Optimize control-flow analysis algorithm

There's no need to recalculate results if all of the
previous instructions' results remain unchanged.

It's a crucial optimizations because otherwise algorithm
can degrate to O(n * m) [n - instructions number, m - variables number]
even in a linear code like this:
var a_1 = 1
var a_2 = 1
...
var a_m = 1

We perform analysis iteration once, then we repeat it to be sure
that no changes happened and here for each instruction we're
starting to check if recomputed value is the same, that basically
compares maps of all the variables, so it works O(n * m)

After this change on the second iteration we won't recompute new values
as none of predecessor has been changed

compiler/frontend/src/org/jetbrains/kotlin/cfg/PseudocodeTraverser.kt

@@ -64,14 +64,13 @@ fun <I : ControlFlowInfo<*, *>> Pseudocode.collectData(
     val edgesMap = LinkedHashMap<Instruction, Edges<I>>()
     edgesMap.put(getStartInstruction(traversalOrder), Edges(initialInfo, initialInfo))
 
-    val changed = BooleanArray(1)
-    changed[0] = true
-    while (changed[0]) {
-        changed[0] = false
+    val changed = mutableMapOf<Instruction, Boolean>()
+    do {
         collectDataFromSubgraph(
                 traversalOrder, edgesMap,
                 mergeEdges, updateEdge, Collections.emptyList<Instruction>(), changed, false)
-    }
+    } while (changed.any { it.value })
+
     return edgesMap
 }
 
@@ -81,7 +80,7 @@ private fun <I : ControlFlowInfo<*, *>> Pseudocode.collectDataFromSubgraph(
         mergeEdges: (Instruction, Collection<I>) -> Edges<I>,
         updateEdge: (Instruction, Instruction, I) -> I,
         previousSubGraphInstructions: Collection<Instruction>,
-        changed: BooleanArray,
+        changed: MutableMap<Instruction, Boolean>,
         isLocal: Boolean
 ) {
     val instructions = getInstructions(traversalOrder)
@@ -107,7 +106,13 @@ private fun <I : ControlFlowInfo<*, *>> Pseudocode.collectDataFromSubgraph(
             updateEdgeDataForInstruction(instruction, previousValue, updatedValue, edgesMap, changed)
             continue
         }
+
+
         val previousDataValue = edgesMap[instruction]
+        if (previousDataValue != null && previousInstructions.all { changed[it] == false }) {
+            changed[instruction] = false
+            continue
+        }
 
         val incomingEdgesData = HashSet<I>()
 
@@ -139,11 +144,19 @@ private fun getPreviousIncludingSubGraphInstructions(
 }
 
 private fun <I : ControlFlowInfo<*, *>> updateEdgeDataForInstruction(
-        instruction: Instruction, previousValue: Edges<I>?, newValue: Edges<I>?, edgesMap: MutableMap<Instruction, Edges<I>>, changed: BooleanArray) {
+        instruction: Instruction,
+        previousValue: Edges<I>?,
+        newValue: Edges<I>?,
+        edgesMap: MutableMap<Instruction, Edges<I>>,
+        changed: MutableMap<Instruction, Boolean>
+) {
     if (previousValue != newValue && newValue != null) {
-        changed[0] = true
+        changed[instruction] = true
         edgesMap.put(instruction, newValue)
     }
+    else {
+        changed[instruction] = false
+    }
 }
 
 data class Edges<out T>(val incoming: T, val outgoing: T)