Add a new class to analyze whether an expression is mutated within a statement.

ExprMutationAnalyzer is a generally useful helper that can be used in different clang-tidy checks for checking whether a given expression is (potentially) mutated within a statement (typically the enclosing compound statement.) This is a more general and more powerful/accurate version of isOnlyUsedAsConst, which is used in ForRangeCopyCheck, UnnecessaryCopyInitialization.

Patch by Shuai Wang

llvm-svn: 334604

3 files changed, 318 insertions, 0 deletions

diff --git a/clang-tools-extra/clang-tidy/utils/CMakeLists.txt b/clang-tools-extra/clang-tidy/utils/CMakeLists.txt
index 9162bce1e29..487b09ac8f2 100644
--- a/clang-tools-extra/clang-tidy/utils/CMakeLists.txt
+++ b/clang-tools-extra/clang-tidy/utils/CMakeLists.txt
@@ -3,6 +3,7 @@ set(LLVM_LINK_COMPONENTS support)
 add_clang_library(clangTidyUtils
   ASTUtils.cpp
   DeclRefExprUtils.cpp
+  ExprMutationAnalyzer.cpp
   ExprSequence.cpp
   FixItHintUtils.cpp
   HeaderFileExtensionsUtils.cpp
diff --git a/clang-tools-extra/clang-tidy/utils/ExprMutationAnalyzer.cpp b/clang-tools-extra/clang-tidy/utils/ExprMutationAnalyzer.cpp
new file mode 100644
index 00000000000..ea994e44131
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/utils/ExprMutationAnalyzer.cpp
@@ -0,0 +1,261 @@
+//===---------- ExprMutationAnalyzer.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 "ExprMutationAnalyzer.h"
+
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "llvm/ADT/STLExtras.h"
+
+namespace clang {
+namespace tidy {
+namespace utils {
+using namespace ast_matchers;
+
+namespace {
+
+AST_MATCHER_P(LambdaExpr, hasCaptureInit, const Expr *, E) {
+  return llvm::is_contained(Node.capture_inits(), E);
+}
+
+AST_MATCHER_P(CXXForRangeStmt, hasRangeStmt,
+              ast_matchers::internal::Matcher<DeclStmt>, InnerMatcher) {
+  const DeclStmt *const Range = Node.getRangeStmt();
+  return InnerMatcher.matches(*Range, Finder, Builder);
+}
+
+const ast_matchers::internal::VariadicDynCastAllOfMatcher<Stmt, CXXTypeidExpr>
+    cxxTypeidExpr;
+
+AST_MATCHER(CXXTypeidExpr, isPotentiallyEvaluated) {
+  return Node.isPotentiallyEvaluated();
+}
+
+const ast_matchers::internal::VariadicDynCastAllOfMatcher<Stmt, CXXNoexceptExpr>
+    cxxNoexceptExpr;
+
+const ast_matchers::internal::VariadicDynCastAllOfMatcher<Stmt,
+                                                          GenericSelectionExpr>
+    genericSelectionExpr;
+
+AST_MATCHER_P(GenericSelectionExpr, hasControllingExpr,
+              ast_matchers::internal::Matcher<Expr>, InnerMatcher) {
+  return InnerMatcher.matches(*Node.getControllingExpr(), Finder, Builder);
+}
+
+const auto nonConstReferenceType = [] {
+  return referenceType(pointee(unless(isConstQualified())));
+};
+
+} // namespace
+
+const Stmt *ExprMutationAnalyzer::findMutation(const Expr *Exp) {
+  const auto Memoized = Results.find(Exp);
+  if (Memoized != Results.end())
+    return Memoized->second;
+
+  if (isUnevaluated(Exp))
+    return Results[Exp] = nullptr;
+
+  for (const auto &Finder : {&ExprMutationAnalyzer::findDirectMutation,
+                             &ExprMutationAnalyzer::findMemberMutation,
+                             &ExprMutationAnalyzer::findArrayElementMutation,
+                             &ExprMutationAnalyzer::findCastMutation,
+                             &ExprMutationAnalyzer::findRangeLoopMutation,
+                             &ExprMutationAnalyzer::findReferenceMutation}) {
+    if (const Stmt *S = (this->*Finder)(Exp))
+      return Results[Exp] = S;
+  }
+
+  return Results[Exp] = nullptr;
+}
+
+bool ExprMutationAnalyzer::isUnevaluated(const Expr *Exp) {
+  return selectFirst<Expr>(
+             "expr",
+             match(
+                 findAll(
+                     expr(equalsNode(Exp),
+                          anyOf(
+                              // `Exp` is part of the underlying expression of
+                              // decltype/typeof if it has an ancestor of
+                              // typeLoc.
+                              hasAncestor(typeLoc(unless(
+                                  hasAncestor(unaryExprOrTypeTraitExpr())))),
+                              hasAncestor(expr(anyOf(
+                                  // `UnaryExprOrTypeTraitExpr` is unevaluated
+                                  // unless it's sizeof on VLA.
+                                  unaryExprOrTypeTraitExpr(unless(sizeOfExpr(
+                                      hasArgumentOfType(variableArrayType())))),
+                                  // `CXXTypeidExpr` is unevaluated unless it's
