1 //===-- Local.cpp - Functions to perform local transformations ------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This family of functions perform various local transformations to the
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Transforms/Utils/Local.h"
16 #include "llvm/Constants.h"
17 #include "llvm/GlobalAlias.h"
18 #include "llvm/GlobalVariable.h"
19 #include "llvm/DerivedTypes.h"
20 #include "llvm/Instructions.h"
21 #include "llvm/Intrinsics.h"
22 #include "llvm/IntrinsicInst.h"
23 #include "llvm/ADT/DenseMap.h"
24 #include "llvm/ADT/SmallPtrSet.h"
25 #include "llvm/Analysis/ConstantFolding.h"
26 #include "llvm/Analysis/InstructionSimplify.h"
27 #include "llvm/Analysis/ProfileInfo.h"
28 #include "llvm/Target/TargetData.h"
29 #include "llvm/Support/CFG.h"
30 #include "llvm/Support/Debug.h"
31 #include "llvm/Support/GetElementPtrTypeIterator.h"
32 #include "llvm/Support/MathExtras.h"
33 #include "llvm/Support/ValueHandle.h"
34 #include "llvm/Support/raw_ostream.h"
37 //===----------------------------------------------------------------------===//
41 /// getUnderlyingObjectWithOffset - Strip off up to MaxLookup GEPs and
42 /// bitcasts to get back to the underlying object being addressed, keeping
43 /// track of the offset in bytes from the GEPs relative to the result.
44 /// This is closely related to Value::getUnderlyingObject but is located
45 /// here to avoid making VMCore depend on TargetData.
46 static Value *getUnderlyingObjectWithOffset(Value *V, const TargetData *TD,
48 unsigned MaxLookup = 6) {
49 if (!isa<PointerType>(V->getType()))
51 for (unsigned Count = 0; MaxLookup == 0 || Count < MaxLookup; ++Count) {
52 if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
53 if (!GEP->hasAllConstantIndices())
55 SmallVector<Value*, 8> Indices(GEP->op_begin() + 1, GEP->op_end());
56 ByteOffset += TD->getIndexedOffset(GEP->getPointerOperandType(),
57 &Indices[0], Indices.size());
58 V = GEP->getPointerOperand();
59 } else if (Operator::getOpcode(V) == Instruction::BitCast) {
60 V = cast<Operator>(V)->getOperand(0);
61 } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
62 if (GA->mayBeOverridden())
68 assert(isa<PointerType>(V->getType()) && "Unexpected operand type!");
73 /// isSafeToLoadUnconditionally - Return true if we know that executing a load
74 /// from this value cannot trap. If it is not obviously safe to load from the
75 /// specified pointer, we do a quick local scan of the basic block containing
76 /// ScanFrom, to determine if the address is already accessed.
77 bool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom,
78 unsigned Align, const TargetData *TD) {
79 uint64_t ByteOffset = 0;
82 Base = getUnderlyingObjectWithOffset(V, TD, ByteOffset);
84 const Type *BaseType = 0;
85 unsigned BaseAlign = 0;
86 if (const AllocaInst *AI = dyn_cast<AllocaInst>(Base)) {
87 // An alloca is safe to load from as load as it is suitably aligned.
88 BaseType = AI->getAllocatedType();
89 BaseAlign = AI->getAlignment();
90 } else if (const GlobalValue *GV = dyn_cast<GlobalValue>(Base)) {
91 // Global variables are safe to load from but their size cannot be
92 // guaranteed if they are overridden.
93 if (!isa<GlobalAlias>(GV) && !GV->mayBeOverridden()) {
94 BaseType = GV->getType()->getElementType();
95 BaseAlign = GV->getAlignment();
99 if (BaseType && BaseType->isSized()) {
100 if (TD && BaseAlign == 0)
101 BaseAlign = TD->getPrefTypeAlignment(BaseType);
103 if (Align <= BaseAlign) {
105 return true; // Loading directly from an alloca or global is OK.
107 // Check if the load is within the bounds of the underlying object.
108 const PointerType *AddrTy = cast<PointerType>(V->getType());
109 uint64_t LoadSize = TD->getTypeStoreSize(AddrTy->getElementType());
110 if (ByteOffset + LoadSize <= TD->getTypeAllocSize(BaseType) &&
111 (Align == 0 || (ByteOffset % Align) == 0))
116 // Otherwise, be a little bit aggressive by scanning the local block where we
117 // want to check to see if the pointer is already being loaded or stored
118 // from/to. If so, the previous load or store would have already trapped,
119 // so there is no harm doing an extra load (also, CSE will later eliminate
120 // the load entirely).
