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//===--- NonConstParameterCheck.cpp - clang-tidy---------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "NonConstParameterCheck.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
using namespace clang::ast_matchers;
namespace clang::tidy::readability {
void NonConstParameterCheck::registerMatchers(MatchFinder *Finder) {
// Add parameters to Parameters.
Finder->addMatcher(parmVarDecl().bind("Parm"), this);
// C++ constructor.
Finder->addMatcher(cxxConstructorDecl().bind("Ctor"), this);
// Track unused parameters, there is Wunused-parameter about unused
// parameters.
Finder->addMatcher(declRefExpr().bind("Ref"), this);
// Analyse parameter usage in function.
Finder->addMatcher(stmt(anyOf(unaryOperator(hasAnyOperatorName("++", "--")),
binaryOperator(), callExpr(), returnStmt(),
cxxConstructExpr()))
.bind("Mark"),
this);
Finder->addMatcher(varDecl(hasInitializer(anything())).bind("Mark"), this);
}
void NonConstParameterCheck::check(const MatchFinder::MatchResult &Result) {
if (const auto *Parm = Result.Nodes.getNodeAs<ParmVarDecl>("Parm")) {
if (const DeclContext *D = Parm->getParentFunctionOrMethod()) {
if (const auto *M = dyn_cast<CXXMethodDecl>(D)) {
if (M->isVirtual() || M->size_overridden_methods() != 0)
return;
}
}
addParm(Parm);
} else if (const auto *Ctor =
Result.Nodes.getNodeAs<CXXConstructorDecl>("Ctor")) {
for (const auto *Parm : Ctor->parameters())
addParm(Parm);
for (const auto *Init : Ctor->inits())
markCanNotBeConst(Init->getInit(), true);
} else if (const auto *Ref = Result.Nodes.getNodeAs<DeclRefExpr>("Ref")) {
setReferenced(Ref);
} else if (const auto *S = Result.Nodes.getNodeAs<Stmt>("Mark")) {
if (const auto *B = dyn_cast<BinaryOperator>(S)) {
if (B->isAssignmentOp())
markCanNotBeConst(B, false);
} else if (const auto *CE = dyn_cast<CallExpr>(S)) {
// Typically, if a parameter is const then it is fine to make the data
// const. But sometimes the data is written even though the parameter
// is const. Mark all data passed by address to the function.
for (const auto *Arg : CE->arguments()) {
markCanNotBeConst(Arg->IgnoreParenCasts(), true);
}
// Data passed by nonconst reference should not be made const.
if (const FunctionDecl *FD = CE->getDirectCallee()) {
unsigned ArgNr = 0U;
for (const auto *Par : FD->parameters()) {
if (ArgNr >= CE->getNumArgs())
break;
const Expr *Arg = CE->getArg(ArgNr++);
// Is this a non constant reference parameter?
const Type *ParType = Par->getType().getTypePtr();
if (!ParType->isReferenceType() || Par->getType().isConstQualified())
continue;
markCanNotBeConst(Arg->IgnoreParenCasts(), false);
}
}
} else if (const auto *CE = dyn_cast<CXXConstructExpr>(S)) {
for (const auto *Arg : CE->arguments()) {
markCanNotBeConst(Arg->IgnoreParenCasts(), true);
}
// Data passed by nonconst reference should not be made const.
unsigned ArgNr = 0U;
if (const auto *CD = CE->getConstructor()) {
for (const auto *Par : CD->parameters()) {
if (ArgNr >= CE->getNumArgs())
break;
const Expr *Arg = CE->getArg(ArgNr++);
// Is this a non constant reference parameter?
const Type *ParType = Par->getType().getTypePtr();
if (!ParType->isReferenceType() || Par->getType().isConstQualified())
continue;
markCanNotBeConst(Arg->IgnoreParenCasts(), false);
}
}
} else if (const auto *R = dyn_cast<ReturnStmt>(S)) {
markCanNotBeConst(R->getRetValue(), true);
} else if (const auto *U = dyn_cast<UnaryOperator>(S)) {
markCanNotBeConst(U, true);
}
} else if (const auto *VD = Result.Nodes.getNodeAs<VarDecl>("Mark")) {
const QualType T = VD->getType();
if ((T->isPointerType() && !T->getPointeeType().isConstQualified()) ||
T->isArrayType())
markCanNotBeConst(VD->getInit(), true);
else if (T->isLValueReferenceType() &&
!T->getPointeeType().isConstQualified())
markCanNotBeConst(VD->getInit(), false);
}
}
void NonConstParameterCheck::addParm(const ParmVarDecl *Parm) {
// Only add nonconst integer/float pointer parameters.
