Avoid using rvalue references with trivially copyable types.

Summary:
When the dereference operator returns a value that is trivially
copyable (like a pointer), copy it. After this change, modernize-loop-convert
check can be applied to the whole llvm source code without breaking any build
or test.

Reviewers: alexfh, klimek

Subscribers: alexfh, cfe-commits

Differential Revision: http://reviews.llvm.org/D12675

llvm-svn: 246989

4 files changed, 75 insertions, 43 deletions

diff --git a/clang-tools-extra/clang-tidy/modernize/LoopConvertCheck.cpp b/clang-tools-extra/clang-tidy/modernize/LoopConvertCheck.cpp
index b6cb64fa952..9af797927e2 100644
--- a/clang-tools-extra/clang-tidy/modernize/LoopConvertCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/LoopConvertCheck.cpp
@@ -375,7 +375,7 @@ static bool usagesAreConst(const UsageResult &Usages) {
 /// by reference.
 static bool usagesReturnRValues(const UsageResult &Usages) {
   for (const auto &U : Usages) {
-    if (!U.Expression->isRValue())
+    if (U.Expression && !U.Expression->isRValue())
       return false;
   }
   return true;
@@ -400,8 +400,7 @@ void LoopConvertCheck::doConversion(
     ASTContext *Context, const VarDecl *IndexVar, const VarDecl *MaybeContainer,
     StringRef ContainerString, const UsageResult &Usages,
     const DeclStmt *AliasDecl, bool AliasUseRequired, bool AliasFromForInit,
-    const ForStmt *TheLoop, bool ContainerNeedsDereference, bool DerefByValue,
-    bool DerefByConstRef) {
+    const ForStmt *TheLoop, RangeDescriptor Descriptor) {
   auto Diag = diag(TheLoop->getForLoc(), "use range-based for loop instead");
 
   std::string VarName;
@@ -457,16 +456,17 @@ void LoopConvertCheck::doConversion(
     // If an iterator's operator*() returns a 'T&' we can bind that to 'auto&'.
     // If operator*() returns 'T' we can bind that to 'auto&&' which will deduce
     // to 'T&&&'.
-    if (DerefByValue) {
-      AutoRefType = Context->getRValueReferenceType(AutoRefType);
+    if (Descriptor.DerefByValue) {
+      if (!Descriptor.IsTriviallyCopyable)
+        AutoRefType = Context->getRValueReferenceType(AutoRefType);
     } else {
-      if (DerefByConstRef)
+      if (Descriptor.DerefByConstRef)
         AutoRefType = Context->getConstType(AutoRefType);
       AutoRefType = Context->getLValueReferenceType(AutoRefType);
     }
   }
 
-  StringRef MaybeDereference = ContainerNeedsDereference ? "*" : "";
+  StringRef MaybeDereference = Descriptor.ContainerNeedsDereference ? "*" : "";
   std::string TypeString = AutoRefType.getAsString();
   std::string Range = ("(" + TypeString + " " + VarName + " : " +
                        MaybeDereference + ContainerString + ")")
@@ -518,11 +518,11 @@ StringRef LoopConvertCheck::checkRejections(ASTContext *Context,
 /// of the index variable and convert the loop if possible.
 void LoopConvertCheck::findAndVerifyUsages(
     ASTContext *Context, const VarDecl *LoopVar, const VarDecl *EndVar,
-    const Expr *ContainerExpr, const Expr *BoundExpr,
-    bool ContainerNeedsDereference, bool DerefByValue, bool DerefByConstRef,
-    const ForStmt *TheLoop, LoopFixerKind FixerKind) {
+    const Expr *ContainerExpr, const Expr *BoundExpr, const ForStmt *TheLoop,
+    LoopFixerKind FixerKind, RangeDescriptor Descriptor) {
   ForLoopIndexUseVisitor Finder(Context, LoopVar, EndVar, ContainerExpr,
-                                BoundExpr, ContainerNeedsDereference);
+                                BoundExpr,
+                                Descriptor.ContainerNeedsDereference);
 
