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/DIBuilder.h"
18 #include "llvm/DebugInfo.h"
19 #include "llvm/DerivedTypes.h"
20 #include "llvm/GlobalAlias.h"
21 #include "llvm/GlobalVariable.h"
22 #include "llvm/IRBuilder.h"
23 #include "llvm/Instructions.h"
24 #include "llvm/IntrinsicInst.h"
25 #include "llvm/Intrinsics.h"
26 #include "llvm/MDBuilder.h"
27 #include "llvm/Metadata.h"
28 #include "llvm/Operator.h"
29 #include "llvm/ADT/DenseMap.h"
30 #include "llvm/ADT/SmallPtrSet.h"
31 #include "llvm/Analysis/Dominators.h"
32 #include "llvm/Analysis/InstructionSimplify.h"
33 #include "llvm/Analysis/MemoryBuiltins.h"
34 #include "llvm/Analysis/ProfileInfo.h"
35 #include "llvm/Analysis/ValueTracking.h"
36 #include "llvm/Support/CFG.h"
37 #include "llvm/Support/Debug.h"
38 #include "llvm/Support/GetElementPtrTypeIterator.h"
39 #include "llvm/Support/MathExtras.h"
40 #include "llvm/Support/ValueHandle.h"
41 #include "llvm/Support/raw_ostream.h"
42 #include "llvm/Target/TargetData.h"
45 //===----------------------------------------------------------------------===//
46 // Local constant propagation.
49 /// ConstantFoldTerminator - If a terminator instruction is predicated on a
50 /// constant value, convert it into an unconditional branch to the constant
51 /// destination. This is a nontrivial operation because the successors of this
52 /// basic block must have their PHI nodes updated.
53 /// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch
54 /// conditions and indirectbr addresses this might make dead if
55 /// DeleteDeadConditions is true.
56 bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions,
57 const TargetLibraryInfo *TLI) {
58 TerminatorInst *T = BB->getTerminator();
59 IRBuilder<> Builder(T);
61 // Branch - See if we are conditional jumping on constant
62 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
63 if (BI->isUnconditional()) return false; // Can't optimize uncond branch
64 BasicBlock *Dest1 = BI->getSuccessor(0);
65 BasicBlock *Dest2 = BI->getSuccessor(1);
67 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
68 // Are we branching on constant?
69 // YES. Change to unconditional branch...
70 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
71 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1;
73 //cerr << "Function: " << T->getParent()->getParent()
74 // << "\nRemoving branch from " << T->getParent()
75 // << "\n\nTo: " << OldDest << endl;
77 // Let the basic block know that we are letting go of it. Based on this,
78 // it will adjust it's PHI nodes.
79 OldDest->removePredecessor(BB);
81 // Replace the conditional branch with an unconditional one.
82 Builder.CreateBr(Destination);
83 BI->eraseFromParent();
87 if (Dest2 == Dest1) { // Conditional branch to same location?
88 // This branch matches something like this:
89 // br bool %cond, label %Dest, label %Dest
90 // and changes it into: br label %Dest
92 // Let the basic block know that we are letting go of one copy of it.
93 assert(BI->getParent() && "Terminator not inserted in block!");
94 Dest1->removePredecessor(BI->getParent());
96 // Replace the conditional branch with an unconditional one.
97 Builder.CreateBr(Dest1);
98 Value *Cond = BI->getCondition();
99 BI->eraseFromParent();
100 if (DeleteDeadConditions)
101 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
107 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
108 // If we are switching on a constant, we can convert the switch into a
109 // single branch instruction!
110 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
111 BasicBlock *TheOnlyDest = SI->getDefaultDest();
112 BasicBlock *DefaultDest = TheOnlyDest;
114 // Figure out which case it goes to.
115 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
117 // Found case matching a constant operand?
118 if (i.getCaseValue() == CI) {
119 TheOnlyDest = i.getCaseSuccessor();
123 // Check to see if this branch is going to the same place as the default
124 // dest. If so, eliminate it as an explicit compare.