121 BasicBlock::iterator BBI = ScanFrom, E = ScanFrom->getParent()->begin();
126 // If we see a free or a call which may write to memory (i.e. which might do
127 // a free) the pointer could be marked invalid.
128 if (isa<CallInst>(BBI) && BBI->mayWriteToMemory() &&
129 !isa<DbgInfoIntrinsic>(BBI))
132 if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
133 if (LI->getOperand(0) == V) return true;
134 } else if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
135 if (SI->getOperand(1) == V) return true;
142 //===----------------------------------------------------------------------===//
143 // Local constant propagation.
146 // ConstantFoldTerminator - If a terminator instruction is predicated on a
147 // constant value, convert it into an unconditional branch to the constant
150 bool llvm::ConstantFoldTerminator(BasicBlock *BB) {
151 TerminatorInst *T = BB->getTerminator();
153 // Branch - See if we are conditional jumping on constant
154 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
155 if (BI->isUnconditional()) return false; // Can't optimize uncond branch
156 BasicBlock *Dest1 = BI->getSuccessor(0);
157 BasicBlock *Dest2 = BI->getSuccessor(1);
159 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
160 // Are we branching on constant?
161 // YES. Change to unconditional branch...
162 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
163 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1;
165 //cerr << "Function: " << T->getParent()->getParent()
166 // << "\nRemoving branch from " << T->getParent()
167 // << "\n\nTo: " << OldDest << endl;
169 // Let the basic block know that we are letting go of it. Based on this,
170 // it will adjust it's PHI nodes.
171 assert(BI->getParent() && "Terminator not inserted in block!");
172 OldDest->removePredecessor(BI->getParent());
174 // Set the unconditional destination, and change the insn to be an
175 // unconditional branch.
176 BI->setUnconditionalDest(Destination);
180 if (Dest2 == Dest1) { // Conditional branch to same location?
181 // This branch matches something like this:
182 // br bool %cond, label %Dest, label %Dest
183 // and changes it into: br label %Dest
185 // Let the basic block know that we are letting go of one copy of it.
186 assert(BI->getParent() && "Terminator not inserted in block!");
187 Dest1->removePredecessor(BI->getParent());
189 // Change a conditional branch to unconditional.
190 BI->setUnconditionalDest(Dest1);
196 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
197 // If we are switching on a constant, we can convert the switch into a
198 // single branch instruction!
199 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
200 BasicBlock *TheOnlyDest = SI->getSuccessor(0); // The default dest
201 BasicBlock *DefaultDest = TheOnlyDest;
202 assert(TheOnlyDest == SI->getDefaultDest() &&
203 "Default destination is not successor #0?");
205 // Figure out which case it goes to.
206 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
207 // Found case matching a constant operand?
208 if (SI->getSuccessorValue(i) == CI) {
209 TheOnlyDest = SI->getSuccessor(i);
213 // Check to see if this branch is going to the same place as the default
214 // dest. If so, eliminate it as an explicit compare.
215 if (SI->getSuccessor(i) == DefaultDest) {
216 // Remove this entry.
217 DefaultDest->removePredecessor(SI->getParent());
219 --i; --e; // Don't skip an entry...
223 // Otherwise, check to see if the switch only branches to one destination.
224 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
226 if (SI->getSuccessor(i) != TheOnlyDest) TheOnlyDest = 0;
229 if (CI && !TheOnlyDest) {
230 // Branching on a constant, but not any of the cases, go to the default
232 TheOnlyDest = SI->getDefaultDest();
235 // If we found a single destination that we can fold the switch into, do so
238 // Insert the new branch.
239 BranchInst::Create(TheOnlyDest, SI);
240 BasicBlock *BB = SI->getParent();
242 // Remove entries from PHI nodes which we no longer branch to...
243 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
244 // Found case matching a constant operand?
245 BasicBlock *Succ = SI->getSuccessor(i);
246 if (Succ == TheOnlyDest)
247 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest
249 Succ->removePredecessor(BB);
252 // Delete the old switch.
