Reduce memory footprint for basic case of flexible types

The case is when we have a simple type constructor
(not array nor collection) and type is not raw:
A<T1, >..A<T1>?

Actually these types are almost equal besides of nullability,
but we create and resolve two different simple types,
they have different arguments' lists, etc.

The idea is to add NullableSimpleType subclass with delegate
to another simple type

It should help a lot both with common cases and with corner ones:
flexibles types in spark for Function22 having exponential size
because of its flexibility

 #KT-14375 Fixed
 #KT-14323 Fixed

core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/types/JavaTypeResolver.kt

@@ -90,11 +90,11 @@ class JavaTypeResolver(
             return computeSimpleJavaClassifierType(javaType, attr) ?: errorType()
         }
 
-        fun computeBound(flexibility: JavaTypeFlexibility) =
-                computeSimpleJavaClassifierType(javaType, attr.withFlexibility(flexibility))
+        fun computeBound(flexibility: JavaTypeFlexibility, lowerResult: SimpleType? = null) =
+                computeSimpleJavaClassifierType(javaType, attr.withFlexibility(flexibility), lowerResult)
 
         val lower = computeBound(FLEXIBLE_LOWER_BOUND) ?: return errorType()
-        val upper = computeBound(FLEXIBLE_UPPER_BOUND) ?: return errorType()
+        val upper = computeBound(FLEXIBLE_UPPER_BOUND, lowerResult = lower) ?: return errorType()
 
         return if (isRaw) {
             RawTypeImpl(lower, upper)
@@ -104,12 +104,21 @@ class JavaTypeResolver(
         }
     }
 
-    private fun computeSimpleJavaClassifierType(javaType: JavaClassifierType, attr: JavaTypeAttributes): SimpleType? {
-        val annotations = LazyJavaAnnotations(c, javaType)
+    private fun computeSimpleJavaClassifierType(
+            javaType: JavaClassifierType, attr: JavaTypeAttributes,
+            lowerResult: SimpleType? = null
+    ): SimpleType? {
+        val annotations =
+                lowerResult?.annotations ?: LazyJavaAnnotations(c, javaType)
         val constructor = computeTypeConstructor(javaType, attr) ?: return null
-        val arguments = computeArguments(javaType, attr, constructor)
         val isNullable = attr.isNullable()
 
+        if (lowerResult?.constructor == constructor && !javaType.isRaw && isNullable) {
+            return lowerResult.makeNullableAsSpecified(true)
+        }
+
+        val arguments = computeArguments(javaType, attr, constructor)
+
         return KotlinTypeFactory.simpleType(annotations, constructor, arguments, isNullable)
     }
 
@@ -340,4 +349,3 @@ internal fun TypeParameterDescriptor.getErasedUpperBound(
 
     return defaultValue()
 }
-

core/descriptors/src/org/jetbrains/kotlin/types/KotlinTypeFactory.kt

@@ -89,10 +89,18 @@ private class SimpleTypeImpl(
         override val memberScope: MemberScope
 ) : SimpleType() {
     override fun replaceAnnotations(newAnnotations: Annotations) =
-            SimpleTypeImpl(newAnnotations, constructor, arguments, isMarkedNullable, memberScope)
+            if (newAnnotations === annotations)
+                this
+            else
+                SimpleTypeImpl(newAnnotations, constructor, arguments, isMarkedNullable, memberScope)
 
     override fun makeNullableAsSpecified(newNullability: Boolean) =
-            SimpleTypeImpl(annotations, constructor, arguments, newNullability, memberScope)
+            if (newNullability == isMarkedNullable)
+                this
+            else if (newNullability)
+                NullableSimpleType(this)
+            else
+                SimpleTypeImpl(annotations, constructor, arguments, newNullability, memberScope)
 
     init {
         if (memberScope is ErrorUtils.ErrorScope) {
@@ -100,3 +108,19 @@ private class SimpleTypeImpl(
         }
     }
 }
+
+private class NullableSimpleType(override val delegate: SimpleType) : DelegatingSimpleType() {
+    override val isMarkedNullable: Boolean
+        get() = true
+
+    override fun replaceAnnotations(newAnnotations: Annotations) =
+            if (newAnnotations !== delegate.annotations)
+                NullableSimpleType(delegate.replaceAnnotations(newAnnotations))
+            else
+                this
+
+    override fun makeNullableAsSpecified(newNullability: Boolean): SimpleType {
+        if (newNullability) return this
+        return delegate.makeNullableAsSpecified(newNullability)
+    }
+}

core/descriptors/src/org/jetbrains/kotlin/types/checker/NewKotlinTypeChecker.kt

@@ -53,6 +53,9 @@ object StrictEqualityTypeChecker {
         ) {
             return false
         }
+
+        if (a.arguments === b.arguments) return true
+
         for (i in a.arguments.indices) {
             val aArg = a.arguments[i]
             val bArg = b.arguments[i]
@@ -322,6 +325,9 @@ object NewKotlinTypeChecker : KotlinTypeChecker {
             capturedSubArguments: List<TypeProjection>,
             superType: SimpleType
     ): Boolean {
+
+        if (capturedSubArguments === superType.arguments) return true
+
         val parameters = superType.constructor.parameters
 
         for (index in parameters.indices) {
@@ -433,4 +439,4 @@ val SimpleType.isSingleClassifierType: Boolean
             (constructor.declarationDescriptor != null || this is CapturedType || this is NewCapturedType)
 
 val SimpleType.isIntersectionType: Boolean
-    get() = constructor is IntersectionTypeConstructor
+    get() = constructor is IntersectionTypeConstructor