LLVM  6.0.0svn
SCCP.cpp
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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  /// getBlockAddress - If this is a constant with a BlockAddress value, return
144  /// it, otherwise return null.
145  BlockAddress *getBlockAddress() const {
146  if (isConstant())
147  return dyn_cast<BlockAddress>(getConstant());
148  return nullptr;
149  }
150 
151  void markForcedConstant(Constant *V) {
152  assert(isUnknown() && "Can't force a defined value!");
153  Val.setInt(forcedconstant);
154  Val.setPointer(V);
155  }
156 };
157 } // end anonymous namespace.
158 
159 
160 namespace {
161 
162 //===----------------------------------------------------------------------===//
163 //
164 /// SCCPSolver - This class is a general purpose solver for Sparse Conditional
165 /// Constant Propagation.
166 ///
167 class SCCPSolver : public InstVisitor<SCCPSolver> {
168  const DataLayout &DL;
169  const TargetLibraryInfo *TLI;
170  SmallPtrSet<BasicBlock*, 8> BBExecutable; // The BBs that are executable.
171  DenseMap<Value*, LatticeVal> ValueState; // The state each value is in.
172 
173  /// StructValueState - This maintains ValueState for values that have
174  /// StructType, for example for formal arguments, calls, insertelement, etc.
175  ///
176  DenseMap<std::pair<Value*, unsigned>, LatticeVal> StructValueState;
177 
178  /// GlobalValue - If we are tracking any values for the contents of a global
179  /// variable, we keep a mapping from the constant accessor to the element of
180  /// the global, to the currently known value. If the value becomes
181  /// overdefined, it's entry is simply removed from this map.
183 
184  /// TrackedRetVals - If we are tracking arguments into and the return
185  /// value out of a function, it will have an entry in this map, indicating
186  /// what the known return value for the function is.
187  DenseMap<Function*, LatticeVal> TrackedRetVals;
188 
189  /// TrackedMultipleRetVals - Same as TrackedRetVals, but used for functions
190  /// that return multiple values.
191  DenseMap<std::pair<Function*, unsigned>, LatticeVal> TrackedMultipleRetVals;
192 
193  /// MRVFunctionsTracked - Each function in TrackedMultipleRetVals is
194  /// represented here for efficient lookup.
195  SmallPtrSet<Function*, 16> MRVFunctionsTracked;
196 
197  /// TrackingIncomingArguments - This is the set of functions for whose
198  /// arguments we make optimistic assumptions about and try to prove as
199  /// constants.
200  SmallPtrSet<Function*, 16> TrackingIncomingArguments;
201 
202  /// The reason for two worklists is that overdefined is the lowest state
203  /// on the lattice, and moving things to overdefined as fast as possible
204  /// makes SCCP converge much faster.
205  ///
206  /// By having a separate worklist, we accomplish this because everything
207  /// possibly overdefined will become overdefined at the soonest possible
208  /// point.
209  SmallVector<Value*, 64> OverdefinedInstWorkList;
210  SmallVector<Value*, 64> InstWorkList;
211 
212 
213  SmallVector<BasicBlock*, 64> BBWorkList; // The BasicBlock work list
214 
215  /// KnownFeasibleEdges - Entries in this set are edges which have already had
216  /// PHI nodes retriggered.
217  typedef std::pair<BasicBlock*, BasicBlock*> Edge;
218  DenseSet<Edge> KnownFeasibleEdges;
219 public:
220  SCCPSolver(const DataLayout &DL, const TargetLibraryInfo *tli)
221  : DL(DL), TLI(tli) {}
222 
223  /// MarkBlockExecutable - This method can be used by clients to mark all of
224  /// the blocks that are known to be intrinsically live in the processed unit.
225  ///
226  /// This returns true if the block was not considered live before.
227  bool MarkBlockExecutable(BasicBlock *BB) {
228  if (!BBExecutable.insert(BB).second)
229  return false;
230  DEBUG(dbgs() << "Marking Block Executable: " << BB->getName() << '\n');
231  BBWorkList.push_back(BB); // Add the block to the work list!
232  return true;
233  }
234 
235  /// TrackValueOfGlobalVariable - Clients can use this method to
236  /// inform the SCCPSolver that it should track loads and stores to the
237  /// specified global variable if it can. This is only legal to call if
238  /// performing Interprocedural SCCP.
239  void TrackValueOfGlobalVariable(GlobalVariable *GV) {
240  // We only track the contents of scalar globals.
241  if (GV->getValueType()->isSingleValueType()) {
242  LatticeVal &IV = TrackedGlobals[GV];
243  if (!isa<UndefValue>(GV->getInitializer()))
244  IV.markConstant(GV->getInitializer());
245  }
246  }
247 
248  /// AddTrackedFunction - If the SCCP solver is supposed to track calls into
249  /// and out of the specified function (which cannot have its address taken),
250  /// this method must be called.
251  void AddTrackedFunction(Function *F) {
252  // Add an entry, F -> undef.
253  if (auto *STy = dyn_cast<StructType>(F->getReturnType())) {
254  MRVFunctionsTracked.insert(F);
255  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
256  TrackedMultipleRetVals.insert(std::make_pair(std::make_pair(F, i),
257  LatticeVal()));
258  } else
259  TrackedRetVals.insert(std::make_pair(F, LatticeVal()));
260  }
261 
262  void AddArgumentTrackedFunction(Function *F) {
263  TrackingIncomingArguments.insert(F);
264  }
265 
266  /// Solve - Solve for constants and executable blocks.
267  ///
268  void Solve();
269 
270  /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
271  /// that branches on undef values cannot reach any of their successors.
272  /// However, this is not a safe assumption. After we solve dataflow, this
273  /// method should be use to handle this. If this returns true, the solver
274  /// should be rerun.
275  bool ResolvedUndefsIn(Function &F);
276 
277  bool isBlockExecutable(BasicBlock *BB) const {
278  return BBExecutable.count(BB);
279  }
280 
281  std::vector<LatticeVal> getStructLatticeValueFor(Value *V) const {
282  std::vector<LatticeVal> StructValues;
283  auto *STy = dyn_cast<StructType>(V->getType());
284  assert(STy && "getStructLatticeValueFor() can be called only on structs");
285  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
286  auto I = StructValueState.find(std::make_pair(V, i));
287  assert(I != StructValueState.end() && "Value not in valuemap!");
288  StructValues.push_back(I->second);
289  }
290  return StructValues;
291  }
292 
293  LatticeVal getLatticeValueFor(Value *V) const {
295  assert(I != ValueState.end() && "V is not in valuemap!");
296  return I->second;
297  }
298 
299  /// getTrackedRetVals - Get the inferred return value map.
300  ///
301  const DenseMap<Function*, LatticeVal> &getTrackedRetVals() {
302  return TrackedRetVals;
303  }
304 
305  /// getTrackedGlobals - Get and return the set of inferred initializers for
306  /// global variables.
307  const DenseMap<GlobalVariable*, LatticeVal> &getTrackedGlobals() {
308  return TrackedGlobals;
309  }
310 
311  /// getMRVFunctionsTracked - Get the set of functions which return multiple
312  /// values tracked by the pass.
313  const SmallPtrSet<Function *, 16> getMRVFunctionsTracked() {
314  return MRVFunctionsTracked;
315  }
316 
317  /// markOverdefined - Mark the specified value overdefined. This
318  /// works with both scalars and structs.
319  void markOverdefined(Value *V) {
320  if (auto *STy = dyn_cast<StructType>(V->getType()))
321  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
322  markOverdefined(getStructValueState(V, i), V);
323  else
324  markOverdefined(ValueState[V], V);
325  }
326 
327  // isStructLatticeConstant - Return true if all the lattice values
328  // corresponding to elements of the structure are not overdefined,
329  // false otherwise.
330  bool isStructLatticeConstant(Function *F, StructType *STy) {
331  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
332  const auto &It = TrackedMultipleRetVals.find(std::make_pair(F, i));
333  assert(It != TrackedMultipleRetVals.end());
334  LatticeVal LV = It->second;
335  if (LV.isOverdefined())
336  return false;
337  }
338  return true;
339  }
340 
341 private:
342  // pushToWorkList - Helper for markConstant/markForcedConstant/markOverdefined
343  void pushToWorkList(LatticeVal &IV, Value *V) {
344  if (IV.isOverdefined())
345  return OverdefinedInstWorkList.push_back(V);
346  InstWorkList.push_back(V);
347  }
348 
349  // markConstant - Make a value be marked as "constant". If the value
350  // is not already a constant, add it to the instruction work list so that
351  // the users of the instruction are updated later.
352  //
353  void markConstant(LatticeVal &IV, Value *V, Constant *C) {
354  if (!IV.markConstant(C)) return;
355  DEBUG(dbgs() << "markConstant: " << *C << ": " << *V << '\n');
356  pushToWorkList(IV, V);
357  }
358 
359  void markConstant(Value *V, Constant *C) {
360  assert(!V->getType()->isStructTy() && "structs should use mergeInValue");
361  markConstant(ValueState[V], V, C);
362  }
363 
364  void markForcedConstant(Value *V, Constant *C) {
365  assert(!V->getType()->isStructTy() && "structs should use mergeInValue");
366  LatticeVal &IV = ValueState[V];
367  IV.markForcedConstant(C);
368  DEBUG(dbgs() << "markForcedConstant: " << *C << ": " << *V << '\n');
369  pushToWorkList(IV, V);
370  }
371 
372 
373  // markOverdefined - Make a value be marked as "overdefined". If the
374  // value is not already overdefined, add it to the overdefined instruction
375  // work list so that the users of the instruction are updated later.
376  void markOverdefined(LatticeVal &IV, Value *V) {
377  if (!IV.markOverdefined()) return;
378 
379  DEBUG(dbgs() << "markOverdefined: ";
380  if (auto *F = dyn_cast<Function>(V))
381  dbgs() << "Function '" << F->getName() << "'\n";
382  else
383  dbgs() << *V << '\n');
384  // Only instructions go on the work list
385  pushToWorkList(IV, V);
386  }
387 
388  void mergeInValue(LatticeVal &IV, Value *V, LatticeVal MergeWithV) {
389  if (IV.isOverdefined() || MergeWithV.isUnknown())
390  return; // Noop.
391  if (MergeWithV.isOverdefined())
392  return markOverdefined(IV, V);
393  if (IV.isUnknown())
394  return markConstant(IV, V, MergeWithV.getConstant());
395  if (IV.getConstant() != MergeWithV.getConstant())
396  return markOverdefined(IV, V);
397  }
398 
399  void mergeInValue(Value *V, LatticeVal MergeWithV) {
400  assert(!V->getType()->isStructTy() &&
401  "non-structs should use markConstant");
402  mergeInValue(ValueState[V], V, MergeWithV);
403  }
404 
405 
406  /// getValueState - Return the LatticeVal object that corresponds to the
407  /// value. This function handles the case when the value hasn't been seen yet
408  /// by properly seeding constants etc.
