psi2ir: precompute sort keys when generating members

On kotlinx.serialization, this improves the performace of the compiler
with -Xuse-ir by about 5% (average of 30 runs after 10 warmup runs:
3096 ms -> 2970 ms, minimum: 3037 ms -> 2884 ms). Flamegraphs for
comparison (careful, huge SVG images):

https://drive.google.com/open?id=1BlIFN4ivSKrXjY6vZ0xkZymwucGc7bSI
https://drive.google.com/open?id=1xIW2IvW7LMCaAe4P2dOGOG8nCcpWI9PW

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/ClassGenerator.kt

@@ -24,7 +24,6 @@ import org.jetbrains.kotlin.ir.expressions.impl.*
 import org.jetbrains.kotlin.ir.expressions.mapValueParameters
 import org.jetbrains.kotlin.ir.expressions.putTypeArguments
 import org.jetbrains.kotlin.ir.expressions.typeParametersCount
-import org.jetbrains.kotlin.ir.util.StableDescriptorsComparator
 import org.jetbrains.kotlin.ir.util.declareSimpleFunctionWithOverrides
 import org.jetbrains.kotlin.ir.util.referenceFunction
 import org.jetbrains.kotlin.psi.KtClassOrObject
@@ -37,6 +36,10 @@ import org.jetbrains.kotlin.psi.psiUtil.pureStartOffset
 import org.jetbrains.kotlin.psi.psiUtil.startOffsetSkippingComments
 import org.jetbrains.kotlin.psi.synthetics.SyntheticClassOrObjectDescriptor
 import org.jetbrains.kotlin.psi.synthetics.findClassDescriptor
+import org.jetbrains.kotlin.renderer.ClassifierNamePolicy
+import org.jetbrains.kotlin.renderer.DescriptorRenderer
+import org.jetbrains.kotlin.renderer.DescriptorRendererModifier
+import org.jetbrains.kotlin.renderer.OverrideRenderingPolicy
 import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.resolve.DescriptorUtils
 import org.jetbrains.kotlin.resolve.scopes.DescriptorKindFilter
@@ -51,6 +54,23 @@ class ClassGenerator(
     declarationGenerator: DeclarationGenerator
 ) : DeclarationGeneratorExtension(declarationGenerator) {
 
+    companion object {
+        private val DESCRIPTOR_RENDERER = DescriptorRenderer.withOptions {
+            withDefinedIn = false
+            overrideRenderingPolicy = OverrideRenderingPolicy.RENDER_OPEN_OVERRIDE
+            includePropertyConstant = true
+            classifierNamePolicy = ClassifierNamePolicy.FULLY_QUALIFIED
+            verbose = true
+            modifiers = DescriptorRendererModifier.ALL
+        }
+
+        fun <T : DeclarationDescriptor> List<T>.sortedByRenderer(): List<T> {
+            val rendered = map(DESCRIPTOR_RENDERER::render)
+            val sortedIndices = (0 until size).sortedWith(Comparator { i, j -> rendered[i].compareTo(rendered[j]) })
+            return sortedIndices.map { this[it] }
+        }
+    }
+
     fun generateClass(ktClassOrObject: KtPureClassOrObject): IrClass {
         val classDescriptor = ktClassOrObject.findClassDescriptor(this.context.bindingContext)
         val startOffset = ktClassOrObject.getStartOffsetOfClassDeclarationOrNull() ?: ktClassOrObject.pureStartOffset
@@ -125,7 +145,7 @@ class ClassGenerator(
                     it?.kind == CallableMemberDescriptor.Kind.FAKE_OVERRIDE
                 }
             }
-            .sortedWith(StableDescriptorsComparator)
+            .sortedByRenderer()
             .forEach { fakeOverride ->
                 declarationGenerator.generateFakeOverrideDeclaration(fakeOverride, ktClassOrObject)?.let { irClass.declarations.add(it) }
             }
@@ -137,7 +157,7 @@ class ClassGenerator(
             .getContributedDescriptors(DescriptorKindFilter.CALLABLES)
             .filterIsInstance<CallableMemberDescriptor>()
             .filter { it.kind == CallableMemberDescriptor.Kind.DELEGATION }
-            .sortedWith(StableDescriptorsComparator)
+            .sortedByRenderer()
         if (delegatedMembers.isEmpty()) return
 
         for (ktEntry in ktSuperTypeList.entries) {

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/StableDescriptorsComparator.kt

@@ -1,45 +0,0 @@
-/*
- * Copyright 2010-2017 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.jetbrains.kotlin.ir.util
-
-import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
-import org.jetbrains.kotlin.renderer.ClassifierNamePolicy
-import org.jetbrains.kotlin.renderer.DescriptorRenderer
-import org.jetbrains.kotlin.renderer.DescriptorRendererModifier
-import org.jetbrains.kotlin.renderer.OverrideRenderingPolicy
-import java.util.*
-
-object StableDescriptorsComparator : Comparator<DeclarationDescriptor> {
-    override fun compare(member1: DeclarationDescriptor?, member2: DeclarationDescriptor?): Int {
-        if (member1 == member2) return 0
-        if (member1 == null) return -1
-        if (member2 == null) return 1
-
-        val image1 = DESCRIPTOR_RENDERER.render(member1)
-        val image2 = DESCRIPTOR_RENDERER.render(member2)
-        return image1.compareTo(image2)
-    }
-
-    private val DESCRIPTOR_RENDERER = DescriptorRenderer.withOptions {
-        withDefinedIn = false
-        overrideRenderingPolicy = OverrideRenderingPolicy.RENDER_OPEN_OVERRIDE
-        includePropertyConstant = true
-        classifierNamePolicy = ClassifierNamePolicy.FULLY_QUALIFIED
-        verbose = true
-        modifiers = DescriptorRendererModifier.ALL
-    }
-}