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//===--- LoopConvertCheck.cpp - clang-tidy---------------------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "LoopConvertCheck.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include "clang/Basic/LLVM.h"
#include "clang/Basic/LangOptions.h"
#include "clang/Basic/SourceLocation.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Lex/Lexer.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Support/Casting.h"
#include <cassert>
#include <cstring>
#include <utility>
using namespace clang::ast_matchers;
using namespace llvm;
namespace clang {
namespace tidy {
namespace modernize {
static const char LoopNameArray[] = "forLoopArray";
static const char LoopNameIterator[] = "forLoopIterator";
static const char LoopNamePseudoArray[] = "forLoopPseudoArray";
static const char ConditionBoundName[] = "conditionBound";
static const char ConditionVarName[] = "conditionVar";
static const char IncrementVarName[] = "incrementVar";
static const char InitVarName[] = "initVar";
static const char BeginCallName[] = "beginCall";
static const char EndCallName[] = "endCall";
static const char ConditionEndVarName[] = "conditionEndVar";
static const char EndVarName[] = "endVar";
static const char DerefByValueResultName[] = "derefByValueResult";
static const char DerefByRefResultName[] = "derefByRefResult";
// shared matchers
static const TypeMatcher AnyType() { return anything(); }
static const StatementMatcher IntegerComparisonMatcher() {
return expr(ignoringParenImpCasts(
static const DeclarationMatcher InitToZeroMatcher() {
return varDecl(
static const StatementMatcher IncrementVarMatcher() {
return declRefExpr(to(varDecl(hasType(isInteger())).bind(IncrementVarName)));
/// The matcher for loops over arrays.
/// In this general example, assuming 'j' and 'k' are of integral type:
/// \code
/// for (int i = 0; j < 3 + 2; ++k) { ... }
/// \endcode
/// The following string identifiers are bound to these parts of the AST:
/// ConditionVarName: 'j' (as a VarDecl)
/// ConditionBoundName: '3 + 2' (as an Expr)
/// InitVarName: 'i' (as a VarDecl)
/// IncrementVarName: 'k' (as a VarDecl)
/// LoopName: The entire for loop (as a ForStmt)
/// Client code will need to make sure that:
/// - The three index variables identified by the matcher are the same
/// VarDecl.
/// - The index variable is only used as an array index.
/// - All arrays indexed by the loop are the same.
StatementMatcher makeArrayLoopMatcher() {
StatementMatcher ArrayBoundMatcher =
return forStmt(
binaryOperator(hasOperatorName(">"), hasLHS(ArrayBoundMatcher),
/// The matcher used for iterator-based for loops.
/// This matcher is more flexible than array-based loops. It will match
/// catch loops of the following textual forms (regardless of whether the
/// iterator type is actually a pointer type or a class type):
/// Assuming f, g, and h are of type containerType::iterator,
/// \code
/// for (containerType::iterator it = container.begin(),
/// e = createIterator(); f != g; ++h) { ... }
/// for (containerType::iterator it = container.begin();
/// f != anotherContainer.end(); ++h) { ... }
/// \endcode
/// The following string identifiers are bound to the parts of the AST:
/// InitVarName: 'it' (as a VarDecl)
/// ConditionVarName: 'f' (as a VarDecl)
/// LoopName: The entire for loop (as a ForStmt)
/// In the first example only:
/// EndVarName: 'e' (as a VarDecl)
/// ConditionEndVarName: 'g' (as a VarDecl)
/// In the second example only:
/// EndCallName: 'container.end()' (as a CXXMemberCallExpr)
/// Client code will need to make sure that:
/// - The iterator variables 'it', 'f', and 'h' are the same.
/// - The two containers on which 'begin' and 'end' are called are the same.
/// - If the end iterator variable 'g' is defined, it is the same as 'f'.
