Fix for Bug 33471: Preventing operator auto from resolving to a template operator.

As the bug report says,
struct A
{

  template<typename T> operator T();

};

void foo()
{

  A().operator auto();

}

causes: "undeduced type in IR-generation
UNREACHABLE executed at llvm/tools/clang/lib/CodeGen/CodeGenFunction.cpp:208!"

The problem is that in this case, "T" is being deduced as "auto", 
which I believe is incorrect.

The 'operator auto' implementation in Clang is standards compliant, however 
there is a defect report against core (1670).

Differential Revision: https://reviews.llvm.org/D34370

llvm-svn: 305812

1 files changed, 10 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
index 1fb25f4e0e7..9f657a446c0 100644
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -862,6 +862,16 @@ static bool LookupDirect(Sema &S, LookupResult &R, const DeclContext *DC) {
   if (!Record->isCompleteDefinition())
     return Found;
 
+  // For conversion operators, 'operator auto' should only match
+  // 'operator auto'.  Since 'auto' is not a type, it shouldn't be considered
+  // as a candidate for template substitution.
+  auto *ContainedDeducedType =
+      R.getLookupName().getCXXNameType()->getContainedDeducedType();
+  if (R.getLookupName().getNameKind() ==
+          DeclarationName::CXXConversionFunctionName &&
+      ContainedDeducedType && ContainedDeducedType->isUndeducedType())
+    return Found;
+
   for (CXXRecordDecl::conversion_iterator U = Record->conversion_begin(),
          UEnd = Record->conversion_end(); U != UEnd; ++U) {
     FunctionTemplateDecl *ConvTemplate = dyn_cast<FunctionTemplateDecl>(*U);