psi2ir: improve backing field usage generation

Also update corresponding tests data.

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

@@ -19,6 +19,7 @@ package org.jetbrains.kotlin.psi2ir.generators
 import org.jetbrains.kotlin.descriptors.ClassDescriptor
 import org.jetbrains.kotlin.descriptors.TypeParameterDescriptor
 import org.jetbrains.kotlin.descriptors.ValueParameterDescriptor
+import org.jetbrains.kotlin.descriptors.impl.SyntheticFieldDescriptor
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrExpressionWithCopy
 import org.jetbrains.kotlin.ir.expressions.impl.IrGetObjectValueImpl
@@ -86,6 +87,17 @@ private fun generateThisOrSuperReceiver(receiver: ReceiverValue, classDescriptor
     return IrGetValueImpl(ktReceiver.startOffset, ktReceiver.endOffset, classDescriptor.thisAsReceiverParameter)
 }
 
+fun StatementGenerator.generateBackingFieldReceiver(
+        ktDefaultElement: KtElement,
+        resolvedCall: ResolvedCall<*>?,
+        fieldDescriptor: SyntheticFieldDescriptor
+): IntermediateValue? {
+
+    val receiver = resolvedCall?.dispatchReceiver ?: fieldDescriptor.getDispatchReceiverForBackend() ?: return null
+
+    return this.generateReceiver(ktDefaultElement, receiver)
+}
+
 fun StatementGenerator.generateCallReceiver(
         ktDefaultElement: KtElement,
         dispatchReceiver: ReceiverValue?,

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

@@ -110,9 +110,8 @@ class AssignmentGenerator(statementGenerator: StatementGenerator) : StatementGen
 
         return when (descriptor) {
             is SyntheticFieldDescriptor -> {
-                val receiverValue = resolvedCall.dispatchReceiver?.let {
-                    statementGenerator.generateReceiver(ktLeft, it)
-                }
+                val receiverValue = statementGenerator.generateBackingFieldReceiver(ktLeft, resolvedCall, descriptor)
+
                 BackingFieldLValue(ktLeft.startOffset, ktLeft.endOffset, descriptor.propertyDescriptor,
                                    receiverValue, origin)
 

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

@@ -17,6 +17,7 @@
 package org.jetbrains.kotlin.psi2ir.generators
 
 import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.descriptors.impl.SyntheticFieldDescriptor
 import org.jetbrains.kotlin.ir.IrStatement
 import org.jetbrains.kotlin.ir.assertCast
 import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin
@@ -277,6 +278,10 @@ class StatementGenerator(
                 is PropertyDescriptor -> {
                     CallGenerator(this).generateCall(expression.startOffset, expression.endOffset, pregenerateCall(resolvedCall!!))
                 }
+                is SyntheticFieldDescriptor -> {
+                    val receiver = generateBackingFieldReceiver(expression, resolvedCall, descriptor)
+                    IrGetFieldImpl(expression.startOffset, expression.endOffset, descriptor.propertyDescriptor, receiver?.load())
+                }
                 is VariableDescriptor ->
                     CallGenerator(this).generateGetVariable(expression.startOffset, expression.endOffset, descriptor,
                                                             getTypeArguments(resolvedCall))