IRGen: Small fix for opaque return types with variadic types

Author: slavapestov

lib/IRGen/GenReflection.cpp

@@ -490,10 +490,8 @@ IRGenModule::emitWitnessTableRefString(CanType type,
             type = genericEnv->mapTypeIntoContext(type)->getCanonicalType();
           }
           if (origType->hasTypeParameter()) {
-            auto origSig = genericEnv->getGenericSignature();
             conformance = conformance.subst(origType,
-              QueryInterfaceTypeSubstitutions(genericEnv),
-              LookUpConformanceInSignature(origSig.getPointer()));
+                genericEnv->getForwardingSubstitutionMap());
           }
           auto ret = emitWitnessTableRef(IGF, type, conformance);
           IGF.Builder.CreateRet(ret);

test/IRGen/variadic_generic_opaque.swift

@@ -0,0 +1,14 @@
+// RUN: %target-swift-frontend -emit-ir %s -enable-experimental-feature VariadicGenerics -disable-availability-checking
+
+// Because of -enable-experimental-feature VariadicGenerics
+// REQUIRES: asserts
+
+// FIXME: Add more tests
+
+public protocol P {}
+
+public struct G<each T>: P {}
+
+public func returnsG<each T>(_ t: repeat each T) -> some P {
+  return G<repeat each T>()
+}