   if (ContainerExpr) {
     ComponentFinderASTVisitor ComponentFinder;
@@ -544,15 +544,28 @@ void LoopConvertCheck::findAndVerifyUsages(
         !isDirectMemberExpr(ContainerExpr))
       ConfidenceLevel.lowerTo(Confidence::CL_Risky);
   } else if (FixerKind == LFK_PseudoArray) {
-    if (!DerefByValue && !DerefByConstRef) {
+    if (!Descriptor.DerefByValue && !Descriptor.DerefByConstRef) {
       const UsageResult &Usages = Finder.getUsages();
       if (usagesAreConst(Usages)) {
-        // FIXME: check if the type is trivially copiable.
-        DerefByConstRef = true;
+        Descriptor.DerefByConstRef = true;
       } else if (usagesReturnRValues(Usages)) {
         // If the index usages (dereference, subscript, at) return RValues,
         // then we should not use a non-const reference.
-        DerefByValue = true;
+        Descriptor.DerefByValue = true;
+        // Try to find the type of the elements on the container from the
+        // usages.
+        for (const Usage &U : Usages) {
+          if (!U.Expression || U.Expression->getType().isNull())
+            continue;
+          QualType Type = U.Expression->getType().getCanonicalType();
+          if (U.IsArrow) {
+            if (!Type->isPointerType())
+              continue;
+            Type = Type->getPointeeType();
+          }
+          Descriptor.IsTriviallyCopyable =
+              Type.isTriviallyCopyableType(*Context);
+        }
       }
     }
   }
@@ -565,7 +578,7 @@ void LoopConvertCheck::findAndVerifyUsages(
   doConversion(Context, LoopVar, getReferencedVariable(ContainerExpr),
                ContainerString, Finder.getUsages(), Finder.getAliasDecl(),
                Finder.aliasUseRequired(), Finder.aliasFromForInit(), TheLoop,
-               ContainerNeedsDereference, DerefByValue, DerefByConstRef);
+               Descriptor);
 }
 
 void LoopConvertCheck::registerMatchers(MatchFinder *Finder) {
@@ -618,15 +631,13 @@ void LoopConvertCheck::check(const MatchFinder::MatchResult &Result) {
     ConfidenceLevel.lowerTo(Confidence::CL_Reasonable);
 
   const Expr *ContainerExpr = nullptr;
-  bool DerefByValue = false;
-  bool DerefByConstRef = false;
-  bool ContainerNeedsDereference = false;
+  RangeDescriptor Descriptor{false, false, false, false};
   // FIXME: Try to put most of this logic inside a matcher. Currently, matchers
   // don't allow the ight-recursive checks in digThroughConstructors.
   if (FixerKind == LFK_Iterator) {
     ContainerExpr = findContainer(Context, LoopVar->getInit(),
                                   EndVar ? EndVar->getInit() : EndCall,
-                                  &ContainerNeedsDereference);
+                                  &Descriptor.ContainerNeedsDereference);
 
     QualType InitVarType = InitVar->getType();
     QualType CanonicalInitVarType = InitVarType.getCanonicalType();
@@ -643,6 +654,8 @@ void LoopConvertCheck::check(const MatchFinder::MatchResult &Result) {
       // un-qualified pointee types match otherwise we don't use auto.
       if (!Context->hasSameUnqualifiedType(InitPointeeType, BeginPointeeType))
         return;
+      Descriptor.IsTriviallyCopyable =
+          BeginPointeeType.isTriviallyCopyableType(*Context);
     } else {
       // Check for qualified types to avoid conversions from non-const to const
       // iterator types.
@@ -650,17 +663,19 @@ void LoopConvertCheck::check(const MatchFinder::MatchResult &Result) {
         return;
     }
 
