backend: statically instantiate kotlin.Unit

and optimize IrGetObjectValue(Unit)

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

@@ -11,6 +11,7 @@ import org.jetbrains.kotlin.resolve.descriptorUtil.*
 import org.jetbrains.kotlin.resolve.scopes.MemberScope
 import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.kotlin.types.TypeUtils
+import org.jetbrains.kotlin.types.typeUtil.isUnit
 import org.jetbrains.kotlin.util.OperatorNameConventions
 
 /**
@@ -147,3 +148,5 @@ internal val FunctionDescriptor.isFunctionInvoke: Boolean
         return dispatchReceiver.type.isFunctionType &&
                 this.isOperator && this.name == OperatorNameConventions.INVOKE
     }
+
+internal fun ClassDescriptor.isUnit() = this.defaultType.isUnit()

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

@@ -395,9 +395,13 @@ internal class CodeGeneratorVisitor(val context: Context) : IrElementVisitorVoid
 
             if (constructorDescriptor.isPrimary) {
                 if (DescriptorUtils.isObject(classDescriptor)) {
-                    val objectPtr = objectPtrByName(classDescriptor)
+                    if (classDescriptor.isUnit()) {
+                        context.llvm.staticData.createUnitInstance(classDescriptor)
+                    } else {
+                        val objectPtr = objectPtrByName(classDescriptor)
 
-                    LLVMSetInitializer(objectPtr, codegen.kNullObjHeaderPtr)
+                        LLVMSetInitializer(objectPtr, codegen.kNullObjHeaderPtr)
+                    }
                 }
                 val irOfCurrentClass = context.ir.moduleIndex.classes[classDescriptor.classId]
                 irOfCurrentClass!!.acceptChildrenVoid(object : IrElementVisitorVoid {
@@ -732,7 +736,11 @@ internal class CodeGeneratorVisitor(val context: Context) : IrElementVisitorVoid
 
     //-------------------------------------------------------------------------//
 
-    private fun evaluateGetObjectValue(value: IrGetObjectValue): LLVMValueRef? {
+    private fun evaluateGetObjectValue(value: IrGetObjectValue): LLVMValueRef {
+        if (value.descriptor.isUnit()) {
+            return codegen.theUnitInstanceRef.llvm
+        }
+
         var objectPtr = objectPtrByName(value.descriptor)
         val bbCurrent = codegen.currentBlock
         val bbInit    = codegen.basicBlock("label_init")
@@ -1421,6 +1429,7 @@ internal class CodeGeneratorVisitor(val context: Context) : IrElementVisitorVoid
     //-------------------------------------------------------------------------//
 
     private fun objectPtrByName(descriptor: ClassDescriptor): LLVMValueRef? {
+        assert (!descriptor.isUnit())
         val objName = descriptor.fqNameSafe.asString()
         var objectPtr = LLVMGetNamedGlobal(context.llvmModule, objName)
         if (objectPtr == null) {

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

@@ -2,6 +2,7 @@ package org.jetbrains.kotlin.backend.konan.llvm
 
 import llvm.*
 import org.jetbrains.kotlin.backend.konan.KonanPlatform
+import org.jetbrains.kotlin.backend.konan.descriptors.isUnit
 import org.jetbrains.kotlin.descriptors.ClassDescriptor
 import org.jetbrains.kotlin.incremental.components.NoLookupLocation
 import org.jetbrains.kotlin.ir.expressions.IrConst
@@ -115,3 +116,17 @@ internal fun StaticData.createArrayList(elementType: TypeProjection, array: Cons
 
     return createKotlinObject(type, body)
 }
+
+private val theUnitInstanceName = "kobj:kotlin.Unit"
+
+internal fun StaticData.createUnitInstance(descriptor: ClassDescriptor): ConstPointer {
+    assert (descriptor.isUnit())
+    assert (descriptor.fields.isEmpty())
+    val typeInfo = descriptor.defaultType.typeInfoPtr!!
+    val objHeader = objHeader(typeInfo)
+    val global = this.placeGlobal(theUnitInstanceName, objHeader)
+    return global.pointer
+}
+
+internal val ContextUtils.theUnitInstanceRef: ConstPointer
+    get() = constPointer(externalGlobal(theUnitInstanceName, context.llvm.runtime.objHeaderType))