409  LatticeVal &getValueState(Value *V) {
410  assert(!V->getType()->isStructTy() && "Should use getStructValueState");
411 
412  std::pair<DenseMap<Value*, LatticeVal>::iterator, bool> I =
413  ValueState.insert(std::make_pair(V, LatticeVal()));
414  LatticeVal &LV = I.first->second;
415 
416  if (!I.second)
417  return LV; // Common case, already in the map.
418 
419  if (auto *C = dyn_cast<Constant>(V)) {
420  // Undef values remain unknown.
421  if (!isa<UndefValue>(V))
422  LV.markConstant(C); // Constants are constant
423  }
424 
425  // All others are underdefined by default.
426  return LV;
427  }
428 
429  /// getStructValueState - Return the LatticeVal object that corresponds to the
430  /// value/field pair. This function handles the case when the value hasn't
431  /// been seen yet by properly seeding constants etc.
432  LatticeVal &getStructValueState(Value *V, unsigned i) {
433  assert(V->getType()->isStructTy() && "Should use getValueState");
434  assert(i < cast<StructType>(V->getType())->getNumElements() &&
435  "Invalid element #");
436 
437  std::pair<DenseMap<std::pair<Value*, unsigned>, LatticeVal>::iterator,
438  bool> I = StructValueState.insert(
439  std::make_pair(std::make_pair(V, i), LatticeVal()));
440  LatticeVal &LV = I.first->second;
441 
442  if (!I.second)
443  return LV; // Common case, already in the map.
444 
445  if (auto *C = dyn_cast<Constant>(V)) {
446  Constant *Elt = C->getAggregateElement(i);
447 
448  if (!Elt)
449  LV.markOverdefined(); // Unknown sort of constant.
450  else if (isa<UndefValue>(Elt))
451  ; // Undef values remain unknown.
452  else
453  LV.markConstant(Elt); // Constants are constant.
454  }
455 
456  // All others are underdefined by default.
457  return LV;
458  }
459 
460 
461  /// markEdgeExecutable - Mark a basic block as executable, adding it to the BB
462  /// work list if it is not already executable.
463  void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
464  if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
465  return; // This edge is already known to be executable!
466 
467  if (!MarkBlockExecutable(Dest)) {
468  // If the destination is already executable, we just made an *edge*
469  // feasible that wasn't before. Revisit the PHI nodes in the block
470  // because they have potentially new operands.
471  DEBUG(dbgs() << "Marking Edge Executable: " << Source->getName()
472  << " -> " << Dest->getName() << '\n');
473 
474  PHINode *PN;
475  for (BasicBlock::iterator I = Dest->begin();
476  (PN = dyn_cast<PHINode>(I)); ++I)
477  visitPHINode(*PN);
478  }
479  }
480 
481  // getFeasibleSuccessors - Return a vector of booleans to indicate which
482  // successors are reachable from a given terminator instruction.
483  //
484  void getFeasibleSuccessors(TerminatorInst &TI, SmallVectorImpl<bool> &Succs);
485 
486  // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
487  // block to the 'To' basic block is currently feasible.
488  //
489  bool isEdgeFeasible(BasicBlock *From, BasicBlock *To);
490 
491  // OperandChangedState - This method is invoked on all of the users of an
492  // instruction that was just changed state somehow. Based on this
493  // information, we need to update the specified user of this instruction.
494  //
495  void OperandChangedState(Instruction *I) {
496  if (BBExecutable.count(I->getParent())) // Inst is executable?
497  visit(*I);
498  }
499 
500 private:
501  friend class InstVisitor<SCCPSolver>;
502 
503  // visit implementations - Something changed in this instruction. Either an
504  // operand made a transition, or the instruction is newly executable. Change
505  // the value type of I to reflect these changes if appropriate.
506  void visitPHINode(PHINode &I);
507 
508  // Terminators
509  void visitReturnInst(ReturnInst &I);
510  void visitTerminatorInst(TerminatorInst &TI);
511 
512  void visitCastInst(CastInst &I);
513  void visitSelectInst(SelectInst &I);
514  void visitBinaryOperator(Instruction &I);
515  void visitCmpInst(CmpInst &I);
516  void visitExtractValueInst(ExtractValueInst &EVI);
517  void visitInsertValueInst(InsertValueInst &IVI);
518  void visitCatchSwitchInst(CatchSwitchInst &CPI) {
519  markOverdefined(&CPI);
520  visitTerminatorInst(CPI);
521  }
522 
523  // Instructions that cannot be folded away.
524  void visitStoreInst (StoreInst &I);
525  void visitLoadInst (LoadInst &I);
526  void visitGetElementPtrInst(GetElementPtrInst &I);
527  void visitCallInst (CallInst &I) {
528  visitCallSite(&I);
529  }
530  void visitInvokeInst (InvokeInst &II) {
531  visitCallSite(&II);
532  visitTerminatorInst(II);
533  }
534  void visitCallSite (CallSite CS);
535  void visitResumeInst (TerminatorInst &I) { /*returns void*/ }
536  void visitUnreachableInst(TerminatorInst &I) { /*returns void*/ }
537  void visitFenceInst (FenceInst &I) { /*returns void*/ }
538  void visitInstruction(Instruction &I) {
539  // All the instructions we don't do any special handling for just
540  // go to overdefined.
541  DEBUG(dbgs() << "SCCP: Don't know how to handle: " << I << '\n');
542  markOverdefined(&I);
543  }
544 };
545 
546 } // end anonymous namespace
547 
548 
549 // getFeasibleSuccessors - Return a vector of booleans to indicate which
550 // successors are reachable from a given terminator instruction.
551 //
552 void SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI,
553  SmallVectorImpl<bool> &Succs) {
554  Succs.resize(TI.getNumSuccessors());
555  if (auto *BI = dyn_cast<BranchInst>(&TI)) {
556  if (BI->isUnconditional()) {
557  Succs[0] = true;
558  return;
559  }
560 
561  LatticeVal BCValue = getValueState(BI->getCondition());
562  ConstantInt *CI = BCValue.getConstantInt();
563  if (!CI) {
564  // Overdefined condition variables, and branches on unfoldable constant
565  // conditions, mean the branch could go either way.
566  if (!BCValue.isUnknown())
567  Succs[0] = Succs[1] = true;
568  return;
569  }
570 
571  // Constant condition variables mean the branch can only go a single way.
572  Succs[CI->isZero()] = true;
573  return;
574  }
575 
576  // Unwinding instructions successors are always executable.
577  if (TI.isExceptional()) {
578  Succs.assign(TI.getNumSuccessors(), true);
579  return;
580  }
581 
582  if (auto *SI = dyn_cast<SwitchInst>(&TI)) {
583  if (!SI->getNumCases()) {
584  Succs[0] = true;
585  return;
586  }
587  LatticeVal SCValue = getValueState(SI->getCondition());
588  ConstantInt *CI = SCValue.getConstantInt();
589 
590  if (!CI) { // Overdefined or unknown condition?
591  // All destinations are executable!
592  if (!SCValue.isUnknown())
593  Succs.assign(TI.getNumSuccessors(), true);
594  return;
595  }
596 
597  Succs[SI->findCaseValue(CI)->getSuccessorIndex()] = true;
598  return;
599  }
600 
601  // In case of indirect branch and its address is a blockaddress, we mark
602  // the target as executable.
603  if (auto *IBR = dyn_cast<IndirectBrInst>(&TI)) {
604  // Casts are folded by visitCastInst.
605  LatticeVal IBRValue = getValueState(IBR->getAddress());
606  BlockAddress *Addr = IBRValue.getBlockAddress();
607  if (!Addr) { // Overdefined or unknown condition?
608  // All destinations are executable!
609  if (!IBRValue.isUnknown())
610  Succs.assign(TI.getNumSuccessors(), true);
611  return;
612  }
613 
614  BasicBlock* T = Addr->getBasicBlock();
615  assert(Addr->getFunction() == T->getParent() &&
616  "Block address of a different function ?");
617  for (unsigned i = 0; i < IBR->getNumSuccessors(); ++i) {
618  // This is the target.
619  if (IBR->getDestination(i) == T) {
620  Succs[i] = true;
621  return;
622  }
623  }
624 
625  // If we didn't find our destination in the IBR successor list, then we
626  // have undefined behavior. Its ok to assume no successor is executable.
627  return;
628  }
629 
630  DEBUG(dbgs() << "Unknown terminator instruction: " << TI << '\n');
631  llvm_unreachable("SCCP: Don't know how to handle this terminator!");
632 }
633 
634 
635 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
636 // block to the 'To' basic block is currently feasible.
637 //
638 bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
639  assert(BBExecutable.count(To) && "Dest should always be alive!");
640 
641  // Make sure the source basic block is executable!!
642  if (!BBExecutable.count(From)) return false;
643 
644  // Check to make sure this edge itself is actually feasible now.
645  TerminatorInst *TI = From->getTerminator();
646  if (auto *BI = dyn_cast<BranchInst>(TI)) {
647  if (BI->isUnconditional())
648  return true;
649 
650  LatticeVal BCValue = getValueState(BI->getCondition());
651 
652  // Overdefined condition variables mean the branch could go either way,
653  // undef conditions mean that neither edge is feasible yet.
654  ConstantInt *CI = BCValue.getConstantInt();
655  if (!CI)
656  return !BCValue.isUnknown();
657 
658  // Constant condition variables mean the branch can only go a single way.
659  return BI->getSuccessor(CI->isZero()) == To;
660  }
661 
662  // Unwinding instructions successors are always executable.
663  if (TI->isExceptional())
664  return true;
665 
666  if (auto *SI = dyn_cast<SwitchInst>(TI)) {
667  if (SI->getNumCases() < 1)
668  return true;
669 
670  LatticeVal SCValue = getValueState(SI->getCondition());
671  ConstantInt *CI = SCValue.getConstantInt();
672 
673  if (!CI)
674  return !SCValue.isUnknown();
675 
676  return SI->findCaseValue(CI)->getCaseSuccessor() == To;
677  }
678 
679  // In case of indirect branch and its address is a blockaddress, we mark
680  // the target as executable.
681  if (auto *IBR = dyn_cast<IndirectBrInst>(TI)) {
682  LatticeVal IBRValue = getValueState(IBR->getAddress());
683  BlockAddress *Addr = IBRValue.getBlockAddress();
684 
685  if (!Addr)
686  return !IBRValue.isUnknown();
687 
688  // At this point, the indirectbr is branching on a blockaddress.
