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 //===----------------------------------------------------------------------===//
38 // Local constant propagation.
41 // ConstantFoldTerminator - If a terminator instruction is predicated on a
42 // constant value, convert it into an unconditional branch to the constant
45 bool llvm::ConstantFoldTerminator(BasicBlock
*BB
) {
46 TerminatorInst
*T
= BB
->getTerminator();
48 // Branch - See if we are conditional jumping on constant
49 if (BranchInst
*BI
= dyn_cast
<BranchInst
>(T
)) {
50 if (BI
->isUnconditional()) return false; // Can't optimize uncond branch
51 BasicBlock
*Dest1
= BI
->getSuccessor(0);
52 BasicBlock
*Dest2
= BI
->getSuccessor(1);
54 if (ConstantInt
*Cond
= dyn_cast
<ConstantInt
>(BI
->getCondition())) {
55 // Are we branching on constant?
56 // YES. Change to unconditional branch...
57 BasicBlock
*Destination
= Cond
->getZExtValue() ? Dest1
: Dest2
;
58 BasicBlock
*OldDest
= Cond
->getZExtValue() ? Dest2
: Dest1
;
60 //cerr << "Function: " << T->getParent()->getParent()
61 // << "\nRemoving branch from " << T->getParent()
62 // << "\n\nTo: " << OldDest << endl;
64 // Let the basic block know that we are letting go of it. Based on this,
65 // it will adjust it's PHI nodes.
66 assert(BI
->getParent() && "Terminator not inserted in block!");
67 OldDest
->removePredecessor(BI
->getParent());
69 // Set the unconditional destination, and change the insn to be an
70 // unconditional branch.
71 BI
->setUnconditionalDest(Destination
);
75 if (Dest2
== Dest1
) { // Conditional branch to same location?
76 // This branch matches something like this:
77 // br bool %cond, label %Dest, label %Dest
78 // and changes it into: br label %Dest
80 // Let the basic block know that we are letting go of one copy of it.
81 assert(BI
->getParent() && "Terminator not inserted in block!");
82 Dest1
->removePredecessor(BI
->getParent());
84 // Change a conditional branch to unconditional.
85 BI
->setUnconditionalDest(Dest1
);
91 if (SwitchInst
*SI
= dyn_cast
<SwitchInst
>(T
)) {
92 // If we are switching on a constant, we can convert the switch into a
93 // single branch instruction!
94 ConstantInt
*CI
= dyn_cast
<ConstantInt
>(SI
->getCondition());
95 BasicBlock
*TheOnlyDest
= SI
->getSuccessor(0); // The default dest
96 BasicBlock
*DefaultDest
= TheOnlyDest
;
97 assert(TheOnlyDest
== SI
->getDefaultDest() &&
98 "Default destination is not successor #0?");
100 // Figure out which case it goes to.
101 for (unsigned i
= 1, e
= SI
->getNumSuccessors(); i
!= e
; ++i
) {
102 // Found case matching a constant operand?
103 if (SI
->getSuccessorValue(i
) == CI
) {
104 TheOnlyDest
= SI
->getSuccessor(i
);
108 // Check to see if this branch is going to the same place as the default
109 // dest. If so, eliminate it as an explicit compare.
110 if (SI
->getSuccessor(i
) == DefaultDest
) {
111 // Remove this entry.
112 DefaultDest
->removePredecessor(SI
->getParent());
114 --i
; --e
; // Don't skip an entry...
118 // Otherwise, check to see if the switch only branches to one destination.
119 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
121 if (SI
->getSuccessor(i
) != TheOnlyDest
) TheOnlyDest
= 0;
124 if (CI
&& !TheOnlyDest
) {
125 // Branching on a constant, but not any of the cases, go to the default
127 TheOnlyDest
= SI
->getDefaultDest();
130 // If we found a single destination that we can fold the switch into, do so
133 // Insert the new branch.
134 BranchInst::Create(TheOnlyDest
, SI
);
135 BasicBlock
*BB
= SI
->getParent();
137 // Remove entries from PHI nodes which we no longer branch to...
