[clang-tidy] ForRangeCopyCheck that warns on and fixes unnecessary co…

…pies of loop variables.

Patch by Felix Berger!

Differential revision: http://reviews.llvm.org/D13849

llvm-svn: 259199

clang-tools-extra/clang-tidy/add_new_check.py

@@ -214,8 +214,8 @@ def write_test(module_path, module, check_name):
 """ % {"check_name_dashes" : check_name_dashes})
 
 # Recreates the list of checks in the docs/clang-tidy/checks directory.
-def update_checks_list(module_path):
-  docs_dir = os.path.join(module_path, '../../docs/clang-tidy/checks')
+def update_checks_list(clang_tidy_path):
+  docs_dir = os.path.join(clang_tidy_path, '../docs/clang-tidy/checks')
   filename = os.path.normpath(os.path.join(docs_dir, 'list.rst'))
   with open(filename, 'r') as f:
     lines = f.readlines()
@@ -262,9 +262,17 @@ def write_docs(module_path, module, check_name):
        "underline" : "=" * len(check_name_dashes)})
 
 def main():
+  if len(sys.argv) == 2 and sys.argv[1] == '--update-docs':
+    update_checks_list(os.path.dirname(sys.argv[0]))
+    return
+
   if len(sys.argv) != 3:
-    print 'Usage: add_new_check.py <module> <check>, e.g.\n'
-    print 'add_new_check.py misc awesome-functions\n'
+    print """\
+Usage: add_new_check.py <module> <check>, e.g.
+  add_new_check.py misc awesome-functions
+
+Alternatively, run 'add_new_check.py --update-docs' to just update the list of
+documentation files."""
     return
 
   module = sys.argv[1]
@@ -281,7 +289,7 @@ def main():
   adapt_module(module_path, module, check_name, check_name_camel)
   write_test(module_path, module, check_name)
   write_docs(module_path, module, check_name)
-  update_checks_list(module_path)
+  update_checks_list(clang_tidy_path)
   print('Done. Now it\'s your turn!')
 
 if __name__ == '__main__':

clang-tools-extra/clang-tidy/performance/CMakeLists.txt

@@ -1,6 +1,7 @@
 set(LLVM_LINK_COMPONENTS support)
 
 add_clang_library(clangTidyPerformanceModule
+  ForRangeCopyCheck.cpp
   ImplicitCastInLoopCheck.cpp
   PerformanceTidyModule.cpp
   UnnecessaryCopyInitialization.cpp

