Bug Summary

File:lib/Transforms/Scalar/JumpThreading.cpp
Location:line 968, column 7
Description:Called C++ object pointer is null

Annotated Source Code

1//===- JumpThreading.cpp - Thread control through conditional blocks ------===//
2//
3// The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements the Jump Threading pass.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/Transforms/Scalar.h"
15#include "llvm/ADT/DenseMap.h"
16#include "llvm/ADT/DenseSet.h"
17#include "llvm/ADT/STLExtras.h"
18#include "llvm/ADT/SmallPtrSet.h"
19#include "llvm/ADT/SmallSet.h"
20#include "llvm/ADT/Statistic.h"
21#include "llvm/Analysis/CFG.h"
22#include "llvm/Analysis/ConstantFolding.h"
23#include "llvm/Analysis/InstructionSimplify.h"
24#include "llvm/Analysis/LazyValueInfo.h"
25#include "llvm/Analysis/Loads.h"
26#include "llvm/IR/DataLayout.h"
27#include "llvm/IR/IntrinsicInst.h"
28#include "llvm/IR/LLVMContext.h"
29#include "llvm/IR/Metadata.h"
30#include "llvm/IR/ValueHandle.h"
31#include "llvm/Pass.h"
32#include "llvm/Support/CommandLine.h"
33#include "llvm/Support/Debug.h"
34#include "llvm/Support/raw_ostream.h"
35#include "llvm/Target/TargetLibraryInfo.h"
36#include "llvm/Transforms/Utils/BasicBlockUtils.h"
37#include "llvm/Transforms/Utils/Local.h"
38#include "llvm/Transforms/Utils/SSAUpdater.h"
39using namespace llvm;
40
41#define DEBUG_TYPE"jump-threading" "jump-threading"
42
43STATISTIC(NumThreads, "Number of jumps threaded")static llvm::Statistic NumThreads = { "jump-threading", "Number of jumps threaded"
, 0, 0 };
44STATISTIC(NumFolds, "Number of terminators folded")static llvm::Statistic NumFolds = { "jump-threading", "Number of terminators folded"
, 0, 0 };
45STATISTIC(NumDupes, "Number of branch blocks duplicated to eliminate phi")static llvm::Statistic NumDupes = { "jump-threading", "Number of branch blocks duplicated to eliminate phi"
, 0, 0 };
46
47static cl::opt<unsigned>
48BBDuplicateThreshold("jump-threading-threshold",
49 cl::desc("Max block size to duplicate for jump threading"),
50 cl::init(6), cl::Hidden);
51
52namespace {
53 // These are at global scope so static functions can use them too.
54 typedef SmallVectorImpl<std::pair<Constant*, BasicBlock*> > PredValueInfo;
55 typedef SmallVector<std::pair<Constant*, BasicBlock*>, 8> PredValueInfoTy;
56
57 // This is used to keep track of what kind of constant we're currently hoping
58 // to find.
59 enum ConstantPreference {
60 WantInteger,
61 WantBlockAddress
62 };
63
64 /// This pass performs 'jump threading', which looks at blocks that have
65 /// multiple predecessors and multiple successors. If one or more of the
66 /// predecessors of the block can be proven to always jump to one of the
67 /// successors, we forward the edge from the predecessor to the successor by
68 /// duplicating the contents of this block.
69 ///
70 /// An example of when this can occur is code like this:
71 ///
72 /// if () { ...
73 /// X = 4;
74 /// }
75 /// if (X < 3) {
76 ///
77 /// In this case, the unconditional branch at the end of the first if can be
78 /// revectored to the false side of the second if.
79 ///
80 class JumpThreading : public FunctionPass {
81 const DataLayout *DL;
82 TargetLibraryInfo *TLI;
83 LazyValueInfo *LVI;
84#ifdef NDEBUG
85 SmallPtrSet<BasicBlock*, 16> LoopHeaders;
86#else
87 SmallSet<AssertingVH<BasicBlock>, 16> LoopHeaders;
88#endif
89 DenseSet<std::pair<Value*, BasicBlock*> > RecursionSet;
90
91 unsigned BBDupThreshold;
92
93 // RAII helper for updating the recursion stack.
94 struct RecursionSetRemover {
95 DenseSet<std::pair<Value*, BasicBlock*> > &TheSet;
96 std::pair<Value*, BasicBlock*> ThePair;
97
98 RecursionSetRemover(DenseSet<std::pair<Value*, BasicBlock*> > &S,
99 std::pair<Value*, BasicBlock*> P)
100 : TheSet(S), ThePair(P) { }
101
102 ~RecursionSetRemover() {
103 TheSet.erase(ThePair);
104 }
105 };
106 public:
107 static char ID; // Pass identification
108 JumpThreading(int T = -1) : FunctionPass(ID) {
109 BBDupThreshold = (T == -1) ? BBDuplicateThreshold : unsigned(T);
110 initializeJumpThreadingPass(*PassRegistry::getPassRegistry());
111 }
112
113 bool runOnFunction(Function &F) override;
114
115 void getAnalysisUsage(AnalysisUsage &AU) const override {
116 AU.addRequired<LazyValueInfo>();
117 AU.addPreserved<LazyValueInfo>();
118 AU.addRequired<TargetLibraryInfo>();
119 }
120
121 void FindLoopHeaders(Function &F);
122 bool ProcessBlock(BasicBlock *BB);
123 bool ThreadEdge(BasicBlock *BB, const SmallVectorImpl<BasicBlock*> &PredBBs,
124 BasicBlock *SuccBB);
125 bool DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
126 const SmallVectorImpl<BasicBlock *> &PredBBs);
127
128 bool ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,
129 PredValueInfo &Result,
130 ConstantPreference Preference,
131 Instruction *CxtI = nullptr);
132 bool ProcessThreadableEdges(Value *Cond, BasicBlock *BB,
133 ConstantPreference Preference,
134 Instruction *CxtI = nullptr);
135
136 bool ProcessBranchOnPHI(PHINode *PN);
137 bool ProcessBranchOnXOR(BinaryOperator *BO);
138
139 bool SimplifyPartiallyRedundantLoad(LoadInst *LI);
140 bool TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB);
141 };
142}
143
144char JumpThreading::ID = 0;
145INITIALIZE_PASS_BEGIN(JumpThreading, "jump-threading",static void* initializeJumpThreadingPassOnce(PassRegistry &
Registry) {
146 "Jump Threading", false, false)static void* initializeJumpThreadingPassOnce(PassRegistry &
Registry) {
147INITIALIZE_PASS_DEPENDENCY(LazyValueInfo)initializeLazyValueInfoPass(Registry);
148INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)initializeTargetLibraryInfoPass(Registry);
149INITIALIZE_PASS_END(JumpThreading, "jump-threading",PassInfo *PI = new PassInfo("Jump Threading", "jump-threading"
, & JumpThreading ::ID, PassInfo::NormalCtor_t(callDefaultCtor
< JumpThreading >), false, false); Registry.registerPass
(*PI, true); return PI; } void llvm::initializeJumpThreadingPass
(PassRegistry &Registry) { static volatile sys::cas_flag initialized
= 0; sys::cas_flag old_val = sys::CompareAndSwap(&initialized
, 1, 0); if (old_val == 0) { initializeJumpThreadingPassOnce(
Registry); sys::MemoryFence(); AnnotateIgnoreWritesBegin("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 150); AnnotateHappensBefore("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 150, &initialized); initialized = 2; AnnotateIgnoreWritesEnd
("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 150); } else { sys::cas_flag tmp = initialized; sys::MemoryFence
(); while (tmp != 2) { tmp = initialized; sys::MemoryFence();
} } AnnotateHappensAfter("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 150, &initialized); }
150 "Jump Threading", false, false)PassInfo *PI = new PassInfo("Jump Threading", "jump-threading"
, & JumpThreading ::ID, PassInfo::NormalCtor_t(callDefaultCtor
< JumpThreading >), false, false); Registry.registerPass
(*PI, true); return PI; } void llvm::initializeJumpThreadingPass
(PassRegistry &Registry) { static volatile sys::cas_flag initialized
= 0; sys::cas_flag old_val = sys::CompareAndSwap(&initialized
, 1, 0); if (old_val == 0) { initializeJumpThreadingPassOnce(
Registry); sys::MemoryFence(); AnnotateIgnoreWritesBegin("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 150); AnnotateHappensBefore("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 150, &initialized); initialized = 2; AnnotateIgnoreWritesEnd
("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 150); } else { sys::cas_flag tmp = initialized; sys::MemoryFence
(); while (tmp != 2) { tmp = initialized; sys::MemoryFence();
} } AnnotateHappensAfter("/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 150, &initialized); }
151
152// Public interface to the Jump Threading pass
153FunctionPass *llvm::createJumpThreadingPass(int Threshold) { return new JumpThreading(Threshold); }
154
155/// runOnFunction - Top level algorithm.
156///
157bool JumpThreading::runOnFunction(Function &F) {
158 if (skipOptnoneFunction(F))
159 return false;
160
161 DEBUG(dbgs() << "Jump threading on function '" << F.getName() << "'\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "Jump threading on function '"
<< F.getName() << "'\n"; } } while (0);
162 DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
163 DL = DLP ? &DLP->getDataLayout() : nullptr;
164 TLI = &getAnalysis<TargetLibraryInfo>();
165 LVI = &getAnalysis<LazyValueInfo>();
166
167 // Remove unreachable blocks from function as they may result in infinite
168 // loop. We do threading if we found something profitable. Jump threading a
169 // branch can create other opportunities. If these opportunities form a cycle
170 // i.e. if any jump treading is undoing previous threading in the path, then
171 // we will loop forever. We take care of this issue by not jump threading for
172 // back edges. This works for normal cases but not for unreachable blocks as
173 // they may have cycle with no back edge.
174 removeUnreachableBlocks(F);
175
176 FindLoopHeaders(F);
177
178 bool Changed, EverChanged = false;
179 do {
180 Changed = false;
181 for (Function::iterator I = F.begin(), E = F.end(); I != E;) {
182 BasicBlock *BB = I;
183 // Thread all of the branches we can over this block.
184 while (ProcessBlock(BB))
185 Changed = true;
186
187 ++I;
188
189 // If the block is trivially dead, zap it. This eliminates the successor
190 // edges which simplifies the CFG.
191 if (pred_begin(BB) == pred_end(BB) &&
192 BB != &BB->getParent()->getEntryBlock()) {
193 DEBUG(dbgs() << " JT: Deleting dead block '" << BB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " JT: Deleting dead block '"
<< BB->getName() << "' with terminator: " <<
*BB->getTerminator() << '\n'; } } while (0)
194 << "' with terminator: " << *BB->getTerminator() << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " JT: Deleting dead block '"
<< BB->getName() << "' with terminator: " <<
*BB->getTerminator() << '\n'; } } while (0);
195 LoopHeaders.erase(BB);
196 LVI->eraseBlock(BB);
197 DeleteDeadBlock(BB);
198 Changed = true;
199 continue;
200 }
201
202 BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
203
204 // Can't thread an unconditional jump, but if the block is "almost
205 // empty", we can replace uses of it with uses of the successor and make
206 // this dead.