689  return Addr->getBasicBlock() == To;
690  }
691 
692  DEBUG(dbgs() << "Unknown terminator instruction: " << *TI << '\n');
693  llvm_unreachable("SCCP: Don't know how to handle this terminator!");
694 }
695 
696 // visit Implementations - Something changed in this instruction, either an
697 // operand made a transition, or the instruction is newly executable. Change
698 // the value type of I to reflect these changes if appropriate. This method
699 // makes sure to do the following actions:
700 //
701 // 1. If a phi node merges two constants in, and has conflicting value coming
702 // from different branches, or if the PHI node merges in an overdefined
703 // value, then the PHI node becomes overdefined.
704 // 2. If a phi node merges only constants in, and they all agree on value, the
705 // PHI node becomes a constant value equal to that.
706 // 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant
707 // 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined
708 // 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined
709 // 6. If a conditional branch has a value that is constant, make the selected
710 // destination executable
711 // 7. If a conditional branch has a value that is overdefined, make all
712 // successors executable.
713 //
714 void SCCPSolver::visitPHINode(PHINode &PN) {
715  // If this PN returns a struct, just mark the result overdefined.
716  // TODO: We could do a lot better than this if code actually uses this.
717  if (PN.getType()->isStructTy())
718  return markOverdefined(&PN);
719 
720  if (getValueState(&PN).isOverdefined())
721  return; // Quick exit
722 
723  // Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
724  // and slow us down a lot. Just mark them overdefined.
725  if (PN.getNumIncomingValues() > 64)
726  return markOverdefined(&PN);
727 
728  // Look at all of the executable operands of the PHI node. If any of them
729  // are overdefined, the PHI becomes overdefined as well. If they are all
730  // constant, and they agree with each other, the PHI becomes the identical
731  // constant. If they are constant and don't agree, the PHI is overdefined.
732  // If there are no executable operands, the PHI remains unknown.
733  //
734  Constant *OperandVal = nullptr;
735  for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
736  LatticeVal IV = getValueState(PN.getIncomingValue(i));
737  if (IV.isUnknown()) continue; // Doesn't influence PHI node.
738 
739  if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent()))
740  continue;
741 
742  if (IV.isOverdefined()) // PHI node becomes overdefined!
743  return markOverdefined(&PN);
744 
745  if (!OperandVal) { // Grab the first value.
746  OperandVal = IV.getConstant();
747  continue;
748  }
749 
750  // There is already a reachable operand. If we conflict with it,
751  // then the PHI node becomes overdefined. If we agree with it, we
752  // can continue on.
753 
754  // Check to see if there are two different constants merging, if so, the PHI
755  // node is overdefined.
756  if (IV.getConstant() != OperandVal)
757  return markOverdefined(&PN);
758  }
759 
760  // If we exited the loop, this means that the PHI node only has constant
761  // arguments that agree with each other(and OperandVal is the constant) or
762  // OperandVal is null because there are no defined incoming arguments. If
763  // this is the case, the PHI remains unknown.
764  //
765  if (OperandVal)
766  markConstant(&PN, OperandVal); // Acquire operand value
767 }
768 
769 void SCCPSolver::visitReturnInst(ReturnInst &I) {
770  if (I.getNumOperands() == 0) return; // ret void
771 
772  Function *F = I.getParent()->getParent();
773  Value *ResultOp = I.getOperand(0);
774 
775  // If we are tracking the return value of this function, merge it in.
776  if (!TrackedRetVals.empty() && !ResultOp->getType()->isStructTy()) {
778  TrackedRetVals.find(F);
779  if (TFRVI != TrackedRetVals.end()) {
780  mergeInValue(TFRVI->second, F, getValueState(ResultOp));
781  return;
782  }
783  }
784 
785  // Handle functions that return multiple values.
786  if (!TrackedMultipleRetVals.empty()) {
787  if (auto *STy = dyn_cast<StructType>(ResultOp->getType()))
788  if (MRVFunctionsTracked.count(F))
789  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
790  mergeInValue(TrackedMultipleRetVals[std::make_pair(F, i)], F,
791  getStructValueState(ResultOp, i));
792 
793  }
794 }
795 
796 void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) {
797  SmallVector<bool, 16> SuccFeasible;
798  getFeasibleSuccessors(TI, SuccFeasible);
799 
800  BasicBlock *BB = TI.getParent();
801 
802  // Mark all feasible successors executable.
803  for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
804  if (SuccFeasible[i])
805  markEdgeExecutable(BB, TI.getSuccessor(i));
806 }
807 
808 void SCCPSolver::visitCastInst(CastInst &I) {
809  LatticeVal OpSt = getValueState(I.getOperand(0));
810  if (OpSt.isOverdefined()) // Inherit overdefinedness of operand
811  markOverdefined(&I);
812  else if (OpSt.isConstant()) {
813  // Fold the constant as we build.
814  Constant *C = ConstantFoldCastOperand(I.getOpcode(), OpSt.getConstant(),
815  I.getType(), DL);
816  if (isa<UndefValue>(C))
817  return;
818  // Propagate constant value
819  markConstant(&I, C);
820  }
821 }
822 
823 
824 void SCCPSolver::visitExtractValueInst(ExtractValueInst &EVI) {
825  // If this returns a struct, mark all elements over defined, we don't track
826  // structs in structs.
827  if (EVI.getType()->isStructTy())
828  return markOverdefined(&EVI);
829 
830  // If this is extracting from more than one level of struct, we don't know.
831  if (EVI.getNumIndices() != 1)
832  return markOverdefined(&EVI);
833 
834  Value *AggVal = EVI.getAggregateOperand();
835  if (AggVal->getType()->isStructTy()) {
836  unsigned i = *EVI.idx_begin();
837  LatticeVal EltVal = getStructValueState(AggVal, i);
838  mergeInValue(getValueState(&EVI), &EVI, EltVal);
839  } else {
840  // Otherwise, must be extracting from an array.
841  return markOverdefined(&EVI);
842  }
843 }
844 
845 void SCCPSolver::visitInsertValueInst(InsertValueInst &IVI) {
846  auto *STy = dyn_cast<StructType>(IVI.getType());
847  if (!STy)
848  return markOverdefined(&IVI);
849 
850  // If this has more than one index, we can't handle it, drive all results to
851  // undef.
852  if (IVI.getNumIndices() != 1)
853  return markOverdefined(&IVI);
854 
855  Value *Aggr = IVI.getAggregateOperand();
856  unsigned Idx = *IVI.idx_begin();
857 
858  // Compute the result based on what we're inserting.
859  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
860  // This passes through all values that aren't the inserted element.
861  if (i != Idx) {
862  LatticeVal EltVal = getStructValueState(Aggr, i);
863  mergeInValue(getStructValueState(&IVI, i), &IVI, EltVal);
864  continue;
865  }
866 
867  Value *Val = IVI.getInsertedValueOperand();
868  if (Val->getType()->isStructTy())
869  // We don't track structs in structs.
870  markOverdefined(getStructValueState(&IVI, i), &IVI);
871  else {
872  LatticeVal InVal = getValueState(Val);
873  mergeInValue(getStructValueState(&IVI, i), &IVI, InVal);
874  }
875  }
876 }
877 
878 void SCCPSolver::visitSelectInst(SelectInst &I) {
879  // If this select returns a struct, just mark the result overdefined.
880  // TODO: We could do a lot better than this if code actually uses this.
881  if (I.getType()->isStructTy())
882  return markOverdefined(&I);
883 
884  LatticeVal CondValue = getValueState(I.getCondition());
885  if (CondValue.isUnknown())
886  return;
887 
888  if (ConstantInt *CondCB = CondValue.getConstantInt()) {
889  Value *OpVal = CondCB->isZero() ? I.getFalseValue() : I.getTrueValue();
890  mergeInValue(&I, getValueState(OpVal));
891  return;
892  }
893 
894  // Otherwise, the condition is overdefined or a constant we can't evaluate.
895  // See if we can produce something better than overdefined based on the T/F
896  // value.
897  LatticeVal TVal = getValueState(I.getTrueValue());
898  LatticeVal FVal = getValueState(I.getFalseValue());
899 
900  // select ?, C, C -> C.
901  if (TVal.isConstant() && FVal.isConstant() &&
902  TVal.getConstant() == FVal.getConstant())
903  return markConstant(&I, FVal.getConstant());
904 
905  if (TVal.isUnknown()) // select ?, undef, X -> X.
906  return mergeInValue(&I, FVal);
907  if (FVal.isUnknown()) // select ?, X, undef -> X.
908  return mergeInValue(&I, TVal);
909  markOverdefined(&I);
910 }
911 
912 // Handle Binary Operators.
913 void SCCPSolver::visitBinaryOperator(Instruction &I) {
914  LatticeVal V1State = getValueState(I.getOperand(0));
915  LatticeVal V2State = getValueState(I.getOperand(1));
916 
917  LatticeVal &IV = ValueState[&I];
918  if (IV.isOverdefined()) return;
919 
920  if (V1State.isConstant() && V2State.isConstant()) {
921  Constant *C = ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
922  V2State.getConstant());
923  // X op Y -> undef.
924  if (isa<UndefValue>(C))
925  return;
926  return markConstant(IV, &I, C);
927  }
928 
929  // If something is undef, wait for it to resolve.
930  if (!V1State.isOverdefined() && !V2State.isOverdefined())
931  return;
932 
933  // Otherwise, one of our operands is overdefined. Try to produce something
934  // better than overdefined with some tricks.
935  // If this is 0 / Y, it doesn't matter that the second operand is
936  // overdefined, and we can replace it with zero.
937  if (I.getOpcode() == Instruction::UDiv || I.getOpcode() == Instruction::SDiv)
938  if (V1State.isConstant() && V1State.getConstant()->isNullValue())
939  return markConstant(IV, &I, V1State.getConstant());
940 
941  // If this is:
942  // -> AND/MUL with 0
943  // -> OR with -1
944  // it doesn't matter that the other operand is overdefined.
945  if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Mul ||
946  I.getOpcode() == Instruction::Or) {
947  LatticeVal *NonOverdefVal = nullptr;
948  if (!V1State.isOverdefined())
949  NonOverdefVal = &V1State;
950  else if (!V2State.isOverdefined())
951  NonOverdefVal = &V2State;
952 
953  if (NonOverdefVal) {
954  if (NonOverdefVal->isUnknown())
955  return;
956 
957  if (I.getOpcode() == Instruction::And ||
958  I.getOpcode() == Instruction::Mul) {
959  // X and 0 = 0
960  // X * 0 = 0
961  if (NonOverdefVal->getConstant()->isNullValue())
962  return markConstant(IV, &I, NonOverdefVal->getConstant());
963  } else {
964  // X or -1 = -1
965  if (ConstantInt *CI = NonOverdefVal->getConstantInt())
966  if (CI->isMinusOne())
967  return markConstant(IV, &I, NonOverdefVal->getConstant());
968  }
969  }
970  }
971 
972 
973  markOverdefined(&I);
974 }
975 
976 // Handle ICmpInst instruction.