clang-tools-extra/clang-tidy/performance/ForRangeCopyCheck.cpp

@@ -0,0 +1,177 @@
+//===--- ForRangeCopyCheck.cpp - clang-tidy--------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "ForRangeCopyCheck.h"
+#include "../utils/LexerUtils.h"
+#include "../utils/TypeTraits.h"
+#include "clang/Lex/Lexer.h"
+#include "llvm/ADT/SmallPtrSet.h"
+
+namespace clang {
+namespace tidy {
+namespace performance {
+
+using namespace ::clang::ast_matchers;
+using llvm::SmallPtrSet;
+
+namespace {
+
+template <typename S> bool isSetDifferenceEmpty(const S &S1, const S &S2) {
+  for (const auto &E : S1)
+    if (S2.count(E) == 0)
+      return false;
+  return true;
+}
+
+// Extracts all Nodes keyed by ID from Matches and inserts them into Nodes.
+template <typename Node>
+void extractNodesByIdTo(ArrayRef<BoundNodes> Matches, StringRef ID,
+                        SmallPtrSet<const Node *, 16> &Nodes) {
+  for (const auto &Match : Matches)
+    Nodes.insert(Match.getNodeAs<Node>(ID));
+}
+
+// Finds all DeclRefExprs to VarDecl in Stmt.
+SmallPtrSet<const DeclRefExpr *, 16>
+declRefExprs(const VarDecl &VarDecl, const Stmt &Stmt, ASTContext &Context) {
+  auto Matches = match(
+      findAll(declRefExpr(to(varDecl(equalsNode(&VarDecl)))).bind("declRef")),
+      Stmt, Context);
+  SmallPtrSet<const DeclRefExpr *, 16> DeclRefs;
+  extractNodesByIdTo(Matches, "declRef", DeclRefs);
+  return DeclRefs;
+}
+
+// Finds all DeclRefExprs where a const method is called on VarDecl or VarDecl
+// is the a const reference or value argument to a CallExpr or CXXConstructExpr.
+SmallPtrSet<const DeclRefExpr *, 16>
+constReferenceDeclRefExprs(const VarDecl &VarDecl, const Stmt &Stmt,
+                           ASTContext &Context) {
+  auto DeclRefToVar =
+      declRefExpr(to(varDecl(equalsNode(&VarDecl)))).bind("declRef");
+  auto ConstMethodCallee = callee(cxxMethodDecl(isConst()));
+  // Match method call expressions where the variable is referenced as the this
+  // implicit object argument and opertor call expression for member operators
+  // where the variable is the 0-th argument.
+  auto Matches = match(
+      findAll(expr(anyOf(cxxMemberCallExpr(ConstMethodCallee, on(DeclRefToVar)),
+                         cxxOperatorCallExpr(ConstMethodCallee,
+                                             hasArgument(0, DeclRefToVar))))),
+      Stmt, Context);
+  SmallPtrSet<const DeclRefExpr *, 16> DeclRefs;
+  extractNodesByIdTo(Matches, "declRef", DeclRefs);
+  auto ConstReferenceOrValue =
+      qualType(anyOf(referenceType(pointee(qualType(isConstQualified()))),
+                     unless(anyOf(referenceType(), pointerType()))));
+  auto UsedAsConstRefOrValueArg = forEachArgumentWithParam(
+      DeclRefToVar, parmVarDecl(hasType(ConstReferenceOrValue)));
+  Matches = match(findAll(callExpr(UsedAsConstRefOrValueArg)), Stmt, Context);
+  extractNodesByIdTo(Matches, "declRef", DeclRefs);
+  Matches =
+      match(findAll(cxxConstructExpr(UsedAsConstRefOrValueArg)), Stmt, Context);
+  extractNodesByIdTo(Matches, "declRef", DeclRefs);
+  return DeclRefs;
+}
+
+// Modifies VarDecl to be a reference.
+FixItHint createAmpersandFix(const VarDecl &VarDecl, ASTContext &Context) {
+  SourceLocation AmpLocation = VarDecl.getLocation();
+  auto Token = lexer_utils::getPreviousNonCommentToken(Context, AmpLocation);
+  if (!Token.is(tok::unknown))
+    AmpLocation = Token.getLocation().getLocWithOffset(Token.getLength());
+  return FixItHint::CreateInsertion(AmpLocation, "&");
+}
+
+// Modifies VarDecl to be const.
+FixItHint createConstFix(const VarDecl &VarDecl) {
+  return FixItHint::CreateInsertion(VarDecl.getTypeSpecStartLoc(), "const ");
+}
+
+} // namespace
+
+ForRangeCopyCheck::ForRangeCopyCheck(StringRef Name, ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      WarnOnAllAutoCopies(Options.get("WarnOnAllAutoCopies", 0)) {}
+
+void ForRangeCopyCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
+  Options.store(Opts, "WarnOnAllAutoCopies", WarnOnAllAutoCopies);
+}
+
+void ForRangeCopyCheck::registerMatchers(MatchFinder *Finder) {
+  // Match loop variables that are not references or pointers or are already
+  // initialized through MaterializeTemporaryExpr which indicates a type
+  // conversion.
+  auto LoopVar = varDecl(
+      hasType(hasCanonicalType(unless(anyOf(referenceType(), pointerType())))),
+      unless(hasInitializer(expr(hasDescendant(materializeTemporaryExpr())))));
+  Finder->addMatcher(cxxForRangeStmt(hasLoopVariable(LoopVar.bind("loopVar")))
+                         .bind("forRange"),
+                     this);
+}
+
+void ForRangeCopyCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *Var = Result.Nodes.getNodeAs<VarDecl>("loopVar");
+  // Ignore code in macros since we can't place the fixes correctly.
+  if (Var->getLocStart().isMacroID())
+    return;
+  if (handleConstValueCopy(*Var, *Result.Context))
+    return;
+  const auto *ForRange = Result.Nodes.getNodeAs<CXXForRangeStmt>("forRange");
+  handleCopyIsOnlyConstReferenced(*Var, *ForRange, *Result.Context);
+}
+
+bool ForRangeCopyCheck::handleConstValueCopy(const VarDecl &LoopVar,
+                                             ASTContext &Context) {
+  if (WarnOnAllAutoCopies) {
+    // For aggressive check just test that loop variable has auto type.
+    if (!isa<AutoType>(LoopVar.getType()))
+      return false;
+  } else if (!LoopVar.getType().isConstQualified()) {
+    return false;
+  }
+  if (!type_traits::isExpensiveToCopy(LoopVar.getType(), Context))
+    return false;
+  auto Diagnostic =
+      diag(LoopVar.getLocation(),
+           "the loop variable's type is not a reference type; this creates a "
+           "copy in each iteration; consider making this a reference")
+      << createAmpersandFix(LoopVar, Context);
+  if (!LoopVar.getType().isConstQualified())
+    Diagnostic << createConstFix(LoopVar);
+  return true;
+}
+
+bool ForRangeCopyCheck::handleCopyIsOnlyConstReferenced(
+    const VarDecl &LoopVar, const CXXForRangeStmt &ForRange,
+    ASTContext &Context) {
+  if (LoopVar.getType().isConstQualified() ||
+      !type_traits::isExpensiveToCopy(LoopVar.getType(), Context)) {
+    return false;
+  }
+  // Collect all DeclRefExprs to the loop variable and all CallExprs and
+  // CXXConstructExprs where the loop variable is used as argument to a const
+  // reference parameter.
+  // If the difference is empty it is safe for the loop variable to be a const
+  // reference.
+  auto AllDeclRefs = declRefExprs(LoopVar, *ForRange.getBody(), Context);
+  auto ConstReferenceDeclRefs =
+      constReferenceDeclRefExprs(LoopVar, *ForRange.getBody(), Context);
+  if (AllDeclRefs.empty() ||
+      !isSetDifferenceEmpty(AllDeclRefs, ConstReferenceDeclRefs))
+    return false;
+  diag(LoopVar.getLocation(),
+       "loop variable is copied but only used as const reference; consider "
+       "making it a const reference")
+      << createConstFix(LoopVar) << createAmpersandFix(LoopVar, Context);
+  return true;
+}
+
+} // namespace performance
+} // namespace tidy
+} // namespace clang

