Provide optimized code generation for for-in-withIndex for CharSequences

#KT-5177 In Progress

compiler/testData/codegen/box/controlStructures/forInCharSequenceWithIndex/forInCharSeqWithIndexStops.kt

@@ -0,0 +1,16 @@
+// IGNORE_BACKEND: JS, NATIVE
+// WITH_RUNTIME
+
+fun box(): String {
+    val s = StringBuilder()
+
+    val xs = StringBuilder("abcd")
+
+    for ((index, x) in xs.withIndex()) {
+        s.append("$index:$x;")
+        xs.setLength(0)
+    }
+
+    val ss = s.toString()
+    return if (ss == "0:a;") "OK" else "fail: '$ss'"
+}

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

@@ -0,0 +1,14 @@
+// WITH_RUNTIME
+
+val cs: CharSequence = "abcd"
+
+fun box(): String {
+    val s = StringBuilder()
+
+    for ((index, x) in cs.withIndex()) {
+        s.append("$index:$x;")
+    }
+
+    val ss = s.toString()
+    return if (ss == "0:a;1:b;2:c;3:d;") "OK" else "fail: '$ss'"
+}

compiler/testData/codegen/box/controlStructures/forInCharSequenceWithIndex/forInEmptyStringWithIndex.kt

@@ -0,0 +1,8 @@
+// WITH_RUNTIME
+
+fun box(): String {
+    for ((index, x) in "".withIndex()) {
+        return "Loop over empty String should not be executed"
+    }
+    return "OK"
+}

compiler/testData/codegen/box/controlStructures/forInCharSequenceWithIndex/forInStringWithIndex.kt

@@ -0,0 +1,12 @@
+// WITH_RUNTIME
+
+fun box(): String {
+    val s = StringBuilder()
+
+    for ((index, x) in "abcd".withIndex()) {
+        s.append("$index:$x;")
+    }
+
+    val ss = s.toString()
+    return if (ss == "0:a;1:b;2:c;3:d;") "OK" else "fail: '$ss'"
+}

compiler/testData/codegen/box/controlStructures/forInCharSequenceWithIndex/forInStringWithIndexNoElementVar.kt

@@ -0,0 +1,14 @@
+// WITH_RUNTIME
+
+val xs = "abcd"
+
+fun box(): String {
+    val s = StringBuilder()
+
+    for ((i, _) in xs.withIndex()) {
+        s.append("$i;")
+    }
+
+    val ss = s.toString()
+    return if (ss == "0;1;2;3;") "OK" else "fail: '$ss'"
+}

compiler/testData/codegen/box/controlStructures/forInCharSequenceWithIndex/forInStringWithIndexNoIndexVar.kt

@@ -0,0 +1,14 @@
+// WITH_RUNTIME
+
+val xs = "abcd"
+
+fun box(): String {
+    val s = StringBuilder()
+
+    for ((_, x) in xs.withIndex()) {
+        s.append("$x;")
+    }
+
+    val ss = s.toString()
+    return if (ss == "a;b;c;d;") "OK" else "fail: '$ss'"
+}

compiler/testData/codegen/box/controlStructures/forInCharSequenceWithIndex/forInStringWithIndexWithExplicitlyTypedIndexVariable.kt

@@ -0,0 +1,17 @@
+// WITH_RUNTIME
+
+val xs = "abcd"
+
+fun useAny(x: Any) {}
+
+fun box(): String {
+    val s = StringBuilder()
+
+    for ((index: Any, x) in xs.withIndex()) {
+        useAny(index)
+        s.append("$index:$x;")
+    }
+
+    val ss = s.toString()
+    return if (ss == "0:a;1:b;2:c;3:d;") "OK" else "fail: '$ss'"
+}