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Pietro Albini 1997c706bd Rollup merge of #52908 - lnicola:vec-truncate-opt, r=alexcrichton Use SetLenOnDrop in Vec::truncate() This avoids a redundant length check in some cases when calling `Vec::truncate` or `Vec::clear`. Fixes #51802 Note that the generated code still seems suboptimal. I tested with the following functions: ```rust #[no_mangle] pub extern fn foo(x: &mut Vec<u8>) { x.clear(); } #[no_mangle] pub extern fn bar(x: &mut Vec<u8>) { x.truncate(5); } #[no_mangle] pub extern fn baz(x: &mut Vec<u8>, n: usize) { x.truncate(n); } #[no_mangle] pub extern fn foo_string(x: &mut Vec<String>) { x.clear(); } #[no_mangle] pub extern fn bar_string(x: &mut Vec<String>) { x.truncate(5); } #[no_mangle] pub extern fn baz_string(x: &mut Vec<String>, n: usize) { x.truncate(n); } ``` <details> <summary>Old output</summary> ```asm 00000000000460a0 <foo>: 460a0: 48 83 7f 10 00 cmpq $0x0,0x10(%rdi) 460a5: 74 08 je 460af <foo+0xf> 460a7: 48 c7 47 10 00 00 00 movq $0x0,0x10(%rdi) 460ae: 00 460af: c3 retq 00000000000460b0 <bar>: 460b0: 48 83 7f 10 06 cmpq $0x6,0x10(%rdi) 460b5: 72 08 jb 460bf <bar+0xf> 460b7: 48 c7 47 10 05 00 00 movq $0x5,0x10(%rdi) 460be: 00 460bf: c3 retq 00000000000460c0 <baz>: 460c0: 48 39 77 10 cmp %rsi,0x10(%rdi) 460c4: 76 04 jbe 460ca <baz+0xa> 460c6: 48 89 77 10 mov %rsi,0x10(%rdi) 460ca: c3 retq 460cb: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1) 00000000000460d0 <foo_string>: 460d0: 41 57 push %r15 460d2: 41 56 push %r14 460d4: 53 push %rbx 460d5: 48 8b 47 10 mov 0x10(%rdi),%rax 460d9: 48 85 c0 test %rax,%rax 460dc: 74 4a je 46128 <foo_string+0x58> 460de: 49 89 fe mov %rdi,%r14 460e1: 48 8b 0f mov (%rdi),%rcx 460e4: 48 8d 14 40 lea (%rax,%rax,2),%rdx 460e8: 48 8d 58 ff lea -0x1(%rax),%rbx 460ec: 4c 8d 3c d1 lea (%rcx,%rdx,8),%r15 460f0: 49 83 c7 f0 add $0xfffffffffffffff0,%r15 460f4: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1) 460fb: 00 00 00 460fe: 66 90 xchg %ax,%ax 46100: 49 89 5e 10 mov %rbx,0x10(%r14) 46104: 49 8b 37 mov (%r15),%rsi 46107: 48 85 f6 test %rsi,%rsi 4610a: 74 0e je 4611a <foo_string+0x4a> 4610c: 49 8b 7f f8 mov -0x8(%r15),%rdi 46110: ba 01 00 00 00 mov $0x1,%edx 46115: e8 a6 e9 ff ff callq 44ac0 <__rust_dealloc@plt> 4611a: 48 83 c3 ff add $0xffffffffffffffff,%rbx 4611e: 49 83 c7 e8 add $0xffffffffffffffe8,%r15 46122: 48 83 fb ff cmp $0xffffffffffffffff,%rbx 46126: 75 d8 jne 46100 <foo_string+0x30> 46128: 5b pop %rbx 46129: 41 5e pop %r14 4612b: 41 5f pop %r15 4612d: c3 retq 4612e: 66 90 xchg %ax,%ax 0000000000046130 <bar_string>: 46130: 41 57 push %r15 46132: 41 56 push %r14 46134: 53 push %rbx 46135: 4c 8b 7f 10 mov 0x10(%rdi),%r15 46139: 49 83 ff 06 cmp $0x6,%r15 4613d: 72 49 jb 46188 <bar_string+0x58> 4613f: 49 89 fe mov %rdi,%r14 46142: 48 8b 07 mov (%rdi),%rax 46145: 4b 8d 0c 7f lea (%r15,%r15,2),%rcx 46149: 48 8d 1c c8 lea (%rax,%rcx,8),%rbx 4614d: 48 83 c3 f0 add $0xfffffffffffffff0,%rbx 46151: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1) 46158: 00 00 00 4615b: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1) 46160: 49 83 c7 ff add $0xffffffffffffffff,%r15 46164: 4d 89 7e 10 mov %r15,0x10(%r14) 46168: 48 8b 33 mov (%rbx),%rsi 4616b: 48 85 f6 test %rsi,%rsi 4616e: 74 0e je 4617e <bar_string+0x4e> 46170: 48 8b 7b f8 mov -0x8(%rbx),%rdi 