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/Metadata.h"
24 #include "llvm/Operator.h"
25 #include "llvm/ADT/DenseMap.h"
26 #include "llvm/ADT/SmallPtrSet.h"
27 #include "llvm/Analysis/DebugInfo.h"
28 #include "llvm/Analysis/DIBuilder.h"
29 #include "llvm/Analysis/Dominators.h"
30 #include "llvm/Analysis/InstructionSimplify.h"
31 #include "llvm/Analysis/MemoryBuiltins.h"
32 #include "llvm/Analysis/ProfileInfo.h"
33 #include "llvm/Analysis/ValueTracking.h"
34 #include "llvm/Target/TargetData.h"
35 #include "llvm/Support/CFG.h"
36 #include "llvm/Support/Debug.h"
37 #include "llvm/Support/GetElementPtrTypeIterator.h"
38 #include "llvm/Support/IRBuilder.h"
39 #include "llvm/Support/MathExtras.h"
40 #include "llvm/Support/ValueHandle.h"
41 #include "llvm/Support/raw_ostream.h"
44 //===----------------------------------------------------------------------===//
45 // Local constant propagation.
48 /// ConstantFoldTerminator - If a terminator instruction is predicated on a
49 /// constant value, convert it into an unconditional branch to the constant
50 /// destination. This is a nontrivial operation because the successors of this
51 /// basic block must have their PHI nodes updated.
52 /// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch
53 /// conditions and indirectbr addresses this might make dead if
54 /// DeleteDeadConditions is true.
55 bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions) {
56 TerminatorInst *T = BB->getTerminator();
57 IRBuilder<> Builder(T);
59 // Branch - See if we are conditional jumping on constant
60 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
61 if (BI->isUnconditional()) return false; // Can't optimize uncond branch
62 BasicBlock *Dest1 = BI->getSuccessor(0);
63 BasicBlock *Dest2 = BI->getSuccessor(1);
65 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
66 // Are we branching on constant?
67 // YES. Change to unconditional branch...
68 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
69 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1;
71 //cerr << "Function: " << T->getParent()->getParent()
72 // << "\nRemoving branch from " << T->getParent()
73 // << "\n\nTo: " << OldDest << endl;
75 // Let the basic block know that we are letting go of it. Based on this,
76 // it will adjust it's PHI nodes.
77 OldDest->removePredecessor(BB);
79 // Replace the conditional branch with an unconditional one.
80 Builder.CreateBr(Destination);
81 BI->eraseFromParent();
85 if (Dest2 == Dest1) { // Conditional branch to same location?
86 // This branch matches something like this:
87 // br bool %cond, label %Dest, label %Dest
88 // and changes it into: br label %Dest
90 // Let the basic block know that we are letting go of one copy of it.
91 assert(BI->getParent() && "Terminator not inserted in block!");
92 Dest1->removePredecessor(BI->getParent());
94 // Replace the conditional branch with an unconditional one.
95 Builder.CreateBr(Dest1);
96 Value *Cond = BI->getCondition();
97 BI->eraseFromParent();
98 if (DeleteDeadConditions)
99 RecursivelyDeleteTriviallyDeadInstructions(Cond);
105 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
106 // If we are switching on a constant, we can convert the switch into a
107 // single branch instruction!
108 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
109 BasicBlock *TheOnlyDest = SI->getDefaultDest();
110 BasicBlock *DefaultDest = TheOnlyDest;
112 // Figure out which case it goes to.
113 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
115 // Found case matching a constant operand?
116 if (i.getCaseValue() == CI) {
117 TheOnlyDest = i.getCaseSuccessor();
121 // Check to see if this branch is going to the same place as the default
122 // dest. If so, eliminate it as an explicit compare.
123 if (i.getCaseSuccessor() == DefaultDest) {
124 // Remove this entry.
125 DefaultDest->removePredecessor(SI->getParent());
131 // Otherwise, check to see if the switch only branches to one destination.
132 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
134 if (i.getCaseSuccessor() != TheOnlyDest) TheOnlyDest = 0;
137 if (CI && !TheOnlyDest) {
138 // Branching on a constant, but not any of the cases, go to the default
140 TheOnlyDest = SI->getDefaultDest();
143 // If we found a single destination that we can fold the switch into, do so
146 // Insert the new branch.
147 Builder.CreateBr(TheOnlyDest);
148 BasicBlock *BB = SI->getParent();
150 // Remove entries from PHI nodes which we no longer branch to...