StatementMatcher makeIteratorLoopMatcher() {
StatementMatcher BeginCallMatcher =
callee(cxxMethodDecl(anyOf(hasName("begin"), hasName("cbegin")))))
DeclarationMatcher InitDeclMatcher =
DeclarationMatcher EndDeclMatcher =
StatementMatcher EndCallMatcher = cxxMemberCallExpr(
callee(cxxMethodDecl(anyOf(hasName("end"), hasName("cend")))));
StatementMatcher IteratorBoundMatcher =
StatementMatcher IteratorComparisonMatcher = expr(
auto OverloadedNEQMatcher = ignoringImplicit(
cxxOperatorCallExpr(hasOverloadedOperatorName("!="), argumentCountIs(2),
hasArgument(0, IteratorComparisonMatcher),
hasArgument(1, IteratorBoundMatcher)));
// This matcher tests that a declaration is a CXXRecordDecl that has an
// overloaded operator*(). If the operator*() returns by value instead of by
// reference then the return type is tagged with DerefByValueResultName.
internal::Matcher<VarDecl> TestDerefReturnsByValue =
// Tag the return type if it's by value.
// Skip loops where the iterator's operator* returns an
// rvalue reference. This is just weird.
return forStmt(
containsDeclaration(0, InitDeclMatcher),
containsDeclaration(1, EndDeclMatcher)),
0, declRefExpr(to(varDecl(TestDerefReturnsByValue)
/// The matcher used for array-like containers (pseudoarrays).
/// This matcher is more flexible than array-based loops. It will match
/// loops of the following textual forms (regardless of whether the
/// iterator type is actually a pointer type or a class type):
/// Assuming f, g, and h are of type containerType::iterator,
/// \code
/// for (int i = 0, j = container.size(); f < g; ++h) { ... }
/// for (int i = 0; f < container.size(); ++h) { ... }
/// \endcode
/// The following string identifiers are bound to the parts of the AST:
/// InitVarName: 'i' (as a VarDecl)
/// ConditionVarName: 'f' (as a VarDecl)
/// LoopName: The entire for loop (as a ForStmt)
/// In the first example only:
/// EndVarName: 'j' (as a VarDecl)
/// ConditionEndVarName: 'g' (as a VarDecl)
/// In the second example only:
/// EndCallName: 'container.size()' (as a CXXMemberCallExpr)
/// Client code will need to make sure that:
/// - The index variables 'i', 'f', and 'h' are the same.
/// - The containers on which 'size()' is called is the container indexed.
/// - The index variable is only used in overloaded operator[] or
/// - If the end iterator variable 'g' is defined, it is the same as 'j'.
/// - The container's iterators would not be invalidated during the loop.
StatementMatcher makePseudoArrayLoopMatcher() {
// Test that the incoming type has a record declaration that has methods
// called 'begin' and 'end'. If the incoming type is const, then make sure
// these methods are also marked const.
// FIXME: To be completely thorough this matcher should also ensure the
// return type of begin/end is an iterator that dereferences to the same as
// what operator[] or at() returns. Such a test isn't likely to fail except
// for pathological cases.
// FIXME: Also, a record doesn't necessarily need begin() and end(). Free
// functions called begin() and end() taking the container as an argument
// are also allowed.
TypeMatcher RecordWithBeginEnd = qualType(anyOf(
hasMethod(cxxMethodDecl(hasName("begin"), isConst())),
isConst())))) // hasDeclaration
))), // qualType
hasMethod(hasName("end"))))))) // qualType
StatementMatcher SizeCallMatcher = cxxMemberCallExpr(
callee(cxxMethodDecl(anyOf(hasName("size"), hasName("length")))),
StatementMatcher EndInitMatcher =
DeclarationMatcher EndDeclMatcher =
StatementMatcher IndexBoundMatcher =
return forStmt(
containsDeclaration(0, InitToZeroMatcher()),
containsDeclaration(1, EndDeclMatcher)),
binaryOperator(hasOperatorName(">"), hasLHS(IndexBoundMatcher),
/// Determine whether Init appears to be an initializing an iterator.
