1 files changed, 11 insertions, 10 deletions

diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 46cda5e9ac7..0930fdd653b 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -1837,7 +1837,6 @@ void Sema::DeclareImplicitDeductionGuides(TemplateDecl *Template,
   // for which some class template parameter without a default argument never
   // appears in a deduced context).
   bool AddedAny = false;
-  bool AddedCopyOrMove = false;
   for (NamedDecl *D : LookupConstructors(Transform.Primary)) {
     D = D->getUnderlyingDecl();
     if (D->isInvalidDecl() || D->isImplicit())
@@ -1854,20 +1853,22 @@ void Sema::DeclareImplicitDeductionGuides(TemplateDecl *Template,
 
     Transform.transformConstructor(FTD, CD);
     AddedAny = true;
-
-    AddedCopyOrMove |= CD->isCopyOrMoveConstructor();
   }
 
-  // Synthesize an X() -> X<...> guide if there were no declared constructors.
-  // FIXME: The standard doesn't say (how) to do this.
+  // C++17 [over.match.class.deduct]
+  //    --  If C is not defined or does not declare any constructors, an
+  //    additional function template derived as above from a hypothetical
+  //    constructor C().
   if (!AddedAny)
     Transform.buildSimpleDeductionGuide(None);
 
-  // Synthesize an X(X<...>) -> X<...> guide if there was no declared constructor
-  // resembling a copy or move constructor.
-  // FIXME: The standard doesn't say (how) to do this.
-  if (!AddedCopyOrMove)
-    Transform.buildSimpleDeductionGuide(Transform.DeducedType);
+  //    -- An additional function template derived as above from a hypothetical
+  //    constructor C(C), called the copy deduction candidate.
+  cast<CXXDeductionGuideDecl>(
+      cast<FunctionTemplateDecl>(
+          Transform.buildSimpleDeductionGuide(Transform.DeducedType))
+          ->getTemplatedDecl())
+      ->setIsCopyDeductionCandidate();
 }
 
 /// \brief Diagnose the presence of a default template argument on a