151 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
152 // Found case matching a constant operand?
153 BasicBlock *Succ = SI->getSuccessor(i);
154 if (Succ == TheOnlyDest)
155 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest
157 Succ->removePredecessor(BB);
160 // Delete the old switch.
161 Value *Cond = SI->getCondition();
162 SI->eraseFromParent();
163 if (DeleteDeadConditions)
164 RecursivelyDeleteTriviallyDeadInstructions(Cond);
168 if (SI->getNumCases() == 1) {
169 // Otherwise, we can fold this switch into a conditional branch
170 // instruction if it has only one non-default destination.
171 SwitchInst::CaseIt FirstCase = SI->case_begin();
172 IntegersSubset CaseRanges = FirstCase.getCaseValueEx();
173 if (CaseRanges.getNumItems() == 1 && CaseRanges.isSingleNumber(0)) {
174 // FIXME: Currently work with ConstantInt based numbers.
175 Value *Cond = Builder.CreateICmpEQ(SI->getCondition(),
176 CaseRanges.getItem(0).getLow().toConstantInt(),
179 // Insert the new branch.
180 Builder.CreateCondBr(Cond, FirstCase.getCaseSuccessor(),
181 SI->getDefaultDest());
183 // Delete the old switch.
184 SI->eraseFromParent();
192 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
193 // indirectbr blockaddress(@F, @BB) -> br label @BB
194 if (BlockAddress *BA =
195 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
196 BasicBlock *TheOnlyDest = BA->getBasicBlock();
197 // Insert the new branch.
198 Builder.CreateBr(TheOnlyDest);
200 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
201 if (IBI->getDestination(i) == TheOnlyDest)
204 IBI->getDestination(i)->removePredecessor(IBI->getParent());
206 Value *Address = IBI->getAddress();
207 IBI->eraseFromParent();
208 if (DeleteDeadConditions)
209 RecursivelyDeleteTriviallyDeadInstructions(Address);
211 // If we didn't find our destination in the IBI successor list, then we
212 // have undefined behavior. Replace the unconditional branch with an
213 // 'unreachable' instruction.
215 BB->getTerminator()->eraseFromParent();
216 new UnreachableInst(BB->getContext(), BB);
227 //===----------------------------------------------------------------------===//
228 // Local dead code elimination.
231 /// isInstructionTriviallyDead - Return true if the result produced by the
232 /// instruction is not used, and the instruction has no side effects.
234 bool llvm::isInstructionTriviallyDead(Instruction *I) {
235 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
237 // We don't want the landingpad instruction removed by anything this general.
238 if (isa<LandingPadInst>(I))
241 // We don't want debug info removed by anything this general, unless
242 // debug info is empty.
243 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) {
244 if (DDI->getAddress())
248 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) {
254 if (!I->mayHaveSideEffects()) return true;
256 // Special case intrinsics that "may have side effects" but can be deleted
258 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
259 // Safe to delete llvm.stacksave if dead.
260 if (II->getIntrinsicID() == Intrinsic::stacksave)
263 // Lifetime intrinsics are dead when their right-hand is undef.
264 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
265 II->getIntrinsicID() == Intrinsic::lifetime_end)
266 return isa<UndefValue>(II->getArgOperand(1));
269 if (extractMallocCall(I) || extractCallocCall(I)) return true;
271 if (CallInst *CI = isFreeCall(I))
272 if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
273 return C->isNullValue() || isa<UndefValue>(C);
278 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
279 /// trivially dead instruction, delete it. If that makes any of its operands
280 /// trivially dead, delete them too, recursively. Return true if any
281 /// instructions were deleted.
282 bool llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V) {
283 Instruction *I = dyn_cast<Instruction>(V);
284 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I))
287 SmallVector<Instruction*, 16> DeadInsts;
288 DeadInsts.push_back(I);
291 I = DeadInsts.pop_back_val();
293 // Null out all of the instruction's operands to see if any operand becomes
295 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
296 Value *OpV = I->getOperand(i);
299 if (!OpV->use_empty()) continue;
301 // If the operand is an instruction that became dead as we nulled out the
302 // operand, and if it is 'trivially' dead, delete it in a future loop
304 if (Instruction *OpI = dyn_cast<Instruction>(OpV))
305 if (isInstructionTriviallyDead(OpI))
306 DeadInsts.push_back(OpI);
309 I->eraseFromParent();
310 } while (!DeadInsts.empty());
315 /// areAllUsesEqual - Check whether the uses of a value are all the same.
