LLVM  4.0.0
SCCP.cpp
Go to the documentation of this file.
1 //===- SCCP.cpp - Sparse Conditional Constant Propagation -----------------===//
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 sparse conditional constant propagation and merging:
11 //
12 // Specifically, this:
13 // * Assumes values are constant unless proven otherwise
14 // * Assumes BasicBlocks are dead unless proven otherwise
15 // * Proves values to be constant, and replaces them with constants
16 // * Proves conditional branches to be unconditional
17 //
18 //===----------------------------------------------------------------------===//
19 
21 #include "llvm/ADT/DenseMap.h"
22 #include "llvm/ADT/DenseSet.h"
24 #include "llvm/ADT/SmallPtrSet.h"
25 #include "llvm/ADT/SmallVector.h"
26 #include "llvm/ADT/Statistic.h"
30 #include "llvm/IR/CallSite.h"
31 #include "llvm/IR/Constants.h"
32 #include "llvm/IR/DataLayout.h"
33 #include "llvm/IR/DerivedTypes.h"
34 #include "llvm/IR/InstVisitor.h"
35 #include "llvm/IR/Instructions.h"
36 #include "llvm/Pass.h"
37 #include "llvm/Support/Debug.h"
40 #include "llvm/Transforms/IPO.h"
41 #include "llvm/Transforms/Scalar.h"
44 #include <algorithm>
45 using namespace llvm;
46 
47 #define DEBUG_TYPE "sccp"
48 
49 STATISTIC(NumInstRemoved, "Number of instructions removed");
50 STATISTIC(NumDeadBlocks , "Number of basic blocks unreachable");
51 
52 STATISTIC(IPNumInstRemoved, "Number of instructions removed by IPSCCP");
53 STATISTIC(IPNumArgsElimed ,"Number of arguments constant propagated by IPSCCP");
54 STATISTIC(IPNumGlobalConst, "Number of globals found to be constant by IPSCCP");
55 
56 namespace {
57 /// LatticeVal class - This class represents the different lattice values that
58 /// an LLVM value may occupy. It is a simple class with value semantics.
59 ///
60 class LatticeVal {
61  enum LatticeValueTy {
62  /// unknown - This LLVM Value has no known value yet.
63  unknown,
64 
65  /// constant - This LLVM Value has a specific constant value.
66  constant,
67 
68  /// forcedconstant - This LLVM Value was thought to be undef until
69  /// ResolvedUndefsIn. This is treated just like 'constant', but if merged
70  /// with another (different) constant, it goes to overdefined, instead of
71  /// asserting.
72  forcedconstant,
73 
74  /// overdefined - This instruction is not known to be constant, and we know
75  /// it has a value.
76  overdefined
77  };
78 
79  /// Val: This stores the current lattice value along with the Constant* for
80  /// the constant if this is a 'constant' or 'forcedconstant' value.
82 
83  LatticeValueTy getLatticeValue() const {
84  return Val.getInt();
85  }
86 
87 public:
88  LatticeVal() : Val(nullptr, unknown) {}
89 
90  bool isUnknown() const { return getLatticeValue() == unknown; }
91  bool isConstant() const {
92  return getLatticeValue() == constant || getLatticeValue() == forcedconstant;
93  }
94  bool isOverdefined() const { return getLatticeValue() == overdefined; }
95 
96  Constant *getConstant() const {
97  assert(isConstant() && "Cannot get the constant of a non-constant!");
98  return Val.getPointer();
99  }
100 
101  /// markOverdefined - Return true if this is a change in status.
102  bool markOverdefined() {
103  if (isOverdefined())
104  return false;
105 
106  Val.setInt(overdefined);
107  return true;
108  }
109 
110  /// markConstant - Return true if this is a change in status.
111  bool markConstant(Constant *V) {
112  if (getLatticeValue() == constant) { // Constant but not forcedconstant.
113  assert(getConstant() == V && "Marking constant with different value");
114  return false;
115  }
116 
117  if (isUnknown()) {
118  Val.setInt(constant);
119  assert(V && "Marking constant with NULL");
120  Val.setPointer(V);
121  } else {
122  assert(getLatticeValue() == forcedconstant &&
123  "Cannot move from overdefined to constant!");
124  // Stay at forcedconstant if the constant is the same.
125  if (V == getConstant()) return false;
126 
127  // Otherwise, we go to overdefined. Assumptions made based on the
128  // forced value are possibly wrong. Assuming this is another constant
129  // could expose a contradiction.
130  Val.setInt(overdefined);
131  }
132  return true;
133  }
134 
135  /// getConstantInt - If this is a constant with a ConstantInt value, return it
136  /// otherwise return null.
137  ConstantInt *getConstantInt() const {
138  if (isConstant())
139  return dyn_cast<ConstantInt>(getConstant());
140  return nullptr;
141  }
142 
143  void markForcedConstant(Constant *V) {
144  assert(isUnknown() && "Can't force a defined value!");
145  Val.setInt(forcedconstant);
146  Val.setPointer(V);
147  }
148 };
149 } // end anonymous namespace.
150 
151 
152 namespace {
153 
154 //===----------------------------------------------------------------------===//
155 //
156 /// SCCPSolver - This class is a general purpose solver for Sparse Conditional
157 /// Constant Propagation.
158 ///
159 class SCCPSolver : public InstVisitor<SCCPSolver> {
160  const DataLayout &DL;
161  const TargetLibraryInfo *TLI;
162  SmallPtrSet<BasicBlock*, 8> BBExecutable; // The BBs that are executable.
163  DenseMap<Value*, LatticeVal> ValueState; // The state each value is in.
164 
165  /// StructValueState - This maintains ValueState for values that have
166  /// StructType, for example for formal arguments, calls, insertelement, etc.
167  ///
168  DenseMap<std::pair<Value*, unsigned>, LatticeVal> StructValueState;
169 
170  /// GlobalValue - If we are tracking any values for the contents of a global
171  /// variable, we keep a mapping from the constant accessor to the element of
172  /// the global, to the currently known value. If the value becomes
173  /// overdefined, it's entry is simply removed from this map.
175 
176  /// TrackedRetVals - If we are tracking arguments into and the return
177  /// value out of a function, it will have an entry in this map, indicating
178  /// what the known return value for the function is.
179  DenseMap<Function*, LatticeVal> TrackedRetVals;
180 
181  /// TrackedMultipleRetVals - Same as TrackedRetVals, but used for functions
182  /// that return multiple values.
183  DenseMap<std::pair<Function*, unsigned>, LatticeVal> TrackedMultipleRetVals;
184 
185  /// MRVFunctionsTracked - Each function in TrackedMultipleRetVals is
186  /// represented here for efficient lookup.
187  SmallPtrSet<Function*, 16> MRVFunctionsTracked;
188 
189  /// TrackingIncomingArguments - This is the set of functions for whose
190  /// arguments we make optimistic assumptions about and try to prove as
191  /// constants.
192  SmallPtrSet<Function*, 16> TrackingIncomingArguments;
193 
194  /// The reason for two worklists is that overdefined is the lowest state
195  /// on the lattice, and moving things to overdefined as fast as possible
196  /// makes SCCP converge much faster.
197  ///
198  /// By having a separate worklist, we accomplish this because everything
199  /// possibly overdefined will become overdefined at the soonest possible
200  /// point.
201  SmallVector<Value*, 64> OverdefinedInstWorkList;
202  SmallVector<Value*, 64> InstWorkList;
203 
204 
205  SmallVector<BasicBlock*, 64> BBWorkList; // The BasicBlock work list
206 
207  /// KnownFeasibleEdges - Entries in this set are edges which have already had
208  /// PHI nodes retriggered.
209  typedef std::pair<BasicBlock*, BasicBlock*> Edge;
210  DenseSet<Edge> KnownFeasibleEdges;
211 public:
212  SCCPSolver(const DataLayout &DL, const TargetLibraryInfo *tli)
213  : DL(DL), TLI(tli) {}
214 
215  /// MarkBlockExecutable - This method can be used by clients to mark all of
216  /// the blocks that are known to be intrinsically live in the processed unit.
217  ///
218  /// This returns true if the block was not considered live before.
219  bool MarkBlockExecutable(BasicBlock *BB) {
220  if (!BBExecutable.insert(BB).second)
221  return false;
222  DEBUG(dbgs() << "Marking Block Executable: " << BB->getName() << '\n');
223  BBWorkList.push_back(BB); // Add the block to the work list!
224  return true;
225  }
226 
227  /// TrackValueOfGlobalVariable - Clients can use this method to
228  /// inform the SCCPSolver that it should track loads and stores to the
229  /// specified global variable if it can. This is only legal to call if
230  /// performing Interprocedural SCCP.
231  void TrackValueOfGlobalVariable(GlobalVariable *GV) {
232  // We only track the contents of scalar globals.
233  if (GV->getValueType()->isSingleValueType()) {
234  LatticeVal &IV = TrackedGlobals[GV];
235  if (!isa<UndefValue>(GV->getInitializer()))
236  IV.markConstant(GV->getInitializer());
237  }
238  }
239 
240  /// AddTrackedFunction - If the SCCP solver is supposed to track calls into
241  /// and out of the specified function (which cannot have its address taken),
242  /// this method must be called.
243  void AddTrackedFunction(Function *F) {
244  // Add an entry, F -> undef.
245  if (auto *STy = dyn_cast<StructType>(F->getReturnType())) {
246  MRVFunctionsTracked.insert(F);
247  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
248  TrackedMultipleRetVals.insert(std::make_pair(std::make_pair(F, i),
249  LatticeVal()));
250  } else
251  TrackedRetVals.insert(std::make_pair(F, LatticeVal()));
252  }
253 
254  void AddArgumentTrackedFunction(Function *F) {
255  TrackingIncomingArguments.insert(F);
256  }
257 
258  /// Solve - Solve for constants and executable blocks.
259  ///
260  void Solve();
261 
262  /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
263  /// that branches on undef values cannot reach any of their successors.
264  /// However, this is not a safe assumption. After we solve dataflow, this
265  /// method should be use to handle this. If this returns true, the solver
266  /// should be rerun.
267  bool ResolvedUndefsIn(Function &F);
268 
269  bool isBlockExecutable(BasicBlock *BB) const {
270  return BBExecutable.count(BB);
271  }
272 
273  std::vector<LatticeVal> getStructLatticeValueFor(Value *V) const {
274  std::vector<LatticeVal> StructValues;
275  auto *STy = dyn_cast<StructType>(V->getType());
276  assert(STy && "getStructLatticeValueFor() can be called only on structs");
277  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
278  auto I = StructValueState.find(std::make_pair(V, i));
279  assert(I != StructValueState.end() && "Value not in valuemap!");
280  StructValues.push_back(I->second);
281  }
282  return StructValues;
283  }
284 
285  LatticeVal getLatticeValueFor(Value *V) const {
286  DenseMap<Value*, LatticeVal>::const_iterator I = ValueState.find(V);
287  assert(I != ValueState.end() && "V is not in valuemap!");
288  return I->second;
289  }
290 
291  /// getTrackedRetVals - Get the inferred return value map.
292  ///
293  const DenseMap<Function*, LatticeVal> &getTrackedRetVals() {
294  return TrackedRetVals;
295  }
296 
297  /// getTrackedGlobals - Get and return the set of inferred initializers for
298  /// global variables.
299  const DenseMap<GlobalVariable*, LatticeVal> &getTrackedGlobals() {
300  return TrackedGlobals;
301  }
302 
303  /// getMRVFunctionsTracked - Get the set of functions which return multiple
304  /// values tracked by the pass.