+                                  // applied to an expression of glvalue of
+                                  // polymorphic class type.
+                                  cxxTypeidExpr(
+                                      unless(isPotentiallyEvaluated())),
+                                  // The controlling expression of
+                                  // `GenericSelectionExpr` is unevaluated.
+                                  genericSelectionExpr(hasControllingExpr(
+                                      hasDescendant(equalsNode(Exp)))),
+                                  cxxNoexceptExpr())))))
+                         .bind("expr")),
+                 *Stm, *Context)) != nullptr;
+}
+
+const Stmt *
+ExprMutationAnalyzer::findExprMutation(ArrayRef<BoundNodes> Matches) {
+  for (const auto &Nodes : Matches) {
+    if (const Stmt *S = findMutation(Nodes.getNodeAs<Expr>("expr")))
+      return S;
+  }
+  return nullptr;
+}
+
+const Stmt *
+ExprMutationAnalyzer::findDeclMutation(ArrayRef<BoundNodes> Matches) {
+  for (const auto &DeclNodes : Matches) {
+    if (const Stmt *S = findDeclMutation(DeclNodes.getNodeAs<Decl>("decl")))
+      return S;
+  }
+  return nullptr;
+}
+
+const Stmt *ExprMutationAnalyzer::findDeclMutation(const Decl *Dec) {
+  const auto Refs = match(
+      findAll(declRefExpr(to(equalsNode(Dec))).bind("expr")), *Stm, *Context);
+  for (const auto &RefNodes : Refs) {
+    const auto *E = RefNodes.getNodeAs<Expr>("expr");
+    if (findMutation(E))
+      return E;
+  }
+  return nullptr;
+}
+
+const Stmt *ExprMutationAnalyzer::findDirectMutation(const Expr *Exp) {
+  // LHS of any assignment operators.
+  const auto AsAssignmentLhs =
+      binaryOperator(isAssignmentOperator(), hasLHS(equalsNode(Exp)));
+
+  // Operand of increment/decrement operators.
+  const auto AsIncDecOperand =
+      unaryOperator(anyOf(hasOperatorName("++"), hasOperatorName("--")),
+                    hasUnaryOperand(equalsNode(Exp)));
+
+  // Invoking non-const member function.
+  const auto NonConstMethod = cxxMethodDecl(unless(isConst()));
+  const auto AsNonConstThis =
+      expr(anyOf(cxxMemberCallExpr(callee(NonConstMethod), on(equalsNode(Exp))),
+                 cxxOperatorCallExpr(callee(NonConstMethod),
+                                     hasArgument(0, equalsNode(Exp)))));
+
+  // Taking address of 'Exp'.
+  // We're assuming 'Exp' is mutated as soon as its address is taken, though in
+  // theory we can follow the pointer and see whether it escaped `Stm` or is
+  // dereferenced and then mutated. This is left for future improvements.
+  const auto AsAmpersandOperand =
+      unaryOperator(hasOperatorName("&"),
+                    // A NoOp implicit cast is adding const.
+                    unless(hasParent(implicitCastExpr(hasCastKind(CK_NoOp)))),
+                    hasUnaryOperand(equalsNode(Exp)));
+  const auto AsPointerFromArrayDecay =
+      castExpr(hasCastKind(CK_ArrayToPointerDecay),
+               unless(hasParent(arraySubscriptExpr())), has(equalsNode(Exp)));
+
+  // Used as non-const-ref argument when calling a function.
+  const auto NonConstRefParam = forEachArgumentWithParam(
+      equalsNode(Exp), parmVarDecl(hasType(nonConstReferenceType())));
+  const auto AsNonConstRefArg =
+      anyOf(callExpr(NonConstRefParam), cxxConstructExpr(NonConstRefParam));
+
+  // Captured by a lambda by reference.
+  // If we're initializing a capture with 'Exp' directly then we're initializing
+  // a reference capture.
+  // For value captures there will be an ImplicitCastExpr <LValueToRValue>.
+  const auto AsLambdaRefCaptureInit = lambdaExpr(hasCaptureInit(Exp));
+
+  // Returned as non-const-ref.
+  // If we're returning 'Exp' directly then it's returned as non-const-ref.
+  // For returning by value there will be an ImplicitCastExpr <LValueToRValue>.
+  // For returning by const-ref there will be an ImplicitCastExpr <NoOp> (for
+  // adding const.)
+  const auto AsNonConstRefReturn = returnStmt(hasReturnValue(equalsNode(Exp)));
+
+  const auto Matches =
+      match(findAll(stmt(anyOf(AsAssignmentLhs, AsIncDecOperand, AsNonConstThis,
+                               AsAmpersandOperand, AsPointerFromArrayDecay,
+                               AsNonConstRefArg, AsLambdaRefCaptureInit,
+                               AsNonConstRefReturn))
+                        .bind("stmt")),
+            *Stm, *Context);
+  return selectFirst<Stmt>("stmt", Matches);
+}
+
+const Stmt *ExprMutationAnalyzer::findMemberMutation(const Expr *Exp) {
+  // Check whether any member of 'Exp' is mutated.
+  const auto MemberExprs = match(