316 /// This is similar to Instruction::hasOneUse() except this will also return
317 /// true when there are no uses or multiple uses that all refer to the same
319 static bool areAllUsesEqual(Instruction *I) {
320 Value::use_iterator UI = I->use_begin();
321 Value::use_iterator UE = I->use_end();
326 for (++UI; UI != UE; ++UI) {
333 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
334 /// dead PHI node, due to being a def-use chain of single-use nodes that
335 /// either forms a cycle or is terminated by a trivially dead instruction,
336 /// delete it. If that makes any of its operands trivially dead, delete them
337 /// too, recursively. Return true if a change was made.
338 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) {
339 SmallPtrSet<Instruction*, 4> Visited;
340 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
341 I = cast<Instruction>(*I->use_begin())) {
343 return RecursivelyDeleteTriviallyDeadInstructions(I);
345 // If we find an instruction more than once, we're on a cycle that
346 // won't prove fruitful.
347 if (!Visited.insert(I)) {
348 // Break the cycle and delete the instruction and its operands.
349 I->replaceAllUsesWith(UndefValue::get(I->getType()));
350 (void)RecursivelyDeleteTriviallyDeadInstructions(I);
357 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
358 /// simplify any instructions in it and recursively delete dead instructions.
360 /// This returns true if it changed the code, note that it can delete
361 /// instructions in other blocks as well in this block.
362 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD) {
363 bool MadeChange = false;
366 // In debug builds, ensure that the terminator of the block is never replaced
367 // or deleted by these simplifications. The idea of simplification is that it
368 // cannot introduce new instructions, and there is no way to replace the
369 // terminator of a block without introducing a new instruction.
370 AssertingVH<Instruction> TerminatorVH(--BB->end());
373 for (BasicBlock::iterator BI = BB->begin(), E = --BB->end(); BI != E; ) {
374 assert(!BI->isTerminator());
375 Instruction *Inst = BI++;
378 if (recursivelySimplifyInstruction(Inst, TD)) {
385 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst);
392 //===----------------------------------------------------------------------===//
393 // Control Flow Graph Restructuring.
397 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
398 /// method is called when we're about to delete Pred as a predecessor of BB. If
399 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
401 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
402 /// nodes that collapse into identity values. For example, if we have:
403 /// x = phi(1, 0, 0, 0)
406 /// .. and delete the predecessor corresponding to the '1', this will attempt to
407 /// recursively fold the and to 0.
408 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
410 // This only adjusts blocks with PHI nodes.
411 if (!isa<PHINode>(BB->begin()))
414 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
415 // them down. This will leave us with single entry phi nodes and other phis
416 // that can be removed.
417 BB->removePredecessor(Pred, true);
419 WeakVH PhiIt = &BB->front();
420 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
421 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
422 Value *OldPhiIt = PhiIt;
424 if (!recursivelySimplifyInstruction(PN, TD))
427 // If recursive simplification ended up deleting the next PHI node we would
428 // iterate to, then our iterator is invalid, restart scanning from the top
430 if (PhiIt != OldPhiIt) PhiIt = &BB->front();
435 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
436 /// predecessor is known to have one successor (DestBB!). Eliminate the edge
437 /// between them, moving the instructions in the predecessor into DestBB and
438 /// deleting the predecessor block.
440 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) {
441 // If BB has single-entry PHI nodes, fold them.
442 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
443 Value *NewVal = PN->getIncomingValue(0);
444 // Replace self referencing PHI with undef, it must be dead.
445 if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
446 PN->replaceAllUsesWith(NewVal);
447 PN->eraseFromParent();
450 BasicBlock *PredBB = DestBB->getSinglePredecessor();
451 assert(PredBB && "Block doesn't have a single predecessor!");
453 // Zap anything that took the address of DestBB. Not doing this will give the
454 // address an invalid value.
455 if (DestBB->hasAddressTaken()) {
456 BlockAddress *BA = BlockAddress::get(DestBB);
457 Constant *Replacement =
458 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1);
459 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
461 BA->destroyConstant();
464 // Anything that branched to PredBB now branches to DestBB.
465 PredBB->replaceAllUsesWith(DestBB);
467 // Splice all the instructions from PredBB to DestBB.
