1 files changed, 19 insertions, 0 deletions
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index d1512c271c0..3989c56ccd8 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -4174,6 +4174,25 @@ DeclContext *Sema::FindInstantiatedContext(SourceLocation Loc, DeclContext* DC,
 NamedDecl *Sema::FindInstantiatedDecl(SourceLocation Loc, NamedDecl *D,
                           const MultiLevelTemplateArgumentList &TemplateArgs) {
   DeclContext *ParentDC = D->getDeclContext();
+  // FIXME: Parmeters of pointer to functions (y below) that are themselves 
+  // parameters (p below) can have their ParentDC set to the translation-unit
+  // - thus we can not consistently check if the ParentDC of such a parameter 
+  // is Dependent or/and a FunctionOrMethod.
+  // For e.g. this code, during Template argument deduction tries to 
+  // find an instantiated decl for (T y) when the ParentDC for y is
+  // the translation unit.  
+  //   e.g. template <class T> void Foo(auto (*p)(T y) -> decltype(y())) {} 
+  //   float baz(float(*)()) { return 0.0; }
+  //   Foo(baz);
+  // The better fix here is perhaps to ensure that a ParmVarDecl, by the time
+  // it gets here, always has a FunctionOrMethod as its ParentDC??
+  // For now:
+  //  - as long as we have a ParmVarDecl whose parent is non-dependent and
+  //    whose type is not instantiation dependent, do nothing to the decl
+  //  - otherwise find its instantiated decl.
+  if (isa<ParmVarDecl>(D) && !ParentDC->isDependentContext() &&
+      !cast<ParmVarDecl>(D)->getType()->isInstantiationDependentType())
+    return D;
   if (isa<ParmVarDecl>(D) || isa<NonTypeTemplateParmDecl>(D) ||
       isa<TemplateTypeParmDecl>(D) || isa<TemplateTemplateParmDecl>(D) ||
       (ParentDC->isFunctionOrMethod() && ParentDC->isDependentContext()) ||