-    DerefByValue = Nodes.getNodeAs<QualType>(DerefByValueResultName) != nullptr;
-    if (!DerefByValue) {
+    const auto *DerefByValueType =
+        Nodes.getNodeAs<QualType>(DerefByValueResultName);
+    Descriptor.DerefByValue = DerefByValueType;
+    if (!Descriptor.DerefByValue) {
       if (const auto *DerefType =
               Nodes.getNodeAs<QualType>(DerefByRefResultName)) {
         // A node will only be bound with DerefByRefResultName if we're dealing
         // with a user-defined iterator type. Test the const qualification of
         // the reference type.
-        DerefByConstRef = (*DerefType)
-                              ->getAs<ReferenceType>()
-                              ->getPointeeType()
-                              .isConstQualified();
+        Descriptor.DerefByConstRef = (*DerefType)
+                                         ->getAs<ReferenceType>()
+                                         ->getPointeeType()
+                                         .isConstQualified();
       } else {
         // By nature of the matcher this case is triggered only for built-in
         // iterator types (i.e. pointers).
@@ -671,12 +686,14 @@ void LoopConvertCheck::check(const MatchFinder::MatchResult &Result) {
         // If the initializer and variable have both the same type just use auto
         // otherwise we test for const qualification of the pointed-at type.
         if (!Context->hasSameType(InitPointeeType, BeginPointeeType))
-          DerefByConstRef = InitPointeeType.isConstQualified();
+          Descriptor.DerefByConstRef = InitPointeeType.isConstQualified();
       }
     } else {
       // If the dereference operator returns by value then test for the
       // canonical const qualification of the init variable type.
-      DerefByConstRef = CanonicalInitVarType.isConstQualified();
+      Descriptor.DerefByConstRef = CanonicalInitVarType.isConstQualified();
+      Descriptor.IsTriviallyCopyable =
+          DerefByValueType->isTriviallyCopyableType(*Context);
     }
   } else if (FixerKind == LFK_PseudoArray) {
     if (!EndCall)
@@ -685,7 +702,7 @@ void LoopConvertCheck::check(const MatchFinder::MatchResult &Result) {
     const auto *Member = dyn_cast<MemberExpr>(EndCall->getCallee());
     if (!Member)
       return;
-    ContainerNeedsDereference = Member->isArrow();
+    Descriptor.ContainerNeedsDereference = Member->isArrow();
   }
 
   // We must know the container or an array length bound.
@@ -696,8 +713,7 @@ void LoopConvertCheck::check(const MatchFinder::MatchResult &Result) {
     return;
 
   findAndVerifyUsages(Context, LoopVar, EndVar, ContainerExpr, BoundExpr,
-                      ContainerNeedsDereference, DerefByValue, DerefByConstRef,
-                      TheLoop, FixerKind);
+                      TheLoop, FixerKind, Descriptor);
 }
 
 } // namespace modernize
diff --git a/clang-tools-extra/clang-tidy/modernize/LoopConvertCheck.h b/clang-tools-extra/clang-tidy/modernize/LoopConvertCheck.h
index b7590638d77..6773b1918e3 100644
--- a/clang-tools-extra/clang-tidy/modernize/LoopConvertCheck.h
+++ b/clang-tools-extra/clang-tidy/modernize/LoopConvertCheck.h
@@ -25,22 +25,27 @@ public:
   void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
 
 private:
+  struct RangeDescriptor {
+    bool ContainerNeedsDereference;
+    bool DerefByValue;
+    bool IsTriviallyCopyable;
+    bool DerefByConstRef;
+  };
+
   void doConversion(ASTContext *Context, const VarDecl *IndexVar,
                     const VarDecl *MaybeContainer, StringRef ContainerString,
                     const UsageResult &Usages, const DeclStmt *AliasDecl,
                     bool AliasUseRequired, bool AliasFromForInit,
-                    const ForStmt *TheLoop, bool ContainerNeedsDereference,
-                    bool DerefByValue, bool DerefByConstRef);
+                    const ForStmt *TheLoop, RangeDescriptor Descriptor);
 