468 PredBB->getTerminator()->eraseFromParent();
469 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
472 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>();
474 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock();
475 DT->changeImmediateDominator(DestBB, PredBBIDom);
476 DT->eraseNode(PredBB);
478 ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>();
480 PI->replaceAllUses(PredBB, DestBB);
481 PI->removeEdge(ProfileInfo::getEdge(PredBB, DestBB));
485 PredBB->eraseFromParent();
488 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
489 /// almost-empty BB ending in an unconditional branch to Succ, into succ.
491 /// Assumption: Succ is the single successor for BB.
493 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
494 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
496 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
497 << Succ->getName() << "\n");
498 // Shortcut, if there is only a single predecessor it must be BB and merging
500 if (Succ->getSinglePredecessor()) return true;
502 // Make a list of the predecessors of BB
503 SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
505 // Look at all the phi nodes in Succ, to see if they present a conflict when
506 // merging these blocks
507 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
508 PHINode *PN = cast<PHINode>(I);
510 // If the incoming value from BB is again a PHINode in
511 // BB which has the same incoming value for *PI as PN does, we can
512 // merge the phi nodes and then the blocks can still be merged
513 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
514 if (BBPN && BBPN->getParent() == BB) {
515 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
516 BasicBlock *IBB = PN->getIncomingBlock(PI);
517 if (BBPreds.count(IBB) &&
518 BBPN->getIncomingValueForBlock(IBB) != PN->getIncomingValue(PI)) {
519 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
520 << Succ->getName() << " is conflicting with "
521 << BBPN->getName() << " with regard to common predecessor "
522 << IBB->getName() << "\n");
527 Value* Val = PN->getIncomingValueForBlock(BB);
528 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
529 // See if the incoming value for the common predecessor is equal to the
530 // one for BB, in which case this phi node will not prevent the merging
532 BasicBlock *IBB = PN->getIncomingBlock(PI);
533 if (BBPreds.count(IBB) && Val != PN->getIncomingValue(PI)) {
534 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
535 << Succ->getName() << " is conflicting with regard to common "
536 << "predecessor " << IBB->getName() << "\n");
546 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
547 /// unconditional branch, and contains no instructions other than PHI nodes,
548 /// potential side-effect free intrinsics and the branch. If possible,
549 /// eliminate BB by rewriting all the predecessors to branch to the successor
550 /// block and return true. If we can't transform, return false.
551 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
552 assert(BB != &BB->getParent()->getEntryBlock() &&
553 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
555 // We can't eliminate infinite loops.
556 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
557 if (BB == Succ) return false;
559 // Check to see if merging these blocks would cause conflicts for any of the
560 // phi nodes in BB or Succ. If not, we can safely merge.
561 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
563 // Check for cases where Succ has multiple predecessors and a PHI node in BB
564 // has uses which will not disappear when the PHI nodes are merged. It is
565 // possible to handle such cases, but difficult: it requires checking whether
566 // BB dominates Succ, which is non-trivial to calculate in the case where
567 // Succ has multiple predecessors. Also, it requires checking whether
568 // constructing the necessary self-referential PHI node doesn't intoduce any
569 // conflicts; this isn't too difficult, but the previous code for doing this
572 // Note that if this check finds a live use, BB dominates Succ, so BB is
573 // something like a loop pre-header (or rarely, a part of an irreducible CFG);
574 // folding the branch isn't profitable in that case anyway.
575 if (!Succ->getSinglePredecessor()) {
576 BasicBlock::iterator BBI = BB->begin();
577 while (isa<PHINode>(*BBI)) {
578 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
580 if (PHINode* PN = dyn_cast<PHINode>(*UI)) {
581 if (PN->getIncomingBlock(UI) != BB)
591 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
593 if (isa<PHINode>(Succ->begin())) {
594 // If there is more than one pred of succ, and there are PHI nodes in
595 // the successor, then we need to add incoming edges for the PHI nodes
597 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
599 // Loop over all of the PHI nodes in the successor of BB.
600 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
601 PHINode *PN = cast<PHINode>(I);
602 Value *OldVal = PN->removeIncomingValue(BB, false);
603 assert(OldVal && "No entry in PHI for Pred BB!");
605 // If this incoming value is one of the PHI nodes in BB, the new entries
606 // in the PHI node are the entries from the old PHI.
607 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
608 PHINode *OldValPN = cast<PHINode>(OldVal);
609 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
610 // Note that, since we are merging phi nodes and BB and Succ might
611 // have common predecessors, we could end up with a phi node with
612 // identical incoming branches. This will be cleaned up later (and
613 // will trigger asserts if we try to clean it up now, without also
614 // simplifying the corresponding conditional branch).
