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//! Rustc internal tooling for hand-writing MIR.
//!
//! If for some reasons you are not writing rustc tests and have found yourself considering using
//! this feature, turn back. This is *exceptionally* unstable. There is no attempt at all to make
//! anything work besides those things which the rustc test suite happened to need. If you make a
//! typo you'll probably ICE. Really, this is not the solution to your problems. Consider instead
//! supporting the [stable MIR project group](https://github.com/rust-lang/project-stable-mir).
//!
//! The documentation for this module describes how to use this feature. If you are interested in
//! hacking on the implementation, most of that documentation lives at
//! `rustc_mir_building/src/build/custom/mod.rs`.
//!
//! Typical usage will look like this:
//!
//! ```rust
//! #![feature(core_intrinsics, custom_mir)]
//!
//! extern crate core;
//! use core::intrinsics::mir::*;
//!
//! #[custom_mir(dialect = "built")]
//! pub fn simple(x: i32) -> i32 {
//! mir!(
//! let temp2: i32;
//!
//! {
//! let temp1 = x;
//! Goto(my_second_block)
//! }
//!
//! my_second_block = {
//! temp2 = Move(temp1);
//! RET = temp2;
//! Return()
//! }
//! )
//! }
//! ```
//!
//! The `custom_mir` attribute tells the compiler to treat the function as being custom MIR. This
//! attribute only works on functions - there is no way to insert custom MIR into the middle of
//! another function. The `dialect` and `phase` parameters indicate which [version of MIR][dialect
//! docs] you are inserting here. Generally you'll want to use `#![custom_mir(dialect = "built")]`
//! if you want your MIR to be modified by the full MIR pipeline, or `#![custom_mir(dialect =
//! "runtime", phase = "optimized")] if you don't.
//!
//! [dialect docs]:
//! https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/mir/enum.MirPhase.html
//!
//! The input to the [`mir!`] macro is:
//!
//! - A possibly empty list of local declarations. Locals can also be declared inline on
//! assignments via `let`. Type inference generally works. Shadowing does not.
//! - A list of basic blocks. The first of these is the start block and is where execution begins.
//! All blocks other than the start block need to be given a name, so that they can be referred
//! to later.
//! - Each block is a list of semicolon terminated statements, followed by a terminator. The
//! syntax for the various statements and terminators is designed to be as similar as possible
//! to the syntax for analogous concepts in native Rust. See below for a list.
//!
//! # Examples
//!
#![cfg_attr(bootstrap, doc = "```rust,compile_fail")]
#![cfg_attr(not(bootstrap), doc = "```rust")]
//! #![feature(core_intrinsics, custom_mir)]
//!
//! extern crate core;
//! use core::intrinsics::mir::*;
//!
//! #[custom_mir(dialect = "built")]
//! pub fn choose_load(a: &i32, b: &i32, c: bool) -> i32 {
//! mir!(
//! {
//! match c {
//! true => t,
//! _ => f,
//! }
//! }
//!
//! t = {
//! let temp = a;
//! Goto(load_and_exit)
//! }
//!
//! f = {
//! temp = b;
//! Goto(load_and_exit)
//! }
//!
//! load_and_exit = {
//! RET = *temp;
//! Return()
//! }
//! )
//! }
//!
//! #[custom_mir(dialect = "built")]
//! fn unwrap_unchecked<T>(opt: Option<T>) -> T {
//! mir!({
//! RET = Move(Field(Variant(opt, 1), 0));
//! Return()
//! })
//! }
//!
//! #[custom_mir(dialect = "runtime", phase = "optimized")]
//! fn push_and_pop<T>(v: &mut Vec<T>, value: T) {
//! mir!(
//! let unused;
//! let popped;
//!
//! {
//! Call(unused, pop, Vec::push(v, value))
//! }
//!
//! pop = {
//! Call(popped, drop, Vec::pop(v))
//! }
//!
//! drop = {
//! Drop(popped, ret)
//! }
//!
