[clang-tools-extra] [clang-tidy] Add performance-expensive-value-or check (PR #200166)

[Yanzuo Liu via cfe-commits]

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Message-ID:
In-Reply-To: <llvm.org/llvm/llvm-project/pull/200166 at github.com>


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@@ -0,0 +1,171 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 "ExpensiveValueOrCheck.h"
+#include "../utils/Matchers.h"
+#include "../utils/OptionsUtils.h"
+#include "../utils/TypeTraits.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Tooling/FixIt.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::performance {
+
+static bool hasOperatorStar(const CXXRecordDecl *RD) {
+  const DeclarationName OpStar =
+      RD->getASTContext().DeclarationNames.getCXXOperatorName(OO_Star);
+  return !RD->lookup(OpStar).empty();
+}
+
+static StringRef findValueMethod(const CXXRecordDecl *RD) {
+  ASTContext &Ctx = RD->getASTContext();
+  for (StringRef Name : {"value", "Value"}) {
+    const DeclarationName DN = &Ctx.Idents.get(Name);
+    if (!RD->lookup(DN).empty())
+      return Name;
+  }
+  return {};
+}
+
+static std::string buildSuggestion(const CXXRecordDecl *OptionalClass) {
+  const bool HasDeref = hasOperatorStar(OptionalClass);
+  StringRef ValueName = findValueMethod(OptionalClass);
+
+  if (HasDeref && !ValueName.empty())
+    return (llvm::Twine("consider using 'operator*' or '") + ValueName +
+            "()' with a separate fallback")
+        .str();
+  if (HasDeref)
+    return "consider using 'operator*' with a separate fallback";
+  if (!ValueName.empty())
+    return (llvm::Twine("consider using '") + ValueName +
+            "()' with a separate fallback")
+        .str();
+  return "consider avoiding the copy";
+}
+
+static std::optional<FixItHint> buildFixIt(const CXXMemberCallExpr *Call,
+                                           const Expr *ObjExpr,
+                                           const Expr *FallbackArg,
+                                           const CXXRecordDecl *OptionalClass,
+                                           const ASTContext &Ctx) {
+  if (Call->getBeginLoc().isMacroID())
+    return std::nullopt;
+  if (!ObjExpr->isLValue())
+    return std::nullopt;
+  if (!hasOperatorStar(OptionalClass))
+    return std::nullopt;
+
+  StringRef ObjText = tooling::fixit::getText(*ObjExpr, Ctx);
+  StringRef ArgText = tooling::fixit::getText(*FallbackArg, Ctx);
+
+  if (ObjText.empty() || ArgText.empty())
+    return std::nullopt;
+
+  const std::string Replacement =
+      ("(" + ObjText + " ? *" + ObjText + " : " + ArgText + ")").str();
+  return FixItHint::CreateReplacement(Call->getSourceRange(), Replacement);
+}
+
+ExpensiveValueOrCheck::ExpensiveValueOrCheck(StringRef Name,
+                                             ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      SizeThreshold(Options.get("SizeThreshold", 16U)),
+      OptionalTypes(utils::options::parseStringList(
+          Options.get("OptionalTypes",
+                      "::std::optional;::absl::optional;::boost::optional"))),
+      WarnOnOwnershipTaking(Options.get("WarnOnOwnershipTaking", false)) {}
+
+void ExpensiveValueOrCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
+  Options.store(Opts, "SizeThreshold", SizeThreshold);
+  Options.store(Opts, "OptionalTypes",
+                utils::options::serializeStringList(OptionalTypes));
+  Options.store(Opts, "WarnOnOwnershipTaking", WarnOnOwnershipTaking);
+}
+
+void ExpensiveValueOrCheck::registerMatchers(MatchFinder *Finder) {
+  auto OptionalTypesMatcher =
+      matchers::matchesAnyListedRegexName(OptionalTypes);
+  auto ValueOrMatcher = hasAnyName("value_or", "valueOr", "ValueOr");
+  auto ValueOrCall = cxxMemberCallExpr(
+      callee(cxxMethodDecl(ValueOrMatcher, ofClass(OptionalTypesMatcher))));
+
+  if (WarnOnOwnershipTaking) {
+    Finder->addMatcher(ValueOrCall.bind("call"), this);
+    return;
+  }
+
+  // Binding to const T& variable.
+  Finder->addMatcher(
+      varDecl(hasType(lValueReferenceType(pointee(isConstQualified()))),
+              hasInitializer(ignoringImplicit(ValueOrCall.bind("call")))),
+      this);
+
+  // Passing to a const T& parameter.
+  Finder->addMatcher(callExpr(forEachArgumentWithParam(
+                         ignoringImplicit(ValueOrCall.bind("call")),
+                         parmVarDecl(hasType(lValueReferenceType(
+                             pointee(isConstQualified())))))),
+                     this);
+
+  // Calling a const member function on the result.
+  Finder->addMatcher(
+      cxxMemberCallExpr(on(ignoringImplicit(ValueOrCall.bind("call"))),
+                        callee(cxxMethodDecl(isConst()))),
+      this);
+}
+
+void ExpensiveValueOrCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *Call = Result.Nodes.getNodeAs<CXXMemberCallExpr>("call");
+  assert(Call && "Matcher guaranteed a bound 'call' node");
+  const Expr *ObjExpr = Call->getImplicitObjectArgument();
+  assert(ObjExpr && "CXXMemberCallExpr must have an implicit object argument");
+
+  const ASTContext &Ctx = *Result.Context;
+  const QualType ValueType = Call->getType();
+
+  // Rvalue optional uses && overload which moves. Suppress if move is cheap.
+  if (!ObjExpr->isLValue() &&
+      utils::type_traits::hasNonTrivialMoveConstructor(ValueType))
+    return;
+
+  const bool IsExpensiveType =
+      utils::type_traits::isExpensiveToCopy(ValueType, Ctx).value_or(false);
+  const int64_t ValueSize = Ctx.getTypeSizeInChars(ValueType).getQuantity();
+  const bool IsExpensive =
+      IsExpensiveType || ValueSize > static_cast<int64_t>(SizeThreshold);
+
+  if (!IsExpensive)
+    return;
----------------
zwuis wrote:

Move them to AST matchers.

```
cxxMemberCallExpr(
    ...,
    anyOf(on(/* is lvalue */), hasType(/* no non trivial move ctor */)),
    hasType(/* expensive to copy */(SizeThreshold)))
```

https://github.com/llvm/llvm-project/pull/200166