207 if (BI && BI->isUnconditional() &&
208 BB != &BB->getParent()->getEntryBlock() &&
209 // If the terminator is the only non-phi instruction, try to nuke it.
210 BB->getFirstNonPHIOrDbg()->isTerminator()) {
211 // Since TryToSimplifyUncondBranchFromEmptyBlock may delete the
212 // block, we have to make sure it isn't in the LoopHeaders set. We
213 // reinsert afterward if needed.
214 bool ErasedFromLoopHeaders = LoopHeaders.erase(BB);
215 BasicBlock *Succ = BI->getSuccessor(0);
216
217 // FIXME: It is always conservatively correct to drop the info
218 // for a block even if it doesn't get erased. This isn't totally
219 // awesome, but it allows us to use AssertingVH to prevent nasty
220 // dangling pointer issues within LazyValueInfo.
221 LVI->eraseBlock(BB);
222 if (TryToSimplifyUncondBranchFromEmptyBlock(BB)) {
223 Changed = true;
224 // If we deleted BB and BB was the header of a loop, then the
225 // successor is now the header of the loop.
226 BB = Succ;
227 }
228
229 if (ErasedFromLoopHeaders)
230 LoopHeaders.insert(BB);
231 }
232 }
233 EverChanged |= Changed;
234 } while (Changed);
235
236 LoopHeaders.clear();
237 return EverChanged;
238}
239
240/// getJumpThreadDuplicationCost - Return the cost of duplicating this block to
241/// thread across it. Stop scanning the block when passing the threshold.
242static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB,
243 unsigned Threshold) {
244 /// Ignore PHI nodes, these will be flattened when duplication happens.
245 BasicBlock::const_iterator I = BB->getFirstNonPHI();
246
247 // FIXME: THREADING will delete values that are just used to compute the
248 // branch, so they shouldn't count against the duplication cost.
249
250 // Sum up the cost of each instruction until we get to the terminator. Don't
251 // include the terminator because the copy won't include it.
252 unsigned Size = 0;
253 for (; !isa<TerminatorInst>(I); ++I) {
254
255 // Stop scanning the block if we've reached the threshold.
256 if (Size > Threshold)
257 return Size;
258
259 // Debugger intrinsics don't incur code size.
260 if (isa<DbgInfoIntrinsic>(I)) continue;
261
262 // If this is a pointer->pointer bitcast, it is free.
263 if (isa<BitCastInst>(I) && I->getType()->isPointerTy())
264 continue;
265
266 // All other instructions count for at least one unit.
267 ++Size;
268
269 // Calls are more expensive. If they are non-intrinsic calls, we model them
270 // as having cost of 4. If they are a non-vector intrinsic, we model them
271 // as having cost of 2 total, and if they are a vector intrinsic, we model
272 // them as having cost 1.
273 if (const CallInst *CI = dyn_cast<CallInst>(I)) {
274 if (CI->cannotDuplicate())
275 // Blocks with NoDuplicate are modelled as having infinite cost, so they
276 // are never duplicated.
277 return ~0U;
278 else if (!isa<IntrinsicInst>(CI))
279 Size += 3;
280 else if (!CI->getType()->isVectorTy())
281 Size += 1;
282 }
283 }
284
285 // Threading through a switch statement is particularly profitable. If this
286 // block ends in a switch, decrease its cost to make it more likely to happen.
287 if (isa<SwitchInst>(I))
288 Size = Size > 6 ? Size-6 : 0;
289
290 // The same holds for indirect branches, but slightly more so.
291 if (isa<IndirectBrInst>(I))
292 Size = Size > 8 ? Size-8 : 0;
293
294 return Size;
295}
296
297/// FindLoopHeaders - We do not want jump threading to turn proper loop
298/// structures into irreducible loops. Doing this breaks up the loop nesting
299/// hierarchy and pessimizes later transformations. To prevent this from
300/// happening, we first have to find the loop headers. Here we approximate this
301/// by finding targets of backedges in the CFG.
302///
303/// Note that there definitely are cases when we want to allow threading of
304/// edges across a loop header. For example, threading a jump from outside the
305/// loop (the preheader) to an exit block of the loop is definitely profitable.
306/// It is also almost always profitable to thread backedges from within the loop
307/// to exit blocks, and is often profitable to thread backedges to other blocks
308/// within the loop (forming a nested loop). This simple analysis is not rich
309/// enough to track all of these properties and keep it up-to-date as the CFG
310/// mutates, so we don't allow any of these transformations.
311///
312void JumpThreading::FindLoopHeaders(Function &F) {
313 SmallVector<std::pair<const BasicBlock*,const BasicBlock*>, 32> Edges;
314 FindFunctionBackedges(F, Edges);
315
316 for (unsigned i = 0, e = Edges.size(); i != e; ++i)
317 LoopHeaders.insert(const_cast<BasicBlock*>(Edges[i].second));
318}
319
320/// getKnownConstant - Helper method to determine if we can thread over a
321/// terminator with the given value as its condition, and if so what value to
322/// use for that. What kind of value this is depends on whether we want an
323/// integer or a block address, but an undef is always accepted.
324/// Returns null if Val is null or not an appropriate constant.
325static Constant *getKnownConstant(Value *Val, ConstantPreference Preference) {
326 if (!Val)
327 return nullptr;
328
329 // Undef is "known" enough.
330 if (UndefValue *U = dyn_cast<UndefValue>(Val))
331 return U;
332
333 if (Preference == WantBlockAddress)
334 return dyn_cast<BlockAddress>(Val->stripPointerCasts());
335
336 return dyn_cast<ConstantInt>(Val);
337}
338
339/// ComputeValueKnownInPredecessors - Given a basic block BB and a value V, see
340/// if we can infer that the value is a known ConstantInt/BlockAddress or undef
341/// in any of our predecessors. If so, return the known list of value and pred
342/// BB in the result vector.
343///
344/// This returns true if there were any known values.
345///
346bool JumpThreading::
347ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB, PredValueInfo &Result,
348 ConstantPreference Preference,
349 Instruction *CxtI) {
350 // This method walks up use-def chains recursively. Because of this, we could
351 // get into an infinite loop going around loops in the use-def chain. To
352 // prevent this, keep track of what (value, block) pairs we've already visited
353 // and terminate the search if we loop back to them
354 if (!RecursionSet.insert(std::make_pair(V, BB)).second)
355 return false;
356
357 // An RAII help to remove this pair from the recursion set once the recursion
358 // stack pops back out again.
359 RecursionSetRemover remover(RecursionSet, std::make_pair(V, BB));
360
361 // If V is a constant, then it is known in all predecessors.
362 if (Constant *KC = getKnownConstant(V, Preference)) {
363 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
364 Result.push_back(std::make_pair(KC, *PI));
365
366 return true;
367 }
368
369 // If V is a non-instruction value, or an instruction in a different block,
370 // then it can't be derived from a PHI.
371 Instruction *I = dyn_cast<Instruction>(V);
372 if (!I || I->getParent() != BB) {
373
374 // Okay, if this is a live-in value, see if it has a known value at the end
375 // of any of our predecessors.
376 //
377 // FIXME: This should be an edge property, not a block end property.
378 /// TODO: Per PR2563, we could infer value range information about a
379 /// predecessor based on its terminator.
380 //
381 // FIXME: change this to use the more-rich 'getPredicateOnEdge' method if
382 // "I" is a non-local compare-with-a-constant instruction. This would be
383 // able to handle value inequalities better, for example if the compare is
384 // "X < 4" and "X < 3" is known true but "X < 4" itself is not available.
385 // Perhaps getConstantOnEdge should be smart enough to do this?
386
387 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
388 BasicBlock *P = *PI;
389 // If the value is known by LazyValueInfo to be a constant in a
390 // predecessor, use that information to try to thread this block.
391 Constant *PredCst = LVI->getConstantOnEdge(V, P, BB, CxtI);
392 if (Constant *KC = getKnownConstant(PredCst, Preference))
393 Result.push_back(std::make_pair(KC, P));
394 }
395
396 return !Result.empty();
397 }
398
399 /// If I is a PHI node, then we know the incoming values for any constants.
400 if (PHINode *PN = dyn_cast<PHINode>(I)) {
401 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
402 Value *InVal = PN->getIncomingValue(i);
403 if (Constant *KC = getKnownConstant(InVal, Preference)) {
404 Result.push_back(std::make_pair(KC, PN->getIncomingBlock(i)));
405 } else {
406 Constant *CI = LVI->getConstantOnEdge(InVal,
407 PN->getIncomingBlock(i),
408 BB, CxtI);
409 if (Constant *KC = getKnownConstant(CI, Preference))
410 Result.push_back(std::make_pair(KC, PN->getIncomingBlock(i)));
411 }
412 }
413
414 return !Result.empty();
415 }
416
417 PredValueInfoTy LHSVals, RHSVals;
418
419 // Handle some boolean conditions.
420 if (I->getType()->getPrimitiveSizeInBits() == 1) {
421 assert(Preference == WantInteger && "One-bit non-integer type?")((Preference == WantInteger && "One-bit non-integer type?"
) ? static_cast<void> (0) : __assert_fail ("Preference == WantInteger && \"One-bit non-integer type?\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 421, __PRETTY_FUNCTION__));
422 // X | true -> true
423 // X & false -> false
424 if (I->getOpcode() == Instruction::Or ||
425 I->getOpcode() == Instruction::And) {
426 ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals,
427 WantInteger, CxtI);
428 ComputeValueKnownInPredecessors(I->getOperand(1), BB, RHSVals,
429 WantInteger, CxtI);
430
431 if (LHSVals.empty() && RHSVals.empty())
432 return false;
433
434 ConstantInt *InterestingVal;
435 if (I->getOpcode() == Instruction::Or)
436 InterestingVal = ConstantInt::getTrue(I->getContext());
437 else
438 InterestingVal = ConstantInt::getFalse(I->getContext());
439
440 SmallPtrSet<BasicBlock*, 4> LHSKnownBBs;
441
442 // Scan for the sentinel. If we find an undef, force it to the
443 // interesting value: x|undef -> true and x&undef -> false.
444 for (unsigned i = 0, e = LHSVals.size(); i != e; ++i)
445 if (LHSVals[i].first == InterestingVal ||
446 isa<UndefValue>(LHSVals[i].first)) {
447 Result.push_back(LHSVals[i]);
448 Result.back().first = InterestingVal;
449 LHSKnownBBs.insert(LHSVals[i].second);
450 }
451 for (unsigned i = 0, e = RHSVals.size(); i != e; ++i)
452 if (RHSVals[i].first == InterestingVal ||
453 isa<UndefValue>(RHSVals[i].first)) {
454 // If we already inferred a value for this block on the LHS, don't
455 // re-add it.
456 if (!LHSKnownBBs.count(RHSVals[i].second)) {
457 Result.push_back(RHSVals[i]);
458 Result.back().first = InterestingVal;
459 }
460 }
461
462 return !Result.empty();
463 }
464
465 // Handle the NOT form of XOR.
