From e72d24960d827ca3ad2a22abfc47099dbfe76748 Mon Sep 17 00:00:00 2001
From: Dmitry Petrov <dmitry.petrov@jetbrains.com>
Date: Tue, 20 Jul 2021 08:08:11 +0300
Subject: [PATCH] JVM we don't merge frames in stack normalization

---
 .../optimization/fixStack/FixStackAnalyzer.kt | 23 +------------------
 .../HackedFixStackMethodAnalyzerBase.kt       |  3 +++
 2 files changed, 4 insertions(+), 22 deletions(-)

diff --git a/compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/fixStack/FixStackAnalyzer.kt b/compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/fixStack/FixStackAnalyzer.kt
index 85a45ce1261..6cd24cbb5d0 100644
--- a/compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/fixStack/FixStackAnalyzer.kt
+++ b/compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/fixStack/FixStackAnalyzer.kt
@@ -179,28 +179,7 @@ internal class FixStackAnalyzer(
             }
 
             override fun merge(frame: Frame<out FixStackValue>, interpreter: Interpreter<FixStackValue>): Boolean {
-                val other = frame as FixStackFrame
-                if (stackSizeWithExtra != other.stackSizeWithExtra) {
-                    throw AnalyzerException(null, "Incompatible stack heights")
-                }
-                var changed = false
-                for (i in 0 until stackSize) {
-                    val v0 = super.getStack(i)
-                    val vm = interpreter.merge(v0, other.getStack(i))
-                    if (vm != v0) {
-                        super.setStack(i, vm)
-                        changed = true
-                    }
-                }
-                for (i in 0 until extraStack.size) {
-                    val v0 = extraStack[i]
-                    val vm = interpreter.merge(v0, other.extraStack[i])
-                    if (vm != v0) {
-                        extraStack[i] = vm
-                        changed = true
-                    }
-                }
-                return changed
+                throw UnsupportedOperationException("Stack normalization should not merge frames")
             }
         }
 
diff --git a/compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/fixStack/HackedFixStackMethodAnalyzerBase.kt b/compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/fixStack/HackedFixStackMethodAnalyzerBase.kt
index 9b1aa1e0737..fc4e699c187 100644
--- a/compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/fixStack/HackedFixStackMethodAnalyzerBase.kt
+++ b/compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/fixStack/HackedFixStackMethodAnalyzerBase.kt
@@ -72,6 +72,9 @@ internal open class HackedFixStackMethodAnalyzerBase<V : Value>(
     fun analyze(): Array<Frame<V>?> {
         if (nInsns == 0) return frames
 
+        // This is a very specific version of method bytecode analyzer that doesn't perform any DFA,
+        // but infers stack types for reachable instructions instead.
+
         checkAssertions()
 
         computeExceptionEdges()