JVM_IR: fix a bug when isInlineParameter is applied to default stubs

If an inline parameter has a default value, its type is nullable.
There's already code to handle this in `IrInlineCodegen`, but it
really should be in `isInlineParameter` instead, otherwise e.g.
SyntheticAccessorLowering fails.

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/IrInlineCodegen.kt

@@ -82,8 +82,7 @@ class IrInlineCodegen(
             super.genValueAndPut(irValueParameter, argumentExpression, parameterType, codegen, blockInfo)
         }
 
-        // after transformation inlinable lambda parameter with default value would have nullable type: check default value type first
-        val isInlineParameter = irValueParameter.isInlineParameter(irValueParameter.defaultValue?.expression?.type ?: irValueParameter.type)
+        val isInlineParameter = irValueParameter.isInlineParameter()
         if (isInlineParameter && isInlineIrExpression(argumentExpression)) {
             val irReference: IrFunctionReference =
                 (argumentExpression as IrBlock).statements.filterIsInstance<IrFunctionReference>().single()

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/defaultMethodUtilIr.kt

@@ -20,9 +20,7 @@ fun extractDefaultLambdaOffsetAndDescriptor(
 
     val valueParameterOffset = if (irFunction.extensionReceiverParameter != null) 1 else 0
 
-    return irFunction.valueParameters.filter {
-        it.defaultValue != null && it.isInlineParameter(it.defaultValue!!.expression.type)
-    }.associateBy {
+    return irFunction.valueParameters.filter { it.defaultValue != null && it.isInlineParameter() }.associateBy {
         parameterOffsets[valueParameterOffset + it.index]
     }
 }

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/ir/IrUtils.kt

@@ -168,8 +168,12 @@ fun IrFunction.hasPlatformDependent(): Boolean = propertyIfAccessor.hasAnnotatio
 fun IrFunction.getJvmVisibilityOfDefaultArgumentStub() =
     if (Visibilities.isPrivate(visibility) || isInlineOnly()) JavaVisibilities.PACKAGE_VISIBILITY else Visibilities.PUBLIC
 
-fun IrValueParameter.isInlineParameter(type: IrType = this.type) =
-    index >= 0 && !isNoinline && !type.isNullable() && (type.isFunction() || type.isSuspendFunctionTypeOrSubtype())
+fun IrValueParameter.isInlineParameter() =
+    index >= 0 && !isNoinline && (type.isFunction() || type.isSuspendFunctionTypeOrSubtype()) &&
+            // Parameters with default values are always nullable, so check the expression too.
+            // Note that the frontend has a diagnostic for nullable inline parameters, so actually
+            // making this return `false` requires using `@Suppress`.
+            (!type.isNullable() || defaultValue?.expression?.type?.isNullable() == false)
 
 val IrStatementOrigin?.isLambda: Boolean
     get() = this == IrStatementOrigin.LAMBDA || this == IrStatementOrigin.ANONYMOUS_FUNCTION