253 BB->getInstList().erase(SI);
257 if (SI->getNumSuccessors() == 2) {
258 // Otherwise, we can fold this switch into a conditional branch
259 // instruction if it has only one non-default destination.
260 Value *Cond = new ICmpInst(SI, ICmpInst::ICMP_EQ, SI->getCondition(),
261 SI->getSuccessorValue(1), "cond");
262 // Insert the new branch.
263 BranchInst::Create(SI->getSuccessor(1), SI->getSuccessor(0), Cond, SI);
265 // Delete the old switch.
266 SI->eraseFromParent();
272 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
273 // indirectbr blockaddress(@F, @BB) -> br label @BB
274 if (BlockAddress *BA =
275 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
276 BasicBlock *TheOnlyDest = BA->getBasicBlock();
277 // Insert the new branch.
278 BranchInst::Create(TheOnlyDest, IBI);
280 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
281 if (IBI->getDestination(i) == TheOnlyDest)
284 IBI->getDestination(i)->removePredecessor(IBI->getParent());
286 IBI->eraseFromParent();
288 // If we didn't find our destination in the IBI successor list, then we
289 // have undefined behavior. Replace the unconditional branch with an
290 // 'unreachable' instruction.
292 BB->getTerminator()->eraseFromParent();
293 new UnreachableInst(BB->getContext(), BB);
304 //===----------------------------------------------------------------------===//
305 // Local dead code elimination.
308 /// isInstructionTriviallyDead - Return true if the result produced by the
309 /// instruction is not used, and the instruction has no side effects.
311 bool llvm::isInstructionTriviallyDead(Instruction *I) {
312 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
314 // We don't want debug info removed by anything this general.
315 if (isa<DbgInfoIntrinsic>(I)) return false;
317 // Likewise for memory use markers.
318 if (isa<MemoryUseIntrinsic>(I)) return false;
320 if (!I->mayHaveSideEffects()) return true;
322 // Special case intrinsics that "may have side effects" but can be deleted
324 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
325 // Safe to delete llvm.stacksave if dead.
326 if (II->getIntrinsicID() == Intrinsic::stacksave)
331 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
332 /// trivially dead instruction, delete it. If that makes any of its operands
333 /// trivially dead, delete them too, recursively. Return true if any
334 /// instructions were deleted.
335 bool llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V) {
336 Instruction *I = dyn_cast<Instruction>(V);
337 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I))
340 SmallVector<Instruction*, 16> DeadInsts;
341 DeadInsts.push_back(I);
344 I = DeadInsts.pop_back_val();
346 // Null out all of the instruction's operands to see if any operand becomes
348 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
349 Value *OpV = I->getOperand(i);
352 if (!OpV->use_empty()) continue;
354 // If the operand is an instruction that became dead as we nulled out the
355 // operand, and if it is 'trivially' dead, delete it in a future loop
357 if (Instruction *OpI = dyn_cast<Instruction>(OpV))
358 if (isInstructionTriviallyDead(OpI))
359 DeadInsts.push_back(OpI);
362 I->eraseFromParent();
363 } while (!DeadInsts.empty());
368 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
369 /// dead PHI node, due to being a def-use chain of single-use nodes that
370 /// either forms a cycle or is terminated by a trivially dead instruction,
371 /// delete it. If that makes any of its operands trivially dead, delete them
372 /// too, recursively. Return true if the PHI node is actually deleted.
374 llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) {
375 // We can remove a PHI if it is on a cycle in the def-use graph
376 // where each node in the cycle has degree one, i.e. only one use,
377 // and is an instruction with no side effects.
378 if (!PN->hasOneUse())
381 bool Changed = false;
382 SmallPtrSet<PHINode *, 4> PHIs;
384 for (Instruction *J = cast<Instruction>(*PN->use_begin());
385 J->hasOneUse() && !J->mayHaveSideEffects();
386 J = cast<Instruction>(*J->use_begin()))
387 // If we find a PHI more than once, we're on a cycle that
388 // won't prove fruitful.
389 if (PHINode *JP = dyn_cast<PHINode>(J))
390 if (!PHIs.insert(cast<PHINode>(JP))) {
391 // Break the cycle and delete the PHI and its operands.
392 JP->replaceAllUsesWith(UndefValue::get(JP->getType()));
393 (void)RecursivelyDeleteTriviallyDeadInstructions(JP);
400 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
401 /// simplify any instructions in it and recursively delete dead instructions.
