clang-tools  10.0.0git
LoopConvertCheck.cpp
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1 //===--- LoopConvertCheck.cpp - clang-tidy---------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #include "LoopConvertCheck.h"
10 #include "clang/AST/ASTContext.h"
11 #include "clang/ASTMatchers/ASTMatchFinder.h"
12 #include "clang/Basic/LLVM.h"
13 #include "clang/Basic/LangOptions.h"
14 #include "clang/Basic/SourceLocation.h"
15 #include "clang/Basic/SourceManager.h"
16 #include "clang/Lex/Lexer.h"
17 #include "llvm/ADT/SmallVector.h"
18 #include "llvm/ADT/StringRef.h"
19 #include "llvm/ADT/StringSwitch.h"
20 #include "llvm/Support/Casting.h"
21 #include <cassert>
22 #include <cstring>
23 #include <utility>
24 
25 using namespace clang::ast_matchers;
26 using namespace llvm;
27 
28 namespace clang {
29 namespace tidy {
30 namespace modernize {
31 
32 static const char LoopNameArray[] = "forLoopArray";
33 static const char LoopNameIterator[] = "forLoopIterator";
34 static const char LoopNamePseudoArray[] = "forLoopPseudoArray";
35 static const char ConditionBoundName[] = "conditionBound";
36 static const char ConditionVarName[] = "conditionVar";
37 static const char IncrementVarName[] = "incrementVar";
38 static const char InitVarName[] = "initVar";
39 static const char BeginCallName[] = "beginCall";
40 static const char EndCallName[] = "endCall";
41 static const char ConditionEndVarName[] = "conditionEndVar";
42 static const char EndVarName[] = "endVar";
43 static const char DerefByValueResultName[] = "derefByValueResult";
44 static const char DerefByRefResultName[] = "derefByRefResult";
45 
46 // shared matchers
47 static const TypeMatcher AnyType() { return anything(); }
48 
49 static const StatementMatcher IntegerComparisonMatcher() {
50  return expr(ignoringParenImpCasts(
51  declRefExpr(to(varDecl(hasType(isInteger())).bind(ConditionVarName)))));
52 }
53 
54 static const DeclarationMatcher InitToZeroMatcher() {
55  return varDecl(
56  hasInitializer(ignoringParenImpCasts(integerLiteral(equals(0)))))
57  .bind(InitVarName);
58 }
59 
60 static const StatementMatcher IncrementVarMatcher() {
61  return declRefExpr(to(varDecl(hasType(isInteger())).bind(IncrementVarName)));
62 }
63 
64 /// The matcher for loops over arrays.
65 ///
66 /// In this general example, assuming 'j' and 'k' are of integral type:
67 /// \code
68 /// for (int i = 0; j < 3 + 2; ++k) { ... }
69 /// \endcode
70 /// The following string identifiers are bound to these parts of the AST:
71 /// ConditionVarName: 'j' (as a VarDecl)
72 /// ConditionBoundName: '3 + 2' (as an Expr)
73 /// InitVarName: 'i' (as a VarDecl)
74 /// IncrementVarName: 'k' (as a VarDecl)
75 /// LoopName: The entire for loop (as a ForStmt)
76 ///
77 /// Client code will need to make sure that:
78 /// - The three index variables identified by the matcher are the same
79 /// VarDecl.
80 /// - The index variable is only used as an array index.
81 /// - All arrays indexed by the loop are the same.
82 StatementMatcher makeArrayLoopMatcher() {
83  StatementMatcher ArrayBoundMatcher =
84  expr(hasType(isInteger())).bind(ConditionBoundName);
85 
86  return forStmt(
87  unless(isInTemplateInstantiation()),
88  hasLoopInit(declStmt(hasSingleDecl(InitToZeroMatcher()))),
89  hasCondition(anyOf(
90  binaryOperator(hasOperatorName("<"),
91  hasLHS(IntegerComparisonMatcher()),
92  hasRHS(ArrayBoundMatcher)),
93  binaryOperator(hasOperatorName(">"), hasLHS(ArrayBoundMatcher),
94  hasRHS(IntegerComparisonMatcher())))),
95  hasIncrement(unaryOperator(hasOperatorName("++"),
96  hasUnaryOperand(IncrementVarMatcher()))))
97  .bind(LoopNameArray);
98 }
99 
100 /// The matcher used for iterator-based for loops.
101 ///
102 /// This matcher is more flexible than array-based loops. It will match
103 /// catch loops of the following textual forms (regardless of whether the
104 /// iterator type is actually a pointer type or a class type):
105 ///
106 /// Assuming f, g, and h are of type containerType::iterator,
107 /// \code
108 /// for (containerType::iterator it = container.begin(),
109 /// e = createIterator(); f != g; ++h) { ... }
110 /// for (containerType::iterator it = container.begin();
111 /// f != anotherContainer.end(); ++h) { ... }
112 /// \endcode
113 /// The following string identifiers are bound to the parts of the AST:
114 /// InitVarName: 'it' (as a VarDecl)
115 /// ConditionVarName: 'f' (as a VarDecl)
116 /// LoopName: The entire for loop (as a ForStmt)
117 /// In the first example only:
118 /// EndVarName: 'e' (as a VarDecl)
119 /// ConditionEndVarName: 'g' (as a VarDecl)
120 /// In the second example only:
121 /// EndCallName: 'container.end()' (as a CXXMemberCallExpr)
122 ///
123 /// Client code will need to make sure that:
124 /// - The iterator variables 'it', 'f', and 'h' are the same.
125 /// - The two containers on which 'begin' and 'end' are called are the same.
126 /// - If the end iterator variable 'g' is defined, it is the same as 'f'.
