collections: flesh out Vec benchmarks
collections: Optimize Vec when cloning from a slice

llvm is currently not able to conver `Vec::extend` into a memcpy
for `Copy` types, which results in methods like `Vec::push_all`
to run twice as slow as it should be running. This patch takes
the unsafe `Vec::clone` optimization to speed up all the operations
that are cloning a slice into a `Vec`.

before:

test vec::tests::bench_clone_from_0000_0000                ... bench:        12 ns/iter (+/- 2)
test vec::tests::bench_clone_from_0000_0010                ... bench:       125 ns/iter (+/- 4) = 80 MB/s
test vec::tests::bench_clone_from_0000_0100                ... bench:       360 ns/iter (+/- 33) = 277 MB/s
test vec::tests::bench_clone_from_0000_1000                ... bench:      2601 ns/iter (+/- 175) = 384 MB/s
test vec::tests::bench_clone_from_0010_0000                ... bench:        12 ns/iter (+/- 2)
test vec::tests::bench_clone_from_0010_0010                ... bench:       125 ns/iter (+/- 10) = 80 MB/s
test vec::tests::bench_clone_from_0010_0100                ... bench:       361 ns/iter (+/- 28) = 277 MB/s
test vec::tests::bench_clone_from_0100_0010                ... bench:       131 ns/iter (+/- 13) = 76 MB/s
test vec::tests::bench_clone_from_0100_0100                ... bench:       360 ns/iter (+/- 9) = 277 MB/s
test vec::tests::bench_clone_from_0100_1000                ... bench:      2575 ns/iter (+/- 168) = 388 MB/s
test vec::tests::bench_clone_from_1000_0100                ... bench:       356 ns/iter (+/- 20) = 280 MB/s
test vec::tests::bench_clone_from_1000_1000                ... bench:      2605 ns/iter (+/- 167) = 383 MB/s
test vec::tests::bench_from_slice_0000                     ... bench:        11 ns/iter (+/- 0)
test vec::tests::bench_from_slice_0010                     ... bench:       115 ns/iter (+/- 5) = 86 MB/s
test vec::tests::bench_from_slice_0100                     ... bench:       309 ns/iter (+/- 170) = 323 MB/s
test vec::tests::bench_from_slice_1000                     ... bench:      2065 ns/iter (+/- 198) = 484 MB/s
test vec::tests::bench_push_all_0000_0000                  ... bench:         7 ns/iter (+/- 0)
test vec::tests::bench_push_all_0000_0010                  ... bench:        79 ns/iter (+/- 7) = 126 MB/s
test vec::tests::bench_push_all_0000_0100                  ... bench:       342 ns/iter (+/- 18) = 292 MB/s
test vec::tests::bench_push_all_0000_1000                  ... bench:      2873 ns/iter (+/- 75) = 348 MB/s
test vec::tests::bench_push_all_0010_0010                  ... bench:       154 ns/iter (+/- 8) = 64 MB/s
test vec::tests::bench_push_all_0100_0100                  ... bench:       518 ns/iter (+/- 18) = 193 MB/s
test vec::tests::bench_push_all_1000_1000                  ... bench:      4490 ns/iter (+/- 223) = 222 MB/s

after:

test vec::tests::bench_clone_from_0000_0000                ... bench:        12 ns/iter (+/- 1)
test vec::tests::bench_clone_from_0000_0010                ... bench:       123 ns/iter (+/- 5) = 81 MB/s
test vec::tests::bench_clone_from_0000_0100                ... bench:       367 ns/iter (+/- 23) = 272 MB/s
test vec::tests::bench_clone_from_0000_1000                ... bench:      2618 ns/iter (+/- 252) = 381 MB/s
test vec::tests::bench_clone_from_0010_0000                ... bench:        12 ns/iter (+/- 1)
test vec::tests::bench_clone_from_0010_0010                ... bench:       124 ns/iter (+/- 7) = 80 MB/s
test vec::tests::bench_clone_from_0010_0100                ... bench:       369 ns/iter (+/- 34) = 271 MB/s
test vec::tests::bench_clone_from_0100_0010                ... bench:       123 ns/iter (+/- 6) = 81 MB/s
test vec::tests::bench_clone_from_0100_0100                ... bench:       371 ns/iter (+/- 25) = 269 MB/s
test vec::tests::bench_clone_from_0100_1000                ... bench:      2713 ns/iter (+/- 532) = 368 MB/s
test vec::tests::bench_clone_from_1000_0100                ... bench:       369 ns/iter (+/- 14) = 271 MB/s
test vec::tests::bench_clone_from_1000_1000                ... bench:      2611 ns/iter (+/- 194) = 382 MB/s
test vec::tests::bench_from_slice_0000                     ... bench:         7 ns/iter (+/- 0)
test vec::tests::bench_from_slice_0010                     ... bench:       108 ns/iter (+/- 4) = 92 MB/s
test vec::tests::bench_from_slice_0100                     ... bench:       235 ns/iter (+/- 24) = 425 MB/s
test vec::tests::bench_from_slice_1000                     ... bench:      1318 ns/iter (+/- 96) = 758 MB/s
test vec::tests::bench_push_all_0000_0000                  ... bench:         7 ns/iter (+/- 0)
test vec::tests::bench_push_all_0000_0010                  ... bench:        70 ns/iter (+/- 4) = 142 MB/s
test vec::tests::bench_push_all_0000_0100                  ... bench:       176 ns/iter (+/- 16) = 568 MB/s
test vec::tests::bench_push_all_0000_1000                  ... bench:      1125 ns/iter (+/- 94) = 888 MB/s
test vec::tests::bench_push_all_0010_0010                  ... bench:       159 ns/iter (+/- 15) = 62 MB/s
test vec::tests::bench_push_all_0100_0100                  ... bench:       363 ns/iter (+/- 12) = 275 MB/s
test vec::tests::bench_push_all_1000_1000                  ... bench:      2860 ns/iter (+/- 415) = 349 MB/s
std: flesh out MemWriter benchmarks
collections: flesh out the Vec::clone_from benchmarks to cover reuse
collections: minimize code that's in unsafe blocks