138 for (unsigned i
= 0, e
= SI
->getNumSuccessors(); i
!= e
; ++i
) {
139 // Found case matching a constant operand?
140 BasicBlock
*Succ
= SI
->getSuccessor(i
);
141 if (Succ
== TheOnlyDest
)
142 TheOnlyDest
= 0; // Don't modify the first branch to TheOnlyDest
144 Succ
->removePredecessor(BB
);
147 // Delete the old switch.
148 BB
->getInstList().erase(SI
);
152 if (SI
->getNumSuccessors() == 2) {
153 // Otherwise, we can fold this switch into a conditional branch
154 // instruction if it has only one non-default destination.
155 Value
*Cond
= new ICmpInst(SI
, ICmpInst::ICMP_EQ
, SI
->getCondition(),
156 SI
->getSuccessorValue(1), "cond");
157 // Insert the new branch.
158 BranchInst::Create(SI
->getSuccessor(1), SI
->getSuccessor(0), Cond
, SI
);
160 // Delete the old switch.
161 SI
->eraseFromParent();
167 if (IndirectBrInst
*IBI
= dyn_cast
<IndirectBrInst
>(T
)) {
168 // indirectbr blockaddress(@F, @BB) -> br label @BB
169 if (BlockAddress
*BA
=
170 dyn_cast
<BlockAddress
>(IBI
->getAddress()->stripPointerCasts())) {
171 BasicBlock
*TheOnlyDest
= BA
->getBasicBlock();
172 // Insert the new branch.
173 BranchInst::Create(TheOnlyDest
, IBI
);
175 for (unsigned i
= 0, e
= IBI
->getNumDestinations(); i
!= e
; ++i
) {
176 if (IBI
->getDestination(i
) == TheOnlyDest
)
179 IBI
->getDestination(i
)->removePredecessor(IBI
->getParent());
181 IBI
->eraseFromParent();
183 // If we didn't find our destination in the IBI successor list, then we
184 // have undefined behavior. Replace the unconditional branch with an
185 // 'unreachable' instruction.
187 BB
->getTerminator()->eraseFromParent();
188 new UnreachableInst(BB
->getContext(), BB
);
199 //===----------------------------------------------------------------------===//
200 // Local dead code elimination.
203 /// isInstructionTriviallyDead - Return true if the result produced by the
204 /// instruction is not used, and the instruction has no side effects.
206 bool llvm::isInstructionTriviallyDead(Instruction
*I
) {
207 if (!I
->use_empty() || isa
<TerminatorInst
>(I
)) return false;
209 // We don't want debug info removed by anything this general.
210 if (isa
<DbgInfoIntrinsic
>(I
)) return false;
212 if (!I
->mayHaveSideEffects()) return true;
214 // Special case intrinsics that "may have side effects" but can be deleted
216 if (IntrinsicInst
*II
= dyn_cast
<IntrinsicInst
>(I
))
217 // Safe to delete llvm.stacksave if dead.
218 if (II
->getIntrinsicID() == Intrinsic::stacksave
)
223 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
224 /// trivially dead instruction, delete it. If that makes any of its operands
225 /// trivially dead, delete them too, recursively. Return true if any
226 /// instructions were deleted.
227 bool llvm::RecursivelyDeleteTriviallyDeadInstructions(Value
*V
) {
228 Instruction
*I
= dyn_cast
<Instruction
>(V
);
229 if (!I
|| !I
->use_empty() || !isInstructionTriviallyDead(I
))
232 SmallVector
<Instruction
*, 16> DeadInsts
;
233 DeadInsts
.push_back(I
);
236 I
= DeadInsts
.pop_back_val();
238 // Null out all of the instruction's operands to see if any operand becomes
240 for (unsigned i
= 0, e
= I
->getNumOperands(); i
!= e
; ++i
) {
241 Value
*OpV
= I
->getOperand(i
);
244 if (!OpV
->use_empty()) continue;
246 // If the operand is an instruction that became dead as we nulled out the
247 // operand, and if it is 'trivially' dead, delete it in a future loop
249 if (Instruction
*OpI
= dyn_cast
<Instruction
>(OpV
))
250 if (isInstructionTriviallyDead(OpI
))
251 DeadInsts
.push_back(OpI
);
254 I
->eraseFromParent();
255 } while (!DeadInsts
.empty());
260 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
261 /// dead PHI node, due to being a def-use chain of single-use nodes that
262 /// either forms a cycle or is terminated by a trivially dead instruction,
263 /// delete it. If that makes any of its operands trivially dead, delete them
264 /// too, recursively. Return true if the PHI node is actually deleted.
