Lint.cpp revision 13ec30b6a1184c590ed93d81764a0314202abeaf 
1//===-- Lint.cpp - Check for common errors in LLVM IR ---------------------===//
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 pass statically checks for common and easily-identified constructs
11// which produce undefined or likely unintended behavior in LLVM IR.
12//
13// It is not a guarantee of correctness, in two ways. First, it isn't
14// comprehensive. There are checks which could be done statically which are
15// not yet implemented. Some of these are indicated by TODO comments, but
16// those aren't comprehensive either. Second, many conditions cannot be
17// checked statically. This pass does no dynamic instrumentation, so it
18// can't check for all possible problems.
19//
20// Another limitation is that it assumes all code will be executed. A store
21// through a null pointer in a basic block which is never reached is harmless,
22// but this pass will warn about it anyway.
23//
24// Optimization passes may make conditions that this pass checks for more or
25// less obvious. If an optimization pass appears to be introducing a warning,
26// it may be that the optimization pass is merely exposing an existing
27// condition in the code.
28//
29// This code may be run before instcombine. In many cases, instcombine checks
30// for the same kinds of things and turns instructions with undefined behavior
31// into unreachable (or equivalent). Because of this, this pass makes some
32// effort to look through bitcasts and so on.
33//
34//===----------------------------------------------------------------------===//
35
36#include "llvm/Analysis/Passes.h"
37#include "llvm/Analysis/AliasAnalysis.h"
38#include "llvm/Analysis/InstructionSimplify.h"
39#include "llvm/Analysis/ConstantFolding.h"
40#include "llvm/Analysis/Dominators.h"
41#include "llvm/Analysis/Lint.h"
42#include "llvm/Analysis/Loads.h"
43#include "llvm/Analysis/ValueTracking.h"
44#include "llvm/Assembly/Writer.h"
45#include "llvm/Target/TargetData.h"
46#include "llvm/Pass.h"
47#include "llvm/PassManager.h"
48#include "llvm/IntrinsicInst.h"
49#include "llvm/Function.h"
50#include "llvm/Support/CallSite.h"
51#include "llvm/Support/Debug.h"
52#include "llvm/Support/InstVisitor.h"
53#include "llvm/Support/raw_ostream.h"
54#include "llvm/ADT/STLExtras.h"
55using namespace llvm;
56
57namespace {
58  namespace MemRef {
59    static unsigned Read     = 1;
60    static unsigned Write    = 2;
61    static unsigned Callee   = 4;
62    static unsigned Branchee = 8;
63  }
64
65  class Lint : public FunctionPass, public InstVisitor<Lint> {
66    friend class InstVisitor<Lint>;
67
68    void visitFunction(Function &F);
69
70    void visitCallSite(CallSite CS);
71    void visitMemoryReference(Instruction &I, Value *Ptr, unsigned Align,
72                              const Type *Ty, unsigned Flags);
73
74    void visitCallInst(CallInst &I);
75    void visitInvokeInst(InvokeInst &I);
76    void visitReturnInst(ReturnInst &I);
77    void visitLoadInst(LoadInst &I);
78    void visitStoreInst(StoreInst &I);
79    void visitXor(BinaryOperator &I);
80    void visitSub(BinaryOperator &I);
81    void visitLShr(BinaryOperator &I);
82    void visitAShr(BinaryOperator &I);
83    void visitShl(BinaryOperator &I);
84    void visitSDiv(BinaryOperator &I);
85    void visitUDiv(BinaryOperator &I);
86    void visitSRem(BinaryOperator &I);
87    void visitURem(BinaryOperator &I);
88    void visitAllocaInst(AllocaInst &I);
89    void visitVAArgInst(VAArgInst &I);
90    void visitIndirectBrInst(IndirectBrInst &I);
91    void visitExtractElementInst(ExtractElementInst &I);
92    void visitInsertElementInst(InsertElementInst &I);
