SIL: Don't recursively lower ExistentialType and ParameterizedProtocolType

Author: slavapestov

lib/SIL/IR/TypeLowering.cpp

@@ -2912,47 +2912,6 @@ TypeConverter::computeLoweredRValueType(TypeExpansionContext forExpansion,
                                              MetatypeRepresentation::Thick);
     }
 
-    CanType visitExistentialType(CanExistentialType substExistType) {
-      // Try to avoid walking into the constraint type if we can help it
-      if (!substExistType->hasTypeParameter() &&
-          !substExistType->hasArchetype() &&
-          !substExistType->hasOpaqueArchetype()) {
-        return substExistType;
-      }
-
-      return CanExistentialType::get(visit(substExistType.getConstraintType()));
-    }
-
-    CanType
-    visitParameterizedProtocolType(CanParameterizedProtocolType substPPT) {
-      bool changed = false;
-      SmallVector<Type, 4> loweredSubstArgs;
-      loweredSubstArgs.reserve(substPPT.getArgs().size());
-
-      auto origConstraint = origType.getExistentialConstraintType();
-      auto origPPT = origConstraint.getAs<ParameterizedProtocolType>();
-      if (!origPPT)
-        return substPPT;
-      
-      for (auto i : indices(substPPT.getArgs())) {
-        auto origArgTy = AbstractionPattern(
-            origConstraint.getGenericSignatureOrNull(), origPPT.getArgs()[i]);
-        auto substArgType = substPPT.getArgs()[i];
-
-        CanType loweredSubstEltType =
-            TC.getLoweredRValueType(forExpansion, origArgTy, substArgType);
-        changed = changed || substArgType != loweredSubstEltType;
-
-        loweredSubstArgs.push_back(loweredSubstEltType);
-      }
-
-      if (!changed)
-        return substPPT;
-
-      return CanParameterizedProtocolType::get(
-          TC.Context, substPPT->getBaseType(), loweredSubstArgs);
-    }
-
     // Lower pack element types.
     CanType visitPackType(CanPackType substPackType) {
       return computeLoweredPackType(TC, forExpansion, origType,

test/SILGen/parameterized_existentials.swift

@@ -98,3 +98,14 @@ func upcastResult() {
 func force<T, U, V>() -> any P<T, U, V> {
   return R(force: { force() }).force()
 }
+
+protocol Box<Contents> {
+  associatedtype Contents
+
+  var contents: Contents { get }
+}
+
+// CHECK-LABEL: sil hidden [ossa] @$s13parameterized13functionTypes3box5valueq_AA3Box_pq_xc8ContentsRts_XP_xtr0_lF : $@convention(thin) <T, U> (@in_guaranteed any Box<(T) -> U>, @in_guaranteed T) -> @out U {
+func functionTypes<T, U>(box: any Box<(T) -> U>, value: T) -> U {
+  return box.contents(value)
+}