977 void SCCPSolver::visitCmpInst(CmpInst &I) {
978  LatticeVal V1State = getValueState(I.getOperand(0));
979  LatticeVal V2State = getValueState(I.getOperand(1));
980 
981  LatticeVal &IV = ValueState[&I];
982  if (IV.isOverdefined()) return;
983 
984  if (V1State.isConstant() && V2State.isConstant()) {
986  I.getPredicate(), V1State.getConstant(), V2State.getConstant());
987  if (isa<UndefValue>(C))
988  return;
989  return markConstant(IV, &I, C);
990  }
991 
992  // If operands are still unknown, wait for it to resolve.
993  if (!V1State.isOverdefined() && !V2State.isOverdefined())
994  return;
995 
996  markOverdefined(&I);
997 }
998 
999 // Handle getelementptr instructions. If all operands are constants then we
1000 // can turn this into a getelementptr ConstantExpr.
1001 //
1002 void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
1003  if (ValueState[&I].isOverdefined()) return;
1004 
1005  SmallVector<Constant*, 8> Operands;
1006  Operands.reserve(I.getNumOperands());
1007 
1008  for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
1009  LatticeVal State = getValueState(I.getOperand(i));
1010  if (State.isUnknown())
1011  return; // Operands are not resolved yet.
1012 
1013  if (State.isOverdefined())
1014  return markOverdefined(&I);
1015 
1016  assert(State.isConstant() && "Unknown state!");
1017  Operands.push_back(State.getConstant());
1018  }
1019 
1020  Constant *Ptr = Operands[0];
1021  auto Indices = makeArrayRef(Operands.begin() + 1, Operands.end());
1022  Constant *C =
1024  if (isa<UndefValue>(C))
1025  return;
1026  markConstant(&I, C);
1027 }
1028 
1029 void SCCPSolver::visitStoreInst(StoreInst &SI) {
1030  // If this store is of a struct, ignore it.
1031  if (SI.getOperand(0)->getType()->isStructTy())
1032  return;
1033 
1034  if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
1035  return;
1036 
1037  GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
1039  if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
1040 
1041  // Get the value we are storing into the global, then merge it.
1042  mergeInValue(I->second, GV, getValueState(SI.getOperand(0)));
1043  if (I->second.isOverdefined())
1044  TrackedGlobals.erase(I); // No need to keep tracking this!
1045 }
1046 
1047 
1048 // Handle load instructions. If the operand is a constant pointer to a constant
1049 // global, we can replace the load with the loaded constant value!
1050 void SCCPSolver::visitLoadInst(LoadInst &I) {
1051  // If this load is of a struct, just mark the result overdefined.
1052  if (I.getType()->isStructTy())
1053  return markOverdefined(&I);
1054 
1055  LatticeVal PtrVal = getValueState(I.getOperand(0));
1056  if (PtrVal.isUnknown()) return; // The pointer is not resolved yet!
1057 
1058  LatticeVal &IV = ValueState[&I];
1059  if (IV.isOverdefined()) return;
1060 
1061  if (!PtrVal.isConstant() || I.isVolatile())
1062  return markOverdefined(IV, &I);
1063 
1064  Constant *Ptr = PtrVal.getConstant();
1065 
1066  // load null is undefined.
1067  if (isa<ConstantPointerNull>(Ptr) && I.getPointerAddressSpace() == 0)
1068  return;
1069 
1070  // Transform load (constant global) into the value loaded.
1071  if (auto *GV = dyn_cast<GlobalVariable>(Ptr)) {
1072  if (!TrackedGlobals.empty()) {
1073  // If we are tracking this global, merge in the known value for it.
1075  TrackedGlobals.find(GV);
1076  if (It != TrackedGlobals.end()) {
1077  mergeInValue(IV, &I, It->second);
1078  return;
1079  }
1080  }
1081  }
1082 
1083  // Transform load from a constant into a constant if possible.
1084  if (Constant *C = ConstantFoldLoadFromConstPtr(Ptr, I.getType(), DL)) {
1085  if (isa<UndefValue>(C))
1086  return;
1087  return markConstant(IV, &I, C);
1088  }
1089 
1090  // Otherwise we cannot say for certain what value this load will produce.
1091  // Bail out.
1092  markOverdefined(IV, &I);
1093 }
1094 
1095 void SCCPSolver::visitCallSite(CallSite CS) {
1096  Function *F = CS.getCalledFunction();
1097  Instruction *I = CS.getInstruction();
1098 
1099  // The common case is that we aren't tracking the callee, either because we
1100  // are not doing interprocedural analysis or the callee is indirect, or is
1101  // external. Handle these cases first.
1102  if (!F || F->isDeclaration()) {
1103 CallOverdefined:
1104  // Void return and not tracking callee, just bail.
1105  if (I->getType()->isVoidTy()) return;
1106 
1107  // Otherwise, if we have a single return value case, and if the function is
1108  // a declaration, maybe we can constant fold it.
1109  if (F && F->isDeclaration() && !I->getType()->isStructTy() &&
1110  canConstantFoldCallTo(CS, F)) {
1111 
1112  SmallVector<Constant*, 8> Operands;
1113  for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
1114  AI != E; ++AI) {
1115  LatticeVal State = getValueState(*AI);
1116 
1117  if (State.isUnknown())
1118  return; // Operands are not resolved yet.
1119  if (State.isOverdefined())
1120  return markOverdefined(I);
1121  assert(State.isConstant() && "Unknown state!");
1122  Operands.push_back(State.getConstant());
1123  }
1124 
1125  if (getValueState(I).isOverdefined())
1126  return;
1127 
1128  // If we can constant fold this, mark the result of the call as a
1129  // constant.
1130  if (Constant *C = ConstantFoldCall(CS, F, Operands, TLI)) {
1131  // call -> undef.
1132  if (isa<UndefValue>(C))
1133  return;
1134  return markConstant(I, C);
1135  }
1136  }
1137 
1138  // Otherwise, we don't know anything about this call, mark it overdefined.
1139  return markOverdefined(I);
1140  }
1141 
1142  // If this is a local function that doesn't have its address taken, mark its
1143  // entry block executable and merge in the actual arguments to the call into
1144  // the formal arguments of the function.
1145  if (!TrackingIncomingArguments.empty() && TrackingIncomingArguments.count(F)){
1146  MarkBlockExecutable(&F->front());
1147 
1148  // Propagate information from this call site into the callee.
1149  CallSite::arg_iterator CAI = CS.arg_begin();
1150  for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1151  AI != E; ++AI, ++CAI) {
1152  // If this argument is byval, and if the function is not readonly, there
1153  // will be an implicit copy formed of the input aggregate.
1154  if (AI->hasByValAttr() && !F->onlyReadsMemory()) {
1155  markOverdefined(&*AI);
1156  continue;
1157  }
1158 
1159  if (auto *STy = dyn_cast<StructType>(AI->getType())) {
1160  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1161  LatticeVal CallArg = getStructValueState(*CAI, i);
1162  mergeInValue(getStructValueState(&*AI, i), &*AI, CallArg);
1163  }
1164  } else {
1165  mergeInValue(&*AI, getValueState(*CAI));
1166  }
1167  }
1168  }
1169 
1170  // If this is a single/zero retval case, see if we're tracking the function.
1171  if (auto *STy = dyn_cast<StructType>(F->getReturnType())) {
1172  if (!MRVFunctionsTracked.count(F))
1173  goto CallOverdefined; // Not tracking this callee.
1174 
1175  // If we are tracking this callee, propagate the result of the function
1176  // into this call site.
1177  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
1178  mergeInValue(getStructValueState(I, i), I,
1179  TrackedMultipleRetVals[std::make_pair(F, i)]);
1180  } else {
1181  DenseMap<Function*, LatticeVal>::iterator TFRVI = TrackedRetVals.find(F);
1182  if (TFRVI == TrackedRetVals.end())
1183  goto CallOverdefined; // Not tracking this callee.
1184 
1185  // If so, propagate the return value of the callee into this call result.
1186  mergeInValue(I, TFRVI->second);
1187  }
1188 }
1189 
1190 void SCCPSolver::Solve() {
1191  // Process the work lists until they are empty!
1192  while (!BBWorkList.empty() || !InstWorkList.empty() ||
1193  !OverdefinedInstWorkList.empty()) {
1194  // Process the overdefined instruction's work list first, which drives other
1195  // things to overdefined more quickly.
1196  while (!OverdefinedInstWorkList.empty()) {
1197  Value *I = OverdefinedInstWorkList.pop_back_val();
1198 
1199  DEBUG(dbgs() << "\nPopped off OI-WL: " << *I << '\n');
1200 
1201  // "I" got into the work list because it either made the transition from
1202  // bottom to constant, or to overdefined.
1203  //
1204  // Anything on this worklist that is overdefined need not be visited
1205  // since all of its users will have already been marked as overdefined
1206  // Update all of the users of this instruction's value.
1207  //
1208  for (User *U : I->users())
1209  if (auto *UI = dyn_cast<Instruction>(U))
1210  OperandChangedState(UI);
1211  }
1212 
1213  // Process the instruction work list.
1214  while (!InstWorkList.empty()) {
1215  Value *I = InstWorkList.pop_back_val();
1216 
1217  DEBUG(dbgs() << "\nPopped off I-WL: " << *I << '\n');
1218 
1219  // "I" got into the work list because it made the transition from undef to
1220  // constant.
1221  //
1222  // Anything on this worklist that is overdefined need not be visited
1223  // since all of its users will have already been marked as overdefined.
1224  // Update all of the users of this instruction's value.
1225  //
1226  if (I->getType()->isStructTy() || !getValueState(I).isOverdefined())
1227  for (User *U : I->users())
1228  if (auto *UI = dyn_cast<Instruction>(U))
1229  OperandChangedState(UI);
1230  }
1231 
1232  // Process the basic block work list.
1233  while (!BBWorkList.empty()) {
1234  BasicBlock *BB = BBWorkList.back();
1235  BBWorkList.pop_back();
1236 
1237  DEBUG(dbgs() << "\nPopped off BBWL: " << *BB << '\n');
1238 
1239  // Notify all instructions in this basic block that they are newly
1240  // executable.
1241  visit(BB);
1242  }
1243  }
1244 }
1245 
1246 /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
1247 /// that branches on undef values cannot reach any of their successors.
