SILGen: Replace calls to subst() on a GenericFunctionType with substGenericArgs()

Author: slavapestov

lib/SILGen/SILGenExpr.cpp

@@ -4265,16 +4265,16 @@ static void lowerKeyPathMemberIndexTypes(
   if (auto subscript = dyn_cast<SubscriptDecl>(decl)) {
     auto subscriptSubstTy = subscript->getInterfaceType();
     auto sig = subscript->getGenericSignature();
-    if (sig) {
-      subscriptSubstTy = subscriptSubstTy.subst(memberSubs);
+    if (auto *subscriptGenericTy = subscriptSubstTy->getAs<GenericFunctionType>()) {
+      subscriptSubstTy = subscriptGenericTy->substGenericArgs(memberSubs);
     }
     needsGenericContext |= subscriptSubstTy->hasArchetype();
     processIndicesOrParameters(subscript->getIndices(), &sig);
   } else if (auto method = dyn_cast<AbstractFunctionDecl>(decl)) {
     auto methodSubstTy = method->getInterfaceType();
     auto sig = method->getGenericSignature();
-    if (sig) {
-      methodSubstTy = methodSubstTy.subst(memberSubs);
+    if (auto *methodGenericTy = methodSubstTy->getAs<GenericFunctionType>()) {
+      methodSubstTy = methodGenericTy->substGenericArgs(memberSubs);
     }
     needsGenericContext |= methodSubstTy->hasArchetype();
     processIndicesOrParameters(method->getParameters(), &sig);

lib/SILGen/SILGenType.cpp

@@ -946,8 +946,7 @@ static SILFunction *emitSelfConformanceWitness(SILGenModule &SGM,
                                           openedConf);
 
   // Substitute to get the formal substituted type of the thunk.
-  auto reqtSubstTy =
-    cast<AnyFunctionType>(reqtOrigTy.subst(reqtSubs)->getCanonicalType());
+  auto reqtSubstTy = reqtOrigTy.substGenericArgs(reqtSubs);
 
   // Substitute into the requirement type to get the type of the thunk.
   auto witnessSILFnType = requirementInfo.SILFnType->substGenericArgs(