[NFC] IRGen: Forming signatures of functions.

Author: nate-chandler

lib/IRGen/GenCall.cpp

@@ -2491,6 +2491,12 @@ SignatureExpansionABIDetails Signature::getUncachedABIDetails(
   return result;
 }
 
+Signature Signature::forFunction(llvm::Function *fn) {
+  auto sig = Signature(fn->getFunctionType(), fn->getAttributes(),
+                       fn->getCallingConv());
+  return sig;
+}
+
 Signature Signature::forCoroutineContinuation(IRGenModule &IGM,
                                               CanSILFunctionType fnType) {
   assert(fnType->isCoroutine());

lib/IRGen/Signature.h

@@ -212,6 +212,8 @@ class Signature {
   getUncachedABIDetails(IRGenModule &IGM, CanSILFunctionType formalType,
                         FunctionPointerKind kind);
 
+  static Signature forFunction(llvm::Function *fn);
+
   /// Compute the signature of a coroutine's continuation function.
   static Signature forCoroutineContinuation(IRGenModule &IGM,
                                             CanSILFunctionType coroType);