1248 /// However, this is not a safe assumption. After we solve dataflow, this
1249 /// method should be use to handle this. If this returns true, the solver
1250 /// should be rerun.
1251 ///
1252 /// This method handles this by finding an unresolved branch and marking it one
1253 /// of the edges from the block as being feasible, even though the condition
1254 /// doesn't say it would otherwise be. This allows SCCP to find the rest of the
1255 /// CFG and only slightly pessimizes the analysis results (by marking one,
1256 /// potentially infeasible, edge feasible). This cannot usefully modify the
1257 /// constraints on the condition of the branch, as that would impact other users
1258 /// of the value.
1259 ///
1260 /// This scan also checks for values that use undefs, whose results are actually
1261 /// defined. For example, 'zext i8 undef to i32' should produce all zeros
1262 /// conservatively, as "(zext i8 X -> i32) & 0xFF00" must always return zero,
1263 /// even if X isn't defined.
1264 bool SCCPSolver::ResolvedUndefsIn(Function &F) {
1265  for (BasicBlock &BB : F) {
1266  if (!BBExecutable.count(&BB))
1267  continue;
1268 
1269  for (Instruction &I : BB) {
1270  // Look for instructions which produce undef values.
1271  if (I.getType()->isVoidTy()) continue;
1272 
1273  if (auto *STy = dyn_cast<StructType>(I.getType())) {
1274  // Only a few things that can be structs matter for undef.
1275 
1276  // Tracked calls must never be marked overdefined in ResolvedUndefsIn.
1277  if (CallSite CS = CallSite(&I))
1278  if (Function *F = CS.getCalledFunction())
1279  if (MRVFunctionsTracked.count(F))
1280  continue;
1281 
1282  // extractvalue and insertvalue don't need to be marked; they are
1283  // tracked as precisely as their operands.
1284  if (isa<ExtractValueInst>(I) || isa<InsertValueInst>(I))
1285  continue;
1286 
1287  // Send the results of everything else to overdefined. We could be
1288  // more precise than this but it isn't worth bothering.
1289  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1290  LatticeVal &LV = getStructValueState(&I, i);
1291  if (LV.isUnknown())
1292  markOverdefined(LV, &I);
1293  }
1294  continue;
1295  }
1296 
1297  LatticeVal &LV = getValueState(&I);
1298  if (!LV.isUnknown()) continue;
1299 
1300  // extractvalue is safe; check here because the argument is a struct.
1301  if (isa<ExtractValueInst>(I))
1302  continue;
1303 
1304  // Compute the operand LatticeVals, for convenience below.
1305  // Anything taking a struct is conservatively assumed to require
1306  // overdefined markings.
1307  if (I.getOperand(0)->getType()->isStructTy()) {
1308  markOverdefined(&I);
1309  return true;
1310  }
1311  LatticeVal Op0LV = getValueState(I.getOperand(0));
1312  LatticeVal Op1LV;
1313  if (I.getNumOperands() == 2) {
1314  if (I.getOperand(1)->getType()->isStructTy()) {
1315  markOverdefined(&I);
1316  return true;
1317  }
1318 
1319  Op1LV = getValueState(I.getOperand(1));
1320  }
1321  // If this is an instructions whose result is defined even if the input is
1322  // not fully defined, propagate the information.
1323  Type *ITy = I.getType();
1324  switch (I.getOpcode()) {
1325  case Instruction::Add:
1326  case Instruction::Sub:
1327  case Instruction::Trunc:
1328  case Instruction::FPTrunc:
1329  case Instruction::BitCast:
1330  break; // Any undef -> undef
1331  case Instruction::FSub:
1332  case Instruction::FAdd:
1333  case Instruction::FMul:
1334  case Instruction::FDiv:
1335  case Instruction::FRem:
1336  // Floating-point binary operation: be conservative.
1337  if (Op0LV.isUnknown() && Op1LV.isUnknown())
1338  markForcedConstant(&I, Constant::getNullValue(ITy));
1339  else
1340  markOverdefined(&I);
1341  return true;
1342  case Instruction::ZExt:
1343  case Instruction::SExt:
1344  case Instruction::FPToUI:
1345  case Instruction::FPToSI:
1346  case Instruction::FPExt:
1347  case Instruction::PtrToInt:
1348  case Instruction::IntToPtr:
1349  case Instruction::SIToFP:
1350  case Instruction::UIToFP:
1351  // undef -> 0; some outputs are impossible
1352  markForcedConstant(&I, Constant::getNullValue(ITy));
1353  return true;
1354  case Instruction::Mul:
1355  case Instruction::And:
1356  // Both operands undef -> undef
1357  if (Op0LV.isUnknown() && Op1LV.isUnknown())
1358  break;
1359  // undef * X -> 0. X could be zero.
1360  // undef & X -> 0. X could be zero.
1361  markForcedConstant(&I, Constant::getNullValue(ITy));
1362  return true;
1363 
1364  case Instruction::Or:
1365  // Both operands undef -> undef
1366  if (Op0LV.isUnknown() && Op1LV.isUnknown())
1367  break;
1368  // undef | X -> -1. X could be -1.
1369  markForcedConstant(&I, Constant::getAllOnesValue(ITy));
1370  return true;
1371 
1372  case Instruction::Xor:
1373  // undef ^ undef -> 0; strictly speaking, this is not strictly
1374  // necessary, but we try to be nice to people who expect this
1375  // behavior in simple cases
1376  if (Op0LV.isUnknown() && Op1LV.isUnknown()) {
1377  markForcedConstant(&I, Constant::getNullValue(ITy));
1378  return true;
1379  }
1380  // undef ^ X -> undef
1381  break;
1382 
1383  case Instruction::SDiv:
1384  case Instruction::UDiv:
1385  case Instruction::SRem:
1386  case Instruction::URem:
1387  // X / undef -> undef. No change.
1388  // X % undef -> undef. No change.
1389  if (Op1LV.isUnknown()) break;
1390 
1391  // X / 0 -> undef. No change.
1392  // X % 0 -> undef. No change.
1393  if (Op1LV.isConstant() && Op1LV.getConstant()->isZeroValue())
1394  break;
1395 
1396  // undef / X -> 0. X could be maxint.
1397  // undef % X -> 0. X could be 1.
1398  markForcedConstant(&I, Constant::getNullValue(ITy));
1399  return true;
1400 
1401  case Instruction::AShr:
1402  // X >>a undef -> undef.
1403  if (Op1LV.isUnknown()) break;
1404 
1405  // Shifting by the bitwidth or more is undefined.
1406  if (Op1LV.isConstant()) {
1407  if (auto *ShiftAmt = Op1LV.getConstantInt())
1408  if (ShiftAmt->getLimitedValue() >=
1409  ShiftAmt->getType()->getScalarSizeInBits())
1410  break;
1411  }
1412 
1413  // undef >>a X -> 0
1414  markForcedConstant(&I, Constant::getNullValue(ITy));
1415  return true;
1416  case Instruction::LShr:
1417  case Instruction::Shl:
1418  // X << undef -> undef.
1419  // X >> undef -> undef.
1420  if (Op1LV.isUnknown()) break;
1421 
1422  // Shifting by the bitwidth or more is undefined.
1423  if (Op1LV.isConstant()) {
1424  if (auto *ShiftAmt = Op1LV.getConstantInt())
1425  if (ShiftAmt->getLimitedValue() >=
1426  ShiftAmt->getType()->getScalarSizeInBits())
1427  break;
1428  }
1429 
1430  // undef << X -> 0
1431  // undef >> X -> 0
1432  markForcedConstant(&I, Constant::getNullValue(ITy));
1433  return true;
1434  case Instruction::Select:
1435  Op1LV = getValueState(I.getOperand(1));
1436  // undef ? X : Y -> X or Y. There could be commonality between X/Y.
1437  if (Op0LV.isUnknown()) {
1438  if (!Op1LV.isConstant()) // Pick the constant one if there is any.
1439  Op1LV = getValueState(I.getOperand(2));
1440  } else if (Op1LV.isUnknown()) {
1441  // c ? undef : undef -> undef. No change.
1442  Op1LV = getValueState(I.getOperand(2));
1443  if (Op1LV.isUnknown())
1444  break;
1445  // Otherwise, c ? undef : x -> x.
1446  } else {
1447  // Leave Op1LV as Operand(1)'s LatticeValue.
1448  }
1449 
1450  if (Op1LV.isConstant())
1451  markForcedConstant(&I, Op1LV.getConstant());
1452  else
1453  markOverdefined(&I);
1454  return true;
1455  case Instruction::Load:
1456  // A load here means one of two things: a load of undef from a global,
1457  // a load from an unknown pointer. Either way, having it return undef
1458  // is okay.
1459  break;
1460  case Instruction::ICmp:
1461  // X == undef -> undef. Other comparisons get more complicated.
1462  if (cast<ICmpInst>(&I)->isEquality())
1463  break;
1464  markOverdefined(&I);
1465  return true;
1466  case Instruction::Call:
1467  case Instruction::Invoke: {
1468  // There are two reasons a call can have an undef result
1469  // 1. It could be tracked.
1470  // 2. It could be constant-foldable.
1471  // Because of the way we solve return values, tracked calls must
1472  // never be marked overdefined in ResolvedUndefsIn.
1473  if (Function *F = CallSite(&I).getCalledFunction())
1474  if (TrackedRetVals.count(F))
1475  break;
1476 
1477  // If the call is constant-foldable, we mark it overdefined because
1478  // we do not know what return values are valid.
1479  markOverdefined(&I);
1480  return true;
1481  }
1482  default:
1483  // If we don't know what should happen here, conservatively mark it
1484  // overdefined.
1485  markOverdefined(&I);
1486  return true;
1487  }
1488  }
1489 
1490  // Check to see if we have a branch or switch on an undefined value. If so
1491  // we force the branch to go one way or the other to make the successor
1492  // values live. It doesn't really matter which way we force it.
1493  TerminatorInst *TI = BB.getTerminator();
1494  if (auto *BI = dyn_cast<BranchInst>(TI)) {
1495  if (!BI->isConditional()) continue;
1496  if (!getValueState(BI->getCondition()).isUnknown())
1497  continue;
1498 
1499  // If the input to SCCP is actually branch on undef, fix the undef to
1500  // false.
1501  if (isa<UndefValue>(BI->getCondition())) {
1502  BI->setCondition(ConstantInt::getFalse(BI->getContext()));
1503  markEdgeExecutable(&BB, TI->getSuccessor(1));
1504  return true;
1505  }
1506 
1507  // Otherwise, it is a branch on a symbolic value which is currently
1508  // considered to be undef. Handle this by forcing the input value to the
1509  // branch to false.
