Add an option to stage in substituted type lowering for function values

Author: jckarter

include/swift/Basic/LangOptions.h

@@ -211,6 +211,9 @@ namespace swift {
     /// Enable experimental operator designated types feature.
     bool EnableOperatorDesignatedTypes = false;
 
+    /// Enable SIL type lowering
+    bool EnableSubstSILFunctionTypesForFunctionValues = false;
+
     /// Enable constraint solver support for experimental
     ///        operator protocol designator feature.
     bool SolverEnableOperatorDesignatedTypes = false;

include/swift/Option/FrontendOptions.td

@@ -344,6 +344,10 @@ def enable_experimental_static_assert :
   Flag<["-"], "enable-experimental-static-assert">,
   HelpText<"Enable experimental #assert">;
 
+def enable_subst_sil_function_types_for_function_values :
+  Flag<["-"], "enable-subst-sil-function-types-for-function-values">,
+  HelpText<"Use substituted function types for SIL type lowering of function values">;
+  
 def enable_deserialization_recovery :
   Flag<["-"], "enable-deserialization-recovery">,
   HelpText<"Attempt to recover from missing xrefs (etc) in swiftmodules">;

lib/Frontend/CompilerInvocation.cpp

@@ -274,6 +274,9 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   Opts.EnableExperimentalStaticAssert |=
     Args.hasArg(OPT_enable_experimental_static_assert);
 
+  Opts.EnableSubstSILFunctionTypesForFunctionValues |=
+    Args.hasArg(OPT_enable_subst_sil_function_types_for_function_values);
+
   Opts.EnableOperatorDesignatedTypes |=
       Args.hasArg(OPT_enable_operator_designated_types);