From 50d258e7f47eb5b4db7f3499a6cd0b271b4f03ba Mon Sep 17 00:00:00 2001
From: Denis Zharkov <denis.zharkov@jetbrains.com>
Date: Thu, 10 Mar 2016 14:29:28 +0300
Subject: [PATCH] Optimize CF merge operations

Return incoming value if it's single
---
 .../kotlin/cfg/PseudocodeVariablesData.kt     | 20 +++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/compiler/frontend/src/org/jetbrains/kotlin/cfg/PseudocodeVariablesData.kt b/compiler/frontend/src/org/jetbrains/kotlin/cfg/PseudocodeVariablesData.kt
index 3167a0ce7bd..71b2a98d157 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/cfg/PseudocodeVariablesData.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/cfg/PseudocodeVariablesData.kt
@@ -155,12 +155,19 @@ class PseudocodeVariablesData(val pseudocode: Pseudocode, private val bindingCon
                 TraversalOrder.BACKWARD, true, UseControlFlowInfo()
         ) {
             instruction: Instruction, incomingEdgesData: Collection<UseControlFlowInfo> ->
-            val enterResult = UseControlFlowInfo()
-            for (edgeData in incomingEdgesData) {
-                for (entry in edgeData.entries) {
-                    val variableDescriptor = entry.key
-                    val variableUseState = entry.value
-                    enterResult.put(variableDescriptor, variableUseState.merge(enterResult[variableDescriptor]))
+            val enterResult: UseControlFlowInfo
+
+            if (incomingEdgesData.size == 1) {
+                enterResult = incomingEdgesData.single()
+            }
+            else {
+                enterResult = UseControlFlowInfo()
+                for (edgeData in incomingEdgesData) {
+                    for (entry in edgeData.entries) {
+                        val variableDescriptor = entry.key
+                        val variableUseState = entry.value
+                        enterResult.put(variableDescriptor, variableUseState.merge(enterResult[variableDescriptor]))
+                    }
                 }
             }
             val variableDescriptor = PseudocodeUtil.extractVariableDescriptorIfAny(instruction, true, bindingContext)
@@ -207,6 +214,7 @@ class PseudocodeVariablesData(val pseudocode: Pseudocode, private val bindingCon
         private fun mergeIncomingEdgesDataForInitializers(
                 incomingEdgesData: Collection<InitControlFlowInfo>
         ): InitControlFlowInfo {
+            if (incomingEdgesData.size == 1) return incomingEdgesData.single()
             val variablesInScope = Sets.newHashSet<VariableDescriptor>()
             for (edgeData in incomingEdgesData) {
                 variablesInScope.addAll(edgeData.keys)