[Import as memory] SILGen for delegation to a C function imported as an initializer.

Always statically dispatch to C functions imported as members, and
call to the foreign entry point. This gets us through SILGen, but DI
is still deeply unhappy with the resulting SIL.

Author: DougGregor

lib/SIL/SILDeclRef.cpp

@@ -35,6 +35,10 @@ swift::getMethodDispatch(AbstractFunctionDecl *method) {
   if (method->hasForcedStaticDispatch())
     return MethodDispatch::Static;
 
+  // Import-as-member declarations are always statically referenced.
+  if (method->isImportAsMember())
+    return MethodDispatch::Static;
+
   // If this declaration is in a class but not marked final, then it is
   // always dynamically dispatched.
   auto dc = method->getDeclContext();

lib/SILGen/SILGenApply.cpp

@@ -1440,7 +1440,8 @@ class SILGenApply : public Lowering::ExprVisitor<SILGenApply> {
     // that's the only thing that's witnessed. For classes,
     // this is the initializing constructor, to which we will dynamically
     // dispatch.
-    if (SelfParam.getSubstRValueType()->getRValueInstanceType()->is<ArchetypeType>()
+    if (SelfParam.getSubstRValueType()->getRValueInstanceType()
+          ->is<ArchetypeType>()
         && isa<ProtocolDecl>(ctorRef->getDecl()->getDeclContext())) {
       // Look up the witness for the constructor.
       auto constant = SILDeclRef(ctorRef->getDecl(),
@@ -1470,13 +1471,17 @@ class SILGenApply : public Lowering::ExprVisitor<SILGenApply> {
                   getSubstFnType(), fn));
     } else {
       // Directly call the peer constructor.
-      setCallee(Callee::forDirect(SGF,
-                                  SILDeclRef(ctorRef->getDecl(),
-                                             useAllocatingCtor
-                                               ? SILDeclRef::Kind::Allocator
-                                               : SILDeclRef::Kind::Initializer,
-                               SILDeclRef::ConstructAtBestResilienceExpansion),
-                                  getSubstFnType(useAllocatingCtor), fn));
+      setCallee(
+        Callee::forDirect(
+          SGF,
+          SILDeclRef(ctorRef->getDecl(),
+                     useAllocatingCtor
+                       ? SILDeclRef::Kind::Allocator
+                       : SILDeclRef::Kind::Initializer,
+                     SILDeclRef::ConstructAtBestResilienceExpansion,
+                     SILDeclRef::ConstructAtNaturalUncurryLevel,
+                     requiresForeignEntryPoint(ctorRef->getDecl())),
+            getSubstFnType(useAllocatingCtor), fn));
     }
 
     // Set up the substitutions, if we have any.

test/SILGen/import_as_member.swift

@@ -1,7 +1,8 @@
-// RUN: %target-swift-frontend -emit-sil -I %S/../IDE/Inputs/custom-modules %s 2>&1 | FileCheck --check-prefix=SIL %s
+// RUN: %target-swift-frontend -emit-silgen -I %S/../IDE/Inputs/custom-modules %s 2>&1 | FileCheck --check-prefix=SIL %s
 // REQUIRES: objc_interop
 import ImportAsMember.A
 import ImportAsMember.Proto
+import ImportAsMember.Class
 
 public func returnGlobalVar() -> Double {
 	return Struct1.globalVar
@@ -22,3 +23,25 @@ public func useProto(p: IAMProto) {
 
 // SIL-LABEL: sil {{.*}}anchor{{.*}} () -> () {
 func anchor() {}
+
+// SIL-LABEL: sil {{.*}}useClass{{.*}}
+// SIL: bb0([[D:%[0-9]+]] : $Double, [[OPTS:%[0-9]+]] : $SomeClass.Options):
+public func useClass(d: Double, opts: SomeClass.Options) {
+  // SIL: [[CTOR:%[0-9]+]] = function_ref @MakeIAMSomeClass : $@convention(c) (Double) -> @autoreleased SomeClass
+  // SIL: [[OBJ:%[0-9]+]] = apply [[CTOR]]([[D]])
+  let o = SomeClass(value: d)
+
+  // SIL: [[APPLY_FN:%[0-9]+]] = function_ref @IAMSomeClassApplyOptions : $@convention(c) (SomeClass, SomeClass.Options) -> ()
+  // SIL: apply [[APPLY_FN]]([[OBJ]], [[OPTS]])
+  o.applyOptions(opts)
+}
+
+extension SomeClass {
+  // SIL-LABEL: sil hidden @_TFE16import_as_memberCSo9SomeClasscfT6doubleSd_S0_
+  // SIL: bb0([[DOUBLE:%[0-9]+]] : $Double
+  // SIL: [[FNREF:%[0-9]+]] = function_ref @MakeIAMSomeClass
+  // SIL: apply [[FNREF]]([[DOUBLE]])
+  convenience init(double: Double) {
+    self.init(value: double)
+  }
+}