-
Notifications
You must be signed in to change notification settings - Fork 13.4k
Add #[loop_match]
for improved DFA codegen
#138780
New issue
Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.
By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.
Already on GitHub? Sign in to your account
base: master
Are you sure you want to change the base?
Add #[loop_match]
for improved DFA codegen
#138780
Conversation
Some changes occurred in match checking cc @Nadrieril Some changes occurred in compiler/rustc_passes/src/check_attr.rs Some changes occurred in cc @BoxyUwU |
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Thanks @folkertdev for putting up this PR. The big picture looks right, in terms of the behavior of the tests and how to approach the experiment in terms of starting with the attributes for thiis.
This is a first partial pass on the details.
@rustbot author
This comment has been minimized.
This comment has been minimized.
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Thanks for the detailed review!
I've fixed a bunch of the low-hanging fruit (e.g. in the tests). For the actual pattern matching logic, I have a branch with what I believe is a better solution that re-uses more existing pattern matching infra. We'll come back to that here once björn has had a chance to look at it.
Some changes occurred in exhaustiveness checking cc @Nadrieril Some changes occurred in match lowering cc @Nadrieril |
☔ The latest upstream changes (presumably #138974) made this pull request unmergeable. Please resolve the merge conflicts. |
368f722
to
a89dcbe
Compare
This comment has been minimized.
This comment has been minimized.
This comment has been minimized.
This comment has been minimized.
f294773
to
6fe6909
Compare
This comment has been minimized.
This comment has been minimized.
b3a87ed
to
7d88da4
Compare
We've done a bunch of work here, and I believe all of the earlier review comments have now been dealt with. @rustbot ready |
@rustbot author As a lang matter, this is looking reasonable to me in terms of a lang experiment. As an impl matter, this is starting to look not unreasonable to me, but I'd like for @Nadrieril to also have a look if he's able. r? @Nadrieril @Nadrieril: I still need to raise this in a lang meeting to confirm that everyone is happy to see the experiment here in light of earlier objections, so please don't merge this just yet. You can leave it back in my hands after you're happy with the impl. Also CC @oli-obk as this work is carrying over some |
Reminder, once the PR becomes ready for a review, use |
Co-authored-by: Travis Cross <[email protected]>
516c380
to
2ea5bc8
Compare
It had skipped my mind that I was the one assigned to this. I have reviewed and approve of the r? compiler |
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Whoops thought I submitted my reviews a couple weeks ago
[first @ last] | [first, .., last] => dcx | ||
.emit_fatal(LoopMatchBadStatements { span: first.span.to(last.span) }), |
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Will this not error on:
#[loop_match]
loop {
struct A;
struct B;
state = 'a: match {
...
}
}
Even though attempting to support it down below. I think it'd make sense to just not support defining items here tbh. The full feature will have actual loop match
syntax so why go out of our way to support this case.
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Exactly. We do support it below because it is useful to be able to define macros that capture the label of the labeled block. Here we've not needed it, so we're stricter than necessary but for now that should be OK.
hir::ExprKind::Break(dest, ref value) => { | ||
let is_const_continue = self |
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
You're writing const continue
as break
so that you dont have to go and change all of HIR to have special nodes for const continue and loop match with their own typing rules?
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Basically, we minimize code duplication in this way, and also const continue
as syntax has not yet been agreed on.
/// A `#[loop_match] loop { state = 'blk: { match state { ... } } }` expression. | ||
LoopMatch { |
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Why do you have const_continue
but no const_loop_match
? is const loop match unnecessary for getting codegen improvements from the direct jumps with const continues?
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Only const_continue
is needed (really because in rust you can't add more patterns to a match
at runtime): the "const" part of the continue just makes sure that we know statically which arm of the match to jump to. Nothing special is needed from the loop.
tracking issue: #132306
project goal: rust-lang/rust-project-goals#258
This PR adds the
#[loop_match]
attribute, which aims to improve code generation for state machines. For some (very exciting) benchmarks, see rust-lang/rust-project-goals#258 (comment)Currently, a very restricted syntax pattern is accepted. We'd like to get feedback and merge this now before we go too far in a direction that others have concerns with.
current state
We accept code that looks like this
#[loop_match]
: normalcontinue
andbreak
continue to work#[const_continue]
is only allowed in loops annotated with#[loop_match]
future work
break
valuemaybe future work
continue 'label value
syntax, which#[const_continue]
could then use.State::Initial
)break
/continue
expressions that are not marked with#[const_continue]
r? @traviscross