266 llvm::RecursivelyDeleteDeadPHINode(PHINode
*PN
) {
267 // We can remove a PHI if it is on a cycle in the def-use graph
268 // where each node in the cycle has degree one, i.e. only one use,
269 // and is an instruction with no side effects.
270 if (!PN
->hasOneUse())
273 bool Changed
= false;
274 SmallPtrSet
<PHINode
*, 4> PHIs
;
276 for (Instruction
*J
= cast
<Instruction
>(*PN
->use_begin());
277 J
->hasOneUse() && !J
->mayHaveSideEffects();
278 J
= cast
<Instruction
>(*J
->use_begin()))
279 // If we find a PHI more than once, we're on a cycle that
280 // won't prove fruitful.
281 if (PHINode
*JP
= dyn_cast
<PHINode
>(J
))
282 if (!PHIs
.insert(cast
<PHINode
>(JP
))) {
283 // Break the cycle and delete the PHI and its operands.
284 JP
->replaceAllUsesWith(UndefValue::get(JP
->getType()));
285 (void)RecursivelyDeleteTriviallyDeadInstructions(JP
);
292 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
293 /// simplify any instructions in it and recursively delete dead instructions.
295 /// This returns true if it changed the code, note that it can delete
296 /// instructions in other blocks as well in this block.
297 bool llvm::SimplifyInstructionsInBlock(BasicBlock
*BB
, const TargetData
*TD
) {
298 bool MadeChange
= false;
299 for (BasicBlock::iterator BI
= BB
->begin(), E
= BB
->end(); BI
!= E
; ) {
300 Instruction
*Inst
= BI
++;
302 if (Value
*V
= SimplifyInstruction(Inst
, TD
)) {
304 ReplaceAndSimplifyAllUses(Inst
, V
, TD
);
311 MadeChange
|= RecursivelyDeleteTriviallyDeadInstructions(Inst
);
316 //===----------------------------------------------------------------------===//
317 // Control Flow Graph Restructuring.
321 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
322 /// method is called when we're about to delete Pred as a predecessor of BB. If
323 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
325 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
326 /// nodes that collapse into identity values. For example, if we have:
327 /// x = phi(1, 0, 0, 0)
330 /// .. and delete the predecessor corresponding to the '1', this will attempt to
331 /// recursively fold the and to 0.
332 void llvm::RemovePredecessorAndSimplify(BasicBlock
*BB
, BasicBlock
*Pred
,
334 // This only adjusts blocks with PHI nodes.
335 if (!isa
<PHINode
>(BB
->begin()))
338 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
339 // them down. This will leave us with single entry phi nodes and other phis
340 // that can be removed.
341 BB
->removePredecessor(Pred
, true);
343 WeakVH PhiIt
= &BB
->front();
344 while (PHINode
*PN
= dyn_cast
<PHINode
>(PhiIt
)) {
345 PhiIt
= &*++BasicBlock::iterator(cast
<Instruction
>(PhiIt
));
347 Value
*PNV
= SimplifyInstruction(PN
, TD
);
348 if (PNV
== 0) continue;
350 // If we're able to simplify the phi to a single value, substitute the new
351 // value into all of its uses.
352 assert(PNV
!= PN
&& "SimplifyInstruction broken!");
354 Value
*OldPhiIt
= PhiIt
;
355 ReplaceAndSimplifyAllUses(PN
, PNV
, TD
);
357 // If recursive simplification ended up deleting the next PHI node we would
358 // iterate to, then our iterator is invalid, restart scanning from the top
360 if (PhiIt
!= OldPhiIt
) PhiIt
= &BB
->front();
365 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
366 /// predecessor is known to have one successor (DestBB!). Eliminate the edge
367 /// between them, moving the instructions in the predecessor into DestBB and
368 /// deleting the predecessor block.
