KT-6916: do not create Progression instances in for-in-downTo loops

compiler/testData/codegen/box/ranges/forInDownTo/forIntInDownTo.kt

@@ -0,0 +1,13 @@
+// WITH_RUNTIME
+
+import kotlin.test.assertEquals
+
+fun box(): String {
+    var sum = 0
+    for (i in 4 downTo 1) {
+        sum = sum * 10 + i
+    }
+    assertEquals(4321, sum)
+
+    return "OK"
+}

compiler/testData/codegen/box/ranges/forInDownTo/forIntInNonOptimizedDownTo.kt

@@ -0,0 +1,14 @@
+// WITH_RUNTIME
+
+import kotlin.test.assertEquals
+
+fun box(): String {
+    var sum = 0
+    val dt = 4 downTo 1
+    for (i in dt) {
+        sum = sum * 10 + i
+    }
+    assertEquals(4321, sum)
+
+    return "OK"
+}

compiler/testData/codegen/box/ranges/forInDownTo/forLongInDownTo.kt

@@ -0,0 +1,13 @@
+// WITH_RUNTIME
+
+import kotlin.test.assertEquals
+
+fun box(): String {
+    var sum = 0L
+    for (i in 4L downTo 1L) {
+        sum = sum * 10L + i
+    }
+    assertEquals(4321L, sum)
+
+    return "OK"
+}

compiler/testData/codegen/box/ranges/forInDownTo/forNullableIntInDownTo.kt

@@ -0,0 +1,13 @@
+// WITH_RUNTIME
+
+import kotlin.test.assertEquals
+
+fun box(): String {
+    var sum = 0
+    for (i: Int? in 4 downTo 1) {
+        sum = sum * 10 + (i ?: 0)
+    }
+    assertEquals(4321, sum)
+
+    return "OK"
+}

compiler/testData/codegen/bytecodeText/forLoop/forIntInDownTo.kt

@@ -0,0 +1,15 @@
+// WITH_RUNTIME
+
+fun test(): Int {
+    var sum = 0
+    for (i in 4 downTo 1) {
+        sum = sum * 10 + i
+    }
+    return sum
+}
+
+// 0 iterator
+// 0 getStart
+// 0 getEnd
+// 0 getFirst
+// 0 getLast

compiler/testData/codegen/bytecodeText/forLoop/primitiveProgression.kt

@@ -1,7 +1,8 @@
 fun f() {
     for (i in 0..5 step 2) {
     }
-    for (i in 5 downTo 1) {
+
+    for (i in 5 downTo 1 step 1) { // suppress optimized code generation for 'for-in-downTo'
     }
 }