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(); // The default dest
110 BasicBlock *DefaultDest = TheOnlyDest;
112 // Figure out which case it goes to.
113 for (unsigned i = 0, e = SI->getNumCases(); i != e; ++i) {
114 // Found case matching a constant operand?
115 if (SI->getCaseValue(i) == CI) {
116 TheOnlyDest = SI->getCaseSuccessor(i);
120 // Check to see if this branch is going to the same place as the default
121 // dest. If so, eliminate it as an explicit compare.
122 if (SI->getCaseSuccessor(i) == DefaultDest) {
123 // Remove this entry.
124 DefaultDest->removePredecessor(SI->getParent());
126 --i; --e; // Don't skip an entry...
130 // Otherwise, check to see if the switch only branches to one destination.
131 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
133 if (SI->getCaseSuccessor(i) != TheOnlyDest) TheOnlyDest = 0;
136 if (CI && !TheOnlyDest) {
137 // Branching on a constant, but not any of the cases, go to the default
139 TheOnlyDest = SI->getDefaultDest();
142 // If we found a single destination that we can fold the switch into, do so
145 // Insert the new branch.
146 Builder.CreateBr(TheOnlyDest);
147 BasicBlock *BB = SI->getParent();
149 // Remove entries from PHI nodes which we no longer branch to...
150 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
151 // Found case matching a constant operand?
152 BasicBlock *Succ = SI->getSuccessor(i);
153 if (Succ == TheOnlyDest)
154 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest
156 Succ->removePredecessor(BB);
159 // Delete the old switch.
160 Value *Cond = SI->getCondition();
161 SI->eraseFromParent();
162 if (DeleteDeadConditions)
163 RecursivelyDeleteTriviallyDeadInstructions(Cond);
167 if (SI->getNumCases() == 1) {
168 // Otherwise, we can fold this switch into a conditional branch
169 // instruction if it has only one non-default destination.
170 Value *Cond = Builder.CreateICmpEQ(SI->getCondition(),
171 SI->getCaseValue(0), "cond");
173 // Insert the new branch.
174 Builder.CreateCondBr(Cond, SI->getCaseSuccessor(0), SI->getDefaultDest());
176 // Delete the old switch.
177 SI->eraseFromParent();
183 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
184 // indirectbr blockaddress(@F, @BB) -> br label @BB
185 if (BlockAddress *BA =
186 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
187 BasicBlock *TheOnlyDest = BA->getBasicBlock();
188 // Insert the new branch.
189 Builder.CreateBr(TheOnlyDest);
191 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
192 if (IBI->getDestination(i) == TheOnlyDest)
195 IBI->getDestination(i)->removePredecessor(IBI->getParent());
197 Value *Address = IBI->getAddress();
198 IBI->eraseFromParent();
199 if (DeleteDeadConditions)
200 RecursivelyDeleteTriviallyDeadInstructions(Address);
202 // If we didn't find our destination in the IBI successor list, then we
203 // have undefined behavior. Replace the unconditional branch with an
204 // 'unreachable' instruction.
206 BB->getTerminator()->eraseFromParent();
207 new UnreachableInst(BB->getContext(), BB);
218 //===----------------------------------------------------------------------===//
219 // Local dead code elimination.
222 /// isInstructionTriviallyDead - Return true if the result produced by the
223 /// instruction is not used, and the instruction has no side effects.
225 bool llvm::isInstructionTriviallyDead(Instruction *I) {
226 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
228 // We don't want the landingpad instruction removed by anything this general.
229 if (isa<LandingPadInst>(I))
232 // We don't want debug info removed by anything this general, unless
233 // debug info is empty.
234 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) {
235 if (DDI->getAddress())
239 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) {
245 if (!I->mayHaveSideEffects()) return true;
247 // Special case intrinsics that "may have side effects" but can be deleted
249 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
250 // Safe to delete llvm.stacksave if dead.
251 if (II->getIntrinsicID() == Intrinsic::stacksave)
254 // Lifetime intrinsics are dead when their right-hand is undef.
255 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
256 II->getIntrinsicID() == Intrinsic::lifetime_end)
257 return isa<UndefValue>(II->getArgOperand(1));
260 if (extractMallocCall(I)) return true;
262 if (CallInst *CI = isFreeCall(I))
263 if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
264 return C->isNullValue() || isa<UndefValue>(C);
269 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
270 /// trivially dead instruction, delete it. If that makes any of its operands
271 /// trivially dead, delete them too, recursively. Return true if any
272 /// instructions were deleted.