   StringRef checkRejections(ASTContext *Context, const Expr *ContainerExpr,
                             const ForStmt *TheLoop);
 
   void findAndVerifyUsages(ASTContext *Context, const VarDecl *LoopVar,
                            const VarDecl *EndVar, const Expr *ContainerExpr,
-                           const Expr *BoundExpr,
-                           bool ContainerNeedsDereference, bool DerefByValue,
-                           bool DerefByConstRef, const ForStmt *TheLoop,
-                           LoopFixerKind FixerKind);
+                           const Expr *BoundExpr, const ForStmt *TheLoop,
+                           LoopFixerKind FixerKind, RangeDescriptor Descriptor);
+
   std::unique_ptr<TUTrackingInfo> TUInfo;
   Confidence::Level MinConfidence;
 };
diff --git a/clang-tools-extra/clang-tidy/modernize/LoopConvertUtils.cpp b/clang-tools-extra/clang-tidy/modernize/LoopConvertUtils.cpp
index 116ec5c46c5..d0b2e8177a9 100644
--- a/clang-tools-extra/clang-tidy/modernize/LoopConvertUtils.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/LoopConvertUtils.cpp
@@ -349,11 +349,13 @@ static bool isAliasDecl(ASTContext *Context, const Decl *TheDecl,
 
   // Check that the declared type is the same as (or a reference to) the
   // container type.
+  QualType InitType = Init->getType();
   QualType DeclarationType = VDecl->getType();
-  if (DeclarationType->isReferenceType())
+  if (!DeclarationType.isNull() && DeclarationType->isReferenceType())
     DeclarationType = DeclarationType.getNonReferenceType();
-  QualType InitType = Init->getType();
-  if (!Context->hasSameUnqualifiedType(DeclarationType, InitType))
+
+  if (InitType.isNull() || DeclarationType.isNull() ||
+      !Context->hasSameUnqualifiedType(DeclarationType, InitType))
     return false;
 
   switch (Init->getStmtClass()) {
diff --git a/clang-tools-extra/test/clang-tidy/modernize-loop-convert-basic.cpp b/clang-tools-extra/test/clang-tidy/modernize-loop-convert-basic.cpp
index 7f31a5f4ca4..1979f1467ad 100644
--- a/clang-tools-extra/test/clang-tidy/modernize-loop-convert-basic.cpp
+++ b/clang-tools-extra/test/clang-tidy/modernize-loop-convert-basic.cpp
@@ -291,7 +291,7 @@ void f() {
          I != E; ++I) {
     }
     // CHECK-MESSAGES: :[[@LINE-4]]:5: warning: use range-based for loop instead
-    // CHECK-FIXES: for (auto && int_ptr : int_ptrs) {
+    // CHECK-FIXES: for (auto int_ptr : int_ptrs) {
   }
 
   // This container uses an iterator where the derefence type is a typedef of
@@ -564,14 +564,23 @@ struct DerefByValue {
   unsigned operator[](int);
 };
 
-void DerefByValueTest() {
+void derefByValueTest() {
   DerefByValue DBV;
   for (unsigned i = 0, e = DBV.size(); i < e; ++i) {
     printf("%d\n", DBV[i]);
   }
   // CHECK-MESSAGES: :[[@LINE-3]]:3: warning: use range-based for loop instead
-  // CHECK-FIXES: for (auto && elem : DBV) {
+  // CHECK-FIXES: for (auto elem : DBV) {
+  // CHECK-FIXES-NEXT: printf("%d\n", elem);
 
+  for (unsigned i = 0, e = DBV.size(); i < e; ++i) {
+    auto f = [DBV, i]() {};
+    printf("%d\n", DBV[i]);
+  }
+  // CHECK-MESSAGES: :[[@LINE-4]]:3: warning: use range-based for loop instead
+  // CHECK-FIXES: for (auto elem : DBV) {
+  // CHECK-FIXES-NEXT: auto f = [DBV, elem]() {};
+  // CHECK-FIXES-NEXT: printf("%d\n", elem);
 }
 
 } // namespace PseudoArray