clang-tools-extra/clang-tidy/performance/ForRangeCopyCheck.h

@@ -0,0 +1,49 @@
+//===--- ForRangeCopyCheck.h - clang-tidy------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_PERFORMANCE_FORRANGECOPYCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_PERFORMANCE_FORRANGECOPYCHECK_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+namespace performance {
+
+/// A check that detects copied loop variables and suggests using const
+/// references.
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/performance-for-range-copy.html
+class ForRangeCopyCheck : public ClangTidyCheck {
+public:
+  ForRangeCopyCheck(StringRef Name, ClangTidyContext *Context);
+  void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+
+private:
+  // Checks if the loop variable is a const value and expensive to copy. If so
+  // suggests it be converted to a const reference.
+  bool handleConstValueCopy(const VarDecl &LoopVar, ASTContext &Context);
+
+  // Checks if the loop variable is a non-const value and whether only
+  // const methods are invoked on it or whether it is only used as a const
+  // reference argument. If so it suggests it be made a const reference.
+  bool handleCopyIsOnlyConstReferenced(const VarDecl &LoopVar,
+                                       const CXXForRangeStmt &ForRange,
+                                       ASTContext &Context);
+
+  const bool WarnOnAllAutoCopies;
+};
+
+} // namespace performance
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_PERFORMANCE_FORRANGECOPYCHECK_H