This changes Vec::from_slice to call unsafe_push_all_clone
directly to avoid doing an unnecessary reserve_additional call
collections: merge unsafe_push_all_clone and push_all
Add libunicode; move unicode functions from core

- created new crate, libunicode, below libstd
- split Char trait into Char (libcore) and UnicodeChar (libunicode)
  - Unicode-aware functions now live in libunicode
    - is_alphabetic, is_XID_start, is_XID_continue, is_lowercase,
      is_uppercase, is_whitespace, is_alphanumeric, is_control,
      is_digit, to_uppercase, to_lowercase
  - added width method in UnicodeChar trait
    - determines printed width of character in columns, or None if it is
      a non-NULL control character
    - takes a boolean argument indicating whether the present context is
      CJK or not (characters with 'A'mbiguous widths are double-wide in
      CJK contexts, single-wide otherwise)
- split StrSlice into StrSlice (libcore) and UnicodeStrSlice
  (libunicode)
  - functionality formerly in StrSlice that relied upon Unicode
    functionality from Char is now in UnicodeStrSlice
    - words, is_whitespace, is_alphanumeric, trim, trim_left, trim_right
  - also moved Words type alias into libunicode because words method is
    in UnicodeStrSlice
- unified Unicode tables from libcollections, libcore, and libregex into
  libunicode
- updated unicode.py in src/etc to generate aforementioned tables
- generated new tables based on latest Unicode data
- added UnicodeChar and UnicodeStrSlice traits to prelude
- libunicode is now the collection point for the std::char module,
  combining the libunicode functionality with the Char functionality
  from libcore
  - thus, moved doc comment for char from core::char to unicode::char
- libcollections remains the collection point for std::str

The Unicode-aware functions that previously lived in the Char and
StrSlice traits are no longer available to programs that only use
libcore. To regain use of these methods, include the libunicode crate
and use the UnicodeChar and/or UnicodeStrSlice traits:

    extern crate unicode;
    use unicode::UnicodeChar;
    use unicode::UnicodeStrSlice;
    use unicode::Words; // if you want to use the words() method

NOTE: this does *not* impact programs that use libstd, since UnicodeChar
and UnicodeStrSlice have been added to the prelude.

closes #15224
[breaking-change]
fix test failures

- unicode tests live in coretest crate
- libcollections str tests need UnicodeChar trait.
- libregex perlw tests were checking a char in the Alphabetic category,
  \x2161. Confirmed perl 5.18 considers this a \w character. Changed to
  \x2961, which is not \w as the test expects.
etc: Fix install script for rpath removal

This adds detection of the relevant LD_LIBRARY_PATH-like environment variable
and appropriately sets it when testing whether binaries can run or not.
Additionally, the installation prints a recommended value if one is necessary.
Remove car analogy.

This was super silly anyway.