305  const SmallPtrSet<Function *, 16> getMRVFunctionsTracked() {
306  return MRVFunctionsTracked;
307  }
308 
309  void markOverdefined(Value *V) {
310  assert(!V->getType()->isStructTy() &&
311  "structs should use markAnythingOverdefined");
312  markOverdefined(ValueState[V], V);
313  }
314 
315  /// markAnythingOverdefined - Mark the specified value overdefined. This
316  /// works with both scalars and structs.
317  void markAnythingOverdefined(Value *V) {
318  if (auto *STy = dyn_cast<StructType>(V->getType()))
319  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
320  markOverdefined(getStructValueState(V, i), V);
321  else
322  markOverdefined(V);
323  }
324 
325  // isStructLatticeConstant - Return true if all the lattice values
326  // corresponding to elements of the structure are not overdefined,
327  // false otherwise.
328  bool isStructLatticeConstant(Function *F, StructType *STy) {
329  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
330  const auto &It = TrackedMultipleRetVals.find(std::make_pair(F, i));
331  assert(It != TrackedMultipleRetVals.end());
332  LatticeVal LV = It->second;
333  if (LV.isOverdefined())
334  return false;
335  }
336  return true;
337  }
338 
339 private:
340  // pushToWorkList - Helper for markConstant/markForcedConstant/markOverdefined
341  void pushToWorkList(LatticeVal &IV, Value *V) {
342  if (IV.isOverdefined())
343  return OverdefinedInstWorkList.push_back(V);
344  InstWorkList.push_back(V);
345  }
346 
347  // markConstant - Make a value be marked as "constant". If the value
348  // is not already a constant, add it to the instruction work list so that
349  // the users of the instruction are updated later.
350  //
351  void markConstant(LatticeVal &IV, Value *V, Constant *C) {
352  if (!IV.markConstant(C)) return;
353  DEBUG(dbgs() << "markConstant: " << *C << ": " << *V << '\n');
354  pushToWorkList(IV, V);
355  }
356 
357  void markConstant(Value *V, Constant *C) {
358  assert(!V->getType()->isStructTy() && "structs should use mergeInValue");
359  markConstant(ValueState[V], V, C);
360  }
361 
362  void markForcedConstant(Value *V, Constant *C) {
363  assert(!V->getType()->isStructTy() && "structs should use mergeInValue");
364  LatticeVal &IV = ValueState[V];
365  IV.markForcedConstant(C);
366  DEBUG(dbgs() << "markForcedConstant: " << *C << ": " << *V << '\n');
367  pushToWorkList(IV, V);
368  }
369 
370 
371  // markOverdefined - Make a value be marked as "overdefined". If the
372  // value is not already overdefined, add it to the overdefined instruction
373  // work list so that the users of the instruction are updated later.
374  void markOverdefined(LatticeVal &IV, Value *V) {
375  if (!IV.markOverdefined()) return;
376 
377  DEBUG(dbgs() << "markOverdefined: ";
378  if (auto *F = dyn_cast<Function>(V))
379  dbgs() << "Function '" << F->getName() << "'\n";
380  else
381  dbgs() << *V << '\n');
382  // Only instructions go on the work list
383  pushToWorkList(IV, V);
384  }
385 
386  void mergeInValue(LatticeVal &IV, Value *V, LatticeVal MergeWithV) {
387  if (IV.isOverdefined() || MergeWithV.isUnknown())
388  return; // Noop.
389  if (MergeWithV.isOverdefined())
390  return markOverdefined(IV, V);
391  if (IV.isUnknown())
392  return markConstant(IV, V, MergeWithV.getConstant());
393  if (IV.getConstant() != MergeWithV.getConstant())
394  return markOverdefined(IV, V);
395  }
396 
397  void mergeInValue(Value *V, LatticeVal MergeWithV) {
398  assert(!V->getType()->isStructTy() &&
399  "non-structs should use markConstant");
400  mergeInValue(ValueState[V], V, MergeWithV);
401  }
402 
403 
404  /// getValueState - Return the LatticeVal object that corresponds to the
405  /// value. This function handles the case when the value hasn't been seen yet
406  /// by properly seeding constants etc.
407  LatticeVal &getValueState(Value *V) {
408  assert(!V->getType()->isStructTy() && "Should use getStructValueState");
409 
410  std::pair<DenseMap<Value*, LatticeVal>::iterator, bool> I =
411  ValueState.insert(std::make_pair(V, LatticeVal()));
412  LatticeVal &LV = I.first->second;
413 
414  if (!I.second)
415  return LV; // Common case, already in the map.
416 
417  if (auto *C = dyn_cast<Constant>(V)) {
418  // Undef values remain unknown.
419  if (!isa<UndefValue>(V))
420  LV.markConstant(C); // Constants are constant
421  }
422 
423  // All others are underdefined by default.
424  return LV;
425  }
426 
427  /// getStructValueState - Return the LatticeVal object that corresponds to the
428  /// value/field pair. This function handles the case when the value hasn't
429  /// been seen yet by properly seeding constants etc.
430  LatticeVal &getStructValueState(Value *V, unsigned i) {
431  assert(V->getType()->isStructTy() && "Should use getValueState");
432  assert(i < cast<StructType>(V->getType())->getNumElements() &&
433  "Invalid element #");
434 
435  std::pair<DenseMap<std::pair<Value*, unsigned>, LatticeVal>::iterator,
436  bool> I = StructValueState.insert(
437  std::make_pair(std::make_pair(V, i), LatticeVal()));
438  LatticeVal &LV = I.first->second;
439 
440  if (!I.second)
441  return LV; // Common case, already in the map.
442 
443  if (auto *C = dyn_cast<Constant>(V)) {
444  Constant *Elt = C->getAggregateElement(i);
445 
446  if (!Elt)
447  LV.markOverdefined(); // Unknown sort of constant.
448  else if (isa<UndefValue>(Elt))
449  ; // Undef values remain unknown.
450  else
451  LV.markConstant(Elt); // Constants are constant.
452  }
453 
454  // All others are underdefined by default.
455  return LV;
456  }
457 
458 
459  /// markEdgeExecutable - Mark a basic block as executable, adding it to the BB
460  /// work list if it is not already executable.
461  void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
462  if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
463  return; // This edge is already known to be executable!
464 
465  if (!MarkBlockExecutable(Dest)) {
466  // If the destination is already executable, we just made an *edge*
467  // feasible that wasn't before. Revisit the PHI nodes in the block
468  // because they have potentially new operands.
469  DEBUG(dbgs() << "Marking Edge Executable: " << Source->getName()
470  << " -> " << Dest->getName() << '\n');
471 
472  PHINode *PN;
473  for (BasicBlock::iterator I = Dest->begin();
474  (PN = dyn_cast<PHINode>(I)); ++I)
475  visitPHINode(*PN);
476  }
477  }
478 
479  // getFeasibleSuccessors - Return a vector of booleans to indicate which
480  // successors are reachable from a given terminator instruction.
481  //
482  void getFeasibleSuccessors(TerminatorInst &TI, SmallVectorImpl<bool> &Succs);
483 
484  // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
485  // block to the 'To' basic block is currently feasible.
486  //
487  bool isEdgeFeasible(BasicBlock *From, BasicBlock *To);
488 
489  // OperandChangedState - This method is invoked on all of the users of an
490  // instruction that was just changed state somehow. Based on this
491  // information, we need to update the specified user of this instruction.
492  //
493  void OperandChangedState(Instruction *I) {
494  if (BBExecutable.count(I->getParent())) // Inst is executable?
495  visit(*I);
496  }
497 
498 private:
499  friend class InstVisitor<SCCPSolver>;
500 
501  // visit implementations - Something changed in this instruction. Either an
502  // operand made a transition, or the instruction is newly executable. Change
503  // the value type of I to reflect these changes if appropriate.
504  void visitPHINode(PHINode &I);
505 
506  // Terminators
507  void visitReturnInst(ReturnInst &I);
508  void visitTerminatorInst(TerminatorInst &TI);
509 
510  void visitCastInst(CastInst &I);
511  void visitSelectInst(SelectInst &I);
512  void visitBinaryOperator(Instruction &I);
513  void visitCmpInst(CmpInst &I);
514  void visitExtractValueInst(ExtractValueInst &EVI);
515  void visitInsertValueInst(InsertValueInst &IVI);
516  void visitLandingPadInst(LandingPadInst &I) { markAnythingOverdefined(&I); }
517  void visitFuncletPadInst(FuncletPadInst &FPI) {
518  markAnythingOverdefined(&FPI);
519  }
520  void visitCatchSwitchInst(CatchSwitchInst &CPI) {
521  markAnythingOverdefined(&CPI);
522  visitTerminatorInst(CPI);
523  }
524 
525  // Instructions that cannot be folded away.
526  void visitStoreInst (StoreInst &I);
527  void visitLoadInst (LoadInst &I);
528  void visitGetElementPtrInst(GetElementPtrInst &I);
529  void visitCallInst (CallInst &I) {
530  visitCallSite(&I);
531  }
532  void visitInvokeInst (InvokeInst &II) {
533  visitCallSite(&II);
534  visitTerminatorInst(II);
535  }
536  void visitCallSite (CallSite CS);
537  void visitResumeInst (TerminatorInst &I) { /*returns void*/ }
538  void visitUnreachableInst(TerminatorInst &I) { /*returns void*/ }
539  void visitFenceInst (FenceInst &I) { /*returns void*/ }
540  void visitAtomicCmpXchgInst(AtomicCmpXchgInst &I) {
541  markAnythingOverdefined(&I);
542  }
543  void visitAtomicRMWInst (AtomicRMWInst &I) { markOverdefined(&I); }
544  void visitAllocaInst (Instruction &I) { markOverdefined(&I); }
545  void visitVAArgInst (Instruction &I) { markAnythingOverdefined(&I); }
546 
547  void visitInstruction(Instruction &I) {
548  // If a new instruction is added to LLVM that we don't handle.
549  DEBUG(dbgs() << "SCCP: Don't know how to handle: " << I << '\n');
550  markAnythingOverdefined(&I); // Just in case
551  }
552 };
553 
554 } // end anonymous namespace
555 
556 
557 // getFeasibleSuccessors - Return a vector of booleans to indicate which
558 // successors are reachable from a given terminator instruction.
559 //
560 void SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI,
561  SmallVectorImpl<bool> &Succs) {
562  Succs.resize(TI.getNumSuccessors());
563  if (auto *BI = dyn_cast<BranchInst>(&TI)) {
564  if (BI->isUnconditional()) {
565  Succs[0] = true;
566  return;
567  }
568 
569  LatticeVal BCValue = getValueState(BI->getCondition());
570  ConstantInt *CI = BCValue.getConstantInt();
571  if (!CI) {
572  // Overdefined condition variables, and branches on unfoldable constant
573  // conditions, mean the branch could go either way.
574  if (!BCValue.isUnknown())
575  Succs[0] = Succs[1] = true;
576  return;
577  }
578 
579  // Constant condition variables mean the branch can only go a single way.
580  Succs[CI->isZero()] = true;
581  return;
582  }
583 
584  // Unwinding instructions successors are always executable.
585  if (TI.isExceptional()) {
586  Succs.assign(TI.getNumSuccessors(), true);
587  return;
588  }
589 
590  if (auto *SI = dyn_cast<SwitchInst>(&TI)) {
591  if (!SI->getNumCases()) {
592  Succs[0] = true;
593  return;
594  }
595  LatticeVal SCValue = getValueState(SI->getCondition());
596  ConstantInt *CI = SCValue.getConstantInt();
597 
598  if (!CI) { // Overdefined or unknown condition?