615 PN->addIncoming(OldValPN->getIncomingValue(i),
616 OldValPN->getIncomingBlock(i));
618 // Add an incoming value for each of the new incoming values.
619 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
620 PN->addIncoming(OldVal, BBPreds[i]);
625 if (Succ->getSinglePredecessor()) {
626 // BB is the only predecessor of Succ, so Succ will end up with exactly
627 // the same predecessors BB had.
629 // Copy over any phi, debug or lifetime instruction.
630 BB->getTerminator()->eraseFromParent();
631 Succ->getInstList().splice(Succ->getFirstNonPHI(), BB->getInstList());
633 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
634 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
635 assert(PN->use_empty() && "There shouldn't be any uses here!");
636 PN->eraseFromParent();
640 // Everything that jumped to BB now goes to Succ.
641 BB->replaceAllUsesWith(Succ);
642 if (!Succ->hasName()) Succ->takeName(BB);
643 BB->eraseFromParent(); // Delete the old basic block.
647 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
648 /// nodes in this block. This doesn't try to be clever about PHI nodes
649 /// which differ only in the order of the incoming values, but instcombine
650 /// orders them so it usually won't matter.
652 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
653 bool Changed = false;
655 // This implementation doesn't currently consider undef operands
656 // specially. Theoretically, two phis which are identical except for
657 // one having an undef where the other doesn't could be collapsed.
659 // Map from PHI hash values to PHI nodes. If multiple PHIs have
660 // the same hash value, the element is the first PHI in the
661 // linked list in CollisionMap.
662 DenseMap<uintptr_t, PHINode *> HashMap;
664 // Maintain linked lists of PHI nodes with common hash values.
665 DenseMap<PHINode *, PHINode *> CollisionMap;
668 for (BasicBlock::iterator I = BB->begin();
669 PHINode *PN = dyn_cast<PHINode>(I++); ) {
670 // Compute a hash value on the operands. Instcombine will likely have sorted
671 // them, which helps expose duplicates, but we have to check all the
672 // operands to be safe in case instcombine hasn't run.
674 // This hash algorithm is quite weak as hash functions go, but it seems
675 // to do a good enough job for this particular purpose, and is very quick.
676 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
677 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
678 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
680 for (PHINode::block_iterator I = PN->block_begin(), E = PN->block_end();
682 Hash ^= reinterpret_cast<uintptr_t>(static_cast<BasicBlock *>(*I));
683 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
685 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1.
687 // If we've never seen this hash value before, it's a unique PHI.
688 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
689 HashMap.insert(std::make_pair(Hash, PN));
690 if (Pair.second) continue;
691 // Otherwise it's either a duplicate or a hash collision.
692 for (PHINode *OtherPN = Pair.first->second; ; ) {
693 if (OtherPN->isIdenticalTo(PN)) {
694 // A duplicate. Replace this PHI with its duplicate.
695 PN->replaceAllUsesWith(OtherPN);
696 PN->eraseFromParent();
700 // A non-duplicate hash collision.
701 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
702 if (I == CollisionMap.end()) {
703 // Set this PHI to be the head of the linked list of colliding PHIs.
704 PHINode *Old = Pair.first->second;
705 Pair.first->second = PN;
706 CollisionMap[PN] = Old;
709 // Procede to the next PHI in the list.
717 /// enforceKnownAlignment - If the specified pointer points to an object that
718 /// we control, modify the object's alignment to PrefAlign. This isn't
719 /// often possible though. If alignment is important, a more reliable approach
720 /// is to simply align all global variables and allocation instructions to
721 /// their preferred alignment from the beginning.
723 static unsigned enforceKnownAlignment(Value *V, unsigned Align,
724 unsigned PrefAlign, const TargetData *TD) {
725 V = V->stripPointerCasts();
727 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
728 // If the preferred alignment is greater than the natural stack alignment
729 // then don't round up. This avoids dynamic stack realignment.
730 if (TD && TD->exceedsNaturalStackAlignment(PrefAlign))
732 // If there is a requested alignment and if this is an alloca, round up.
733 if (AI->getAlignment() >= PrefAlign)
734 return AI->getAlignment();
735 AI->setAlignment(PrefAlign);
739 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
740 // If there is a large requested alignment and we can, bump up the alignment
742 if (GV->isDeclaration()) return Align;
743 // If the memory we set aside for the global may not be the memory used by
744 // the final program then it is impossible for us to reliably enforce the
745 // preferred alignment.
