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bors 3a7dfda40a Auto merge of #69171 - Amanieu:new-asm, r=nagisa,nikomatsakis

Implement new asm! syntax from RFC 2850

This PR implements the new `asm!` syntax proposed in https://github.com/rust-lang/rfcs/pull/2850.

# Design

A large part of this PR revolves around taking an `asm!` macro invocation and plumbing it through all of the compiler layers down to LLVM codegen. Throughout the various stages, an `InlineAsm` generally consists of 3 components:

- The template string, which is stored as an array of `InlineAsmTemplatePiece`. Each piece represents either a literal or a placeholder for an operand (just like format strings).
```rust
pub enum InlineAsmTemplatePiece {
    String(String),
    Placeholder { operand_idx: usize, modifier: Option<char>, span: Span },
}
```

- The list of operands to the `asm!` (`in`, `[late]out`, `in[late]out`, `sym`, `const`). These are represented differently at each stage of lowering, but follow a common pattern:
  - `in`, `out` and `inout` all have an associated register class (`reg`) or explicit register (`"eax"`).
  - `inout` has 2 forms: one with a single expression that is both read from and written to, and one with two separate expressions for the input and output parts.
  - `out` and `inout` have a `late` flag (`lateout` / `inlateout`) to indicate that the register allocator is allowed to reuse an input register for this output.
  - `out` and the split variant of `inout` allow `_` to be specified for an output, which means that the output is discarded. This is used to allocate scratch registers for assembly code.
  - `sym` is a bit special since it only accepts a path expression, which must point to a `static` or a `fn`.

- The options set at the end of the `asm!` macro. The only one that is particularly of interest to rustc is `NORETURN` which makes `asm!` return `!` instead of `()`.
```rust
bitflags::bitflags! {
    pub struct InlineAsmOptions: u8 {
        const PURE = 1 << 0;
        const NOMEM = 1 << 1;
        const READONLY = 1 << 2;
        const PRESERVES_FLAGS = 1 << 3;
        const NORETURN = 1 << 4;
        const NOSTACK = 1 << 5;
    }
}
```

## AST

`InlineAsm` is represented as an expression in the AST:

```rust
pub struct InlineAsm {
    pub template: Vec<InlineAsmTemplatePiece>,
    pub operands: Vec<(InlineAsmOperand, Span)>,
    pub options: InlineAsmOptions,
}

pub enum InlineAsmRegOrRegClass {
    Reg(Symbol),
    RegClass(Symbol),
}

pub enum InlineAsmOperand {
    In {
        reg: InlineAsmRegOrRegClass,
        expr: P<Expr>,
    },
    Out {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        expr: Option<P<Expr>>,
    },
    InOut {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        expr: P<Expr>,
    },
    SplitInOut {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        in_expr: P<Expr>,
        out_expr: Option<P<Expr>>,
    },
    Const {
        expr: P<Expr>,
    },
    Sym {
        expr: P<Expr>,
    },
}
```

The `asm!` macro is implemented in librustc_builtin_macros and outputs an `InlineAsm` AST node. The template string is parsed using libfmt_macros, positional and named operands are resolved to explicit operand indicies. Since target information is not available to macro invocations, validation of the registers and register classes is deferred to AST lowering.

## HIR

`InlineAsm` is represented as an expression in the HIR:

```rust
pub struct InlineAsm<'hir> {
    pub template: &'hir [InlineAsmTemplatePiece],
    pub operands: &'hir [InlineAsmOperand<'hir>],
    pub options: InlineAsmOptions,
}

pub enum InlineAsmRegOrRegClass {
    Reg(InlineAsmReg),
    RegClass(InlineAsmRegClass),
}

pub enum InlineAsmOperand<'hir> {
    In {
        reg: InlineAsmRegOrRegClass,
        expr: Expr<'hir>,
    },
    Out {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        expr: Option<Expr<'hir>>,
    },
    InOut {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        expr: Expr<'hir>,
    },
    SplitInOut {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        in_expr: Expr<'hir>,
        out_expr: Option<Expr<'hir>>,
    },
    Const {
        expr: Expr<'hir>,
    },
    Sym {
        expr: Expr<'hir>,
    },
}
```

AST lowering is where `InlineAsmRegOrRegClass` is converted from `Symbol`s to an actual register or register class. If any modifiers are specified for a template string placeholder, these are validated against the set allowed for that operand type. Finally, explicit registers for inputs and outputs are checked for conflicts (same register used for different operands).