127 StatementMatcher makeIteratorLoopMatcher() {
128  StatementMatcher BeginCallMatcher =
129  cxxMemberCallExpr(
130  argumentCountIs(0),
131  callee(cxxMethodDecl(anyOf(hasName("begin"), hasName("cbegin")))))
132  .bind(BeginCallName);
133 
134  DeclarationMatcher InitDeclMatcher =
135  varDecl(hasInitializer(anyOf(ignoringParenImpCasts(BeginCallMatcher),
136  materializeTemporaryExpr(
137  ignoringParenImpCasts(BeginCallMatcher)),
138  hasDescendant(BeginCallMatcher))))
139  .bind(InitVarName);
140 
141  DeclarationMatcher EndDeclMatcher =
142  varDecl(hasInitializer(anything())).bind(EndVarName);
143 
144  StatementMatcher EndCallMatcher = cxxMemberCallExpr(
145  argumentCountIs(0),
146  callee(cxxMethodDecl(anyOf(hasName("end"), hasName("cend")))));
147 
148  StatementMatcher IteratorBoundMatcher =
149  expr(anyOf(ignoringParenImpCasts(
150  declRefExpr(to(varDecl().bind(ConditionEndVarName)))),
151  ignoringParenImpCasts(expr(EndCallMatcher).bind(EndCallName)),
152  materializeTemporaryExpr(ignoringParenImpCasts(
153  expr(EndCallMatcher).bind(EndCallName)))));
154 
155  StatementMatcher IteratorComparisonMatcher = expr(
156  ignoringParenImpCasts(declRefExpr(to(varDecl().bind(ConditionVarName)))));
157 
158  auto OverloadedNEQMatcher = ignoringImplicit(
159  cxxOperatorCallExpr(hasOverloadedOperatorName("!="), argumentCountIs(2),
160  hasArgument(0, IteratorComparisonMatcher),
161  hasArgument(1, IteratorBoundMatcher)));
162 
163  // This matcher tests that a declaration is a CXXRecordDecl that has an
164  // overloaded operator*(). If the operator*() returns by value instead of by
165  // reference then the return type is tagged with DerefByValueResultName.
166  internal::Matcher<VarDecl> TestDerefReturnsByValue =
167  hasType(hasUnqualifiedDesugaredType(
168  recordType(hasDeclaration(cxxRecordDecl(hasMethod(cxxMethodDecl(
169  hasOverloadedOperatorName("*"),
170  anyOf(
171  // Tag the return type if it's by value.
172  returns(qualType(unless(hasCanonicalType(referenceType())))
173  .bind(DerefByValueResultName)),
174  returns(
175  // Skip loops where the iterator's operator* returns an
176  // rvalue reference. This is just weird.
177  qualType(unless(hasCanonicalType(rValueReferenceType())))
178  .bind(DerefByRefResultName))))))))));
179 
180  return forStmt(
181  unless(isInTemplateInstantiation()),
182  hasLoopInit(anyOf(declStmt(declCountIs(2),
183  containsDeclaration(0, InitDeclMatcher),
184  containsDeclaration(1, EndDeclMatcher)),
185  declStmt(hasSingleDecl(InitDeclMatcher)))),
186  hasCondition(
187  anyOf(binaryOperator(hasOperatorName("!="),
188  hasLHS(IteratorComparisonMatcher),
189  hasRHS(IteratorBoundMatcher)),
190  binaryOperator(hasOperatorName("!="),
191  hasLHS(IteratorBoundMatcher),
192  hasRHS(IteratorComparisonMatcher)),
193  OverloadedNEQMatcher)),
194  hasIncrement(anyOf(
195  unaryOperator(hasOperatorName("++"),
196  hasUnaryOperand(declRefExpr(
197  to(varDecl(hasType(pointsTo(AnyType())))
198  .bind(IncrementVarName))))),
199  cxxOperatorCallExpr(
200  hasOverloadedOperatorName("++"),
201  hasArgument(
202  0, declRefExpr(to(varDecl(TestDerefReturnsByValue)
203  .bind(IncrementVarName))))))))
204  .bind(LoopNameIterator);
205 }
206 
207 /// The matcher used for array-like containers (pseudoarrays).
208 ///
209 /// This matcher is more flexible than array-based loops. It will match
210 /// loops of the following textual forms (regardless of whether the
211 /// iterator type is actually a pointer type or a class type):
212 ///
213 /// Assuming f, g, and h are of type containerType::iterator,
214 /// \code
215 /// for (int i = 0, j = container.size(); f < g; ++h) { ... }
216 /// for (int i = 0; f < container.size(); ++h) { ... }
217 /// \endcode
218 /// The following string identifiers are bound to the parts of the AST:
219 /// InitVarName: 'i' (as a VarDecl)
220 /// ConditionVarName: 'f' (as a VarDecl)
221 /// LoopName: The entire for loop (as a ForStmt)
222 /// In the first example only:
223 /// EndVarName: 'j' (as a VarDecl)
224 /// ConditionEndVarName: 'g' (as a VarDecl)
225 /// In the second example only:
226 /// EndCallName: 'container.size()' (as a CXXMemberCallExpr)
227 ///
228 /// Client code will need to make sure that:
229 /// - The index variables 'i', 'f', and 'h' are the same.
230 /// - The containers on which 'size()' is called is the container indexed.
231 /// - The index variable is only used in overloaded operator[] or
232 /// container.at().
233 /// - If the end iterator variable 'g' is defined, it is the same as 'j'.
234 /// - The container's iterators would not be invalidated during the loop.
235 StatementMatcher makePseudoArrayLoopMatcher() {
236  // Test that the incoming type has a record declaration that has methods
237  // called 'begin' and 'end'. If the incoming type is const, then make sure
238  // these methods are also marked const.
239  //
240  // FIXME: To be completely thorough this matcher should also ensure the
241  // return type of begin/end is an iterator that dereferences to the same as
242  // what operator[] or at() returns. Such a test isn't likely to fail except
243  // for pathological cases.
244  //
245  // FIXME: Also, a record doesn't necessarily need begin() and end(). Free
246  // functions called begin() and end() taking the container as an argument
247  // are also allowed.