273 bool llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V) {
274 Instruction *I = dyn_cast<Instruction>(V);
275 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I))
278 SmallVector<Instruction*, 16> DeadInsts;
279 DeadInsts.push_back(I);
282 I = DeadInsts.pop_back_val();
284 // Null out all of the instruction's operands to see if any operand becomes
286 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
287 Value *OpV = I->getOperand(i);
290 if (!OpV->use_empty()) continue;
292 // If the operand is an instruction that became dead as we nulled out the
293 // operand, and if it is 'trivially' dead, delete it in a future loop
295 if (Instruction *OpI = dyn_cast<Instruction>(OpV))
296 if (isInstructionTriviallyDead(OpI))
297 DeadInsts.push_back(OpI);
300 I->eraseFromParent();
301 } while (!DeadInsts.empty());
306 /// areAllUsesEqual - Check whether the uses of a value are all the same.
307 /// This is similar to Instruction::hasOneUse() except this will also return
308 /// true when there are no uses or multiple uses that all refer to the same
310 static bool areAllUsesEqual(Instruction *I) {
311 Value::use_iterator UI = I->use_begin();
312 Value::use_iterator UE = I->use_end();
317 for (++UI; UI != UE; ++UI) {
324 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
325 /// dead PHI node, due to being a def-use chain of single-use nodes that
326 /// either forms a cycle or is terminated by a trivially dead instruction,
327 /// delete it. If that makes any of its operands trivially dead, delete them
328 /// too, recursively. Return true if a change was made.
329 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) {
330 SmallPtrSet<Instruction*, 4> Visited;
331 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
332 I = cast<Instruction>(*I->use_begin())) {
334 return RecursivelyDeleteTriviallyDeadInstructions(I);
336 // If we find an instruction more than once, we're on a cycle that
337 // won't prove fruitful.
338 if (!Visited.insert(I)) {
339 // Break the cycle and delete the instruction and its operands.
340 I->replaceAllUsesWith(UndefValue::get(I->getType()));
341 (void)RecursivelyDeleteTriviallyDeadInstructions(I);
348 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
349 /// simplify any instructions in it and recursively delete dead instructions.
351 /// This returns true if it changed the code, note that it can delete
352 /// instructions in other blocks as well in this block.
353 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD) {
354 bool MadeChange = false;
355 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
356 Instruction *Inst = BI++;
358 if (Value *V = SimplifyInstruction(Inst, TD)) {
360 ReplaceAndSimplifyAllUses(Inst, V, TD);
367 if (Inst->isTerminator())
371 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst);
378 //===----------------------------------------------------------------------===//
379 // Control Flow Graph Restructuring.
383 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
384 /// method is called when we're about to delete Pred as a predecessor of BB. If
385 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
387 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
388 /// nodes that collapse into identity values. For example, if we have:
389 /// x = phi(1, 0, 0, 0)
392 /// .. and delete the predecessor corresponding to the '1', this will attempt to
393 /// recursively fold the and to 0.
394 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
396 // This only adjusts blocks with PHI nodes.
397 if (!isa<PHINode>(BB->begin()))
400 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
401 // them down. This will leave us with single entry phi nodes and other phis
402 // that can be removed.
403 BB->removePredecessor(Pred, true);
405 WeakVH PhiIt = &BB->front();
406 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
407 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
409 Value *PNV = SimplifyInstruction(PN, TD);
410 if (PNV == 0) continue;
412 // If we're able to simplify the phi to a single value, substitute the new
413 // value into all of its uses.
414 assert(PNV != PN && "SimplifyInstruction broken!");
416 Value *OldPhiIt = PhiIt;
417 ReplaceAndSimplifyAllUses(PN, PNV, TD);
419 // If recursive simplification ended up deleting the next PHI node we would
420 // iterate to, then our iterator is invalid, restart scanning from the top
422 if (PhiIt != OldPhiIt) PhiIt = &BB->front();
427 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
428 /// predecessor is known to have one successor (DestBB!). Eliminate the edge
429 /// between them, moving the instructions in the predecessor into DestBB and
430 /// deleting the predecessor block.
432 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) {
433 // If BB has single-entry PHI nodes, fold them.
434 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
435 Value *NewVal = PN->getIncomingValue(0);
436 // Replace self referencing PHI with undef, it must be dead.
437 if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
438 PN->replaceAllUsesWith(NewVal);
439 PN->eraseFromParent();
442 BasicBlock *PredBB = DestBB->getSinglePredecessor();
443 assert(PredBB && "Block doesn't have a single predecessor!");
445 // Zap anything that took the address of DestBB. Not doing this will give the
446 // address an invalid value.