## Type checking

Each register class has a whitelist of types that it may be used with. After the types of all operands have been determined, the `intrinsicck` pass will check that these types are in the whitelist. It also checks that split `inout` operands have compatible types and that `const` operands are integers or floats. Suggestions are emitted where needed if a template modifier should be used for an operand based on the type that was passed into it.

## HAIR

`InlineAsm` is represented as an expression in the HAIR:

```rust
crate enum ExprKind<'tcx> {
    // [..]
    InlineAsm {
        template: &'tcx [InlineAsmTemplatePiece],
        operands: Vec<InlineAsmOperand<'tcx>>,
        options: InlineAsmOptions,
    },
}
crate enum InlineAsmOperand<'tcx> {
    In {
        reg: InlineAsmRegOrRegClass,
        expr: ExprRef<'tcx>,
    },
    Out {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        expr: Option<ExprRef<'tcx>>,
    },
    InOut {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        expr: ExprRef<'tcx>,
    },
    SplitInOut {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        in_expr: ExprRef<'tcx>,
        out_expr: Option<ExprRef<'tcx>>,
    },
    Const {
        expr: ExprRef<'tcx>,
    },
    SymFn {
        expr: ExprRef<'tcx>,
    },
    SymStatic {
        expr: ExprRef<'tcx>,
    },
}
```

The only significant change compared to HIR is that `Sym` has been lowered to either a `SymFn` whose `expr` is a `Literal` ZST of the `fn`, or a `SymStatic` whose `expr` is a `StaticRef`.

## MIR

`InlineAsm` is represented as a `Terminator` in the MIR:

```rust
pub enum TerminatorKind<'tcx> {
    // [..]

    /// Block ends with an inline assembly block. This is a terminator since
    /// inline assembly is allowed to diverge.
    InlineAsm {
        /// The template for the inline assembly, with placeholders.
        template: &'tcx [InlineAsmTemplatePiece],

        /// The operands for the inline assembly, as `Operand`s or `Place`s.
        operands: Vec<InlineAsmOperand<'tcx>>,

        /// Miscellaneous options for the inline assembly.
        options: InlineAsmOptions,

        /// Destination block after the inline assembly returns, unless it is
        /// diverging (InlineAsmOptions::NORETURN).
        destination: Option<BasicBlock>,
    },
}

pub enum InlineAsmOperand<'tcx> {
    In {
        reg: InlineAsmRegOrRegClass,
        value: Operand<'tcx>,
    },
    Out {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        place: Option<Place<'tcx>>,
    },
    InOut {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        in_value: Operand<'tcx>,
        out_place: Option<Place<'tcx>>,
    },
    Const {
        value: Operand<'tcx>,
    },
    SymFn {
        value: Box<Constant<'tcx>>,
    },
    SymStatic {
        value: Box<Constant<'tcx>>,
    },
}
```

As part of HAIR lowering, `InOut` and `SplitInOut` operands are lowered to a split form with a separate `in_value` and `out_place`.

Semantically, the `InlineAsm` terminator is similar to the `Call` terminator except that it has multiple output places where a `Call` only has a single return place output.

The constant promotion pass is used to ensure that `const` operands are actually constants (using the same logic as `#[rustc_args_required_const]`).

## Codegen

Operands are lowered one more time before being passed to LLVM codegen:

```rust
pub enum InlineAsmOperandRef<'tcx, B: BackendTypes + ?Sized> {
    In {
        reg: InlineAsmRegOrRegClass,
        value: OperandRef<'tcx, B::Value>,
    },
    Out {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        place: Option<PlaceRef<'tcx, B::Value>>,
    },
    InOut {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        in_value: OperandRef<'tcx, B::Value>,
        out_place: Option<PlaceRef<'tcx, B::Value>>,
    },
    Const {
        string: String,
    },
    SymFn {
        instance: Instance<'tcx>,
    },
    SymStatic {
        def_id: DefId,
    },
}
```

The operands are lowered to LLVM operands and constraint codes as follow:
- `out` and the output part of `inout` operands are added first, as required by LLVM. Late output operands have a `=` prefix added to their constraint code, non-late output operands have a `=&` prefix added to their constraint code.
- `in` operands are added normally.
- `inout` operands are tied to the matching output operand.
- `sym` operands are passed as function pointers or pointers, using the `"s"` constraint.
- `const` operands are formatted to a string and directly inserted in the template string.