248  TypeMatcher RecordWithBeginEnd = qualType(anyOf(
249  qualType(
250  isConstQualified(),
251  hasUnqualifiedDesugaredType(recordType(hasDeclaration(cxxRecordDecl(
252  hasMethod(cxxMethodDecl(hasName("begin"), isConst())),
253  hasMethod(cxxMethodDecl(hasName("end"),
254  isConst())))) // hasDeclaration
255  ))), // qualType
256  qualType(unless(isConstQualified()),
257  hasUnqualifiedDesugaredType(recordType(hasDeclaration(
258  cxxRecordDecl(hasMethod(hasName("begin")),
259  hasMethod(hasName("end"))))))) // qualType
260  ));
261 
262  StatementMatcher SizeCallMatcher = cxxMemberCallExpr(
263  argumentCountIs(0),
264  callee(cxxMethodDecl(anyOf(hasName("size"), hasName("length")))),
265  on(anyOf(hasType(pointsTo(RecordWithBeginEnd)),
266  hasType(RecordWithBeginEnd))));
267 
268  StatementMatcher EndInitMatcher =
269  expr(anyOf(ignoringParenImpCasts(expr(SizeCallMatcher).bind(EndCallName)),
270  explicitCastExpr(hasSourceExpression(ignoringParenImpCasts(
271  expr(SizeCallMatcher).bind(EndCallName))))));
272 
273  DeclarationMatcher EndDeclMatcher =
274  varDecl(hasInitializer(EndInitMatcher)).bind(EndVarName);
275 
276  StatementMatcher IndexBoundMatcher =
277  expr(anyOf(ignoringParenImpCasts(declRefExpr(to(
278  varDecl(hasType(isInteger())).bind(ConditionEndVarName)))),
279  EndInitMatcher));
280 
281  return forStmt(
282  unless(isInTemplateInstantiation()),
283  hasLoopInit(
284  anyOf(declStmt(declCountIs(2),
285  containsDeclaration(0, InitToZeroMatcher()),
286  containsDeclaration(1, EndDeclMatcher)),
287  declStmt(hasSingleDecl(InitToZeroMatcher())))),
288  hasCondition(anyOf(
289  binaryOperator(hasOperatorName("<"),
290  hasLHS(IntegerComparisonMatcher()),
291  hasRHS(IndexBoundMatcher)),
292  binaryOperator(hasOperatorName(">"), hasLHS(IndexBoundMatcher),
293  hasRHS(IntegerComparisonMatcher())))),
294  hasIncrement(unaryOperator(hasOperatorName("++"),
295  hasUnaryOperand(IncrementVarMatcher()))))
296  .bind(LoopNamePseudoArray);
297 }
298 
299 /// Determine whether Init appears to be an initializing an iterator.
300 ///
301 /// If it is, returns the object whose begin() or end() method is called, and
302 /// the output parameter isArrow is set to indicate whether the initialization
303 /// is called via . or ->.
304 static const Expr *getContainerFromBeginEndCall(const Expr *Init, bool IsBegin,
305  bool *IsArrow) {
306  // FIXME: Maybe allow declaration/initialization outside of the for loop.
307  const auto *TheCall =
308  dyn_cast_or_null<CXXMemberCallExpr>(digThroughConstructors(Init));
309  if (!TheCall || TheCall->getNumArgs() != 0)
310  return nullptr;
311 
312  const auto *Member = dyn_cast<MemberExpr>(TheCall->getCallee());
313  if (!Member)
314  return nullptr;
315  StringRef Name = Member->getMemberDecl()->getName();
316  StringRef TargetName = IsBegin ? "begin" : "end";
317  StringRef ConstTargetName = IsBegin ? "cbegin" : "cend";
318  if (Name != TargetName && Name != ConstTargetName)
319  return nullptr;
320 
321  const Expr *SourceExpr = Member->getBase();
322  if (!SourceExpr)
323  return nullptr;
324 
325  *IsArrow = Member->isArrow();
326  return SourceExpr;
327 }
328 
329 /// Determines the container whose begin() and end() functions are called
330 /// for an iterator-based loop.
331 ///
332 /// BeginExpr must be a member call to a function named "begin()", and EndExpr
333 /// must be a member.
334 static const Expr *findContainer(ASTContext *Context, const Expr *BeginExpr,
335  const Expr *EndExpr,
336  bool *ContainerNeedsDereference) {
337  // Now that we know the loop variable and test expression, make sure they are
338  // valid.
339  bool BeginIsArrow = false;
340  bool EndIsArrow = false;
341  const Expr *BeginContainerExpr =
342  getContainerFromBeginEndCall(BeginExpr, /*IsBegin=*/true, &BeginIsArrow);
343  if (!BeginContainerExpr)
344  return nullptr;
345 
346  const Expr *EndContainerExpr =
347  getContainerFromBeginEndCall(EndExpr, /*IsBegin=*/false, &EndIsArrow);
348  // Disallow loops that try evil things like this (note the dot and arrow):
349  // for (IteratorType It = Obj.begin(), E = Obj->end(); It != E; ++It) { }
350  if (!EndContainerExpr || BeginIsArrow != EndIsArrow ||
351  !areSameExpr(Context, EndContainerExpr, BeginContainerExpr))
352  return nullptr;
353 
354  *ContainerNeedsDereference = BeginIsArrow;
355  return BeginContainerExpr;
356 }
357 
358 /// Obtain the original source code text from a SourceRange.
359 static StringRef getStringFromRange(SourceManager &SourceMgr,
360  const LangOptions &LangOpts,
361  SourceRange Range) {
362  if (SourceMgr.getFileID(Range.getBegin()) !=
363  SourceMgr.getFileID(Range.getEnd())) {
364  return StringRef(); // Empty string.
365  }
366 
367  return Lexer::getSourceText(CharSourceRange(Range, true), SourceMgr,
368  LangOpts);
369 }
370 
371 /// If the given expression is actually a DeclRefExpr or a MemberExpr,
372 /// find and return the underlying ValueDecl; otherwise, return NULL.
373 static const ValueDecl *getReferencedVariable(const Expr *E) {
374  if (const DeclRefExpr *DRE = getDeclRef(E))
375  return dyn_cast<VarDecl>(DRE->getDecl());
376  if (const auto *Mem = dyn_cast<MemberExpr>(E->IgnoreParenImpCasts()))
377  return dyn_cast<FieldDecl>(Mem->getMemberDecl());
378  return nullptr;
379 }
380 
381 /// Returns true when the given expression is a member expression
382 /// whose base is `this` (implicitly or not).
383 static bool isDirectMemberExpr(const Expr *E) {
384  if (const auto *Member = dyn_cast<MemberExpr>(E->IgnoreParenImpCasts()))
385  return isa<CXXThisExpr>(Member->getBase()->IgnoreParenImpCasts());
386  return false;
387 }
388 
389 /// Given an expression that represents an usage of an element from the
390 /// containter that we are iterating over, returns false when it can be
391 /// guaranteed this element cannot be modified as a result of this usage.