447 if (DestBB->hasAddressTaken()) {
448 BlockAddress *BA = BlockAddress::get(DestBB);
449 Constant *Replacement =
450 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1);
451 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
453 BA->destroyConstant();
456 // Anything that branched to PredBB now branches to DestBB.
457 PredBB->replaceAllUsesWith(DestBB);
459 // Splice all the instructions from PredBB to DestBB.
460 PredBB->getTerminator()->eraseFromParent();
461 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
464 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>();
466 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock();
467 DT->changeImmediateDominator(DestBB, PredBBIDom);
468 DT->eraseNode(PredBB);
470 ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>();
472 PI->replaceAllUses(PredBB, DestBB);
473 PI->removeEdge(ProfileInfo::getEdge(PredBB, DestBB));
477 PredBB->eraseFromParent();
480 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
481 /// almost-empty BB ending in an unconditional branch to Succ, into succ.
483 /// Assumption: Succ is the single successor for BB.
485 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
486 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
488 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
489 << Succ->getName() << "\n");
490 // Shortcut, if there is only a single predecessor it must be BB and merging
492 if (Succ->getSinglePredecessor()) return true;
494 // Make a list of the predecessors of BB
495 SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
497 // Look at all the phi nodes in Succ, to see if they present a conflict when
498 // merging these blocks
499 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
500 PHINode *PN = cast<PHINode>(I);
502 // If the incoming value from BB is again a PHINode in
503 // BB which has the same incoming value for *PI as PN does, we can
504 // merge the phi nodes and then the blocks can still be merged
505 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
506 if (BBPN && BBPN->getParent() == BB) {
507 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
508 BasicBlock *IBB = PN->getIncomingBlock(PI);
509 if (BBPreds.count(IBB) &&
510 BBPN->getIncomingValueForBlock(IBB) != PN->getIncomingValue(PI)) {
511 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
512 << Succ->getName() << " is conflicting with "
513 << BBPN->getName() << " with regard to common predecessor "
514 << IBB->getName() << "\n");
519 Value* Val = PN->getIncomingValueForBlock(BB);
520 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
521 // See if the incoming value for the common predecessor is equal to the
522 // one for BB, in which case this phi node will not prevent the merging
524 BasicBlock *IBB = PN->getIncomingBlock(PI);
525 if (BBPreds.count(IBB) && Val != PN->getIncomingValue(PI)) {
526 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
527 << Succ->getName() << " is conflicting with regard to common "
528 << "predecessor " << IBB->getName() << "\n");
538 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
539 /// unconditional branch, and contains no instructions other than PHI nodes,
540 /// potential side-effect free intrinsics and the branch. If possible,
541 /// eliminate BB by rewriting all the predecessors to branch to the successor
542 /// block and return true. If we can't transform, return false.
543 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
544 assert(BB != &BB->getParent()->getEntryBlock() &&
545 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
547 // We can't eliminate infinite loops.
548 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
549 if (BB == Succ) return false;
551 // Check to see if merging these blocks would cause conflicts for any of the
552 // phi nodes in BB or Succ. If not, we can safely merge.
553 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
555 // Check for cases where Succ has multiple predecessors and a PHI node in BB
556 // has uses which will not disappear when the PHI nodes are merged. It is
557 // possible to handle such cases, but difficult: it requires checking whether
558 // BB dominates Succ, which is non-trivial to calculate in the case where
559 // Succ has multiple predecessors. Also, it requires checking whether
560 // constructing the necessary self-referential PHI node doesn't intoduce any
561 // conflicts; this isn't too difficult, but the previous code for doing this
564 // Note that if this check finds a live use, BB dominates Succ, so BB is
565 // something like a loop pre-header (or rarely, a part of an irreducible CFG);
566 // folding the branch isn't profitable in that case anyway.
567 if (!Succ->getSinglePredecessor()) {
568 BasicBlock::iterator BBI = BB->begin();
569 while (isa<PHINode>(*BBI)) {
570 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
572 if (PHINode* PN = dyn_cast<PHINode>(*UI)) {
573 if (PN->getIncomingBlock(UI) != BB)
583 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
585 if (isa<PHINode>(Succ->begin())) {
586 // If there is more than one pred of succ, and there are PHI nodes in
587 // the successor, then we need to add incoming edges for the PHI nodes
589 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
591 // Loop over all of the PHI nodes in the successor of BB.
592 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
593 PHINode *PN = cast<PHINode>(I);
594 Value *OldVal = PN->removeIncomingValue(BB, false);
595 assert(OldVal && "No entry in PHI for Pred BB!");
597 // If this incoming value is one of the PHI nodes in BB, the new entries
598 // in the PHI node are the entries from the old PHI.
