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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_build/src/build/custom/mod.rs`.
//!
//! Typical usage will look like this:
//!
//! ```rust
//! #![feature(core_intrinsics, custom_mir)]
//! #![allow(internal_features)]
//!
//! 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:
//!
//! - An optional return type annotation in the form of `type RET = ...;`. This may be required
//! if the compiler cannot infer the type of RET.
//! - 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
//!
//! ```rust
//! #![feature(core_intrinsics, custom_mir)]
//! #![allow(internal_features)]
//! #![allow(unused_assignments)]
//!
//! 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")]
#![cfg_attr(bootstrap, doc = "#[cfg(any())]")] // disable the following function in doctests when `bootstrap` is set
//! fn push_and_pop<T>(v: &mut Vec<T>, value: T) {
//! mir!(
//! let _unused;
//! let popped;
//!
//! {
//! Call(_unused = Vec::push(v, value), ReturnTo(pop), UnwindContinue())
//! }
//!
//! pop = {
//! Call(popped = Vec::pop(v), ReturnTo(drop), UnwindContinue())
//! }
//!
//! drop = {
//! Drop(popped, ReturnTo(ret), UnwindContinue())
//! }
//!
//! ret = {
//! Return()
//! }
//! )
//! }
//!
//! #[custom_mir(dialect = "runtime", phase = "optimized")]
//! fn annotated_return_type() -> (i32, bool) {
//! mir!(
//! type RET = (i32, bool);
//! {
//! RET.0 = 1;
//! RET.1 = true;
//! 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 1 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`], [`StorageLive`], [`StorageDead`], [`Deinit`] 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`], [`Len`], and [`CopyForDeref`] have associated functions.
//! - Unary and binary operations use their normal Rust syntax - `a * b`, `!c`, etc.
//! - The binary operation `Offset` can be created via [`Offset`].
//! - Checked binary operations are represented by wrapping the associated binop in [`Checked`].
//! - Array repetition syntax (`[foo; 10]`) creates the associated rvalue.
//!
//! #### Terminators
//!
//! - [`Goto`], [`Return`], [`Unreachable`] and [`Drop`](Drop()) 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, with special syntax:
//! `Call(ret_val = function(arg1, arg2, ...), ReturnTo(next_block), UnwindContinue())`.
#![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.
#[rustc_diagnostic_item = "mir_basic_block"]
pub enum BasicBlock {
/// A non-cleanup basic block.
Normal,
/// A basic block that lies on an unwind path.
Cleanup,
}
/// The reason we are terminating the process during unwinding.
#[rustc_diagnostic_item = "mir_unwind_terminate_reason"]
pub enum UnwindTerminateReason {
/// Unwinding is just not possible given the ABI of this function.
Abi,
/// We were already cleaning up for an ongoing unwind, and a *second*, *nested* unwind was
/// triggered by the drop glue.
InCleanup,
}
pub use UnwindTerminateReason::Abi as ReasonAbi;
pub use UnwindTerminateReason::InCleanup as ReasonInCleanup;
macro_rules! define {
($name:literal, $( #[ $meta:meta ] )* fn $($sig:tt)*) => {
#[rustc_diagnostic_item = $name]
#[inline]
$( #[ $meta ] )*
pub fn $($sig)* { panic!() }
}
}
// Unwind actions
pub struct UnwindActionArg;
define!(
"mir_unwind_continue",
/// An unwind action that continues unwinding.
fn UnwindContinue() -> UnwindActionArg
);
define!(
"mir_unwind_unreachable",
/// An unwind action that triggers undefined behaviour.
fn UnwindUnreachable() -> UnwindActionArg
);
define!(
"mir_unwind_terminate",
/// An unwind action that terminates the execution.
///
/// `UnwindTerminate` can also be used as a terminator.
fn UnwindTerminate(reason: UnwindTerminateReason) -> UnwindActionArg
);
define!(
"mir_unwind_cleanup",
/// An unwind action that continues execution in a given basic blok.
fn UnwindCleanup(goto: BasicBlock) -> UnwindActionArg
);
// Return destination for `Call`
pub struct ReturnToArg;
define!("mir_return_to", fn ReturnTo(goto: BasicBlock) -> ReturnToArg);
// Terminators
define!("mir_return", fn Return() -> BasicBlock);
define!("mir_goto", fn Goto(destination: BasicBlock) -> BasicBlock);
define!("mir_unreachable", fn Unreachable() -> BasicBlock);
define!("mir_drop",
/// Drop the contents of a place.