//! ret = {
//! Return()
//! }
//! )
//! }
//! ```
//!
//! We can also set off compilation failures that happen in sufficiently late stages of the
//! compiler:
//!
//! ```rust,compile_fail
//! #![feature(core_intrinsics, custom_mir)]
//!
//! extern crate core;
//! use core::intrinsics::mir::*;
//!
//! #[custom_mir(dialect = "built")]
//! fn borrow_error(should_init: bool) -> i32 {
//! mir!(
//! let temp: i32;
//!
//! {
//! match should_init {
//! true => init,
//! _ => use_temp,
//! }
//! }
//!
//! init = {
//! temp = 0;
//! Goto(use_temp)
//! }
//!
//! use_temp = {
//! RET = temp;
//! Return()
//! }
//! )
//! }
//! ```
//!
//! ```text
//! error[E0381]: used binding is possibly-uninitialized
//! --> test.rs:24:13
//! |
//! 8 | / mir!(
//! 9 | | let temp: i32;
//! 10 | |
//! 11 | | {
//! ... |
//! 19 | | temp = 0;
//! | | -------- binding initialized here in some conditions
//! ... |
//! 24 | | RET = temp;
//! | | ^^^^^^^^^^ value used here but it is possibly-uninitialized
//! 25 | | Return()
//! 26 | | }
//! 27 | | )
//! | |_____- binding declared here but left uninitialized
//!
//! error: aborting due to previous error
//!
//! For more information about this error, try `rustc --explain E0381`.
//! ```
//!
//! # Syntax
//!
//! The lists below are an exhaustive description of how various MIR constructs can be created.
//! Anything missing from the list should be assumed to not be supported, PRs welcome.
//!
//! #### Locals
//!
//! - The `_0` return local can always be accessed via `RET`.
//! - Arguments can be accessed via their regular name.
//! - All other locals need to be declared with `let` somewhere and then can be accessed by name.
//!
//! #### Places
//! - Locals implicit convert to places.
//! - Field accesses, derefs, and indexing work normally.
//! - Fields in variants can be accessed via the [`Variant`] and [`Field`] associated functions,
//! see their documentation for details.
//!
//! #### Operands
//! - Places implicitly convert to `Copy` operands.
//! - `Move` operands can be created via [`Move`].
//! - Const blocks, literals, named constants, and const params all just work.
//! - [`Static`] and [`StaticMut`] can be used to create `&T` and `*mut T`s to statics. These are
//! constants in MIR and the only way to access statics.
//!
//! #### Statements
//! - Assign statements work via normal Rust assignment.
//! - [`Retag`] statements have an associated function.
//!
//! #### Rvalues
//!
//! - Operands implicitly convert to `Use` rvalues.
//! - `&`, `&mut`, `addr_of!`, and `addr_of_mut!` all work to create their associated rvalue.
//! - [`Discriminant`] has an associated function.
//!
//! #### Terminators
//!
//! Custom MIR does not currently support cleanup blocks or non-trivial unwind paths. As such, there
//! are no resume and abort terminators, and terminators that might unwind do not have any way to
//! indicate the unwind block.
//!
//! - [`Goto`], [`Return`], [`Unreachable`], [`Drop`](Drop()), and [`DropAndReplace`] have associated functions.
//! - `match some_int_operand` becomes a `SwitchInt`. Each arm should be `literal => basic_block`
//! - The exception is the last arm, which must be `_ => basic_block` and corresponds to the
//! otherwise branch.
//! - [`Call`] has an associated function as well. The third argument of this function is a normal
//! function call expresion, for example `my_other_function(a, 5)`.
//!
#![unstable(
feature = "custom_mir",
reason = "MIR is an implementation detail and extremely unstable",
issue = "none"
)]
#![allow(unused_variables, non_snake_case, missing_debug_implementations)]
/// Type representing basic blocks.