125 if (i.getCaseSuccessor() == DefaultDest) {
126 MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
127 // MD should have 2 + NumCases operands.
128 if (MD && MD->getNumOperands() == 2 + SI->getNumCases()) {
129 // Collect branch weights into a vector.
130 SmallVector<uint32_t, 8> Weights;
131 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
133 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(MD_i));
135 Weights.push_back(CI->getValue().getZExtValue());
137 // Merge weight of this case to the default weight.
138 unsigned idx = i.getCaseIndex();
139 Weights[0] += Weights[idx+1];
140 // Remove weight for this case.
141 std::swap(Weights[idx+1], Weights.back());
143 SI->setMetadata(LLVMContext::MD_prof,
144 MDBuilder(BB->getContext()).
145 createBranchWeights(Weights));
147 // Remove this entry.
148 DefaultDest->removePredecessor(SI->getParent());
154 // Otherwise, check to see if the switch only branches to one destination.
155 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
157 if (i.getCaseSuccessor() != TheOnlyDest) TheOnlyDest = 0;
160 if (CI && !TheOnlyDest) {
161 // Branching on a constant, but not any of the cases, go to the default
163 TheOnlyDest = SI->getDefaultDest();
166 // If we found a single destination that we can fold the switch into, do so
169 // Insert the new branch.
170 Builder.CreateBr(TheOnlyDest);
171 BasicBlock *BB = SI->getParent();
173 // Remove entries from PHI nodes which we no longer branch to...
174 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
175 // Found case matching a constant operand?
176 BasicBlock *Succ = SI->getSuccessor(i);
177 if (Succ == TheOnlyDest)
178 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest
180 Succ->removePredecessor(BB);
183 // Delete the old switch.
184 Value *Cond = SI->getCondition();
185 SI->eraseFromParent();
186 if (DeleteDeadConditions)
187 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
191 if (SI->getNumCases() == 1) {
192 // Otherwise, we can fold this switch into a conditional branch
193 // instruction if it has only one non-default destination.
194 SwitchInst::CaseIt FirstCase = SI->case_begin();
195 IntegersSubset& Case = FirstCase.getCaseValueEx();
196 if (Case.isSingleNumber()) {
197 // FIXME: Currently work with ConstantInt based numbers.
198 Value *Cond = Builder.CreateICmpEQ(SI->getCondition(),
199 Case.getSingleNumber(0).toConstantInt(),
202 // Insert the new branch.
203 Builder.CreateCondBr(Cond, FirstCase.getCaseSuccessor(),
204 SI->getDefaultDest());
206 // Delete the old switch.
207 SI->eraseFromParent();
214 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
215 // indirectbr blockaddress(@F, @BB) -> br label @BB
216 if (BlockAddress *BA =
217 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
218 BasicBlock *TheOnlyDest = BA->getBasicBlock();
219 // Insert the new branch.
220 Builder.CreateBr(TheOnlyDest);
222 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
223 if (IBI->getDestination(i) == TheOnlyDest)
226 IBI->getDestination(i)->removePredecessor(IBI->getParent());
228 Value *Address = IBI->getAddress();
229 IBI->eraseFromParent();
230 if (DeleteDeadConditions)
231 RecursivelyDeleteTriviallyDeadInstructions(Address, TLI);
233 // If we didn't find our destination in the IBI successor list, then we
234 // have undefined behavior. Replace the unconditional branch with an
235 // 'unreachable' instruction.
237 BB->getTerminator()->eraseFromParent();
238 new UnreachableInst(BB->getContext(), BB);
249 //===----------------------------------------------------------------------===//
250 // Local dead code elimination.
253 /// isInstructionTriviallyDead - Return true if the result produced by the
254 /// instruction is not used, and the instruction has no side effects.
256 bool llvm::isInstructionTriviallyDead(Instruction *I,
257 const TargetLibraryInfo *TLI) {
258 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
260 // We don't want the landingpad instruction removed by anything this general.