370 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock
*DestBB
, Pass
*P
) {
371 // If BB has single-entry PHI nodes, fold them.
372 while (PHINode
*PN
= dyn_cast
<PHINode
>(DestBB
->begin())) {
373 Value
*NewVal
= PN
->getIncomingValue(0);
374 // Replace self referencing PHI with undef, it must be dead.
375 if (NewVal
== PN
) NewVal
= UndefValue::get(PN
->getType());
376 PN
->replaceAllUsesWith(NewVal
);
377 PN
->eraseFromParent();
380 BasicBlock
*PredBB
= DestBB
->getSinglePredecessor();
381 assert(PredBB
&& "Block doesn't have a single predecessor!");
383 // Splice all the instructions from PredBB to DestBB.
384 PredBB
->getTerminator()->eraseFromParent();
385 DestBB
->getInstList().splice(DestBB
->begin(), PredBB
->getInstList());
387 // Zap anything that took the address of DestBB. Not doing this will give the
388 // address an invalid value.
389 if (DestBB
->hasAddressTaken()) {
390 BlockAddress
*BA
= BlockAddress::get(DestBB
);
391 Constant
*Replacement
=
392 ConstantInt::get(llvm::Type::getInt32Ty(BA
->getContext()), 1);
393 BA
->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement
,
395 BA
->destroyConstant();
398 // Anything that branched to PredBB now branches to DestBB.
399 PredBB
->replaceAllUsesWith(DestBB
);
402 ProfileInfo
*PI
= P
->getAnalysisIfAvailable
<ProfileInfo
>();
404 PI
->replaceAllUses(PredBB
, DestBB
);
405 PI
->removeEdge(ProfileInfo::getEdge(PredBB
, DestBB
));
409 PredBB
->eraseFromParent();
412 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
413 /// almost-empty BB ending in an unconditional branch to Succ, into succ.
415 /// Assumption: Succ is the single successor for BB.
417 static bool CanPropagatePredecessorsForPHIs(BasicBlock
*BB
, BasicBlock
*Succ
) {
418 assert(*succ_begin(BB
) == Succ
&& "Succ is not successor of BB!");
420 DEBUG(dbgs() << "Looking to fold " << BB
->getName() << " into "
421 << Succ
->getName() << "\n");
422 // Shortcut, if there is only a single predecessor it must be BB and merging
424 if (Succ
->getSinglePredecessor()) return true;
426 // Make a list of the predecessors of BB
427 typedef SmallPtrSet
<BasicBlock
*, 16> BlockSet
;
428 BlockSet
BBPreds(pred_begin(BB
), pred_end(BB
));
430 // Use that list to make another list of common predecessors of BB and Succ
431 BlockSet CommonPreds
;
432 for (pred_iterator PI
= pred_begin(Succ
), PE
= pred_end(Succ
);
435 if (BBPreds
.count(P
))
436 CommonPreds
.insert(P
);
439 // Shortcut, if there are no common predecessors, merging is always safe
440 if (CommonPreds
.empty())
443 // Look at all the phi nodes in Succ, to see if they present a conflict when
444 // merging these blocks
445 for (BasicBlock::iterator I
= Succ
->begin(); isa
<PHINode
>(I
); ++I
) {
446 PHINode
*PN
= cast
<PHINode
>(I
);
448 // If the incoming value from BB is again a PHINode in
449 // BB which has the same incoming value for *PI as PN does, we can
450 // merge the phi nodes and then the blocks can still be merged
451 PHINode
*BBPN
= dyn_cast
<PHINode
>(PN
->getIncomingValueForBlock(BB
));
452 if (BBPN
&& BBPN
->getParent() == BB
) {
453 for (BlockSet::iterator PI
= CommonPreds
.begin(), PE
= CommonPreds
.end();
455 if (BBPN
->getIncomingValueForBlock(*PI
)
456 != PN
->getIncomingValueForBlock(*PI
)) {
457 DEBUG(dbgs() << "Can't fold, phi node " << PN
->getName() << " in "
458 << Succ
->getName() << " is conflicting with "
459 << BBPN
->getName() << " with regard to common predecessor "
460 << (*PI
)->getName() << "\n");
465 Value
* Val
= PN
->getIncomingValueForBlock(BB
);
466 for (BlockSet::iterator PI
= CommonPreds
.begin(), PE
= CommonPreds
.end();
468 // See if the incoming value for the common predecessor is equal to the
469 // one for BB, in which case this phi node will not prevent the merging
471 if (Val
!= PN
->getIncomingValueForBlock(*PI
)) {
472 DEBUG(dbgs() << "Can't fold, phi node " << PN
->getName() << " in "
473 << Succ
->getName() << " is conflicting with regard to common "
474 << "predecessor " << (*PI
)->getName() << "\n");
484 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
485 /// unconditional branch, and contains no instructions other than PHI nodes,
486 /// potential debug intrinsics and the branch. If possible, eliminate BB by
487 /// rewriting all the predecessors to branch to the successor block and return
488 /// true. If we can't transform, return false.
