mark private functions/globals not used in inline functions as internal

[thestinger]

We'll need to keep track of whether they're used in functions marked for cross-crate inlining, which may be tricky as this code isn't entirely centralized yet. I've been working towards getting it all passing through one place in base.rs so we're part of the way there...

[huonw]

I assume that rustc will have to handle something like

fn foo() {}
fn bar() {}
fn baz() {}

pub static FUNCS: &'static [extern "Rust" fn()] = &[foo, bar, baz];

too?

[alexcrichton]

This I think needs some sort of dependency-graph-style abstraction for knowing when a function can never be called from an outside crate. Functions which can be called from outside crates are:

• All functions located in exported_items
• All non-generic functions called by some chain of generic functions rooted in an exported generic function.

Although that's probably not a complete list, I think to do this we need a hash of function id to a list of functions that could possibly be called, and then crawling can commence from there.

I'm also not sure if we're marking all instantiations of generic functions as internal, but we certainly can...

@huonw, that looks like an LLVM problem, and it still wouldn't matter too much because you can't cal foo by its name from an external crate, only by indexing into the FUNCS array which will just be pointers anyway.

[thestinger]

This seems to be at least partly working as part of the reachable pass now. I'll open up more specific issues if I encounter them.