261 if (isa<LandingPadInst>(I))
264 // We don't want debug info removed by anything this general, unless
265 // debug info is empty.
266 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) {
267 if (DDI->getAddress())
271 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) {
277 if (!I->mayHaveSideEffects()) return true;
279 // Special case intrinsics that "may have side effects" but can be deleted
281 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
282 // Safe to delete llvm.stacksave if dead.
283 if (II->getIntrinsicID() == Intrinsic::stacksave)
286 // Lifetime intrinsics are dead when their right-hand is undef.
287 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
288 II->getIntrinsicID() == Intrinsic::lifetime_end)
289 return isa<UndefValue>(II->getArgOperand(1));
292 if (isAllocLikeFn(I, TLI)) return true;
294 if (CallInst *CI = isFreeCall(I, TLI))
295 if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
296 return C->isNullValue() || isa<UndefValue>(C);
301 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
302 /// trivially dead instruction, delete it. If that makes any of its operands
303 /// trivially dead, delete them too, recursively. Return true if any
304 /// instructions were deleted.
306 llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V,
307 const TargetLibraryInfo *TLI) {
308 Instruction *I = dyn_cast<Instruction>(V);
309 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I, TLI))
312 SmallVector<Instruction*, 16> DeadInsts;
313 DeadInsts.push_back(I);
316 I = DeadInsts.pop_back_val();
318 // Null out all of the instruction's operands to see if any operand becomes
320 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
321 Value *OpV = I->getOperand(i);
324 if (!OpV->use_empty()) continue;
326 // If the operand is an instruction that became dead as we nulled out the
327 // operand, and if it is 'trivially' dead, delete it in a future loop
329 if (Instruction *OpI = dyn_cast<Instruction>(OpV))
330 if (isInstructionTriviallyDead(OpI, TLI))
331 DeadInsts.push_back(OpI);
334 I->eraseFromParent();
335 } while (!DeadInsts.empty());
340 /// areAllUsesEqual - Check whether the uses of a value are all the same.
341 /// This is similar to Instruction::hasOneUse() except this will also return
342 /// true when there are no uses or multiple uses that all refer to the same
344 static bool areAllUsesEqual(Instruction *I) {
345 Value::use_iterator UI = I->use_begin();
346 Value::use_iterator UE = I->use_end();
351 for (++UI; UI != UE; ++UI) {
358 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
359 /// dead PHI node, due to being a def-use chain of single-use nodes that
360 /// either forms a cycle or is terminated by a trivially dead instruction,
361 /// delete it. If that makes any of its operands trivially dead, delete them
362 /// too, recursively. Return true if a change was made.
363 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN,
364 const TargetLibraryInfo *TLI) {
365 SmallPtrSet<Instruction*, 4> Visited;
366 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
367 I = cast<Instruction>(*I->use_begin())) {
369 return RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
371 // If we find an instruction more than once, we're on a cycle that
372 // won't prove fruitful.
373 if (!Visited.insert(I)) {
374 // Break the cycle and delete the instruction and its operands.
375 I->replaceAllUsesWith(UndefValue::get(I->getType()));
376 (void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
383 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
384 /// simplify any instructions in it and recursively delete dead instructions.
386 /// This returns true if it changed the code, note that it can delete
387 /// instructions in other blocks as well in this block.
388 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD,
389 const TargetLibraryInfo *TLI) {
390 bool MadeChange = false;
393 // In debug builds, ensure that the terminator of the block is never replaced
394 // or deleted by these simplifications. The idea of simplification is that it
395 // cannot introduce new instructions, and there is no way to replace the
396 // terminator of a block without introducing a new instruction.