599 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
600 PHINode *OldValPN = cast<PHINode>(OldVal);
601 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
602 // Note that, since we are merging phi nodes and BB and Succ might
603 // have common predecessors, we could end up with a phi node with
604 // identical incoming branches. This will be cleaned up later (and
605 // will trigger asserts if we try to clean it up now, without also
606 // simplifying the corresponding conditional branch).
607 PN->addIncoming(OldValPN->getIncomingValue(i),
608 OldValPN->getIncomingBlock(i));
610 // Add an incoming value for each of the new incoming values.
611 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
612 PN->addIncoming(OldVal, BBPreds[i]);
617 if (Succ->getSinglePredecessor()) {
618 // BB is the only predecessor of Succ, so Succ will end up with exactly
619 // the same predecessors BB had.
621 // Copy over any phi, debug or lifetime instruction.
622 BB->getTerminator()->eraseFromParent();
623 Succ->getInstList().splice(Succ->getFirstNonPHI(), BB->getInstList());
625 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
626 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
627 assert(PN->use_empty() && "There shouldn't be any uses here!");
628 PN->eraseFromParent();
632 // Everything that jumped to BB now goes to Succ.
633 BB->replaceAllUsesWith(Succ);
634 if (!Succ->hasName()) Succ->takeName(BB);
635 BB->eraseFromParent(); // Delete the old basic block.
639 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
640 /// nodes in this block. This doesn't try to be clever about PHI nodes
641 /// which differ only in the order of the incoming values, but instcombine
642 /// orders them so it usually won't matter.
644 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
645 bool Changed = false;
647 // This implementation doesn't currently consider undef operands
648 // specially. Theoretically, two phis which are identical except for
649 // one having an undef where the other doesn't could be collapsed.
651 // Map from PHI hash values to PHI nodes. If multiple PHIs have
652 // the same hash value, the element is the first PHI in the
653 // linked list in CollisionMap.
654 DenseMap<uintptr_t, PHINode *> HashMap;
656 // Maintain linked lists of PHI nodes with common hash values.
657 DenseMap<PHINode *, PHINode *> CollisionMap;
660 for (BasicBlock::iterator I = BB->begin();
661 PHINode *PN = dyn_cast<PHINode>(I++); ) {
662 // Compute a hash value on the operands. Instcombine will likely have sorted
663 // them, which helps expose duplicates, but we have to check all the
664 // operands to be safe in case instcombine hasn't run.
666 // This hash algorithm is quite weak as hash functions go, but it seems
667 // to do a good enough job for this particular purpose, and is very quick.
668 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
669 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
670 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
672 for (PHINode::block_iterator I = PN->block_begin(), E = PN->block_end();
674 Hash ^= reinterpret_cast<uintptr_t>(static_cast<BasicBlock *>(*I));
675 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
677 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1.
679 // If we've never seen this hash value before, it's a unique PHI.
680 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
681 HashMap.insert(std::make_pair(Hash, PN));
682 if (Pair.second) continue;
683 // Otherwise it's either a duplicate or a hash collision.
684 for (PHINode *OtherPN = Pair.first->second; ; ) {
685 if (OtherPN->isIdenticalTo(PN)) {
686 // A duplicate. Replace this PHI with its duplicate.
687 PN->replaceAllUsesWith(OtherPN);
688 PN->eraseFromParent();
692 // A non-duplicate hash collision.
693 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
694 if (I == CollisionMap.end()) {
695 // Set this PHI to be the head of the linked list of colliding PHIs.
696 PHINode *Old = Pair.first->second;
697 Pair.first->second = PN;
698 CollisionMap[PN] = Old;
701 // Procede to the next PHI in the list.
709 /// enforceKnownAlignment - If the specified pointer points to an object that
710 /// we control, modify the object's alignment to PrefAlign. This isn't
711 /// often possible though. If alignment is important, a more reliable approach
712 /// is to simply align all global variables and allocation instructions to
713 /// their preferred alignment from the beginning.
715 static unsigned enforceKnownAlignment(Value *V, unsigned Align,
716 unsigned PrefAlign, const TargetData *TD) {
717 V = V->stripPointerCasts();
719 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
720 // If the preferred alignment is greater than the natural stack alignment
721 // then don't round up. This avoids dynamic stack realignment.
722 if (TD && TD->exceedsNaturalStackAlignment(PrefAlign))
724 // If there is a requested alignment and if this is an alloca, round up.
