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

   1 //===--- InefficientVectorOperationCheck.cpp - clang-tidy------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "InefficientVectorOperationCheck.h"
  10 #include "../utils/DeclRefExprUtils.h"
  11 #include "../utils/OptionsUtils.h"
  12 #include "clang/AST/ASTContext.h"
  13 #include "clang/ASTMatchers/ASTMatchFinder.h"
  14 #include "clang/Lex/Lexer.h"
  15
  16 using namespace clang::ast_matchers;
  17
  18 namespace clang::tidy::performance {
  19
  20 namespace {
  21
  22 // Matcher names. Given the code:
  23 //
  24 // \code
  25 // void f() {
  26 //   vector<T> v;
  27 //   for (int i = 0; i < 10 + 1; ++i) {
  28 //     v.push_back(i);
  29 //   }
  30 //
  31 //   SomeProto p;
  32 //   for (int i = 0; i < 10 + 1; ++i) {
  33 //     p.add_xxx(i);
  34 //   }
  35 // }
  36 // \endcode
  37 //
  38 // The matcher names are bound to following parts of the AST:
  39 //   - LoopCounterName: The entire for loop (as ForStmt).
  40 //   - LoopParentName: The body of function f (as CompoundStmt).
  41 //   - VectorVarDeclName: 'v' (as VarDecl).
  42 //   - VectorVarDeclStmatName: The entire 'std::vector<T> v;' statement (as
  43 //     DeclStmt).
  44 //   - PushBackOrEmplaceBackCallName: 'v.push_back(i)' (as cxxMemberCallExpr).
  45 //   - LoopInitVarName: 'i' (as VarDecl).
  46 //   - LoopEndExpr: '10+1' (as Expr).
  47 // If EnableProto, the proto related names are bound to the following parts:
  48 //   - ProtoVarDeclName: 'p' (as VarDecl).
  49 //   - ProtoVarDeclStmtName: The entire 'SomeProto p;' statement (as DeclStmt).
  50 //   - ProtoAddFieldCallName: 'p.add_xxx(i)' (as cxxMemberCallExpr).
  51 static const char LoopCounterName[] = "for_loop_counter";
  52 static const char LoopParentName[] = "loop_parent";
  53 static const char VectorVarDeclName[] = "vector_var_decl";
  54 static const char VectorVarDeclStmtName[] = "vector_var_decl_stmt";
  55 static const char PushBackOrEmplaceBackCallName[] = "append_call";
  56 static const char ProtoVarDeclName[] = "proto_var_decl";
  57 static const char ProtoVarDeclStmtName[] = "proto_var_decl_stmt";
  58 static const char ProtoAddFieldCallName[] = "proto_add_field";
  59 static const char LoopInitVarName[] = "loop_init_var";
  60 static const char LoopEndExprName[] = "loop_end_expr";
  61 static const char RangeLoopName[] = "for_range_loop";
  62
  63 ast_matchers::internal::Matcher<Expr> supportedContainerTypesMatcher() {
  64   return hasType(cxxRecordDecl(hasAnyName(
  65       "::std::vector", "::std::set", "::std::unordered_set", "::std::map",
  66       "::std::unordered_map", "::std::array", "::std::deque")));
  67 }
  68
  69 AST_MATCHER(Expr, hasSideEffects) {
  70   return Node.HasSideEffects(Finder->getASTContext());
  71 }
  72
  73 } // namespace
  74
  75 InefficientVectorOperationCheck::InefficientVectorOperationCheck(
  76     StringRef Name, ClangTidyContext *Context)
  77     : ClangTidyCheck(Name, Context),
  78       VectorLikeClasses(utils::options::parseStringList(
  79           Options.get("VectorLikeClasses", "::std::vector"))),
  80       EnableProto(Options.getLocalOrGlobal("EnableProto", false)) {}
  81
  82 void InefficientVectorOperationCheck::storeOptions(
  83     ClangTidyOptions::OptionMap &Opts) {
  84   Options.store(Opts, "VectorLikeClasses",
  85                 utils::options::serializeStringList(VectorLikeClasses));
  86   Options.store(Opts, "EnableProto", EnableProto);
  87 }
  88
  89 void InefficientVectorOperationCheck::addMatcher(
  90     const DeclarationMatcher &TargetRecordDecl, StringRef VarDeclName,
  91     StringRef VarDeclStmtName, const DeclarationMatcher &AppendMethodDecl,
  92     StringRef AppendCallName, MatchFinder *Finder) {
  93   const auto DefaultConstructorCall = cxxConstructExpr(
  94       hasType(TargetRecordDecl),
  95       hasDeclaration(cxxConstructorDecl(isDefaultConstructor())));
  96   const auto TargetVarDecl =
  97       varDecl(hasInitializer(DefaultConstructorCall)).bind(VarDeclName);
  98   const auto TargetVarDefStmt =
  99       declStmt(hasSingleDecl(equalsBoundNode(std::string(VarDeclName))))
 100           .bind(VarDeclStmtName);
 101
 102   const auto AppendCallExpr =
 103       cxxMemberCallExpr(
 104           callee(AppendMethodDecl), on(hasType(TargetRecordDecl)),
 105           onImplicitObjectArgument(declRefExpr(to(TargetVarDecl))))
 106           .bind(AppendCallName);
 107   const auto AppendCall = expr(ignoringImplicit(AppendCallExpr));
 108   const auto LoopVarInit = declStmt(hasSingleDecl(
 109       varDecl(hasInitializer(ignoringParenImpCasts(integerLiteral(equals(0)))))
 110           .bind(LoopInitVarName)));
 111   const auto RefersToLoopVar = ignoringParenImpCasts(
 112       declRefExpr(to(varDecl(equalsBoundNode(LoopInitVarName)))));
 113
 114   // Matchers for the loop whose body has only 1 push_back/emplace_back calling
 115   // statement.