397 AssertingVH<Instruction> TerminatorVH(--BB->end());
400 for (BasicBlock::iterator BI = BB->begin(), E = --BB->end(); BI != E; ) {
401 assert(!BI->isTerminator());
402 Instruction *Inst = BI++;
405 if (recursivelySimplifyInstruction(Inst, TD)) {
412 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI);
419 //===----------------------------------------------------------------------===//
420 // Control Flow Graph Restructuring.
424 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
425 /// method is called when we're about to delete Pred as a predecessor of BB. If
426 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
428 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
429 /// nodes that collapse into identity values. For example, if we have:
430 /// x = phi(1, 0, 0, 0)
433 /// .. and delete the predecessor corresponding to the '1', this will attempt to
434 /// recursively fold the and to 0.
435 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
437 // This only adjusts blocks with PHI nodes.
438 if (!isa<PHINode>(BB->begin()))
441 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
442 // them down. This will leave us with single entry phi nodes and other phis
443 // that can be removed.
444 BB->removePredecessor(Pred, true);
446 WeakVH PhiIt = &BB->front();
447 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
448 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
449 Value *OldPhiIt = PhiIt;
451 if (!recursivelySimplifyInstruction(PN, TD))
454 // If recursive simplification ended up deleting the next PHI node we would
455 // iterate to, then our iterator is invalid, restart scanning from the top
457 if (PhiIt != OldPhiIt) PhiIt = &BB->front();
462 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
463 /// predecessor is known to have one successor (DestBB!). Eliminate the edge
464 /// between them, moving the instructions in the predecessor into DestBB and
465 /// deleting the predecessor block.
467 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) {
468 // If BB has single-entry PHI nodes, fold them.
469 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
470 Value *NewVal = PN->getIncomingValue(0);
471 // Replace self referencing PHI with undef, it must be dead.
472 if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
473 PN->replaceAllUsesWith(NewVal);
474 PN->eraseFromParent();
477 BasicBlock *PredBB = DestBB->getSinglePredecessor();
478 assert(PredBB && "Block doesn't have a single predecessor!");
480 // Zap anything that took the address of DestBB. Not doing this will give the
481 // address an invalid value.
482 if (DestBB->hasAddressTaken()) {
483 BlockAddress *BA = BlockAddress::get(DestBB);
484 Constant *Replacement =
485 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1);
486 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
488 BA->destroyConstant();
491 // Anything that branched to PredBB now branches to DestBB.
492 PredBB->replaceAllUsesWith(DestBB);
494 // Splice all the instructions from PredBB to DestBB.
495 PredBB->getTerminator()->eraseFromParent();
496 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
499 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>();
501 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock();
502 DT->changeImmediateDominator(DestBB, PredBBIDom);
503 DT->eraseNode(PredBB);
505 ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>();
507 PI->replaceAllUses(PredBB, DestBB);
508 PI->removeEdge(ProfileInfo::getEdge(PredBB, DestBB));
512 PredBB->eraseFromParent();
515 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
516 /// almost-empty BB ending in an unconditional branch to Succ, into succ.
518 /// Assumption: Succ is the single successor for BB.
520 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
521 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
523 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
524 << Succ->getName() << "\n");
525 // Shortcut, if there is only a single predecessor it must be BB and merging
527 if (Succ->getSinglePredecessor()) return true;
529 // Make a list of the predecessors of BB
530 SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
532 // Look at all the phi nodes in Succ, to see if they present a conflict when
533 // merging these blocks
534 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
535 PHINode *PN = cast<PHINode>(I);
537 // If the incoming value from BB is again a PHINode in
538 // BB which has the same incoming value for *PI as PN does, we can
539 // merge the phi nodes and then the blocks can still be merged
540 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
541 if (BBPN && BBPN->getParent() == BB) {
542 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
543 BasicBlock *IBB = PN->getIncomingBlock(PI);
544 if (BBPreds.count(IBB) &&
545 BBPN->getIncomingValueForBlock(IBB) != PN->getIncomingValue(PI)) {
546 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
547 << Succ->getName() << " is conflicting with "
548 << BBPN->getName() << " with regard to common predecessor "
549 << IBB->getName() << "\n");
554 Value* Val = PN->getIncomingValueForBlock(BB);
555 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
556 // See if the incoming value for the common predecessor is equal to the
557 // one for BB, in which case this phi node will not prevent the merging
559 BasicBlock *IBB = PN->getIncomingBlock(PI);
560 if (BBPreds.count(IBB) && Val != PN->getIncomingValue(PI)) {
561 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
562 << Succ->getName() << " is conflicting with regard to common "
563 << "predecessor " << IBB->getName() << "\n");
573 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
574 /// unconditional branch, and contains no instructions other than PHI nodes,
575 /// potential side-effect free intrinsics and the branch. If possible,
576 /// eliminate BB by rewriting all the predecessors to branch to the successor
577 /// block and return true. If we can't transform, return false.
