Is there a tool to determine what minimum OS my deployment target should be?

I've read several of the posts on stack overflow already about this topic, but none of them seem to have real answers.

Here is my question:

The Apple documentation clearly shows what OS is required for each method, so why isn't there a tool to let me know if I'm using any methods that require an OS later than my d开发者_开发知识库eployment target?

If there is such a tool I'd like to know.

I'm currently building an App that I think will run fine on iOS 3.2, but I want to make sure. It seems to work fine in the 3.2 iPad simulator, but like I said, I want to make sure.

I don't want to go through each method one by one, and I don't want to set the deployment target to anything >= 4.0 because of how many people with 3Gs phones haven't upgraded to 4.0.

BTW: I'm running XCode 4.0.2

Generally one sets this to the oldest firmware version one has tested on, if you aren't entirely sure about what APIs you're using.

Protip: Get an old device if you want to test on old versions. Set your deployment target ALWAYS to the oldest firmware version you've tested on.

It looks like there is no tool that does exactly what I'm asking. If anyone else discovers something, please let me know. It seems like it would be fairly easy for Apple to implement something like this.