599  // All destinations are executable!
600  if (!SCValue.isUnknown())
601  Succs.assign(TI.getNumSuccessors(), true);
602  return;
603  }
604 
605  Succs[SI->findCaseValue(CI).getSuccessorIndex()] = true;
606  return;
607  }
608 
609  // TODO: This could be improved if the operand is a [cast of a] BlockAddress.
610  if (isa<IndirectBrInst>(&TI)) {
611  // Just mark all destinations executable!
612  Succs.assign(TI.getNumSuccessors(), true);
613  return;
614  }
615 
616  DEBUG(dbgs() << "Unknown terminator instruction: " << TI << '\n');
617  llvm_unreachable("SCCP: Don't know how to handle this terminator!");
618 }
619 
620 
621 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
622 // block to the 'To' basic block is currently feasible.
623 //
624 bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
625  assert(BBExecutable.count(To) && "Dest should always be alive!");
626 
627  // Make sure the source basic block is executable!!
628  if (!BBExecutable.count(From)) return false;
629 
630  // Check to make sure this edge itself is actually feasible now.
631  TerminatorInst *TI = From->getTerminator();
632  if (auto *BI = dyn_cast<BranchInst>(TI)) {
633  if (BI->isUnconditional())
634  return true;
635 
636  LatticeVal BCValue = getValueState(BI->getCondition());
637 
638  // Overdefined condition variables mean the branch could go either way,
639  // undef conditions mean that neither edge is feasible yet.
640  ConstantInt *CI = BCValue.getConstantInt();
641  if (!CI)
642  return !BCValue.isUnknown();
643 
644  // Constant condition variables mean the branch can only go a single way.
645  return BI->getSuccessor(CI->isZero()) == To;
646  }
647 
648  // Unwinding instructions successors are always executable.
649  if (TI->isExceptional())
650  return true;
651 
652  if (auto *SI = dyn_cast<SwitchInst>(TI)) {
653  if (SI->getNumCases() < 1)
654  return true;
655 
656  LatticeVal SCValue = getValueState(SI->getCondition());
657  ConstantInt *CI = SCValue.getConstantInt();
658 
659  if (!CI)
660  return !SCValue.isUnknown();
661 
662  return SI->findCaseValue(CI).getCaseSuccessor() == To;
663  }
664 
665  // Just mark all destinations executable!
666  // TODO: This could be improved if the operand is a [cast of a] BlockAddress.
667  if (isa<IndirectBrInst>(TI))
668  return true;
669 
670  DEBUG(dbgs() << "Unknown terminator instruction: " << *TI << '\n');
671  llvm_unreachable("SCCP: Don't know how to handle this terminator!");
672 }
673 
674 // visit Implementations - Something changed in this instruction, either an
675 // operand made a transition, or the instruction is newly executable. Change
676 // the value type of I to reflect these changes if appropriate. This method
677 // makes sure to do the following actions:
678 //
679 // 1. If a phi node merges two constants in, and has conflicting value coming
680 // from different branches, or if the PHI node merges in an overdefined
681 // value, then the PHI node becomes overdefined.
682 // 2. If a phi node merges only constants in, and they all agree on value, the
683 // PHI node becomes a constant value equal to that.
684 // 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant
685 // 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined
686 // 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined
687 // 6. If a conditional branch has a value that is constant, make the selected
688 // destination executable
689 // 7. If a conditional branch has a value that is overdefined, make all
690 // successors executable.
691 //
692 void SCCPSolver::visitPHINode(PHINode &PN) {
693  // If this PN returns a struct, just mark the result overdefined.
694  // TODO: We could do a lot better than this if code actually uses this.
695  if (PN.getType()->isStructTy())
696  return markAnythingOverdefined(&PN);
697 
698  if (getValueState(&PN).isOverdefined())
699  return; // Quick exit
700 
701  // Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
702  // and slow us down a lot. Just mark them overdefined.
703  if (PN.getNumIncomingValues() > 64)
704  return markOverdefined(&PN);
705 
706  // Look at all of the executable operands of the PHI node. If any of them
707  // are overdefined, the PHI becomes overdefined as well. If they are all
708  // constant, and they agree with each other, the PHI becomes the identical
709  // constant. If they are constant and don't agree, the PHI is overdefined.
710  // If there are no executable operands, the PHI remains unknown.
711  //
712  Constant *OperandVal = nullptr;
713  for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
714  LatticeVal IV = getValueState(PN.getIncomingValue(i));
715  if (IV.isUnknown()) continue; // Doesn't influence PHI node.
716 
717  if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent()))
718  continue;
719 
720  if (IV.isOverdefined()) // PHI node becomes overdefined!
721  return markOverdefined(&PN);
722 
723  if (!OperandVal) { // Grab the first value.
724  OperandVal = IV.getConstant();
725  continue;
726  }
727 
728  // There is already a reachable operand. If we conflict with it,
729  // then the PHI node becomes overdefined. If we agree with it, we
730  // can continue on.
731 
732  // Check to see if there are two different constants merging, if so, the PHI
733  // node is overdefined.
734  if (IV.getConstant() != OperandVal)
735  return markOverdefined(&PN);
736  }
737 
738  // If we exited the loop, this means that the PHI node only has constant
739  // arguments that agree with each other(and OperandVal is the constant) or
740  // OperandVal is null because there are no defined incoming arguments. If
741  // this is the case, the PHI remains unknown.
742  //
743  if (OperandVal)
744  markConstant(&PN, OperandVal); // Acquire operand value
745 }
746 
747 void SCCPSolver::visitReturnInst(ReturnInst &I) {
748  if (I.getNumOperands() == 0) return; // ret void
749 
750  Function *F = I.getParent()->getParent();
751  Value *ResultOp = I.getOperand(0);
752 
753  // If we are tracking the return value of this function, merge it in.
754  if (!TrackedRetVals.empty() && !ResultOp->getType()->isStructTy()) {
756  TrackedRetVals.find(F);
757  if (TFRVI != TrackedRetVals.end()) {
758  mergeInValue(TFRVI->second, F, getValueState(ResultOp));
759  return;
760  }
761  }
762 
763  // Handle functions that return multiple values.
764  if (!TrackedMultipleRetVals.empty()) {
765  if (auto *STy = dyn_cast<StructType>(ResultOp->getType()))
766  if (MRVFunctionsTracked.count(F))
767  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
768  mergeInValue(TrackedMultipleRetVals[std::make_pair(F, i)], F,
769  getStructValueState(ResultOp, i));
770 
771  }
772 }
773 
774 void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) {
775  SmallVector<bool, 16> SuccFeasible;
776  getFeasibleSuccessors(TI, SuccFeasible);
777 
778  BasicBlock *BB = TI.getParent();
779 
780  // Mark all feasible successors executable.
781  for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
782  if (SuccFeasible[i])
783  markEdgeExecutable(BB, TI.getSuccessor(i));
784 }
785 
786 void SCCPSolver::visitCastInst(CastInst &I) {
787  LatticeVal OpSt = getValueState(I.getOperand(0));
788  if (OpSt.isOverdefined()) // Inherit overdefinedness of operand
789  markOverdefined(&I);
790  else if (OpSt.isConstant()) {
791  // Fold the constant as we build.
792  Constant *C = ConstantFoldCastOperand(I.getOpcode(), OpSt.getConstant(),
793  I.getType(), DL);
794  if (isa<UndefValue>(C))
795  return;
796  // Propagate constant value
797  markConstant(&I, C);
798  }
799 }
800 
801 
802 void SCCPSolver::visitExtractValueInst(ExtractValueInst &EVI) {
803  // If this returns a struct, mark all elements over defined, we don't track
804  // structs in structs.
805  if (EVI.getType()->isStructTy())
806  return markAnythingOverdefined(&EVI);
807 
808  // If this is extracting from more than one level of struct, we don't know.
809  if (EVI.getNumIndices() != 1)
810  return markOverdefined(&EVI);
811 
812  Value *AggVal = EVI.getAggregateOperand();
813  if (AggVal->getType()->isStructTy()) {
814  unsigned i = *EVI.idx_begin();
815  LatticeVal EltVal = getStructValueState(AggVal, i);
816  mergeInValue(getValueState(&EVI), &EVI, EltVal);
817  } else {
818  // Otherwise, must be extracting from an array.
819  return markOverdefined(&EVI);
820  }
821 }
822 
823 void SCCPSolver::visitInsertValueInst(InsertValueInst &IVI) {
824  auto *STy = dyn_cast<StructType>(IVI.getType());
825  if (!STy)
826  return markOverdefined(&IVI);
827 
828  // If this has more than one index, we can't handle it, drive all results to
829  // undef.
830  if (IVI.getNumIndices() != 1)
831  return markAnythingOverdefined(&IVI);
832 
833  Value *Aggr = IVI.getAggregateOperand();
834  unsigned Idx = *IVI.idx_begin();
835 
836  // Compute the result based on what we're inserting.
837  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
838  // This passes through all values that aren't the inserted element.
839  if (i != Idx) {
840  LatticeVal EltVal = getStructValueState(Aggr, i);
841  mergeInValue(getStructValueState(&IVI, i), &IVI, EltVal);
842  continue;
843  }
844 
845  Value *Val = IVI.getInsertedValueOperand();
846  if (Val->getType()->isStructTy())
847  // We don't track structs in structs.
848  markOverdefined(getStructValueState(&IVI, i), &IVI);
849  else {
850  LatticeVal InVal = getValueState(Val);
851  mergeInValue(getStructValueState(&IVI, i), &IVI, InVal);
852  }
853  }
854 }
855 
856 void SCCPSolver::visitSelectInst(SelectInst &I) {
857  // If this select returns a struct, just mark the result overdefined.
858  // TODO: We could do a lot better than this if code actually uses this.
859  if (I.getType()->isStructTy())
860  return markAnythingOverdefined(&I);
861 
862  LatticeVal CondValue = getValueState(I.getCondition());
863  if (CondValue.isUnknown())
864  return;
865 
866  if (ConstantInt *CondCB = CondValue.getConstantInt()) {
867  Value *OpVal = CondCB->isZero() ? I.getFalseValue() : I.getTrueValue();
868  mergeInValue(&I, getValueState(OpVal));
869  return;
870  }
871 
872  // Otherwise, the condition is overdefined or a constant we can't evaluate.
873  // See if we can produce something better than overdefined based on the T/F
874  // value.
875  LatticeVal TVal = getValueState(I.getTrueValue());
876  LatticeVal FVal = getValueState(I.getFalseValue());
877 
878  // select ?, C, C -> C.
879  if (TVal.isConstant() && FVal.isConstant() &&
880  TVal.getConstant() == FVal.getConstant())
881  return markConstant(&I, FVal.getConstant());
882 
883  if (TVal.isUnknown()) // select ?, undef, X -> X.
884  return mergeInValue(&I, FVal);
885  if (FVal.isUnknown()) // select ?, X, undef -> X.
886  return mergeInValue(&I, TVal);
887  markOverdefined(&I);
888 }
889 
890 // Handle Binary Operators.
891 void SCCPSolver::visitBinaryOperator(Instruction &I) {
892  LatticeVal V1State = getValueState(I.getOperand(0));
893  LatticeVal V2State = getValueState(I.getOperand(1));
894 
895  LatticeVal &IV = ValueState[&I];
896  if (IV.isOverdefined()) return;
897 
898  if (V1State.isConstant() && V2State.isConstant()) {
899  Constant *C = ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
900  V2State.getConstant());
901  // X op Y -> undef.
902  if (isa<UndefValue>(C))
903  return;
904  return markConstant(IV, &I, C);
905  }
906 
907  // If something is undef, wait for it to resolve.