392 static bool canBeModified(ASTContext *Context, const Expr *E) {
393  if (E->getType().isConstQualified())
394  return false;
395  auto Parents = Context->getParents(*E);
396  if (Parents.size() != 1)
397  return true;
398  if (const auto *Cast = Parents[0].get<ImplicitCastExpr>()) {
399  if ((Cast->getCastKind() == CK_NoOp &&
400  Cast->getType() == E->getType().withConst()) ||
401  (Cast->getCastKind() == CK_LValueToRValue &&
402  !Cast->getType().isNull() && Cast->getType()->isFundamentalType()))
403  return false;
404  }
405  // FIXME: Make this function more generic.
406  return true;
407 }
408 
409 /// Returns true when it can be guaranteed that the elements of the
410 /// container are not being modified.
411 static bool usagesAreConst(ASTContext *Context, const UsageResult &Usages) {
412  for (const Usage &U : Usages) {
413  // Lambda captures are just redeclarations (VarDecl) of the same variable,
414  // not expressions. If we want to know if a variable that is captured by
415  // reference can be modified in an usage inside the lambda's body, we need
416  // to find the expression corresponding to that particular usage, later in
417  // this loop.
418  if (U.Kind != Usage::UK_CaptureByCopy && U.Kind != Usage::UK_CaptureByRef &&
419  canBeModified(Context, U.Expression))
420  return false;
421  }
422  return true;
423 }
424 
425 /// Returns true if the elements of the container are never accessed
426 /// by reference.
427 static bool usagesReturnRValues(const UsageResult &Usages) {
428  for (const auto &U : Usages) {
429  if (U.Expression && !U.Expression->isRValue())
430  return false;
431  }
432  return true;
433 }
434 
435 /// Returns true if the container is const-qualified.
436 static bool containerIsConst(const Expr *ContainerExpr, bool Dereference) {
437  if (const auto *VDec = getReferencedVariable(ContainerExpr)) {
438  QualType CType = VDec->getType();
439  if (Dereference) {
440  if (!CType->isPointerType())
441  return false;
442  CType = CType->getPointeeType();
443  }
444  // If VDec is a reference to a container, Dereference is false,
445  // but we still need to check the const-ness of the underlying container
446  // type.
447  CType = CType.getNonReferenceType();
448  return CType.isConstQualified();
449  }
450  return false;
451 }
452 
453 LoopConvertCheck::RangeDescriptor::RangeDescriptor()
454  : ContainerNeedsDereference(false), DerefByConstRef(false),
455  DerefByValue(false) {}
456 
457 LoopConvertCheck::LoopConvertCheck(StringRef Name, ClangTidyContext *Context)
458  : ClangTidyCheck(Name, Context), TUInfo(new TUTrackingInfo),
459  MaxCopySize(std::stoull(Options.get("MaxCopySize", "16"))),
460  MinConfidence(StringSwitch<Confidence::Level>(
461  Options.get("MinConfidence", "reasonable"))
462  .Case("safe", Confidence::CL_Safe)
463  .Case("risky", Confidence::CL_Risky)
464  .Default(Confidence::CL_Reasonable)),
465  NamingStyle(StringSwitch<VariableNamer::NamingStyle>(
466  Options.get("NamingStyle", "CamelCase"))
467  .Case("camelBack", VariableNamer::NS_CamelBack)
468  .Case("lower_case", VariableNamer::NS_LowerCase)
469  .Case("UPPER_CASE", VariableNamer::NS_UpperCase)
470  .Default(VariableNamer::NS_CamelCase)) {}
471 
473  Options.store(Opts, "MaxCopySize", std::to_string(MaxCopySize));
474  SmallVector<std::string, 3> Confs{"risky", "reasonable", "safe"};
475  Options.store(Opts, "MinConfidence", Confs[static_cast<int>(MinConfidence)]);
476 
477  SmallVector<std::string, 4> Styles{"camelBack", "CamelCase", "lower_case",
478  "UPPER_CASE"};
479  Options.store(Opts, "NamingStyle", Styles[static_cast<int>(NamingStyle)]);
480 }
481 
482 void LoopConvertCheck::registerMatchers(MatchFinder *Finder) {
483  // Only register the matchers for C++. Because this checker is used for
484  // modernization, it is reasonable to run it on any C++ standard with the
485  // assumption the user is trying to modernize their codebase.
486  if (!getLangOpts().CPlusPlus)
487  return;
488 
489  Finder->addMatcher(makeArrayLoopMatcher(), this);
490  Finder->addMatcher(makeIteratorLoopMatcher(), this);
491  Finder->addMatcher(makePseudoArrayLoopMatcher(), this);
492 }
493 
494 /// Given the range of a single declaration, such as:
495 /// \code
496 /// unsigned &ThisIsADeclarationThatCanSpanSeveralLinesOfCode =
497 /// InitializationValues[I];
498 /// next_instruction;
499 /// \endcode
500 /// Finds the range that has to be erased to remove this declaration without
501 /// leaving empty lines, by extending the range until the beginning of the
502 /// next instruction.
503 ///
504 /// We need to delete a potential newline after the deleted alias, as
505 /// clang-format will leave empty lines untouched. For all other formatting we
506 /// rely on clang-format to fix it.
507 void LoopConvertCheck::getAliasRange(SourceManager &SM, SourceRange &Range) {
508  bool Invalid = false;
509  const char *TextAfter =
510  SM.getCharacterData(Range.getEnd().getLocWithOffset(1), &Invalid);
511  if (Invalid)
512  return;
513  unsigned Offset = std::strspn(TextAfter, " \t\r\n");
514  Range =
515  SourceRange(Range.getBegin(), Range.getEnd().getLocWithOffset(Offset));
516 }
517 
518 /// Computes the changes needed to convert a given for loop, and
519 /// applies them.