Fixes #15539.
Register new snapshots

Closes #15544
auto merge of #15283 : kwantam/rust/master, r=alexcrichton

Add libunicode; move unicode functions from core

- created new crate, libunicode, below libstd
- split `Char` trait into `Char` (libcore) and `UnicodeChar` (libunicode)
  - Unicode-aware functions now live in libunicode
    - `is_alphabetic`, `is_XID_start`, `is_XID_continue`, `is_lowercase`,
      `is_uppercase`, `is_whitespace`, `is_alphanumeric`, `is_control`, `is_digit`,
      `to_uppercase`, `to_lowercase`
  - added `width` method in UnicodeChar trait
    - determines printed width of character in columns, or None if it is a non-NULL control character
    - takes a boolean argument indicating whether the present context is CJK or not (characters with 'A'mbiguous widths are double-wide in CJK contexts, single-wide otherwise)
- split `StrSlice` into `StrSlice` (libcore) and `UnicodeStrSlice` (libunicode)
  - functionality formerly in `StrSlice` that relied upon Unicode functionality from `Char` is now in `UnicodeStrSlice`
    - `words`, `is_whitespace`, `is_alphanumeric`, `trim`, `trim_left`, `trim_right`
  - also moved `Words` type alias into libunicode because `words` method is in `UnicodeStrSlice`
- unified Unicode tables from libcollections, libcore, and libregex into libunicode
- updated `unicode.py` in `src/etc` to generate aforementioned tables
- generated new tables based on latest Unicode data
- added `UnicodeChar` and `UnicodeStrSlice` traits to prelude
- libunicode is now the collection point for the `std::char` module, combining the libunicode functionality with the `Char` functionality from libcore
  - thus, moved doc comment for `char` from `core::char` to `unicode::char`
- libcollections remains the collection point for `std::str`

The Unicode-aware functions that previously lived in the `Char` and `StrSlice` traits are no longer available to programs that only use libcore. To regain use of these methods, include the libunicode crate and `use` the `UnicodeChar` and/or `UnicodeStrSlice` traits:

    extern crate unicode;
    use unicode::UnicodeChar;
    use unicode::UnicodeStrSlice;
    use unicode::Words; // if you want to use the words() method

NOTE: this does *not* impact programs that use libstd, since UnicodeChar and UnicodeStrSlice have been added to the prelude.

closes #15224
[breaking-change]
auto merge of #15471 : erickt/rust/push_all, r=acrichto

llvm is currently not able to conver `Vec::extend` into a memcpy for `Copy` types, which results in methods like `Vec::push_all` to run twice as slow as it should be running. This patch takes the unsafe `Vec::clone` optimization to speed up all the operations that are cloning a slice into a `Vec`.

before:

```
test vec::tests::bench_clone_from_0000_0000                ... bench:        12 ns/iter (+/- 2)
test vec::tests::bench_clone_from_0000_0010                ... bench:       125 ns/iter (+/- 4) = 80 MB/s
test vec::tests::bench_clone_from_0000_0100                ... bench:       360 ns/iter (+/- 33) = 277 MB/s
test vec::tests::bench_clone_from_0000_1000                ... bench:      2601 ns/iter (+/- 175) = 384 MB/s
test vec::tests::bench_clone_from_0010_0000                ... bench:        12 ns/iter (+/- 2)
test vec::tests::bench_clone_from_0010_0010                ... bench:       125 ns/iter (+/- 10) = 80 MB/s
test vec::tests::bench_clone_from_0010_0100                ... bench:       361 ns/iter (+/- 28) = 277 MB/s
test vec::tests::bench_clone_from_0100_0010                ... bench:       131 ns/iter (+/- 13) = 76 MB/s
test vec::tests::bench_clone_from_0100_0100                ... bench:       360 ns/iter (+/- 9) = 277 MB/s
test vec::tests::bench_clone_from_0100_1000                ... bench:      2575 ns/iter (+/- 168) = 388 MB/s
test vec::tests::bench_clone_from_1000_0100                ... bench:       356 ns/iter (+/- 20) = 280 MB/s
test vec::tests::bench_clone_from_1000_1000                ... bench:      2605 ns/iter (+/- 167) = 383 MB/s
test vec::tests::bench_from_slice_0000                     ... bench:        11 ns/iter (+/- 0)
test vec::tests::bench_from_slice_0010                     ... bench:       115 ns/iter (+/- 5) = 86 MB/s
test vec::tests::bench_from_slice_0100                     ... bench:       309 ns/iter (+/- 170) = 323 MB/s
test vec::tests::bench_from_slice_1000                     ... bench:      2065 ns/iter (+/- 198) = 484 MB/s
test vec::tests::bench_push_all_0000_0000                  ... bench:         7 ns/iter (+/- 0)
test vec::tests::bench_push_all_0000_0010                  ... bench:        79 ns/iter (+/- 7) = 126 MB/s
test vec::tests::bench_push_all_0000_0100                  ... bench:       342 ns/iter (+/- 18) = 292 MB/s
test vec::tests::bench_push_all_0000_1000                  ... bench:      2873 ns/iter (+/- 75) = 348 MB/s
test vec::tests::bench_push_all_0010_0010                  ... bench:       154 ns/iter (+/- 8) = 64 MB/s
test vec::tests::bench_push_all_0100_0100                  ... bench:       518 ns/iter (+/- 18) = 193 MB/s
test vec::tests::bench_push_all_1000_1000                  ... bench:      4490 ns/iter (+/- 223) = 222 MB/s
```