908  if (!V1State.isOverdefined() && !V2State.isOverdefined())
909  return;
910 
911  // Otherwise, one of our operands is overdefined. Try to produce something
912  // better than overdefined with some tricks.
913 
914  // If this is an AND or OR with 0 or -1, it doesn't matter that the other
915  // operand is overdefined.
916  if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Mul ||
917  I.getOpcode() == Instruction::Or) {
918  LatticeVal *NonOverdefVal = nullptr;
919  if (!V1State.isOverdefined())
920  NonOverdefVal = &V1State;
921  else if (!V2State.isOverdefined())
922  NonOverdefVal = &V2State;
923 
924  if (NonOverdefVal) {
925  if (NonOverdefVal->isUnknown())
926  return;
927 
928  if (I.getOpcode() == Instruction::And ||
929  I.getOpcode() == Instruction::Mul) {
930  // X and 0 = 0
931  // X * 0 = 0
932  if (NonOverdefVal->getConstant()->isNullValue())
933  return markConstant(IV, &I, NonOverdefVal->getConstant());
934  } else {
935  // X or -1 = -1
936  if (ConstantInt *CI = NonOverdefVal->getConstantInt())
937  if (CI->isAllOnesValue())
938  return markConstant(IV, &I, NonOverdefVal->getConstant());
939  }
940  }
941  }
942 
943 
944  markOverdefined(&I);
945 }
946 
947 // Handle ICmpInst instruction.
948 void SCCPSolver::visitCmpInst(CmpInst &I) {
949  LatticeVal V1State = getValueState(I.getOperand(0));
950  LatticeVal V2State = getValueState(I.getOperand(1));
951 
952  LatticeVal &IV = ValueState[&I];
953  if (IV.isOverdefined()) return;
954 
955  if (V1State.isConstant() && V2State.isConstant()) {
957  I.getPredicate(), V1State.getConstant(), V2State.getConstant());
958  if (isa<UndefValue>(C))
959  return;
960  return markConstant(IV, &I, C);
961  }
962 
963  // If operands are still unknown, wait for it to resolve.
964  if (!V1State.isOverdefined() && !V2State.isOverdefined())
965  return;
966 
967  markOverdefined(&I);
968 }
969 
970 // Handle getelementptr instructions. If all operands are constants then we
971 // can turn this into a getelementptr ConstantExpr.
972 //
973 void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
974  if (ValueState[&I].isOverdefined()) return;
975 
976  SmallVector<Constant*, 8> Operands;
977  Operands.reserve(I.getNumOperands());
978 
979  for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
980  LatticeVal State = getValueState(I.getOperand(i));
981  if (State.isUnknown())
982  return; // Operands are not resolved yet.
983 
984  if (State.isOverdefined())
985  return markOverdefined(&I);
986 
987  assert(State.isConstant() && "Unknown state!");
988  Operands.push_back(State.getConstant());
989  }
990 
991  Constant *Ptr = Operands[0];
992  auto Indices = makeArrayRef(Operands.begin() + 1, Operands.end());
993  Constant *C =
995  if (isa<UndefValue>(C))
996  return;
997  markConstant(&I, C);
998 }
999 
1000 void SCCPSolver::visitStoreInst(StoreInst &SI) {
1001  // If this store is of a struct, ignore it.
1002  if (SI.getOperand(0)->getType()->isStructTy())
1003  return;
1004 
1005  if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
1006  return;
1007 
1008  GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
1009  DenseMap<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
1010  if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
1011 
1012  // Get the value we are storing into the global, then merge it.
1013  mergeInValue(I->second, GV, getValueState(SI.getOperand(0)));
1014  if (I->second.isOverdefined())
1015  TrackedGlobals.erase(I); // No need to keep tracking this!
1016 }
1017 
1018 
1019 // Handle load instructions. If the operand is a constant pointer to a constant
1020 // global, we can replace the load with the loaded constant value!
1021 void SCCPSolver::visitLoadInst(LoadInst &I) {
1022  // If this load is of a struct, just mark the result overdefined.
1023  if (I.getType()->isStructTy())
1024  return markAnythingOverdefined(&I);
1025 
1026  LatticeVal PtrVal = getValueState(I.getOperand(0));
1027  if (PtrVal.isUnknown()) return; // The pointer is not resolved yet!
1028 
1029  LatticeVal &IV = ValueState[&I];
1030  if (IV.isOverdefined()) return;
1031 
1032  if (!PtrVal.isConstant() || I.isVolatile())
1033  return markOverdefined(IV, &I);
1034 
1035  Constant *Ptr = PtrVal.getConstant();
1036 
1037  // load null is undefined.
1038  if (isa<ConstantPointerNull>(Ptr) && I.getPointerAddressSpace() == 0)
1039  return;
1040 
1041  // Transform load (constant global) into the value loaded.
1042  if (auto *GV = dyn_cast<GlobalVariable>(Ptr)) {
1043  if (!TrackedGlobals.empty()) {
1044  // If we are tracking this global, merge in the known value for it.
1046  TrackedGlobals.find(GV);
1047  if (It != TrackedGlobals.end()) {
1048  mergeInValue(IV, &I, It->second);
1049  return;
1050  }
1051  }
1052  }
1053 
1054  // Transform load from a constant into a constant if possible.
1055  if (Constant *C = ConstantFoldLoadFromConstPtr(Ptr, I.getType(), DL)) {
1056  if (isa<UndefValue>(C))
1057  return;
1058  return markConstant(IV, &I, C);
1059  }
1060 
1061  // Otherwise we cannot say for certain what value this load will produce.
1062  // Bail out.
1063  markOverdefined(IV, &I);
1064 }
1065 
1066 void SCCPSolver::visitCallSite(CallSite CS) {
1067  Function *F = CS.getCalledFunction();
1068  Instruction *I = CS.getInstruction();
1069 
1070  // The common case is that we aren't tracking the callee, either because we
1071  // are not doing interprocedural analysis or the callee is indirect, or is
1072  // external. Handle these cases first.
1073  if (!F || F->isDeclaration()) {
1074 CallOverdefined:
1075  // Void return and not tracking callee, just bail.
1076  if (I->getType()->isVoidTy()) return;
1077 
1078  // Otherwise, if we have a single return value case, and if the function is
1079  // a declaration, maybe we can constant fold it.
1080  if (F && F->isDeclaration() && !I->getType()->isStructTy() &&
1081  canConstantFoldCallTo(F)) {
1082 
1083  SmallVector<Constant*, 8> Operands;
1084  for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
1085  AI != E; ++AI) {
1086  LatticeVal State = getValueState(*AI);
1087 
1088  if (State.isUnknown())
1089  return; // Operands are not resolved yet.
1090  if (State.isOverdefined())
1091  return markOverdefined(I);
1092  assert(State.isConstant() && "Unknown state!");
1093  Operands.push_back(State.getConstant());
1094  }
1095 
1096  if (getValueState(I).isOverdefined())
1097  return;
1098 
1099  // If we can constant fold this, mark the result of the call as a
1100  // constant.
1101  if (Constant *C = ConstantFoldCall(F, Operands, TLI)) {
1102  // call -> undef.
1103  if (isa<UndefValue>(C))
1104  return;
1105  return markConstant(I, C);
1106  }
1107  }
1108 
1109  // Otherwise, we don't know anything about this call, mark it overdefined.
1110  return markAnythingOverdefined(I);
1111  }
1112 
1113  // If this is a local function that doesn't have its address taken, mark its
1114  // entry block executable and merge in the actual arguments to the call into
1115  // the formal arguments of the function.
1116  if (!TrackingIncomingArguments.empty() && TrackingIncomingArguments.count(F)){
1117  MarkBlockExecutable(&F->front());
1118 
1119  // Propagate information from this call site into the callee.
1120  CallSite::arg_iterator CAI = CS.arg_begin();
1121  for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1122  AI != E; ++AI, ++CAI) {
1123  // If this argument is byval, and if the function is not readonly, there
1124  // will be an implicit copy formed of the input aggregate.
1125  if (AI->hasByValAttr() && !F->onlyReadsMemory()) {
1126  markOverdefined(&*AI);
1127  continue;
1128  }
1129 
1130  if (auto *STy = dyn_cast<StructType>(AI->getType())) {
1131  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1132  LatticeVal CallArg = getStructValueState(*CAI, i);
1133  mergeInValue(getStructValueState(&*AI, i), &*AI, CallArg);
1134  }
1135  } else {
1136  mergeInValue(&*AI, getValueState(*CAI));
1137  }
1138  }
1139  }
1140 
1141  // If this is a single/zero retval case, see if we're tracking the function.
1142  if (auto *STy = dyn_cast<StructType>(F->getReturnType())) {
1143  if (!MRVFunctionsTracked.count(F))
1144  goto CallOverdefined; // Not tracking this callee.
1145 
1146  // If we are tracking this callee, propagate the result of the function
1147  // into this call site.
1148  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
1149  mergeInValue(getStructValueState(I, i), I,
1150  TrackedMultipleRetVals[std::make_pair(F, i)]);
1151  } else {
1152  DenseMap<Function*, LatticeVal>::iterator TFRVI = TrackedRetVals.find(F);
1153  if (TFRVI == TrackedRetVals.end())
1154  goto CallOverdefined; // Not tracking this callee.
1155 
1156  // If so, propagate the return value of the callee into this call result.
1157  mergeInValue(I, TFRVI->second);
1158  }
1159 }
1160 
1161 void SCCPSolver::Solve() {
1162  // Process the work lists until they are empty!
1163  while (!BBWorkList.empty() || !InstWorkList.empty() ||
1164  !OverdefinedInstWorkList.empty()) {
1165  // Process the overdefined instruction's work list first, which drives other
1166  // things to overdefined more quickly.
1167  while (!OverdefinedInstWorkList.empty()) {
1168  Value *I = OverdefinedInstWorkList.pop_back_val();
1169 
1170  DEBUG(dbgs() << "\nPopped off OI-WL: " << *I << '\n');
1171 
1172  // "I" got into the work list because it either made the transition from
1173  // bottom to constant, or to overdefined.
1174  //
1175  // Anything on this worklist that is overdefined need not be visited
1176  // since all of its users will have already been marked as overdefined
1177  // Update all of the users of this instruction's value.
1178  //
1179  for (User *U : I->users())
1180  if (auto *UI = dyn_cast<Instruction>(U))
1181  OperandChangedState(UI);
1182  }
1183 
1184  // Process the instruction work list.
1185  while (!InstWorkList.empty()) {
1186  Value *I = InstWorkList.pop_back_val();
1187 
1188  DEBUG(dbgs() << "\nPopped off I-WL: " << *I << '\n');
1189 
1190  // "I" got into the work list because it made the transition from undef to
1191  // constant.
1192  //
1193  // Anything on this worklist that is overdefined need not be visited
1194  // since all of its users will have already been marked as overdefined.
1195  // Update all of the users of this instruction's value.
1196  //
1197  if (I->getType()->isStructTy() || !getValueState(I).isOverdefined())
1198  for (User *U : I->users())
1199  if (auto *UI = dyn_cast<Instruction>(U))
1200  OperandChangedState(UI);
1201  }
1202 
1203  // Process the basic block work list.
1204  while (!BBWorkList.empty()) {
1205  BasicBlock *BB = BBWorkList.back();
1206  BBWorkList.pop_back();
1207 
1208  DEBUG(dbgs() << "\nPopped off BBWL: " << *BB << '\n');
1209 
1210  // Notify all instructions in this basic block that they are newly
1211  // executable.
