Pull in r291403 from upstream clang trunk (by Richard Smith):

  PR30305: Implement proposed DR resolution to prevent slicing via
  inherited constructor.

  The rule we use is that a construction of a class type T from an
  argument of type U cannot use an inherited constructor if U is the
  same as T or is derived from T (or if the initialization would first
  convert it to such a type). This (approximately) matches the rule in
  use by GCC, and matches the current proposed DR resolution.

Pull in r291955 from upstream clang trunk (by Richard Smith):

  PR31606: Generalize our tentative DR resolution for inheriting
  copy/move constructors to better match the pre-P0136R1 behavior.

Together, these fix an issue with C++ using declarations sometimes
enabling illegal implicit casts.

Direct commit to stable/11, since head already has clang 4.0.0, which
includes this change.

Reported by:	kami
PR:		215969

3 files changed, 41 insertions, 1 deletions

diff --git a/contrib/llvm/tools/clang/include/clang/Basic/DiagnosticSemaKinds.td b/contrib/llvm/tools/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 98b687b..c49adc3 100644
--- a/contrib/llvm/tools/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/contrib/llvm/tools/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -3180,6 +3180,9 @@ def note_ovl_candidate : Note<"candidate "
 
 def note_ovl_candidate_inherited_constructor : Note<
     "constructor from base class %0 inherited here">;
+def note_ovl_candidate_inherited_constructor_slice : Note<
+    "candidate %select{constructor|template}0 ignored: "
+    "inherited constructor cannot be used to %select{copy|move}1 object">;
 def note_ovl_candidate_illegal_constructor : Note<
     "candidate %select{constructor|template}0 ignored: "
     "instantiation %select{takes|would take}0 its own class type by value">;
diff --git a/contrib/llvm/tools/clang/include/clang/Sema/Overload.h b/contrib/llvm/tools/clang/include/clang/Sema/Overload.h
index d0f21cd..898b12e 100644
--- a/contrib/llvm/tools/clang/include/clang/Sema/Overload.h
+++ b/contrib/llvm/tools/clang/include/clang/Sema/Overload.h
@@ -586,7 +586,11 @@ namespace clang {
     ovl_fail_enable_if,
 
     /// This candidate was not viable because its address could not be taken.
-    ovl_fail_addr_not_available
+    ovl_fail_addr_not_available,
+
+    /// This inherited constructor is not viable because it would slice the
+    /// argument.
+    ovl_fail_inhctor_slice,
   };
 
   /// OverloadCandidate - A single candidate in an overload set (C++ 13.3).
diff --git a/contrib/llvm/tools/clang/lib/Sema/SemaOverload.cpp b/contrib/llvm/tools/clang/lib/Sema/SemaOverload.cpp
index 40d6e91..f148c2d 100644
--- a/contrib/llvm/tools/clang/lib/Sema/SemaOverload.cpp
+++ b/contrib/llvm/tools/clang/lib/Sema/SemaOverload.cpp
@@ -5783,6 +5783,28 @@ Sema::AddOverloadCandidate(FunctionDecl *Function,
       Candidate.FailureKind = ovl_fail_illegal_constructor;
       return;
     }
+
+    // C++ [over.match.funcs]p8: (proposed DR resolution)
+    //   A constructor inherited from class type C that has a first parameter
+    //   of type "reference to P" (including such a constructor instantiated
+    //   from a template) is excluded from the set of candidate functions when
+    //   constructing an object of type cv D if the argument list has exactly
+    //   one argument and D is reference-related to P and P is reference-related
+    //   to C.
+    auto *Shadow = dyn_cast<ConstructorUsingShadowDecl>(FoundDecl.getDecl());
+    if (Shadow && Args.size() == 1 && Constructor->getNumParams() >= 1 &&
+        Constructor->getParamDecl(0)->getType()->isReferenceType()) {
+      QualType P = Constructor->getParamDecl(0)->getType()->getPointeeType();
+      QualType C = Context.getRecordType(Constructor->getParent());
+      QualType D = Context.getRecordType(Shadow->getParent());
+      SourceLocation Loc = Args.front()->getExprLoc();
+      if ((Context.hasSameUnqualifiedType(P, C) || IsDerivedFrom(Loc, P, C)) &&
+          (Context.hasSameUnqualifiedType(D, P) || IsDerivedFrom(Loc, D, P))) {
+        Candidate.Viable = false;
+        Candidate.FailureKind = ovl_fail_inhctor_slice;
+        return;
+      }
+    }
   }
 
   unsigned NumParams = Proto->getNumParams();
@@ -9750,6 +9772,17 @@ static void NoteFunctionCandidate(Sema &S, OverloadCandidate *Cand,
   case ovl_fail_enable_if:
     return DiagnoseFailedEnableIfAttr(S, Cand);
 
+  case ovl_fail_inhctor_slice:
+    // It's generally not interesting to note copy/move constructors here.
+    if (cast<CXXConstructorDecl>(Fn)->isCopyOrMoveConstructor())
+      return;
+    S.Diag(Fn->getLocation(),
+           diag::note_ovl_candidate_inherited_constructor_slice)
+      << (Fn->getPrimaryTemplate() ? 1 : 0)
+      << Fn->getParamDecl(0)->getType()->isRValueReferenceType();
+    MaybeEmitInheritedConstructorNote(S, Cand->FoundDecl);
+    return;
+
   case ovl_fail_addr_not_available: {
     bool Available = checkAddressOfCandidateIsAvailable(S, Cand->Function);
     (void)Available;