[Clang] Fix ResolveConstructorOverload to not select a conversion function if we are going use copy elision

ResolveConstructorOverload needs to check properly if we are going to use copy
elision we can't use a conversion function.

This fixes:

#39319
#60182
#62157
#64885
#65568

Differential Revision: https://reviews.llvm.org/D148474

Author: shafik

clang/docs/ReleaseNotes.rst

@@ -669,6 +669,12 @@ Bug Fixes in This Version
   Fixes (`#64467 <https://github.com/llvm/llvm-project/issues/64467>`_)
 - Clang's ``-Wchar-subscripts`` no longer warns on chars whose values are known non-negative constants.
   Fixes (`#18763 <https://github.com/llvm/llvm-project/issues/18763>`_)
+- Fix crash due to incorrectly allowing conversion functions in copy elision.
+  Fixes (`#39319 <https://github.com/llvm/llvm-project/issues/39319>`_) and
+  (`#60182 <https://github.com/llvm/llvm-project/issues/60182>`_) and
+  (`#62157 <https://github.com/llvm/llvm-project/issues/62157>`_) and
+  (`#64885 <https://github.com/llvm/llvm-project/issues/64885>`_) and
+  (`#65568 <https://github.com/llvm/llvm-project/issues/65568>`_)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaInit.cpp

@@ -4085,16 +4085,13 @@ static bool hasCopyOrMoveCtorParam(ASTContext &Ctx,
   return Ctx.hasSameUnqualifiedType(ParmT, ClassT);
 }
 
-static OverloadingResult
-ResolveConstructorOverload(Sema &S, SourceLocation DeclLoc,
-                           MultiExprArg Args,
-                           OverloadCandidateSet &CandidateSet,
-                           QualType DestType,
-                           DeclContext::lookup_result Ctors,
-                           OverloadCandidateSet::iterator &Best,
-                           bool CopyInitializing, bool AllowExplicit,
-                           bool OnlyListConstructors, bool IsListInit,
-                           bool SecondStepOfCopyInit = false) {
+static OverloadingResult ResolveConstructorOverload(
+    Sema &S, SourceLocation DeclLoc, MultiExprArg Args,
+    OverloadCandidateSet &CandidateSet, QualType DestType,
+    DeclContext::lookup_result Ctors, OverloadCandidateSet::iterator &Best,
+    bool CopyInitializing, bool AllowExplicit, bool OnlyListConstructors,
+    bool IsListInit, bool RequireActualConstructor,
+    bool SecondStepOfCopyInit = false) {
   CandidateSet.clear(OverloadCandidateSet::CSK_InitByConstructor);
   CandidateSet.setDestAS(DestType.getQualifiers().getAddressSpace());
 
@@ -4157,7 +4154,7 @@ ResolveConstructorOverload(Sema &S, SourceLocation DeclLoc,
   // Note: SecondStepOfCopyInit is only ever true in this case when
   // evaluating whether to produce a C++98 compatibility warning.
   if (S.getLangOpts().CPlusPlus17 && Args.size() == 1 &&
-      !SecondStepOfCopyInit) {
+      !RequireActualConstructor && !SecondStepOfCopyInit) {
     Expr *Initializer = Args[0];
     auto *SourceRD = Initializer->getType()->getAsCXXRecordDecl();
     if (SourceRD && S.isCompleteType(DeclLoc, Initializer->getType())) {
@@ -4225,6 +4222,12 @@ static void TryConstructorInitialization(Sema &S,
     return;
   }
 
+  bool RequireActualConstructor =
+      !(Entity.getKind() != InitializedEntity::EK_Base &&
+        Entity.getKind() != InitializedEntity::EK_Delegating &&
+        Entity.getKind() !=
+            InitializedEntity::EK_LambdaToBlockConversionBlockElement);
+
   // C++17 [dcl.init]p17:
   //     - If the initializer expression is a prvalue and the cv-unqualified
   //       version of the source type is the same class as the class of the
@@ -4234,11 +4237,7 @@ static void TryConstructorInitialization(Sema &S,
   // class or delegating to another constructor from a mem-initializer.
   // ObjC++: Lambda captured by the block in the lambda to block conversion
   // should avoid copy elision.
-  if (S.getLangOpts().CPlusPlus17 &&
-      Entity.getKind() != InitializedEntity::EK_Base &&
-      Entity.getKind() != InitializedEntity::EK_Delegating &&
-      Entity.getKind() !=
-          InitializedEntity::EK_LambdaToBlockConversionBlockElement &&
+  if (S.getLangOpts().CPlusPlus17 && !RequireActualConstructor &&
       UnwrappedArgs.size() == 1 && UnwrappedArgs[0]->isPRValue() &&
       S.Context.hasSameUnqualifiedType(UnwrappedArgs[0]->getType(), DestType)) {
     // Convert qualifications if necessary.
@@ -4286,11 +4285,10 @@ static void TryConstructorInitialization(Sema &S,
     // If the initializer list has no elements and T has a default constructor,
     // the first phase is omitted.
     if (!(UnwrappedArgs.empty() && S.LookupDefaultConstructor(DestRecordDecl)))
-      Result = ResolveConstructorOverload(S, Kind.getLocation(), Args,
-                                          CandidateSet, DestType, Ctors, Best,
-                                          CopyInitialization, AllowExplicit,
-                                          /*OnlyListConstructors=*/true,
-                                          IsListInit);
+      Result = ResolveConstructorOverload(
+          S, Kind.getLocation(), Args, CandidateSet, DestType, Ctors, Best,
+          CopyInitialization, AllowExplicit,
+          /*OnlyListConstructors=*/true, IsListInit, RequireActualConstructor);
   }
 
