1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696
//! 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")]
//! 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));
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_ptr_metadata",
fn PtrMetadata<P: ?Sized>(place: *const P) -> <P as ::core::ptr::Pointee>::Metadata
);
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_cast_ptr_to_ptr",
/// Emits a `CastKind::PtrToPtr` cast.
///
/// This allows bypassing normal validation to generate strange casts.
fn CastPtrToPtr<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)*)
},
}