520 void LoopConvertCheck::doConversion(
521  ASTContext *Context, const VarDecl *IndexVar,
522  const ValueDecl *MaybeContainer, const UsageResult &Usages,
523  const DeclStmt *AliasDecl, bool AliasUseRequired, bool AliasFromForInit,
524  const ForStmt *Loop, RangeDescriptor Descriptor) {
525  auto Diag = diag(Loop->getForLoc(), "use range-based for loop instead");
526 
527  std::string VarName;
528  bool VarNameFromAlias = (Usages.size() == 1) && AliasDecl;
529  bool AliasVarIsRef = false;
530  bool CanCopy = true;
531 
532  if (VarNameFromAlias) {
533  const auto *AliasVar = cast<VarDecl>(AliasDecl->getSingleDecl());
534  VarName = AliasVar->getName().str();
535 
536  // Use the type of the alias if it's not the same
537  QualType AliasVarType = AliasVar->getType();
538  assert(!AliasVarType.isNull() && "Type in VarDecl is null");
539  if (AliasVarType->isReferenceType()) {
540  AliasVarType = AliasVarType.getNonReferenceType();
541  AliasVarIsRef = true;
542  }
543  if (Descriptor.ElemType.isNull() ||
544  !Context->hasSameUnqualifiedType(AliasVarType, Descriptor.ElemType))
545  Descriptor.ElemType = AliasVarType;
546 
547  // We keep along the entire DeclStmt to keep the correct range here.
548  SourceRange ReplaceRange = AliasDecl->getSourceRange();
549 
550  std::string ReplacementText;
551  if (AliasUseRequired) {
552  ReplacementText = VarName;
553  } else if (AliasFromForInit) {
554  // FIXME: Clang includes the location of the ';' but only for DeclStmt's
555  // in a for loop's init clause. Need to put this ';' back while removing
556  // the declaration of the alias variable. This is probably a bug.
557  ReplacementText = ";";
558  } else {
559  // Avoid leaving empty lines or trailing whitespaces.
560  getAliasRange(Context->getSourceManager(), ReplaceRange);
561  }
562 
563  Diag << FixItHint::CreateReplacement(
564  CharSourceRange::getTokenRange(ReplaceRange), ReplacementText);
565  // No further replacements are made to the loop, since the iterator or index
566  // was used exactly once - in the initialization of AliasVar.
567  } else {
568  VariableNamer Namer(&TUInfo->getGeneratedDecls(),
569  &TUInfo->getParentFinder().getStmtToParentStmtMap(),
570  Loop, IndexVar, MaybeContainer, Context, NamingStyle);
571  VarName = Namer.createIndexName();
572  // First, replace all usages of the array subscript expression with our new
573  // variable.
574  for (const auto &Usage : Usages) {
575  std::string ReplaceText;
576  SourceRange Range = Usage.Range;
577  if (Usage.Expression) {
578  // If this is an access to a member through the arrow operator, after
579  // the replacement it must be accessed through the '.' operator.
580  ReplaceText = Usage.Kind == Usage::UK_MemberThroughArrow ? VarName + "."
581  : VarName;
582  auto Parents = Context->getParents(*Usage.Expression);
583  if (Parents.size() == 1) {
584  if (const auto *Paren = Parents[0].get<ParenExpr>()) {
585  // Usage.Expression will be replaced with the new index variable,
586  // and parenthesis around a simple DeclRefExpr can always be
587  // removed.
588  Range = Paren->getSourceRange();
589  } else if (const auto *UOP = Parents[0].get<UnaryOperator>()) {
590  // If we are taking the address of the loop variable, then we must
591  // not use a copy, as it would mean taking the address of the loop's
592  // local index instead.
593  // FIXME: This won't catch cases where the address is taken outside
594  // of the loop's body (for instance, in a function that got the
595  // loop's index as a const reference parameter), or where we take
596  // the address of a member (like "&Arr[i].A.B.C").
597  if (UOP->getOpcode() == UO_AddrOf)
598  CanCopy = false;
599  }
600  }
601  } else {
602  // The Usage expression is only null in case of lambda captures (which
603  // are VarDecl). If the index is captured by value, add '&' to capture
604  // by reference instead.
605  ReplaceText =
606  Usage.Kind == Usage::UK_CaptureByCopy ? "&" + VarName : VarName;
607  }
608  TUInfo->getReplacedVars().insert(std::make_pair(Loop, IndexVar));
609  Diag << FixItHint::CreateReplacement(
610  CharSourceRange::getTokenRange(Range), ReplaceText);
611  }
612  }
613 
614  // Now, we need to construct the new range expression.
615  SourceRange ParenRange(Loop->getLParenLoc(), Loop->getRParenLoc());
616 
617  QualType Type = Context->getAutoDeductType();
618  if (!Descriptor.ElemType.isNull() && Descriptor.ElemType->isFundamentalType())
619  Type = Descriptor.ElemType.getUnqualifiedType();
620 
621  // If the new variable name is from the aliased variable, then the reference
622  // type for the new variable should only be used if the aliased variable was
623  // declared as a reference.
624  bool IsCheapToCopy =
625  !Descriptor.ElemType.isNull() &&
626  Descriptor.ElemType.isTriviallyCopyableType(*Context) &&
627  // TypeInfo::Width is in bits.
628  Context->getTypeInfo(Descriptor.ElemType).Width <= 8 * MaxCopySize;
629  bool UseCopy = CanCopy && ((VarNameFromAlias && !AliasVarIsRef) ||
630  (Descriptor.DerefByConstRef && IsCheapToCopy));
631 
632  if (!UseCopy) {
633  if (Descriptor.DerefByConstRef) {
634  Type = Context->getLValueReferenceType(Context->getConstType(Type));
635  } else if (Descriptor.DerefByValue) {
636  if (!IsCheapToCopy)
637  Type = Context->getRValueReferenceType(Type);
638  } else {
639  Type = Context->getLValueReferenceType(Type);
640  }
641  }
642 
643  StringRef MaybeDereference = Descriptor.ContainerNeedsDereference ? "*" : "";
644  std::string TypeString = Type.getAsString(getLangOpts());
645  std::string Range = ("(" + TypeString + " " + VarName + " : " +
646  MaybeDereference + Descriptor.ContainerString + ")")
647  .str();
648  Diag << FixItHint::CreateReplacement(
649  CharSourceRange::getTokenRange(ParenRange), Range);
650  TUInfo->getGeneratedDecls().insert(make_pair(Loop, VarName));
651 }
652 
653 /// Returns a string which refers to the container iterated over.
