[IR] Copied string concat lowering back to K/N

It is only used in K/N backend - no reason to keep it in the common part

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/KonanLoweringPhases.kt

@@ -12,6 +12,7 @@ import org.jetbrains.kotlin.backend.common.phaser.*
 import org.jetbrains.kotlin.backend.konan.lower.*
 import org.jetbrains.kotlin.backend.konan.lower.FinallyBlocksLowering
 import org.jetbrains.kotlin.backend.konan.lower.InitializersLowering
+import org.jetbrains.kotlin.backend.konan.lower.StringConcatenationLowering
 import org.jetbrains.kotlin.ir.declarations.IrFile
 import org.jetbrains.kotlin.ir.declarations.IrModuleFragment
 

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/lower/StringConcatenationLowering.kt

@@ -0,0 +1,126 @@
+package org.jetbrains.kotlin.backend.konan.lower
+
+import org.jetbrains.kotlin.backend.common.CommonBackendContext
+import org.jetbrains.kotlin.backend.common.FileLoweringPass
+import org.jetbrains.kotlin.backend.common.atMostOne
+import org.jetbrains.kotlin.backend.common.lower.createIrBuilder
+import org.jetbrains.kotlin.backend.common.lower.irBlock
+import org.jetbrains.kotlin.ir.IrStatement
+import org.jetbrains.kotlin.ir.builders.*
+import org.jetbrains.kotlin.ir.declarations.IrDeclarationBase
+import org.jetbrains.kotlin.ir.declarations.IrFile
+import org.jetbrains.kotlin.ir.declarations.IrSimpleFunction
+import org.jetbrains.kotlin.ir.declarations.IrSymbolDeclaration
+import org.jetbrains.kotlin.ir.expressions.IrExpression
+import org.jetbrains.kotlin.ir.expressions.IrStringConcatenation
+import org.jetbrains.kotlin.ir.types.IrType
+import org.jetbrains.kotlin.ir.types.isNullable
+import org.jetbrains.kotlin.ir.types.isNullableAny
+import org.jetbrains.kotlin.ir.util.constructors
+import org.jetbrains.kotlin.ir.util.functions
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
+import org.jetbrains.kotlin.ir.visitors.transformChildrenVoid
+import org.jetbrains.kotlin.name.Name
+
+/**
+ * This lowering pass replaces [IrStringConcatenation]s with StringBuilder appends.
+ */
+class StringConcatenationLowering(val context: CommonBackendContext) : FileLoweringPass {
+    override fun lower(irFile: IrFile) {
+        irFile.transformChildrenVoid(StringConcatenationTransformer(this))
+    }
+}
+
+private class StringConcatenationTransformer(val lower: StringConcatenationLowering) : IrElementTransformerVoid() {
+
+    private val buildersStack = mutableListOf<IrBuilderWithScope>()
+    private val context = lower.context
+    private val irBuiltIns = context.irBuiltIns
+
+    private val typesWithSpecialAppendFunction = irBuiltIns.primitiveIrTypes + irBuiltIns.stringType
+
+    private val nameToString = Name.identifier("toString")
+    private val nameAppend = Name.identifier("append")
+
+    private val stringBuilder = context.ir.symbols.stringBuilder.owner
+
+    //TODO: calculate and pass string length to the constructor.
+    private val constructor = stringBuilder.constructors.single {
+        it.valueParameters.size == 0
+    }
+
+    private val toStringFunction = stringBuilder.functions.single {
+        it.valueParameters.size == 0 && it.name == nameToString
+    }
+
+    private val defaultAppendFunction = stringBuilder.functions.single {
+        it.name == nameAppend &&
+                it.valueParameters.size == 1 &&
+                it.valueParameters.single().type.isNullableAny()
+    }
+
+    private val appendFunctions: Map<IrType, IrSimpleFunction?> =
+            typesWithSpecialAppendFunction.map { type ->
+                type to stringBuilder.functions.toList().atMostOne {
+                    it.name == nameAppend && it.valueParameters.singleOrNull()?.type == type
+                }
+            }.toMap()
+
+    private fun typeToAppendFunction(type: IrType): IrSimpleFunction {
+        return appendFunctions[type] ?: defaultAppendFunction
+    }
+
+    override fun visitStringConcatenation(expression: IrStringConcatenation): IrExpression {
+        assert(!buildersStack.isEmpty())
+
+        expression.transformChildrenVoid(this)
+        val blockBuilder = buildersStack.last()
+
+        val arguments = expression.arguments
+        return when (arguments.size) {
+            0 -> blockBuilder.irString("")
+            1 -> {
+                val argument = arguments[0]
+                if (argument.type.isNullable())
+                    blockBuilder.irCall(context.ir.symbols.extensionToString).apply {
+                        extensionReceiver = argument
+                    }
+                else blockBuilder.irCall(
+                        context.irBuiltIns.anyClass.functions
+                                .single { it.owner.name.asString() == "toString" }).apply {
+                    dispatchReceiver = argument
+                }
+            }
+            else -> {
+                blockBuilder.irBlock(expression) {
+                    val stringBuilderImpl = createTmpVariable(irCall(constructor))
+                    expression.arguments.forEach { arg ->
+                        val appendFunction = typeToAppendFunction(arg.type)
+                        +irCall(appendFunction).apply {
+                            dispatchReceiver = irGet(stringBuilderImpl)
+                            putValueArgument(0, arg)
+                        }
+                    }
+                    +irCall(toStringFunction).apply {
+                        dispatchReceiver = irGet(stringBuilderImpl)
+                    }
+                }
+            }
+        }
+    }
+
+    override fun visitDeclaration(declaration: IrDeclarationBase): IrStatement {
+        if (declaration !is IrSymbolDeclaration<*>) {
+            return super.visitDeclaration(declaration)
+        }
+
+        with(declaration) {
+            buildersStack.add(
+                    context.createIrBuilder(declaration.symbol, startOffset, endOffset)
+            )
+            transformChildrenVoid(this@StringConcatenationTransformer)
+            buildersStack.removeAt(buildersStack.lastIndex)
+            return this@with
+        }
+    }
+}