466 if (I->getOpcode() == Instruction::Xor &&
467 isa<ConstantInt>(I->getOperand(1)) &&
468 cast<ConstantInt>(I->getOperand(1))->isOne()) {
469 ComputeValueKnownInPredecessors(I->getOperand(0), BB, Result,
470 WantInteger, CxtI);
471 if (Result.empty())
472 return false;
473
474 // Invert the known values.
475 for (unsigned i = 0, e = Result.size(); i != e; ++i)
476 Result[i].first = ConstantExpr::getNot(Result[i].first);
477
478 return true;
479 }
480
481 // Try to simplify some other binary operator values.
482 } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(I)) {
483 assert(Preference != WantBlockAddress((Preference != WantBlockAddress && "A binary operator creating a block address?"
) ? static_cast<void> (0) : __assert_fail ("Preference != WantBlockAddress && \"A binary operator creating a block address?\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 484, __PRETTY_FUNCTION__))
484 && "A binary operator creating a block address?")((Preference != WantBlockAddress && "A binary operator creating a block address?"
) ? static_cast<void> (0) : __assert_fail ("Preference != WantBlockAddress && \"A binary operator creating a block address?\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 484, __PRETTY_FUNCTION__));
485 if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->getOperand(1))) {
486 PredValueInfoTy LHSVals;
487 ComputeValueKnownInPredecessors(BO->getOperand(0), BB, LHSVals,
488 WantInteger, CxtI);
489
490 // Try to use constant folding to simplify the binary operator.
491 for (unsigned i = 0, e = LHSVals.size(); i != e; ++i) {
492 Constant *V = LHSVals[i].first;
493 Constant *Folded = ConstantExpr::get(BO->getOpcode(), V, CI);
494
495 if (Constant *KC = getKnownConstant(Folded, WantInteger))
496 Result.push_back(std::make_pair(KC, LHSVals[i].second));
497 }
498 }
499
500 return !Result.empty();
501 }
502
503 // Handle compare with phi operand, where the PHI is defined in this block.
504 if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
505 assert(Preference == WantInteger && "Compares only produce integers")((Preference == WantInteger && "Compares only produce integers"
) ? static_cast<void> (0) : __assert_fail ("Preference == WantInteger && \"Compares only produce integers\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 505, __PRETTY_FUNCTION__));
506 PHINode *PN = dyn_cast<PHINode>(Cmp->getOperand(0));
507 if (PN && PN->getParent() == BB) {
508 // We can do this simplification if any comparisons fold to true or false.
509 // See if any do.
510 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
511 BasicBlock *PredBB = PN->getIncomingBlock(i);
512 Value *LHS = PN->getIncomingValue(i);
513 Value *RHS = Cmp->getOperand(1)->DoPHITranslation(BB, PredBB);
514
515 Value *Res = SimplifyCmpInst(Cmp->getPredicate(), LHS, RHS, DL);
516 if (!Res) {
517 if (!isa<Constant>(RHS))
518 continue;
519
520 LazyValueInfo::Tristate
521 ResT = LVI->getPredicateOnEdge(Cmp->getPredicate(), LHS,
522 cast<Constant>(RHS), PredBB, BB,
523 CxtI ? CxtI : Cmp);
524 if (ResT == LazyValueInfo::Unknown)
525 continue;
526 Res = ConstantInt::get(Type::getInt1Ty(LHS->getContext()), ResT);
527 }
528
529 if (Constant *KC = getKnownConstant(Res, WantInteger))
530 Result.push_back(std::make_pair(KC, PredBB));
531 }
532
533 return !Result.empty();
534 }
535
536 // If comparing a live-in value against a constant, see if we know the
537 // live-in value on any predecessors.
538 if (isa<Constant>(Cmp->getOperand(1)) && Cmp->getType()->isIntegerTy()) {
539 if (!isa<Instruction>(Cmp->getOperand(0)) ||
540 cast<Instruction>(Cmp->getOperand(0))->getParent() != BB) {
541 Constant *RHSCst = cast<Constant>(Cmp->getOperand(1));
542
543 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB);PI != E; ++PI){
544 BasicBlock *P = *PI;
545 // If the value is known by LazyValueInfo to be a constant in a
546 // predecessor, use that information to try to thread this block.
547 LazyValueInfo::Tristate Res =
548 LVI->getPredicateOnEdge(Cmp->getPredicate(), Cmp->getOperand(0),
549 RHSCst, P, BB, CxtI ? CxtI : Cmp);
550 if (Res == LazyValueInfo::Unknown)
551 continue;
552
553 Constant *ResC = ConstantInt::get(Cmp->getType(), Res);
554 Result.push_back(std::make_pair(ResC, P));
555 }
556
557 return !Result.empty();
558 }
559
560 // Try to find a constant value for the LHS of a comparison,
561 // and evaluate it statically if we can.
562 if (Constant *CmpConst = dyn_cast<Constant>(Cmp->getOperand(1))) {
563 PredValueInfoTy LHSVals;
564 ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals,
565 WantInteger, CxtI);
566
567 for (unsigned i = 0, e = LHSVals.size(); i != e; ++i) {
568 Constant *V = LHSVals[i].first;
569 Constant *Folded = ConstantExpr::getCompare(Cmp->getPredicate(),
570 V, CmpConst);
571 if (Constant *KC = getKnownConstant(Folded, WantInteger))
572 Result.push_back(std::make_pair(KC, LHSVals[i].second));
573 }
574
575 return !Result.empty();
576 }
577 }
578 }
579
580 if (SelectInst *SI = dyn_cast<SelectInst>(I)) {
581 // Handle select instructions where at least one operand is a known constant
582 // and we can figure out the condition value for any predecessor block.
583 Constant *TrueVal = getKnownConstant(SI->getTrueValue(), Preference);
584 Constant *FalseVal = getKnownConstant(SI->getFalseValue(), Preference);
585 PredValueInfoTy Conds;
586 if ((TrueVal || FalseVal) &&
587 ComputeValueKnownInPredecessors(SI->getCondition(), BB, Conds,
588 WantInteger, CxtI)) {
589 for (unsigned i = 0, e = Conds.size(); i != e; ++i) {
590 Constant *Cond = Conds[i].first;
591
592 // Figure out what value to use for the condition.
593 bool KnownCond;
594 if (ConstantInt *CI = dyn_cast<ConstantInt>(Cond)) {
595 // A known boolean.
596 KnownCond = CI->isOne();
597 } else {
598 assert(isa<UndefValue>(Cond) && "Unexpected condition value")((isa<UndefValue>(Cond) && "Unexpected condition value"
) ? static_cast<void> (0) : __assert_fail ("isa<UndefValue>(Cond) && \"Unexpected condition value\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 598, __PRETTY_FUNCTION__));
599 // Either operand will do, so be sure to pick the one that's a known
600 // constant.
601 // FIXME: Do this more cleverly if both values are known constants?
602 KnownCond = (TrueVal != nullptr);
603 }
604
605 // See if the select has a known constant value for this predecessor.
606 if (Constant *Val = KnownCond ? TrueVal : FalseVal)
607 Result.push_back(std::make_pair(Val, Conds[i].second));
608 }
609
610 return !Result.empty();
611 }
612 }
613
614 // If all else fails, see if LVI can figure out a constant value for us.
615 Constant *CI = LVI->getConstant(V, BB, CxtI);
616 if (Constant *KC = getKnownConstant(CI, Preference)) {
617 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
618 Result.push_back(std::make_pair(KC, *PI));
619 }
620
621 return !Result.empty();
622}
623
624
625
626/// GetBestDestForBranchOnUndef - If we determine that the specified block ends
627/// in an undefined jump, decide which block is best to revector to.
628///
629/// Since we can pick an arbitrary destination, we pick the successor with the
630/// fewest predecessors. This should reduce the in-degree of the others.
631///
632static unsigned GetBestDestForJumpOnUndef(BasicBlock *BB) {
633 TerminatorInst *BBTerm = BB->getTerminator();
634 unsigned MinSucc = 0;
635 BasicBlock *TestBB = BBTerm->getSuccessor(MinSucc);
636 // Compute the successor with the minimum number of predecessors.
637 unsigned MinNumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB));
638 for (unsigned i = 1, e = BBTerm->getNumSuccessors(); i != e; ++i) {
639 TestBB = BBTerm->getSuccessor(i);
640 unsigned NumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB));
641 if (NumPreds < MinNumPreds) {
642 MinSucc = i;
643 MinNumPreds = NumPreds;
644 }
645 }
646
647 return MinSucc;
648}
649
650static bool hasAddressTakenAndUsed(BasicBlock *BB) {
651 if (!BB->hasAddressTaken()) return false;
652
653 // If the block has its address taken, it may be a tree of dead constants
654 // hanging off of it. These shouldn't keep the block alive.
655 BlockAddress *BA = BlockAddress::get(BB);
656 BA->removeDeadConstantUsers();
657 return !BA->use_empty();
658}
659
660/// ProcessBlock - If there are any predecessors whose control can be threaded
661/// through to a successor, transform them now.
662bool JumpThreading::ProcessBlock(BasicBlock *BB) {
663 // If the block is trivially dead, just return and let the caller nuke it.
664 // This simplifies other transformations.
665 if (pred_begin(BB) == pred_end(BB) &&
666 BB != &BB->getParent()->getEntryBlock())
667 return false;
668
669 // If this block has a single predecessor, and if that pred has a single
670 // successor, merge the blocks. This encourages recursive jump threading
671 // because now the condition in this block can be threaded through
672 // predecessors of our predecessor block.
673 if (BasicBlock *SinglePred = BB->getSinglePredecessor()) {
674 if (SinglePred->getTerminator()->getNumSuccessors() == 1 &&
675 SinglePred != BB && !hasAddressTakenAndUsed(BB)) {
676 // If SinglePred was a loop header, BB becomes one.
677 if (LoopHeaders.erase(SinglePred))
678 LoopHeaders.insert(BB);
679
680 LVI->eraseBlock(SinglePred);
681 MergeBasicBlockIntoOnlyPred(BB);
682
683 return true;
684 }
685 }
686
687 // What kind of constant we're looking for.
688 ConstantPreference Preference = WantInteger;
689
690 // Look to see if the terminator is a conditional branch, switch or indirect
691 // branch, if not we can't thread it.
692 Value *Condition;
693 Instruction *Terminator = BB->getTerminator();
694 if (BranchInst *BI = dyn_cast<BranchInst>(Terminator)) {
695 // Can't thread an unconditional jump.
696 if (BI->isUnconditional()) return false;
697 Condition = BI->getCondition();
698 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(Terminator)) {
699 Condition = SI->getCondition();
700 } else if (IndirectBrInst *IB = dyn_cast<IndirectBrInst>(Terminator)) {
701 // Can't thread indirect branch with no successors.
702 if (IB->getNumSuccessors() == 0) return false;
703 Condition = IB->getAddress()->stripPointerCasts();
704 Preference = WantBlockAddress;
705 } else {
706 return false; // Must be an invoke.