/// If it is, returns the object whose begin() or end() method is called, and
/// the output parameter isArrow is set to indicate whether the initialization
/// is called via . or ->.
static const Expr *getContainerFromBeginEndCall(const Expr *Init, bool IsBegin,
bool *IsArrow) {
// FIXME: Maybe allow declaration/initialization outside of the for loop.
const auto *TheCall =
if (!TheCall || TheCall->getNumArgs() != 0)
return nullptr;
const auto *Member = dyn_cast<MemberExpr>(TheCall->getCallee());
if (!Member)
return nullptr;
StringRef Name = Member->getMemberDecl()->getName();
StringRef TargetName = IsBegin ? "begin" : "end";
StringRef ConstTargetName = IsBegin ? "cbegin" : "cend";
if (Name != TargetName && Name != ConstTargetName)
return nullptr;
const Expr *SourceExpr = Member->getBase();
if (!SourceExpr)
return nullptr;
*IsArrow = Member->isArrow();
return SourceExpr;
/// Determines the container whose begin() and end() functions are called
/// for an iterator-based loop.
/// BeginExpr must be a member call to a function named "begin()", and EndExpr
/// must be a member.
static const Expr *findContainer(ASTContext *Context, const Expr *BeginExpr,
const Expr *EndExpr,
bool *ContainerNeedsDereference) {
// Now that we know the loop variable and test expression, make sure they are
// valid.
bool BeginIsArrow = false;
bool EndIsArrow = false;
const Expr *BeginContainerExpr =
getContainerFromBeginEndCall(BeginExpr, /*IsBegin=*/true, &BeginIsArrow);
if (!BeginContainerExpr)
return nullptr;
const Expr *EndContainerExpr =
getContainerFromBeginEndCall(EndExpr, /*IsBegin=*/false, &EndIsArrow);
// Disallow loops that try evil things like this (note the dot and arrow):
// for (IteratorType It = Obj.begin(), E = Obj->end(); It != E; ++It) { }
if (!EndContainerExpr || BeginIsArrow != EndIsArrow ||
!areSameExpr(Context, EndContainerExpr, BeginContainerExpr))
return nullptr;
*ContainerNeedsDereference = BeginIsArrow;
return BeginContainerExpr;
/// Obtain the original source code text from a SourceRange.
static StringRef getStringFromRange(SourceManager &SourceMgr,
const LangOptions &LangOpts,
SourceRange Range) {
if (SourceMgr.getFileID(Range.getBegin()) !=
SourceMgr.getFileID(Range.getEnd())) {
return StringRef(); // Empty string.
return Lexer::getSourceText(CharSourceRange(Range, true), SourceMgr,
/// If the given expression is actually a DeclRefExpr or a MemberExpr,
/// find and return the underlying ValueDecl; otherwise, return NULL.
static const ValueDecl *getReferencedVariable(const Expr *E) {
if (const DeclRefExpr *DRE = getDeclRef(E))
return dyn_cast<VarDecl>(DRE->getDecl());
if (const auto *Mem = dyn_cast<MemberExpr>(E->IgnoreParenImpCasts()))
return dyn_cast<FieldDecl>(Mem->getMemberDecl());
return nullptr;
/// Returns true when the given expression is a member expression
/// whose base is `this` (implicitly or not).
static bool isDirectMemberExpr(const Expr *E) {
if (const auto *Member = dyn_cast<MemberExpr>(E->IgnoreParenImpCasts()))
return isa<CXXThisExpr>(Member->getBase()->IgnoreParenImpCasts());
return false;
/// Given an expression that represents an usage of an element from the
/// containter that we are iterating over, returns false when it can be
/// guaranteed this element cannot be modified as a result of this usage.
static bool canBeModified(ASTContext *Context, const Expr *E) {
if (E->getType().isConstQualified())
return false;
auto Parents = Context->getParents(*E);
if (Parents.size() != 1)
return true;
if (const auto *Cast = Parents[0].get<ImplicitCastExpr>()) {
if ((Cast->getCastKind() == CK_NoOp &&
Cast->getType() == E->getType().withConst()) ||
(Cast->getCastKind() == CK_LValueToRValue &&
!Cast->getType().isNull() && Cast->getType()->isFundamentalType()))
return false;
// FIXME: Make this function more generic.
