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//===--- SuspiciousMemoryComparisonCheck.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 "SuspiciousMemoryComparisonCheck.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include <optional>
using namespace clang::ast_matchers;
namespace clang::tidy::bugprone {
static std::optional<uint64_t> tryEvaluateSizeExpr(const Expr *SizeExpr,
const ASTContext &Ctx) {
Expr::EvalResult Result;
if (SizeExpr->EvaluateAsRValue(Result, Ctx))
return Ctx.toBits(
CharUnits::fromQuantity(Result.Val.getInt().getExtValue()));
return std::nullopt;
}
void SuspiciousMemoryComparisonCheck::registerMatchers(MatchFinder *Finder) {
Finder->addMatcher(
callExpr(callee(namedDecl(
anyOf(hasName("::memcmp"), hasName("::std::memcmp")))),
unless(isInstantiationDependent()))
.bind("call"),
this);
}
void SuspiciousMemoryComparisonCheck::check(
const MatchFinder::MatchResult &Result) {
const ASTContext &Ctx = *Result.Context;
const auto *CE = Result.Nodes.getNodeAs<CallExpr>("call");
const Expr *SizeExpr = CE->getArg(2);
assert(SizeExpr != nullptr && "Third argument of memcmp is mandatory.");
std::optional<uint64_t> ComparedBits = tryEvaluateSizeExpr(SizeExpr, Ctx);
for (unsigned int ArgIndex = 0; ArgIndex < 2; ++ArgIndex) {
const Expr *ArgExpr = CE->getArg(ArgIndex);
QualType ArgType = ArgExpr->IgnoreImplicit()->getType();
const Type *PointeeType = ArgType->getPointeeOrArrayElementType();
assert(PointeeType != nullptr && "PointeeType should always be available.");
QualType PointeeQualifiedType(PointeeType, 0);
if (PointeeType->isRecordType()) {
if (const RecordDecl *RD =
PointeeType->getAsRecordDecl()->getDefinition()) {
if (const auto *CXXDecl = dyn_cast<CXXRecordDecl>(RD)) {
if (!CXXDecl->isStandardLayout()) {
diag(CE->getBeginLoc(),
"comparing object representation of non-standard-layout type "
"%0; consider using a comparison operator instead")
<< PointeeQualifiedType;
break;
}
}
}
}
if (!PointeeType->isIncompleteType()) {
uint64_t PointeeSize = Ctx.getTypeSize(PointeeType);
if (ComparedBits && *ComparedBits >= PointeeSize &&
!Ctx.hasUniqueObjectRepresentations(PointeeQualifiedType)) {
diag(CE->getBeginLoc(),
"comparing object representation of type %0 which does not have a "
"unique object representation; consider comparing %select{the "
"values|the members of the object}1 manually")
<< PointeeQualifiedType << (PointeeType->isRecordType() ? 1 : 0);
break;
}
}
}
}
} // namespace clang::tidy::bugprone
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