46174: ba 01 00 00 00 mov $0x1,%edx 46179: e8 42 e9 ff ff callq 44ac0 <__rust_dealloc@plt> 4617e: 48 83 c3 e8 add $0xffffffffffffffe8,%rbx 46182: 49 83 ff 05 cmp $0x5,%r15 46186: 77 d8 ja 46160 <bar_string+0x30> 46188: 5b pop %rbx 46189: 41 5e pop %r14 4618b: 41 5f pop %r15 4618d: c3 retq 4618e: 66 90 xchg %ax,%ax 0000000000046190 <baz_string>: 46190: 41 57 push %r15 46192: 41 56 push %r14 46194: 41 54 push %r12 46196: 53 push %rbx 46197: 50 push %rax 46198: 4c 8b 67 10 mov 0x10(%rdi),%r12 4619c: 49 39 f4 cmp %rsi,%r12 4619f: 76 46 jbe 461e7 <baz_string+0x57> 461a1: 49 89 f6 mov %rsi,%r14 461a4: 49 89 ff mov %rdi,%r15 461a7: 48 8b 07 mov (%rdi),%rax 461aa: 4b 8d 0c 64 lea (%r12,%r12,2),%rcx 461ae: 48 8d 1c c8 lea (%rax,%rcx,8),%rbx 461b2: 48 83 c3 f0 add $0xfffffffffffffff0,%rbx 461b6: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1) 461bd: 00 00 00 461c0: 49 83 c4 ff add $0xffffffffffffffff,%r12 461c4: 4d 89 67 10 mov %r12,0x10(%r15) 461c8: 48 8b 33 mov (%rbx),%rsi 461cb: 48 85 f6 test %rsi,%rsi 461ce: 74 0e je 461de <baz_string+0x4e> 461d0: 48 8b 7b f8 mov -0x8(%rbx),%rdi 461d4: ba 01 00 00 00 mov $0x1,%edx 461d9: e8 e2 e8 ff ff callq 44ac0 <__rust_dealloc@plt> 461de: 48 83 c3 e8 add $0xffffffffffffffe8,%rbx 461e2: 4d 39 f4 cmp %r14,%r12 461e5: 77 d9 ja 461c0 <baz_string+0x30> 461e7: 48 83 c4 08 add $0x8,%rsp 461eb: 5b pop %rbx 461ec: 41 5c pop %r12 461ee: 41 5e pop %r14 461f0: 41 5f pop %r15 461f2: c3 retq 461f3: 90 nop 461f4: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1) 461fb: 00 00 00 461fe: 66 90 xchg %ax,%ax ``` </details> <details> <summary>New output</summary> ```asm 0000000000084d10 <foo>: 84d10: 48 c7 47 10 00 00 00 movq $0x0,0x10(%rdi) 84d17: 00 84d18: c3 retq 84d19: 0f 1f 80 00 00 00 00 nopl 0x0(%rax) 0000000000084d20 <bar>: 84d20: 48 8b 47 10 mov 0x10(%rdi),%rax 84d24: 48 83 f8 05 cmp $0x5,%rax 84d28: b9 05 00 00 00 mov $0x5,%ecx 84d2d: 48 0f 42 c8 cmovb %rax,%rcx 84d31: 48 89 4f 10 mov %rcx,0x10(%rdi) 84d35: c3 retq 84d36: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1) 84d3d: 00 00 00 0000000000084d40 <baz>: 84d40: 48 8b 47 10 mov 0x10(%rdi),%rax 84d44: 48 39 f0 cmp %rsi,%rax 84d47: 48 0f 47 c6 cmova %rsi,%rax 84d4b: 48 89 47 10 mov %rax,0x10(%rdi) 84d4f: c3 retq 0000000000084d50 <foo_string>: 84d50: 41 57 push %r15 84d52: 41 56 push %r14 84d54: 53 push %rbx 84d55: 49 89 fe mov %rdi,%r14 84d58: 4c 8b 7f 10 mov 0x10(%rdi),%r15 84d5c: 4d 85 ff test %r15,%r15 84d5f: 74 2f je 84d90 <foo_string+0x40> 84d61: 49 8b 06 mov (%r14),%rax 84d64: 4b 8d 0c 7f lea (%r15,%r15,2),%rcx 84d68: 48 8d 1c c8 lea (%rax,%rcx,8),%rbx 84d6c: 48 83 c3 f0 add $0xfffffffffffffff0,%rbx 84d70: 48 8b 33 mov (%rbx),%rsi 84d73: 48 85 f6 test %rsi,%rsi 84d76: 74 0e je 84d86 <foo_string+0x36> 84d78: 48 8b 7b f8 mov -0x8(%rbx),%rdi 84d7c: ba 01 00 00 00 mov $0x1,%edx 84d81: e8 1a b1 ff ff callq 7fea0 <__rust_dealloc@plt> 84d86: 48 83 c3 e8 add $0xffffffffffffffe8,%rbx 84d8a: 49 83 c7 ff add $0xffffffffffffffff,%r15 84d8e: 75 e0 jne 84d70 <foo_string+0x20> 84d90: 49 c7 46 10 00 00 00 movq $0x0,0x10(%r14) 84d97: 00 84d98: 5b pop %rbx 84d99: 41 5e pop %r14 84d9b: 41 5f pop %r15 84d9d: c3 retq 84d9e: 66 90 xchg %ax,%ax 0000000000084da0 <bar_string>: 84da0: 41 57 push %r15 84da2: 41 56 push %r14 84da4: 53 push %rbx 84da5: 49 89 fe mov %rdi,%r14 84da8: 