[clang-tools-extra] [clang-tidy] Add check performance-lost-std-move (PR #139525)

[Congcong Cai via cfe-commits]

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@@ -0,0 +1,195 @@
+//===--- LostStdMoveCheck.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 "LostStdMoveCheck.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Lex/Lexer.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::performance {
+
+template <typename Node>
+void extractNodesByIdTo(ArrayRef<BoundNodes> Matches, StringRef ID,
+                        llvm::SmallPtrSet<const Node *, 16> &Nodes) {
+  for (const BoundNodes &Match : Matches)
+    Nodes.insert(Match.getNodeAs<Node>(ID));
+}
+
+static llvm::SmallPtrSet<const DeclRefExpr *, 16>
+allDeclRefExprsHonourLambda(const VarDecl &VarDecl, const Decl &Decl,
+                            ASTContext &Context) {
+  auto Matches = match(
+      decl(forEachDescendant(
+          declRefExpr(to(varDecl(equalsNode(&VarDecl))),
+                      unless(hasAncestor(lambdaExpr(hasAnyCapture(lambdaCapture(
+                          capturesVar(varDecl(equalsNode(&VarDecl)))))))))
+              .bind("declRef"))),
+      Decl, Context);
+  llvm::SmallPtrSet<const DeclRefExpr *, 16> DeclRefs;
+  extractNodesByIdTo(Matches, "declRef", DeclRefs);
+  return DeclRefs;
+}
+
+static llvm::SmallPtrSet<const VarDecl *, 16>
+allVarDeclsExprs(const VarDecl &VarDecl, const Decl &Decl,
+                 ASTContext &Context) {
+  auto Matches = match(
+      decl(forEachDescendant(declRefExpr(
+          to(varDecl(equalsNode(&VarDecl))),
+          hasParent(decl(
+              varDecl(hasType(qualType(referenceType()))).bind("varDecl"))),
+          unless(hasAncestor(lambdaExpr(hasAnyCapture(
+              lambdaCapture(capturesVar(varDecl(equalsNode(&VarDecl))))))))))),
+      Decl, Context);
+  llvm::SmallPtrSet<const class VarDecl *, 16> VarDecls;
+  extractNodesByIdTo(Matches, "varDecl", VarDecls);
+  return VarDecls;
+}
+
+static const Expr *
+getLastVarUsage(const llvm::SmallPtrSet<const DeclRefExpr *, 16> &Exprs) {
+  const Expr *LastExpr = nullptr;
+  for (const clang::DeclRefExpr *Expr : Exprs) {
+    if (!LastExpr)
+      LastExpr = Expr;
+
+    if (LastExpr->getBeginLoc() < Expr->getBeginLoc())
+      LastExpr = Expr;
+  }
+
+  return LastExpr;
+}
+
+AST_MATCHER(CXXRecordDecl, hasTrivialMoveConstructor) {
+  return Node.hasDefinition() && Node.hasTrivialMoveConstructor();
+}
+
+void LostStdMoveCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
+  Options.store(Opts, "StrictMode", StrictMode);
+}
+
+LostStdMoveCheck::LostStdMoveCheck(StringRef Name, ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      StrictMode(Options.get("StrictMode", true)) {}
+
+void LostStdMoveCheck::registerMatchers(MatchFinder *Finder) {
+  auto ReturnParent =
+      hasParent(expr(hasParent(cxxConstructExpr(hasParent(returnStmt())))));
+
+  auto OutermostExpr = expr(unless(hasParent(expr())));
+  auto LeafStatement = stmt(OutermostExpr);
+
+  Finder->addMatcher(
+      declRefExpr(
+          // not "return x;"
+          unless(ReturnParent),
+          unless(hasType(namedDecl(hasName("::std::string_view")))),
+          // non-trivial type
+          hasType(hasCanonicalType(hasDeclaration(cxxRecordDecl()))),
+          // non-trivial X(X&&)
+          unless(hasType(hasCanonicalType(
+              hasDeclaration(cxxRecordDecl(hasTrivialMoveConstructor()))))),
+          // Not in a cycle
+          unless(hasAncestor(forStmt())), unless(hasAncestor(doStmt())),
+          unless(hasAncestor(whileStmt())),
+          // Not in a body of lambda
+          unless(hasAncestor(compoundStmt(hasAncestor(lambdaExpr())))),
+          // only non-X&
+          unless(hasDeclaration(
+              varDecl(hasType(qualType(lValueReferenceType()))))),
+          hasAncestor(LeafStatement.bind("leaf_statement")),
+          hasDeclaration(
+              varDecl(hasAncestor(functionDecl().bind("func"))).bind("decl")),
+          anyOf(
+              // f(x)
+              hasParent(expr(hasParent(cxxConstructExpr())).bind("use_parent")),
+              // f((x))
+              hasParent(parenExpr(hasParent(
+                  expr(hasParent(cxxConstructExpr())).bind("use_parent"))))))
+          .bind("use"),
----------------
HerrCai0907 wrote:

I am worry about the performance of this matcher because it will check all `DeclRefExpr`. Could we check the child of `CXXConstructExpr` instead.

Then for `parenExpr`, we can simply use ignoreParen

https://github.com/llvm/llvm-project/pull/139525