return true;
/// Returns true when it can be guaranteed that the elements of the
/// container are not being modified.
static bool usagesAreConst(ASTContext *Context, const UsageResult &Usages) {
for (const Usage &U : Usages) {
// Lambda captures are just redeclarations (VarDecl) of the same variable,
// not expressions. If we want to know if a variable that is captured by
// reference can be modified in an usage inside the lambda's body, we need
// to find the expression corresponding to that particular usage, later in
// this loop.
if (U.Kind != Usage::UK_CaptureByCopy && U.Kind != Usage::UK_CaptureByRef &&
canBeModified(Context, U.Expression))
return false;
return true;
/// Returns true if the elements of the container are never accessed
/// by reference.
static bool usagesReturnRValues(const UsageResult &Usages) {
for (const auto &U : Usages) {
if (U.Expression && !U.Expression->isRValue())
return false;
return true;
/// Returns true if the container is const-qualified.
static bool containerIsConst(const Expr *ContainerExpr, bool Dereference) {
if (const auto *VDec = getReferencedVariable(ContainerExpr)) {
QualType CType = VDec->getType();
if (Dereference) {
if (!CType->isPointerType())
return false;
CType = CType->getPointeeType();
// If VDec is a reference to a container, Dereference is false,
// but we still need to check the const-ness of the underlying container
// type.
CType = CType.getNonReferenceType();
return CType.isConstQualified();
return false;
: ContainerNeedsDereference(false), DerefByConstRef(false),
DerefByValue(false) {}
LoopConvertCheck::LoopConvertCheck(StringRef Name, ClangTidyContext *Context)
: ClangTidyCheck(Name, Context), TUInfo(new TUTrackingInfo),
MaxCopySize(std::stoull(Options.get("MaxCopySize", "16"))),
Options.get("MinConfidence", "reasonable"))
.Case("safe", Confidence::CL_Safe)
.Case("risky", Confidence::CL_Risky)
Options.get("NamingStyle", "CamelCase"))
.Case("camelBack", VariableNamer::NS_CamelBack)
.Case("lower_case", VariableNamer::NS_LowerCase)
.Case("UPPER_CASE", VariableNamer::NS_UpperCase)
.Default(VariableNamer::NS_CamelCase)) {}
void LoopConvertCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {, "MaxCopySize", std::to_string(MaxCopySize));
SmallVector<std::string, 3> Confs{"risky", "reasonable", "safe"};, "MinConfidence", Confs[static_cast<int>(MinConfidence)]);
SmallVector<std::string, 4> Styles{"camelBack", "CamelCase", "lower_case",
"UPPER_CASE"};, "NamingStyle", Styles[static_cast<int>(NamingStyle)]);
void LoopConvertCheck::registerMatchers(MatchFinder *Finder) {
// Only register the matchers for C++. Because this checker is used for
// modernization, it is reasonable to run it on any C++ standard with the
// assumption the user is trying to modernize their codebase.
if (!getLangOpts().CPlusPlus)
Finder->addMatcher(makeArrayLoopMatcher(), this);
Finder->addMatcher(makeIteratorLoopMatcher(), this);
Finder->addMatcher(makePseudoArrayLoopMatcher(), this);
/// Given the range of a single declaration, such as:
/// \code
/// unsigned &ThisIsADeclarationThatCanSpanSeveralLinesOfCode =
/// InitializationValues[I];
/// next_instruction;
/// \endcode
/// Finds the range that has to be erased to remove this declaration without
/// leaving empty lines, by extending the range until the beginning of the
/// next instruction.