1212  visit(BB);
1213  }
1214  }
1215 }
1216 
1217 /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
1218 /// that branches on undef values cannot reach any of their successors.
1219 /// However, this is not a safe assumption. After we solve dataflow, this
1220 /// method should be use to handle this. If this returns true, the solver
1221 /// should be rerun.
1222 ///
1223 /// This method handles this by finding an unresolved branch and marking it one
1224 /// of the edges from the block as being feasible, even though the condition
1225 /// doesn't say it would otherwise be. This allows SCCP to find the rest of the
1226 /// CFG and only slightly pessimizes the analysis results (by marking one,
1227 /// potentially infeasible, edge feasible). This cannot usefully modify the
1228 /// constraints on the condition of the branch, as that would impact other users
1229 /// of the value.
1230 ///
1231 /// This scan also checks for values that use undefs, whose results are actually
1232 /// defined. For example, 'zext i8 undef to i32' should produce all zeros
1233 /// conservatively, as "(zext i8 X -> i32) & 0xFF00" must always return zero,
1234 /// even if X isn't defined.
1235 bool SCCPSolver::ResolvedUndefsIn(Function &F) {
1236  for (BasicBlock &BB : F) {
1237  if (!BBExecutable.count(&BB))
1238  continue;
1239 
1240  for (Instruction &I : BB) {
1241  // Look for instructions which produce undef values.
1242  if (I.getType()->isVoidTy()) continue;
1243 
1244  if (auto *STy = dyn_cast<StructType>(I.getType())) {
1245  // Only a few things that can be structs matter for undef.
1246 
1247  // Tracked calls must never be marked overdefined in ResolvedUndefsIn.
1248  if (CallSite CS = CallSite(&I))
1249  if (Function *F = CS.getCalledFunction())
1250  if (MRVFunctionsTracked.count(F))
1251  continue;
1252 
1253  // extractvalue and insertvalue don't need to be marked; they are
1254  // tracked as precisely as their operands.
1255  if (isa<ExtractValueInst>(I) || isa<InsertValueInst>(I))
1256  continue;
1257 
1258  // Send the results of everything else to overdefined. We could be
1259  // more precise than this but it isn't worth bothering.
1260  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1261  LatticeVal &LV = getStructValueState(&I, i);
1262  if (LV.isUnknown())
1263  markOverdefined(LV, &I);
1264  }
1265  continue;
1266  }
1267 
1268  LatticeVal &LV = getValueState(&I);
1269  if (!LV.isUnknown()) continue;
1270 
1271  // extractvalue is safe; check here because the argument is a struct.
1272  if (isa<ExtractValueInst>(I))
1273  continue;
1274 
1275  // Compute the operand LatticeVals, for convenience below.
1276  // Anything taking a struct is conservatively assumed to require
1277  // overdefined markings.
1278  if (I.getOperand(0)->getType()->isStructTy()) {
1279  markOverdefined(&I);
1280  return true;
1281  }
1282  LatticeVal Op0LV = getValueState(I.getOperand(0));
1283  LatticeVal Op1LV;
1284  if (I.getNumOperands() == 2) {
1285  if (I.getOperand(1)->getType()->isStructTy()) {
1286  markOverdefined(&I);
1287  return true;
1288  }
1289 
1290  Op1LV = getValueState(I.getOperand(1));
1291  }
1292  // If this is an instructions whose result is defined even if the input is
1293  // not fully defined, propagate the information.
1294  Type *ITy = I.getType();
1295  switch (I.getOpcode()) {
1296  case Instruction::Add:
1297  case Instruction::Sub:
1298  case Instruction::Trunc:
1299  case Instruction::FPTrunc:
1300  case Instruction::BitCast:
1301  break; // Any undef -> undef
1302  case Instruction::FSub:
1303  case Instruction::FAdd:
1304  case Instruction::FMul:
1305  case Instruction::FDiv:
1306  case Instruction::FRem:
1307  // Floating-point binary operation: be conservative.
1308  if (Op0LV.isUnknown() && Op1LV.isUnknown())
1309  markForcedConstant(&I, Constant::getNullValue(ITy));
1310  else
1311  markOverdefined(&I);
1312  return true;
1313  case Instruction::ZExt:
1314  case Instruction::SExt:
1315  case Instruction::FPToUI:
1316  case Instruction::FPToSI:
1317  case Instruction::FPExt:
1318  case Instruction::PtrToInt:
1319  case Instruction::IntToPtr:
1320  case Instruction::SIToFP:
1321  case Instruction::UIToFP:
1322  // undef -> 0; some outputs are impossible
1323  markForcedConstant(&I, Constant::getNullValue(ITy));
1324  return true;
1325  case Instruction::Mul:
1326  case Instruction::And:
1327  // Both operands undef -> undef
1328  if (Op0LV.isUnknown() && Op1LV.isUnknown())
1329  break;
1330  // undef * X -> 0. X could be zero.
1331  // undef & X -> 0. X could be zero.
1332  markForcedConstant(&I, Constant::getNullValue(ITy));
1333  return true;
1334 
1335  case Instruction::Or:
1336  // Both operands undef -> undef
1337  if (Op0LV.isUnknown() && Op1LV.isUnknown())
1338  break;
1339  // undef | X -> -1. X could be -1.
1340  markForcedConstant(&I, Constant::getAllOnesValue(ITy));
1341  return true;
1342 
1343  case Instruction::Xor:
1344  // undef ^ undef -> 0; strictly speaking, this is not strictly
1345  // necessary, but we try to be nice to people who expect this
1346  // behavior in simple cases
1347  if (Op0LV.isUnknown() && Op1LV.isUnknown()) {
1348  markForcedConstant(&I, Constant::getNullValue(ITy));
1349  return true;
1350  }
1351  // undef ^ X -> undef
1352  break;
1353 
1354  case Instruction::SDiv:
1355  case Instruction::UDiv:
1356  case Instruction::SRem:
1357  case Instruction::URem:
1358  // X / undef -> undef. No change.
1359  // X % undef -> undef. No change.
1360  if (Op1LV.isUnknown()) break;
1361 
1362  // X / 0 -> undef. No change.
1363  // X % 0 -> undef. No change.
1364  if (Op1LV.isConstant() && Op1LV.getConstant()->isZeroValue())
1365  break;
1366 
1367  // undef / X -> 0. X could be maxint.
1368  // undef % X -> 0. X could be 1.
1369  markForcedConstant(&I, Constant::getNullValue(ITy));
1370  return true;
1371 
1372  case Instruction::AShr:
1373  // X >>a undef -> undef.
1374  if (Op1LV.isUnknown()) break;
1375 
1376  // Shifting by the bitwidth or more is undefined.
1377  if (Op1LV.isConstant()) {
1378  if (auto *ShiftAmt = Op1LV.getConstantInt())
1379  if (ShiftAmt->getLimitedValue() >=
1380  ShiftAmt->getType()->getScalarSizeInBits())
1381  break;
1382  }
1383 
1384  // undef >>a X -> 0
1385  markForcedConstant(&I, Constant::getNullValue(ITy));
1386  return true;
1387  case Instruction::LShr:
1388  case Instruction::Shl:
1389  // X << undef -> undef.
1390  // X >> undef -> undef.
1391  if (Op1LV.isUnknown()) break;
1392 
1393  // Shifting by the bitwidth or more is undefined.
1394  if (Op1LV.isConstant()) {
1395  if (auto *ShiftAmt = Op1LV.getConstantInt())
1396  if (ShiftAmt->getLimitedValue() >=
1397  ShiftAmt->getType()->getScalarSizeInBits())
1398  break;
1399  }
1400 
1401  // undef << X -> 0
1402  // undef >> X -> 0
1403  markForcedConstant(&I, Constant::getNullValue(ITy));
1404  return true;
1405  case Instruction::Select:
1406  Op1LV = getValueState(I.getOperand(1));
1407  // undef ? X : Y -> X or Y. There could be commonality between X/Y.
1408  if (Op0LV.isUnknown()) {
1409  if (!Op1LV.isConstant()) // Pick the constant one if there is any.
1410  Op1LV = getValueState(I.getOperand(2));
1411  } else if (Op1LV.isUnknown()) {
1412  // c ? undef : undef -> undef. No change.
1413  Op1LV = getValueState(I.getOperand(2));
1414  if (Op1LV.isUnknown())
1415  break;
1416  // Otherwise, c ? undef : x -> x.
1417  } else {
1418  // Leave Op1LV as Operand(1)'s LatticeValue.
1419  }
1420 
1421  if (Op1LV.isConstant())
1422  markForcedConstant(&I, Op1LV.getConstant());
1423  else
1424  markOverdefined(&I);
1425  return true;
1426  case Instruction::Load:
1427  // A load here means one of two things: a load of undef from a global,
1428  // a load from an unknown pointer. Either way, having it return undef
1429  // is okay.
1430  break;
1431  case Instruction::ICmp:
1432  // X == undef -> undef. Other comparisons get more complicated.
1433  if (cast<ICmpInst>(&I)->isEquality())
1434  break;
1435  markOverdefined(&I);
1436  return true;
1437  case Instruction::Call:
1438  case Instruction::Invoke: {
1439  // There are two reasons a call can have an undef result
1440  // 1. It could be tracked.
1441  // 2. It could be constant-foldable.
1442  // Because of the way we solve return values, tracked calls must
1443  // never be marked overdefined in ResolvedUndefsIn.
1444  if (Function *F = CallSite(&I).getCalledFunction())
1445  if (TrackedRetVals.count(F))
1446  break;
1447 
1448  // If the call is constant-foldable, we mark it overdefined because
1449  // we do not know what return values are valid.
1450  markOverdefined(&I);
1451  return true;
1452  }
1453  default:
1454  // If we don't know what should happen here, conservatively mark it
1455  // overdefined.
1456  markOverdefined(&I);
1457  return true;
1458  }
1459  }
1460 
1461  // Check to see if we have a branch or switch on an undefined value. If so
1462  // we force the branch to go one way or the other to make the successor
1463  // values live. It doesn't really matter which way we force it.
1464  TerminatorInst *TI = BB.getTerminator();
1465  if (auto *BI = dyn_cast<BranchInst>(TI)) {
1466  if (!BI->isConditional()) continue;
1467  if (!getValueState(BI->getCondition()).isUnknown())
1468  continue;
1469 
1470  // If the input to SCCP is actually branch on undef, fix the undef to
1471  // false.
1472  if (isa<UndefValue>(BI->getCondition())) {
1473  BI->setCondition(ConstantInt::getFalse(BI->getContext()));
1474  markEdgeExecutable(&BB, TI->getSuccessor(1));
1475  return true;
1476  }
1477 
1478  // Otherwise, it is a branch on a symbolic value which is currently
1479  // considered to be undef. Handle this by forcing the input value to the
1480  // branch to false.
1481  markForcedConstant(BI->getCondition(),
1483  return true;
1484  }
1485 
1486  if (auto *SI = dyn_cast<SwitchInst>(TI)) {
1487  if (!SI->getNumCases() || !getValueState(SI->getCondition()).isUnknown())
1488  continue;
1489 
1490  // If the input to SCCP is actually switch on undef, fix the undef to
1491  // the first constant.