707 }
708
709 // Run constant folding to see if we can reduce the condition to a simple
710 // constant.
711 if (Instruction *I = dyn_cast<Instruction>(Condition)) {
712 Value *SimpleVal = ConstantFoldInstruction(I, DL, TLI);
713 if (SimpleVal) {
714 I->replaceAllUsesWith(SimpleVal);
715 I->eraseFromParent();
716 Condition = SimpleVal;
717 }
718 }
719
720 // If the terminator is branching on an undef, we can pick any of the
721 // successors to branch to. Let GetBestDestForJumpOnUndef decide.
722 if (isa<UndefValue>(Condition)) {
723 unsigned BestSucc = GetBestDestForJumpOnUndef(BB);
724
725 // Fold the branch/switch.
726 TerminatorInst *BBTerm = BB->getTerminator();
727 for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i) {
728 if (i == BestSucc) continue;
729 BBTerm->getSuccessor(i)->removePredecessor(BB, true);
730 }
731
732 DEBUG(dbgs() << " In block '" << BB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " In block '" <<
BB->getName() << "' folding undef terminator: " <<
*BBTerm << '\n'; } } while (0)
733 << "' folding undef terminator: " << *BBTerm << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " In block '" <<
BB->getName() << "' folding undef terminator: " <<
*BBTerm << '\n'; } } while (0);
734 BranchInst::Create(BBTerm->getSuccessor(BestSucc), BBTerm);
735 BBTerm->eraseFromParent();
736 return true;
737 }
738
739 // If the terminator of this block is branching on a constant, simplify the
740 // terminator to an unconditional branch. This can occur due to threading in
741 // other blocks.
742 if (getKnownConstant(Condition, Preference)) {
743 DEBUG(dbgs() << " In block '" << BB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " In block '" <<
BB->getName() << "' folding terminator: " << *
BB->getTerminator() << '\n'; } } while (0)
744 << "' folding terminator: " << *BB->getTerminator() << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " In block '" <<
BB->getName() << "' folding terminator: " << *
BB->getTerminator() << '\n'; } } while (0);
745 ++NumFolds;
746 ConstantFoldTerminator(BB, true);
747 return true;
748 }
749
750 Instruction *CondInst = dyn_cast<Instruction>(Condition);
751
752 // All the rest of our checks depend on the condition being an instruction.
753 if (!CondInst) {
754 // FIXME: Unify this with code below.
755 if (ProcessThreadableEdges(Condition, BB, Preference, Terminator))
756 return true;
757 return false;
758 }
759
760
761 if (CmpInst *CondCmp = dyn_cast<CmpInst>(CondInst)) {
762 // For a comparison where the LHS is outside this block, it's possible
763 // that we've branched on it before. Used LVI to see if we can simplify
764 // the branch based on that.
765 BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
766 Constant *CondConst = dyn_cast<Constant>(CondCmp->getOperand(1));
767 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
768 if (CondBr && CondConst && CondBr->isConditional() && PI != PE &&
769 (!isa<Instruction>(CondCmp->getOperand(0)) ||
770 cast<Instruction>(CondCmp->getOperand(0))->getParent() != BB)) {
771 // For predecessor edge, determine if the comparison is true or false
772 // on that edge. If they're all true or all false, we can simplify the
773 // branch.
774 // FIXME: We could handle mixed true/false by duplicating code.
775 LazyValueInfo::Tristate Baseline =
776 LVI->getPredicateOnEdge(CondCmp->getPredicate(), CondCmp->getOperand(0),
777 CondConst, *PI, BB, CondCmp);
778 if (Baseline != LazyValueInfo::Unknown) {
779 // Check that all remaining incoming values match the first one.
780 while (++PI != PE) {
781 LazyValueInfo::Tristate Ret =
782 LVI->getPredicateOnEdge(CondCmp->getPredicate(),
783 CondCmp->getOperand(0), CondConst, *PI, BB,
784 CondCmp);
785 if (Ret != Baseline) break;
786 }
787
788 // If we terminated early, then one of the values didn't match.
789 if (PI == PE) {
790 unsigned ToRemove = Baseline == LazyValueInfo::True ? 1 : 0;
791 unsigned ToKeep = Baseline == LazyValueInfo::True ? 0 : 1;
792 CondBr->getSuccessor(ToRemove)->removePredecessor(BB, true);
793 BranchInst::Create(CondBr->getSuccessor(ToKeep), CondBr);
794 CondBr->eraseFromParent();
795 return true;
796 }
797 }
798
799 } else if (CondBr && CondConst && CondBr->isConditional()) {
800 // There might be an invairant in the same block with the conditional
801 // that can determine the predicate.
802
803 LazyValueInfo::Tristate Ret =
804 LVI->getPredicateAt(CondCmp->getPredicate(), CondCmp->getOperand(0),
805 CondConst, CondCmp);
806 if (Ret != LazyValueInfo::Unknown) {
807 unsigned ToRemove = Ret == LazyValueInfo::True ? 1 : 0;
808 unsigned ToKeep = Ret == LazyValueInfo::True ? 0 : 1;
809 CondBr->getSuccessor(ToRemove)->removePredecessor(BB, true);
810 BranchInst::Create(CondBr->getSuccessor(ToKeep), CondBr);
811 CondBr->eraseFromParent();
812 return true;
813 }
814 }
815
816 if (CondBr && CondConst && TryToUnfoldSelect(CondCmp, BB))
817 return true;
818 }
819
820 // Check for some cases that are worth simplifying. Right now we want to look
821 // for loads that are used by a switch or by the condition for the branch. If
822 // we see one, check to see if it's partially redundant. If so, insert a PHI
823 // which can then be used to thread the values.
824 //
825 Value *SimplifyValue = CondInst;
826 if (CmpInst *CondCmp = dyn_cast<CmpInst>(SimplifyValue))
827 if (isa<Constant>(CondCmp->getOperand(1)))
828 SimplifyValue = CondCmp->getOperand(0);
829
830 // TODO: There are other places where load PRE would be profitable, such as
831 // more complex comparisons.
832 if (LoadInst *LI = dyn_cast<LoadInst>(SimplifyValue))
833 if (SimplifyPartiallyRedundantLoad(LI))
834 return true;
835
836
837 // Handle a variety of cases where we are branching on something derived from
838 // a PHI node in the current block. If we can prove that any predecessors
839 // compute a predictable value based on a PHI node, thread those predecessors.
840 //
841 if (ProcessThreadableEdges(CondInst, BB, Preference, Terminator))
842 return true;
843
844 // If this is an otherwise-unfoldable branch on a phi node in the current
845 // block, see if we can simplify.
846 if (PHINode *PN = dyn_cast<PHINode>(CondInst))
847 if (PN->getParent() == BB && isa<BranchInst>(BB->getTerminator()))
848 return ProcessBranchOnPHI(PN);
849
850
851 // If this is an otherwise-unfoldable branch on a XOR, see if we can simplify.
852 if (CondInst->getOpcode() == Instruction::Xor &&
853 CondInst->getParent() == BB && isa<BranchInst>(BB->getTerminator()))
854 return ProcessBranchOnXOR(cast<BinaryOperator>(CondInst));
855
856
857 // TODO: If we have: "br (X > 0)" and we have a predecessor where we know
858 // "(X == 4)", thread through this block.
859
860 return false;
861}
862
863/// SimplifyPartiallyRedundantLoad - If LI is an obviously partially redundant
864/// load instruction, eliminate it by replacing it with a PHI node. This is an
865/// important optimization that encourages jump threading, and needs to be run
866/// interlaced with other jump threading tasks.
867bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
868 // Don't hack volatile/atomic loads.
869 if (!LI->isSimple()) return false;
1
Taking false branch
→
870
871 // If the load is defined in a block with exactly one predecessor, it can't be
872 // partially redundant.
873 BasicBlock *LoadBB = LI->getParent();
874 if (LoadBB->getSinglePredecessor())
2
←
Taking false branch
→
875 return false;
876
877 // If the load is defined in a landing pad, it can't be partially redundant,
878 // because the edges between the invoke and the landing pad cannot have other
879 // instructions between them.
880 if (LoadBB->isLandingPad())
3
←
Taking false branch
→
881 return false;
882
883 Value *LoadedPtr = LI->getOperand(0);
884
885 // If the loaded operand is defined in the LoadBB, it can't be available.
886 // TODO: Could do simple PHI translation, that would be fun :)
887 if (Instruction *PtrOp = dyn_cast<Instruction>(LoadedPtr))
4
←
Taking false branch
→
888 if (PtrOp->getParent() == LoadBB)
889 return false;
890
891 // Scan a few instructions up from the load, to see if it is obviously live at
892 // the entry to its block.
893 BasicBlock::iterator BBIt = LI;
894
895 if (Value *AvailableVal =
5
←
Assuming 'AvailableVal' is null
→
6
←
Taking false branch
→
896 FindAvailableLoadedValue(LoadedPtr, LoadBB, BBIt, 6)) {
897 // If the value if the load is locally available within the block, just use
898 // it. This frequently occurs for reg2mem'd allocas.
899 //cerr << "LOAD ELIMINATED:\n" << *BBIt << *LI << "\n";
900
901 // If the returned value is the load itself, replace with an undef. This can
902 // only happen in dead loops.
903 if (AvailableVal == LI) AvailableVal = UndefValue::get(LI->getType());
904 LI->replaceAllUsesWith(AvailableVal);
905 LI->eraseFromParent();
906 return true;
907 }
908
909 // Otherwise, if we scanned the whole block and got to the top of the block,
910 // we know the block is locally transparent to the load. If not, something
911 // might clobber its value.
912 if (BBIt != LoadBB->begin())
7
←
Taking false branch
→
913 return false;
914
915 // If all of the loads and stores that feed the value have the same AA tags,
916 // then we can propagate them onto any newly inserted loads.
917 AAMDNodes AATags;
918 LI->getAAMetadata(AATags);
919
920 SmallPtrSet<BasicBlock*, 8> PredsScanned;
921 typedef SmallVector<std::pair<BasicBlock*, Value*>, 8> AvailablePredsTy;
922 AvailablePredsTy AvailablePreds;
923 BasicBlock *OneUnavailablePred = nullptr;
8
←
'OneUnavailablePred' initialized to a null pointer value
→
924
925 // If we got here, the loaded value is transparent through to the start of the
926 // block. Check to see if it is available in any of the predecessor blocks.
927 for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB);
9
←
Loop condition is false. Execution continues on line 955
→
928 PI != PE; ++PI) {
929 BasicBlock *PredBB = *PI;
930
931 // If we already scanned this predecessor, skip it.
932 if (!PredsScanned.insert(PredBB))
933 continue;
934
935 // Scan the predecessor to see if the value is available in the pred.
936 BBIt = PredBB->end();
937 AAMDNodes ThisAATags;
938 Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6,
939 nullptr, &ThisAATags);
940 if (!PredAvailable) {
941 OneUnavailablePred = PredBB;
942 continue;
943 }
944
945 // If AA tags disagree or are not present, forget about them.
