[CodeGen] Tweak isTriviallyRecursive further

isTriviallyRecursive is a hack used to bridge a gap between the
expectations that source code assumes and the semantics that LLVM IR can
provide.  Specifically, asm labels on functions are treated as an
explicit name for a GlobalObject in Clang but treated like an
output-processing step in GCC.  Tweak this hack a little further to emit
calls to library functions instead of emitting an incorrect definition.
The definition in question would have available_externally linkage (this
is OK) but result in a call to itself which will either result in an
infinite loop or stack overflow.

This fixes PR23964.

llvm-svn: 241043

clang/lib/CodeGen/CodeGenModule.cpp

@@ -1457,12 +1457,7 @@ CodeGenModule::isTriviallyRecursive(const FunctionDecl *FD) {
     Name = FD->getName();
   }
 
-  auto &BI = Context.BuiltinInfo;
-  unsigned BuiltinID = Context.Idents.get(Name).getBuiltinID();
-  if (!BuiltinID || !BI.isPredefinedLibFunction(BuiltinID))
-    return false;
-
-  FunctionIsDirectlyRecursive Walker(Name, BI);
+  FunctionIsDirectlyRecursive Walker(Name, Context.BuiltinInfo);
   Walker.TraverseFunctionDecl(const_cast<FunctionDecl*>(FD));
   return Walker.Result;
 }