4c 8b 7f 10 mov 0x10(%rdi),%r15 84dac: 49 83 ff 06 cmp $0x6,%r15 84db0: 72 44 jb 84df6 <bar_string+0x56> 84db2: 49 8b 06 mov (%r14),%rax 84db5: 4b 8d 0c 7f lea (%r15,%r15,2),%rcx 84db9: 48 8d 1c c8 lea (%rax,%rcx,8),%rbx 84dbd: 48 83 c3 f0 add $0xfffffffffffffff0,%rbx 84dc1: 49 83 c7 fb add $0xfffffffffffffffb,%r15 84dc5: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1) 84dcc: 00 00 00 84dcf: 90 nop 84dd0: 48 8b 33 mov (%rbx),%rsi 84dd3: 48 85 f6 test %rsi,%rsi 84dd6: 74 0e je 84de6 <bar_string+0x46> 84dd8: 48 8b 7b f8 mov -0x8(%rbx),%rdi 84ddc: ba 01 00 00 00 mov $0x1,%edx 84de1: e8 ba b0 ff ff callq 7fea0 <__rust_dealloc@plt> 84de6: 48 83 c3 e8 add $0xffffffffffffffe8,%rbx 84dea: 49 83 c7 ff add $0xffffffffffffffff,%r15 84dee: 75 e0 jne 84dd0 <bar_string+0x30> 84df0: 41 bf 05 00 00 00 mov $0x5,%r15d 84df6: 4d 89 7e 10 mov %r15,0x10(%r14) 84dfa: 5b pop %rbx 84dfb: 41 5e pop %r14 84dfd: 41 5f pop %r15 84dff: c3 retq 0000000000084e00 <baz_string>: 84e00: 41 57 push %r15 84e02: 41 56 push %r14 84e04: 41 54 push %r12 84e06: 53 push %rbx 84e07: 50 push %rax 84e08: 49 89 ff mov %rdi,%r15 84e0b: 48 8b 47 10 mov 0x10(%rdi),%rax 84e0f: 49 89 c4 mov %rax,%r12 84e12: 49 29 f4 sub %rsi,%r12 84e15: 76 3c jbe 84e53 <baz_string+0x53> 84e17: 49 89 f6 mov %rsi,%r14 84e1a: 49 8b 0f mov (%r15),%rcx 84e1d: 48 8d 04 40 lea (%rax,%rax,2),%rax 84e21: 48 8d 1c c1 lea (%rcx,%rax,8),%rbx 84e25: 48 83 c3 f0 add $0xfffffffffffffff0,%rbx 84e29: 0f 1f 80 00 00 00 00 nopl 0x0(%rax) 84e30: 48 8b 33 mov (%rbx),%rsi 84e33: 48 85 f6 test %rsi,%rsi 84e36: 74 0e je 84e46 <baz_string+0x46> 84e38: 48 8b 7b f8 mov -0x8(%rbx),%rdi 84e3c: ba 01 00 00 00 mov $0x1,%edx 84e41: e8 5a b0 ff ff callq 7fea0 <__rust_dealloc@plt> 84e46: 48 83 c3 e8 add $0xffffffffffffffe8,%rbx 84e4a: 49 83 c4 ff add $0xffffffffffffffff,%r12 84e4e: 75 e0 jne 84e30 <baz_string+0x30> 84e50: 4c 89 f0 mov %r14,%rax 84e53: 49 89 47 10 mov %rax,0x10(%r15) 84e57: 48 83 c4 08 add $0x8,%rsp 84e5b: 5b pop %rbx 84e5c: 41 5c pop %r12 84e5e: 41 5e pop %r14 84e60: 41 5f pop %r15 84e62: c3 retq 84e63: 90 nop 84e64: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1) 84e6b: 00 00 00 84e6e: 66 90 xchg %ax,%ax ``` </details> For calling `truncate` with non-zero lengths on non-`Drop` types, it seems that a redundant load and comparison gets replaced with an awkward sequence with a conditional move. In the unknown length case, the new code is no longer awkward. Maybe someone moderately proficient at assembly could tell if this looks like a win or not. --- This came up when discussing replacing `unsafe { vec.set_len(0) }` with `vec.clear()` in a project where the author was worried about potential performance degradation. It might be worth replacing some unsafe code, even it it's trivial to see that it's actually safe.		2018-08-01 21:46:31 +02:00
src	Rollup merge of #52908 - lnicola:vec-truncate-opt, r=alexcrichton	2018-08-01 21:46:31 +02:00
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CODE_OF_CONDUCT.md
config.toml.example
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CONTRIBUTING.md
COPYRIGHT	Remove references to AUTHORS.txt file	2018-07-30 07:47:12 +02:00
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README.md
RELEASES.md	Rollup merge of #52929 - Havvy:patch-1, r=alexcrichton	2018-08-01 10:13:10 +02:00
x.py

