[IR] For loop lowering for CharacterSequence.indices.

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/loops/HeaderInfo.kt

@@ -212,7 +212,8 @@ internal class HeaderInfoBuilder(context: CommonBackendContext, private val scop
     )
 
     private val progressionHandlers = listOf(
-        IndicesHandler(context),
+        ArrayIndicesHandler(context),
+        CharSequenceIndicesHandler(context),
         UntilHandler(context, progressionElementTypes),
         DownToHandler(context, progressionElementTypes),
         RangeToHandler(context, progressionElementTypes)

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/loops/ProgressionHandlers.kt

@@ -219,22 +219,17 @@ internal class UntilHandler(private val context: CommonBackendContext, private v
 }
 
 /** Builds a [HeaderInfo] for progressions built using the `indices` extension property. */
-internal class IndicesHandler(private val context: CommonBackendContext) : ProgressionHandler {
+internal abstract class IndicesHandler(private val context: CommonBackendContext) : ProgressionHandler {
 
-    override val matcher = SimpleCalleeMatcher {
+    // TODO: Handle Collection<*>.indices
-        // TODO: Handle Collection<*>.indices
-        // TODO: Handle CharSequence.indices
-        extensionReceiver { it != null && it.type.run { isArray() || isPrimitiveArray() } }
-        fqName { it == FqName("kotlin.collections.<get-indices>") }
-        parameterCount { it == 0 }
-    }
 
     override fun build(expression: IrCall, data: ProgressionType, scopeOwner: IrSymbol): HeaderInfo? =
         with(context.createIrBuilder(scopeOwner, expression.startOffset, expression.endOffset)) {
             // `last = array.size - 1` (last is inclusive) for the loop `for (i in array.indices)`.
-            val arraySizeProperty = expression.extensionReceiver!!.type.getClass()!!.properties.first { it.name.asString() == "size" }
+            val receiver = expression.extensionReceiver!!
-            val last = irCall(arraySizeProperty.getter!!).apply {
+            val sizeProperty = receiver.type.getClass()!!.properties.first { it.name.asString() == sizePropertyName() }
-                dispatchReceiver = expression.extensionReceiver
+            val last = irCall(sizeProperty.getter!!).apply {
+                dispatchReceiver = receiver
             }.decrement()
 
             ProgressionHeaderInfo(
@@ -246,6 +241,29 @@ internal class IndicesHandler(private val context: CommonBackendContext) : Progr
                 direction = ProgressionDirection.INCREASING
             )
         }
+
+    internal abstract fun sizePropertyName() : String
+}
+
+internal class ArrayIndicesHandler(context: CommonBackendContext) : IndicesHandler(context) {
+    override val matcher = SimpleCalleeMatcher {
+        extensionReceiver { it != null && it.type.run { isArray() || isPrimitiveArray() } }
+        fqName { it == FqName("kotlin.collections.<get-indices>") }
+        parameterCount { it == 0 }
+    }
+
+    override fun sizePropertyName(): String = "size"
+}
+
+internal class CharSequenceIndicesHandler(context: CommonBackendContext) : IndicesHandler(context) {
+
+    override val matcher = SimpleCalleeMatcher {
+        extensionReceiver { it != null && it.type.run { isSubtypeOfClass(context.ir.symbols.charSequence)} }
+        fqName { it == FqName("kotlin.text.<get-indices>") }
+        parameterCount { it == 0 }
+    }
+
+    override fun sizePropertyName(): String = "length"
 }
 
 /** Builds a [HeaderInfo] for calls to reverse an iterable. */

compiler/testData/codegen/bytecodeText/forLoop/forInIndices/forInCharSequenceIndices.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
 fun test(s: CharSequence): Int {
     var result = 0
     for (i in s.indices) {
@@ -7,12 +6,22 @@ fun test(s: CharSequence): Int {
     return result
 }
 
+// JVM non-IR uses while.
+// JVM IR uses if + do-while.
+
 // 0 iterator
 // 0 getStart
 // 0 getEnd
 // 0 getFirst
 // 0 getLast
 
+// JVM_TEMPLATES
 // 0 IF_ICMPGT
 // 0 IF_ICMPEQ
 // 1 IF_ICMPGE
+// 1 IF
+
+// JVM_IR_TEMPLATES
+// 1 IF_ICMPGT
+// 1 IF_ICMPLE
+// 2 IF

compiler/testData/codegen/bytecodeText/forLoop/forInReversed/forInReversedCharSequenceIndices.kt

@@ -1,5 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
-// NOTE: Enable once CharSequence.indices is handled
 import kotlin.test.*
 
 fun box(): String {
@@ -13,6 +11,9 @@ fun box(): String {
     return "OK"
 }
 
+// JVM non-IR uses while.
+// JVM IR uses if + do-while.
+
 // 0 reversed
 // 0 iterator
 // 0 getStart
@@ -20,5 +21,12 @@ fun box(): String {
 // 0 getFirst
 // 0 getLast
 // 0 getStep
-// 1 IF(_ICMPG|L)T
+
-// 1 IF
+// JVM_TEMPLATES
+// 1 IFLT
+// 1 IF
+
+// JVM_IR_TEMPLATES
+// 1 IF_ICMPGT
+// 1 IF_ICMPLE
+// 2 IF