/// We need to delete a potential newline after the deleted alias, as
/// clang-format will leave empty lines untouched. For all other formatting we
/// rely on clang-format to fix it.
void LoopConvertCheck::getAliasRange(SourceManager &SM, SourceRange &Range) {
bool Invalid = false;
const char *TextAfter =
SM.getCharacterData(Range.getEnd().getLocWithOffset(1), &Invalid);
if (Invalid)
unsigned Offset = std::strspn(TextAfter, " \t\r\n");
Range =
SourceRange(Range.getBegin(), Range.getEnd().getLocWithOffset(Offset));
/// Computes the changes needed to convert a given for loop, and
/// applies them.
void LoopConvertCheck::doConversion(
ASTContext *Context, const VarDecl *IndexVar,
const ValueDecl *MaybeContainer, const UsageResult &Usages,
const DeclStmt *AliasDecl, bool AliasUseRequired, bool AliasFromForInit,
const ForStmt *Loop, RangeDescriptor Descriptor) {
auto Diag = diag(Loop->getForLoc(), "use range-based for loop instead");
std::string VarName;
bool VarNameFromAlias = (Usages.size() == 1) && AliasDecl;
bool AliasVarIsRef = false;
bool CanCopy = true;
if (VarNameFromAlias) {
const auto *AliasVar = cast<VarDecl>(AliasDecl->getSingleDecl());
VarName = AliasVar->getName().str();
// Use the type of the alias if it's not the same
QualType AliasVarType = AliasVar->getType();
assert(!AliasVarType.isNull() && "Type in VarDecl is null");
if (AliasVarType->isReferenceType()) {
AliasVarType = AliasVarType.getNonReferenceType();
AliasVarIsRef = true;
if (Descriptor.ElemType.isNull() ||
!Context->hasSameUnqualifiedType(AliasVarType, Descriptor.ElemType))
Descriptor.ElemType = AliasVarType;
// We keep along the entire DeclStmt to keep the correct range here.
SourceRange ReplaceRange = AliasDecl->getSourceRange();
std::string ReplacementText;
if (AliasUseRequired) {
ReplacementText = VarName;
} else if (AliasFromForInit) {
// FIXME: Clang includes the location of the ';' but only for DeclStmt's
// in a for loop's init clause. Need to put this ';' back while removing
// the declaration of the alias variable. This is probably a bug.
ReplacementText = ";";
} else {
// Avoid leaving empty lines or trailing whitespaces.
getAliasRange(Context->getSourceManager(), ReplaceRange);
Diag << FixItHint::CreateReplacement(
CharSourceRange::getTokenRange(ReplaceRange), ReplacementText);
// No further replacements are made to the loop, since the iterator or index
// was used exactly once - in the initialization of AliasVar.
} else {
VariableNamer Namer(&TUInfo->getGeneratedDecls(),
Loop, IndexVar, MaybeContainer, Context, NamingStyle);
VarName = Namer.createIndexName();
// First, replace all usages of the array subscript expression with our new
// variable.
for (const auto &Usage : Usages) {
std::string ReplaceText;
SourceRange Range = Usage.Range;
if (Usage.Expression) {
// If this is an access to a member through the arrow operator, after
// the replacement it must be accessed through the '.' operator.
ReplaceText = Usage.Kind == Usage::UK_MemberThroughArrow ? VarName + "."
: VarName;
auto Parents = Context->getParents(*Usage.Expression);
if (Parents.size() == 1) {
if (const auto *Paren = Parents[0].get<ParenExpr>()) {
// Usage.Expression will be replaced with the new index variable,
// and parenthesis around a simple DeclRefExpr can always be
// removed.
Range = Paren->getSourceRange();
} else if (const auto *UOP = Parents[0].get<UnaryOperator>()) {
// If we are taking the address of the loop variable, then we must
// not use a copy, as it would mean taking the address of the loop's
// local index instead.
// FIXME: This won't catch cases where the address is taken outside
// of the loop's body (for instance, in a function that got the
// loop's index as a const reference parameter), or where we take
// the address of a member (like "&Arr[i].A.B.C").
if (UOP->getOpcode() == UO_AddrOf)
CanCopy = false;
} else {
// The Usage expression is only null in case of lambda captures (which
// are VarDecl). If the index is captured by value, add '&' to capture
// by reference instead.
