Rename "lowerBound/upperBound" to "first/last" and move loopVariable to

ForLoopHeader base class.

These terms are less loaded and less confusing, especially with "downTo"
progressions, and once we start handling "reversed()".

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

@@ -8,17 +8,17 @@ package org.jetbrains.kotlin.backend.common.lower.loops
 import org.jetbrains.kotlin.backend.common.CommonBackendContext
 import org.jetbrains.kotlin.backend.common.FileLoweringPass
 import org.jetbrains.kotlin.backend.common.IrElementTransformerVoidWithContext
-import org.jetbrains.kotlin.backend.common.lower.DeclarationIrBuilder
 import org.jetbrains.kotlin.backend.common.lower.createIrBuilder
 import org.jetbrains.kotlin.backend.common.lower.irIfThen
 import org.jetbrains.kotlin.backend.common.phaser.makeIrFilePhase
 import org.jetbrains.kotlin.ir.IrStatement
-import org.jetbrains.kotlin.ir.builders.*
+import org.jetbrains.kotlin.ir.builders.irCallOp
+import org.jetbrains.kotlin.ir.builders.irGet
+import org.jetbrains.kotlin.ir.builders.irSetVar
 import org.jetbrains.kotlin.ir.declarations.IrFile
 import org.jetbrains.kotlin.ir.declarations.IrVariable
 import org.jetbrains.kotlin.ir.expressions.*
 import org.jetbrains.kotlin.ir.expressions.impl.IrCompositeImpl
-import org.jetbrains.kotlin.ir.expressions.impl.IrConstImpl
 import org.jetbrains.kotlin.ir.symbols.IrVariableSymbol
 import org.jetbrains.kotlin.ir.types.toKotlinType
 import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
@@ -178,9 +178,7 @@ private class RangeLoopTransformer(
             forLoopInfo.inductionVariable.type.toKotlinType(),
             forLoopInfo.step.type.toKotlinType()
         )
-        if (forLoopInfo is ProgressionLoopHeader) {
-            forLoopInfo.loopVariable = variable
-        }
+        forLoopInfo.loopVariable = variable
         return with(context.createIrBuilder(getScopeOwnerSymbol(), initializer.startOffset, initializer.endOffset)) {
             variable.initializer = forLoopInfo.initializeLoopVariable(symbols, this)
             val increment = irSetVar(

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

@@ -58,8 +58,8 @@ internal enum class ProgressionDirection { DECREASING, INCREASING, UNKNOWN }
 // Information about loop that is required by HeaderProcessor to build ForLoopHeader
 internal sealed class HeaderInfo(
     val progressionType: ProgressionType,
-    val lowerBound: IrExpression,
-    val upperBound: IrExpression,
+    val first: IrExpression,
+    val last: IrExpression,
     val step: IrExpression,
     val closed: Boolean
 ) {
@@ -78,22 +78,22 @@ internal sealed class HeaderInfo(
 
 internal class ProgressionHeaderInfo(
     progressionType: ProgressionType,
-    lowerBound: IrExpression,
-    upperBound: IrExpression,
+    first: IrExpression,
+    last: IrExpression,
     step: IrExpression,
     closed: Boolean = true,
     val additionalNotEmptyCondition: IrExpression? = null
-) : HeaderInfo(progressionType, lowerBound, upperBound, step, closed)
+) : HeaderInfo(progressionType, first, last, step, closed)
 
 internal class ArrayHeaderInfo(
-    lowerBound: IrExpression,
-    upperBound: IrExpression,
+    first: IrExpression,
+    last: IrExpression,
     step: IrExpression,
     val arrayVariable: IrVariable
 ) : HeaderInfo(
     ProgressionType.INT_PROGRESSION,
-    lowerBound,
-    upperBound,
+    first,
+    last,
     step,
     closed = false
 )

