SILGen: Fix dynamic calls of 'throwing' methods

Fixes <https://bugs.swift.org/browse/SR-2320>.

Author: slavapestov

lib/SILGen/SILGenApply.cpp

@@ -558,14 +558,14 @@ class Callee {
       assert(level <= Constant.uncurryLevel
              && "uncurrying past natural uncurry level of method");
 
-      auto constant = Constant.atUncurryLevel(level);
+      constant = Constant.atUncurryLevel(level);
       // Lower the substituted type from the AST, which should have any generic
       // parameters in the original signature erased to their upper bounds.
       auto objcFormalType = SubstFormalType.withExtInfo(
          SubstFormalType->getExtInfo()
            .withSILRepresentation(SILFunctionTypeRepresentation::ObjCMethod));
       auto fnType = gen.SGM.M.Types
-        .getUncachedSILFunctionTypeForConstant(constant, objcFormalType);
+        .getUncachedSILFunctionTypeForConstant(*constant, objcFormalType);
 
       auto closureType =
         replaceSelfTypeForDynamicLookup(gen.getASTContext(), fnType,
@@ -574,9 +574,9 @@ class Callee {
 
       SILValue fn = gen.B.createDynamicMethod(Loc,
                           SelfValue,
-                          constant,
+                          *constant,
                           SILType::getPrimitiveObjectType(closureType),
-                          /*volatile*/ constant.isForeign);
+                          /*volatile*/ Constant.isForeign);
       mv = ManagedValue::forUnmanaged(fn);
       break;
     }

test/SILGen/dynamic_lookup_throws.swift

@@ -0,0 +1,27 @@
+// RUN: rm -rf %t && mkdir -p %t
+// RUN: %build-clang-importer-objc-overlays
+
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk-nosource -I %t) -emit-silgen -parse-as-library %s | %FileCheck %s
+
+// REQUIRES: objc_interop
+
+import Foundation
+
+class Blub : NSObject {
+   func blub() throws {}
+}
+
+// CHECK-LABEL: sil hidden @_TF21dynamic_lookup_throws8testBlubFzT1aPs9AnyObject__T_ : $@convention(thin) (@owned AnyObject) -> @error Error
+func testBlub(a: AnyObject) throws {
+  // CHECK:   open_existential_ref %0 : $AnyObject to $@opened("[[OPENED:.*]]") AnyObject
+  // CHECK:   dynamic_method [volatile] %4 : $@opened("[[OPENED]]") AnyObject, #Blub.blub!1.foreign : (Blub) -> () throws -> (), $@convention(objc_method) (Optional<AutoreleasingUnsafeMutablePointer<Optional<NSError>>>, @opened("[[OPENED]]") AnyObject) -> ObjCBool
+  // CHECK:   cond_br {{%.*}}, bb1, bb2
+
+  // CHECK: bb1
+  // CHECK:   return
+
+  // CHECK: bb2
+  // CHECK:   function_ref @swift_convertNSErrorToError
+  // CHECK:   throw {{%.*}} : $Error
+  try a.blub()
+}