578 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
579 assert(BB != &BB->getParent()->getEntryBlock() &&
580 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
582 // We can't eliminate infinite loops.
583 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
584 if (BB == Succ) return false;
586 // Check to see if merging these blocks would cause conflicts for any of the
587 // phi nodes in BB or Succ. If not, we can safely merge.
588 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
590 // Check for cases where Succ has multiple predecessors and a PHI node in BB
591 // has uses which will not disappear when the PHI nodes are merged. It is
592 // possible to handle such cases, but difficult: it requires checking whether
593 // BB dominates Succ, which is non-trivial to calculate in the case where
594 // Succ has multiple predecessors. Also, it requires checking whether
595 // constructing the necessary self-referential PHI node doesn't intoduce any
596 // conflicts; this isn't too difficult, but the previous code for doing this
599 // Note that if this check finds a live use, BB dominates Succ, so BB is
600 // something like a loop pre-header (or rarely, a part of an irreducible CFG);
601 // folding the branch isn't profitable in that case anyway.
602 if (!Succ->getSinglePredecessor()) {
603 BasicBlock::iterator BBI = BB->begin();
604 while (isa<PHINode>(*BBI)) {
605 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
607 if (PHINode* PN = dyn_cast<PHINode>(*UI)) {
608 if (PN->getIncomingBlock(UI) != BB)
618 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
620 if (isa<PHINode>(Succ->begin())) {
621 // If there is more than one pred of succ, and there are PHI nodes in
622 // the successor, then we need to add incoming edges for the PHI nodes
624 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
626 // Loop over all of the PHI nodes in the successor of BB.
627 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
628 PHINode *PN = cast<PHINode>(I);
629 Value *OldVal = PN->removeIncomingValue(BB, false);
630 assert(OldVal && "No entry in PHI for Pred BB!");
632 // If this incoming value is one of the PHI nodes in BB, the new entries
633 // in the PHI node are the entries from the old PHI.
634 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
635 PHINode *OldValPN = cast<PHINode>(OldVal);
636 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
637 // Note that, since we are merging phi nodes and BB and Succ might
638 // have common predecessors, we could end up with a phi node with
639 // identical incoming branches. This will be cleaned up later (and
640 // will trigger asserts if we try to clean it up now, without also
641 // simplifying the corresponding conditional branch).
642 PN->addIncoming(OldValPN->getIncomingValue(i),
643 OldValPN->getIncomingBlock(i));
645 // Add an incoming value for each of the new incoming values.
646 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
647 PN->addIncoming(OldVal, BBPreds[i]);
652 if (Succ->getSinglePredecessor()) {
653 // BB is the only predecessor of Succ, so Succ will end up with exactly
654 // the same predecessors BB had.
656 // Copy over any phi, debug or lifetime instruction.
657 BB->getTerminator()->eraseFromParent();
658 Succ->getInstList().splice(Succ->getFirstNonPHI(), BB->getInstList());
660 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
661 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
662 assert(PN->use_empty() && "There shouldn't be any uses here!");
663 PN->eraseFromParent();
667 // Everything that jumped to BB now goes to Succ.