489 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock
*BB
) {
490 assert(BB
!= &BB
->getParent()->getEntryBlock() &&
491 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
493 // We can't eliminate infinite loops.
494 BasicBlock
*Succ
= cast
<BranchInst
>(BB
->getTerminator())->getSuccessor(0);
495 if (BB
== Succ
) return false;
497 // Check to see if merging these blocks would cause conflicts for any of the
498 // phi nodes in BB or Succ. If not, we can safely merge.
499 if (!CanPropagatePredecessorsForPHIs(BB
, Succ
)) return false;
501 // Check for cases where Succ has multiple predecessors and a PHI node in BB
502 // has uses which will not disappear when the PHI nodes are merged. It is
503 // possible to handle such cases, but difficult: it requires checking whether
504 // BB dominates Succ, which is non-trivial to calculate in the case where
505 // Succ has multiple predecessors. Also, it requires checking whether
506 // constructing the necessary self-referential PHI node doesn't intoduce any
507 // conflicts; this isn't too difficult, but the previous code for doing this
510 // Note that if this check finds a live use, BB dominates Succ, so BB is
511 // something like a loop pre-header (or rarely, a part of an irreducible CFG);
512 // folding the branch isn't profitable in that case anyway.
513 if (!Succ
->getSinglePredecessor()) {
514 BasicBlock::iterator BBI
= BB
->begin();
515 while (isa
<PHINode
>(*BBI
)) {
516 for (Value::use_iterator UI
= BBI
->use_begin(), E
= BBI
->use_end();
518 if (PHINode
* PN
= dyn_cast
<PHINode
>(*UI
)) {
519 if (PN
->getIncomingBlock(UI
) != BB
)
529 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB
);
531 if (isa
<PHINode
>(Succ
->begin())) {
532 // If there is more than one pred of succ, and there are PHI nodes in
533 // the successor, then we need to add incoming edges for the PHI nodes
535 const SmallVector
<BasicBlock
*, 16> BBPreds(pred_begin(BB
), pred_end(BB
));
537 // Loop over all of the PHI nodes in the successor of BB.
538 for (BasicBlock::iterator I
= Succ
->begin(); isa
<PHINode
>(I
); ++I
) {
539 PHINode
*PN
= cast
<PHINode
>(I
);
540 Value
*OldVal
= PN
->removeIncomingValue(BB
, false);
541 assert(OldVal
&& "No entry in PHI for Pred BB!");
543 // If this incoming value is one of the PHI nodes in BB, the new entries
544 // in the PHI node are the entries from the old PHI.
545 if (isa
<PHINode
>(OldVal
) && cast
<PHINode
>(OldVal
)->getParent() == BB
) {
546 PHINode
*OldValPN
= cast
<PHINode
>(OldVal
);
547 for (unsigned i
= 0, e
= OldValPN
->getNumIncomingValues(); i
!= e
; ++i
)
548 // Note that, since we are merging phi nodes and BB and Succ might
549 // have common predecessors, we could end up with a phi node with
550 // identical incoming branches. This will be cleaned up later (and
551 // will trigger asserts if we try to clean it up now, without also
552 // simplifying the corresponding conditional branch).
