Closes#3083.
This takes a similar approach to #5797 where a set is present on the `tcx` of used mutable definitions. Everything is by default warned about, and analyses must explicitly add mutable definitions to this set so they're not warned about.
Most of this was pretty straightforward, although there was one caveat that I ran into when implementing it. Apparently when the old modes are used (or maybe `legacy_modes`, I'm not sure) some different code paths are taken to cause spurious warnings to be issued which shouldn't be issued. I'm not really sure how modes even worked, so I was having a lot of trouble tracking this down. I figured that because they're a legacy thing that I'd just de-mode the compiler so that the warnings wouldn't be a problem anymore (or at least for the compiler).
Other than that, the entire compiler compiles without warnings of unused mutable variables. To prevent bad warnings, #5965 should be landed (which in turn is waiting on #5963) before landing this. I figured I'd stick it out for review anyway though.
Specifically: all enums with two variants, where one has zero size (and thus at most one inhabitant) and the other has a field where the null value would not be allowed (such as a safe pointer), are now represented by storing a null pointer in the field in question.
This is a generalization of representing `Option<~T>`, `Option<@T>`, and `Option<&T>` with nullable pointers, thus fixing Tony Hoare's “billion dollar mistake”.
```rust
use core::cell;
fn main() {
let x = cell::Cell(Some(~"foo"));
let y = x.value.get_ref().get_ref();
do x.with_mut_ref |z| { *z = None; }
println(*y) // boom!
}
```
use core::cell;
fn main() {
let x = cell::Cell(Some(~"foo"));
let y = x.value.get_ref().get_ref();
do x.with_mut_ref |z| { *z = None; }
println(*y) // boom!
}
This renaming, proposed in the [Numeric Bikeshed](https://github.com/mozilla/rust/wiki/Bikeshed-Numeric-Traits#rename-modulo-into-rem-or-remainder-in-traits-and-docs), will allow us to implement div and and modulo methods that follow the conventional mathematical definitions for negative numbers without altering the definitions of the operators (and confusing systems programmers). Here is a useful answer on StackOverflow that explains the difference between `div`/`mod` and `quot`/`rem` in Haskell: (When is the difference between quotRem and divMod useful?)[http://stackoverflow.com/a/339823/679485].
This is part of the numeric trait reforms tracked in issue #4819.
Partial fix for #5985
shootout-fasta-redux.rs was calling fwrite with u64 arguments that should have been size_t, which broke on 32-bit systems. I replaced the casts to u64 by casts to size_t.
r?
As the name suggests this replaces many instances of cast::reinterpret_cast by cast::transmute. It's essentially the boring part of fixing #5163, the remaining reinterpret_casts should be more tricky to remove (unless I missed a boring case).
r? @catamorphism
This implements the fixed_stack_segment for items with the rust-intrinsic abi, and then uses it to make f32 and f64 use intrinsics where appropriate, but without overflowing stacks and killing canaries (cf. #5686 and #5697). Hopefully.
@pcwalton, the fixed_stack_segment implementation involved mirroring its implementation in `base.rs` in `trans_closure`, but without adding the `set_no_inline` (reasoning: that would defeat the purpose of intrinsics), which is possibly incorrect.
I'm a little hazy about how the underlying structure works, so I've annotated the 4 that have caused problems so far, but there's no guarantee that the other intrinsics are entirely well-behaved.
Anyway, it has good results (the following are just summing the result of each function for 1 up to 100 million):
```
$ ./intrinsics-perf.sh f32
func new old speedup
sin 0.80 2.75 3.44
cos 0.80 2.76 3.45
sqrt 0.56 2.73 4.88
ln 1.01 2.94 2.91
log10 0.97 2.90 2.99
log2 1.01 2.95 2.92
exp 0.90 2.85 3.17
exp2 0.92 2.87 3.12
pow 6.95 8.57 1.23
geometric mean: 2.97
$ ./intrinsics-perf.sh f64
func new old speedup
sin 12.08 14.06 1.16
cos 12.04 13.67 1.14
sqrt 0.49 2.73 5.57
ln 4.11 5.59 1.36
log10 5.09 6.54 1.28
log2 2.78 5.10 1.83
exp 2.00 3.97 1.99
exp2 1.71 3.71 2.17
pow 5.90 7.51 1.27
geometric mean: 1.72
```
So about 3x faster on average for f32, and 1.7x for f64. This isn't exactly apples to apples though, since this patch also adds #[inline(always)] to all the function definitions too, which possibly gives a speedup.
(fwiw, GitHub is showing 93c0888 after d9c54f8 (since I cherry-picked the latter from #5697), but git's order is the other way.)
