Reduce memory footprint after functions substitution

Do not recreate new instances if descriptors' parts remain
effectively the same

core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/AbstractReceiverParameterDescriptor.java

@@ -56,6 +56,7 @@ public abstract class AbstractReceiverParameterDescriptor extends DeclarationDes
         }
 
         if (substitutedType == null) return null;
+        if (substitutedType == getType()) return this;
 
         return new ReceiverParameterDescriptorImpl(getContainingDeclaration(), new TransientReceiver(substitutedType));
     }

core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/FunctionDescriptorImpl.java

@@ -16,6 +16,7 @@
 
 package org.jetbrains.kotlin.descriptors.impl;
 
+import kotlin.collections.CollectionsKt;
 import kotlin.jvm.functions.Function0;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
@@ -334,7 +335,7 @@ public abstract class FunctionDescriptorImpl extends DeclarationDescriptorNonRoo
         if (originalSubstitutor.isEmpty()) {
             return this;
         }
-        return newCopyBuilder(originalSubstitutor).setOriginal(getOriginal()).build();
+        return newCopyBuilder(originalSubstitutor).setOriginal(getOriginal()).setJustForTypeSubstitution(true).build();
     }
 
     @Nullable
@@ -370,6 +371,7 @@ public abstract class FunctionDescriptorImpl extends DeclarationDescriptorNonRoo
         private boolean isHiddenForResolutionEverywhereBesideSupercalls = isHiddenForResolutionEverywhereBesideSupercalls();
         private Map<UserDataKey<?>, Object> userDataMap = new LinkedHashMap<UserDataKey<?>, Object>();
         private Boolean newHasSynthesizedParameterNames = null;
+        protected boolean justForTypeSubstitution = false;
 
         public CopyConfiguration(
                 @NotNull TypeSubstitution substitution,
@@ -553,6 +555,12 @@ public abstract class FunctionDescriptorImpl extends DeclarationDescriptorNonRoo
         public TypeSubstitution getSubstitution() {
             return substitution;
         }
+
+        @NotNull
+        public CopyConfiguration setJustForTypeSubstitution(boolean value) {
+            justForTypeSubstitution = value;
+            return this;
+        }
     }
 
     @Override
@@ -571,6 +579,7 @@ public abstract class FunctionDescriptorImpl extends DeclarationDescriptorNonRoo
 
     @Nullable
     protected FunctionDescriptor doSubstitute(@NotNull CopyConfiguration configuration) {
+        boolean[] wereChanges = new boolean[1];
         Annotations resultAnnotations =
                 configuration.additionalAnnotations != null
                 ? AnnotationsKt.composeAnnotations(getAnnotations(), configuration.additionalAnnotations)
@@ -583,10 +592,12 @@ public abstract class FunctionDescriptorImpl extends DeclarationDescriptorNonRoo
         List<TypeParameterDescriptor> unsubstitutedTypeParameters =
                 configuration.newTypeParameters == null ? getTypeParameters() : configuration.newTypeParameters;
 
+        wereChanges[0] |= !unsubstitutedTypeParameters.isEmpty();
+
         List<TypeParameterDescriptor> substitutedTypeParameters =
                 new ArrayList<TypeParameterDescriptor>(unsubstitutedTypeParameters.size());
         final TypeSubstitutor substitutor = DescriptorSubstitutor.substituteTypeParameters(
-                unsubstitutedTypeParameters, configuration.substitution, substitutedDescriptor, substitutedTypeParameters
+                unsubstitutedTypeParameters, configuration.substitution, substitutedDescriptor, substitutedTypeParameters, wereChanges
         );
 
         KotlinType substitutedReceiverParameterType = null;
@@ -595,6 +606,8 @@ public abstract class FunctionDescriptorImpl extends DeclarationDescriptorNonRoo
             if (substitutedReceiverParameterType == null) {
                 return null;
             }
+
+            wereChanges[0] |= substitutedReceiverParameterType != configuration.newExtensionReceiverParameterType;
         }
 
         ReceiverParameterDescriptor substitutedExpectedThis = null;
@@ -613,11 +626,13 @@ public abstract class FunctionDescriptorImpl extends DeclarationDescriptorNonRoo
             if (substitutedExpectedThis == null) {
                 return null;
             }
+
+            wereChanges[0] |= substitutedExpectedThis != configuration.dispatchReceiverParameter;
         }
 
         List<ValueParameterDescriptor> substitutedValueParameters = getSubstitutedValueParameters(
                 substitutedDescriptor, configuration.newValueParameterDescriptors, substitutor, configuration.dropOriginalInContainingParts,
-                configuration.preserveSourceElement
+                configuration.preserveSourceElement, wereChanges
         );
         if (substitutedValueParameters == null) {
             return null;
@@ -628,6 +643,12 @@ public abstract class FunctionDescriptorImpl extends DeclarationDescriptorNonRoo
             return null;
         }
 