   // C++11 [over.match.list]p1:
@@ -4300,11 +4298,10 @@ static void TryConstructorInitialization(Sema &S,
   //     elements of the initializer list.
   if (Result == OR_No_Viable_Function) {
     AsInitializerList = false;
-    Result = ResolveConstructorOverload(S, Kind.getLocation(), UnwrappedArgs,
-                                        CandidateSet, DestType, Ctors, Best,
-                                        CopyInitialization, AllowExplicit,
-                                        /*OnlyListConstructors=*/false,
-                                        IsListInit);
+    Result = ResolveConstructorOverload(
+        S, Kind.getLocation(), UnwrappedArgs, CandidateSet, DestType, Ctors,
+        Best, CopyInitialization, AllowExplicit,
+        /*OnlyListConstructors=*/false, IsListInit, RequireActualConstructor);
   }
   if (Result) {
     Sequence.SetOverloadFailure(
@@ -6778,6 +6775,7 @@ static ExprResult CopyObject(Sema &S,
       S, Loc, CurInitExpr, CandidateSet, T, Ctors, Best,
       /*CopyInitializing=*/false, /*AllowExplicit=*/true,
       /*OnlyListConstructors=*/false, /*IsListInit=*/false,
+      /*RequireActualConstructor=*/false,
       /*SecondStepOfCopyInit=*/true)) {
   case OR_Success:
     break;
@@ -6920,6 +6918,7 @@ static void CheckCXX98CompatAccessibleCopy(Sema &S,
       S, Loc, CurInitExpr, CandidateSet, CurInitExpr->getType(), Ctors, Best,
       /*CopyInitializing=*/false, /*AllowExplicit=*/true,
       /*OnlyListConstructors=*/false, /*IsListInit=*/false,
+      /*RequireActualConstructor=*/false,
       /*SecondStepOfCopyInit=*/true);
 
   PartialDiagnostic Diag = S.PDiag(diag::warn_cxx98_compat_temp_copy)

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -810,6 +810,10 @@ void Sema::PrintInstantiationStack() {
         Diags.Report(Active->PointOfInstantiation,
                      diag::note_template_nsdmi_here)
             << FD << Active->InstantiationRange;
+      } else if (ClassTemplateDecl *CTD = dyn_cast<ClassTemplateDecl>(D)) {
+        Diags.Report(Active->PointOfInstantiation,
+                     diag::note_template_class_instantiation_here)
+            << CTD << Active->InstantiationRange;
       } else {
         Diags.Report(Active->PointOfInstantiation,
                      diag::note_template_type_alias_instantiation_here)

clang/test/SemaCXX/cxx1z-copy-omission.cpp

@@ -171,3 +171,30 @@ namespace CtorTemplateBeatsNonTemplateConversionFn {
   Foo f(Derived d) { return d; } // expected-error {{invokes a deleted function}}
   Foo g(Derived d) { return Foo(d); } // ok, calls constructor
 }
+
+// Make sure we don't consider conversion functions for guaranteed copy elision
+namespace GH39319 {
+struct A {
+  A();
+  A(const A&) = delete; // expected-note {{'A' has been explicitly marked deleted here}}
+};
+struct B {
+  operator A();
+} C;
+A::A() : A(C) {} // expected-error {{call to deleted constructor of}}
+
+struct A2 {
+  struct B2 {
+    operator A2();
+  };
+  A2() : A2(B2()) {}  // expected-error {{call to deleted constructor of}}
+  A2(const A2&) = delete; // expected-note {{'A2' has been explicitly marked deleted here}}
+};
+
+template<typename A3>
+class B3 : A3 {
+  template<bool = C3<B3>()> // expected-warning 2{{use of function template name with no prior declaration in function call with explicit}}
+  B3();
+}; B3(); // expected-error {{deduction guide declaration without trailing return type}} \
+         // expected-note {{while building implicit deduction guide first needed here}}
+}