///
/// All terminators will have this type as a return type. It helps achieve some type safety.
pub struct BasicBlock;
macro_rules! define {
($name:literal, $( #[ $meta:meta ] )* fn $($sig:tt)*) => {
#[rustc_diagnostic_item = $name]
$( #[ $meta ] )*
pub fn $($sig)* { panic!() }
}
}
define!("mir_return", fn Return() -> BasicBlock);
define!("mir_goto", fn Goto(destination: BasicBlock) -> BasicBlock);
define!("mir_unreachable", fn Unreachable() -> BasicBlock);
define!("mir_drop", fn Drop<T>(place: T, goto: BasicBlock));
define!("mir_drop_and_replace", fn DropAndReplace<T>(place: T, value: T, goto: BasicBlock));
define!("mir_call", fn Call<T>(place: T, goto: BasicBlock, call: T));
define!("mir_retag", fn Retag<T>(place: T));
define!("mir_move", fn Move<T>(place: T) -> T);
define!("mir_static", fn Static<T>(s: T) -> &'static T);
define!("mir_static_mut", fn StaticMut<T>(s: T) -> *mut T);
define!(
"mir_discriminant",
/// Gets the discriminant of a place.
fn Discriminant<T>(place: T) -> <T as ::core::marker::DiscriminantKind>::Discriminant
);
define!("mir_set_discriminant", fn SetDiscriminant<T>(place: T, index: u32));
define!(
"mir_field",
/// Access the field with the given index of some place.
///
/// This only makes sense to use in conjunction with [`Variant`]. If the type you are looking to
/// access the field of does not have variants, you can use normal field projection syntax.
///
/// There is no proper way to do a place projection to a variant in Rust, and so these two
/// functions are a workaround. You can access a field of a variant via `Field(Variant(place,
/// var_idx), field_idx)`, where `var_idx` and `field_idx` are appropriate literals. Some
/// caveats:
///
/// - The return type of `Variant` is always `()`. Don't worry about that, the correct MIR will
/// still be generated.
/// - In some situations, the return type of `Field` cannot be inferred. You may need to
/// annotate it on the function in these cases.
/// - Since `Field` is a function call which is not a place expression, using this on the left
/// hand side of an expression is rejected by the compiler. [`place!`] is a macro provided to
/// work around that issue. Wrap the left hand side of an assignment in the macro to convince
/// the compiler that it's ok.
///
/// # Examples
///
#[cfg_attr(bootstrap, doc = "```rust,compile_fail")]
#[cfg_attr(not(bootstrap), doc = "```rust")]
/// #![feature(custom_mir, core_intrinsics)]
///
/// extern crate core;
/// use core::intrinsics::mir::*;
///
/// #[custom_mir(dialect = "built")]
/// fn unwrap_deref(opt: Option<&i32>) -> i32 {
/// mir!({
/// RET = *Field::<&i32>(Variant(opt, 1), 0);
/// Return()
/// })
/// }
///
/// #[custom_mir(dialect = "built")]
/// fn set(opt: &mut Option<i32>) {
/// mir!({
/// place!(Field(Variant(*opt, 1), 0)) = 5;
/// Return()
/// })
/// }
/// ```
fn Field<F>(place: (), field: u32) -> F
);
define!(
"mir_variant",
/// Adds a variant projection with the given index to the place.
///
/// See [`Field`] for documentation.
fn Variant<T>(place: T, index: u32) -> ()
);
define!(
"mir_make_place",
#[doc(hidden)]
fn __internal_make_place<T>(place: T) -> *mut T
);
/// Macro for generating custom MIR.
///
/// See the module documentation for syntax details. This macro is not magic - it only transforms
/// your MIR into something that is easier to parse in the compiler.
#[rustc_macro_transparency = "transparent"]
pub macro mir {
(
$(let $local_decl:ident $(: $local_decl_ty:ty)? ;)*
{
$($entry:tt)*
}
$(
$block_name:ident = {
$($block:tt)*
}
)*
) => {{
// First, we declare all basic blocks.
