[PSI2IR] Propagate smart cast information for variable loads.

This gives us more precise type information and can enable backend
optimizations. This was motivated by when expressions not compiled
to table switches in the JVM_IR backend.

Fixed KT-36845.

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

@@ -86,13 +86,14 @@ class CallGenerator(statementGenerator: StatementGenerator) : StatementGenerator
         endOffset: Int,
         descriptor: DeclarationDescriptor,
         resolvedCall: ResolvedCall<*>?,
-        origin: IrStatementOrigin?
+        origin: IrStatementOrigin?,
+        irType: IrType? = null
     ): IrExpression =
         when (descriptor) {
             is FakeCallableDescriptorForObject ->
-                generateValueReference(startOffset, endOffset, descriptor.getReferencedDescriptor(), resolvedCall, origin)
+                generateValueReference(startOffset, endOffset, descriptor.getReferencedDescriptor(), resolvedCall, origin, irType)
             is TypeAliasDescriptor ->
-                generateValueReference(startOffset, endOffset, descriptor.classDescriptor!!, null, origin)
+                generateValueReference(startOffset, endOffset, descriptor.classDescriptor!!, null, origin, irType)
             is ClassDescriptor -> {
                 val classValueType = descriptor.classValueType!!
                 statementGenerator.generateSingletonReference(descriptor, startOffset, endOffset, classValueType)
@@ -107,7 +108,7 @@ class CallGenerator(statementGenerator: StatementGenerator) : StatementGenerator
                 IrGetFieldImpl(startOffset, endOffset, field, fieldType, receiver?.load())
             }
             is VariableDescriptor ->
-                generateGetVariable(startOffset, endOffset, descriptor, getTypeArguments(resolvedCall), origin)
+                generateGetVariable(startOffset, endOffset, descriptor, getTypeArguments(resolvedCall), origin, irType)
             else ->
                 TODO("Unexpected callable descriptor: $descriptor ${descriptor::class.java.simpleName}")
         }
@@ -117,7 +118,8 @@ class CallGenerator(statementGenerator: StatementGenerator) : StatementGenerator
         endOffset: Int,
         descriptor: VariableDescriptor,
         typeArguments: Map<TypeParameterDescriptor, KotlinType>?,
-        origin: IrStatementOrigin? = null
+        origin: IrStatementOrigin? = null,
+        irType: IrType? = null
     ) =
         if (descriptor is LocalVariableDescriptor && descriptor.isDelegated) {
             val getterDescriptor = descriptor.getter!!
@@ -128,8 +130,15 @@ class CallGenerator(statementGenerator: StatementGenerator) : StatementGenerator
                 context.callToSubstitutedDescriptorMap[this] = getterDescriptor
                 putTypeArguments(typeArguments) { it.toIrType() }
             }
-        } else
-            IrGetValueImpl(startOffset, endOffset, descriptor.type.toIrType(), context.symbolTable.referenceValue(descriptor), origin)
+        } else {
+            val getValue =
+                IrGetValueImpl(startOffset, endOffset, descriptor.type.toIrType(), context.symbolTable.referenceValue(descriptor), origin)
+            if (irType != null) {
+                IrTypeOperatorCallImpl(startOffset, endOffset, irType, IrTypeOperator.IMPLICIT_CAST, irType, getValue)
+            } else {
+                getValue
+            }
+        }
 
     fun generateDelegatingConstructorCall(startOffset: Int, endOffset: Int, call: CallBuilder): IrExpression =
         call.callReceiver.call { dispatchReceiver, extensionReceiver ->

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

@@ -37,6 +37,7 @@ import org.jetbrains.kotlin.psi2ir.intermediate.IntermediateValue
 import org.jetbrains.kotlin.psi2ir.intermediate.createTemporaryVariableInBlock
 import org.jetbrains.kotlin.psi2ir.intermediate.setExplicitReceiverValue
 import org.jetbrains.kotlin.resolve.BindingContext
+import org.jetbrains.kotlin.resolve.BindingContext.SMARTCAST
 import org.jetbrains.kotlin.resolve.BindingContextUtils
 import org.jetbrains.kotlin.resolve.DescriptorUtils
 import org.jetbrains.kotlin.resolve.calls.model.ResolvedCall
@@ -327,7 +328,8 @@ class StatementGenerator(
     ): IrExpression =
         CallGenerator(this).generateValueReference(
             expression.startOffsetSkippingComments, expression.endOffset,
-            descriptor, resolvedCall, null
+            descriptor, resolvedCall, null,
+            context.bindingContext.get(SMARTCAST, expression)?.defaultType?.toIrType()
         )
 
     override fun visitCallExpression(expression: KtCallExpression, data: Nothing?): IrStatement {