README.md

The Rust Programming Language

This is the main source code repository for Rust. It contains the compiler, standard library, and documentation.

Quick Start

Read "Installation" from The Book.

Building from Source

Building on *nix

Make sure you have installed the dependencies:
- g++ 4.7 or later or clang++ 3.x or later
- python 2.7 (but not 3.x)
- GNU make 3.81 or later
- cmake 3.4.3 or later
- curl
- git

Clone the source with git:

$ git clone https://github.com/rust-lang/rust.git
$ cd rust

Build and install:
```
$ git submodule update --init --recursive --progress
$ ./x.py build && sudo ./x.py install
```
Note: Install locations can be adjusted by copying the config file from ./config.toml.example to ./config.toml, and adjusting the prefix option under [install]. Various other options, such as enabling debug information, are also supported, and are documented in the config file.

When complete, sudo ./x.py install will place several programs into /usr/local/bin: rustc, the Rust compiler, and rustdoc, the API-documentation tool. This install does not include Cargo, Rust's package manager, which you may also want to build.

Building on Windows

There are two prominent ABIs in use on Windows: the native (MSVC) ABI used by Visual Studio, and the GNU ABI used by the GCC toolchain. Which version of Rust you need depends largely on what C/C++ libraries you want to interoperate with: for interop with software produced by Visual Studio use the MSVC build of Rust; for interop with GNU software built using the MinGW/MSYS2 toolchain use the GNU build.