654 StringRef LoopConvertCheck::getContainerString(ASTContext *Context,
655  const ForStmt *Loop,
656  const Expr *ContainerExpr) {
657  StringRef ContainerString;
658  if (isa<CXXThisExpr>(ContainerExpr->IgnoreParenImpCasts())) {
659  ContainerString = "this";
660  } else {
661  ContainerString =
662  getStringFromRange(Context->getSourceManager(), Context->getLangOpts(),
663  ContainerExpr->getSourceRange());
664  }
665 
666  return ContainerString;
667 }
668 
669 /// Determines what kind of 'auto' must be used after converting a for
670 /// loop that iterates over an array or pseudoarray.
671 void LoopConvertCheck::getArrayLoopQualifiers(ASTContext *Context,
672  const BoundNodes &Nodes,
673  const Expr *ContainerExpr,
674  const UsageResult &Usages,
675  RangeDescriptor &Descriptor) {
676  // On arrays and pseudoarrays, we must figure out the qualifiers from the
677  // usages.
678  if (usagesAreConst(Context, Usages) ||
679  containerIsConst(ContainerExpr, Descriptor.ContainerNeedsDereference)) {
680  Descriptor.DerefByConstRef = true;
681  }
682  if (usagesReturnRValues(Usages)) {
683  // If the index usages (dereference, subscript, at, ...) return rvalues,
684  // then we should not use a reference, because we need to keep the code
685  // correct if it mutates the returned objects.
686  Descriptor.DerefByValue = true;
687  }
688  // Try to find the type of the elements on the container, to check if
689  // they are trivially copyable.
690  for (const Usage &U : Usages) {
691  if (!U.Expression || U.Expression->getType().isNull())
692  continue;
693  QualType Type = U.Expression->getType().getCanonicalType();
694  if (U.Kind == Usage::UK_MemberThroughArrow) {
695  if (!Type->isPointerType()) {
696  continue;
697  }
698  Type = Type->getPointeeType();
699  }
700  Descriptor.ElemType = Type;
701  }
702 }
703 
704 /// Determines what kind of 'auto' must be used after converting an
705 /// iterator based for loop.
706 void LoopConvertCheck::getIteratorLoopQualifiers(ASTContext *Context,
707  const BoundNodes &Nodes,
708  RangeDescriptor &Descriptor) {
709  // The matchers for iterator loops provide bound nodes to obtain this
710  // information.
711  const auto *InitVar = Nodes.getNodeAs<VarDecl>(InitVarName);
712  QualType CanonicalInitVarType = InitVar->getType().getCanonicalType();
713  const auto *DerefByValueType =
714  Nodes.getNodeAs<QualType>(DerefByValueResultName);
715  Descriptor.DerefByValue = DerefByValueType;
716 
717  if (Descriptor.DerefByValue) {
718  // If the dereference operator returns by value then test for the
719  // canonical const qualification of the init variable type.
720  Descriptor.DerefByConstRef = CanonicalInitVarType.isConstQualified();
721  Descriptor.ElemType = *DerefByValueType;
722  } else {
723  if (const auto *DerefType =
724  Nodes.getNodeAs<QualType>(DerefByRefResultName)) {
725  // A node will only be bound with DerefByRefResultName if we're dealing
726  // with a user-defined iterator type. Test the const qualification of
727  // the reference type.
728  auto ValueType = DerefType->getNonReferenceType();
729 
730  Descriptor.DerefByConstRef = ValueType.isConstQualified();
731  Descriptor.ElemType = ValueType;
732  } else {
733  // By nature of the matcher this case is triggered only for built-in
734  // iterator types (i.e. pointers).
735  assert(isa<PointerType>(CanonicalInitVarType) &&
736  "Non-class iterator type is not a pointer type");
737 
738  // We test for const qualification of the pointed-at type.
739  Descriptor.DerefByConstRef =
740  CanonicalInitVarType->getPointeeType().isConstQualified();
741  Descriptor.ElemType = CanonicalInitVarType->getPointeeType();
742  }
743  }
744 }
745 
746 /// Determines the parameters needed to build the range replacement.
747 void LoopConvertCheck::determineRangeDescriptor(
748  ASTContext *Context, const BoundNodes &Nodes, const ForStmt *Loop,
749  LoopFixerKind FixerKind, const Expr *ContainerExpr,
750  const UsageResult &Usages, RangeDescriptor &Descriptor) {
751  Descriptor.ContainerString = getContainerString(Context, Loop, ContainerExpr);
752 
753  if (FixerKind == LFK_Iterator)
754  getIteratorLoopQualifiers(Context, Nodes, Descriptor);
755  else
756  getArrayLoopQualifiers(Context, Nodes, ContainerExpr, Usages, Descriptor);
757 }
758 
759 /// Check some of the conditions that must be met for the loop to be
760 /// convertible.
761 bool LoopConvertCheck::isConvertible(ASTContext *Context,
762  const ast_matchers::BoundNodes &Nodes,
763  const ForStmt *Loop,
764  LoopFixerKind FixerKind) {
765  // If we already modified the range of this for loop, don't do any further
766  // updates on this iteration.
767  if (TUInfo->getReplacedVars().count(Loop))
768  return false;
769 
770  // Check that we have exactly one index variable and at most one end variable.
771  const auto *LoopVar = Nodes.getNodeAs<VarDecl>(IncrementVarName);
772  const auto *CondVar = Nodes.getNodeAs<VarDecl>(ConditionVarName);
773  const auto *InitVar = Nodes.getNodeAs<VarDecl>(InitVarName);
774  if (!areSameVariable(LoopVar, CondVar) || !areSameVariable(LoopVar, InitVar))
775  return false;
776  const auto *EndVar = Nodes.getNodeAs<VarDecl>(EndVarName);
777  const auto *ConditionEndVar = Nodes.getNodeAs<VarDecl>(ConditionEndVarName);
778  if (EndVar && !areSameVariable(EndVar, ConditionEndVar))
779  return false;
780 
781  // FIXME: Try to put most of this logic inside a matcher.
