IR: make allOverridden return Set instead of Sequence, move to IrUtils

This doesn't hurt performance, but improves stack traces, in particular
in JVM's BridgeLowering.

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/ir/IrUtils.kt

@@ -620,3 +620,23 @@ private fun IrSimpleFunction.copyAndRenameConflictingTypeParametersFrom(
 
 val IrSymbol.isSuspend: Boolean
     get() = this is IrSimpleFunctionSymbol && owner.isSuspend
+
+fun IrSimpleFunction.allOverridden(includeSelf: Boolean = false): Set<IrSimpleFunction> {
+    val result = mutableSetOf<IrSimpleFunction>()
+    if (includeSelf) {
+        computeAllOverridden(this, result)
+    } else {
+        for (override in overriddenSymbols) {
+            computeAllOverridden(override.owner, result)
+        }
+    }
+    return result
+}
+
+private fun computeAllOverridden(function: IrSimpleFunction, result: MutableSet<IrSimpleFunction>) {
+    if (result.add(function)) {
+        for (override in function.overriddenSymbols) {
+            computeAllOverridden(override.owner, result)
+        }
+    }
+}

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/SpecialBridgeMethods.kt

@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.backend.common.lower
 
 import org.jetbrains.kotlin.backend.common.CommonBackendContext
+import org.jetbrains.kotlin.backend.common.ir.allOverridden
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
 import org.jetbrains.kotlin.ir.UNDEFINED_OFFSET
 import org.jetbrains.kotlin.ir.declarations.IrSimpleFunction
@@ -107,7 +108,7 @@ class SpecialBridgeMethods(val context: CommonBackendContext) {
     val specialPropertyNames = specialProperties.map { (description) -> description.name }.toHashSet()
 
     fun findSpecialWithOverride(irFunction: IrSimpleFunction): Pair<IrSimpleFunction, SpecialMethodWithDefaultInfo>? {
-        irFunction.allOverridden().forEach { overridden ->
+        for (overridden in irFunction.allOverridden()) {
             val description = overridden.toDescription()
             specialMethodsWithDefaults[description]?.let {
                 return Pair(overridden, it)
@@ -132,18 +133,3 @@ class SpecialBridgeMethods(val context: CommonBackendContext) {
         return specialMethods[irFunction.toDescription()]
     }
 }
-
-fun IrSimpleFunction.allOverridden(includeSelf: Boolean = false): Sequence<IrSimpleFunction> {
-    val visited = mutableSetOf<IrSimpleFunction>()
-
-    fun IrSimpleFunction.search(): Sequence<IrSimpleFunction> {
-        if (this in visited) return emptySequence()
-        return sequence {
-            yield(this@search)
-            visited.add(this@search)
-            overriddenSymbols.forEach { yieldAll(it.owner.search()) }
-        }
-    }
-
-    return if (includeSelf) search() else search().drop(1)
-}