MinGW

MSYS2 can be used to easily build Rust on Windows:

Grab the latest MSYS2 installer and go through the installer.
Run mingw32_shell.bat or mingw64_shell.bat from wherever you installed MSYS2 (i.e. C:\msys64), depending on whether you want 32-bit or 64-bit Rust. (As of the latest version of MSYS2 you have to run msys2_shell.cmd -mingw32 or msys2_shell.cmd -mingw64 from the command line instead)

From this terminal, install the required tools:

# Update package mirrors (may be needed if you have a fresh install of MSYS2)
$ pacman -Sy pacman-mirrors

# Install build tools needed for Rust. If you're building a 32-bit compiler,
# then replace "x86_64" below with "i686". If you've already got git, python,
# or CMake installed and in PATH you can remove them from this list. Note
# that it is important that you do **not** use the 'python2' and 'cmake'
# packages from the 'msys2' subsystem. The build has historically been known
# to fail with these packages.
$ pacman -S git \
            make \
            diffutils \
            tar \
            mingw-w64-x86_64-python2 \
            mingw-w64-x86_64-cmake \
            mingw-w64-x86_64-gcc

Navigate to Rust's source code (or clone it), then build it:
```
$ ./x.py build && ./x.py install
```

MSVC

MSVC builds of Rust additionally require an installation of Visual Studio 2013 (or later) so rustc can use its linker. Make sure to check the “C++ tools” option.

With these dependencies installed, you can build the compiler in a cmd.exe shell with:

> python x.py build

Currently, building Rust only works with some known versions of Visual Studio. If you have a more recent version installed the build system doesn't understand then you may need to force rustbuild to use an older version. This can be done by manually calling the appropriate vcvars file before running the bootstrap.

CALL "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\bin\amd64\vcvars64.bat"
python x.py build

Specifying an ABI

Each specific ABI can also be used from either environment (for example, using the GNU ABI in PowerShell) by using an explicit build triple. The available Windows build triples are:

GNU ABI (using GCC)
- i686-pc-windows-gnu
- x86_64-pc-windows-gnu
The MSVC ABI
- i686-pc-windows-msvc
- x86_64-pc-windows-msvc

The build triple can be specified by either specifying --build=<triple> when invoking x.py commands, or by copying the config.toml file (as described in Building From Source), and modifying the build option under the [build] section.

Configure and Make

While it's not the recommended build system, this project also provides a configure script and makefile (the latter of which just invokes x.py).

$ ./configure
$ make && sudo make install

When using the configure script, the generated config.mk file may override the config.toml file. To go back to the config.toml file, delete the generated config.mk file.

Building Documentation

If you’d like to build the documentation, it’s almost the same:

$ ./x.py doc

The generated documentation will appear under doc in the build directory for the ABI used. I.e., if the ABI was x86_64-pc-windows-msvc, the directory will be build\x86_64-pc-windows-msvc\doc.

Notes

Since the Rust compiler is written in Rust, it must be built by a precompiled "snapshot" version of itself (made in an earlier stage 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:

Platform / Architecture	x86	x86_64
Windows (7, 8, Server 2008 R2)	✓	✓
Linux (2.6.18 or later)	✓	✓
OSX (10.7 Lion or later)	✓	✓

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

Rust currently needs between 600MiB and 1.5GiB of RAM to build, depending on platform. If it hits swap, it will take a very long time to build.

There is more advice about hacking on Rust in CONTRIBUTING.md.

Getting Help

The Rust community congregates in a few places:

Stack Overflow - Direct questions about using the language.
users.rust-lang.org - General discussion and broader questions.
/r/rust - News and general discussion.

Contributing

To contribute to Rust, please see CONTRIBUTING.

Rust has an IRC culture and most real-time collaboration happens in a variety of channels on Mozilla's IRC network, irc.mozilla.org. The most popular channel is #rust, a venue for general discussion about Rust. And a good place to ask for help would be #rust-beginners.

The rustc guide might be a good place to start if you want to find out how various parts of the compiler work.

Also, you may find the rustdocs for the compiler itself useful.

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.

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