$(
let $block_name: ::core::intrinsics::mir::BasicBlock;
)*
{
// Now all locals
#[allow(non_snake_case)]
let RET;
$(
let $local_decl $(: $local_decl_ty)? ;
)*
::core::intrinsics::mir::__internal_extract_let!($($entry)*);
$(
::core::intrinsics::mir::__internal_extract_let!($($block)*);
)*
{
// Finally, the contents of the basic blocks
::core::intrinsics::mir::__internal_remove_let!({
{}
{ $($entry)* }
});
$(
::core::intrinsics::mir::__internal_remove_let!({
{}
{ $($block)* }
});
)*
RET
}
}
}}
}
/// Helper macro that allows you to treat a value expression like a place expression.
///
/// See the documentation on [`Variant`] for why this is necessary and how to use it.
pub macro place($e:expr) {
(*::core::intrinsics::mir::__internal_make_place($e))
}
/// Helper macro that extracts the `let` declarations out of a bunch of statements.
///
/// This macro is written using the "statement muncher" strategy. Each invocation parses the first
/// statement out of the input, does the appropriate thing with it, and then recursively calls the
/// same macro on the remainder of the input.
#[doc(hidden)]
pub macro __internal_extract_let {
// If it's a `let` like statement, keep the `let`
(
let $var:ident $(: $ty:ty)? = $expr:expr; $($rest:tt)*
) => {
let $var $(: $ty)?;
::core::intrinsics::mir::__internal_extract_let!($($rest)*);
},
// Due to #86730, we have to handle const blocks separately
(
let $var:ident $(: $ty:ty)? = const $block:block; $($rest:tt)*
) => {
let $var $(: $ty)?;
::core::intrinsics::mir::__internal_extract_let!($($rest)*);
},
// Otherwise, output nothing
(
$stmt:stmt; $($rest:tt)*
) => {
::core::intrinsics::mir::__internal_extract_let!($($rest)*);
},
(
$expr:expr
) => {}
}
/// Helper macro that removes the `let` declarations from a bunch of statements.
///
/// Because expression position macros cannot expand to statements + expressions, we need to be
/// slightly creative here. The general strategy is also statement munching as above, but the output
/// of the macro is "stored" in the subsequent macro invocation. Easiest understood via example:
/// ```text
/// invoke!(
/// {
/// {
/// x = 5;
/// }
/// {
/// let d = e;
/// Call()
/// }
/// }
/// )
/// ```
/// becomes
/// ```text
/// invoke!(
/// {
/// {
/// x = 5;
/// d = e;
/// }
/// {
/// Call()
/// }
/// }
/// )
/// ```
#[doc(hidden)]
pub macro __internal_remove_let {
// If it's a `let` like statement, remove the `let`
(
{
{
$($already_parsed:tt)*
}
{
let $var:ident $(: $ty:ty)? = $expr:expr;
$($rest:tt)*
}
}
) => { ::core::intrinsics::mir::__internal_remove_let!(
{
{
$($already_parsed)*
$var = $expr;
}
{
$($rest)*
}
}
)},
// Due to #86730 , we have to handle const blocks separately
(
{
{
$($already_parsed:tt)*
}
{
let $var:ident $(: $ty:ty)? = const $block:block;
$($rest:tt)*
}
}
) => { ::core::intrinsics::mir::__internal_remove_let!(
{
{
$($already_parsed)*
$var = const $block;
}
{
$($rest)*
}
}
)},
// Otherwise, keep going
(
{
{
$($already_parsed:tt)*
}
{
$stmt:stmt;
$($rest:tt)*
}
}
) => { ::core::intrinsics::mir::__internal_remove_let!(
{
{
$($already_parsed)*
$stmt;
}
{
$($rest)*
}
}
)},
(
{
{
$($already_parsed:tt)*
}
{
$expr:expr
}
}
) => {
{
$($already_parsed)*
$expr
}
},
}