ReplaceText =
Usage.Kind == Usage::UK_CaptureByCopy ? "&" + VarName : VarName;
TUInfo->getReplacedVars().insert(std::make_pair(Loop, IndexVar));
Diag << FixItHint::CreateReplacement(
CharSourceRange::getTokenRange(Range), ReplaceText);
// Now, we need to construct the new range expression.
SourceRange ParenRange(Loop->getLParenLoc(), Loop->getRParenLoc());
QualType Type = Context->getAutoDeductType();
if (!Descriptor.ElemType.isNull() && Descriptor.ElemType->isFundamentalType())
Type = Descriptor.ElemType.getUnqualifiedType();
// If the new variable name is from the aliased variable, then the reference
// type for the new variable should only be used if the aliased variable was
// declared as a reference.
bool IsCheapToCopy =
!Descriptor.ElemType.isNull() &&
Descriptor.ElemType.isTriviallyCopyableType(*Context) &&
// TypeInfo::Width is in bits.
Context->getTypeInfo(Descriptor.ElemType).Width <= 8 * MaxCopySize;
bool UseCopy = CanCopy && ((VarNameFromAlias && !AliasVarIsRef) ||
(Descriptor.DerefByConstRef && IsCheapToCopy));
if (!UseCopy) {
if (Descriptor.DerefByConstRef) {
Type = Context->getLValueReferenceType(Context->getConstType(Type));
} else if (Descriptor.DerefByValue) {
if (!IsCheapToCopy)
Type = Context->getRValueReferenceType(Type);
} else {
Type = Context->getLValueReferenceType(Type);
StringRef MaybeDereference = Descriptor.ContainerNeedsDereference ? "*" : "";
std::string TypeString = Type.getAsString(getLangOpts());
std::string Range = ("(" + TypeString + " " + VarName + " : " +
MaybeDereference + Descriptor.ContainerString + ")")
Diag << FixItHint::CreateReplacement(
CharSourceRange::getTokenRange(ParenRange), Range);
TUInfo->getGeneratedDecls().insert(make_pair(Loop, VarName));
/// Returns a string which refers to the container iterated over.
StringRef LoopConvertCheck::getContainerString(ASTContext *Context,
const ForStmt *Loop,
const Expr *ContainerExpr) {
StringRef ContainerString;
if (isa<CXXThisExpr>(ContainerExpr->IgnoreParenImpCasts())) {
ContainerString = "this";
} else {
ContainerString =
getStringFromRange(Context->getSourceManager(), Context->getLangOpts(),
return ContainerString;
/// Determines what kind of 'auto' must be used after converting a for
/// loop that iterates over an array or pseudoarray.
void LoopConvertCheck::getArrayLoopQualifiers(ASTContext *Context,
const BoundNodes &Nodes,
const Expr *ContainerExpr,
const UsageResult &Usages,
RangeDescriptor &Descriptor) {
// On arrays and pseudoarrays, we must figure out the qualifiers from the
// usages.
if (usagesAreConst(Context, Usages) ||
containerIsConst(ContainerExpr, Descriptor.ContainerNeedsDereference)) {
Descriptor.DerefByConstRef = true;
if (usagesReturnRValues(Usages)) {
// If the index usages (dereference, subscript, at, ...) return rvalues,
// then we should not use a reference, because we need to keep the code
// correct if it mutates the returned objects.
Descriptor.DerefByValue = true;
// Try to find the type of the elements on the container, to check if
// they are trivially copyable.
for (const Usage &U : Usages) {
if (!U.Expression || U.Expression->getType().isNull())
QualType Type = U.Expression->getType().getCanonicalType();
if (U.Kind == Usage::UK_MemberThroughArrow) {
if (!Type->isPointerType()) {
Type = Type->getPointeeType();
Descriptor.ElemType = Type;
/// Determines what kind of 'auto' must be used after converting an
/// iterator based for loop.
void LoopConvertCheck::getIteratorLoopQualifiers(ASTContext *Context,
const BoundNodes &Nodes,
RangeDescriptor &Descriptor) {
// The matchers for iterator loops provide bound nodes to obtain this
// information.
const auto *InitVar = Nodes.getNodeAs<VarDecl>(InitVarName);
QualType CanonicalInitVarType = InitVar->getType().getCanonicalType();
const auto *DerefByValueType =
Descriptor.DerefByValue = DerefByValueType;
if (Descriptor.DerefByValue) {
// If the dereference operator returns by value then test for the
// canonical const qualification of the init variable type.