const QualType T = Parm->getType();
if (!T->isPointerType() || T->getPointeeType().isConstQualified() ||
!(T->getPointeeType()->isIntegerType() ||
T->getPointeeType()->isFloatingType()))
return;
if (Parameters.find(Parm) != Parameters.end())
return;
ParmInfo PI;
PI.IsReferenced = false;
PI.CanBeConst = true;
Parameters[Parm] = PI;
}
void NonConstParameterCheck::setReferenced(const DeclRefExpr *Ref) {
auto It = Parameters.find(dyn_cast<ParmVarDecl>(Ref->getDecl()));
if (It != Parameters.end())
It->second.IsReferenced = true;
}
void NonConstParameterCheck::onEndOfTranslationUnit() {
diagnoseNonConstParameters();
}
void NonConstParameterCheck::diagnoseNonConstParameters() {
for (const auto &It : Parameters) {
const ParmVarDecl *Par = It.first;
const ParmInfo &ParamInfo = It.second;
// Unused parameter => there are other warnings about this.
if (!ParamInfo.IsReferenced)
continue;
// Parameter can't be const.
if (!ParamInfo.CanBeConst)
continue;
SmallVector<FixItHint, 8> Fixes;
auto *Function =
dyn_cast_or_null<const FunctionDecl>(Par->getParentFunctionOrMethod());
if (!Function)
continue;
unsigned Index = Par->getFunctionScopeIndex();
for (FunctionDecl *FnDecl : Function->redecls())
Fixes.push_back(FixItHint::CreateInsertion(
FnDecl->getParamDecl(Index)->getBeginLoc(), "const "));
diag(Par->getLocation(), "pointer parameter '%0' can be pointer to const")
<< Par->getName() << Fixes;
}
}
void NonConstParameterCheck::markCanNotBeConst(const Expr *E,
bool CanNotBeConst) {
if (!E)
return;
if (const auto *Cast = dyn_cast<ImplicitCastExpr>(E)) {
// If expression is const then ignore usage.
const QualType T = Cast->getType();
if (T->isPointerType() && T->getPointeeType().isConstQualified())
return;
}
E = E->IgnoreParenCasts();
if (const auto *B = dyn_cast<BinaryOperator>(E)) {
if (B->isAdditiveOp()) {
// p + 2
markCanNotBeConst(B->getLHS(), CanNotBeConst);
markCanNotBeConst(B->getRHS(), CanNotBeConst);
} else if (B->isAssignmentOp()) {
markCanNotBeConst(B->getLHS(), false);
// If LHS is not const then RHS can't be const.
const QualType T = B->getLHS()->getType();
if (T->isPointerType() && !T->getPointeeType().isConstQualified())
markCanNotBeConst(B->getRHS(), true);
}
} else if (const auto *C = dyn_cast<ConditionalOperator>(E)) {
markCanNotBeConst(C->getTrueExpr(), CanNotBeConst);
markCanNotBeConst(C->getFalseExpr(), CanNotBeConst);
} else if (const auto *U = dyn_cast<UnaryOperator>(E)) {
if (U->getOpcode() == UO_PreInc || U->getOpcode() == UO_PreDec ||
U->getOpcode() == UO_PostInc || U->getOpcode() == UO_PostDec) {
if (const auto *SubU =
dyn_cast<UnaryOperator>(U->getSubExpr()->IgnoreParenCasts()))
markCanNotBeConst(SubU->getSubExpr(), true);
markCanNotBeConst(U->getSubExpr(), CanNotBeConst);
} else if (U->getOpcode() == UO_Deref) {
if (!CanNotBeConst)
markCanNotBeConst(U->getSubExpr(), true);
} else {
markCanNotBeConst(U->getSubExpr(), CanNotBeConst);
}
} else if (const auto *A = dyn_cast<ArraySubscriptExpr>(E)) {
markCanNotBeConst(A->getBase(), true);
} else if (const auto *CLE = dyn_cast<CompoundLiteralExpr>(E)) {
markCanNotBeConst(CLE->getInitializer(), true);
} else if (const auto *Constr = dyn_cast<CXXConstructExpr>(E)) {
for (const auto *Arg : Constr->arguments()) {
if (const auto *M = dyn_cast<MaterializeTemporaryExpr>(Arg))
markCanNotBeConst(cast<Expr>(M->getSubExpr()), CanNotBeConst);
}
} else if (const auto *ILE = dyn_cast<InitListExpr>(E)) {
for (unsigned I = 0U; I < ILE->getNumInits(); ++I)
markCanNotBeConst(ILE->getInit(I), true);
} else if (CanNotBeConst) {
// Referencing parameter.
if (const auto *D = dyn_cast<DeclRefExpr>(E)) {
auto It = Parameters.find(dyn_cast<ParmVarDecl>(D->getDecl()));
if (It != Parameters.end())
It->second.CanBeConst = false;
}
}
}
} // namespace clang::tidy::readability
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