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bors 872ba2ccd3 auto merge of #19294 : huonw/rust/transmute-inplace, r=nikomatsakis This detects (a subset of) the cases when `transmute::<T, U>(x)` can be lowered to a direct `bitcast T x to U` in LLVM. This assists with efficiently handling a SIMD vector as multiple different types, e.g. swapping bytes/words/double words around inside some larger vector type. C compilers like GCC and Clang handle integer vector types as `__m128i` for all widths, and implicitly insert bitcasts as required. This patch allows Rust to express this, even if it takes a bit of `unsafe`, whereas previously it was impossible to do at all without inline assembly. Example: pub fn reverse_u32s(u: u64x2) -> u64x2 { unsafe { let tmp = mem::transmute::<_, u32x4>(u); let swapped = u32x4(tmp.3, tmp.2, tmp.1, tmp.0); mem::transmute::<_, u64x2>(swapped) } } Compiling with `--opt-level=3` gives: Before define <2 x i64> @_ZN12reverse_u32s20hbdb206aba18a03d8tbaE(<2 x i64>) unnamed_addr #0 { entry-block: %1 = bitcast <2 x i64> %0 to i128 %u.0.extract.trunc = trunc i128 %1 to i32 %u.4.extract.shift = lshr i128 %1, 32 %u.4.extract.trunc = trunc i128 %u.4.extract.shift to i32 %u.8.extract.shift = lshr i128 %1, 64 %u.8.extract.trunc = trunc i128 %u.8.extract.shift to i32 %u.12.extract.shift = lshr i128 %1, 96 %u.12.extract.trunc = trunc i128 %u.12.extract.shift to i32 %2 = insertelement <4 x i32> undef, i32 %u.12.extract.trunc, i64 0 %3 = insertelement <4 x i32> %2, i32 %u.8.extract.trunc, i64 1 %4 = insertelement <4 x i32> %3, i32 %u.4.extract.trunc, i64 2 %5 = insertelement <4 x i32> %4, i32 %u.0.extract.trunc, i64 3 %6 = bitcast <4 x i32> %5 to <2 x i64> ret <2 x i64> %6 } _ZN12reverse_u32s20hbdb206aba18a03d8tbaE: .cfi_startproc movd %xmm0, %rax punpckhqdq %xmm0, %xmm0 movd %xmm0, %rcx movq %rcx, %rdx shrq $32, %rdx movq %rax, %rsi shrq $32, %rsi movd %eax, %xmm0 movd %ecx, %xmm1 punpckldq %xmm0, %xmm1 movd %esi, %xmm2 movd %edx, %xmm0 punpckldq %xmm2, %xmm0 punpckldq %xmm1, %xmm0 retq After define <2 x i64> @_ZN12reverse_u32s20hbdb206aba18a03d8tbaE(<2 x i64>) unnamed_addr #0 { entry-block: %1 = bitcast <2 x i64> %0 to <4 x i32> %2 = shufflevector <4 x i32> %1, <4 x i32> undef, <4 x i32> <i32 3, i32 2, i32 1, i32 0> %3 = bitcast <4 x i32> %2 to <2 x i64> ret <2 x i64> %3 } _ZN12reverse_u32s20hbdb206aba18a03d8tbaE: .cfi_startproc pshufd $27, %xmm0, %xmm0 retq		2014-12-11 00:11:23 +00:00
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README.md

The Rust Programming Language

This is a compiler for Rust, including standard libraries, tools and documentation.

Quick Start

Download a binary installer for your platform.
Read the guide.
Enjoy!

Note: Windows users can read the detailed using Rust on Windows notes on the wiki.

Building from Source

Make sure you have installed the dependencies:
- g++ 4.7 or clang++ 3.x
- python 2.6 or later (but not 3.x)
- perl 5.0 or later
- GNU make 3.81 or later
- curl
- git
Download and build Rust:

You can either download a tarball or build directly from the repo.

To build from the tarball do:
```
 $ curl -O https://static.rust-lang.org/dist/rust-nightly.tar.gz
 $ tar -xzf rust-nightly.tar.gz
 $ cd rust-nightly
```
Or to build from the repo do:
```
 $ git clone https://github.com/rust-lang/rust.git
 $ cd rust
```
Now that you have Rust's source code, you can configure and build it:
```
 $ ./configure
 $ make && make install
```
Note: You may need to use sudo make install if you do not normally have permission to modify the destination directory. The install locations can be adjusted by passing a --prefix argument to configure. Various other options are also supported, pass --help for more information on them.

When complete, make install will place several programs into /usr/local/bin: rustc, the Rust compiler, and rustdoc, the API-documentation tool.
Read the guide.
Enjoy!

Building on Windows

To easily build on windows we can use MSYS2:

Grab the latest MSYS2 installer and go through the installer.
Now from the MSYS2 terminal we want to install the mingw64 toolchain and the other tools we need.
```
 $ pacman -S mingw-w64-i686-toolchain
 $ pacman -S base-devel
```
With that now start mingw32_shell.bat from where you installed MSYS2 (i.e. C:\msys).
From there just navigate to where you have Rust's source code, configure and build it:
```
 $ ./configure
 $ make && make install
```

Notes

Since the Rust compiler is written in Rust, it must be built by a precompiled "snapshot" version of itself (made in an earlier state of development). As such, source builds require a connection to the Internet, to fetch snapshots, and an OS that can execute the available snapshot binaries.

Snapshot binaries are currently built and tested on several platforms:

Windows (7, 8, Server 2008 R2), x86 and x86-64 (64-bit support added in Rust 0.12.0)
Linux (2.6.18 or later, various distributions), x86 and x86-64
OSX 10.7 (Lion) or greater, x86 and x86-64

You may find that other platforms work, but these are our officially supported build environments that are most likely to work.

Rust currently needs about 1.5 GiB of RAM to build without swapping; if it hits swap, it will take a very long time to build.

There is a lot more documentation in the wiki.

Getting help and getting involved

The Rust community congregates in a few places:

StackOverflow - Get help here.
/r/rust - General discussion.
discuss.rust-lang.org - For development of the Rust language itself.

License

Rust is primarily distributed under the terms of both the MIT license and the Apache License (Version 2.0), with portions covered by various BSD-like licenses.