Descriptor.DerefByConstRef = CanonicalInitVarType.isConstQualified();
Descriptor.ElemType = *DerefByValueType;
} else {
if (const auto *DerefType =
Nodes.getNodeAs<QualType>(DerefByRefResultName)) {
// A node will only be bound with DerefByRefResultName if we're dealing
// with a user-defined iterator type. Test the const qualification of
// the reference type.
auto ValueType = DerefType->getNonReferenceType();
Descriptor.DerefByConstRef = ValueType.isConstQualified();
Descriptor.ElemType = ValueType;
} else {
// By nature of the matcher this case is triggered only for built-in
// iterator types (i.e. pointers).
assert(isa<PointerType>(CanonicalInitVarType) &&
"Non-class iterator type is not a pointer type");
// We test for const qualification of the pointed-at type.
Descriptor.DerefByConstRef =
Descriptor.ElemType = CanonicalInitVarType->getPointeeType();
/// Determines the parameters needed to build the range replacement.
void LoopConvertCheck::determineRangeDescriptor(
ASTContext *Context, const BoundNodes &Nodes, const ForStmt *Loop,
LoopFixerKind FixerKind, const Expr *ContainerExpr,
const UsageResult &Usages, RangeDescriptor &Descriptor) {
Descriptor.ContainerString = getContainerString(Context, Loop, ContainerExpr);
if (FixerKind == LFK_Iterator)
getIteratorLoopQualifiers(Context, Nodes, Descriptor);
getArrayLoopQualifiers(Context, Nodes, ContainerExpr, Usages, Descriptor);
/// Check some of the conditions that must be met for the loop to be
/// convertible.
bool LoopConvertCheck::isConvertible(ASTContext *Context,
const ast_matchers::BoundNodes &Nodes,
const ForStmt *Loop,
LoopFixerKind FixerKind) {
// If we already modified the range of this for loop, don't do any further
// updates on this iteration.
if (TUInfo->getReplacedVars().count(Loop))
return false;
// Check that we have exactly one index variable and at most one end variable.
const auto *LoopVar = Nodes.getNodeAs<VarDecl>(IncrementVarName);
const auto *CondVar = Nodes.getNodeAs<VarDecl>(ConditionVarName);
const auto *InitVar = Nodes.getNodeAs<VarDecl>(InitVarName);
if (!areSameVariable(LoopVar, CondVar) || !areSameVariable(LoopVar, InitVar))
return false;
const auto *EndVar = Nodes.getNodeAs<VarDecl>(EndVarName);
const auto *ConditionEndVar = Nodes.getNodeAs<VarDecl>(ConditionEndVarName);
if (EndVar && !areSameVariable(EndVar, ConditionEndVar))
return false;
// FIXME: Try to put most of this logic inside a matcher.
if (FixerKind == LFK_Iterator) {
QualType InitVarType = InitVar->getType();
QualType CanonicalInitVarType = InitVarType.getCanonicalType();
const auto *BeginCall = Nodes.getNodeAs<CXXMemberCallExpr>(BeginCallName);
assert(BeginCall && "Bad Callback. No begin call expression");
QualType CanonicalBeginType =
if (CanonicalBeginType->isPointerType() &&
CanonicalInitVarType->isPointerType()) {
// If the initializer and the variable are both pointers check if the
// un-qualified pointee types match, otherwise we don't use auto.
if (!Context->hasSameUnqualifiedType(
return false;
} else if (FixerKind == LFK_PseudoArray) {
// This call is required to obtain the container.