668 BB->replaceAllUsesWith(Succ);
669 if (!Succ->hasName()) Succ->takeName(BB);
670 BB->eraseFromParent(); // Delete the old basic block.
674 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
675 /// nodes in this block. This doesn't try to be clever about PHI nodes
676 /// which differ only in the order of the incoming values, but instcombine
677 /// orders them so it usually won't matter.
679 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
680 bool Changed = false;
682 // This implementation doesn't currently consider undef operands
683 // specially. Theoretically, two phis which are identical except for
684 // one having an undef where the other doesn't could be collapsed.
686 // Map from PHI hash values to PHI nodes. If multiple PHIs have
687 // the same hash value, the element is the first PHI in the
688 // linked list in CollisionMap.
689 DenseMap<uintptr_t, PHINode *> HashMap;
691 // Maintain linked lists of PHI nodes with common hash values.
692 DenseMap<PHINode *, PHINode *> CollisionMap;
695 for (BasicBlock::iterator I = BB->begin();
696 PHINode *PN = dyn_cast<PHINode>(I++); ) {
697 // Compute a hash value on the operands. Instcombine will likely have sorted
698 // them, which helps expose duplicates, but we have to check all the
699 // operands to be safe in case instcombine hasn't run.
701 // This hash algorithm is quite weak as hash functions go, but it seems
702 // to do a good enough job for this particular purpose, and is very quick.
703 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
704 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
705 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
707 for (PHINode::block_iterator I = PN->block_begin(), E = PN->block_end();
709 Hash ^= reinterpret_cast<uintptr_t>(static_cast<BasicBlock *>(*I));
710 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
712 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1.
714 // If we've never seen this hash value before, it's a unique PHI.
715 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
716 HashMap.insert(std::make_pair(Hash, PN));
717 if (Pair.second) continue;
718 // Otherwise it's either a duplicate or a hash collision.
719 for (PHINode *OtherPN = Pair.first->second; ; ) {
720 if (OtherPN->isIdenticalTo(PN)) {
721 // A duplicate. Replace this PHI with its duplicate.
722 PN->replaceAllUsesWith(OtherPN);
723 PN->eraseFromParent();
727 // A non-duplicate hash collision.
728 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
729 if (I == CollisionMap.end()) {
730 // Set this PHI to be the head of the linked list of colliding PHIs.
731 PHINode *Old = Pair.first->second;
732 Pair.first->second = PN;
733 CollisionMap[PN] = Old;
736 // Proceed to the next PHI in the list.
744 /// enforceKnownAlignment - If the specified pointer points to an object that
745 /// we control, modify the object's alignment to PrefAlign. This isn't
746 /// often possible though. If alignment is important, a more reliable approach
747 /// is to simply align all global variables and allocation instructions to
748 /// their preferred alignment from the beginning.
750 static unsigned enforceKnownAlignment(Value *V, unsigned Align,
751 unsigned PrefAlign, const TargetData *TD) {
752 V = V->stripPointerCasts();
754 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
755 // If the preferred alignment is greater than the natural stack alignment
756 // then don't round up. This avoids dynamic stack realignment.
757 if (TD && TD->exceedsNaturalStackAlignment(PrefAlign))
759 // If there is a requested alignment and if this is an alloca, round up.
760 if (AI->getAlignment() >= PrefAlign)
761 return AI->getAlignment();
762 AI->setAlignment(PrefAlign);
766 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
767 // If there is a large requested alignment and we can, bump up the alignment
769 if (GV->isDeclaration()) return Align;
770 // If the memory we set aside for the global may not be the memory used by
771 // the final program then it is impossible for us to reliably enforce the
772 // preferred alignment.
773 if (GV->isWeakForLinker()) return Align;
775 if (GV->getAlignment() >= PrefAlign)
776 return GV->getAlignment();
777 // We can only increase the alignment of the global if it has no alignment
778 // specified or if it is not assigned a section. If it is assigned a
779 // section, the global could be densely packed with other objects in the
780 // section, increasing the alignment could cause padding issues.
