custom mir: make it clear what the return block is
Custom MIR recently got support for specifying the "unwind action", so now there's two things coming after the actual call part of `Call` terminators. That's not very self-explaining so I propose we change the syntax to imitate keyword arguments:
```
Call(popped = Vec::pop(v), ReturnTo(drop), UnwindContinue())
```
Also fix some outdated docs and add some docs to `Call` and `Drop`.
State transforms retains storage statements for locals that are not
stored inside a coroutine. It ensures those locals are live when
resuming by inserting StorageLive as appropriate. It forgot to end the
storage of those locals when suspending, which is fixed here.
While the end of live range is implicit when executing return, it is
nevertheless useful for inliner which would otherwise extend the live
range beyond return.
Custom MIR: Support cleanup blocks
Cleanup blocks are declared with `bb (cleanup) = { ... }`.
`Call` and `Drop` terminators take an additional argument describing the unwind action, which is one of the following:
* `UnwindContinue()`
* `UnwindUnreachable()`
* `UnwindTerminate(reason)`, where reason is `ReasonAbi` or `ReasonInCleanup`
* `UnwindCleanup(block)`
Also support unwind resume and unwind terminate terminators:
* `UnwindResume()`
* `UnwindTerminate(reason)`
Cleanup blocks are declared with `bb (cleanup) = { ... }`.
`Call` and `Drop` terminators take an additional argument describing the
unwind action, which is one of the following:
* `UnwindContinue()`
* `UnwindUnreachable()`
* `UnwindTerminate(reason)`, where reason is `ReasonAbi` or `ReasonInCleanup`
* `UnwindCleanup(block)`
Also support unwind resume and unwind terminate terminators:
* `UnwindResume()`
* `UnwindTerminate(reason)`
The `Debug` impl for `Ty` just calls the `Display` impl for `Ty`. This
is surprising and annoying. In particular, it means `Debug` doesn't show
as much information as `Debug` for `TyKind` does. And `Debug` is used in
some user-facing error messages, which seems bad.
This commit changes the `Debug` impl for `Ty` to call the `Debug` impl
for `TyKind`. It also does a number of follow-up changes to preserve
existing output, many of which involve inserting
`with_no_trimmed_paths!` calls. It also adds `Display` impls for
`UserType` and `Canonical`.
Some tests have changes to expected output:
- Those that use the `rustc_abi(debug)` attribute.
- Those that use the `EMIT_MIR` annotation.
In each case the output is slightly uglier than before. This isn't
ideal, but it's pretty weird (particularly for the attribute) that the
output is using `Debug` in the first place. They're fairly obscure
attributes (I hadn't heard of them) so I'm not worried by this.
For `async-is-unwindsafe.stderr`, there is one line that now lacks a
full path. This is a consistency improvement, because all the other
mentions of `Context` in this test lack a path.
Add MIR validation for unwind out from nounwind functions + fixes to make validation pass
`@Nilstrieb` This is the MIR validation you asked in https://github.com/rust-lang/rust/pull/112403#discussion_r1222739722.
Two passes need to be fixed to get the validation to pass:
* `RemoveNoopLandingPads` currently unconditionally introduce a resume block (even there is none to begin with!), changed to not do that
* Generator state transform introduces a `assert` which may unwind, and its drop elaboration also introduces many new `UnwindAction`s, so in this case run the AbortUnwindingCalls after the transformation.
I believe this PR should also fixRust-for-Linux/linux#1016, cc `@ojeda`
r? `@Nilstrieb`
It makes it sound like the `ExprKind` and `Rvalue` are supposed to represent all pointer related
casts, when in reality their just used to share a some enum variants. Make it clear there these
are only coercion to make it clear why only some pointer related "casts" are in the enum.