782  if (FixerKind == LFK_Iterator) {
783  QualType InitVarType = InitVar->getType();
784  QualType CanonicalInitVarType = InitVarType.getCanonicalType();
785 
786  const auto *BeginCall = Nodes.getNodeAs<CXXMemberCallExpr>(BeginCallName);
787  assert(BeginCall && "Bad Callback. No begin call expression");
788  QualType CanonicalBeginType =
789  BeginCall->getMethodDecl()->getReturnType().getCanonicalType();
790  if (CanonicalBeginType->isPointerType() &&
791  CanonicalInitVarType->isPointerType()) {
792  // If the initializer and the variable are both pointers check if the
793  // un-qualified pointee types match, otherwise we don't use auto.
794  if (!Context->hasSameUnqualifiedType(
795  CanonicalBeginType->getPointeeType(),
796  CanonicalInitVarType->getPointeeType()))
797  return false;
798  }
799  } else if (FixerKind == LFK_PseudoArray) {
800  // This call is required to obtain the container.
801  const auto *EndCall = Nodes.getNodeAs<CXXMemberCallExpr>(EndCallName);
802  if (!EndCall || !dyn_cast<MemberExpr>(EndCall->getCallee()))
803  return false;
804  }
805  return true;
806 }
807 
808 void LoopConvertCheck::check(const MatchFinder::MatchResult &Result) {
809  const BoundNodes &Nodes = Result.Nodes;
810  Confidence ConfidenceLevel(Confidence::CL_Safe);
811  ASTContext *Context = Result.Context;
812 
813  const ForStmt *Loop;
814  LoopFixerKind FixerKind;
815  RangeDescriptor Descriptor;
816 
817  if ((Loop = Nodes.getNodeAs<ForStmt>(LoopNameArray))) {
818  FixerKind = LFK_Array;
819  } else if ((Loop = Nodes.getNodeAs<ForStmt>(LoopNameIterator))) {
820  FixerKind = LFK_Iterator;
821  } else {
822  Loop = Nodes.getNodeAs<ForStmt>(LoopNamePseudoArray);
823  assert(Loop && "Bad Callback. No for statement");
824  FixerKind = LFK_PseudoArray;
825  }
826 
827  if (!isConvertible(Context, Nodes, Loop, FixerKind))
828  return;
829 
830  const auto *LoopVar = Nodes.getNodeAs<VarDecl>(IncrementVarName);
831  const auto *EndVar = Nodes.getNodeAs<VarDecl>(EndVarName);
832 
833  // If the loop calls end()/size() after each iteration, lower our confidence
834  // level.
835  if (FixerKind != LFK_Array && !EndVar)
836  ConfidenceLevel.lowerTo(Confidence::CL_Reasonable);
837 
838  // If the end comparison isn't a variable, we can try to work with the
839  // expression the loop variable is being tested against instead.
840  const auto *EndCall = Nodes.getNodeAs<CXXMemberCallExpr>(EndCallName);
841  const auto *BoundExpr = Nodes.getNodeAs<Expr>(ConditionBoundName);
842 
843  // Find container expression of iterators and pseudoarrays, and determine if
844  // this expression needs to be dereferenced to obtain the container.
845  // With array loops, the container is often discovered during the
846  // ForLoopIndexUseVisitor traversal.
847  const Expr *ContainerExpr = nullptr;
848  if (FixerKind == LFK_Iterator) {
849  ContainerExpr = findContainer(Context, LoopVar->getInit(),
850  EndVar ? EndVar->getInit() : EndCall,
851  &Descriptor.ContainerNeedsDereference);
852  } else if (FixerKind == LFK_PseudoArray) {
853  ContainerExpr = EndCall->getImplicitObjectArgument();
854  Descriptor.ContainerNeedsDereference =
855  dyn_cast<MemberExpr>(EndCall->getCallee())->isArrow();
856  }
857 
858  // We must know the container or an array length bound.
859  if (!ContainerExpr && !BoundExpr)
860  return;
861 
862  ForLoopIndexUseVisitor Finder(Context, LoopVar, EndVar, ContainerExpr,
863  BoundExpr,
864  Descriptor.ContainerNeedsDereference);
865 
866  // Find expressions and variables on which the container depends.
867  if (ContainerExpr) {
868  ComponentFinderASTVisitor ComponentFinder;
869  ComponentFinder.findExprComponents(ContainerExpr->IgnoreParenImpCasts());
870  Finder.addComponents(ComponentFinder.getComponents());
871  }
872 
873  // Find usages of the loop index. If they are not used in a convertible way,
874  // stop here.
875  if (!Finder.findAndVerifyUsages(Loop->getBody()))
876  return;
877  ConfidenceLevel.lowerTo(Finder.getConfidenceLevel());
878 
879  // Obtain the container expression, if we don't have it yet.
880  if (FixerKind == LFK_Array) {
881  ContainerExpr = Finder.getContainerIndexed()->IgnoreParenImpCasts();
882 
883  // Very few loops are over expressions that generate arrays rather than
884  // array variables. Consider loops over arrays that aren't just represented
885  // by a variable to be risky conversions.
886  if (!getReferencedVariable(ContainerExpr) &&
887  !isDirectMemberExpr(ContainerExpr))
888  ConfidenceLevel.lowerTo(Confidence::CL_Risky);
889  }
890 
891  // Find out which qualifiers we have to use in the loop range.
892  const UsageResult &Usages = Finder.getUsages();
893  determineRangeDescriptor(Context, Nodes, Loop, FixerKind, ContainerExpr,
894  Usages, Descriptor);
895 
896  // Ensure that we do not try to move an expression dependent on a local
897  // variable declared inside the loop outside of it.
898  // FIXME: Determine when the external dependency isn't an expression converted
899  // by another loop.