 116   const auto HasInterestingLoopBody = hasBody(
 117       anyOf(compoundStmt(statementCountIs(1), has(AppendCall)), AppendCall));
 118   const auto InInterestingCompoundStmt =
 119       hasParent(compoundStmt(has(TargetVarDefStmt)).bind(LoopParentName));
 120
 121   // Match counter-based for loops:
 122   //  for (int i = 0; i < n; ++i) {
 123   //    v.push_back(...);
 124   //    // Or: proto.add_xxx(...);
 125   //  }
 126   //
 127   // FIXME: Support more types of counter-based loops like decrement loops.
 128   Finder->addMatcher(
 129       forStmt(
 130           hasLoopInit(LoopVarInit),
 131           hasCondition(binaryOperator(
 132               hasOperatorName("<"), hasLHS(RefersToLoopVar),
 133               hasRHS(expr(unless(hasDescendant(expr(RefersToLoopVar))))
 134                          .bind(LoopEndExprName)))),
 135           hasIncrement(unaryOperator(hasOperatorName("++"),
 136                                      hasUnaryOperand(RefersToLoopVar))),
 137           HasInterestingLoopBody, InInterestingCompoundStmt)
 138           .bind(LoopCounterName),
 139       this);
 140
 141   // Match for-range loops:
 142   //   for (const auto& E : data) {
 143   //     v.push_back(...);
 144   //     // Or: proto.add_xxx(...);
 145   //   }
 146   //
 147   // FIXME: Support more complex range-expressions.
 148   Finder->addMatcher(
 149       cxxForRangeStmt(
 150           hasRangeInit(
 151               anyOf(declRefExpr(supportedContainerTypesMatcher()),
 152                     memberExpr(hasObjectExpression(unless(hasSideEffects())),
 153                                supportedContainerTypesMatcher()))),
 154           HasInterestingLoopBody, InInterestingCompoundStmt)
 155           .bind(RangeLoopName),
 156       this);
 157 }
 158
 159 void InefficientVectorOperationCheck::registerMatchers(MatchFinder *Finder) {
 160   const auto VectorDecl = cxxRecordDecl(hasAnyName(VectorLikeClasses));
 161   const auto AppendMethodDecl =
 162       cxxMethodDecl(hasAnyName("push_back", "emplace_back"));
 163   addMatcher(VectorDecl, VectorVarDeclName, VectorVarDeclStmtName,
 164              AppendMethodDecl, PushBackOrEmplaceBackCallName, Finder);
 165
 166   if (EnableProto) {
 167     const auto ProtoDecl =
 168         cxxRecordDecl(isDerivedFrom("::proto2::MessageLite"));
 169
 170     // A method's name starts with "add_" might not mean it's an add field
 171     // call; it could be the getter for a proto field of which the name starts
 172     // with "add_". So we exclude const methods.
