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//===--- MisplacedWideningCastCheck.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 "MisplacedWideningCastCheck.h"
#include "../utils/Matchers.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
using namespace clang::ast_matchers;
namespace clang::tidy::bugprone {
MisplacedWideningCastCheck::MisplacedWideningCastCheck(
StringRef Name, ClangTidyContext *Context)
: ClangTidyCheck(Name, Context),
CheckImplicitCasts(Options.get("CheckImplicitCasts", false)) {}
void MisplacedWideningCastCheck::storeOptions(
ClangTidyOptions::OptionMap &Opts) {
Options.store(Opts, "CheckImplicitCasts", CheckImplicitCasts);
}
void MisplacedWideningCastCheck::registerMatchers(MatchFinder *Finder) {
const auto Calc =
expr(anyOf(binaryOperator(hasAnyOperatorName("+", "-", "*", "<<")),
unaryOperator(hasOperatorName("~"))),
hasType(isInteger()))
.bind("Calc");
const auto ExplicitCast = explicitCastExpr(hasDestinationType(isInteger()),
has(ignoringParenImpCasts(Calc)));
const auto ImplicitCast =
implicitCastExpr(hasImplicitDestinationType(isInteger()),
has(ignoringParenImpCasts(Calc)));
const auto Cast =
traverse(TK_AsIs, expr(anyOf(ExplicitCast, ImplicitCast)).bind("Cast"));
Finder->addMatcher(varDecl(hasInitializer(Cast)), this);
Finder->addMatcher(returnStmt(hasReturnValue(Cast)), this);
Finder->addMatcher(callExpr(hasAnyArgument(Cast)), this);
Finder->addMatcher(binaryOperator(hasOperatorName("="), hasRHS(Cast)), this);
Finder->addMatcher(
binaryOperator(isComparisonOperator(), hasEitherOperand(Cast)), this);
}
static unsigned getMaxCalculationWidth(const ASTContext &Context,
const Expr *E) {
E = E->IgnoreParenImpCasts();
if (const auto *Bop = dyn_cast<BinaryOperator>(E)) {
unsigned LHSWidth = getMaxCalculationWidth(Context, Bop->getLHS());
unsigned RHSWidth = getMaxCalculationWidth(Context, Bop->getRHS());
if (Bop->getOpcode() == BO_Mul)
return LHSWidth + RHSWidth;
if (Bop->getOpcode() == BO_Add)
return std::max(LHSWidth, RHSWidth) + 1;
if (Bop->getOpcode() == BO_Rem) {
Expr::EvalResult Result;
if (Bop->getRHS()->EvaluateAsInt(Result, Context))
return Result.Val.getInt().getActiveBits();
} else if (Bop->getOpcode() == BO_Shl) {
Expr::EvalResult Result;
if (Bop->getRHS()->EvaluateAsInt(Result, Context)) {
// We don't handle negative values and large values well. It is assumed
// that compiler warnings are written for such values so the user will
// fix that.
return LHSWidth + Result.Val.getInt().getExtValue();
}
// Unknown bitcount, assume there is truncation.
return 1024U;
}
} else if (const auto *Uop = dyn_cast<UnaryOperator>(E)) {
// There is truncation when ~ is used.
if (Uop->getOpcode() == UO_Not)
return 1024U;
QualType T = Uop->getType();
return T->isIntegerType() ? Context.getIntWidth(T) : 1024U;
} else if (const auto *I = dyn_cast<IntegerLiteral>(E)) {
return I->getValue().getActiveBits();
}
return Context.getIntWidth(E->getType());
}
static int relativeIntSizes(BuiltinType::Kind Kind) {
switch (Kind) {
case BuiltinType::UChar:
return 1;
case BuiltinType::SChar:
return 1;
case BuiltinType::Char_U:
return 1;
case BuiltinType::Char_S:
return 1;
case BuiltinType::UShort:
return 2;
case BuiltinType::Short:
return 2;
case BuiltinType::UInt:
return 3;
case BuiltinType::Int:
return 3;
case BuiltinType::ULong:
return 4;
case BuiltinType::Long:
return 4;
case BuiltinType::ULongLong:
return 5;
case BuiltinType::LongLong:
return 5;
case BuiltinType::UInt128:
return 6;
case BuiltinType::Int128:
return 6;
default:
return 0;
}
}
static int relativeCharSizes(BuiltinType::Kind Kind) {
switch (Kind) {
case BuiltinType::UChar:
return 1;
case BuiltinType::SChar:
return 1;
case BuiltinType::Char_U:
return 1;
case BuiltinType::Char_S:
return 1;
case BuiltinType::Char16:
return 2;
case BuiltinType::Char32:
return 3;
default:
return 0;
}
}
static int relativeCharSizesW(BuiltinType::Kind Kind) {
switch (Kind) {
case BuiltinType::UChar:
return 1;
case BuiltinType::SChar:
return 1;
case BuiltinType::Char_U:
return 1;
case BuiltinType::Char_S:
return 1;
case BuiltinType::WChar_U:
return 2;
case BuiltinType::WChar_S:
return 2;
default:
return 0;
}
}
static bool isFirstWider(BuiltinType::Kind First, BuiltinType::Kind Second) {
int FirstSize, SecondSize;
if ((FirstSize = relativeIntSizes(First)) != 0 &&
(SecondSize = relativeIntSizes(Second)) != 0)
return FirstSize > SecondSize;
if ((FirstSize = relativeCharSizes(First)) != 0 &&
(SecondSize = relativeCharSizes(Second)) != 0)
return FirstSize > SecondSize;
if ((FirstSize = relativeCharSizesW(First)) != 0 &&
(SecondSize = relativeCharSizesW(Second)) != 0)
return FirstSize > SecondSize;
return false;
}
void MisplacedWideningCastCheck::check(const MatchFinder::MatchResult &Result) {
const auto *Cast = Result.Nodes.getNodeAs<CastExpr>("Cast");
if (!CheckImplicitCasts && isa<ImplicitCastExpr>(Cast))
return;
if (Cast->getBeginLoc().isMacroID())
return;
const auto *Calc = Result.Nodes.getNodeAs<Expr>("Calc");
if (Calc->getBeginLoc().isMacroID())
return;
if (Cast->isTypeDependent() || Cast->isValueDependent() ||
Calc->isTypeDependent() || Calc->isValueDependent())
return;
ASTContext &Context = *Result.Context;
QualType CastType = Cast->getType();
QualType CalcType = Calc->getType();
// Explicit truncation using cast.
if (Context.getIntWidth(CastType) < Context.getIntWidth(CalcType))
return;
// If CalcType and CastType have same size then there is no real danger, but
// there can be a portability problem.
if (Context.getIntWidth(CastType) == Context.getIntWidth(CalcType)) {
const auto *CastBuiltinType =
dyn_cast<BuiltinType>(CastType->getUnqualifiedDesugaredType());
const auto *CalcBuiltinType =
dyn_cast<BuiltinType>(CalcType->getUnqualifiedDesugaredType());
if (!CastBuiltinType || !CalcBuiltinType)
return;
if (!isFirstWider(CastBuiltinType->getKind(), CalcBuiltinType->getKind()))
return;
}
// Don't write a warning if we can easily see that the result is not
// truncated.
if (Context.getIntWidth(CalcType) >= getMaxCalculationWidth(Context, Calc))
return;
diag(Cast->getBeginLoc(), "either cast from %0 to %1 is ineffective, or "
"there is loss of precision before the conversion")
<< CalcType << CastType;
}
} // namespace clang::tidy::bugprone
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