725 if (AI->getAlignment() >= PrefAlign)
726 return AI->getAlignment();
727 AI->setAlignment(PrefAlign);
731 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
732 // If there is a large requested alignment and we can, bump up the alignment
734 if (GV->isDeclaration()) return Align;
735 // If the memory we set aside for the global may not be the memory used by
736 // the final program then it is impossible for us to reliably enforce the
737 // preferred alignment.
738 if (GV->isWeakForLinker()) return Align;
740 if (GV->getAlignment() >= PrefAlign)
741 return GV->getAlignment();
742 // We can only increase the alignment of the global if it has no alignment
743 // specified or if it is not assigned a section. If it is assigned a
744 // section, the global could be densely packed with other objects in the
745 // section, increasing the alignment could cause padding issues.
746 if (!GV->hasSection() || GV->getAlignment() == 0)
747 GV->setAlignment(PrefAlign);
748 return GV->getAlignment();
754 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
755 /// we can determine, return it, otherwise return 0. If PrefAlign is specified,
756 /// and it is more than the alignment of the ultimate object, see if we can
757 /// increase the alignment of the ultimate object, making this check succeed.
758 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
759 const TargetData *TD) {
760 assert(V->getType()->isPointerTy() &&
761 "getOrEnforceKnownAlignment expects a pointer!");
762 unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64;
763 APInt Mask = APInt::getAllOnesValue(BitWidth);
764 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
765 ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD);
766 unsigned TrailZ = KnownZero.countTrailingOnes();
768 // Avoid trouble with rediculously large TrailZ values, such as
769 // those computed from a null pointer.
770 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
772 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
774 // LLVM doesn't support alignments larger than this currently.
775 Align = std::min(Align, +Value::MaximumAlignment);
777 if (PrefAlign > Align)
778 Align = enforceKnownAlignment(V, Align, PrefAlign, TD);
780 // We don't need to make any adjustment.
784 ///===---------------------------------------------------------------------===//
785 /// Dbg Intrinsic utilities
788 /// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value
789 /// that has an associated llvm.dbg.decl intrinsic.
790 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
791 StoreInst *SI, DIBuilder &Builder) {
792 DIVariable DIVar(DDI->getVariable());
796 Instruction *DbgVal = NULL;
797 // If an argument is zero extended then use argument directly. The ZExt
798 // may be zapped by an optimization pass in future.
799 Argument *ExtendedArg = NULL;
800 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
801 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0));
802 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
803 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0));
805 DbgVal = Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, SI);
807 DbgVal = Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, SI);
809 // Propagate any debug metadata from the store onto the dbg.value.
810 DebugLoc SIDL = SI->getDebugLoc();
811 if (!SIDL.isUnknown())
812 DbgVal->setDebugLoc(SIDL);
813 // Otherwise propagate debug metadata from dbg.declare.
815 DbgVal->setDebugLoc(DDI->getDebugLoc());
819 /// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value
820 /// that has an associated llvm.dbg.decl intrinsic.
821 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
822 LoadInst *LI, DIBuilder &Builder) {
823 DIVariable DIVar(DDI->getVariable());
827 Instruction *DbgVal =
828 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0,
831 // Propagate any debug metadata from the store onto the dbg.value.
832 DebugLoc LIDL = LI->getDebugLoc();
833 if (!LIDL.isUnknown())
834 DbgVal->setDebugLoc(LIDL);
835 // Otherwise propagate debug metadata from dbg.declare.
837 DbgVal->setDebugLoc(DDI->getDebugLoc());
841 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
842 /// of llvm.dbg.value intrinsics.
843 bool llvm::LowerDbgDeclare(Function &F) {
844 DIBuilder DIB(*F.getParent());
845 SmallVector<DbgDeclareInst *, 4> Dbgs;
846 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
847 for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ++BI) {
848 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(BI))
854 for (SmallVector<DbgDeclareInst *, 4>::iterator I = Dbgs.begin(),
855 E = Dbgs.end(); I != E; ++I) {
856 DbgDeclareInst *DDI = *I;
857 if (AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress())) {
858 bool RemoveDDI = true;
859 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
861 if (StoreInst *SI = dyn_cast<StoreInst>(*UI))
862 ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
863 else if (LoadInst *LI = dyn_cast<LoadInst>(*UI))
864 ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
868 DDI->eraseFromParent();
874 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the
875 /// alloca 'V', if any.
876 DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) {
877 if (MDNode *DebugNode = MDNode::getIfExists(V->getContext(), V))
878 for (Value::use_iterator UI = DebugNode->use_begin(),
879 E = DebugNode->use_end(); UI != E; ++UI)
880 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(*UI))