DefaultOperatorNewOnOveralignedTypeCheck.cpp

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//===----------------------------------------------------------------------===//
//
// 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 "DefaultOperatorNewOnOveralignedTypeCheck.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include "clang/Basic/TargetInfo.h"
 
using namespace clang::ast_matchers;
 
namespace clang::tidy::bugprone {
 
void DefaultOperatorNewOnOveralignedTypeCheck::registerMatchers(
    MatchFinder *Finder) {
  Finder->addMatcher(
      cxxNewExpr(unless(hasAnyPlacementArg(anything()))).bind("new"), this);
}
 
void DefaultOperatorNewOnOveralignedTypeCheck::check(
    const MatchFinder::MatchResult &Result) {
  // Get the found 'new' expression.
  const auto *NewExpr = Result.Nodes.getNodeAs<CXXNewExpr>("new");
 
  const QualType T = NewExpr->getAllocatedType();
  // Dependent types do not have fixed alignment.
  if (T->isDependentType())
    return;
  const TagDecl *D = T->getAsTagDecl();
  // Alignment can not be obtained for undefined type.
  if (!D || !D->isCompleteDefinition())
    return;
 
  const ASTContext &Context = D->getASTContext();
 
  // Check if no alignment was specified for the type.
  if (!Context.isAlignmentRequired(T))
    return;
 
  // The user-specified alignment (in bits).
  const unsigned SpecifiedAlignment = D->getMaxAlignment();
  // Double-check if no alignment was specified.
  if (!SpecifiedAlignment)
    return;
  // The alignment used by default 'operator new' (in bits).
  const unsigned DefaultNewAlignment = Context.getTargetInfo().getNewAlign();
 
  const bool OverAligned = SpecifiedAlignment > DefaultNewAlignment;
  const bool HasDefaultOperatorNew =
      !NewExpr->getOperatorNew() || NewExpr->getOperatorNew()->isImplicit();
 
  const unsigned CharWidth = Context.getTargetInfo().getCharWidth();
  if (HasDefaultOperatorNew && OverAligned)
    diag(NewExpr->getBeginLoc(),
         "allocation function returns a pointer with alignment %0 but the "
         "over-aligned type being allocated requires alignment %1")
        << (DefaultNewAlignment / CharWidth)
        << (SpecifiedAlignment / CharWidth);
}
 
} // namespace clang::tidy::bugprone