93    void visitUnreachableInst(UnreachableInst &I);
94
95    Value *findValue(Value *V, bool OffsetOk) const;
96    Value *findValueImpl(Value *V, bool OffsetOk,
97                         SmallPtrSet<Value *, 4> &Visited) const;
98
99  public:
100    Module *Mod;
101    AliasAnalysis *AA;
102    DominatorTree *DT;
103    TargetData *TD;
104
105    std::string Messages;
106    raw_string_ostream MessagesStr;
107
108    static char ID; // Pass identification, replacement for typeid
109    Lint() : FunctionPass(&ID), MessagesStr(Messages) {}
110
111    virtual bool runOnFunction(Function &F);
112
113    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
114      AU.setPreservesAll();
115      AU.addRequired<AliasAnalysis>();
116      AU.addRequired<DominatorTree>();
117    }
118    virtual void print(raw_ostream &O, const Module *M) const {}
119
120    void WriteValue(const Value *V) {
121      if (!V) return;
122      if (isa<Instruction>(V)) {
123        MessagesStr << *V << '\n';
124      } else {
125        WriteAsOperand(MessagesStr, V, true, Mod);
126        MessagesStr << '\n';
127      }
128    }
129
130    void WriteType(const Type *T) {
131      if (!T) return;
132      MessagesStr << ' ';
133      WriteTypeSymbolic(MessagesStr, T, Mod);
134    }
135
136    // CheckFailed - A check failed, so print out the condition and the message
137    // that failed.  This provides a nice place to put a breakpoint if you want
138    // to see why something is not correct.
139    void CheckFailed(const Twine &Message,
140                     const Value *V1 = 0, const Value *V2 = 0,
141                     const Value *V3 = 0, const Value *V4 = 0) {
142      MessagesStr << Message.str() << "\n";
143      WriteValue(V1);
144      WriteValue(V2);
145      WriteValue(V3);
146      WriteValue(V4);
147    }
148
149    void CheckFailed(const Twine &Message, const Value *V1,
150                     const Type *T2, const Value *V3 = 0) {
151      MessagesStr << Message.str() << "\n";
152      WriteValue(V1);
153      WriteType(T2);
154      WriteValue(V3);
155    }
156
157    void CheckFailed(const Twine &Message, const Type *T1,
158                     const Type *T2 = 0, const Type *T3 = 0) {
159      MessagesStr << Message.str() << "\n";
160      WriteType(T1);
161      WriteType(T2);
162      WriteType(T3);
163    }
164  };
165}
166
167char Lint::ID = 0;
168static RegisterPass<Lint>
169X("lint", "Statically lint-checks LLVM IR", false, true);
170
171// Assert - We know that cond should be true, if not print an error message.
172#define Assert(C, M) \
173    do { if (!(C)) { CheckFailed(M); return; } } while (0)
174#define Assert1(C, M, V1) \
175    do { if (!(C)) { CheckFailed(M, V1); return; } } while (0)
176#define Assert2(C, M, V1, V2) \
177    do { if (!(C)) { CheckFailed(M, V1, V2); return; } } while (0)
178#define Assert3(C, M, V1, V2, V3) \
179    do { if (!(C)) { CheckFailed(M, V1, V2, V3); return; } } while (0)
180#define Assert4(C, M, V1, V2, V3, V4) \
181    do { if (!(C)) { CheckFailed(M, V1, V2, V3, V4); return; } } while (0)
182
183// Lint::run - This is the main Analysis entry point for a
184// function.
185//
186bool Lint::runOnFunction(Function &F) {
187  Mod = F.getParent();
188  AA = &getAnalysis<AliasAnalysis>();
189  DT = &getAnalysis<DominatorTree>();
190  TD = getAnalysisIfAvailable<TargetData>();
191  visit(F);
192  dbgs() << MessagesStr.str();
193  Messages.clear();
194  return false;
195}
196
197void Lint::visitFunction(Function &F) {
198  // This isn't undefined behavior, it's just a little unusual, and it's a
199  // fairly common mistake to neglect to name a function.