const auto *EndCall = Nodes.getNodeAs<CXXMemberCallExpr>(EndCallName);
if (!EndCall || !dyn_cast<MemberExpr>(EndCall->getCallee()))
return false;
return true;
void LoopConvertCheck::check(const MatchFinder::MatchResult &Result) {
const BoundNodes &Nodes = Result.Nodes;
Confidence ConfidenceLevel(Confidence::CL_Safe);
ASTContext *Context = Result.Context;
const ForStmt *Loop;
LoopFixerKind FixerKind;
RangeDescriptor Descriptor;
if ((Loop = Nodes.getNodeAs<ForStmt>(LoopNameArray))) {
FixerKind = LFK_Array;
} else if ((Loop = Nodes.getNodeAs<ForStmt>(LoopNameIterator))) {
FixerKind = LFK_Iterator;
} else {
Loop = Nodes.getNodeAs<ForStmt>(LoopNamePseudoArray);
assert(Loop && "Bad Callback. No for statement");
FixerKind = LFK_PseudoArray;
if (!isConvertible(Context, Nodes, Loop, FixerKind))
const auto *LoopVar = Nodes.getNodeAs<VarDecl>(IncrementVarName);
const auto *EndVar = Nodes.getNodeAs<VarDecl>(EndVarName);
// If the loop calls end()/size() after each iteration, lower our confidence
// level.
if (FixerKind != LFK_Array && !EndVar)
// If the end comparison isn't a variable, we can try to work with the
// expression the loop variable is being tested against instead.
const auto *EndCall = Nodes.getNodeAs<CXXMemberCallExpr>(EndCallName);
const auto *BoundExpr = Nodes.getNodeAs<Expr>(ConditionBoundName);
// Find container expression of iterators and pseudoarrays, and determine if
// this expression needs to be dereferenced to obtain the container.
// With array loops, the container is often discovered during the
// ForLoopIndexUseVisitor traversal.
const Expr *ContainerExpr = nullptr;
if (FixerKind == LFK_Iterator) {
ContainerExpr = findContainer(Context, LoopVar->getInit(),
EndVar ? EndVar->getInit() : EndCall,
} else if (FixerKind == LFK_PseudoArray) {
ContainerExpr = EndCall->getImplicitObjectArgument();
Descriptor.ContainerNeedsDereference =
// We must know the container or an array length bound.
if (!ContainerExpr && !BoundExpr)
ForLoopIndexUseVisitor Finder(Context, LoopVar, EndVar, ContainerExpr,
// Find expressions and variables on which the container depends.
if (ContainerExpr) {
ComponentFinderASTVisitor ComponentFinder;
// Find usages of the loop index. If they are not used in a convertible way,
// stop here.
if (!Finder.findAndVerifyUsages(Loop->getBody()))
// Obtain the container expression, if we don't have it yet.
if (FixerKind == LFK_Array) {
ContainerExpr = Finder.getContainerIndexed()->IgnoreParenImpCasts();
// Very few loops are over expressions that generate arrays rather than
// array variables. Consider loops over arrays that aren't just represented
// by a variable to be risky conversions.
if (!getReferencedVariable(ContainerExpr) &&
// Find out which qualifiers we have to use in the loop range.
const UsageResult &Usages = Finder.getUsages();
determineRangeDescriptor(Context, Nodes, Loop, FixerKind, ContainerExpr,
Usages, Descriptor);
// Ensure that we do not try to move an expression dependent on a local
// variable declared inside the loop outside of it.
// FIXME: Determine when the external dependency isn't an expression converted
// by another loop.
DependencyFinderASTVisitor DependencyFinder(
&TUInfo->getReplacedVars(), Loop);
if (DependencyFinder.dependsOnInsideVariable(ContainerExpr) ||
Descriptor.ContainerString.empty() || Usages.empty() ||
ConfidenceLevel.getLevel() < MinConfidence)
doConversion(Context, LoopVar, getReferencedVariable(ContainerExpr), Usages,
Finder.getAliasDecl(), Finder.aliasUseRequired(),
Finder.aliasFromForInit(), Loop, Descriptor);
} // namespace modernize
} // namespace tidy
} // namespace clang