1492  if (isa<UndefValue>(SI->getCondition())) {
1493  SI->setCondition(SI->case_begin().getCaseValue());
1494  markEdgeExecutable(&BB, SI->case_begin().getCaseSuccessor());
1495  return true;
1496  }
1497 
1498  markForcedConstant(SI->getCondition(), SI->case_begin().getCaseValue());
1499  return true;
1500  }
1501  }
1502 
1503  return false;
1504 }
1505 
1506 static bool tryToReplaceWithConstant(SCCPSolver &Solver, Value *V) {
1507  Constant *Const = nullptr;
1508  if (V->getType()->isStructTy()) {
1509  std::vector<LatticeVal> IVs = Solver.getStructLatticeValueFor(V);
1510  if (any_of(IVs, [](const LatticeVal &LV) { return LV.isOverdefined(); }))
1511  return false;
1512  std::vector<Constant *> ConstVals;
1513  auto *ST = dyn_cast<StructType>(V->getType());
1514  for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) {
1515  LatticeVal V = IVs[i];
1516  ConstVals.push_back(V.isConstant()
1517  ? V.getConstant()
1518  : UndefValue::get(ST->getElementType(i)));
1519  }
1520  Const = ConstantStruct::get(ST, ConstVals);
1521  } else {
1522  LatticeVal IV = Solver.getLatticeValueFor(V);
1523  if (IV.isOverdefined())
1524  return false;
1525  Const = IV.isConstant() ? IV.getConstant() : UndefValue::get(V->getType());
1526  }
1527  assert(Const && "Constant is nullptr here!");
1528  DEBUG(dbgs() << " Constant: " << *Const << " = " << *V << '\n');
1529 
1530  // Replaces all of the uses of a variable with uses of the constant.
1531  V->replaceAllUsesWith(Const);
1532  return true;
1533 }
1534 
1535 // runSCCP() - Run the Sparse Conditional Constant Propagation algorithm,
1536 // and return true if the function was modified.
1537 //
1538 static bool runSCCP(Function &F, const DataLayout &DL,
1539  const TargetLibraryInfo *TLI) {
1540  DEBUG(dbgs() << "SCCP on function '" << F.getName() << "'\n");
1541  SCCPSolver Solver(DL, TLI);
1542 
1543  // Mark the first block of the function as being executable.
1544  Solver.MarkBlockExecutable(&F.front());
1545 
1546  // Mark all arguments to the function as being overdefined.
1547  for (Argument &AI : F.args())
1548  Solver.markAnythingOverdefined(&AI);
1549 
1550  // Solve for constants.
1551  bool ResolvedUndefs = true;
1552  while (ResolvedUndefs) {
1553  Solver.Solve();
1554  DEBUG(dbgs() << "RESOLVING UNDEFs\n");
1555  ResolvedUndefs = Solver.ResolvedUndefsIn(F);
1556  }
1557 
1558  bool MadeChanges = false;
1559 
1560  // If we decided that there are basic blocks that are dead in this function,
1561  // delete their contents now. Note that we cannot actually delete the blocks,
1562  // as we cannot modify the CFG of the function.
1563 
1564  for (BasicBlock &BB : F) {
1565  if (!Solver.isBlockExecutable(&BB)) {
1566  DEBUG(dbgs() << " BasicBlock Dead:" << BB);
1567 
1568  ++NumDeadBlocks;
1569  NumInstRemoved += removeAllNonTerminatorAndEHPadInstructions(&BB);
1570 
1571  MadeChanges = true;
1572  continue;
1573  }
1574 
1575  // Iterate over all of the instructions in a function, replacing them with
1576  // constants if we have found them to be of constant values.
1577  //
1578  for (BasicBlock::iterator BI = BB.begin(), E = BB.end(); BI != E;) {
1579  Instruction *Inst = &*BI++;
1580  if (Inst->getType()->isVoidTy() || isa<TerminatorInst>(Inst))
1581  continue;
1582 
1583  if (tryToReplaceWithConstant(Solver, Inst)) {
1584  if (isInstructionTriviallyDead(Inst))
1585  Inst->eraseFromParent();
1586  // Hey, we just changed something!
1587  MadeChanges = true;
1588  ++NumInstRemoved;
1589  }
1590  }
1591  }
1592 
1593  return MadeChanges;
1594 }
1595 
1597  const DataLayout &DL = F.getParent()->getDataLayout();
1598  auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
1599  if (!runSCCP(F, DL, &TLI))
1600  return PreservedAnalyses::all();
1601 
1602  auto PA = PreservedAnalyses();
1603  PA.preserve<GlobalsAA>();
1604  return PA;
1605 }
1606 
1607 namespace {
1608 //===--------------------------------------------------------------------===//
1609 //
1610 /// SCCP Class - This class uses the SCCPSolver to implement a per-function
1611 /// Sparse Conditional Constant Propagator.
1612 ///
1613 class SCCPLegacyPass : public FunctionPass {
1614 public:
1615  void getAnalysisUsage(AnalysisUsage &AU) const override {
1618  }
1619  static char ID; // Pass identification, replacement for typeid
1620  SCCPLegacyPass() : FunctionPass(ID) {
1622  }
1623 
1624  // runOnFunction - Run the Sparse Conditional Constant Propagation
1625  // algorithm, and return true if the function was modified.
1626  //
1627  bool runOnFunction(Function &F) override {
1628  if (skipFunction(F))
1629  return false;
1630  const DataLayout &DL = F.getParent()->getDataLayout();
1631  const TargetLibraryInfo *TLI =
1632  &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
1633  return runSCCP(F, DL, TLI);
1634  }
1635 };
1636 } // end anonymous namespace
1637 
1638 char SCCPLegacyPass::ID = 0;
1639 INITIALIZE_PASS_BEGIN(SCCPLegacyPass, "sccp",
1640  "Sparse Conditional Constant Propagation", false, false)
1642 INITIALIZE_PASS_END(SCCPLegacyPass, "sccp",
1643  "Sparse Conditional Constant Propagation", false, false)
1644 
1645 // createSCCPPass - This is the public interface to this file.
1646 FunctionPass *llvm::createSCCPPass() { return new SCCPLegacyPass(); }
1647 
1648 static bool AddressIsTaken(const GlobalValue *GV) {
1649  // Delete any dead constantexpr klingons.
1651 
1652  for (const Use &U : GV->uses()) {
1653  const User *UR = U.getUser();
1654  if (const auto *SI = dyn_cast<StoreInst>(UR)) {
1655  if (SI->getOperand(0) == GV || SI->isVolatile())
1656  return true; // Storing addr of GV.
1657  } else if (isa<InvokeInst>(UR) || isa<CallInst>(UR)) {
1658  // Make sure we are calling the function, not passing the address.
1659  ImmutableCallSite CS(cast<Instruction>(UR));
1660  if (!CS.isCallee(&U))
1661  return true;
1662  } else if (const auto *LI = dyn_cast<LoadInst>(UR)) {
1663  if (LI->isVolatile())
1664  return true;
1665  } else if (isa<BlockAddress>(UR)) {
1666  // blockaddress doesn't take the address of the function, it takes addr
1667  // of label.
1668  } else {
1669  return true;
1670  }
1671  }
1672  return false;
1673 }
1674 
1676  SmallPtrSet<Function *, 32> &AddressTakenFunctions,
1677  SmallVector<ReturnInst *, 8> &ReturnsToZap) {
1678  // We can only do this if we know that nothing else can call the function.
1679  if (!F.hasLocalLinkage() || AddressTakenFunctions.count(&F))
1680  return;
1681 
1682  for (BasicBlock &BB : F)
1683  if (auto *RI = dyn_cast<ReturnInst>(BB.getTerminator()))
1684  if (!isa<UndefValue>(RI->getOperand(0)))
1685  ReturnsToZap.push_back(RI);
1686 }
1687 
1688 static bool runIPSCCP(Module &M, const DataLayout &DL,
1689  const TargetLibraryInfo *TLI) {
1690  SCCPSolver Solver(DL, TLI);
1691 
1692  // AddressTakenFunctions - This set keeps track of the address-taken functions
1693  // that are in the input. As IPSCCP runs through and simplifies code,
1694  // functions that were address taken can end up losing their
1695  // address-taken-ness. Because of this, we keep track of their addresses from
1696  // the first pass so we can use them for the later simplification pass.
1697  SmallPtrSet<Function*, 32> AddressTakenFunctions;
1698 
1699  // Loop over all functions, marking arguments to those with their addresses
1700  // taken or that are external as overdefined.
1701  //
1702  for (Function &F : M) {
1703  if (F.isDeclaration())
1704  continue;
1705 
1706  // If this is an exact definition of this function, then we can propagate
1707  // information about its result into callsites of it.
1708  // Don't touch naked functions. They may contain asm returning a
1709  // value we don't see, so we may end up interprocedurally propagating
1710  // the return value incorrectly.
1711  if (F.hasExactDefinition() && !F.hasFnAttribute(Attribute::Naked))
1712  Solver.AddTrackedFunction(&F);
1713 
1714  // If this function only has direct calls that we can see, we can track its
1715  // arguments and return value aggressively, and can assume it is not called
1716  // unless we see evidence to the contrary.
1717  if (F.hasLocalLinkage()) {
1718  if (AddressIsTaken(&F))
1719  AddressTakenFunctions.insert(&F);
1720  else {
1721  Solver.AddArgumentTrackedFunction(&F);
1722  continue;
1723  }
1724  }
1725 
1726  // Assume the function is called.
1727  Solver.MarkBlockExecutable(&F.front());
1728 
1729  // Assume nothing about the incoming arguments.
1730  for (Argument &AI : F.args())
1731  Solver.markAnythingOverdefined(&AI);
1732  }
1733 
1734  // Loop over global variables. We inform the solver about any internal global
1735  // variables that do not have their 'addresses taken'. If they don't have
1736  // their addresses taken, we can propagate constants through them.
1737  for (GlobalVariable &G : M.globals())
1738  if (!G.isConstant() && G.hasLocalLinkage() && !AddressIsTaken(&G))
1739  Solver.TrackValueOfGlobalVariable(&G);
1740 
1741  // Solve for constants.
1742  bool ResolvedUndefs = true;
1743  while (ResolvedUndefs) {
1744  Solver.Solve();
1745 
1746  DEBUG(dbgs() << "RESOLVING UNDEFS\n");
1747  ResolvedUndefs = false;
1748  for (Function &F : M)
1749  ResolvedUndefs |= Solver.ResolvedUndefsIn(F);
1750  }
1751 
1752  bool MadeChanges = false;
1753 
1754  // Iterate over all of the instructions in the module, replacing them with
1755  // constants if we have found them to be of constant values.
1756  //
1757  SmallVector<BasicBlock*, 512> BlocksToErase;
1758 
1759  for (Function &F : M) {
1760  if (F.isDeclaration())
1761  continue;
1762 
1763  if (Solver.isBlockExecutable(&F.front())) {
1764  for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E;
1765  ++AI) {
1766  if (AI->use_empty())
1767  continue;
1768  if (tryToReplaceWithConstant(Solver, &*AI))
1769  ++IPNumArgsElimed;
1770  }
1771  }
1772 
1773  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1774  if (!Solver.isBlockExecutable(&*BB)) {
1775  DEBUG(dbgs() << " BasicBlock Dead:" << *BB);
1776 
1777  ++NumDeadBlocks;
1778  NumInstRemoved +=
1779  changeToUnreachable(BB->getFirstNonPHI(), /*UseLLVMTrap=*/false);
1780 
1781  MadeChanges = true;
1782 
1783  if (&*BB != &F.front())
1784  BlocksToErase.push_back(&*BB);
1785  continue;
1786  }
1787 
1788  for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1789  Instruction *Inst = &*BI++;
1790  if (Inst->getType()->isVoidTy())
1791  continue;
1792  if (tryToReplaceWithConstant(Solver, Inst)) {
1793  if (!isa<CallInst>(Inst) && !isa<TerminatorInst>(Inst))
1794  Inst->eraseFromParent();
1795  // Hey, we just changed something!
