[JVM_IR, IR] Remove more needless temporary variables.

Avoid using a separate origin for temporary variables introduced
for for loops. That doesn't add anything and gives one more case
for optimizations to deal with.

Extend the JVM specific optimizations to remove temporary
variables to deal with more cases encountered in for loops
lowering.

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

@@ -310,8 +310,7 @@ internal class HeaderProcessor(
                         progressionType.elementCastFunctionName
                     ),
                     nameHint = "inductionVariable",
-                    isMutable = true,
-                    origin = IrDeclarationOrigin.FOR_LOOP_IMPLICIT_VARIABLE
+                    isMutable = true
                 )
 
                 // Due to features of PSI2IR we can obtain nullable arguments here while actually
@@ -325,8 +324,7 @@ internal class HeaderProcessor(
                             progressionType.elementCastFunctionName
                         )
                     ),
-                    nameHint = "last",
-                    origin = IrDeclarationOrigin.FOR_LOOP_IMPLICIT_VARIABLE
+                    nameHint = "last"
                 )
 
                 val stepValue = scope.createTemporaryVariable(
@@ -336,8 +334,7 @@ internal class HeaderProcessor(
                             progressionType.stepCastFunctionName
                         )
                     ),
-                    nameHint = "step",
-                    origin = IrDeclarationOrigin.FOR_LOOP_IMPLICIT_VARIABLE
+                    nameHint = "step"
                 )
 
                 return when (headerInfo) {

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

@@ -351,8 +351,7 @@ internal abstract class IndexedGetIterationHandler(protected val context: Common
             // This also ensures that the semantics of re-assignment of array variables used in the loop is consistent with the semantics
             // proposed in https://youtrack.jetbrains.com/issue/KT-21354.
             val arrayReference = scope.createTemporaryVariable(
-                expression, nameHint = "indexedObject",
-                origin = IrDeclarationOrigin.FOR_LOOP_IMPLICIT_VARIABLE
+                expression, nameHint = "indexedObject"
             )
 
             val last = irCall(expression.type.sizePropertyGetter).apply {

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/ExpressionCodegen.kt

@@ -262,8 +262,7 @@ class ExpressionCodegen(
         info.variables.forEach {
             when (it.declaration.origin) {
                 IrDeclarationOrigin.IR_TEMPORARY_VARIABLE,
-                IrDeclarationOrigin.FOR_LOOP_ITERATOR,
-                IrDeclarationOrigin.FOR_LOOP_IMPLICIT_VARIABLE -> {
+                IrDeclarationOrigin.FOR_LOOP_ITERATOR -> {
                     // Ignore implicitly created variables
                 }
                 else -> {

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/JvmBuiltinOptimizationLowering.kt

@@ -178,8 +178,7 @@ class JvmBuiltinOptimizationLowering(val context: JvmBackendContext) : FileLower
                         statement.initializer is IrConst<*>
             }
 
-            override fun visitBlock(expression: IrBlock): IrExpression {
-                expression.transformChildrenVoid(this)
+            private fun removeUnnecessaryTemporaryVariables(statements: MutableList<IrStatement>) {
                 // Remove declarations of immutable temporary variables with constant values.
                 // IrGetValue operations for such temporary variables are replaced
                 // by the initializer IrConst. This makes sure that we do not load and
@@ -208,9 +207,10 @@ class JvmBuiltinOptimizationLowering(val context: JvmBackendContext) : FileLower
                 //
                 // which allows the equality check to be simplified away and we end up with
                 // just a const string load.
-                expression.statements.removeIf {
+                statements.removeIf {
                     isImmutableTemporaryVariableWithConstantValue(it)
                 }
+
                 // Remove a block that contains only two statements: the declaration of a temporary
                 // variable and a load of the value of that temporary variable with just the initializer
                 // for the temporary variable. We only perform this transformation for compiler generated
@@ -242,18 +242,28 @@ class JvmBuiltinOptimizationLowering(val context: JvmBackendContext) : FileLower
                 //      42.toLong()
                 //
                 // Doing so we avoid local loads and stores.
-                if (expression.statements.size == 2) {
-                    val first = expression.statements[0]
-                    val second = expression.statements[1]
+                if (statements.size == 2) {
+                    val first = statements[0]
+                    val second = statements[1]
                     if (first is IrVariable
                         && first.origin == IrDeclarationOrigin.IR_TEMPORARY_VARIABLE
                         && second is IrGetValue
-                        && first.symbol == second.symbol
-                    ) {
-                        expression.statements.clear()
-                        first.initializer?.let { expression.statements.add(it) }
+                        && first.symbol == second.symbol) {
+                        statements.clear()
+                        first.initializer?.let { statements.add(it) }
                     }
                 }
+            }
+
+            override fun visitBlockBody(body: IrBlockBody): IrBody {
+                body.transformChildrenVoid(this)
+                removeUnnecessaryTemporaryVariables(body.statements)
+                return body
+            }
+
+            override fun visitContainerExpression(expression: IrContainerExpression): IrExpression {
+                expression.transformChildrenVoid(this)
+                removeUnnecessaryTemporaryVariables(expression.statements)
                 return expression
             }
 

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/LoopExpressionGenerator.kt

@@ -197,7 +197,7 @@ class LoopExpressionGenerator(statementGenerator: StatementGenerator) : Statemen
                     irNextCall
                 )
             } else {
-                scope.createTemporaryVariable(irNextCall, "loop_parameter", origin = IrDeclarationOrigin.FOR_LOOP_IMPLICIT_VARIABLE)
+                scope.createTemporaryVariable(irNextCall, "loop_parameter")
             }
         irInnerBody.statements.add(irLoopParameter)
 

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

@@ -9,5 +9,5 @@ fun test() {
 // 0 hasNext
 // 0 nextChar
 // 0 INVOKEINTERFACE
-// 1 ISTORE 4
-// 1 ILOAD 4
+// 1 charAt \(I\)C
+// 1 length \(\)I

compiler/testData/ir/irText/expressions/for.txt

@@ -41,7 +41,7 @@ FILE fqName:<root> fileName:/for.kt
           condition: CALL 'public abstract fun hasNext (): kotlin.Boolean declared in kotlin.collections.Iterator' type=kotlin.Boolean origin=FOR_LOOP_HAS_NEXT
             $this: GET_VAR 'val tmp0_iterator: kotlin.collections.Iterator<kotlin.Pair<kotlin.Int, kotlin.String>> [val] declared in <root>.testDestructuring' type=kotlin.collections.Iterator<kotlin.Pair<kotlin.Int, kotlin.String>> origin=null
           body: BLOCK type=kotlin.Unit origin=FOR_LOOP_INNER_WHILE
-            VAR FOR_LOOP_IMPLICIT_VARIABLE name:tmp1_loop_parameter type:kotlin.Pair<kotlin.Int, kotlin.String> [val]
+            VAR IR_TEMPORARY_VARIABLE name:tmp1_loop_parameter type:kotlin.Pair<kotlin.Int, kotlin.String> [val]
               CALL 'public abstract fun next (): T of kotlin.collections.Iterator declared in kotlin.collections.Iterator' type=kotlin.Pair<kotlin.Int, kotlin.String> origin=FOR_LOOP_NEXT
                 $this: GET_VAR 'val tmp0_iterator: kotlin.collections.Iterator<kotlin.Pair<kotlin.Int, kotlin.String>> [val] declared in <root>.testDestructuring' type=kotlin.collections.Iterator<kotlin.Pair<kotlin.Int, kotlin.String>> origin=null
             VAR name:i type:kotlin.Int [val]