JVM don't merge local values in FixStackAnalyzer

We care only about stacks there.
This yields about 10-15% in a pathological case such as KT-41510.

compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/fixStack/FixStackAnalyzer.kt

@@ -29,6 +29,7 @@ import org.jetbrains.org.objectweb.asm.tree.AbstractInsnNode
 import org.jetbrains.org.objectweb.asm.tree.JumpInsnNode
 import org.jetbrains.org.objectweb.asm.tree.LabelNode
 import org.jetbrains.org.objectweb.asm.tree.MethodNode
+import org.jetbrains.org.objectweb.asm.tree.analysis.AnalyzerException
 import org.jetbrains.org.objectweb.asm.tree.analysis.BasicValue
 import org.jetbrains.org.objectweb.asm.tree.analysis.Frame
 import org.jetbrains.org.objectweb.asm.tree.analysis.Interpreter
@@ -88,7 +89,9 @@ internal class FixStackAnalyzer(
 
     private val analyzer = InternalAnalyzer(owner)
 
-    private inner class InternalAnalyzer(owner: String) : FlexibleMethodAnalyzer<BasicValue>(owner, method, OptimizationBasicInterpreter()) {
+    private inner class InternalAnalyzer(owner: String) :
+        FlexibleMethodAnalyzer<BasicValue>(owner, method, OptimizationBasicInterpreter()) {
+
         val spilledStacks = hashMapOf<AbstractInsnNode, List<BasicValue>>()
         var maxExtraStackSize = 0; private set
 
@@ -166,13 +169,38 @@ internal class FixStackAnalyzer(
                 }
             }
 
-            override fun getStack(i: Int): BasicValue {
-                return if (i < super.getMaxStackSize()) {
-                    super.getStack(i)
+            override fun setStack(i: Int, value: BasicValue) {
+                if (i < super.getMaxStackSize()) {
+                    super.setStack(i, value)
                 } else {
-                    extraStack[i - maxStackSize]
+                    extraStack[i - maxStackSize] = value
                 }
             }
+
+            override fun merge(frame: Frame<out BasicValue>, interpreter: Interpreter<BasicValue>): 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
+            }
         }
 
         private fun FixStackFrame.executeBeforeInlineCallMarker(insn: AbstractInsnNode) {

compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirBlackBoxCodegenTestGenerated.java

@@ -8112,6 +8112,12 @@ public class FirBlackBoxCodegenTestGenerated extends AbstractFirBlackBoxCodegenT
             runTest("compiler/testData/codegen/box/controlStructures/quicksort.kt");
         }
 
+        @Test
+        @TestMetadata("slowHtmlLikeDsl.kt")
+        public void testSlowHtmlLikeDsl() throws Exception {
+            runTest("compiler/testData/codegen/box/controlStructures/slowHtmlLikeDsl.kt");
+        }
+
         @Test
         @TestMetadata("tcbInEliminatedCondition.kt")
         public void testTcbInEliminatedCondition() throws Exception {

compiler/testData/codegen/box/controlStructures/slowHtmlLikeDsl.kt

@@ -0,0 +1,45 @@
+// TARGET_BACKEND: JVM
+//  ^ this test might be rather slow
+
+class Builder(var content: String)
+
+fun Builder.begin(t: String) {
+    content += "<$t>"
+}
+
+fun Builder.text(t: String) {
+    content += t
+}
+
+fun Builder.end(t: String) {
+    content += "</$t>"
+}
+
+fun err(e: Throwable) {}
+
+inline fun Builder.tag(t: String, body: Builder.() -> Unit) {
+    begin(t)
+    try {
+        body()
+    } catch (e: Throwable) {
+        err(e)
+    } finally {
+        end(t)
+    }
+}
+
+inline fun Builder.t2(body: Builder.() -> Unit) {
+    tag("t", body)
+    tag("t", body)
+}
+
+val expectedLength = 1906
+
+fun box(): String {
+    val b = Builder("")
+    b.t2 { t2 { t2 { t2 { t2 { t2 { t2 { text("1") } } } } } } }
+    if (b.content.length != expectedLength)
+        return "${b.content.length}"
+    else
+        return "OK"
+}

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/BlackBoxCodegenTestGenerated.java

@@ -8112,6 +8112,12 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             runTest("compiler/testData/codegen/box/controlStructures/quicksort.kt");
         }
 
+        @Test
+        @TestMetadata("slowHtmlLikeDsl.kt")
+        public void testSlowHtmlLikeDsl() throws Exception {
+            runTest("compiler/testData/codegen/box/controlStructures/slowHtmlLikeDsl.kt");
+        }
+
         @Test
         @TestMetadata("tcbInEliminatedCondition.kt")
         public void testTcbInEliminatedCondition() throws Exception {

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/IrBlackBoxCodegenTestGenerated.java

@@ -8112,6 +8112,12 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
             runTest("compiler/testData/codegen/box/controlStructures/quicksort.kt");
         }
 
+        @Test
+        @TestMetadata("slowHtmlLikeDsl.kt")
+        public void testSlowHtmlLikeDsl() throws Exception {
+            runTest("compiler/testData/codegen/box/controlStructures/slowHtmlLikeDsl.kt");
+        }
+
         @Test
         @TestMetadata("tcbInEliminatedCondition.kt")
         public void testTcbInEliminatedCondition() throws Exception {

compiler/tests-gen/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java

@@ -6217,6 +6217,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
             runTest("compiler/testData/codegen/box/controlStructures/quicksort.kt");
         }
 
+        @TestMetadata("slowHtmlLikeDsl.kt")
+        public void testSlowHtmlLikeDsl() throws Exception {
+            runTest("compiler/testData/codegen/box/controlStructures/slowHtmlLikeDsl.kt");
+        }
+
         @TestMetadata("tcbInEliminatedCondition.kt")
         public void testTcbInEliminatedCondition() throws Exception {
             runTest("compiler/testData/codegen/box/controlStructures/tcbInEliminatedCondition.kt");