200  Assert1(F.hasName() || F.hasLocalLinkage(),
201          "Unusual: Unnamed function with non-local linkage", &F);
202}
203
204void Lint::visitCallSite(CallSite CS) {
205  Instruction &I = *CS.getInstruction();
206  Value *Callee = CS.getCalledValue();
207
208  visitMemoryReference(I, Callee, 0, 0, MemRef::Callee);
209
210  if (Function *F = dyn_cast<Function>(findValue(Callee, /*OffsetOk=*/false))) {
211    Assert1(CS.getCallingConv() == F->getCallingConv(),
212            "Undefined behavior: Caller and callee calling convention differ",
213            &I);
214
215    const FunctionType *FT = F->getFunctionType();
216    unsigned NumActualArgs = unsigned(CS.arg_end()-CS.arg_begin());
217
218    Assert1(FT->isVarArg() ?
219              FT->getNumParams() <= NumActualArgs :
220              FT->getNumParams() == NumActualArgs,
221            "Undefined behavior: Call argument count mismatches callee "
222            "argument count", &I);
223
224    // TODO: Check argument types (in case the callee was casted)
225
226    // TODO: Check ABI-significant attributes.
227
228    // TODO: Check noalias attribute.
229
230    // TODO: Check sret attribute.
231  }
232
233  if (CS.isCall() && cast<CallInst>(CS.getInstruction())->isTailCall())
234    for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
235         AI != AE; ++AI) {
236      Value *Obj = findValue(*AI, /*OffsetOk=*/true);
237      Assert1(!isa<AllocaInst>(Obj),
238              "Undefined behavior: Call with \"tail\" keyword references "
239              "alloca", &I);
240    }
241
242
243  if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I))
244    switch (II->getIntrinsicID()) {
245    default: break;
246
247    // TODO: Check more intrinsics
248
249    case Intrinsic::memcpy: {
250      MemCpyInst *MCI = cast<MemCpyInst>(&I);
251      visitMemoryReference(I, MCI->getDest(), MCI->getAlignment(), 0,
252                           MemRef::Write);
253      visitMemoryReference(I, MCI->getSource(), MCI->getAlignment(), 0,
254                           MemRef::Read);
255
256      // Check that the memcpy arguments don't overlap. The AliasAnalysis API
257      // isn't expressive enough for what we really want to do. Known partial
258      // overlap is not distinguished from the case where nothing is known.
259      unsigned Size = 0;
260      if (const ConstantInt *Len =
261            dyn_cast<ConstantInt>(findValue(MCI->getLength(),
262                                            /*OffsetOk=*/false)))
263        if (Len->getValue().isIntN(32))
264          Size = Len->getValue().getZExtValue();
265      Assert1(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
266              AliasAnalysis::MustAlias,
267              "Undefined behavior: memcpy source and destination overlap", &I);
268      break;
269    }
270    case Intrinsic::memmove: {
271      MemMoveInst *MMI = cast<MemMoveInst>(&I);
272      visitMemoryReference(I, MMI->getDest(), MMI->getAlignment(), 0,
273                           MemRef::Write);
274      visitMemoryReference(I, MMI->getSource(), MMI->getAlignment(), 0,
275                           MemRef::Read);
276      break;
277    }
278    case Intrinsic::memset: {
279      MemSetInst *MSI = cast<MemSetInst>(&I);
280      visitMemoryReference(I, MSI->getDest(), MSI->getAlignment(), 0,
281                           MemRef::Write);
282      break;
283    }
284
285    case Intrinsic::vastart:
286      Assert1(I.getParent()->getParent()->isVarArg(),
287              "Undefined behavior: va_start called in a non-varargs function",
288              &I);
289
290      visitMemoryReference(I, CS.getArgument(0), 0, 0,
291                           MemRef::Read | MemRef::Write);
292      break;
293    case Intrinsic::vacopy:
294      visitMemoryReference(I, CS.getArgument(0), 0, 0, MemRef::Write);
295      visitMemoryReference(I, CS.getArgument(1), 0, 0, MemRef::Read);
296      break;
297    case Intrinsic::vaend:
298      visitMemoryReference(I, CS.getArgument(0), 0, 0,
299                           MemRef::Read | MemRef::Write);
300      break;
301
302    case Intrinsic::stackrestore:
303      // Stackrestore doesn't read or write memory, but it sets the
304      // stack pointer, which the compiler may read from or write to
305      // at any time, so check it for both readability and writeability.