946 if (AATags != ThisAATags) AATags = AAMDNodes();
947
948 // If so, this load is partially redundant. Remember this info so that we
949 // can create a PHI node.
950 AvailablePreds.push_back(std::make_pair(PredBB, PredAvailable));
951 }
952
953 // If the loaded value isn't available in any predecessor, it isn't partially
954 // redundant.
955 if (AvailablePreds.empty()) return false;
10
←
Taking false branch
→
956
957 // Okay, the loaded value is available in at least one (and maybe all!)
958 // predecessors. If the value is unavailable in more than one unique
959 // predecessor, we want to insert a merge block for those common predecessors.
960 // This ensures that we only have to insert one reload, thus not increasing
961 // code size.
962 BasicBlock *UnavailablePred = nullptr;
963
964 // If there is exactly one predecessor where the value is unavailable, the
965 // already computed 'OneUnavailablePred' block is it. If it ends in an
966 // unconditional branch, we know that it isn't a critical edge.
967 if (PredsScanned.size() == AvailablePreds.size()+1 &&
968 OneUnavailablePred->getTerminator()->getNumSuccessors() == 1) {
11
←
Called C++ object pointer is null
969 UnavailablePred = OneUnavailablePred;
970 } else if (PredsScanned.size() != AvailablePreds.size()) {
971 // Otherwise, we had multiple unavailable predecessors or we had a critical
972 // edge from the one.
973 SmallVector<BasicBlock*, 8> PredsToSplit;
974 SmallPtrSet<BasicBlock*, 8> AvailablePredSet;
975
976 for (unsigned i = 0, e = AvailablePreds.size(); i != e; ++i)
977 AvailablePredSet.insert(AvailablePreds[i].first);
978
979 // Add all the unavailable predecessors to the PredsToSplit list.
980 for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB);
981 PI != PE; ++PI) {
982 BasicBlock *P = *PI;
983 // If the predecessor is an indirect goto, we can't split the edge.
984 if (isa<IndirectBrInst>(P->getTerminator()))
985 return false;
986
987 if (!AvailablePredSet.count(P))
988 PredsToSplit.push_back(P);
989 }
990
991 // Split them out to their own block.
992 UnavailablePred =
993 SplitBlockPredecessors(LoadBB, PredsToSplit, "thread-pre-split", this);
994 }
995
996 // If the value isn't available in all predecessors, then there will be
997 // exactly one where it isn't available. Insert a load on that edge and add
998 // it to the AvailablePreds list.
999 if (UnavailablePred) {
1000 assert(UnavailablePred->getTerminator()->getNumSuccessors() == 1 &&((UnavailablePred->getTerminator()->getNumSuccessors() ==
1 && "Can't handle critical edge here!") ? static_cast
<void> (0) : __assert_fail ("UnavailablePred->getTerminator()->getNumSuccessors() == 1 && \"Can't handle critical edge here!\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 1001, __PRETTY_FUNCTION__))
1001 "Can't handle critical edge here!")((UnavailablePred->getTerminator()->getNumSuccessors() ==
1 && "Can't handle critical edge here!") ? static_cast
<void> (0) : __assert_fail ("UnavailablePred->getTerminator()->getNumSuccessors() == 1 && \"Can't handle critical edge here!\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 1001, __PRETTY_FUNCTION__));
1002 LoadInst *NewVal = new LoadInst(LoadedPtr, LI->getName()+".pr", false,
1003 LI->getAlignment(),
1004 UnavailablePred->getTerminator());
1005 NewVal->setDebugLoc(LI->getDebugLoc());
1006 if (AATags)
1007 NewVal->setAAMetadata(AATags);
1008
1009 AvailablePreds.push_back(std::make_pair(UnavailablePred, NewVal));
1010 }
1011
1012 // Now we know that each predecessor of this block has a value in
1013 // AvailablePreds, sort them for efficient access as we're walking the preds.
1014 array_pod_sort(AvailablePreds.begin(), AvailablePreds.end());
1015
1016 // Create a PHI node at the start of the block for the PRE'd load value.
1017 pred_iterator PB = pred_begin(LoadBB), PE = pred_end(LoadBB);
1018 PHINode *PN = PHINode::Create(LI->getType(), std::distance(PB, PE), "",
1019 LoadBB->begin());
1020 PN->takeName(LI);
1021 PN->setDebugLoc(LI->getDebugLoc());
1022
1023 // Insert new entries into the PHI for each predecessor. A single block may
1024 // have multiple entries here.
1025 for (pred_iterator PI = PB; PI != PE; ++PI) {
1026 BasicBlock *P = *PI;
1027 AvailablePredsTy::iterator I =
1028 std::lower_bound(AvailablePreds.begin(), AvailablePreds.end(),
1029 std::make_pair(P, (Value*)nullptr));
1030
1031 assert(I != AvailablePreds.end() && I->first == P &&((I != AvailablePreds.end() && I->first == P &&
"Didn't find entry for predecessor!") ? static_cast<void>
(0) : __assert_fail ("I != AvailablePreds.end() && I->first == P && \"Didn't find entry for predecessor!\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 1032, __PRETTY_FUNCTION__))
1032 "Didn't find entry for predecessor!")((I != AvailablePreds.end() && I->first == P &&
"Didn't find entry for predecessor!") ? static_cast<void>
(0) : __assert_fail ("I != AvailablePreds.end() && I->first == P && \"Didn't find entry for predecessor!\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 1032, __PRETTY_FUNCTION__));
1033
1034 PN->addIncoming(I->second, I->first);
1035 }
1036
1037 //cerr << "PRE: " << *LI << *PN << "\n";
1038
1039 LI->replaceAllUsesWith(PN);
1040 LI->eraseFromParent();
1041
1042 return true;
1043}
1044
1045/// FindMostPopularDest - The specified list contains multiple possible
1046/// threadable destinations. Pick the one that occurs the most frequently in
1047/// the list.
1048static BasicBlock *
1049FindMostPopularDest(BasicBlock *BB,
1050 const SmallVectorImpl<std::pair<BasicBlock*,
1051 BasicBlock*> > &PredToDestList) {
1052 assert(!PredToDestList.empty())((!PredToDestList.empty()) ? static_cast<void> (0) : __assert_fail
("!PredToDestList.empty()", "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 1052, __PRETTY_FUNCTION__));
1053
1054 // Determine popularity. If there are multiple possible destinations, we
1055 // explicitly choose to ignore 'undef' destinations. We prefer to thread
1056 // blocks with known and real destinations to threading undef. We'll handle
1057 // them later if interesting.
1058 DenseMap<BasicBlock*, unsigned> DestPopularity;
1059 for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i)
1060 if (PredToDestList[i].second)
1061 DestPopularity[PredToDestList[i].second]++;
1062
1063 // Find the most popular dest.
1064 DenseMap<BasicBlock*, unsigned>::iterator DPI = DestPopularity.begin();
1065 BasicBlock *MostPopularDest = DPI->first;
1066 unsigned Popularity = DPI->second;
1067 SmallVector<BasicBlock*, 4> SamePopularity;
1068
1069 for (++DPI; DPI != DestPopularity.end(); ++DPI) {
1070 // If the popularity of this entry isn't higher than the popularity we've
1071 // seen so far, ignore it.
1072 if (DPI->second < Popularity)
1073 ; // ignore.
1074 else if (DPI->second == Popularity) {
1075 // If it is the same as what we've seen so far, keep track of it.
1076 SamePopularity.push_back(DPI->first);
1077 } else {
1078 // If it is more popular, remember it.
1079 SamePopularity.clear();
1080 MostPopularDest = DPI->first;
1081 Popularity = DPI->second;
1082 }
1083 }
1084
1085 // Okay, now we know the most popular destination. If there is more than one
1086 // destination, we need to determine one. This is arbitrary, but we need
1087 // to make a deterministic decision. Pick the first one that appears in the
1088 // successor list.
1089 if (!SamePopularity.empty()) {
1090 SamePopularity.push_back(MostPopularDest);
1091 TerminatorInst *TI = BB->getTerminator();
1092 for (unsigned i = 0; ; ++i) {
1093 assert(i != TI->getNumSuccessors() && "Didn't find any successor!")((i != TI->getNumSuccessors() && "Didn't find any successor!"
) ? static_cast<void> (0) : __assert_fail ("i != TI->getNumSuccessors() && \"Didn't find any successor!\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 1093, __PRETTY_FUNCTION__));
1094
1095 if (std::find(SamePopularity.begin(), SamePopularity.end(),
1096 TI->getSuccessor(i)) == SamePopularity.end())
1097 continue;
1098
1099 MostPopularDest = TI->getSuccessor(i);
1100 break;
1101 }
1102 }
1103
1104 // Okay, we have finally picked the most popular destination.
1105 return MostPopularDest;
1106}
1107
1108bool JumpThreading::ProcessThreadableEdges(Value *Cond, BasicBlock *BB,
1109 ConstantPreference Preference,
1110 Instruction *CxtI) {
1111 // If threading this would thread across a loop header, don't even try to
1112 // thread the edge.
1113 if (LoopHeaders.count(BB))
1114 return false;
1115
1116 PredValueInfoTy PredValues;
1117 if (!ComputeValueKnownInPredecessors(Cond, BB, PredValues, Preference, CxtI))
1118 return false;
1119
1120 assert(!PredValues.empty() &&((!PredValues.empty() && "ComputeValueKnownInPredecessors returned true with no values"
) ? static_cast<void> (0) : __assert_fail ("!PredValues.empty() && \"ComputeValueKnownInPredecessors returned true with no values\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 1121, __PRETTY_FUNCTION__))
1121 "ComputeValueKnownInPredecessors returned true with no values")((!PredValues.empty() && "ComputeValueKnownInPredecessors returned true with no values"
) ? static_cast<void> (0) : __assert_fail ("!PredValues.empty() && \"ComputeValueKnownInPredecessors returned true with no values\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 1121, __PRETTY_FUNCTION__));
1122
1123 DEBUG(dbgs() << "IN BB: " << *BB;do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "IN BB: " << *BB;
for (unsigned i = 0, e = PredValues.size(); i != e; ++i) { dbgs
() << " BB '" << BB->getName() << "': FOUND condition = "
<< *PredValues[i].first << " for pred '" <<
PredValues[i].second->getName() << "'.\n"; }; } } while
(0)
1124 for (unsigned i = 0, e = PredValues.size(); i != e; ++i) {do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "IN BB: " << *BB;
for (unsigned i = 0, e = PredValues.size(); i != e; ++i) { dbgs
() << " BB '" << BB->getName() << "': FOUND condition = "
<< *PredValues[i].first << " for pred '" <<
PredValues[i].second->getName() << "'.\n"; }; } } while
(0)
1125 dbgs() << " BB '" << BB->getName() << "': FOUND condition = "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "IN BB: " << *BB;
for (unsigned i = 0, e = PredValues.size(); i != e; ++i) { dbgs
() << " BB '" << BB->getName() << "': FOUND condition = "
<< *PredValues[i].first << " for pred '" <<
PredValues[i].second->getName() << "'.\n"; }; } } while
(0)
1126 << *PredValues[i].firstdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "IN BB: " << *BB;
for (unsigned i = 0, e = PredValues.size(); i != e; ++i) { dbgs
() << " BB '" << BB->getName() << "': FOUND condition = "
<< *PredValues[i].first << " for pred '" <<
PredValues[i].second->getName() << "'.\n"; }; } } while
(0)
1127 << " for pred '" << PredValues[i].second->getName() << "'.\n";do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "IN BB: " << *BB;
for (unsigned i = 0, e = PredValues.size(); i != e; ++i) { dbgs
() << " BB '" << BB->getName() << "': FOUND condition = "
<< *PredValues[i].first << " for pred '" <<
PredValues[i].second->getName() << "'.\n"; }; } } while
(0)
1128 })do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "IN BB: " << *BB;
for (unsigned i = 0, e = PredValues.size(); i != e; ++i) { dbgs
() << " BB '" << BB->getName() << "': FOUND condition = "
<< *PredValues[i].first << " for pred '" <<
PredValues[i].second->getName() << "'.\n"; }; } } while
(0);
1129
1130 // Decide what we want to thread through. Convert our list of known values to
1131 // a list of known destinations for each pred. This also discards duplicate
1132 // predecessors and keeps track of the undefined inputs (which are represented
1133 // as a null dest in the PredToDestList).