553 PN
->addIncoming(OldValPN
->getIncomingValue(i
),
554 OldValPN
->getIncomingBlock(i
));
556 // Add an incoming value for each of the new incoming values.
557 for (unsigned i
= 0, e
= BBPreds
.size(); i
!= e
; ++i
)
558 PN
->addIncoming(OldVal
, BBPreds
[i
]);
563 while (PHINode
*PN
= dyn_cast
<PHINode
>(&BB
->front())) {
564 if (Succ
->getSinglePredecessor()) {
565 // BB is the only predecessor of Succ, so Succ will end up with exactly
566 // the same predecessors BB had.
567 Succ
->getInstList().splice(Succ
->begin(),
568 BB
->getInstList(), BB
->begin());
570 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
571 assert(PN
->use_empty() && "There shouldn't be any uses here!");
572 PN
->eraseFromParent();
576 // Everything that jumped to BB now goes to Succ.
577 BB
->replaceAllUsesWith(Succ
);
578 if (!Succ
->hasName()) Succ
->takeName(BB
);
579 BB
->eraseFromParent(); // Delete the old basic block.
583 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
584 /// nodes in this block. This doesn't try to be clever about PHI nodes
585 /// which differ only in the order of the incoming values, but instcombine
586 /// orders them so it usually won't matter.
588 bool llvm::EliminateDuplicatePHINodes(BasicBlock
*BB
) {
589 bool Changed
= false;
591 // This implementation doesn't currently consider undef operands
592 // specially. Theroetically, two phis which are identical except for
593 // one having an undef where the other doesn't could be collapsed.
595 // Map from PHI hash values to PHI nodes. If multiple PHIs have
596 // the same hash value, the element is the first PHI in the
597 // linked list in CollisionMap.
598 DenseMap
<uintptr_t, PHINode
*> HashMap
;
600 // Maintain linked lists of PHI nodes with common hash values.
601 DenseMap
<PHINode
*, PHINode
*> CollisionMap
;
604 for (BasicBlock::iterator I
= BB
->begin();
605 PHINode
*PN
= dyn_cast
<PHINode
>(I
++); ) {
606 // Compute a hash value on the operands. Instcombine will likely have sorted
607 // them, which helps expose duplicates, but we have to check all the
608 // operands to be safe in case instcombine hasn't run.
610 for (User::op_iterator I
= PN
->op_begin(), E
= PN
->op_end(); I
!= E
; ++I
) {
611 // This hash algorithm is quite weak as hash functions go, but it seems
612 // to do a good enough job for this particular purpose, and is very quick.
613 Hash
^= reinterpret_cast<uintptr_t>(static_cast<Value
*>(*I
));
614 Hash
= (Hash
<< 7) | (Hash
>> (sizeof(uintptr_t) * CHAR_BIT
- 7));
616 // If we've never seen this hash value before, it's a unique PHI.
617 std::pair
<DenseMap
<uintptr_t, PHINode
*>::iterator
, bool> Pair
=
618 HashMap
.insert(std::make_pair(Hash
, PN
));
619 if (Pair
.second
) continue;
620 // Otherwise it's either a duplicate or a hash collision.
621 for (PHINode
*OtherPN
= Pair
.first
->second
; ; ) {
622 if (OtherPN
->isIdenticalTo(PN
)) {
623 // A duplicate. Replace this PHI with its duplicate.
624 PN
->replaceAllUsesWith(OtherPN
);
625 PN
->eraseFromParent();
629 // A non-duplicate hash collision.
630 DenseMap
<PHINode
*, PHINode
*>::iterator I
= CollisionMap
.find(OtherPN
);
631 if (I
== CollisionMap
.end()) {
632 // Set this PHI to be the head of the linked list of colliding PHIs.
633 PHINode
*Old
= Pair
.first
->second
;
634 Pair
.first
->second
= PN
;
635 CollisionMap
[PN
] = Old
;
638 // Procede to the next PHI in the list.