746 if (GV->isWeakForLinker()) return Align;
748 if (GV->getAlignment() >= PrefAlign)
749 return GV->getAlignment();
750 // We can only increase the alignment of the global if it has no alignment
751 // specified or if it is not assigned a section. If it is assigned a
752 // section, the global could be densely packed with other objects in the
753 // section, increasing the alignment could cause padding issues.
754 if (!GV->hasSection() || GV->getAlignment() == 0)
755 GV->setAlignment(PrefAlign);
756 return GV->getAlignment();
762 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
763 /// we can determine, return it, otherwise return 0. If PrefAlign is specified,
764 /// and it is more than the alignment of the ultimate object, see if we can
765 /// increase the alignment of the ultimate object, making this check succeed.
766 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
767 const TargetData *TD) {
768 assert(V->getType()->isPointerTy() &&
769 "getOrEnforceKnownAlignment expects a pointer!");
770 unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64;
771 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
772 ComputeMaskedBits(V, KnownZero, KnownOne, TD);
773 unsigned TrailZ = KnownZero.countTrailingOnes();
775 // Avoid trouble with rediculously large TrailZ values, such as
776 // those computed from a null pointer.
777 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
779 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
781 // LLVM doesn't support alignments larger than this currently.
782 Align = std::min(Align, +Value::MaximumAlignment);
784 if (PrefAlign > Align)
785 Align = enforceKnownAlignment(V, Align, PrefAlign, TD);
787 // We don't need to make any adjustment.
791 ///===---------------------------------------------------------------------===//
792 /// Dbg Intrinsic utilities
795 /// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value
796 /// that has an associated llvm.dbg.decl intrinsic.
797 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
798 StoreInst *SI, DIBuilder &Builder) {
799 DIVariable DIVar(DDI->getVariable());
803 Instruction *DbgVal = NULL;
804 // If an argument is zero extended then use argument directly. The ZExt
805 // may be zapped by an optimization pass in future.
806 Argument *ExtendedArg = NULL;
807 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
808 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0));
809 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
810 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0));
812 DbgVal = Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, SI);
814 DbgVal = Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, SI);
816 // Propagate any debug metadata from the store onto the dbg.value.
817 DebugLoc SIDL = SI->getDebugLoc();
818 if (!SIDL.isUnknown())
819 DbgVal->setDebugLoc(SIDL);
820 // Otherwise propagate debug metadata from dbg.declare.
822 DbgVal->setDebugLoc(DDI->getDebugLoc());
826 /// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value
827 /// that has an associated llvm.dbg.decl intrinsic.
828 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
829 LoadInst *LI, DIBuilder &Builder) {
830 DIVariable DIVar(DDI->getVariable());
834 Instruction *DbgVal =
835 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0,
838 // Propagate any debug metadata from the store onto the dbg.value.
839 DebugLoc LIDL = LI->getDebugLoc();
840 if (!LIDL.isUnknown())
841 DbgVal->setDebugLoc(LIDL);
842 // Otherwise propagate debug metadata from dbg.declare.
844 DbgVal->setDebugLoc(DDI->getDebugLoc());
848 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
849 /// of llvm.dbg.value intrinsics.
850 bool llvm::LowerDbgDeclare(Function &F) {
851 DIBuilder DIB(*F.getParent());
852 SmallVector<DbgDeclareInst *, 4> Dbgs;
853 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
854 for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ++BI) {
855 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(BI))
861 for (SmallVector<DbgDeclareInst *, 4>::iterator I = Dbgs.begin(),
862 E = Dbgs.end(); I != E; ++I) {
863 DbgDeclareInst *DDI = *I;
864 if (AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress())) {
865 bool RemoveDDI = true;
866 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
868 if (StoreInst *SI = dyn_cast<StoreInst>(*UI))
869 ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
870 else if (LoadInst *LI = dyn_cast<LoadInst>(*UI))
871 ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
875 DDI->eraseFromParent();
881 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the
882 /// alloca 'V', if any.
883 DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) {
884 if (MDNode *DebugNode = MDNode::getIfExists(V->getContext(), V))
885 for (Value::use_iterator UI = DebugNode->use_begin(),
886 E = DebugNode->use_end(); UI != E; ++UI)
887 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(*UI))