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

@@ -32,7 +32,8 @@ internal sealed class ForLoopHeader(
     val last: IrVariable,
     val step: IrVariable,
     val progressionType: ProgressionType,
-    val needsEmptinessCheck: Boolean
+    val needsEmptinessCheck: Boolean,
+    var loopVariable: IrVariable? = null
 ) {
     abstract fun initializeLoopVariable(symbols: Symbols<CommonBackendContext>, builder: DeclarationIrBuilder): IrExpression
 
@@ -48,8 +49,7 @@ internal class ProgressionLoopHeader(
     inductionVariable: IrVariable,
     bound: IrVariable,
     last: IrVariable,
-    step: IrVariable,
-    var loopVariable: IrVariable? = null
+    step: IrVariable
 ) : ForLoopHeader(inductionVariable, bound, last, step, headerInfo.progressionType, needsEmptinessCheck = true) {
 
     override fun initializeLoopVariable(symbols: Symbols<CommonBackendContext>, builder: DeclarationIrBuilder) = with(builder) {
@@ -200,14 +200,14 @@ internal class HeaderProcessor(
                 // Due to features of PSI2IR we can obtain nullable arguments here while actually
                 // they are non-nullable (the frontend takes care about this). So we need to cast them to non-nullable.
                 val inductionVariable = scope.createTemporaryVariable(
-                    lowerBound.castIfNecessary(progressionType),
+                    first.castIfNecessary(progressionType),
                     nameHint = "inductionVariable",
                     isMutable = true,
                     origin = IrDeclarationOrigin.FOR_LOOP_IMPLICIT_VARIABLE
                 )
 
                 val upperBoundTmpVariable = scope.createTemporaryVariable(
-                    ensureNotNullable(upperBound.castIfNecessary(progressionType)),
+                    ensureNotNullable(last.castIfNecessary(progressionType)),
                     nameHint = "upperBound",
                     origin = IrDeclarationOrigin.FOR_LOOP_IMPLICIT_VARIABLE
                 )

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

@@ -38,8 +38,8 @@ internal class RangeToHandler(private val context: CommonBackendContext, private
         with(context.createIrBuilder(call.symbol, call.startOffset, call.endOffset)) {
             ProgressionHeaderInfo(
                 data,
-                lowerBound = call.dispatchReceiver!!,
-                upperBound = call.getValueArgument(0)!!,
+                first = call.dispatchReceiver!!,
+                last = call.getValueArgument(0)!!,
                 step = irInt(1)
             )
         }
@@ -57,8 +57,8 @@ internal class DownToHandler(private val context: CommonBackendContext, private
         with(context.createIrBuilder(call.symbol, call.startOffset, call.endOffset)) {
             ProgressionHeaderInfo(
                 data,
-                lowerBound = call.extensionReceiver!!,
-                upperBound = call.getValueArgument(0)!!,
+                first = call.extensionReceiver!!,
+                last = call.getValueArgument(0)!!,
                 step = irInt(-1)
             )
         }
@@ -98,8 +98,8 @@ internal class UntilHandler(private val context: CommonBackendContext, private v
             // TODO: Do not add additionalEmptinessCondition if "bound" is const and > MIN_VALUE
             ProgressionHeaderInfo(
                 data,
-                lowerBound = call.extensionReceiver!!,
-                upperBound = call.getValueArgument(0)!!,
+                first = call.extensionReceiver!!,
+                last = call.getValueArgument(0)!!,
                 step = irInt(1),
                 closed = false,
                 additionalNotEmptyCondition = buildMinValueConditionIfNecessary(data, call.getValueArgument(0)!!)
@@ -194,8 +194,8 @@ internal class ArrayIterationHandler(val context: CommonBackendContext) : Header
                 dispatchReceiver = irGet(arrayReference)
             }
             ArrayHeaderInfo(
-                lowerBound = irInt(0),
-                upperBound = upperBound,
+                first = irInt(0),
+                last = upperBound,
                 step = irInt(1),
                 arrayVariable = arrayReference
             )