The template string is converted to LLVM form:
- `$` characters are escaped as `$$`.
- `const` operands are converted to strings and inserted directly.
- Placeholders are formatted as `${X:M}` where `X` is the operand index and `M` is the modifier character. Modifiers are converted from the Rust form to the LLVM form.

The various options are converted to clobber constraints or LLVM attributes, refer to the [RFC](https://github.com/Amanieu/rfcs/blob/inline-asm/text/0000-inline-asm.md#mapping-to-llvm-ir) for more details.

Note that LLVM is sometimes rather picky about what types it accepts for certain constraint codes so we sometimes need to insert conversions to/from a supported type. See the target-specific ISelLowering.cpp files in LLVM for details.

# Adding support for new architectures

Adding inline assembly support to an architecture is mostly a matter of defining the registers and register classes for that architecture. All the definitions for register classes are located in `src/librustc_target/asm/`.

Additionally you will need to implement lowering of these register classes to LLVM constraint codes in `src/librustc_codegen_llvm/asm.rs`.

2020-05-19 18:32:40 +00:00

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Configure cache domain for GHA

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Auto merge of #69171 - Amanieu:new-asm, r=nagisa,nikomatsakis

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Update dlmalloc dependency to 0.1.4

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Merge commit '43a1777b89cf6791f9e20878b4e5e3ae907867a5' into clippyup

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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.

Installing from Source

Note: If you wish to contribute to the compiler, you should read this chapter of the rustc-dev-guide instead of this section.

The Rust build system has a Python script called x.py to bootstrap building the compiler. More information about it may be found by running ./x.py --help or reading the rustc dev guide.

Building on *nix

Make sure you have installed the dependencies:
- g++ 5.1 or later or clang++ 3.5 or later
- python 3 or 2.7
- GNU make 3.81 or later
- cmake 3.4.3 or later
- curl
- git
- ssl which comes in libssl-dev or openssl-devel
- pkg-config if you are compiling on Linux and targeting Linux

Clone the source with git:

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

Configure the build settings:

The Rust build system uses a file named config.toml in the root of the source tree to determine various configuration settings for the build. Copy the default config.toml.example to config.toml to get started.
```
$ cp config.toml.example config.toml
```
It is recommended that if you plan to use the Rust build system to create an installation (using ./x.py install) that you set the prefix value in the [install] section to a directory that you have write permissions.

Create install directory if you are not installing in default directory
Build and install:
```
$ ./x.py build && ./x.py install
```
When complete, ./x.py install will place several programs into $PREFIX/bin: rustc, the Rust compiler, and rustdoc, the API-documentation tool. This install does not include Cargo, Rust's package manager. To build and install Cargo, you may run ./x.py install cargo or set the build.extended key in config.toml to true to build and install all tools.

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-python \
            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 2017 (or later) so rustc can use its linker. The simplest way is to get the Visual Studio, check the “C++ build tools” and “Windows 10 SDK” workload.

(If you're installing cmake yourself, be careful that “C++ CMake tools for Windows” doesn't get included under “Individual components”.)

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\2019\Community\VC\Auxiliary\Build\vcvars64.bat"
> python x.py build

Building rustc with older host toolchains

It is still possible to build Rust with the older toolchain versions listed below, but only if the LLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN option is set to true in the config.toml file.

Clang 3.1
Apple Clang 3.1
GCC 4.8
Visual Studio 2015 (Update 3)

Toolchain versions older than what is listed above cannot be used to build rustc.

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 Installing 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, 10, ...)	✓	✓
Linux (2.6.18 or later)	✓	✓
macOS (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.

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.

Most real-time collaboration happens in a variety of channels on the Rust Discord server, with channels dedicated for getting help, community, documentation, and all major contribution areas in the Rust ecosystem. A good place to ask for help would be the #help channel.

The rustc dev 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.

See LICENSE-APACHE, LICENSE-MIT, and COPYRIGHT for details.

Trademark

The Rust programming language is an open source, community project governed by a core team. It is also sponsored by the Mozilla Foundation (“Mozilla”), which owns and protects the Rust and Cargo trademarks and logos (the “Rust Trademarks”).

If you want to use these names or brands, please read the media guide.

Third-party logos may be subject to third-party copyrights and trademarks. See Licenses for details.

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README.md Unescape Escape

The Rust Programming Language

Quick Start

Installing from Source

Building on *nix

Building on Windows

MinGW

MSVC

Building rustc with older host toolchains

Specifying an ABI

Configure and Make

Building Documentation

Notes

Getting Help

Contributing

License

Trademark

README.md