403 /// This returns true if it changed the code, note that it can delete
404 /// instructions in other blocks as well in this block.
405 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD) {
406 bool MadeChange = false;
407 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
408 Instruction *Inst = BI++;
410 if (Value *V = SimplifyInstruction(Inst, TD)) {
412 ReplaceAndSimplifyAllUses(Inst, V, TD);
419 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst);
424 //===----------------------------------------------------------------------===//
425 // Control Flow Graph Restructuring.
429 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
430 /// method is called when we're about to delete Pred as a predecessor of BB. If
431 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
433 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
434 /// nodes that collapse into identity values. For example, if we have:
435 /// x = phi(1, 0, 0, 0)
438 /// .. and delete the predecessor corresponding to the '1', this will attempt to
439 /// recursively fold the and to 0.
440 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
442 // This only adjusts blocks with PHI nodes.
443 if (!isa<PHINode>(BB->begin()))
446 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
447 // them down. This will leave us with single entry phi nodes and other phis
448 // that can be removed.
449 BB->removePredecessor(Pred, true);
451 WeakVH PhiIt = &BB->front();
452 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
453 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
455 Value *PNV = PN->hasConstantValue();
456 if (PNV == 0) continue;
458 // If we're able to simplify the phi to a single value, substitute the new
459 // value into all of its uses.
460 assert(PNV != PN && "hasConstantValue broken");
462 ReplaceAndSimplifyAllUses(PN, PNV, TD);
464 // If recursive simplification ended up deleting the next PHI node we would
465 // iterate to, then our iterator is invalid, restart scanning from the top
467 if (PhiIt == 0) PhiIt = &BB->front();
472 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
473 /// predecessor is known to have one successor (DestBB!). Eliminate the edge
474 /// between them, moving the instructions in the predecessor into DestBB and
475 /// deleting the predecessor block.
477 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) {
478 // If BB has single-entry PHI nodes, fold them.
479 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
480 Value *NewVal = PN->getIncomingValue(0);
481 // Replace self referencing PHI with undef, it must be dead.
482 if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
483 PN->replaceAllUsesWith(NewVal);
484 PN->eraseFromParent();
487 BasicBlock *PredBB = DestBB->getSinglePredecessor();
488 assert(PredBB && "Block doesn't have a single predecessor!");
490 // Splice all the instructions from PredBB to DestBB.
491 PredBB->getTerminator()->eraseFromParent();
492 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
494 // Anything that branched to PredBB now branches to DestBB.
495 PredBB->replaceAllUsesWith(DestBB);
498 ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>();
500 PI->replaceAllUses(PredBB, DestBB);
501 PI->removeEdge(ProfileInfo::getEdge(PredBB, DestBB));
505 PredBB->eraseFromParent();
508 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
509 /// almost-empty BB ending in an unconditional branch to Succ, into succ.
511 /// Assumption: Succ is the single successor for BB.
513 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
514 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
516 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
517 << Succ->getName() << "\n");
518 // Shortcut, if there is only a single predecessor it must be BB and merging
520 if (Succ->getSinglePredecessor()) return true;
522 // Make a list of the predecessors of BB
523 typedef SmallPtrSet<BasicBlock*, 16> BlockSet;
524 BlockSet BBPreds(pred_begin(BB), pred_end(BB));
526 // Use that list to make another list of common predecessors of BB and Succ
527 BlockSet CommonPreds;
528 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
530 if (BBPreds.count(*PI))
531 CommonPreds.insert(*PI);
533 // Shortcut, if there are no common predecessors, merging is always safe
534 if (CommonPreds.empty())
537 // Look at all the phi nodes in Succ, to see if they present a conflict when
538 // merging these blocks
539 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
540 PHINode *PN = cast<PHINode>(I);
542 // If the incoming value from BB is again a PHINode in
543 // BB which has the same incoming value for *PI as PN does, we can
544 // merge the phi nodes and then the blocks can still be merged
545 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
546 if (BBPN && BBPN->getParent() == BB) {
547 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
549 if (BBPN->getIncomingValueForBlock(*PI)
550 != PN->getIncomingValueForBlock(*PI)) {
551 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
552 << Succ->getName() << " is conflicting with "
553 << BBPN->getName() << " with regard to common predecessor "
554 << (*PI)->getName() << "\n");
559 Value* Val = PN->getIncomingValueForBlock(BB);
560 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
562 // See if the incoming value for the common predecessor is equal to the
563 // one for BB, in which case this phi node will not prevent the merging
565 if (Val != PN->getIncomingValueForBlock(*PI)) {
566 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
567 << Succ->getName() << " is conflicting with regard to common "
568 << "predecessor " << (*PI)->getName() << "\n");
578 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
579 /// unconditional branch, and contains no instructions other than PHI nodes,
580 /// potential debug intrinsics and the branch. If possible, eliminate BB by
581 /// rewriting all the predecessors to branch to the successor block and return
582 /// true. If we can't transform, return false.