1134 SmallPtrSet<BasicBlock*, 16> SeenPreds;
1135 SmallVector<std::pair<BasicBlock*, BasicBlock*>, 16> PredToDestList;
1136
1137 BasicBlock *OnlyDest = nullptr;
1138 BasicBlock *MultipleDestSentinel = (BasicBlock*)(intptr_t)~0ULL;
1139
1140 for (unsigned i = 0, e = PredValues.size(); i != e; ++i) {
1141 BasicBlock *Pred = PredValues[i].second;
1142 if (!SeenPreds.insert(Pred))
1143 continue; // Duplicate predecessor entry.
1144
1145 // If the predecessor ends with an indirect goto, we can't change its
1146 // destination.
1147 if (isa<IndirectBrInst>(Pred->getTerminator()))
1148 continue;
1149
1150 Constant *Val = PredValues[i].first;
1151
1152 BasicBlock *DestBB;
1153 if (isa<UndefValue>(Val))
1154 DestBB = nullptr;
1155 else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()))
1156 DestBB = BI->getSuccessor(cast<ConstantInt>(Val)->isZero());
1157 else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1158 DestBB = SI->findCaseValue(cast<ConstantInt>(Val)).getCaseSuccessor();
1159 } else {
1160 assert(isa<IndirectBrInst>(BB->getTerminator())((isa<IndirectBrInst>(BB->getTerminator()) &&
"Unexpected terminator") ? static_cast<void> (0) : __assert_fail
("isa<IndirectBrInst>(BB->getTerminator()) && \"Unexpected terminator\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 1161, __PRETTY_FUNCTION__))
1161 && "Unexpected terminator")((isa<IndirectBrInst>(BB->getTerminator()) &&
"Unexpected terminator") ? static_cast<void> (0) : __assert_fail
("isa<IndirectBrInst>(BB->getTerminator()) && \"Unexpected terminator\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 1161, __PRETTY_FUNCTION__));
1162 DestBB = cast<BlockAddress>(Val)->getBasicBlock();
1163 }
1164
1165 // If we have exactly one destination, remember it for efficiency below.
1166 if (PredToDestList.empty())
1167 OnlyDest = DestBB;
1168 else if (OnlyDest != DestBB)
1169 OnlyDest = MultipleDestSentinel;
1170
1171 PredToDestList.push_back(std::make_pair(Pred, DestBB));
1172 }
1173
1174 // If all edges were unthreadable, we fail.
1175 if (PredToDestList.empty())
1176 return false;
1177
1178 // Determine which is the most common successor. If we have many inputs and
1179 // this block is a switch, we want to start by threading the batch that goes
1180 // to the most popular destination first. If we only know about one
1181 // threadable destination (the common case) we can avoid this.
1182 BasicBlock *MostPopularDest = OnlyDest;
1183
1184 if (MostPopularDest == MultipleDestSentinel)
1185 MostPopularDest = FindMostPopularDest(BB, PredToDestList);
1186
1187 // Now that we know what the most popular destination is, factor all
1188 // predecessors that will jump to it into a single predecessor.
1189 SmallVector<BasicBlock*, 16> PredsToFactor;
1190 for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i)
1191 if (PredToDestList[i].second == MostPopularDest) {
1192 BasicBlock *Pred = PredToDestList[i].first;
1193
1194 // This predecessor may be a switch or something else that has multiple
1195 // edges to the block. Factor each of these edges by listing them
1196 // according to # occurrences in PredsToFactor.
1197 TerminatorInst *PredTI = Pred->getTerminator();
1198 for (unsigned i = 0, e = PredTI->getNumSuccessors(); i != e; ++i)
1199 if (PredTI->getSuccessor(i) == BB)
1200 PredsToFactor.push_back(Pred);
1201 }
1202
1203 // If the threadable edges are branching on an undefined value, we get to pick
1204 // the destination that these predecessors should get to.
1205 if (!MostPopularDest)
1206 MostPopularDest = BB->getTerminator()->
1207 getSuccessor(GetBestDestForJumpOnUndef(BB));
1208
1209 // Ok, try to thread it!
1210 return ThreadEdge(BB, PredsToFactor, MostPopularDest);
1211}
1212
1213/// ProcessBranchOnPHI - We have an otherwise unthreadable conditional branch on
1214/// a PHI node in the current block. See if there are any simplifications we
1215/// can do based on inputs to the phi node.
1216///
1217bool JumpThreading::ProcessBranchOnPHI(PHINode *PN) {
1218 BasicBlock *BB = PN->getParent();
1219
1220 // TODO: We could make use of this to do it once for blocks with common PHI
1221 // values.
1222 SmallVector<BasicBlock*, 1> PredBBs;
1223 PredBBs.resize(1);
1224
1225 // If any of the predecessor blocks end in an unconditional branch, we can
1226 // *duplicate* the conditional branch into that block in order to further
1227 // encourage jump threading and to eliminate cases where we have branch on a
1228 // phi of an icmp (branch on icmp is much better).
1229 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1230 BasicBlock *PredBB = PN->getIncomingBlock(i);
1231 if (BranchInst *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator()))
1232 if (PredBr->isUnconditional()) {
1233 PredBBs[0] = PredBB;
1234 // Try to duplicate BB into PredBB.
1235 if (DuplicateCondBranchOnPHIIntoPred(BB, PredBBs))
1236 return true;
1237 }
1238 }
1239
1240 return false;
1241}
1242
1243/// ProcessBranchOnXOR - We have an otherwise unthreadable conditional branch on
1244/// a xor instruction in the current block. See if there are any
1245/// simplifications we can do based on inputs to the xor.
1246///
1247bool JumpThreading::ProcessBranchOnXOR(BinaryOperator *BO) {
1248 BasicBlock *BB = BO->getParent();
1249
1250 // If either the LHS or RHS of the xor is a constant, don't do this
1251 // optimization.
1252 if (isa<ConstantInt>(BO->getOperand(0)) ||
1253 isa<ConstantInt>(BO->getOperand(1)))
1254 return false;
1255
1256 // If the first instruction in BB isn't a phi, we won't be able to infer
1257 // anything special about any particular predecessor.
1258 if (!isa<PHINode>(BB->front()))
1259 return false;
1260
1261 // If we have a xor as the branch input to this block, and we know that the
1262 // LHS or RHS of the xor in any predecessor is true/false, then we can clone
1263 // the condition into the predecessor and fix that value to true, saving some
1264 // logical ops on that path and encouraging other paths to simplify.
1265 //
1266 // This copies something like this:
1267 //
1268 // BB:
1269 // %X = phi i1 [1], [%X']
1270 // %Y = icmp eq i32 %A, %B
1271 // %Z = xor i1 %X, %Y
1272 // br i1 %Z, ...
1273 //
1274 // Into:
1275 // BB':
1276 // %Y = icmp ne i32 %A, %B
1277 // br i1 %Z, ...
1278
1279 PredValueInfoTy XorOpValues;
1280 bool isLHS = true;
1281 if (!ComputeValueKnownInPredecessors(BO->getOperand(0), BB, XorOpValues,
1282 WantInteger, BO)) {
1283 assert(XorOpValues.empty())((XorOpValues.empty()) ? static_cast<void> (0) : __assert_fail
("XorOpValues.empty()", "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 1283, __PRETTY_FUNCTION__));
1284 if (!ComputeValueKnownInPredecessors(BO->getOperand(1), BB, XorOpValues,
1285 WantInteger, BO))
1286 return false;
1287 isLHS = false;
1288 }
1289
1290 assert(!XorOpValues.empty() &&((!XorOpValues.empty() && "ComputeValueKnownInPredecessors returned true with no values"
) ? static_cast<void> (0) : __assert_fail ("!XorOpValues.empty() && \"ComputeValueKnownInPredecessors returned true with no values\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 1291, __PRETTY_FUNCTION__))
1291 "ComputeValueKnownInPredecessors returned true with no values")((!XorOpValues.empty() && "ComputeValueKnownInPredecessors returned true with no values"
) ? static_cast<void> (0) : __assert_fail ("!XorOpValues.empty() && \"ComputeValueKnownInPredecessors returned true with no values\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 1291, __PRETTY_FUNCTION__));
1292
1293 // Scan the information to see which is most popular: true or false. The
1294 // predecessors can be of the set true, false, or undef.
1295 unsigned NumTrue = 0, NumFalse = 0;
1296 for (unsigned i = 0, e = XorOpValues.size(); i != e; ++i) {
1297 if (isa<UndefValue>(XorOpValues[i].first))
1298 // Ignore undefs for the count.
1299 continue;
1300 if (cast<ConstantInt>(XorOpValues[i].first)->isZero())
1301 ++NumFalse;
1302 else
1303 ++NumTrue;
1304 }
1305
1306 // Determine which value to split on, true, false, or undef if neither.
1307 ConstantInt *SplitVal = nullptr;
1308 if (NumTrue > NumFalse)
1309 SplitVal = ConstantInt::getTrue(BB->getContext());
1310 else if (NumTrue != 0 || NumFalse != 0)
1311 SplitVal = ConstantInt::getFalse(BB->getContext());
1312
1313 // Collect all of the blocks that this can be folded into so that we can
1314 // factor this once and clone it once.
1315 SmallVector<BasicBlock*, 8> BlocksToFoldInto;
1316 for (unsigned i = 0, e = XorOpValues.size(); i != e; ++i) {
1317 if (XorOpValues[i].first != SplitVal &&
1318 !isa<UndefValue>(XorOpValues[i].first))
1319 continue;
1320
1321 BlocksToFoldInto.push_back(XorOpValues[i].second);
1322 }
1323
1324 // If we inferred a value for all of the predecessors, then duplication won't
1325 // help us. However, we can just replace the LHS or RHS with the constant.
