Debugger: Fix missing NOPs in optimized Unit.INSTANCE calls (KT-31702)

compiler/backend/src/org/jetbrains/kotlin/codegen/coroutines/RedundantLocalsEliminationMethodTransformer.kt

@@ -113,6 +113,7 @@ class RedundantLocalsEliminationMethodTransformer(private val languageVersionSet
         val insns =
             findPopPredecessors(methodNode) { it.isUnitInstance() || it.opcode == Opcodes.ACONST_NULL || it.opcode == Opcodes.ALOAD }
         for ((pred, pop) in insns) {
+            methodNode.instructions.insertBefore(pred, InsnNode(Opcodes.NOP))
             methodNode.instructions.removeAll(listOf(pred, pop))
         }
         return insns.isNotEmpty()

idea/testData/debugger/tinyApp/src/stepping/custom/coroutineUnitElimination.kt

@@ -0,0 +1,12 @@
+package coroutineUnitElimination
+
+suspend fun main() {
+    //Breakpoint!
+    Unit
+    //Breakpoint!
+    42
+    //Breakpoint!
+    Unit
+}
+
+// RESUME: 3

idea/testData/debugger/tinyApp/src/stepping/custom/coroutineUnitElimination.out

@@ -0,0 +1,11 @@
+LineBreakpoint created at coroutineUnitElimination.kt:5
+LineBreakpoint created at coroutineUnitElimination.kt:7
+LineBreakpoint created at coroutineUnitElimination.kt:9
+Run Java
+Connected to the target VM
+coroutineUnitElimination.kt:5
+coroutineUnitElimination.kt:7
+coroutineUnitElimination.kt:9
+Disconnected from the target VM
+
+Process finished with exit code 0

idea/tests/org/jetbrains/kotlin/idea/debugger/KotlinSteppingTestGenerated.java

@@ -1047,6 +1047,11 @@ public class KotlinSteppingTestGenerated extends AbstractKotlinSteppingTest {
             runTest("idea/testData/debugger/tinyApp/src/stepping/custom/coroutine.kt");
         }
 
+        @TestMetadata("coroutineUnitElimination.kt")
+        public void testCoroutineUnitElimination() throws Exception {
+            runTest("idea/testData/debugger/tinyApp/src/stepping/custom/coroutineUnitElimination.kt");
+        }
+
         @TestMetadata("crossinlineLiteral.kt")
         public void testCrossinlineLiteral() throws Exception {
             runTest("idea/testData/debugger/tinyApp/src/stepping/custom/crossinlineLiteral.kt");