1510  markForcedConstant(BI->getCondition(),
1512  return true;
1513  }
1514 
1515  if (auto *IBR = dyn_cast<IndirectBrInst>(TI)) {
1516  // Indirect branch with no successor ?. Its ok to assume it branches
1517  // to no target.
1518  if (IBR->getNumSuccessors() < 1)
1519  continue;
1520 
1521  if (!getValueState(IBR->getAddress()).isUnknown())
1522  continue;
1523 
1524  // If the input to SCCP is actually branch on undef, fix the undef to
1525  // the first successor of the indirect branch.
1526  if (isa<UndefValue>(IBR->getAddress())) {
1527  IBR->setAddress(BlockAddress::get(IBR->getSuccessor(0)));
1528  markEdgeExecutable(&BB, IBR->getSuccessor(0));
1529  return true;
1530  }
1531 
1532  // Otherwise, it is a branch on a symbolic value which is currently
1533  // considered to be undef. Handle this by forcing the input value to the
1534  // branch to the first successor.
1535  markForcedConstant(IBR->getAddress(),
1536  BlockAddress::get(IBR->getSuccessor(0)));
1537  return true;
1538  }
1539 
1540  if (auto *SI = dyn_cast<SwitchInst>(TI)) {
1541  if (!SI->getNumCases() || !getValueState(SI->getCondition()).isUnknown())
1542  continue;
1543 
1544  // If the input to SCCP is actually switch on undef, fix the undef to
1545  // the first constant.
1546  if (isa<UndefValue>(SI->getCondition())) {
1547  SI->setCondition(SI->case_begin()->getCaseValue());
1548  markEdgeExecutable(&BB, SI->case_begin()->getCaseSuccessor());
1549  return true;
1550  }
1551 
1552  markForcedConstant(SI->getCondition(), SI->case_begin()->getCaseValue());
1553  return true;
1554  }
1555  }
1556 
1557  return false;
1558 }
1559 
1560 static bool tryToReplaceWithConstant(SCCPSolver &Solver, Value *V) {
1561  Constant *Const = nullptr;
1562  if (V->getType()->isStructTy()) {
1563  std::vector<LatticeVal> IVs = Solver.getStructLatticeValueFor(V);
1564  if (any_of(IVs, [](const LatticeVal &LV) { return LV.isOverdefined(); }))
1565  return false;
1566  std::vector<Constant *> ConstVals;
1567  auto *ST = dyn_cast<StructType>(V->getType());
1568  for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) {
1569  LatticeVal V = IVs[i];
1570  ConstVals.push_back(V.isConstant()
1571  ? V.getConstant()
1572  : UndefValue::get(ST->getElementType(i)));
1573  }
1574  Const = ConstantStruct::get(ST, ConstVals);
1575  } else {
1576  LatticeVal IV = Solver.getLatticeValueFor(V);
1577  if (IV.isOverdefined())
1578  return false;
1579  Const = IV.isConstant() ? IV.getConstant() : UndefValue::get(V->getType());
1580  }
1581  assert(Const && "Constant is nullptr here!");
1582  DEBUG(dbgs() << " Constant: " << *Const << " = " << *V << '\n');
1583 
1584  // Replaces all of the uses of a variable with uses of the constant.
1585  V->replaceAllUsesWith(Const);
1586  return true;
1587 }
1588 
1589 // runSCCP() - Run the Sparse Conditional Constant Propagation algorithm,
1590 // and return true if the function was modified.
1591 //
1592 static bool runSCCP(Function &F, const DataLayout &DL,
1593  const TargetLibraryInfo *TLI) {
1594  DEBUG(dbgs() << "SCCP on function '" << F.getName() << "'\n");
1595  SCCPSolver Solver(DL, TLI);
1596 
1597  // Mark the first block of the function as being executable.
1598  Solver.MarkBlockExecutable(&F.front());
1599 
1600  // Mark all arguments to the function as being overdefined.
1601  for (Argument &AI : F.args())
1602  Solver.markOverdefined(&AI);
1603 
1604  // Solve for constants.
1605  bool ResolvedUndefs = true;
1606  while (ResolvedUndefs) {
1607  Solver.Solve();
1608  DEBUG(dbgs() << "RESOLVING UNDEFs\n");
1609  ResolvedUndefs = Solver.ResolvedUndefsIn(F);
1610  }
1611 
1612  bool MadeChanges = false;
1613 
1614  // If we decided that there are basic blocks that are dead in this function,
1615  // delete their contents now. Note that we cannot actually delete the blocks,
1616  // as we cannot modify the CFG of the function.
1617 
1618  for (BasicBlock &BB : F) {
1619  if (!Solver.isBlockExecutable(&BB)) {
1620  DEBUG(dbgs() << " BasicBlock Dead:" << BB);
1621 
1622  ++NumDeadBlocks;
1623  NumInstRemoved += removeAllNonTerminatorAndEHPadInstructions(&BB);
1624 
1625  MadeChanges = true;
1626  continue;
1627  }
1628 
1629  // Iterate over all of the instructions in a function, replacing them with
1630  // constants if we have found them to be of constant values.
1631  //
1632  for (BasicBlock::iterator BI = BB.begin(), E = BB.end(); BI != E;) {
1633  Instruction *Inst = &*BI++;
1634  if (Inst->getType()->isVoidTy() || isa<TerminatorInst>(Inst))
1635  continue;
1636 
1637  if (tryToReplaceWithConstant(Solver, Inst)) {
1638  if (isInstructionTriviallyDead(Inst))
1639  Inst->eraseFromParent();
1640  // Hey, we just changed something!
1641  MadeChanges = true;
1642  ++NumInstRemoved;
1643  }
1644  }
1645  }
1646 
1647  return MadeChanges;
1648 }
1649 
1651  const DataLayout &DL = F.getParent()->getDataLayout();
1652  auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
1653  if (!runSCCP(F, DL, &TLI))
1654  return PreservedAnalyses::all();
1655 
1656  auto PA = PreservedAnalyses();
1657  PA.preserve<GlobalsAA>();
1658  return PA;
1659 }
1660 
1661 namespace {
1662 //===--------------------------------------------------------------------===//
1663 //
1664 /// SCCP Class - This class uses the SCCPSolver to implement a per-function
1665 /// Sparse Conditional Constant Propagator.
1666 ///
1667 class SCCPLegacyPass : public FunctionPass {
1668 public:
1669  void getAnalysisUsage(AnalysisUsage &AU) const override {
1672  }
1673  static char ID; // Pass identification, replacement for typeid
1674  SCCPLegacyPass() : FunctionPass(ID) {
1676  }
1677 
1678  // runOnFunction - Run the Sparse Conditional Constant Propagation
1679  // algorithm, and return true if the function was modified.
1680  //
1681  bool runOnFunction(Function &F) override {
1682  if (skipFunction(F))
1683  return false;
1684  const DataLayout &DL = F.getParent()->getDataLayout();
1685  const TargetLibraryInfo *TLI =
1686  &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
1687  return runSCCP(F, DL, TLI);
1688  }
1689 };
1690 } // end anonymous namespace
1691 
1692 char SCCPLegacyPass::ID = 0;
1693 INITIALIZE_PASS_BEGIN(SCCPLegacyPass, "sccp",
1694  "Sparse Conditional Constant Propagation", false, false)
1696 INITIALIZE_PASS_END(SCCPLegacyPass, "sccp",
1697  "Sparse Conditional Constant Propagation", false, false)
1698 
1699 // createSCCPPass - This is the public interface to this file.
1700 FunctionPass *llvm::createSCCPPass() { return new SCCPLegacyPass(); }
1701 
1702 static bool AddressIsTaken(const GlobalValue *GV) {
1703  // Delete any dead constantexpr klingons.
1705 
1706  for (const Use &U : GV->uses()) {
1707  const User *UR = U.getUser();
1708  if (const auto *SI = dyn_cast<StoreInst>(UR)) {
1709  if (SI->getOperand(0) == GV || SI->isVolatile())
1710  return true; // Storing addr of GV.
1711  } else if (isa<InvokeInst>(UR) || isa<CallInst>(UR)) {
1712  // Make sure we are calling the function, not passing the address.
1713  ImmutableCallSite CS(cast<Instruction>(UR));
1714  if (!CS.isCallee(&U))
1715  return true;
1716  } else if (const auto *LI = dyn_cast<LoadInst>(UR)) {
1717  if (LI->isVolatile())
1718  return true;
1719  } else if (isa<BlockAddress>(UR)) {
1720  // blockaddress doesn't take the address of the function, it takes addr
1721  // of label.
1722  } else {
1723  return true;
1724  }
1725  }
1726  return false;
1727 }
1728 
1730  SmallPtrSet<Function *, 32> &AddressTakenFunctions,
1731  SmallVector<ReturnInst *, 8> &ReturnsToZap) {
1732  // We can only do this if we know that nothing else can call the function.
1733  if (!F.hasLocalLinkage() || AddressTakenFunctions.count(&F))
1734  return;
1735 
1736  for (BasicBlock &BB : F)
1737  if (auto *RI = dyn_cast<ReturnInst>(BB.getTerminator()))
1738  if (!isa<UndefValue>(RI->getOperand(0)))
1739  ReturnsToZap.push_back(RI);
1740 }
1741 
1742 static bool runIPSCCP(Module &M, const DataLayout &DL,
1743  const TargetLibraryInfo *TLI) {
1744  SCCPSolver Solver(DL, TLI);
1745 
1746  // AddressTakenFunctions - This set keeps track of the address-taken functions
1747  // that are in the input. As IPSCCP runs through and simplifies code,
1748  // functions that were address taken can end up losing their
1749  // address-taken-ness. Because of this, we keep track of their addresses from
1750  // the first pass so we can use them for the later simplification pass.
1751  SmallPtrSet<Function*, 32> AddressTakenFunctions;
1752 
1753  // Loop over all functions, marking arguments to those with their addresses
1754  // taken or that are external as overdefined.
1755  //
1756  for (Function &F : M) {
1757  if (F.isDeclaration())
1758  continue;
1759 
1760  // If this is an exact definition of this function, then we can propagate
1761  // information about its result into callsites of it.
1762  // Don't touch naked functions. They may contain asm returning a
1763  // value we don't see, so we may end up interprocedurally propagating
1764  // the return value incorrectly.
1765  if (F.hasExactDefinition() && !F.hasFnAttribute(Attribute::Naked))
1766  Solver.AddTrackedFunction(&F);
1767 
1768  // If this function only has direct calls that we can see, we can track its
1769  // arguments and return value aggressively, and can assume it is not called
1770  // unless we see evidence to the contrary.