1326 if (BlocksToFoldInto.size() ==
1327 cast<PHINode>(BB->front()).getNumIncomingValues()) {
1328 if (!SplitVal) {
1329 // If all preds provide undef, just nuke the xor, because it is undef too.
1330 BO->replaceAllUsesWith(UndefValue::get(BO->getType()));
1331 BO->eraseFromParent();
1332 } else if (SplitVal->isZero()) {
1333 // If all preds provide 0, replace the xor with the other input.
1334 BO->replaceAllUsesWith(BO->getOperand(isLHS));
1335 BO->eraseFromParent();
1336 } else {
1337 // If all preds provide 1, set the computed value to 1.
1338 BO->setOperand(!isLHS, SplitVal);
1339 }
1340
1341 return true;
1342 }
1343
1344 // Try to duplicate BB into PredBB.
1345 return DuplicateCondBranchOnPHIIntoPred(BB, BlocksToFoldInto);
1346}
1347
1348
1349/// AddPHINodeEntriesForMappedBlock - We're adding 'NewPred' as a new
1350/// predecessor to the PHIBB block. If it has PHI nodes, add entries for
1351/// NewPred using the entries from OldPred (suitably mapped).
1352static void AddPHINodeEntriesForMappedBlock(BasicBlock *PHIBB,
1353 BasicBlock *OldPred,
1354 BasicBlock *NewPred,
1355 DenseMap<Instruction*, Value*> &ValueMap) {
1356 for (BasicBlock::iterator PNI = PHIBB->begin();
1357 PHINode *PN = dyn_cast<PHINode>(PNI); ++PNI) {
1358 // Ok, we have a PHI node. Figure out what the incoming value was for the
1359 // DestBlock.
1360 Value *IV = PN->getIncomingValueForBlock(OldPred);
1361
1362 // Remap the value if necessary.
1363 if (Instruction *Inst = dyn_cast<Instruction>(IV)) {
1364 DenseMap<Instruction*, Value*>::iterator I = ValueMap.find(Inst);
1365 if (I != ValueMap.end())
1366 IV = I->second;
1367 }
1368
1369 PN->addIncoming(IV, NewPred);
1370 }
1371}
1372
1373/// ThreadEdge - We have decided that it is safe and profitable to factor the
1374/// blocks in PredBBs to one predecessor, then thread an edge from it to SuccBB
1375/// across BB. Transform the IR to reflect this change.
1376bool JumpThreading::ThreadEdge(BasicBlock *BB,
1377 const SmallVectorImpl<BasicBlock*> &PredBBs,
1378 BasicBlock *SuccBB) {
1379 // If threading to the same block as we come from, we would infinite loop.
1380 if (SuccBB == BB) {
1381 DEBUG(dbgs() << " Not threading across BB '" << BB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not threading across BB '"
<< BB->getName() << "' - would thread to self!\n"
; } } while (0)
1382 << "' - would thread to self!\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not threading across BB '"
<< BB->getName() << "' - would thread to self!\n"
; } } while (0);
1383 return false;
1384 }
1385
1386 // If threading this would thread across a loop header, don't thread the edge.
1387 // See the comments above FindLoopHeaders for justifications and caveats.
1388 if (LoopHeaders.count(BB)) {
1389 DEBUG(dbgs() << " Not threading across loop header BB '" << BB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not threading across loop header BB '"
<< BB->getName() << "' to dest BB '" <<
SuccBB->getName() << "' - it might create an irreducible loop!\n"
; } } while (0)
1390 << "' to dest BB '" << SuccBB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not threading across loop header BB '"
<< BB->getName() << "' to dest BB '" <<
SuccBB->getName() << "' - it might create an irreducible loop!\n"
; } } while (0)
1391 << "' - it might create an irreducible loop!\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not threading across loop header BB '"
<< BB->getName() << "' to dest BB '" <<
SuccBB->getName() << "' - it might create an irreducible loop!\n"
; } } while (0);
1392 return false;
1393 }
1394
1395 unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB, BBDupThreshold);
1396 if (JumpThreadCost > BBDupThreshold) {
1397 DEBUG(dbgs() << " Not threading BB '" << BB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not threading BB '" <<
BB->getName() << "' - Cost is too high: " << JumpThreadCost
<< "\n"; } } while (0)
1398 << "' - Cost is too high: " << JumpThreadCost << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not threading BB '" <<
BB->getName() << "' - Cost is too high: " << JumpThreadCost
<< "\n"; } } while (0);
1399 return false;
1400 }
1401
1402 // And finally, do it! Start by factoring the predecessors is needed.
1403 BasicBlock *PredBB;
1404 if (PredBBs.size() == 1)
1405 PredBB = PredBBs[0];
1406 else {
1407 DEBUG(dbgs() << " Factoring out " << PredBBs.size()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Factoring out " <<
PredBBs.size() << " common predecessors.\n"; } } while
(0)
1408 << " common predecessors.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Factoring out " <<
PredBBs.size() << " common predecessors.\n"; } } while
(0);
1409 PredBB = SplitBlockPredecessors(BB, PredBBs, ".thr_comm", this);
1410 }
1411
1412 // And finally, do it!
1413 DEBUG(dbgs() << " Threading edge from '" << PredBB->getName() << "' to '"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Threading edge from '"
<< PredBB->getName() << "' to '" << SuccBB
->getName() << "' with cost: " << JumpThreadCost
<< ", across block:\n " << *BB << "\n";
} } while (0)
1414 << SuccBB->getName() << "' with cost: " << JumpThreadCostdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Threading edge from '"
<< PredBB->getName() << "' to '" << SuccBB
->getName() << "' with cost: " << JumpThreadCost
<< ", across block:\n " << *BB << "\n";
} } while (0)
1415 << ", across block:\n "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Threading edge from '"
<< PredBB->getName() << "' to '" << SuccBB
->getName() << "' with cost: " << JumpThreadCost
<< ", across block:\n " << *BB << "\n";
} } while (0)
1416 << *BB << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Threading edge from '"
<< PredBB->getName() << "' to '" << SuccBB
->getName() << "' with cost: " << JumpThreadCost
<< ", across block:\n " << *BB << "\n";
} } while (0);
1417
1418 LVI->threadEdge(PredBB, BB, SuccBB);
1419
1420 // We are going to have to map operands from the original BB block to the new
1421 // copy of the block 'NewBB'. If there are PHI nodes in BB, evaluate them to
1422 // account for entry from PredBB.
1423 DenseMap<Instruction*, Value*> ValueMapping;
1424
1425 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(),
1426 BB->getName()+".thread",
1427 BB->getParent(), BB);
1428 NewBB->moveAfter(PredBB);
1429
1430 BasicBlock::iterator BI = BB->begin();
1431 for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
1432 ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
1433
1434 // Clone the non-phi instructions of BB into NewBB, keeping track of the
1435 // mapping and using it to remap operands in the cloned instructions.
1436 for (; !isa<TerminatorInst>(BI); ++BI) {
1437 Instruction *New = BI->clone();
1438 New->setName(BI->getName());
1439 NewBB->getInstList().push_back(New);
1440 ValueMapping[BI] = New;
1441
1442 // Remap operands to patch up intra-block references.
1443 for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
1444 if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
1445 DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst);
1446 if (I != ValueMapping.end())
1447 New->setOperand(i, I->second);
1448 }
1449 }
1450
1451 // We didn't copy the terminator from BB over to NewBB, because there is now
1452 // an unconditional jump to SuccBB. Insert the unconditional jump.
1453 BranchInst *NewBI =BranchInst::Create(SuccBB, NewBB);
1454 NewBI->setDebugLoc(BB->getTerminator()->getDebugLoc());
1455
1456 // Check to see if SuccBB has PHI nodes. If so, we need to add entries to the
1457 // PHI nodes for NewBB now.
1458 AddPHINodeEntriesForMappedBlock(SuccBB, BB, NewBB, ValueMapping);
1459
1460 // If there were values defined in BB that are used outside the block, then we
1461 // now have to update all uses of the value to use either the original value,
1462 // the cloned value, or some PHI derived value. This can require arbitrary
1463 // PHI insertion, of which we are prepared to do, clean these up now.
1464 SSAUpdater SSAUpdate;
1465 SmallVector<Use*, 16> UsesToRename;
1466 for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
1467 // Scan all uses of this instruction to see if it is used outside of its
1468 // block, and if so, record them in UsesToRename.
1469 for (Use &U : I->uses()) {
1470 Instruction *User = cast<Instruction>(U.getUser());
1471 if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
1472 if (UserPN->getIncomingBlock(U) == BB)
1473 continue;
1474 } else if (User->getParent() == BB)
1475 continue;
1476
1477 UsesToRename.push_back(&U);
1478 }
1479
1480 // If there are no uses outside the block, we're done with this instruction.
1481 if (UsesToRename.empty())
1482 continue;
1483
1484 DEBUG(dbgs() << "JT: Renaming non-local uses of: " << *I << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "JT: Renaming non-local uses of: "
<< *I << "\n"; } } while (0);
1485
1486 // We found a use of I outside of BB. Rename all uses of I that are outside
1487 // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks
1488 // with the two values we know.
1489 SSAUpdate.Initialize(I->getType(), I->getName());
1490 SSAUpdate.AddAvailableValue(BB, I);
1491 SSAUpdate.AddAvailableValue(NewBB, ValueMapping[I]);
1492
1493 while (!UsesToRename.empty())
1494 SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
1495 DEBUG(dbgs() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "\n"; } } while (0);
1496 }
1497
1498
1499 // Ok, NewBB is good to go. Update the terminator of PredBB to jump to
1500 // NewBB instead of BB. This eliminates predecessors from BB, which requires
1501 // us to simplify any PHI nodes in BB.
1502 TerminatorInst *PredTerm = PredBB->getTerminator();
1503 for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i)
1504 if (PredTerm->getSuccessor(i) == BB) {
1505 BB->removePredecessor(PredBB, true);
1506 PredTerm->setSuccessor(i, NewBB);
1507 }
1508
1509 // At this point, the IR is fully up to date and consistent. Do a quick scan
1510 // over the new instructions and zap any that are constants or dead. This
1511 // frequently happens because of phi translation.
1512 SimplifyInstructionsInBlock(NewBB, DL, TLI);
1513
1514 // Threaded an edge!
1515 ++NumThreads;
1516 return true;
1517}
1518
1519/// DuplicateCondBranchOnPHIIntoPred - PredBB contains an unconditional branch
1520/// to BB which contains an i1 PHI node and a conditional branch on that PHI.
1521/// If we can duplicate the contents of BB up into PredBB do so now, this
1522/// improves the odds that the branch will be on an analyzable instruction like
1523/// a compare.