583 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
584 // We can't eliminate infinite loops.
585 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
586 if (BB == Succ) return false;
588 // Check to see if merging these blocks would cause conflicts for any of the
589 // phi nodes in BB or Succ. If not, we can safely merge.
590 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
592 // Check for cases where Succ has multiple predecessors and a PHI node in BB
593 // has uses which will not disappear when the PHI nodes are merged. It is
594 // possible to handle such cases, but difficult: it requires checking whether
595 // BB dominates Succ, which is non-trivial to calculate in the case where
596 // Succ has multiple predecessors. Also, it requires checking whether
597 // constructing the necessary self-referential PHI node doesn't intoduce any
598 // conflicts; this isn't too difficult, but the previous code for doing this
601 // Note that if this check finds a live use, BB dominates Succ, so BB is
602 // something like a loop pre-header (or rarely, a part of an irreducible CFG);
603 // folding the branch isn't profitable in that case anyway.
604 if (!Succ->getSinglePredecessor()) {
605 BasicBlock::iterator BBI = BB->begin();
606 while (isa<PHINode>(*BBI)) {
607 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
609 if (PHINode* PN = dyn_cast<PHINode>(*UI)) {
610 if (PN->getIncomingBlock(UI) != BB)
620 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
622 if (isa<PHINode>(Succ->begin())) {
623 // If there is more than one pred of succ, and there are PHI nodes in
624 // the successor, then we need to add incoming edges for the PHI nodes
626 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
628 // Loop over all of the PHI nodes in the successor of BB.
629 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
630 PHINode *PN = cast<PHINode>(I);
631 Value *OldVal = PN->removeIncomingValue(BB, false);
632 assert(OldVal && "No entry in PHI for Pred BB!");
634 // If this incoming value is one of the PHI nodes in BB, the new entries
635 // in the PHI node are the entries from the old PHI.
636 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
637 PHINode *OldValPN = cast<PHINode>(OldVal);
638 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
639 // Note that, since we are merging phi nodes and BB and Succ might
640 // have common predecessors, we could end up with a phi node with
641 // identical incoming branches. This will be cleaned up later (and
642 // will trigger asserts if we try to clean it up now, without also
643 // simplifying the corresponding conditional branch).
644 PN->addIncoming(OldValPN->getIncomingValue(i),
645 OldValPN->getIncomingBlock(i));
647 // Add an incoming value for each of the new incoming values.
648 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
649 PN->addIncoming(OldVal, BBPreds[i]);
654 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
655 if (Succ->getSinglePredecessor()) {
656 // BB is the only predecessor of Succ, so Succ will end up with exactly
657 // the same predecessors BB had.
658 Succ->getInstList().splice(Succ->begin(),
659 BB->getInstList(), BB->begin());
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. Theroetically, 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 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
702 // This hash algorithm is quite weak as hash functions go, but it seems
703 // to do a good enough job for this particular purpose, and is very quick.
704 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
705 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
707 // If we've never seen this hash value before, it's a unique PHI.
708 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
709 HashMap.insert(std::make_pair(Hash, PN));
710 if (Pair.second) continue;
711 // Otherwise it's either a duplicate or a hash collision.
712 for (PHINode *OtherPN = Pair.first->second; ; ) {
713 if (OtherPN->isIdenticalTo(PN)) {
714 // A duplicate. Replace this PHI with its duplicate.
715 PN->replaceAllUsesWith(OtherPN);
716 PN->eraseFromParent();
720 // A non-duplicate hash collision.
721 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
722 if (I == CollisionMap.end()) {
723 // Set this PHI to be the head of the linked list of colliding PHIs.
724 PHINode *Old = Pair.first->second;
725 Pair.first->second = PN;
726 CollisionMap[PN] = Old;
729 // Procede to the next PHI in the list.