1771  if (F.hasLocalLinkage()) {
1772  if (F.hasAddressTaken()) {
1773  AddressTakenFunctions.insert(&F);
1774  }
1775  else {
1776  Solver.AddArgumentTrackedFunction(&F);
1777  continue;
1778  }
1779  }
1780 
1781  // Assume the function is called.
1782  Solver.MarkBlockExecutable(&F.front());
1783 
1784  // Assume nothing about the incoming arguments.
1785  for (Argument &AI : F.args())
1786  Solver.markOverdefined(&AI);
1787  }
1788 
1789  // Loop over global variables. We inform the solver about any internal global
1790  // variables that do not have their 'addresses taken'. If they don't have
1791  // their addresses taken, we can propagate constants through them.
1792  for (GlobalVariable &G : M.globals())
1793  if (!G.isConstant() && G.hasLocalLinkage() &&
1794  G.hasDefinitiveInitializer() && !AddressIsTaken(&G))
1795  Solver.TrackValueOfGlobalVariable(&G);
1796 
1797  // Solve for constants.
1798  bool ResolvedUndefs = true;
1799  while (ResolvedUndefs) {
1800  Solver.Solve();
1801 
1802  DEBUG(dbgs() << "RESOLVING UNDEFS\n");
1803  ResolvedUndefs = false;
1804  for (Function &F : M)
1805  ResolvedUndefs |= Solver.ResolvedUndefsIn(F);
1806  }
1807 
1808  bool MadeChanges = false;
1809 
1810  // Iterate over all of the instructions in the module, replacing them with
1811  // constants if we have found them to be of constant values.
1812  //
1813  SmallVector<BasicBlock*, 512> BlocksToErase;
1814 
1815  for (Function &F : M) {
1816  if (F.isDeclaration())
1817  continue;
1818 
1819  if (Solver.isBlockExecutable(&F.front()))
1820  for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E;
1821  ++AI)
1822  if (!AI->use_empty() && tryToReplaceWithConstant(Solver, &*AI))
1823  ++IPNumArgsElimed;
1824 
1825  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1826  if (!Solver.isBlockExecutable(&*BB)) {
1827  DEBUG(dbgs() << " BasicBlock Dead:" << *BB);
1828 
1829  ++NumDeadBlocks;
1830  NumInstRemoved +=
1831  changeToUnreachable(BB->getFirstNonPHI(), /*UseLLVMTrap=*/false);
1832 
1833  MadeChanges = true;
1834 
1835  if (&*BB != &F.front())
1836  BlocksToErase.push_back(&*BB);
1837  continue;
1838  }
1839 
1840  for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1841  Instruction *Inst = &*BI++;
1842  if (Inst->getType()->isVoidTy())
1843  continue;
1844  if (tryToReplaceWithConstant(Solver, Inst)) {
1845  if (!isa<CallInst>(Inst) && !isa<TerminatorInst>(Inst))
1846  Inst->eraseFromParent();
1847  // Hey, we just changed something!
1848  MadeChanges = true;
1849  ++IPNumInstRemoved;
1850  }
1851  }
1852  }
1853 
1854  // Now that all instructions in the function are constant folded, erase dead
1855  // blocks, because we can now use ConstantFoldTerminator to get rid of
1856  // in-edges.
1857  for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) {
1858  // If there are any PHI nodes in this successor, drop entries for BB now.
1859  BasicBlock *DeadBB = BlocksToErase[i];
1860  for (Value::user_iterator UI = DeadBB->user_begin(),
1861  UE = DeadBB->user_end();
1862  UI != UE;) {
1863  // Grab the user and then increment the iterator early, as the user
1864  // will be deleted. Step past all adjacent uses from the same user.
1865  auto *I = dyn_cast<Instruction>(*UI);
1866  do { ++UI; } while (UI != UE && *UI == I);
1867 
1868  // Ignore blockaddress users; BasicBlock's dtor will handle them.
1869  if (!I) continue;
1870 
1871  bool Folded = ConstantFoldTerminator(I->getParent());
1872  assert(Folded &&
1873  "Expect TermInst on constantint or blockaddress to be folded");
1874  (void) Folded;
1875  }
1876 
1877  // Finally, delete the basic block.
1878  F.getBasicBlockList().erase(DeadBB);
1879  }
1880  BlocksToErase.clear();
1881  }
1882 
1883  // If we inferred constant or undef return values for a function, we replaced
1884  // all call uses with the inferred value. This means we don't need to bother
1885  // actually returning anything from the function. Replace all return
1886  // instructions with return undef.
1887  //
1888  // Do this in two stages: first identify the functions we should process, then
1889  // actually zap their returns. This is important because we can only do this
1890  // if the address of the function isn't taken. In cases where a return is the
1891  // last use of a function, the order of processing functions would affect
1892  // whether other functions are optimizable.
1893  SmallVector<ReturnInst*, 8> ReturnsToZap;
1894 
1895  const DenseMap<Function*, LatticeVal> &RV = Solver.getTrackedRetVals();
1896  for (const auto &I : RV) {
1897  Function *F = I.first;
1898  if (I.second.isOverdefined() || F->getReturnType()->isVoidTy())
1899  continue;
1900  findReturnsToZap(*F, AddressTakenFunctions, ReturnsToZap);
1901  }
1902 
1903  for (const auto &F : Solver.getMRVFunctionsTracked()) {
1904  assert(F->getReturnType()->isStructTy() &&
1905  "The return type should be a struct");
1906  StructType *STy = cast<StructType>(F->getReturnType());
1907  if (Solver.isStructLatticeConstant(F, STy))
1908  findReturnsToZap(*F, AddressTakenFunctions, ReturnsToZap);
1909  }
1910 
1911  // Zap all returns which we've identified as zap to change.
1912  for (unsigned i = 0, e = ReturnsToZap.size(); i != e; ++i) {
1913  Function *F = ReturnsToZap[i]->getParent()->getParent();
1914  ReturnsToZap[i]->setOperand(0, UndefValue::get(F->getReturnType()));
1915  }
1916 
1917  // If we inferred constant or undef values for globals variables, we can
1918  // delete the global and any stores that remain to it.
1919  const DenseMap<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
1921  E = TG.end(); I != E; ++I) {
1922  GlobalVariable *GV = I->first;
1923  assert(!I->second.isOverdefined() &&
1924  "Overdefined values should have been taken out of the map!");
1925  DEBUG(dbgs() << "Found that GV '" << GV->getName() << "' is constant!\n");
1926  while (!GV->use_empty()) {
1927  StoreInst *SI = cast<StoreInst>(GV->user_back());
1928  SI->eraseFromParent();
1929  }
1930  M.getGlobalList().erase(GV);
1931  ++IPNumGlobalConst;
1932  }
1933 
1934  return MadeChanges;
1935 }
1936 
1938  const DataLayout &DL = M.getDataLayout();
1939  auto &TLI = AM.getResult<TargetLibraryAnalysis>(M);
1940  if (!runIPSCCP(M, DL, &TLI))
1941  return PreservedAnalyses::all();
1942  return PreservedAnalyses::none();
1943 }
1944 
1945 namespace {
1946 //===--------------------------------------------------------------------===//
1947 //
1948 /// IPSCCP Class - This class implements interprocedural Sparse Conditional
1949 /// Constant Propagation.
1950 ///
1951 class IPSCCPLegacyPass : public ModulePass {
1952 public:
1953  static char ID;
1954 
1955  IPSCCPLegacyPass() : ModulePass(ID) {
1957  }
1958 
1959  bool runOnModule(Module &M) override {
1960  if (skipModule(M))
1961  return false;
1962  const DataLayout &DL = M.getDataLayout();
1963  const TargetLibraryInfo *TLI =
1964  &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
1965  return runIPSCCP(M, DL, TLI);
1966  }
1967 
1968  void getAnalysisUsage(AnalysisUsage &AU) const override {
1970  }
1971 };
1972 } // end anonymous namespace
1973 
1974 char IPSCCPLegacyPass::ID = 0;
1975 INITIALIZE_PASS_BEGIN(IPSCCPLegacyPass, "ipsccp",
1976  "Interprocedural Sparse Conditional Constant Propagation",
1977  false, false)
1979 INITIALIZE_PASS_END(IPSCCPLegacyPass, "ipsccp",
1980  "Interprocedural Sparse Conditional Constant Propagation",
1981  false, false)
1982 
1983 // createIPSCCPPass - This is the public interface to this file.
1984 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.
bool onlyReadsMemory() const
Determine if the function does not access or only reads memory.
Definition: Function.h:403
uint64_t CallInst * C
Return a value (possibly void), from a function.
User::op_iterator arg_iterator
The type of iterator to use when looping over actual arguments at this call site. ...
Definition: CallSite.h:213
SymbolTableList< Instruction >::iterator eraseFromParent()
This method unlinks &#39;this&#39; from the containing basic block and deletes it.
Definition: Instruction.cpp:69
A parsed version of the target data layout string in and methods for querying it. ...
Definition: DataLayout.h:109
static ConstantInt * getFalse(LLVMContext &Context)
Definition: Constants.cpp:523
This class is the base class for the comparison instructions.
Definition: InstrTypes.h:850
void setInt(IntType IntVal)
iterator_range< use_iterator > uses()
Definition: Value.h:350
static bool isConstant(const MachineInstr &MI)
AnalysisUsage & addPreserved()
Add the specified Pass class to the set of analyses preserved by this pass.
bool hasLocalLinkage() const
Definition: GlobalValue.h:416
static bool runIPSCCP(Module &M, const DataLayout &DL, const TargetLibraryInfo *TLI)
Definition: SCCP.cpp:1742
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...
This class represents an incoming formal argument to a Function.
Definition: Argument.h:30
Base class for instruction visitors.
Definition: InstVisitor.h:81
Value * getAggregateOperand()
PassT::Result & getResult(IRUnitT &IR, ExtraArgTs... ExtraArgs)
Get the result of an analysis pass for a given IR unit.
Definition: PassManager.h:687
iterator erase(iterator where)
Definition: ilist.h:280
const Constant * getInitializer() const
getInitializer - Return the initializer for this global variable.
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
PointerTy getPointer() const
This is the interface for a simple mod/ref and alias analysis over globals.
unsigned getNumIndices() const
A Module instance is used to store all the information related to an LLVM module. ...
Definition: Module.h:63
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:1115
BasicBlock * getSuccessor(unsigned idx) const
Return the specified successor.
LLVM_ATTRIBUTE_ALWAYS_INLINE size_type size() const
Definition: SmallVector.h:136
An instruction for ordering other memory operations.
Definition: Instructions.h:440
static bool AddressIsTaken(const GlobalValue *GV)
Definition: SCCP.cpp:1702
Implements a dense probed hash-table based set.
Definition: DenseSet.h:221
unsigned getNumElements() const
Random access to the elements.