781 if (!GV->hasSection() || GV->getAlignment() == 0)
782 GV->setAlignment(PrefAlign);
783 return GV->getAlignment();
789 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
790 /// we can determine, return it, otherwise return 0. If PrefAlign is specified,
791 /// and it is more than the alignment of the ultimate object, see if we can
792 /// increase the alignment of the ultimate object, making this check succeed.
793 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
794 const TargetData *TD) {
795 assert(V->getType()->isPointerTy() &&
796 "getOrEnforceKnownAlignment expects a pointer!");
797 unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64;
798 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
799 ComputeMaskedBits(V, KnownZero, KnownOne, TD);
800 unsigned TrailZ = KnownZero.countTrailingOnes();
802 // Avoid trouble with rediculously large TrailZ values, such as
803 // those computed from a null pointer.
804 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
806 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
808 // LLVM doesn't support alignments larger than this currently.
809 Align = std::min(Align, +Value::MaximumAlignment);
811 if (PrefAlign > Align)
812 Align = enforceKnownAlignment(V, Align, PrefAlign, TD);
814 // We don't need to make any adjustment.
818 ///===---------------------------------------------------------------------===//
819 /// Dbg Intrinsic utilities
822 /// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value
823 /// that has an associated llvm.dbg.decl intrinsic.
824 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
825 StoreInst *SI, DIBuilder &Builder) {
826 DIVariable DIVar(DDI->getVariable());
830 Instruction *DbgVal = NULL;
831 // If an argument is zero extended then use argument directly. The ZExt
832 // may be zapped by an optimization pass in future.
833 Argument *ExtendedArg = NULL;
834 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
835 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0));
836 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
837 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0));
839 DbgVal = Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, SI);
841 DbgVal = Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, SI);
843 // Propagate any debug metadata from the store onto the dbg.value.
844 DebugLoc SIDL = SI->getDebugLoc();
845 if (!SIDL.isUnknown())
846 DbgVal->setDebugLoc(SIDL);
847 // Otherwise propagate debug metadata from dbg.declare.
849 DbgVal->setDebugLoc(DDI->getDebugLoc());
853 /// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value
854 /// that has an associated llvm.dbg.decl intrinsic.
855 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
856 LoadInst *LI, DIBuilder &Builder) {
857 DIVariable DIVar(DDI->getVariable());
861 Instruction *DbgVal =
862 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0,
865 // Propagate any debug metadata from the store onto the dbg.value.
866 DebugLoc LIDL = LI->getDebugLoc();
867 if (!LIDL.isUnknown())
868 DbgVal->setDebugLoc(LIDL);
869 // Otherwise propagate debug metadata from dbg.declare.
871 DbgVal->setDebugLoc(DDI->getDebugLoc());
875 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
876 /// of llvm.dbg.value intrinsics.
877 bool llvm::LowerDbgDeclare(Function &F) {
878 DIBuilder DIB(*F.getParent());
879 SmallVector<DbgDeclareInst *, 4> Dbgs;
880 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
881 for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ++BI) {
882 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(BI))
888 for (SmallVector<DbgDeclareInst *, 4>::iterator I = Dbgs.begin(),
889 E = Dbgs.end(); I != E; ++I) {
890 DbgDeclareInst *DDI = *I;
891 if (AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress())) {
892 bool RemoveDDI = true;
893 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
895 if (StoreInst *SI = dyn_cast<StoreInst>(*UI))
896 ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
897 else if (LoadInst *LI = dyn_cast<LoadInst>(*UI))
898 ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
902 DDI->eraseFromParent();
908 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the
909 /// alloca 'V', if any.
910 DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) {
911 if (MDNode *DebugNode = MDNode::getIfExists(V->getContext(), V))
912 for (Value::use_iterator UI = DebugNode->use_begin(),
913 E = DebugNode->use_end(); UI != E; ++UI)
914 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(*UI))