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//===--- SuspiciousEnumUsageCheck.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 "SuspiciousEnumUsageCheck.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include <algorithm>
using namespace clang::ast_matchers;
namespace clang::tidy::bugprone {
static const char DifferentEnumErrorMessage[] =
"enum values are from different enum types";
static const char BitmaskErrorMessage[] =
"enum type seems like a bitmask (contains mostly "
"power-of-2 literals), but this literal is not a "
"power-of-2";
static const char BitmaskVarErrorMessage[] =
"enum type seems like a bitmask (contains mostly "
"power-of-2 literals) but %plural{1:a literal is|:some literals are}0 not "
"power-of-2";
static const char BitmaskNoteMessage[] = "used here as a bitmask";
/// Stores a min and a max value which describe an interval.
struct ValueRange {
llvm::APSInt MinVal;
llvm::APSInt MaxVal;
ValueRange(const EnumDecl *EnumDec) {
const auto MinMaxVal = std::minmax_element(
EnumDec->enumerator_begin(), EnumDec->enumerator_end(),
[](const EnumConstantDecl *E1, const EnumConstantDecl *E2) {
return llvm::APSInt::compareValues(E1->getInitVal(),
E2->getInitVal()) < 0;
});
MinVal = MinMaxVal.first->getInitVal();
MaxVal = MinMaxVal.second->getInitVal();
}
};
/// Return the number of EnumConstantDecls in an EnumDecl.
static int enumLength(const EnumDecl *EnumDec) {
return std::distance(EnumDec->enumerator_begin(), EnumDec->enumerator_end());
}
static bool hasDisjointValueRange(const EnumDecl *Enum1,
const EnumDecl *Enum2) {
ValueRange Range1(Enum1), Range2(Enum2);
return llvm::APSInt::compareValues(Range1.MaxVal, Range2.MinVal) < 0 ||
llvm::APSInt::compareValues(Range2.MaxVal, Range1.MinVal) < 0;
}
static bool isNonPowerOf2NorNullLiteral(const EnumConstantDecl *EnumConst) {
llvm::APSInt Val = EnumConst->getInitVal();
if (Val.isPowerOf2() || !Val.getBoolValue())
return false;
const Expr *InitExpr = EnumConst->getInitExpr();
if (!InitExpr)
return true;
return isa<IntegerLiteral>(InitExpr->IgnoreImpCasts());
}
static bool isMaxValAllBitSetLiteral(const EnumDecl *EnumDec) {
auto EnumConst = std::max_element(
EnumDec->enumerator_begin(), EnumDec->enumerator_end(),
[](const EnumConstantDecl *E1, const EnumConstantDecl *E2) {
return E1->getInitVal() < E2->getInitVal();
});
if (const Expr *InitExpr = EnumConst->getInitExpr()) {
return EnumConst->getInitVal().countr_one() ==
EnumConst->getInitVal().getActiveBits() &&
isa<IntegerLiteral>(InitExpr->IgnoreImpCasts());
}
return false;
}
static int countNonPowOfTwoLiteralNum(const EnumDecl *EnumDec) {
return llvm::count_if(EnumDec->enumerators(), isNonPowerOf2NorNullLiteral);
}
/// Check if there is one or two enumerators that are not a power of 2 and are
/// initialized by a literal in the enum type, and that the enumeration contains
/// enough elements to reasonably act as a bitmask. Exclude the case where the
/// last enumerator is the sum of the lesser values (and initialized by a
/// literal) or when it could contain consecutive values.