Permit the MIR inliner to inline diverging functions
This heuristic prevents inlining of `hint::unreachable_unchecked`, which in turn makes `Option/Result::unwrap_unchecked` a bad inlining candidate. I looked through the changes to `core`, `alloc`, `std`, and `hashbrown` by hand and they all seem reasonable. Let's see how this looks in perf...
---
Based on rustc-perf it looks like this regresses ctfe-stress, and the cachegrind diff indicates that this regression is in `InterpCx::statement`. I don't know how to do any deeper analysis because that function is _enormous_ in the try toolchain, which has no debuginfo in it. And a local build produces significantly different codegen for that function, even with LTO.
Simpler checked shifts in MIR building
Doing masking to check unsigned shift amounts is overcomplicated; just comparing the shift directly saves a statement and a temporary, as well as is much easier to read as a human. And shifting by unsigned is the canonical case -- notably, all the library shifting methods (that don't support every type) take shift RHSs as `u32` -- so we might as well make that simpler since it's easy to do so.
This PR also changes *signed* shift amounts to `IntToInt` casts and then uses the same check as for unsigned. The bit-masking is a nice trick, but for example LLVM actually canonicalizes it to an unsigned comparison anyway <https://rust.godbolt.org/z/8h59fMGT4> so I don't think it's worth the effort and the extra `Constant`. (If MIR's `assert` was `assert_nz` then the masking might make sense, but when the `!=` uses another statement I think the comparison is better.)
To review, I suggest looking at 2ee0468c49 first -- that's the interesting code change and has a MIR diff.
My favourite part of the diff:
```diff
- _20 = BitAnd(_19, const 340282366920938463463374607431768211448_u128); // scope 0 at $DIR/shifts.rs:+2:34: +2:44
- _21 = Ne(move _20, const 0_u128); // scope 0 at $DIR/shifts.rs:+2:34: +2:44
- assert(!move _21, "attempt to shift right by `{}`, which would overflow", _19) -> [success: bb3, unwind: bb7]; // scope 0 at $DIR/shifts.rs:+2:34: +2:44
+ _18 = Lt(_17, const 8_u128); // scope 0 at $DIR/shifts.rs:+2:34: +2:44
+ assert(move _18, "attempt to shift right by `{}`, which would overflow", _17) -> [success: bb3, unwind: bb7]; // scope 0 at $DIR/shifts.rs:+2:34: +2:44
```
Custom MIR: Allow optional RET type annotation
This currently doesn't compile because the type of `RET` is inferred, which fails if RET is a composite type and fields are initialised separately.
```rust
#![feature(custom_mir, core_intrinsics)]
extern crate core;
use core::intrinsics::mir::*;
#[custom_mir(dialect = "runtime", phase = "optimized")]
fn fn0() -> (i32, bool) {
mir! ({
RET.0 = 0;
RET.1 = true;
Return()
})
}
```
```
error[E0282]: type annotations needed
--> src/lib.rs:8:9
|
8 | RET.0 = 0;
| ^^^ cannot infer type
For more information about this error, try `rustc --explain E0282`.
```
This PR allows the user to manually specify the return type with `type RET = ...;` if required:
```rust
#[custom_mir(dialect = "runtime", phase = "optimized")]
fn fn0() -> (i32, bool) {
mir! (
type RET = (i32, bool);
{
RET.0 = 0;
RET.1 = true;
Return()
}
)
}
```
The syntax is not optimal, I'm happy to see other suggestions. Ideally I wanted it to be a normal type annotation like `let RET: ...;`, but this runs into the multiple parsing options error during macro expansion, as it can be parsed as a normal `let` declaration as well.
r? ```@oli-obk``` or ```@tmiasko``` or ```@JakobDegen```
Remove `identity_future` indirection
This was previously needed because the indirection used to hide some unexplained lifetime errors, which it turned out were related to the `min_choice` algorithm.
Removing the indirection also solves a couple of cycle errors, large moves and makes async blocks support the `#[track_caller]`annotation.
Fixes https://github.com/rust-lang/rust/issues/104826.
