Note: for now, this change only affects `-windows-gnu` builds.
So why was this `libgcc` dylib dependency needed in the first place?
The stack unwinder needs to know about locations of unwind tables of all the modules loaded in the current process. The easiest portable way of achieving this is to have each module register itself with the unwinder when loaded into the process. All modules compiled by GCC do this by calling the __register_frame_info() in their startup code (that's `crtbegin.o` and `crtend.o`, which are automatically linked into any gcc output).
Another important piece is that there should be only one copy of the unwinder (and thus unwind tables registry) in the process. This pretty much means that the unwinder must be in a shared library (unless everything is statically linked).
Now, Rust compiler tries very hard to make sure that any given Rust crate appears in the final output just once. So if we link the unwinder statically to one of Rust's crates, everything should be fine.
Unfortunately, GCC startup objects are built under assumption that `libgcc` is the one true place for the unwind info registry, so I couldn't find any better way than to replace them. So out go `crtbegin`/`crtend`, in come `rsbegin`/`rsend`!
A side benefit of this change is that rustc is now more in control of the command line that goes to the linker, so we could stop using `gcc` as the linker driver and just invoke `ld` directly.
Motivation:
- It is not actually a pattern
- It is not actually needed, except for...
Drawback:
- Slice patterns like `[a, _.., b]` are pretty-printed as `[a, .., b]`. Great loss :(
plugin-[breaking-change], as always
Similarly to the simd intrinsics. I believe this is a better solution than #29288, and I could implement it as well for overflowing_add/sub/mul. Also rename from udiv/sdiv to div, and same for rem.
These two commits do a few things:
1. reformat to 80 cols
2. use the reference-style links where appropriate for improved in-source readability
3. adds a few links, tweaks a couple of words, `3` -> `three`, stuff like that
While the diff is big due to these edits, there's no significant content change.
r? @brson
Before this patch `reserve` function allocated twice as requested
amount elements (not twice as capacity). It leaded to unnecessary
excessive memory usage in scenarios like this:
```
let mut v = Vec::new();
v.push(17);
v.extend(0..10);
println!("{}", v.capacity());
```
`Vec` allocated 22 elements, while it could allocate just 11.
`reserve` function must have a property of keeping `push` operation
cost (which calls `reserve`) `O(1)`. To achieve this `reserve` must
exponentialy grow its capacity when it does reallocation.
There's better strategy to implement `reserve`:
```
let new_capacity = max(current_capacity * 2, requested_capacity);
```
This strategy still guarantees that capacity grows at `O(1)` with
`reserve`, and fixes the issue with `extend`.
Patch imlpements this strategy.
Before this patch `reserve` function allocated twice as requested
amount elements (not twice as capacity). It leaded to unnecessary
excessive memory usage in scenarios like this:
```
let mut v = Vec::new();
v.push(17);
v.extend(0..10);
println!("{}", v.capacity());
```
`Vec` allocated 22 elements, while it could allocate just 11.
`reserve` function must have a property of keeping `push` operation
cost (which calls `reserve`) `O(1)`. To achieve this `reserve` must
exponentialy grow its capacity when it does reallocation.
There's better strategy to implement `reserve`:
```
let new_capacity = max(current_capacity * 2, requested_capacity);
```
This strategy still guarantees that capacity grows at `O(1)` with
`reserve`, and fixes the issue with `extend`.
Patch imlpements this strategy.
This documentation confused me when trying to use truncate on a project. Originally, it was unclear whether truncate removed the last `len` elements, or whether it cut down the vector to be exactly `len` elements long. The example was also ambiguous.
This fixes#29048 (though I think adding better transactional support would be a better fix for that issue, but that is more difficult). It also simplifies region inference and changes the model to a pure data flow one, as discussed in [this internals thread](https://internals.rust-lang.org/t/rough-thoughts-on-the-impl-of-region-inference-mir-etc/2800). I am not 100% sure though if this PR is the right thing to do -- or at least maybe not at this moment, so thoughts on that would be appreciated.
r? @pnkfelix
cc @arielb1
This is two sentences that have been comma spliced, and should
be split with a full stop. (This error made me stop and re-read,
and I submit this as an actual improvement to readability, not
as a grammar weird-o!)
This helps for the case where a match, such as below:
```rust
let foo = match foo {
Some(x) => x,
None => 0
};
```
gets refactored to no longer need the match, but the match keyword has been left accidentally:
```rust
let foo = match foo.unwrap_or(0);
```
This can be hard to spot as the expression grows more complex.
r? @alexcrichton
This documentation confused me when trying to use truncate on a project. Originally, it was unclear whether truncate removed the last `len` elements, or whether it cut down the vector to be exactly `len` elements long. The example was also ambiguous.
This is two sentences that have been comma spliced, and should
be split with a full stop. (This error made me stop and re-read,
and I submit this as an actual improvement to readability, not
as a grammar weird-o!)