306      visitMemoryReference(I, CS.getArgument(0), 0, 0,
307                           MemRef::Read | MemRef::Write);
308      break;
309    }
310}
311
312void Lint::visitCallInst(CallInst &I) {
313  return visitCallSite(&I);
314}
315
316void Lint::visitInvokeInst(InvokeInst &I) {
317  return visitCallSite(&I);
318}
319
320void Lint::visitReturnInst(ReturnInst &I) {
321  Function *F = I.getParent()->getParent();
322  Assert1(!F->doesNotReturn(),
323          "Unusual: Return statement in function with noreturn attribute",
324          &I);
325
326  if (Value *V = I.getReturnValue()) {
327    Value *Obj = findValue(V, /*OffsetOk=*/true);
328    Assert1(!isa<AllocaInst>(Obj),
329            "Unusual: Returning alloca value", &I);
330  }
331}
332
333// TODO: Add a length argument and check that the reference is in bounds
334void Lint::visitMemoryReference(Instruction &I,
335                                Value *Ptr, unsigned Align, const Type *Ty,
336                                unsigned Flags) {
337  Value *UnderlyingObject = findValue(Ptr, /*OffsetOk=*/true);
338  Assert1(!isa<ConstantPointerNull>(UnderlyingObject),
339          "Undefined behavior: Null pointer dereference", &I);
340  Assert1(!isa<UndefValue>(UnderlyingObject),
341          "Undefined behavior: Undef pointer dereference", &I);
342
343  if (Flags & MemRef::Write) {
344    if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(UnderlyingObject))
345      Assert1(!GV->isConstant(),
346              "Undefined behavior: Write to read-only memory", &I);
347    Assert1(!isa<Function>(UnderlyingObject) &&
348            !isa<BlockAddress>(UnderlyingObject),
349            "Undefined behavior: Write to text section", &I);
350  }
351  if (Flags & MemRef::Read) {
352    Assert1(!isa<Function>(UnderlyingObject),
353            "Unusual: Load from function body", &I);
354    Assert1(!isa<BlockAddress>(UnderlyingObject),
355            "Undefined behavior: Load from block address", &I);
356  }
357  if (Flags & MemRef::Callee) {
358    Assert1(!isa<BlockAddress>(UnderlyingObject),
359            "Undefined behavior: Call to block address", &I);
360  }
361  if (Flags & MemRef::Branchee) {
362    Assert1(!isa<Constant>(UnderlyingObject) ||
363            isa<BlockAddress>(UnderlyingObject),
364            "Undefined behavior: Branch to non-blockaddress", &I);
365  }
366
367  if (TD) {
368    if (Align == 0 && Ty) Align = TD->getABITypeAlignment(Ty);
369
370    if (Align != 0) {
371      unsigned BitWidth = TD->getTypeSizeInBits(Ptr->getType());
372      APInt Mask = APInt::getAllOnesValue(BitWidth),
373                   KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
374      ComputeMaskedBits(Ptr, Mask, KnownZero, KnownOne, TD);
375      Assert1(!(KnownOne & APInt::getLowBitsSet(BitWidth, Log2_32(Align))),
376              "Undefined behavior: Memory reference address is misaligned", &I);
377    }
378  }
379}
380
381void Lint::visitLoadInst(LoadInst &I) {
382  visitMemoryReference(I, I.getPointerOperand(), I.getAlignment(), I.getType(),
383                       MemRef::Read);
384}
385
386void Lint::visitStoreInst(StoreInst &I) {
387  visitMemoryReference(I, I.getPointerOperand(), I.getAlignment(),
388                  I.getOperand(0)->getType(), MemRef::Write);
389}
390
391void Lint::visitXor(BinaryOperator &I) {
392  Assert1(!isa<UndefValue>(I.getOperand(0)) ||
393          !isa<UndefValue>(I.getOperand(1)),
394          "Undefined result: xor(undef, undef)", &I);
395}
396
397void Lint::visitSub(BinaryOperator &I) {
398  Assert1(!isa<UndefValue>(I.getOperand(0)) ||
399          !isa<UndefValue>(I.getOperand(1)),
400          "Undefined result: sub(undef, undef)", &I);
401}
402
403void Lint::visitLShr(BinaryOperator &I) {
404  if (ConstantInt *CI =
405        dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
406    Assert1(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
407            "Undefined result: Shift count out of range", &I);
408}
409
410void Lint::visitAShr(BinaryOperator &I) {
411  if (ConstantInt *CI =
412        dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
413    Assert1(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
414            "Undefined result: Shift count out of range", &I);
415}
416
417void Lint::visitShl(BinaryOperator &I) {
418  if (ConstantInt *CI =
419        dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
420    Assert1(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
421            "Undefined result: Shift count out of range", &I);
422}
423
424static bool isZero(Value *V, TargetData *TD) {
425  // Assume undef could be zero.