1524bool JumpThreading::DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
1525 const SmallVectorImpl<BasicBlock *> &PredBBs) {
1526 assert(!PredBBs.empty() && "Can't handle an empty set")((!PredBBs.empty() && "Can't handle an empty set") ? static_cast
<void> (0) : __assert_fail ("!PredBBs.empty() && \"Can't handle an empty set\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn219601/lib/Transforms/Scalar/JumpThreading.cpp"
, 1526, __PRETTY_FUNCTION__));
1527
1528 // If BB is a loop header, then duplicating this block outside the loop would
1529 // cause us to transform this into an irreducible loop, don't do this.
1530 // See the comments above FindLoopHeaders for justifications and caveats.
1531 if (LoopHeaders.count(BB)) {
1532 DEBUG(dbgs() << " Not duplicating loop header '" << BB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not duplicating loop header '"
<< BB->getName() << "' into predecessor block '"
<< PredBBs[0]->getName() << "' - it might create an irreducible loop!\n"
; } } while (0)
1533 << "' into predecessor block '" << PredBBs[0]->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not duplicating loop header '"
<< BB->getName() << "' into predecessor block '"
<< PredBBs[0]->getName() << "' - it might create an irreducible loop!\n"
; } } while (0)
1534 << "' - it might create an irreducible loop!\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not duplicating loop header '"
<< BB->getName() << "' into predecessor block '"
<< PredBBs[0]->getName() << "' - it might create an irreducible loop!\n"
; } } while (0);
1535 return false;
1536 }
1537
1538 unsigned DuplicationCost = getJumpThreadDuplicationCost(BB, BBDupThreshold);
1539 if (DuplicationCost > BBDupThreshold) {
1540 DEBUG(dbgs() << " Not duplicating BB '" << BB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not duplicating BB '"
<< BB->getName() << "' - Cost is too high: " <<
DuplicationCost << "\n"; } } while (0)
1541 << "' - Cost is too high: " << DuplicationCost << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not duplicating BB '"
<< BB->getName() << "' - Cost is too high: " <<
DuplicationCost << "\n"; } } while (0);
1542 return false;
1543 }
1544
1545 // And finally, do it! Start by factoring the predecessors is needed.
1546 BasicBlock *PredBB;
1547 if (PredBBs.size() == 1)
1548 PredBB = PredBBs[0];
1549 else {
1550 DEBUG(dbgs() << " Factoring out " << PredBBs.size()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Factoring out " <<
PredBBs.size() << " common predecessors.\n"; } } while
(0)
1551 << " common predecessors.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Factoring out " <<
PredBBs.size() << " common predecessors.\n"; } } while
(0);
1552 PredBB = SplitBlockPredecessors(BB, PredBBs, ".thr_comm", this);
1553 }
1554
1555 // Okay, we decided to do this! Clone all the instructions in BB onto the end
1556 // of PredBB.
1557 DEBUG(dbgs() << " Duplicating block '" << BB->getName() << "' into end of '"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Duplicating block '"
<< BB->getName() << "' into end of '" <<
PredBB->getName() << "' to eliminate branch on phi. Cost: "
<< DuplicationCost << " block is:" << *BB <<
"\n"; } } while (0)
1558 << PredBB->getName() << "' to eliminate branch on phi. Cost: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Duplicating block '"
<< BB->getName() << "' into end of '" <<
PredBB->getName() << "' to eliminate branch on phi. Cost: "
<< DuplicationCost << " block is:" << *BB <<
"\n"; } } while (0)
1559 << DuplicationCost << " block is:" << *BB << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Duplicating block '"
<< BB->getName() << "' into end of '" <<
PredBB->getName() << "' to eliminate branch on phi. Cost: "
<< DuplicationCost << " block is:" << *BB <<
"\n"; } } while (0);
1560
1561 // Unless PredBB ends with an unconditional branch, split the edge so that we
1562 // can just clone the bits from BB into the end of the new PredBB.
1563 BranchInst *OldPredBranch = dyn_cast<BranchInst>(PredBB->getTerminator());
1564
1565 if (!OldPredBranch || !OldPredBranch->isUnconditional()) {
1566 PredBB = SplitEdge(PredBB, BB, this);
1567 OldPredBranch = cast<BranchInst>(PredBB->getTerminator());
1568 }
1569
1570 // We are going to have to map operands from the original BB block into the
1571 // PredBB block. Evaluate PHI nodes in BB.
1572 DenseMap<Instruction*, Value*> ValueMapping;
1573
1574 BasicBlock::iterator BI = BB->begin();
1575 for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
1576 ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
1577
1578 // Clone the non-phi instructions of BB into PredBB, keeping track of the
1579 // mapping and using it to remap operands in the cloned instructions.
1580 for (; BI != BB->end(); ++BI) {
1581 Instruction *New = BI->clone();
1582
1583 // Remap operands to patch up intra-block references.
1584 for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
1585 if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
1586 DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst);
1587 if (I != ValueMapping.end())
1588 New->setOperand(i, I->second);
1589 }
1590
1591 // If this instruction can be simplified after the operands are updated,
1592 // just use the simplified value instead. This frequently happens due to
1593 // phi translation.
1594 if (Value *IV = SimplifyInstruction(New, DL)) {
1595 delete New;
1596 ValueMapping[BI] = IV;
1597 } else {
1598 // Otherwise, insert the new instruction into the block.
1599 New->setName(BI->getName());
1600 PredBB->getInstList().insert(OldPredBranch, New);
1601 ValueMapping[BI] = New;
1602 }
1603 }
1604
1605 // Check to see if the targets of the branch had PHI nodes. If so, we need to
1606 // add entries to the PHI nodes for branch from PredBB now.
1607 BranchInst *BBBranch = cast<BranchInst>(BB->getTerminator());
1608 AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(0), BB, PredBB,
1609 ValueMapping);
1610 AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(1), BB, PredBB,
1611 ValueMapping);
1612
1613 // If there were values defined in BB that are used outside the block, then we
1614 // now have to update all uses of the value to use either the original value,
1615 // the cloned value, or some PHI derived value. This can require arbitrary
1616 // PHI insertion, of which we are prepared to do, clean these up now.
1617 SSAUpdater SSAUpdate;
1618 SmallVector<Use*, 16> UsesToRename;
1619 for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
1620 // Scan all uses of this instruction to see if it is used outside of its
1621 // block, and if so, record them in UsesToRename.
1622 for (Use &U : I->uses()) {
1623 Instruction *User = cast<Instruction>(U.getUser());
1624 if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
1625 if (UserPN->getIncomingBlock(U) == BB)
1626 continue;
1627 } else if (User->getParent() == BB)
1628 continue;
1629
1630 UsesToRename.push_back(&U);
1631 }
1632
1633 // If there are no uses outside the block, we're done with this instruction.
1634 if (UsesToRename.empty())
1635 continue;
1636
1637 DEBUG(dbgs() << "JT: Renaming non-local uses of: " << *I << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "JT: Renaming non-local uses of: "
<< *I << "\n"; } } while (0);
1638
1639 // We found a use of I outside of BB. Rename all uses of I that are outside
1640 // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks
1641 // with the two values we know.
1642 SSAUpdate.Initialize(I->getType(), I->getName());
1643 SSAUpdate.AddAvailableValue(BB, I);
1644 SSAUpdate.AddAvailableValue(PredBB, ValueMapping[I]);
1645
1646 while (!UsesToRename.empty())
1647 SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
1648 DEBUG(dbgs() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "\n"; } } while (0);
1649 }
1650
1651 // PredBB no longer jumps to BB, remove entries in the PHI node for the edge
1652 // that we nuked.
1653 BB->removePredecessor(PredBB, true);
1654
1655 // Remove the unconditional branch at the end of the PredBB block.
1656 OldPredBranch->eraseFromParent();
1657
1658 ++NumDupes;
1659 return true;
1660}
1661
1662/// TryToUnfoldSelect - Look for blocks of the form
1663/// bb1:
1664/// %a = select
1665/// br bb
1666///
1667/// bb2:
1668/// %p = phi [%a, %bb] ...
1669/// %c = icmp %p
1670/// br i1 %c
1671///
1672/// And expand the select into a branch structure if one of its arms allows %c
1673/// to be folded. This later enables threading from bb1 over bb2.
1674bool JumpThreading::TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB) {
1675 BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
1676 PHINode *CondLHS = dyn_cast<PHINode>(CondCmp->getOperand(0));
1677 Constant *CondRHS = cast<Constant>(CondCmp->getOperand(1));
1678
1679 if (!CondBr || !CondBr->isConditional() || !CondLHS ||
1680 CondLHS->getParent() != BB)
1681 return false;
1682
1683 for (unsigned I = 0, E = CondLHS->getNumIncomingValues(); I != E; ++I) {
1684 BasicBlock *Pred = CondLHS->getIncomingBlock(I);
1685 SelectInst *SI = dyn_cast<SelectInst>(CondLHS->getIncomingValue(I));
1686
1687 // Look if one of the incoming values is a select in the corresponding
1688 // predecessor.
1689 if (!SI || SI->getParent() != Pred || !SI->hasOneUse())
1690 continue;
1691
1692 BranchInst *PredTerm = dyn_cast<BranchInst>(Pred->getTerminator());
1693 if (!PredTerm || !PredTerm->isUnconditional())
1694 continue;
1695
1696 // Now check if one of the select values would allow us to constant fold the
1697 // terminator in BB. We don't do the transform if both sides fold, those
1698 // cases will be threaded in any case.
1699 LazyValueInfo::Tristate LHSFolds =
1700 LVI->getPredicateOnEdge(CondCmp->getPredicate(), SI->getOperand(1),
1701 CondRHS, Pred, BB, CondCmp);
1702 LazyValueInfo::Tristate RHSFolds =
1703 LVI->getPredicateOnEdge(CondCmp->getPredicate(), SI->getOperand(2),
1704 CondRHS, Pred, BB, CondCmp);
1705 if ((LHSFolds != LazyValueInfo::Unknown ||
1706 RHSFolds != LazyValueInfo::Unknown) &&
1707 LHSFolds != RHSFolds) {
1708 // Expand the select.
1709 //
1710 // Pred --
1711 // | v
1712 // | NewBB
1713 // | |
1714 // |-----
1715 // v
1716 // BB
1717 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "select.unfold",
1718 BB->getParent(), BB);
1719 // Move the unconditional branch to NewBB.
1720 PredTerm->removeFromParent();
1721 NewBB->getInstList().insert(NewBB->end(), PredTerm);
1722 // Create a conditional branch and update PHI nodes.
1723 BranchInst::Create(NewBB, BB, SI->getCondition(), Pred);
1724 CondLHS->setIncomingValue(I, SI->getFalseValue());
1725 CondLHS->addIncoming(SI->getTrueValue(), NewBB);
1726 // The select is now dead.
1727 SI->eraseFromParent();
1728
1729 // Update any other PHI nodes in BB.
1730 for (BasicBlock::iterator BI = BB->begin();
1731 PHINode *Phi = dyn_cast<PHINode>(BI); ++BI)
1732 if (Phi != CondLHS)
1733 Phi->addIncoming(Phi->getIncomingValueForBlock(Pred), NewBB);
1734 return true;
1735 }
1736 }
1737 return false;
1738}