///
/// The first argument must be a place.
///
/// The second argument must be of the form `ReturnTo(bb)`, where `bb` is the basic block that
/// will be jumped to after the destructor returns.
///
/// The third argument describes what happens on unwind. It can be one of:
/// - [`UnwindContinue`]
/// - [`UnwindUnreachable`]
/// - [`UnwindTerminate`]
/// - [`UnwindCleanup`]
fn Drop<T>(place: T, goto: ReturnToArg, unwind_action: UnwindActionArg)
);
define!("mir_call",
/// Call a function.
///
/// The first argument must be of the form `ret_val = fun(arg1, arg2, ...)`.
///
/// The second argument must be of the form `ReturnTo(bb)`, where `bb` is the basic block that
/// will be jumped to after the function returns.
///
/// The third argument describes what happens on unwind. It can be one of:
/// - [`UnwindContinue`]
/// - [`UnwindUnreachable`]
/// - [`UnwindTerminate`]
/// - [`UnwindCleanup`]
fn Call(call: (), goto: ReturnToArg, unwind_action: UnwindActionArg)
);
define!("mir_unwind_resume",
/// A terminator that resumes the unwinding.
fn UnwindResume()
);
define!("mir_storage_live", fn StorageLive<T>(local: T));
define!("mir_storage_dead", fn StorageDead<T>(local: T));
#[cfg(not(bootstrap))]
define!("mir_assume", fn Assume(operand: bool));
define!("mir_deinit", fn Deinit<T>(place: T));
define!("mir_checked", fn Checked<T>(binop: T) -> (T, bool));
define!("mir_len", fn Len<T>(place: T) -> usize);
define!("mir_copy_for_deref", fn CopyForDeref<T>(place: T) -> 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_offset", fn Offset<T, U>(ptr: T, count: U) -> T);
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
///
/// ```rust
/// #![allow(internal_features)]
/// #![feature(custom_mir, core_intrinsics)]
///
/// 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_cast_transmute",
/// Emits a `CastKind::Transmute` cast.
///
/// Needed to test the UB when `sizeof(T) != sizeof(U)`, which can't be
/// generated via the normal `mem::transmute`.
fn CastTransmute<T, U>(operand: T) -> U
);
define!(
"mir_make_place",
#[doc(hidden)]
fn __internal_make_place<T>(place: T) -> *mut T
);
define!(
"mir_debuginfo",
#[doc(hidden)]
fn __debuginfo<T>(name: &'static str, s: 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 {
(
$(type RET = $ret_ty:ty ;)?
$(let $local_decl:ident $(: $local_decl_ty:ty)? ;)*
$(debug $dbg_name:ident => $dbg_data:expr ;)*
{
$($entry:tt)*
}
$(
$block_name:ident $(($block_cleanup:ident))? = {
$($block:tt)*
}
)*
) => {{
// First, we declare all basic blocks.
__internal_declare_basic_blocks!($(
$block_name $(($block_cleanup))?
)*);
{
// Now all locals
#[allow(non_snake_case)]
let RET $(: $ret_ty)?;
$(
let $local_decl $(: $local_decl_ty)? ;
)*
::core::intrinsics::mir::__internal_extract_let!($($entry)*);
$(
::core::intrinsics::mir::__internal_extract_let!($($block)*);
)*
{
// Now debuginfo
$(
__debuginfo(stringify!($dbg_name), $dbg_data);
)*
{
// 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)*
$expr
}
},
}
/// Helper macro that declares the basic blocks.
#[doc(hidden)]
pub macro __internal_declare_basic_blocks {
() => {},
($name:ident (cleanup) $($rest:tt)*) => {
let $name = ::core::intrinsics::mir::BasicBlock::Cleanup;
__internal_declare_basic_blocks!($($rest)*)
},
($name:ident $($rest:tt)*) => {
let $name = ::core::intrinsics::mir::BasicBlock::Normal;
__internal_declare_basic_blocks!($($rest)*)
},
}