, TD);
827 // We don't need to make any adjustment.
831 ///===---------------------------------------------------------------------===//
832 /// Dbg Intrinsic utilities
835 /// See if there is a dbg.value intrinsic for DIVar before I.
836 static bool LdStHasDebugValue(DIVariable &DIVar, Instruction *I) {
837 // Since we can't guarantee that the original dbg.declare instrinsic
838 // is removed by LowerDbgDeclare(), we need to make sure that we are
839 // not inserting the same dbg.value intrinsic over and over.
840 llvm::BasicBlock::InstListType::iterator PrevI(I);
841 if (PrevI != I->getParent()->getInstList().begin()) {
843 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(PrevI))
844 if (DVI->getValue() == I->getOperand(0) &&
845 DVI->getOffset() == 0 &&
846 DVI->getVariable() == DIVar)
852 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
853 /// that has an associated llvm.dbg.decl intrinsic.
854 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
855 StoreInst *SI, DIBuilder &Builder) {
856 DIVariable DIVar(DDI->getVariable());
857 assert((!DIVar || DIVar.isVariable()) &&
858 "Variable in DbgDeclareInst should be either null or a DIVariable.");
862 if (LdStHasDebugValue(DIVar, SI))
865 Instruction *DbgVal = NULL;
866 // If an argument is zero extended then use argument directly. The ZExt
867 // may be zapped by an optimization pass in future.
868 Argument *ExtendedArg = NULL;
869 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
870 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0));
871 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
872 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0));
874 DbgVal = Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, SI);
876 DbgVal = Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, SI);
878 // Propagate any debug metadata from the store onto the dbg.value.
879 DebugLoc SIDL = SI->getDebugLoc();
880 if (!SIDL.isUnknown())
881 DbgVal->setDebugLoc(SIDL);
882 // Otherwise propagate debug metadata from dbg.declare.
884 DbgVal->setDebugLoc(DDI->getDebugLoc());
888 /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
889 /// that has an associated llvm.dbg.decl intrinsic.
890 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
891 LoadInst *LI, DIBuilder &Builder) {
892 DIVariable DIVar(DDI->getVariable());
893 assert((!DIVar || DIVar.isVariable()) &&
894 "Variable in DbgDeclareInst should be either null or a DIVariable.");
898 if (LdStHasDebugValue(DIVar, LI))
901 Instruction *DbgVal =
902 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0,
905 // Propagate any debug metadata from the store onto the dbg.value.
906 DebugLoc LIDL = LI->getDebugLoc();
907 if (!LIDL.isUnknown())
908 DbgVal->setDebugLoc(LIDL);
909 // Otherwise propagate debug metadata from dbg.declare.
911 DbgVal->setDebugLoc(DDI->getDebugLoc());
915 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
916 /// of llvm.dbg.value intrinsics.
917 bool llvm::LowerDbgDeclare(Function &F) {
918 DIBuilder DIB(*F.getParent());
919 SmallVector<DbgDeclareInst *, 4> Dbgs;
920 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
921 for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ++BI) {
922 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(BI))
928 for (SmallVectorImpl<DbgDeclareInst *>::iterator I = Dbgs.begin(),
929 E = Dbgs.end(); I != E; ++I) {
930 DbgDeclareInst *DDI = *I;
931 if (AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress())) {
932 // We only remove the dbg.declare intrinsic if all uses are
933 // converted to dbg.value intrinsics.
934 bool RemoveDDI = true;
935 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
937 if (StoreInst *SI = dyn_cast<StoreInst>(*UI))
938 ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
939 else if (LoadInst *LI = dyn_cast<LoadInst>(*UI))
940 ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
944 DDI->eraseFromParent();
950 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the
951 /// alloca 'V', if any.
952 DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) {
953 if (MDNode *DebugNode = MDNode::getIfExists(V->getContext(), V))
954 for (Value::use_iterator UI = DebugNode->use_begin(),
955 E = DebugNode->use_end(); UI != E; ++UI)
956 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(*UI))
962 bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
963 DIBuilder &Builder) {
964 DbgDeclareInst *DDI = FindAllocaDbgDeclare(AI);
967 DIVariable DIVar(DDI->getVariable());
968 assert((!DIVar || DIVar.isVariable()) &&
969 "Variable in DbgDeclareInst should be either null or a DIVariable.");
973 // Create a copy of the original DIDescriptor for user variable, appending
974 // "deref" operation to a list of address elements, as new llvm.dbg.declare
975 // will take a value storing address of the memory for variable, not
977 Type *Int64Ty = Type::getInt64Ty(AI->getContext());
978 SmallVector<Value*, 4> NewDIVarAddress;
979 if (DIVar.hasComplexAddress()) {
980 for (unsigned i = 0, n = DIVar.getNumAddrElements(); i < n; ++i) {
981 NewDIVarAddress.push_back(
982 ConstantInt::get(Int64Ty, DIVar.getAddrElement(i)));
985 NewDIVarAddress.push_back(ConstantInt::get(Int64Ty, DIBuilder::OpDeref));
986 DIVariable NewDIVar = Builder.createComplexVariable(
987 DIVar.getTag(), DIVar.getContext(), DIVar.getName(),
988 DIVar.getFile(), DIVar.getLineNumber(), DIVar.getType(),
989 NewDIVarAddress, DIVar.getArgNumber());
991 // Insert llvm.dbg.declare in the same basic block as the original alloca,
992 // and remove old llvm.dbg.declare.
993 BasicBlock *BB = AI->getParent();
994 Builder.insertDeclare(NewAllocaAddress, NewDIVar, BB);
995 DDI->eraseFromParent();
999 bool llvm::removeUnreachableBlocks(Function &F) {
1000 SmallPtrSet<BasicBlock*, 16> Reachable;
1001 SmallVector<BasicBlock*, 128> Worklist;
1002 Worklist.push_back(&F.getEntryBlock());
1003 Reachable.insert(&F.getEntryBlock());
1005 BasicBlock *BB = Worklist.pop_back_val();
1006 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1007 if (Reachable.insert(*SI))
1008 Worklist.push_back(*SI);
1009 } while (!Worklist.empty());
1011 if (Reachable.size() == F.size())
1014 assert(Reachable.size() < F.size());
1015 for (Function::iterator I = llvm::next(F.begin()), E = F.end(); I != E; ++I) {
1016 if (Reachable.count(I))
1019 for (succ_iterator SI = succ_begin(I), SE = succ_end(I); SI != SE; ++SI)
1020 if (Reachable.count(*SI))
1021 (*SI)->removePredecessor(I);
1022 I->dropAllReferences();
1025 for (Function::iterator I = llvm::next(F.begin()), E=F.end(); I != E;)
1026 if (!Reachable.count(I))
1027 I = F.getBasicBlockList().erase(I);