[clang] [clang-tools-extra] [clang-tidy] New performance linter: performance-inefficient-copy-assign (PR #179467)

[Yanzuo Liu via cfe-commits]

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@@ -0,0 +1,99 @@
+//===--- InefficientCopyAssignCheck.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 "InefficientCopyAssignCheck.h"
+
+#include "clang/AST/Expr.h"
+#include "clang/AST/ExprCXX.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/Analysis/Analyses/CFGReachabilityAnalysis.h"
+#include "clang/Lex/Lexer.h"
+#include "llvm/ADT/STLExtras.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::performance {
+
+void InefficientCopyAssignCheck::registerMatchers(MatchFinder *Finder) {
+  auto AssignOperatorExpr =
+      cxxOperatorCallExpr(
+          hasOperatorName("="),
+          hasArgument(
+              0, hasType(cxxRecordDecl(hasMethod(isMoveAssignmentOperator()))
+                             .bind("assign-target-type"))),
+          hasArgument(1, declRefExpr(to(varDecl().bind("assign-value-decl")))
+                             .bind("assign-value")),
+          hasAncestor(functionDecl().bind("within-func")))
+          .bind("assign");
+  Finder->addMatcher(AssignOperatorExpr, this);
+}
+
+CFG *InefficientCopyAssignCheck::getCFG(const FunctionDecl *FD,
+                                        ASTContext *Context) {
+  std::unique_ptr<CFG> &TheCFG = CFGCache[FD];
+  if (!TheCFG) {
+    const CFG::BuildOptions Options;
+    std::unique_ptr<CFG> FCFG =
+        CFG::buildCFG(nullptr, FD->getBody(), Context, Options);
+    if (!FCFG)
+      return nullptr;
+    TheCFG.swap(FCFG);
+  }
+  return TheCFG.get();
+}
+
+void InefficientCopyAssignCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *AssignExpr = Result.Nodes.getNodeAs<Expr>("assign");
+  const auto *AssignValue = Result.Nodes.getNodeAs<DeclRefExpr>("assign-value");
+  const auto *AssignValueDecl =
+      Result.Nodes.getNodeAs<VarDecl>("assign-value-decl");
+  const auto *AssignTargetType =
+      Result.Nodes.getNodeAs<CXXRecordDecl>("assign-target-type");
+  const auto *WithinFunctionDecl =
+      Result.Nodes.getNodeAs<FunctionDecl>("within-func");
+
+  const QualType AssignValueQual = AssignValueDecl->getType();
+  if (AssignValueQual->isLValueReferenceType() ||
+      AssignValueQual.isConstQualified() || AssignValueQual->isPointerType() ||
+      AssignValueQual->isScalarType())
+    return;
+
+  if (!AssignValueDecl->hasLocalStorage())
+    return;
+
+  if (AssignTargetType->hasTrivialMoveAssignment())
+    return;
+
+  if (CFG *TheCFG = getCFG(WithinFunctionDecl, Result.Context)) {
+    // Walk the CFG bottom-up, starting with the exit node.
+    // TODO: traverse the whole CFG instead of only considering terminator
+    // nodes.
+
+    CFGBlock &TheExit = TheCFG->getExit();
+    for (auto &Pred : TheExit.preds()) {
+      for (const CFGElement &Elt : llvm::reverse(*Pred)) {
+        if (Elt.getKind() == CFGElement::Kind::Statement) {
+          const Stmt *EltStmt = Elt.castAs<CFGStmt>().getStmt();
+          if (EltStmt == AssignExpr) {
+            diag(AssignValue->getBeginLoc(), "'%0' could be moved here")
+                << AssignValue->getDecl()->getName();
+            break;
+          }
+          // The reference is being referenced before the assignment, bail out.
+          auto DeclRefMatcher =
+              declRefExpr(hasDeclaration(equalsNode(AssignValue->getDecl())));
+          if (!match(findAll(DeclRefMatcher), *EltStmt, *Result.Context)
----------------
zwuis wrote:

We have `allDeclRefExprs()`in "../utils/DeclRefExprUtils.h".

https://github.com/llvm/llvm-project/pull/179467