1796  MadeChanges = true;
1797  ++IPNumInstRemoved;
1798  }
1799  }
1800  }
1801 
1802  // Now that all instructions in the function are constant folded, erase dead
1803  // blocks, because we can now use ConstantFoldTerminator to get rid of
1804  // in-edges.
1805  for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) {
1806  // If there are any PHI nodes in this successor, drop entries for BB now.
1807  BasicBlock *DeadBB = BlocksToErase[i];
1808  for (Value::user_iterator UI = DeadBB->user_begin(),
1809  UE = DeadBB->user_end();
1810  UI != UE;) {
1811  // Grab the user and then increment the iterator early, as the user
1812  // will be deleted. Step past all adjacent uses from the same user.
1813  auto *I = dyn_cast<Instruction>(*UI);
1814  do { ++UI; } while (UI != UE && *UI == I);
1815 
1816  // Ignore blockaddress users; BasicBlock's dtor will handle them.
1817  if (!I) continue;
1818 
1819  bool Folded = ConstantFoldTerminator(I->getParent());
1820  if (!Folded) {
1821  // The constant folder may not have been able to fold the terminator
1822  // if this is a branch or switch on undef. Fold it manually as a
1823  // branch to the first successor.
1824 #ifndef NDEBUG
1825  if (auto *BI = dyn_cast<BranchInst>(I)) {
1826  assert(BI->isConditional() && isa<UndefValue>(BI->getCondition()) &&
1827  "Branch should be foldable!");
1828  } else if (auto *SI = dyn_cast<SwitchInst>(I)) {
1829  assert(isa<UndefValue>(SI->getCondition()) && "Switch should fold");
1830  } else {
1831  llvm_unreachable("Didn't fold away reference to block!");
1832  }
1833 #endif
1834 
1835  // Make this an uncond branch to the first successor.
1836  TerminatorInst *TI = I->getParent()->getTerminator();
1837  BranchInst::Create(TI->getSuccessor(0), TI);
1838 
1839  // Remove entries in successor phi nodes to remove edges.
1840  for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
1841  TI->getSuccessor(i)->removePredecessor(TI->getParent());
1842 
1843  // Remove the old terminator.
1844  TI->eraseFromParent();
1845  }
1846  }
1847 
1848  // Finally, delete the basic block.
1849  F.getBasicBlockList().erase(DeadBB);
1850  }
1851  BlocksToErase.clear();
1852  }
1853 
1854  // If we inferred constant or undef return values for a function, we replaced
1855  // all call uses with the inferred value. This means we don't need to bother
1856  // actually returning anything from the function. Replace all return
1857  // instructions with return undef.
1858  //
1859  // Do this in two stages: first identify the functions we should process, then
1860  // actually zap their returns. This is important because we can only do this
1861  // if the address of the function isn't taken. In cases where a return is the
1862  // last use of a function, the order of processing functions would affect
1863  // whether other functions are optimizable.
1864  SmallVector<ReturnInst*, 8> ReturnsToZap;
1865 
1866  const DenseMap<Function*, LatticeVal> &RV = Solver.getTrackedRetVals();
1867  for (const auto &I : RV) {
1868  Function *F = I.first;
1869  if (I.second.isOverdefined() || F->getReturnType()->isVoidTy())
1870  continue;
1871  findReturnsToZap(*F, AddressTakenFunctions, ReturnsToZap);
1872  }
1873 
1874  for (const auto &F : Solver.getMRVFunctionsTracked()) {
1875  assert(F->getReturnType()->isStructTy() &&
1876  "The return type should be a struct");
1877  StructType *STy = cast<StructType>(F->getReturnType());
1878  if (Solver.isStructLatticeConstant(F, STy))
1879  findReturnsToZap(*F, AddressTakenFunctions, ReturnsToZap);
1880  }
1881 
1882  // Zap all returns which we've identified as zap to change.
1883  for (unsigned i = 0, e = ReturnsToZap.size(); i != e; ++i) {
1884  Function *F = ReturnsToZap[i]->getParent()->getParent();
1885  ReturnsToZap[i]->setOperand(0, UndefValue::get(F->getReturnType()));
1886  }
1887 
1888  // If we inferred constant or undef values for globals variables, we can
1889  // delete the global and any stores that remain to it.
1890  const DenseMap<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
1892  E = TG.end(); I != E; ++I) {
1893  GlobalVariable *GV = I->first;
1894  assert(!I->second.isOverdefined() &&
1895  "Overdefined values should have been taken out of the map!");
1896  DEBUG(dbgs() << "Found that GV '" << GV->getName() << "' is constant!\n");
1897  while (!GV->use_empty()) {
1898  StoreInst *SI = cast<StoreInst>(GV->user_back());
1899  SI->eraseFromParent();
1900  }
1901  M.getGlobalList().erase(GV);
1902  ++IPNumGlobalConst;
1903  }
1904 
1905  return MadeChanges;
1906 }
1907 
1909  const DataLayout &DL = M.getDataLayout();
1910  auto &TLI = AM.getResult<TargetLibraryAnalysis>(M);
1911  if (!runIPSCCP(M, DL, &TLI))
1912  return PreservedAnalyses::all();
1913  return PreservedAnalyses::none();
1914 }
1915 
1916 namespace {
1917 //===--------------------------------------------------------------------===//
1918 //
1919 /// IPSCCP Class - This class implements interprocedural Sparse Conditional
1920 /// Constant Propagation.
1921 ///
1922 class IPSCCPLegacyPass : public ModulePass {
1923 public:
1924  static char ID;
1925 
1926  IPSCCPLegacyPass() : ModulePass(ID) {
1928  }
1929 
1930  bool runOnModule(Module &M) override {
1931  if (skipModule(M))
1932  return false;
1933  const DataLayout &DL = M.getDataLayout();
1934  const TargetLibraryInfo *TLI =
1935  &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
1936  return runIPSCCP(M, DL, TLI);
1937  }
1938 
1939  void getAnalysisUsage(AnalysisUsage &AU) const override {
1941  }
1942 };
1943 } // end anonymous namespace
1944 
1945 char IPSCCPLegacyPass::ID = 0;
1946 INITIALIZE_PASS_BEGIN(IPSCCPLegacyPass, "ipsccp",
1947  "Interprocedural Sparse Conditional Constant Propagation",
1948  false, false)
1950 INITIALIZE_PASS_END(IPSCCPLegacyPass, "ipsccp",
1951  "Interprocedural Sparse Conditional Constant Propagation",
1952  false, false)
1953 
1954 // createIPSCCPPass - This is the public interface to this file.
1955 ModulePass *llvm::createIPSCCPPass() { return new IPSCCPLegacyPass(); }
Legacy wrapper pass to provide the GlobalsAAResult object.
Constant * ConstantFoldCastOperand(unsigned Opcode, Constant *C, Type *DestTy, const DataLayout &DL)
Attempt to constant fold a cast with the specified operand.
IterTy arg_end() const
Definition: CallSite.h:532
Return a value (possibly void), from a function.
SymbolTableList< Instruction >::iterator eraseFromParent()
This method unlinks 'this' from the containing basic block and deletes it.
Definition: Instruction.cpp:76
A parsed version of the target data layout string in and methods for querying it. ...
Definition: DataLayout.h:102
static ConstantInt * getFalse(LLVMContext &Context)
Definition: Constants.cpp:513
Instruction::CastOps getOpcode() const
Return the opcode of this CastInst.
Definition: InstrTypes.h:840
This class is the base class for the comparison instructions.
Definition: InstrTypes.h:870
INITIALIZE_PASS_BEGIN(SCCPLegacyPass,"sccp","Sparse Conditional Constant Propagation", false, false) INITIALIZE_PASS_END(SCCPLegacyPass
iterator_range< use_iterator > uses()
Definition: Value.h:326
AnalysisUsage & addPreserved()
Add the specified Pass class to the set of analyses preserved by this pass.
void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs=false)
Notify the BasicBlock that the predecessor Pred is no longer able to reach it.
Definition: BasicBlock.cpp:281
static bool runIPSCCP(Module &M, const DataLayout &DL, const TargetLibraryInfo *TLI)
Definition: SCCP.cpp:1688
This instruction extracts a struct member or array element value from an aggregate value...
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
LLVM Argument representation.
Definition: Argument.h:34
Base class for instruction visitors.
Definition: InstVisitor.h:81
Value * getAggregateOperand()
const Instruction & back() const
Definition: BasicBlock.h:242
Type * getSourceElementType() const
Definition: Instructions.h:928
STATISTIC(NumFunctions,"Total number of functions")
iterator erase(iterator where)
Definition: ilist.h:280
size_t i
bool isVolatile() const
Return true if this is a store to a volatile memory location.
Definition: Instructions.h:336
This is the interface for a simple mod/ref and alias analysis over globals.
bool onlyReadsMemory() const
Determine if the function does not access or only reads memory.
Definition: Function.h:321
bool canConstantFoldCallTo(const Function *F)
canConstantFoldCallTo - Return true if its even possible to fold a call to the specified function...
A Module instance is used to store all the information related to an LLVM module. ...
Definition: Module.h:52
An instruction for ordering other memory operations.
Definition: Instructions.h:430
iterator end()
Definition: Function.h:537
an instruction that atomically checks whether a specified value is in a memory location, and, if it is, stores a new value there.
Definition: Instructions.h:504
static bool AddressIsTaken(const GlobalValue *GV)
Definition: SCCP.cpp:1648
Implements a dense probed hash-table based set.
Definition: DenseSet.h:202
unsigned getNumOperands() const
Definition: User.h:167
Type * getValueType() const
Definition: GlobalValue.h:261
This class represents a function call, abstracting a target machine's calling convention.
size_type count(PtrType Ptr) const
count - Return 1 if the specified pointer is in the set, 0 otherwise.
Definition: SmallPtrSet.h:380
static Constant * getGetElementPtr(Type *Ty, Constant *C, ArrayRef< Constant * > IdxList, bool InBounds=false, Optional< unsigned > InRangeIndex=None, Type *OnlyIfReducedTy=nullptr)
Getelementptr form.
Definition: Constants.h:1126
ModulePass * createIPSCCPPass()
createIPSCCPPass - This pass propagates constants from call sites into the bodies of functions...
Definition: SCCP.cpp:1955
bool hasExactDefinition() const
Return true if this global has an exact defintion.
Definition: GlobalValue.h:386
Type * getReturnType() const
Returns the type of the ret val.
Definition: Function.cpp:238
unsigned getNumIndices() const
const Function * getParent() const
Return the enclosing method, or null if none.
Definition: BasicBlock.h:100
arg_iterator arg_end()
Definition: Function.h:559
An instruction for reading from memory.
Definition: Instructions.h:164
an instruction that atomically reads a memory location, combines it with another value, and then stores the result back.
Definition: Instructions.h:669
static Constant * getCompare(unsigned short pred, Constant *C1, Constant *C2, bool OnlyIfReduced=false)
Return an ICmp or FCmp comparison operator constant expression.
Definition: Constants.cpp:1850
static bool runSCCP(Function &F, const DataLayout &DL, const TargetLibraryInfo *TLI)
Definition: SCCP.cpp:1538
void reserve(size_type N)
Definition: SmallVector.h:377
unsigned changeToUnreachable(Instruction *I, bool UseLLVMTrap, bool PreserveLCSSA=false)
Insert an unreachable instruction before the specified instruction, making it and the rest of the cod...
Definition: Local.cpp:1373
const Constant * getInitializer() const
getInitializer - Return the initializer for this global variable.
static Constant * getNullValue(Type *Ty)
Constructor to create a '0' constant of arbitrary type.