static bool isPossiblyBitMask(const EnumDecl *EnumDec) {
ValueRange VR(EnumDec);
int EnumLen = enumLength(EnumDec);
int NonPowOfTwoCounter = countNonPowOfTwoLiteralNum(EnumDec);
return NonPowOfTwoCounter >= 1 && NonPowOfTwoCounter <= 2 &&
NonPowOfTwoCounter < EnumLen / 2 &&
(VR.MaxVal - VR.MinVal != EnumLen - 1) &&
!(NonPowOfTwoCounter == 1 && isMaxValAllBitSetLiteral(EnumDec));
}
SuspiciousEnumUsageCheck::SuspiciousEnumUsageCheck(StringRef Name,
ClangTidyContext *Context)
: ClangTidyCheck(Name, Context),
StrictMode(Options.getLocalOrGlobal("StrictMode", false)) {}
void SuspiciousEnumUsageCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
Options.store(Opts, "StrictMode", StrictMode);
}
void SuspiciousEnumUsageCheck::registerMatchers(MatchFinder *Finder) {
const auto EnumExpr = [](StringRef RefName, StringRef DeclName) {
return expr(hasType(enumDecl().bind(DeclName))).bind(RefName);
};
Finder->addMatcher(
binaryOperator(
hasOperatorName("|"), hasLHS(hasType(enumDecl().bind("enumDecl"))),
hasRHS(hasType(enumDecl(unless(equalsBoundNode("enumDecl")))
.bind("otherEnumDecl"))))
.bind("diffEnumOp"),
this);
Finder->addMatcher(
binaryOperator(hasAnyOperatorName("+", "|"),
hasLHS(EnumExpr("lhsExpr", "enumDecl")),
hasRHS(expr(hasType(enumDecl(equalsBoundNode("enumDecl"))))
.bind("rhsExpr"))),
this);
Finder->addMatcher(
binaryOperator(
hasAnyOperatorName("+", "|"),
hasOperands(expr(hasType(isInteger()), unless(hasType(enumDecl()))),
EnumExpr("enumExpr", "enumDecl"))),
this);
Finder->addMatcher(binaryOperator(hasAnyOperatorName("|=", "+="),
hasRHS(EnumExpr("enumExpr", "enumDecl"))),
this);
}
void SuspiciousEnumUsageCheck::checkSuspiciousBitmaskUsage(
const Expr *NodeExpr, const EnumDecl *EnumDec) {
const auto *EnumExpr = dyn_cast<DeclRefExpr>(NodeExpr);
const auto *EnumConst =
EnumExpr ? dyn_cast<EnumConstantDecl>(EnumExpr->getDecl()) : nullptr;
// Report the parameter if necessary.
if (!EnumConst) {
diag(EnumDec->getInnerLocStart(), BitmaskVarErrorMessage)
<< countNonPowOfTwoLiteralNum(EnumDec);
diag(EnumExpr->getExprLoc(), BitmaskNoteMessage, DiagnosticIDs::Note);
} else if (isNonPowerOf2NorNullLiteral(EnumConst)) {
diag(EnumConst->getSourceRange().getBegin(), BitmaskErrorMessage);
diag(EnumExpr->getExprLoc(), BitmaskNoteMessage, DiagnosticIDs::Note);
}
}
void SuspiciousEnumUsageCheck::check(const MatchFinder::MatchResult &Result) {
// Case 1: The two enum values come from different types.
if (const auto *DiffEnumOp =
Result.Nodes.getNodeAs<BinaryOperator>("diffEnumOp")) {
const auto *EnumDec = Result.Nodes.getNodeAs<EnumDecl>("enumDecl");
const auto *OtherEnumDec =
Result.Nodes.getNodeAs<EnumDecl>("otherEnumDecl");
// Skip when one of the parameters is an empty enum. The
// hasDisjointValueRange function could not decide the values properly in
// case of an empty enum.
if (EnumDec->enumerator_begin() == EnumDec->enumerator_end() ||
OtherEnumDec->enumerator_begin() == OtherEnumDec->enumerator_end())
return;
if (!hasDisjointValueRange(EnumDec, OtherEnumDec))
diag(DiffEnumOp->getOperatorLoc(), DifferentEnumErrorMessage);
return;
}
// Case 2 and 3 only checked in strict mode. The checker tries to detect
// suspicious bitmasks which contains values initialized by non power-of-2
// literals.
if (!StrictMode)
return;
const auto *EnumDec = Result.Nodes.getNodeAs<EnumDecl>("enumDecl");
if (!isPossiblyBitMask(EnumDec))
return;
// Case 2:
// a. Investigating the right hand side of `+=` or `|=` operator.
// b. When the operator is `|` or `+` but only one of them is an EnumExpr
if (const auto *EnumExpr = Result.Nodes.getNodeAs<Expr>("enumExpr")) {
checkSuspiciousBitmaskUsage(EnumExpr, EnumDec);
return;
}
// Case 3:
// '|' or '+' operator where both argument comes from the same enum type
const auto *LhsExpr = Result.Nodes.getNodeAs<Expr>("lhsExpr");
checkSuspiciousBitmaskUsage(LhsExpr, EnumDec);
const auto *RhsExpr = Result.Nodes.getNodeAs<Expr>("rhsExpr");
checkSuspiciousBitmaskUsage(RhsExpr, EnumDec);
}
} // namespace clang::tidy::bugprone
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