900  TUInfo->getParentFinder().gatherAncestors(*Context);
901  DependencyFinderASTVisitor DependencyFinder(
902  &TUInfo->getParentFinder().getStmtToParentStmtMap(),
903  &TUInfo->getParentFinder().getDeclToParentStmtMap(),
904  &TUInfo->getReplacedVars(), Loop);
905 
906  if (DependencyFinder.dependsOnInsideVariable(ContainerExpr) ||
907  Descriptor.ContainerString.empty() || Usages.empty() ||
908  ConfidenceLevel.getLevel() < MinConfidence)
909  return;
910 
911  doConversion(Context, LoopVar, getReferencedVariable(ContainerExpr), Usages,
912  Finder.getAliasDecl(), Finder.aliasUseRequired(),
913  Finder.aliasFromForInit(), Loop, Descriptor);
914 }
915 
916 } // namespace modernize
917 } // namespace tidy
918 } // namespace clang
static const char DerefByRefResultName[]
static const DeclarationMatcher InitToZeroMatcher()
Confidence::Level getConfidenceLevel() const
Accessor for ConfidenceLevel.
Discover usages of expressions consisting of index or iterator access.
Some operations such as code completion produce a set of candidates.
StatementMatcher makeIteratorLoopMatcher()
The matcher used for iterator-based for loops.
void storeOptions(ClangTidyOptions::OptionMap &Opts) override
Should store all options supported by this check with their current values or default values for opti...
static const char ConditionVarName[]
static const Expr * getContainerFromBeginEndCall(const Expr *Init, bool IsBegin, bool *IsArrow)
Determine whether Init appears to be an initializing an iterator.
StatementMatcher makeArrayLoopMatcher()
The matcher for loops over arrays.
llvm::SmallVector< Usage, 8 > UsageResult
static const StatementMatcher IntegerComparisonMatcher()
static const char EndCallName[]
A class to encapsulate lowering of the tool&#39;s confidence level.
const Expr * getContainerIndexed() const
Get the container indexed by IndexVar, if any.
Class used to determine if an expression is dependent on a variable declared inside of the loop where...
Base class for all clang-tidy checks.
bool aliasUseRequired() const
Indicates if the alias declaration was in a place where it cannot simply be removed but rather replac...
const Expr * digThroughConstructors(const Expr *E)
Look through conversion/copy constructors to find the explicit initialization expression, returning it is found.
const LangOptions & getLangOpts() const
Returns the language options from the context.
static const Expr * findContainer(ASTContext *Context, const Expr *BeginExpr, const Expr *EndExpr, bool *ContainerNeedsDereference)
Determines the container whose begin() and end() functions are called for an iterator-based loop...
static const char InitVarName[]
static const ValueDecl * getReferencedVariable(const Expr *E)
If the given expression is actually a DeclRefExpr or a MemberExpr, find and return the underlying Val...
static const char EndVarName[]
bool aliasFromForInit() const
Indicates if the alias declaration came from the init clause of a nested for loop.
void registerMatchers(ast_matchers::MatchFinder *Finder) override
Override this to register AST matchers with Finder.
static const TypeMatcher AnyType()
const DeclRefExpr * getDeclRef(const Expr *E)
Returns the DeclRefExpr represented by E, or NULL if there isn&#39;t one.
void findExprComponents(const clang::Expr *SourceExpr)
Find the components of an expression and place them in a ComponentVector.
std::string createIndexName()
Generate a new index name.
const ComponentVector & getComponents()
Accessor for Components.
Level getLevel() const
Return the internal confidence level.
bool areSameVariable(const ValueDecl *First, const ValueDecl *Second)
Returns true when two ValueDecls are the same variable.
static bool usagesReturnRValues(const UsageResult &Usages)
Returns true if the elements of the container are never accessed by reference.
static const char ConditionBoundName[]
Create names for generated variables within a particular statement.
void store(ClangTidyOptions::OptionMap &Options, StringRef LocalName, StringRef Value) const
Stores an option with the check-local name LocalName with string value Value to Options.
static bool usagesAreConst(ASTContext *Context, const UsageResult &Usages)
Returns true when it can be guaranteed that the elements of the container are not being modified...
static const char IncrementVarName[]
bool areSameExpr(ASTContext *Context, const Expr *First, const Expr *Second)
Returns true when two Exprs are equivalent.
static bool canBeModified(ASTContext *Context, const Expr *E)
Given an expression that represents an usage of an element from the containter that we are iterating ...
static constexpr llvm::StringLiteral Name
std::map< std::string, std::string > OptionMap
static const char ConditionEndVarName[]
static const char LoopNameArray[]
llvm::Optional< Range > getTokenRange(const SourceManager &SM, const LangOptions &LangOpts, SourceLocation TokLoc)
Returns the taken range at TokLoc.
Definition: SourceCode.cpp:227
static StringRef getStringFromRange(SourceManager &SourceMgr, const LangOptions &LangOpts, SourceRange Range)
Obtain the original source code text from a SourceRange.
static const char DerefByValueResultName[]
static const StatementMatcher IncrementVarMatcher()
void check(const ast_matchers::MatchFinder::MatchResult &Result) override
ClangTidyChecks that register ASTMatchers should do the actual work in here.
static bool isDirectMemberExpr(const Expr *E)
Returns true when the given expression is a member expression whose base is this (implicitly or not)...
size_t Offset
static const char LoopNamePseudoArray[]
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//
bool findAndVerifyUsages(const Stmt *Body)
Finds all uses of IndexVar in Body, placing all usages in Usages, and returns true if IndexVar was on...
The information needed to describe a valid convertible usage of an array index or iterator...
CharSourceRange Range
SourceRange for the file name.
void addComponents(const ComponentVector &Components)
Add a set of components that we should consider relevant to the container.
void lowerTo(Confidence::Level Level)
Lower the internal confidence level to Level, but do not raise it.
static const char BeginCallName[]
Every ClangTidyCheck reports errors through a DiagnosticsEngine provided by this context.
const Expr * E
Class used to find the variables and member expressions on which an arbitrary expression depends...
static const char LoopNameIterator[]
static bool containerIsConst(const Expr *ContainerExpr, bool Dereference)
Returns true if the container is const-qualified.
StatementMatcher makePseudoArrayLoopMatcher()
The matcher used for array-like containers (pseudoarrays).
NodeType Type
DiagnosticBuilder diag(SourceLocation Loc, StringRef Description, DiagnosticIDs::Level Level=DiagnosticIDs::Warning)
Add a diagnostic with the check&#39;s name.
const UsageResult & getUsages() const
Accessor for Usages.
const DeclStmt * getAliasDecl() const
Returns the statement declaring the variable created as an alias for the loop element, if any.