--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang-tools-extra/clang-tidy/bugprone/MisplacedWideningCastCheck.cpp	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,233 @@
+//===--- 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 {
+namespace tidy {
+namespace 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(
+                     anyOf(hasOperatorName("+"), hasOperatorName("-"),
+                           hasOperatorName("*"), hasOperatorName("<<"))),
+                 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 = 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(matchers::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 bugprone
+} // namespace tidy
+} // namespace clang