Definition: Constants.cpp:195
StringRef getName() const
Return a constant reference to the value's name.
Definition: Value.cpp:191
iterator begin()
Instruction iterator methods.
Definition: BasicBlock.h:228
bool isSingleValueType() const
Return true if the type is a valid type for a register in codegen.
Definition: Type.h:239
std::pair< iterator, bool > insert(const std::pair< KeyT, ValueT > &KV)
Definition: DenseMap.h:172
AnalysisUsage & addRequired()
#define INITIALIZE_PASS_DEPENDENCY(depName)
Definition: PassSupport.h:53
This class represents the LLVM 'select' instruction.
This is the base class for all instructions that perform data casts.
Definition: InstrTypes.h:578
ArrayRef< T > makeArrayRef(const T &OneElt)
Construct an ArrayRef from a single element.
Definition: ArrayRef.h:440
Class to represent struct types.
Definition: DerivedTypes.h:199
A Use represents the edge between a Value definition and its users.
Definition: Use.h:56
void initializeSCCPLegacyPassPass(PassRegistry &)
bool ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions=false, const TargetLibraryInfo *TLI=nullptr)
If a terminator instruction is predicated on a constant value, convert it into an unconditional branc...
Definition: Local.cpp:68
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
Definition: SCCP.cpp:1596
unsigned getNumIndices() const
FunctionPass * createSCCPPass()
Definition: SCCP.cpp:1646
void assign(size_type NumElts, const T &Elt)
Definition: SmallVector.h:418
static Constant * get(unsigned Opcode, Constant *C1, Constant *C2, unsigned Flags=0, Type *OnlyIfReducedTy=nullptr)
get - Return a binary or shift operator constant expression, folding if possible. ...
Definition: Constants.cpp:1728
user_iterator_impl< User > user_iterator
Definition: Value.h:340
sccp
Definition: SCCP.cpp:1642
#define F(x, y, z)
Definition: MD5.cpp:51
Value * getInsertedValueOperand()
An instruction for storing to memory.
Definition: Instructions.h:300
void replaceAllUsesWith(Value *V)
Change all uses of this to point to a new Value.
Definition: Value.cpp:401
IntType getInt() const
iterator begin()
Definition: Function.h:535
static PreservedAnalyses none()
Convenience factory function for the empty preserved set.
Definition: PassManager.h:110
static GCRegistry::Add< CoreCLRGC > E("coreclr","CoreCLR-compatible GC")
unsigned getNumIncomingValues() const
Return the number of incoming edges.
unsigned getNumSuccessors() const
Return the number of successors that this terminator has.
Definition: InstrTypes.h:74
an instruction for type-safe pointer arithmetic to access elements of arrays and structs ...
Definition: Instructions.h:830
The landingpad instruction holds all of the information necessary to generate correct exception handl...
Subclasses of this class are all able to terminate a basic block.
Definition: InstrTypes.h:52
A set of analyses that are preserved following a run of a transformation pass.
Definition: PassManager.h:107
PassT::Result & getResult(IRUnitT &IR, ExtraArgTs...ExtraArgs)
Get the result of an analysis pass for a given IR unit.
Definition: PassManager.h:653
LLVM Basic Block Representation.
Definition: BasicBlock.h:51
PointerIntPair - This class implements a pair of a pointer and small integer.
The instances of the Type class are immutable: once they are created, they are never changed...
Definition: Type.h:45
BasicBlock * getSuccessor(unsigned idx) const
Return the specified successor.
Definition: InstrTypes.h:79
ipsccp
Definition: SCCP.cpp:1950
This is an important base class in LLVM.
Definition: Constant.h:42
const Value * getCondition() const
LLVM_ATTRIBUTE_ALWAYS_INLINE iterator begin()
Definition: SmallVector.h:115
This file contains the declarations for the subclasses of Constant, which represent the different fla...
APInt Or(const APInt &LHS, const APInt &RHS)
Bitwise OR function for APInt.
Definition: APInt.h:1947
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
Definition: SmallPtrSet.h:368
APInt Xor(const APInt &LHS, const APInt &RHS)
Bitwise XOR function for APInt.
Definition: APInt.h:1952
Represent the analysis usage information of a pass.
BasicBlock * getIncomingBlock(unsigned i) const
Return incoming basic block number i.
bool any_of(R &&Range, UnaryPredicate P)
Provide wrappers to std::any_of which take ranges instead of having to pass begin/end explicitly...
Definition: STLExtras.h:743
Analysis pass providing a never-invalidated alias analysis result.
INITIALIZE_PASS_END(RegBankSelect, DEBUG_TYPE,"Assign register bank of generic virtual registers", false, false) RegBankSelect
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:298
Value * getOperand(unsigned i) const
Definition: User.h:145
arg_iterator arg_begin()
Definition: Function.h:550
Predicate getPredicate() const
Return the predicate for this instruction.
Definition: InstrTypes.h:960
static Constant * get(StructType *T, ArrayRef< Constant * > V)
Definition: Constants.cpp:949
Constant * getAggregateElement(unsigned Elt) const
For aggregates (struct/array/vector) return the constant that corresponds to the specified element if...
Definition: Constants.cpp:265
Constant * ConstantFoldLoadFromConstPtr(Constant *C, Type *Ty, const DataLayout &DL)
ConstantFoldLoadFromConstPtr - Return the value that a load from C would produce if it is constant an...
static Constant * getAllOnesValue(Type *Ty)
Get the all ones value.
Definition: Constants.cpp:249
static UndefValue * get(Type *T)
Static factory methods - Return an 'undef' object of the specified type.
Definition: Constants.cpp:1337
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: PassManager.h:113
LLVMContext & getContext() const
All values hold a context through their type.
Definition: Value.cpp:654
const Value * getTrueValue() const
#define llvm_unreachable(msg)
Marks that the current location is not supposed to be reachable.
User::op_iterator arg_iterator
arg_iterator - The type of iterator to use when looping over actual arguments at this call site...
Definition: CallSite.h:205
Sparse Conditional Constant Propagation
Definition: SCCP.cpp:1642
IterTy arg_begin() const
Definition: CallSite.h:528
idx_iterator idx_begin() const
Iterator for intrusive lists based on ilist_node.
const BasicBlockListType & getBasicBlockList() const
Definition: Function.h:512
static bool tryToReplaceWithConstant(SCCPSolver &Solver, Value *V)
Definition: SCCP.cpp:1506
Sparse Conditional Constant false
Definition: SCCP.cpp:1642
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements...
Definition: SmallPtrSet.h:425
This is the shared class of boolean and integer constants.
Definition: Constants.h:88
InstrTy * getInstruction() const
Definition: CallSite.h:93
Value * getIncomingValue(unsigned i) const
Return incoming value number x.
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:843
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:230
Provides information about what library functions are available for the current target.
bool isVolatile() const
Return true if this is a load from a volatile memory location.
Definition: Instructions.h:218
const DataFlowGraph & G
Definition: RDFGraph.cpp:206
static BranchInst * Create(BasicBlock *IfTrue, Instruction *InsertBefore=nullptr)
unsigned getPointerAddressSpace() const
Returns the address space of the pointer operand.
Definition: Instructions.h:275
unsigned removeAllNonTerminatorAndEHPadInstructions(BasicBlock *BB)
Remove all instructions from a basic block other than it's terminator and any present EH pad instruct...
Definition: Local.cpp:1352
static GCRegistry::Add< ShadowStackGC > C("shadow-stack","Very portable GC for uncooperative code generators")
static void findReturnsToZap(Function &F, SmallPtrSet< Function *, 32 > &AddressTakenFunctions, SmallVector< ReturnInst *, 8 > &ReturnsToZap)
Definition: SCCP.cpp:1675
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:132
PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM)
Definition: SCCP.cpp:1908
iterator_range< user_iterator > users()
Definition: Value.h:370
APInt And(const APInt &LHS, const APInt &RHS)
Bitwise AND function for APInt.
Definition: APInt.h:1942
bool isStructTy() const
True if this is an instance of StructType.
Definition: Type.h:207
const DataLayout & getDataLayout() const
Get the data layout for the module's target platform.
Definition: Module.cpp:384
LLVM_ATTRIBUTE_ALWAYS_INLINE iterator end()
Definition: SmallVector.h:119
bool hasFnAttribute(Attribute::AttrKind Kind) const
Return true if the function has the attribute.
Definition: Function.h:226
bool isDeclaration() const
Return true if the primary definition of this global value is outside of the current translation unit...
Definition: Globals.cpp:188
void initializeIPSCCPLegacyPassPass(PassRegistry &)
ImmutableCallSite - establish a view to a call site for examination.
Definition: CallSite.h:665
#define I(x, y, z)
Definition: MD5.cpp:54
TerminatorInst * getTerminator()
Returns the terminator instruction if the block is well formed or null if the block is not well forme...
Definition: BasicBlock.cpp:124
LLVM_ATTRIBUTE_ALWAYS_INLINE size_type size() const
Definition: SmallVector.h:135
ModulePass class - This class is used to implement unstructured interprocedural optimizations and ana...
Definition: Pass.h:235
iterator find(const KeyT &Val)
Definition: DenseMap.h:127
LLVM_NODISCARD std::enable_if<!is_simple_type< Y >::value, typename cast_retty< X, const Y >::ret_type >::type dyn_cast(const Y &Val)
Definition: Casting.h:287
static Function * getCalledFunction(const Value *V, bool LookThroughBitCast, bool &IsNoBuiltin)
bool hasLocalLinkage() const
Definition: GlobalValue.h:415
Analysis pass providing the TargetLibraryInfo.
bool use_empty() const
Definition: Value.h:299
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
user_iterator user_begin()
Definition: Value.h:346
const BasicBlock & front() const
Definition: Function.h:542
void removeDeadConstantUsers() const
If there are any dead constant users dangling off of this constant, remove them.
Definition: Constants.cpp:463
FunTy * getCalledFunction() const
getCalledFunction - Return the function being called if this is a direct call, otherwise return null ...
Definition: CallSite.h:110
Module * getParent()
Get the module that this global value is contained inside of...
Definition: GlobalValue.h:537
bool isInstructionTriviallyDead(Instruction *I, const TargetLibraryInfo *TLI=nullptr)
Return true if the result produced by the instruction is not used, and the instruction has no side ef...
Definition: Local.cpp:288
LLVM Value Representation.
Definition: Value.h:71
unsigned getOpcode() const
Returns a member of one of the enums like Instruction::Add.
Definition: Instruction.h:111
Invoke instruction.
#define DEBUG(X)
Definition: Debug.h:100
bool isExceptional() const
Definition: InstrTypes.h:97
const Value * getFalseValue() const
A container for analyses that lazily runs them and caches their results.
idx_iterator idx_begin() const
int * Ptr
unsigned getNumElements() const
Random access to the elements.
Definition: DerivedTypes.h:289
const BasicBlock * getParent() const
Definition: Instruction.h:62
iterator_range< arg_iterator > args()
Definition: Function.h:568
User * user_back()
Definition: Value.h:356
Constant * ConstantFoldCall(Function *F, ArrayRef< Constant * > Operands, const TargetLibraryInfo *TLI=nullptr)
ConstantFoldCall - Attempt to constant fold a call to the specified function with the specified argum...
bool isCallee(Value::const_user_iterator UI) const
isCallee - Determine whether the passed iterator points to the callee operand's Use.
Definition: CallSite.h:134
bool isVoidTy() const
Return true if this is 'void'.
Definition: Type.h:139
This instruction inserts a struct field of array element value into an aggregate value.
void resize(size_type N)
Definition: SmallVector.h:352
user_iterator user_end()
Definition: Value.h:354