426  if (isa<UndefValue>(V)) return true;
427
428  unsigned BitWidth = cast<IntegerType>(V->getType())->getBitWidth();
429  APInt Mask = APInt::getAllOnesValue(BitWidth),
430               KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
431  ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD);
432  return KnownZero.isAllOnesValue();
433}
434
435void Lint::visitSDiv(BinaryOperator &I) {
436  Assert1(!isZero(I.getOperand(1), TD),
437          "Undefined behavior: Division by zero", &I);
438}
439
440void Lint::visitUDiv(BinaryOperator &I) {
441  Assert1(!isZero(I.getOperand(1), TD),
442          "Undefined behavior: Division by zero", &I);
443}
444
445void Lint::visitSRem(BinaryOperator &I) {
446  Assert1(!isZero(I.getOperand(1), TD),
447          "Undefined behavior: Division by zero", &I);
448}
449
450void Lint::visitURem(BinaryOperator &I) {
451  Assert1(!isZero(I.getOperand(1), TD),
452          "Undefined behavior: Division by zero", &I);
453}
454
455void Lint::visitAllocaInst(AllocaInst &I) {
456  if (isa<ConstantInt>(I.getArraySize()))
457    // This isn't undefined behavior, it's just an obvious pessimization.
458    Assert1(&I.getParent()->getParent()->getEntryBlock() == I.getParent(),
459            "Pessimization: Static alloca outside of entry block", &I);
460}
461
462void Lint::visitVAArgInst(VAArgInst &I) {
463  visitMemoryReference(I, I.getOperand(0), 0, 0,
464                       MemRef::Read | MemRef::Write);
465}
466
467void Lint::visitIndirectBrInst(IndirectBrInst &I) {
468  visitMemoryReference(I, I.getAddress(), 0, 0, MemRef::Branchee);
469}
470
471void Lint::visitExtractElementInst(ExtractElementInst &I) {
472  if (ConstantInt *CI =
473        dyn_cast<ConstantInt>(findValue(I.getIndexOperand(),
474                                        /*OffsetOk=*/false)))
475    Assert1(CI->getValue().ult(I.getVectorOperandType()->getNumElements()),
476            "Undefined result: extractelement index out of range", &I);
477}
478
479void Lint::visitInsertElementInst(InsertElementInst &I) {
480  if (ConstantInt *CI =
481        dyn_cast<ConstantInt>(findValue(I.getOperand(2),
482                                        /*OffsetOk=*/false)))
483    Assert1(CI->getValue().ult(I.getType()->getNumElements()),
484            "Undefined result: insertelement index out of range", &I);
485}
486
487void Lint::visitUnreachableInst(UnreachableInst &I) {
488  // This isn't undefined behavior, it's merely suspicious.
489  Assert1(&I == I.getParent()->begin() ||
490          prior(BasicBlock::iterator(&I))->mayHaveSideEffects(),
491          "Unusual: unreachable immediately preceded by instruction without "
492          "side effects", &I);
493}
494
495/// findValue - Look through bitcasts and simple memory reference patterns
496/// to identify an equivalent, but more informative, value.  If OffsetOk
497/// is true, look through getelementptrs with non-zero offsets too.