+        wereChanges[0] |= substitutedReturnType != configuration.newReturnType;
+
+        if (!wereChanges[0] && configuration.justForTypeSubstitution) {
+            return this;
+        }
+
         substitutedDescriptor.initialize(
                 substitutedReceiverParameterType,
                 substitutedExpectedThis,
@@ -682,7 +703,7 @@ public abstract class FunctionDescriptorImpl extends DeclarationDescriptorNonRoo
 
         if (configuration.copyOverrides && !getOriginal().getOverriddenDescriptors().isEmpty()) {
             if (configuration.substitution.isEmpty()) {
-                Function0<Set<FunctionDescriptor>> overriddenFunctionsTask = lazyOverriddenFunctionsTask;
+                Function0<Collection<FunctionDescriptor>> overriddenFunctionsTask = lazyOverriddenFunctionsTask;
                 if (overriddenFunctionsTask != null) {
                     substitutedDescriptor.lazyOverriddenFunctionsTask = overriddenFunctionsTask;
                 }
@@ -753,7 +774,8 @@ public abstract class FunctionDescriptorImpl extends DeclarationDescriptorNonRoo
             @NotNull List<ValueParameterDescriptor> unsubstitutedValueParameters,
             @NotNull TypeSubstitutor substitutor,
             boolean dropOriginal,
-            boolean preserveSourceElement
+            boolean preserveSourceElement,
+            @Nullable boolean[] wereChanges
     ) {
         List<ValueParameterDescriptor> result = new ArrayList<ValueParameterDescriptor>(unsubstitutedValueParameters.size());
         for (ValueParameterDescriptor unsubstitutedValueParameter : unsubstitutedValueParameters) {
@@ -763,6 +785,11 @@ public abstract class FunctionDescriptorImpl extends DeclarationDescriptorNonRoo
             KotlinType substituteVarargElementType =
                     varargElementType == null ? null : substitutor.substitute(varargElementType, Variance.IN_VARIANCE);
             if (substitutedType == null) return null;
+            if (substitutedType != unsubstitutedValueParameter.getType() || varargElementType != substituteVarargElementType) {
+                if (wereChanges != null) {
+                    wereChanges[0] = true;
+                }
+            }
             result.add(
                     new ValueParameterDescriptorImpl(
                             substitutedDescriptor,

core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/PropertyDescriptorImpl.java

@@ -385,7 +385,7 @@ public class PropertyDescriptorImpl extends VariableDescriptorWithInitializerImp
         if (newSetter != null) {
             List<ValueParameterDescriptor> substitutedValueParameters = FunctionDescriptorImpl.getSubstitutedValueParameters(
                     newSetter, setter.getValueParameters(), substitutor, /* dropOriginal = */ false,
-                    false
+                    false, null
             );
             if (substitutedValueParameters == null) {
                 // The setter is projected out, e.g. in this case:

core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/TypeAliasConstructorDescriptor.kt

@@ -179,7 +179,8 @@ class TypeAliasConstructorDescriptorImpl private constructor(
 
             val valueParameters =
                     FunctionDescriptorImpl.getSubstitutedValueParameters(
-                            typeAliasConstructor, constructor.valueParameters, substitutorForUnderlyingClass, false, false
+                            typeAliasConstructor, constructor.valueParameters, substitutorForUnderlyingClass, false, false,
+                            null
                     ) ?: return null
 
             val returnType = run {

core/descriptors/src/org/jetbrains/kotlin/types/DescriptorSubstitutor.java

@@ -18,6 +18,7 @@ package org.jetbrains.kotlin.types;
 
 import org.jetbrains.annotations.Mutable;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 import org.jetbrains.annotations.ReadOnly;
 import org.jetbrains.kotlin.descriptors.DeclarationDescriptor;
 import org.jetbrains.kotlin.descriptors.SourceElement;
@@ -38,6 +39,17 @@ public class DescriptorSubstitutor {
             @NotNull TypeSubstitution originalSubstitution,
             @NotNull DeclarationDescriptor newContainingDeclaration,
             @NotNull @Mutable List<TypeParameterDescriptor> result
+    ) {
+        return substituteTypeParameters(typeParameters, originalSubstitution, newContainingDeclaration, result, null);
+    }
+
+    @NotNull
+    public static TypeSubstitutor substituteTypeParameters(
+            @ReadOnly @NotNull List<TypeParameterDescriptor> typeParameters,
+            @NotNull TypeSubstitution originalSubstitution,
+            @NotNull DeclarationDescriptor newContainingDeclaration,
+            @NotNull @Mutable List<TypeParameterDescriptor> result,
+            @Nullable boolean[] wereChanges
     ) {
         Map<TypeConstructor, TypeProjection> mutableSubstitution = new HashMap<TypeConstructor, TypeProjection>();
 
@@ -69,6 +81,11 @@ public class DescriptorSubstitutor {
             for (KotlinType upperBound : descriptor.getUpperBounds()) {
                 KotlinType substitutedBound = substitutor.substitute(upperBound, Variance.IN_VARIANCE);
                 assert substitutedBound != null : "Upper bound failed to substitute: " + descriptor;
+
+                if (substitutedBound != upperBound && wereChanges != null) {
+                    wereChanges[0] = true;
+                }
+
                 substituted.addUpperBound(substitutedBound);
             }
             substituted.setInitialized();