after:

```
test vec::tests::bench_clone_from_0000_0000                ... bench:        12 ns/iter (+/- 1)
test vec::tests::bench_clone_from_0000_0010                ... bench:       123 ns/iter (+/- 5) = 81 MB/s
test vec::tests::bench_clone_from_0000_0100                ... bench:       367 ns/iter (+/- 23) = 272 MB/s
test vec::tests::bench_clone_from_0000_1000                ... bench:      2618 ns/iter (+/- 252) = 381 MB/s
test vec::tests::bench_clone_from_0010_0000                ... bench:        12 ns/iter (+/- 1)
test vec::tests::bench_clone_from_0010_0010                ... bench:       124 ns/iter (+/- 7) = 80 MB/s
test vec::tests::bench_clone_from_0010_0100                ... bench:       369 ns/iter (+/- 34) = 271 MB/s
test vec::tests::bench_clone_from_0100_0010                ... bench:       123 ns/iter (+/- 6) = 81 MB/s
test vec::tests::bench_clone_from_0100_0100                ... bench:       371 ns/iter (+/- 25) = 269 MB/s
test vec::tests::bench_clone_from_0100_1000                ... bench:      2713 ns/iter (+/- 532) = 368 MB/s
test vec::tests::bench_clone_from_1000_0100                ... bench:       369 ns/iter (+/- 14) = 271 MB/s
test vec::tests::bench_clone_from_1000_1000                ... bench:      2611 ns/iter (+/- 194) = 382 MB/s
test vec::tests::bench_from_slice_0000                     ... bench:         7 ns/iter (+/- 0)
test vec::tests::bench_from_slice_0010                     ... bench:       108 ns/iter (+/- 4) = 92 MB/s
test vec::tests::bench_from_slice_0100                     ... bench:       235 ns/iter (+/- 24) = 425 MB/s
test vec::tests::bench_from_slice_1000                     ... bench:      1318 ns/iter (+/- 96) = 758 MB/s
test vec::tests::bench_push_all_0000_0000                  ... bench:         7 ns/iter (+/- 0)
test vec::tests::bench_push_all_0000_0010                  ... bench:        70 ns/iter (+/- 4) = 142 MB/s
test vec::tests::bench_push_all_0000_0100                  ... bench:       176 ns/iter (+/- 16) = 568 MB/s
test vec::tests::bench_push_all_0000_1000                  ... bench:      1125 ns/iter (+/- 94) = 888 MB/s
test vec::tests::bench_push_all_0010_0010                  ... bench:       159 ns/iter (+/- 15) = 62 MB/s
test vec::tests::bench_push_all_0100_0100                  ... bench:       363 ns/iter (+/- 12) = 275 MB/s
test vec::tests::bench_push_all_1000_1000                  ... bench:      2860 ns/iter (+/- 415) = 349 MB/s
```

This also includes extra benchmarks for `Vec` and `MemWriter`.
syntax: De-doc comment to fix nightlies

This reverts the promotion from line-comment to doc-comment in 4989a56 to fix
the compiler-docs target.

Closes #15553
lint: extend `#[must_use]` to handle a message.

Similar to the stability attributes, a type annotated with `#[must_use =
"informative snippet"]` will print the normal warning message along with
"informative snippet". This allows the type author to provide some
guidance about why the type should be used.
core: add `#[must_use]` attributes to iterator adaptor structs.

It can be a little unintuitive that something like `v.iter().map(|x|
println!("{}", x));` does nothing: the majority of the iterator adaptors
are lazy and do not execute anything until something calls `next`, e.g.
a `for` loop, `collect`, `fold`, etc.

The majority of such errors can be seen by someone writing something
like the above, i.e. just calling an iterator adaptor and doing nothing
with it (and doing this is certainly useless), so we can co-opt the
`must_use` lint, using the message functionality to give a hint to the
reason why.

Fixes #14666.
auto merge of #15550 : alexcrichton/rust/install-script, r=brson

This adds detection of the relevant LD_LIBRARY_PATH-like environment variable
and appropriately sets it when testing whether binaries can run or not.
Additionally, the installation prints a recommended value if one is necessary.

Closes #15545
librustc: Don't emit call for intrinsics instead just trans at callsite.
libcore: Deprecate advance method on Iterators.
libcollections: Use iterators instead of old-style loops.