+      findAll(memberExpr(hasObjectExpression(equalsNode(Exp))).bind("expr")),
+      *Stm, *Context);
+  return findExprMutation(MemberExprs);
+}
+
+const Stmt *ExprMutationAnalyzer::findArrayElementMutation(const Expr *Exp) {
+  // Check whether any element of an array is mutated.
+  const auto SubscriptExprs = match(
+      findAll(arraySubscriptExpr(hasBase(ignoringImpCasts(equalsNode(Exp))))
+                  .bind("expr")),
+      *Stm, *Context);
+  return findExprMutation(SubscriptExprs);
+}
+
+const Stmt *ExprMutationAnalyzer::findCastMutation(const Expr *Exp) {
+  // If 'Exp' is casted to any non-const reference type, check the castExpr.
+  const auto Casts =
+      match(findAll(castExpr(hasSourceExpression(equalsNode(Exp)),
+                             anyOf(explicitCastExpr(hasDestinationType(
+                                       nonConstReferenceType())),
+                                   implicitCastExpr(hasImplicitDestinationType(
+                                       nonConstReferenceType()))))
+                        .bind("expr")),
+            *Stm, *Context);
+  return findExprMutation(Casts);
+}
+
+const Stmt *ExprMutationAnalyzer::findRangeLoopMutation(const Expr *Exp) {
+  // If range for looping over 'Exp' with a non-const reference loop variable,
+  // check all declRefExpr of the loop variable.
+  const auto LoopVars =
+      match(findAll(cxxForRangeStmt(
+                hasLoopVariable(
+                    varDecl(hasType(nonConstReferenceType())).bind("decl")),
+                hasRangeInit(equalsNode(Exp)))),
+            *Stm, *Context);
+  return findDeclMutation(LoopVars);
+}
+
+const Stmt *ExprMutationAnalyzer::findReferenceMutation(const Expr *Exp) {
+  // If 'Exp' is bound to a non-const reference, check all declRefExpr to that.
+  const auto Refs = match(
+      stmt(forEachDescendant(
+          varDecl(
+              hasType(nonConstReferenceType()),
+              hasInitializer(anyOf(equalsNode(Exp),
+                                   conditionalOperator(anyOf(
+                                       hasTrueExpression(equalsNode(Exp)),
+                                       hasFalseExpression(equalsNode(Exp)))))),
+              hasParent(declStmt().bind("stmt")),
+              // Don't follow the reference in range statement, we've handled
+              // that separately.
+              unless(hasParent(declStmt(hasParent(
+                  cxxForRangeStmt(hasRangeStmt(equalsBoundNode("stmt"))))))))
+              .bind("decl"))),
+      *Stm, *Context);
+  return findDeclMutation(Refs);
+}
+
+} // namespace utils
+} // namespace tidy
+} // namespace clang
+
diff --git a/clang-tools-extra/clang-tidy/utils/ExprMutationAnalyzer.h b/clang-tools-extra/clang-tidy/utils/ExprMutationAnalyzer.h
new file mode 100644
index 00000000000..256bb712891
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/utils/ExprMutationAnalyzer.h
@@ -0,0 +1,56 @@
+//===---------- ExprMutationAnalyzer.h - clang-tidy -----------------------===//
+//
+//                     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_EXPRMUTATIONANALYZER_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_EXPRMUTATIONANALYZER_H
+
+#include <type_traits>
+
+#include "clang/AST/AST.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "llvm/ADT/DenseMap.h"
+
+namespace clang {
+namespace tidy {
+namespace utils {
+
+/// Analyzes whether any mutative operations are applied to an expression within
+/// a given statement.
+class ExprMutationAnalyzer {
+public:
+  ExprMutationAnalyzer(const Stmt *Stm, ASTContext *Context)
+      : Stm(Stm), Context(Context) {}
+
+  bool isMutated(const Decl *Dec) { return findDeclMutation(Dec) != nullptr; }
+  bool isMutated(const Expr *Exp) { return findMutation(Exp) != nullptr; }
+  const Stmt *findMutation(const Expr *Exp);
+
+private:
+  bool isUnevaluated(const Expr *Exp);
+
+  const Stmt *findExprMutation(ArrayRef<ast_matchers::BoundNodes> Matches);
+  const Stmt *findDeclMutation(ArrayRef<ast_matchers::BoundNodes> Matches);
+  const Stmt *findDeclMutation(const Decl *Dec);
+
+  const Stmt *findDirectMutation(const Expr *Exp);
+  const Stmt *findMemberMutation(const Expr *Exp);
+  const Stmt *findArrayElementMutation(const Expr *Exp);
+  const Stmt *findCastMutation(const Expr *Exp);
+  const Stmt *findRangeLoopMutation(const Expr *Exp);
+  const Stmt *findReferenceMutation(const Expr *Exp);
+
+  const Stmt *const Stm;
+  ASTContext *const Context;
+  llvm::DenseMap<const Expr *, const Stmt *> Results;
+};
+
+} // namespace utils
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_EXPRMUTATIONANALYZER_H