clang-tools-extra/clang-tidy/performance/PerformanceTidyModule.cpp

@@ -11,6 +11,7 @@
 #include "../ClangTidyModule.h"
 #include "../ClangTidyModuleRegistry.h"
 
+#include "ForRangeCopyCheck.h"
 #include "ImplicitCastInLoopCheck.h"
 #include "UnnecessaryCopyInitialization.h"
 
@@ -21,6 +22,8 @@ namespace performance {
 class PerformanceModule : public ClangTidyModule {
 public:
   void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
+    CheckFactories.registerCheck<ForRangeCopyCheck>(
+        "performance-for-range-copy");
     CheckFactories.registerCheck<ImplicitCastInLoopCheck>(
         "performance-implicit-cast-in-loop");
     CheckFactories.registerCheck<UnnecessaryCopyInitialization>(

clang-tools-extra/docs/clang-tidy/checks/list.rst

@@ -76,6 +76,7 @@ Clang-Tidy Checks
    modernize-use-default
    modernize-use-nullptr
    modernize-use-override
+   performance-for-range-copy
    performance-implicit-cast-in-loop
    readability-braces-around-statements
    readability-container-size-empty

clang-tools-extra/docs/clang-tidy/checks/performance-for-range-copy.rst

@@ -0,0 +1,19 @@
+.. title:: clang-tidy - performance-for-range-copy
+
+performance-for-range-copy
+==========================
+
+Finds C++11 for ranges where the loop variable is copied in each iteration but
+it would suffice to obtain it by const reference.
+
+The check is only applied to loop variables of types that are expensive to copy
+which means they are not trivially copyable or have a non-trivial copy
+constructor or destructor.
+
+To ensure that it is safe to replace the copy with const reference the following
+heuristic is employed:
+
+1. The loop variable is const qualified.
+2. The loop variable is not const, but only const methods or operators are
+   invoked on it, or it is used as const reference or value argument in
+   constructors or function calls.

clang-tools-extra/test/clang-tidy/performance-for-range-copy-warn-on-all-auto-copies.cpp

@@ -0,0 +1,39 @@
+// RUN: %check_clang_tidy %s performance-for-range-copy %t -config="{CheckOptions: [{key: "performance-for-range-copy.WarnOnAllAutoCopies", value: 1}]}" -- -std=c++11
+
+template <typename T>
+struct Iterator {
+  void operator++() {}
+  const T& operator*() {
+    static T* TT = new T();
+    return *TT;
+  }
+  bool operator!=(const Iterator &) { return false; }
+};
+template <typename T>
+struct View {
+  T begin() { return T(); }
+  T begin() const { return T(); }
+  T end() { return T(); }
+  T end() const { return T(); }
+};
+
+struct S {
+  S();
+  S(const S &);
+  ~S();
+  S &operator=(const S &);
+};
+
+void NegativeLoopVariableNotAuto() {
+  for (S S1 : View<Iterator<S>>()) {
+    S* S2 = &S1;
+  }
+}
+
+void PositiveTriggeredForAutoLoopVariable() {
+  for (auto S1 : View<Iterator<S>>()) {
+    // CHECK-MESSAGES: [[@LINE-1]]:13: warning: the loop variable's type is not a reference type; this creates a copy in each iteration; consider making this a reference [performance-for-range-copy]
+    // CHECK-FIXES: for (const auto& S1 : View<Iterator<S>>()) {
+    S* S2 = &S1;
+  }
+}