Definition: DerivedTypes.h:313
This class represents a function call, abstracting a target machine&#39;s calling convention.
const Value * getTrueValue() const
ModulePass * createIPSCCPPass()
createIPSCCPPass - This pass propagates constants from call sites into the bodies of functions...
Definition: SCCP.cpp:1984
LLVMContext & getContext() const
All values hold a context through their type.
Definition: Value.cpp:697
arg_iterator arg_end()
Definition: Function.h:612
STATISTIC(NumFunctions, "Total number of functions")
F(f)
An instruction for reading from memory.
Definition: Instructions.h:164
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:1832
static bool runSCCP(Function &F, const DataLayout &DL, const TargetLibraryInfo *TLI)
Definition: SCCP.cpp:1592
void reserve(size_type N)
Definition: SmallVector.h:380
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:1401
static Constant * getNullValue(Type *Ty)
Constructor to create a &#39;0&#39; constant of arbitrary type.
Definition: Constants.cpp:207
iterator begin()
Instruction iterator methods.
Definition: BasicBlock.h:252
std::pair< iterator, bool > insert(const std::pair< KeyT, ValueT > &KV)
Definition: DenseMap.h:191
The address of a basic block.
Definition: Constants.h:813
AnalysisUsage & addRequired()
#define INITIALIZE_PASS_DEPENDENCY(depName)
Definition: PassSupport.h:51
void setPointer(PointerTy PtrVal)
bool isVolatile() const
Return true if this is a load from a volatile memory location.
Definition: Instructions.h:217
This class represents the LLVM &#39;select&#39; instruction.
const DataLayout & getDataLayout() const
Get the data layout for the module&#39;s target platform.
Definition: Module.cpp:361
This is the base class for all instructions that perform data casts.
Definition: InstrTypes.h:560
ArrayRef< T > makeArrayRef(const T &OneElt)
Construct an ArrayRef from a single element.
Definition: ArrayRef.h:451
Class to represent struct types.
Definition: DerivedTypes.h:201
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:70
IterTy arg_end() const
Definition: CallSite.h:557
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
Definition: SCCP.cpp:1650
InstrTy * getInstruction() const
Definition: CallSite.h:92
FunctionPass * createSCCPPass()
Definition: SCCP.cpp:1700
Type * getSourceElementType() const
Definition: Instructions.h:934
INITIALIZE_PASS_BEGIN(SCCPLegacyPass, "sccp", "Sparse Conditional Constant Propagation", false, false) INITIALIZE_PASS_END(SCCPLegacyPass
void assign(size_type NumElts, const T &Elt)
Definition: SmallVector.h:427
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:1711
sccp
Definition: SCCP.cpp:1696
Instruction::CastOps getOpcode() const
Return the opcode of this CastInst.
Definition: InstrTypes.h:820
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:245
IntType getInt() const
#define T
Value * getInsertedValueOperand()
unsigned getOpcode() const
Returns a member of one of the enums like Instruction::Add.
Definition: Instruction.h:125
An instruction for storing to memory.
Definition: Instructions.h:306
void replaceAllUsesWith(Value *V)
Change all uses of this to point to a new Value.
Definition: Value.cpp:428
Value * getOperand(unsigned i) const
Definition: User.h:154
void removeDeadConstantUsers() const
If there are any dead constant users dangling off of this constant, remove them.
Definition: Constants.cpp:475
static PreservedAnalyses none()
Convenience factory function for the empty preserved set.
Definition: PassManager.h:156
Constant * getAggregateElement(unsigned Elt) const
For aggregates (struct/array/vector) return the constant that corresponds to the specified element if...
Definition: Constants.cpp:277
bool isVoidTy() const
Return true if this is &#39;void&#39;.
Definition: Type.h:141
an instruction for type-safe pointer arithmetic to access elements of arrays and structs ...
Definition: Instructions.h:837
Type * getReturnType() const
Returns the type of the ret val.
Definition: Function.h:150
Subclasses of this class are all able to terminate a basic block.
Definition: InstrTypes.h:54
A set of analyses that are preserved following a run of a transformation pass.
Definition: PassManager.h:153
LLVM Basic Block Representation.
Definition: BasicBlock.h:59
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:46
static BlockAddress * get(Function *F, BasicBlock *BB)
Return a BlockAddress for the specified function and basic block.
Definition: Constants.cpp:1339
ipsccp
Definition: SCCP.cpp:1979
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
This is an important base class in LLVM.
Definition: Constant.h:42
LLVM_NODISCARD bool empty() const
Definition: SmallPtrSet.h:91
LLVM_ATTRIBUTE_ALWAYS_INLINE iterator begin()
Definition: SmallVector.h:116
This file contains the declarations for the subclasses of Constant, which represent the different fla...
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:363
unsigned getNumIndices() const
Represent the analysis usage information of a pass.
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:823
Analysis pass providing a never-invalidated alias analysis result.
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:285
static Constant * get(StructType *T, ArrayRef< Constant *> V)
Definition: Constants.cpp:949
arg_iterator arg_begin()
Definition: Function.h:603
size_type count(ConstPtrType Ptr) const
count - Return 1 if the specified pointer is in the set, 0 otherwise.
Definition: SmallPtrSet.h:374
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...
const Value * getCondition() const
static Constant * getAllOnesValue(Type *Ty)
Get the all ones value.
Definition: Constants.cpp:261
static UndefValue * get(Type *T)
Static factory methods - Return an &#39;undef&#39; object of the specified type.
Definition: Constants.cpp:1320
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: PassManager.h:159
Value * getIncomingValue(unsigned i) const
Return incoming value number x.
INITIALIZE_PASS_END(RegBankSelect, DEBUG_TYPE, "Assign register bank of generic virtual registers", false, false) RegBankSelect
#define llvm_unreachable(msg)
Marks that the current location is not supposed to be reachable.
idx_iterator idx_begin() const
Sparse Conditional Constant Propagation
Definition: SCCP.cpp:1696
Iterator for intrusive lists based on ilist_node.
unsigned getNumOperands() const
Definition: User.h:176
static bool tryToReplaceWithConstant(SCCPSolver &Solver, Value *V)
Definition: SCCP.cpp:1560
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements...
Definition: SmallPtrSet.h:410
This is the shared class of boolean and integer constants.
Definition: Constants.h:84
bool isExceptional() const
Definition: InstrTypes.h:84
IterTy arg_begin() const
Definition: CallSite.h:553
This is a &#39;vector&#39; (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:864
Provides information about what library functions are available for the current target.
const DataFlowGraph & G
Definition: RDFGraph.cpp:211
LLVM_NODISCARD T pop_back_val()
Definition: SmallVector.h:385
unsigned removeAllNonTerminatorAndEHPadInstructions(BasicBlock *BB)
Remove all instructions from a basic block other than it&#39;s terminator and any present EH pad instruct...
Definition: Local.cpp:1380
unsigned getNumIncomingValues() const
Return the number of incoming edges.
static const Function * getCalledFunction(const Value *V, bool LookThroughBitCast, bool &IsNoBuiltin)
static void findReturnsToZap(Function &F, SmallPtrSet< Function *, 32 > &AddressTakenFunctions, SmallVector< ReturnInst *, 8 > &ReturnsToZap)
Definition: SCCP.cpp:1729
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:1937
iterator_range< user_iterator > users()
Definition: Value.h:395
const Value * getFalseValue() const
Predicate getPredicate() const
Return the predicate for this instruction.
Definition: InstrTypes.h:934
LLVM_ATTRIBUTE_ALWAYS_INLINE iterator end()
Definition: SmallVector.h:120
bool isVolatile() const
Return true if this is a store to a volatile memory location.
Definition: Instructions.h:339
LLVM_NODISCARD bool empty() const
Definition: SmallVector.h:61
StringRef getName() const
Return a constant reference to the value&#39;s name.
Definition: Value.cpp:218
void initializeIPSCCPLegacyPassPass(PassRegistry &)
Establish a view to a call site for examination.
Definition: CallSite.h:695
BasicBlock * getIncomingBlock(unsigned i) const
Return incoming basic block number i.
const Function * getParent() const
Return the enclosing method, or null if none.
Definition: BasicBlock.h:108
#define I(x, y, z)
Definition: MD5.cpp:58
user_iterator_impl< User > user_iterator
Definition: Value.h:364
ModulePass class - This class is used to implement unstructured interprocedural optimizations and ana...
Definition: Pass.h:225
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:323
idx_iterator idx_begin() const
Type * getValueType() const
Definition: GlobalValue.h:262
size_type count(const_arg_type_t< KeyT > Val) const
Return 1 if the specified key is in the map, 0 otherwise.
Definition: DenseMap.h:141
bool isDeclaration() const
Return true if the primary definition of this global value is outside of the current translation unit...
Definition: Globals.cpp:200
FunTy * getCalledFunction() const
Return the function being called if this is a direct call, otherwise return null (if it&#39;s an indirect...
Definition: CallSite.h:107
Analysis pass providing the TargetLibraryInfo.
unsigned getPointerAddressSpace() const
Returns the address space of the pointer operand.
Definition: Instructions.h:276
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
user_iterator user_begin()
Definition: Value.h:371
const BasicBlock & front() const
Definition: Function.h:595
unsigned getNumSuccessors() const
Return the number of successors that this terminator has.
bool isSingleValueType() const
Return true if the type is a valid type for a register in codegen.
Definition: Type.h:247
Module * getParent()
Get the module that this global value is contained inside of...
Definition: GlobalValue.h:545
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:293
LLVM Value Representation.
Definition: Value.h:73
bool canConstantFoldCallTo(ImmutableCallSite CS, const Function *F)
canConstantFoldCallTo - Return true if its even possible to fold a call to the specified function...
Invoke instruction.
#define DEBUG(X)
Definition: Debug.h:118
A container for analyses that lazily runs them and caches their results.
const TerminatorInst * getTerminator() const LLVM_READONLY
Returns the terminator instruction if the block is well formed or null if the block is not well forme...
Definition: BasicBlock.cpp:120
Constant * ConstantFoldCall(ImmutableCallSite CS, 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 use_empty() const
Definition: Value.h:322
iterator_range< arg_iterator > args()
Definition: Function.h:621
bool isStructTy() const
True if this is an instance of StructType.
Definition: Type.h:215
User * user_back()
Definition: Value.h:381
const BasicBlock * getParent() const
Definition: Instruction.h:66
This instruction inserts a struct field of array element value into an aggregate value.
void resize(size_type N)
Definition: SmallVector.h:355
user_iterator user_end()
Definition: Value.h:379
bool isCallee(Value::const_user_iterator UI) const
Determine whether the passed iterator points to the callee operand&#39;s Use.
Definition: CallSite.h:143