Destroying the LLVM Module is slow

[pcwalton]

About 3.1% of rustc compilation time (2.6 s) is spent destroying the LLVM module. For comparison, that's longer than all of resolve.

The solution is to leak the module and let the OS clean up all the memory.

[catamorphism]

Nominating for milestone 5, production-ready.

[graydon]

just a bug, removing milestone/nomination.

[emberian]

Fixed pending #7659

[brson]

I've not yet convinced myself of the value of this. For large crates it does seem to provide some amount of savings, not for small crates though, so impact on cycle time will probably be minimal. Still want to do some testing. Also want to investigate just calling libc::exit to see if avoiding the final GC accomplishes anything.

[erickt]

Would leaking the LLVM module cause problems when librustc is used in an IDE or some other long running process?

[brson]

@erickt Yes. If we do this it will be optional.

[sanxiyn]

What happened to this?

[brson]

@sanxiyn I don't recall, but I don't think there were any major issues with the patch I had, besides figuring out how to make valgrind happy.

[steveklabnik]

Triage: nothing has moved on this.