 173     const auto AddFieldMethodDecl =
 174         cxxMethodDecl(matchesName("::add_"), unless(isConst()));
 175     addMatcher(ProtoDecl, ProtoVarDeclName, ProtoVarDeclStmtName,
 176                AddFieldMethodDecl, ProtoAddFieldCallName, Finder);
 177   }
 178 }
 179
 180 void InefficientVectorOperationCheck::check(
 181     const MatchFinder::MatchResult &Result) {
 182   auto* Context = Result.Context;
 183   if (Context->getDiagnostics().hasUncompilableErrorOccurred())
 184     return;
 185
 186   const SourceManager &SM = *Result.SourceManager;
 187   const auto *VectorVarDecl =
 188       Result.Nodes.getNodeAs<VarDecl>(VectorVarDeclName);
 189   const auto *ForLoop = Result.Nodes.getNodeAs<ForStmt>(LoopCounterName);
 190   const auto *RangeLoop =
 191       Result.Nodes.getNodeAs<CXXForRangeStmt>(RangeLoopName);
 192   const auto *VectorAppendCall =
 193       Result.Nodes.getNodeAs<CXXMemberCallExpr>(PushBackOrEmplaceBackCallName);
 194   const auto *ProtoVarDecl = Result.Nodes.getNodeAs<VarDecl>(ProtoVarDeclName);
 195   const auto *ProtoAddFieldCall =
 196       Result.Nodes.getNodeAs<CXXMemberCallExpr>(ProtoAddFieldCallName);
 197   const auto *LoopEndExpr = Result.Nodes.getNodeAs<Expr>(LoopEndExprName);
 198   const auto *LoopParent = Result.Nodes.getNodeAs<CompoundStmt>(LoopParentName);
 199
 200   const CXXMemberCallExpr *AppendCall =
 201       VectorAppendCall ? VectorAppendCall : ProtoAddFieldCall;
 202   assert(AppendCall && "no append call expression");
 203
 204   const Stmt *LoopStmt = ForLoop;
 205   if (!LoopStmt)
 206     LoopStmt = RangeLoop;
 207
 208   const auto *TargetVarDecl = VectorVarDecl;
 209   if (!TargetVarDecl)
 210     TargetVarDecl = ProtoVarDecl;
 211
 212   llvm::SmallPtrSet<const DeclRefExpr *, 16> AllVarRefs =
 213       utils::decl_ref_expr::allDeclRefExprs(*TargetVarDecl, *LoopParent,
 214                                             *Context);
 215   for (const auto *Ref : AllVarRefs) {
 216     // Skip cases where there are usages (defined as DeclRefExpr that refers
 217     // to "v") of vector variable / proto variable `v` before the for loop. We
 218     // consider these usages are operations causing memory preallocation (e.g.
 219     // "v.resize(n)", "v.reserve(n)").
 220     //
 221     // FIXME: make it more intelligent to identify the pre-allocating
 222     // operations before the for loop.
 223     if (SM.isBeforeInTranslationUnit(Ref->getLocation(),
 224                                      LoopStmt->getBeginLoc())) {
 225       return;
 226     }
 227   }
 228
 229   std::string PartialReserveStmt;
 230   if (VectorAppendCall != nullptr) {
 231     PartialReserveStmt = ".reserve";
 232   } else {
 233     llvm::StringRef FieldName = ProtoAddFieldCall->getMethodDecl()->getName();
 234     FieldName.consume_front("add_");
 235     std::string MutableFieldName = ("mutable_" + FieldName).str();
 236     PartialReserveStmt = "." + MutableFieldName +
 237                          "()->Reserve"; // e.g., ".mutable_xxx()->Reserve"
 238   }
 239
 240   llvm::StringRef VarName = Lexer::getSourceText(
 241       CharSourceRange::getTokenRange(
 242           AppendCall->getImplicitObjectArgument()->getSourceRange()),
 243       SM, Context->getLangOpts());
 244
 245   std::string ReserveSize;
 246   // Handle for-range loop cases.
 247   if (RangeLoop) {
 248     // Get the range-expression in a for-range statement represented as
 249     // `for (range-declarator: range-expression)`.
 250     StringRef RangeInitExpName =
 251         Lexer::getSourceText(CharSourceRange::getTokenRange(
 252                                  RangeLoop->getRangeInit()->getSourceRange()),
 253                              SM, Context->getLangOpts());
 254     ReserveSize = (RangeInitExpName + ".size()").str();
 255   } else if (ForLoop) {
 256     // Handle counter-based loop cases.
 257     StringRef LoopEndSource = Lexer::getSourceText(
 258         CharSourceRange::getTokenRange(LoopEndExpr->getSourceRange()), SM,
 259         Context->getLangOpts());
 260     ReserveSize = std::string(LoopEndSource);
 261   }
 262
 263   auto Diag = diag(AppendCall->getBeginLoc(),
 264                    "%0 is called inside a loop; consider pre-allocating the "
 265                    "container capacity before the loop")
 266               << AppendCall->getMethodDecl()->getDeclName();
 267   if (!ReserveSize.empty()) {
 268     std::string ReserveStmt =
 269         (VarName + PartialReserveStmt + "(" + ReserveSize + ");\n").str();
 270     Diag << FixItHint::CreateInsertion(LoopStmt->getBeginLoc(), ReserveStmt);
 271   }
 272 }
 273
 274 } // namespace clang::tidy::performance