498///
499/// Most analysis passes don't require this logic, because instcombine
500/// will simplify most of these kinds of things away. But it's a goal of
501/// this Lint pass to be useful even on non-optimized IR.
502Value *Lint::findValue(Value *V, bool OffsetOk) const {
503  SmallPtrSet<Value *, 4> Visited;
504  return findValueImpl(V, OffsetOk, Visited);
505}
506
507/// findValueImpl - Implementation helper for findValue.
508Value *Lint::findValueImpl(Value *V, bool OffsetOk,
509                           SmallPtrSet<Value *, 4> &Visited) const {
510  // Detect self-referential values.
511  if (!Visited.insert(V))
512    return UndefValue::get(V->getType());
513
514  // TODO: Look through sext or zext cast, when the result is known to
515  // be interpreted as signed or unsigned, respectively.
516  // TODO: Look through calls with unique return values.
517  // TODO: Look through vector insert/extract/shuffle.
518  V = OffsetOk ? V->getUnderlyingObject() : V->stripPointerCasts();
519  if (LoadInst *L = dyn_cast<LoadInst>(V)) {
520    BasicBlock::iterator BBI = L;
521    BasicBlock *BB = L->getParent();
522    SmallPtrSet<BasicBlock *, 4> VisitedBlocks;
523    for (;;) {
524      if (!VisitedBlocks.insert(BB)) break;
525      if (Value *U = FindAvailableLoadedValue(L->getPointerOperand(),
526                                              BB, BBI, 6, AA))
527        return findValueImpl(U, OffsetOk, Visited);
528      if (BBI != BB->begin()) break;
529      BB = BB->getUniquePredecessor();
530      if (!BB) break;
531      BBI = BB->end();
532    }
533  } else if (CastInst *CI = dyn_cast<CastInst>(V)) {
534    if (CI->isNoopCast(TD ? TD->getIntPtrType(V->getContext()) :
535                            Type::getInt64Ty(V->getContext())))
536      return findValueImpl(CI->getOperand(0), OffsetOk, Visited);
537  } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
538    if (Value *W = PN->hasConstantValue(DT))
539      return findValueImpl(W, OffsetOk, Visited);
540  } else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(V)) {
541    if (Value *W = FindInsertedValue(Ex->getAggregateOperand(),
542                                     Ex->idx_begin(),
543                                     Ex->idx_end()))
544      if (W != V)
545        return findValueImpl(W, OffsetOk, Visited);
546  }
547
548  // As a last resort, try SimplifyInstruction or constant folding.
549  if (Instruction *Inst = dyn_cast<Instruction>(V)) {
550    if (Value *W = SimplifyInstruction(Inst, TD))
551      if (W != Inst)
552        return findValueImpl(W, OffsetOk, Visited);
553  } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
554    if (Value *W = ConstantFoldConstantExpression(CE, TD))
555      if (W != V)
556        return findValueImpl(W, OffsetOk, Visited);
557  }
558
559  return V;
560}
561
562//===----------------------------------------------------------------------===//
563//  Implement the public interfaces to this file...
564//===----------------------------------------------------------------------===//
565
566FunctionPass *llvm::createLintPass() {
567  return new Lint();
568}
569
570/// lintFunction - Check a function for errors, printing messages on stderr.
571///
572void llvm::lintFunction(const Function &f) {
573  Function &F = const_cast<Function&>(f);
574  assert(!F.isDeclaration() && "Cannot lint external functions");
575
576  FunctionPassManager FPM(F.getParent());
577  Lint *V = new Lint();
578  FPM.add(V);
579  FPM.run(F);
580}
581
582/// lintModule - Check a module for errors, printing messages on stderr.
583///
584void llvm::lintModule(const Module &M) {
585  PassManager PM;
586  Lint *V = new Lint();
587  PM.add(V);
588  PM.run(const_cast<Module&>(M));
589}
590