`#![custom_mir]`: Various improvements #104975

JakobDegen · 2022-11-27T10:42:20Z

This PR makes a bunch of improvements to #![custom_mir]. Ideally this would be 4 PRs, one for each commit, but those would take forever to get merged and be a pain to juggle. Should still be reviewed one commit at a time though.

Commit 1: Support arbitrary `let`

Before this change, all locals used in the body need to be declared at the top of the mir! invocation, which is rather annoying. We attempt to change that.

Unfortunately, we still have the requirement that the output of the mir! macro must resolve, typecheck, etc. Because of that, we can't just accept this in the THIR -> MIR parser because something like

{
    let x = 0;
    Goto(other)
}
other = {
    RET = x;
    Return()
}

will fail to resolve. Instead, the implementation does macro shenanigans to find the let declarations and extract them as part of the mir! macro. That works, but it is fairly complicated and degrades debuginfo by quite a bit. Specifically, the spans for any statements and declarations that are affected by this are completely wrong. My guess is that this is a net improvement though.

One way to recover some of the debuginfo would be to not support type annotations in the let statements, which would allow us to parse like let $stmt:stmt. That seems quite surprising though.

Commit 2: Parse consts

Reuses most of the const parsing from regular Mir building for building custom mir

Commit 3: Parse statics

Statics are slightly weird because the Mir primitive associated with them is a reference/pointer to them, so this is factored out separately.

Commit 4: Fix some spans

A bunch of the spans were non-ideal, so we adjust them to be much more helpful.

r? @oli-obk

rustbot · 2022-11-27T10:42:27Z

Hey! It looks like you've submitted a new PR for the library teams!

If this PR contains changes to any rust-lang/rust public library APIs then please comment with @rustbot label +T-libs-api -T-libs to tag it appropriately. If this PR contains changes to any unstable APIs please edit the PR description to add a link to the relevant API Change Proposal or create one if you haven't already. If you're unsure where your change falls no worries, just leave it as is and the reviewer will take a look and make a decision to forward on if necessary.

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Changing observable runtime behavior of library APIs

oli-obk · 2022-11-28T10:56:41Z

compiler/rustc_mir_build/src/thir/cx/expr.rs

+                if self.is_custom_mir {
+                    kind
+                } else {
+                    ExprKind::Deref {
+                        arg: self.thir.exprs.push(Expr {
+                            ty,
+                            temp_lifetime,
+                            span: expr.span,
+                            kind,
+                        }),
+                    }
                }


I don't like this too much, can we revert it once &Static(Name) is a thing?

Yeah, actually, I can just revert it immediately. I can manually parse and ignore the deref instead

Reverted the changes to this part of the code and pushed an additional commit that has the alternative to this. Should be much better, not sure why I didn't do this in the first place

yea, I like this.

oli-obk · 2022-11-28T13:58:53Z

@bors delegate+

r=me with the new commit squashed into its parent

bors · 2022-11-28T13:58:56Z

✌️ @JakobDegen can now approve this pull request

bors · 2022-11-29T17:12:43Z

☔ The latest upstream changes (presumably #105012) made this pull request unmergeable. Please resolve the merge conflicts.

JakobDegen · 2022-11-30T04:35:38Z

@bors r=oli-obk

bors · 2022-11-30T04:35:40Z

📌 Commit 5a34dbf has been approved by oli-obk

It is now in the queue for this repository.

`#![custom_mir]`: Various improvements This PR makes a bunch of improvements to `#![custom_mir]`. Ideally this would be 4 PRs, one for each commit, but those would take forever to get merged and be a pain to juggle. Should still be reviewed one commit at a time though. ### Commit 1: Support arbitrary `let` Before this change, all locals used in the body need to be declared at the top of the `mir!` invocation, which is rather annoying. We attempt to change that. Unfortunately, we still have the requirement that the output of the `mir!` macro must resolve, typecheck, etc. Because of that, we can't just accept this in the THIR -> MIR parser because something like ```rust { let x = 0; Goto(other) } other = { RET = x; Return() } ``` will fail to resolve. Instead, the implementation does macro shenanigans to find the let declarations and extract them as part of the `mir!` macro. That *works*, but it is fairly complicated and degrades debuginfo by quite a bit. Specifically, the spans for any statements and declarations that are affected by this are completely wrong. My guess is that this is a net improvement though. One way to recover some of the debuginfo would be to not support type annotations in the `let` statements, which would allow us to parse like `let $stmt:stmt`. That seems quite surprising though. ### Commit 2: Parse consts Reuses most of the const parsing from regular Mir building for building custom mir ### Commit 3: Parse statics Statics are slightly weird because the Mir primitive associated with them is a reference/pointer to them, so this is factored out separately. ### Commit 4: Fix some spans A bunch of the spans were non-ideal, so we adjust them to be much more helpful. r? `@oli-obk`

bors · 2022-12-01T10:40:13Z

⌛ Testing commit 5a34dbf with merge 9c0bc30...

bors · 2022-12-01T13:52:58Z

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing 9c0bc30 to master...

rust-timer · 2022-12-01T15:12:22Z

Finished benchmarking commit (9c0bc30): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	5.0%	[4.1%, 5.9%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.0%	[2.0%, 2.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

rustbot assigned oli-obk Nov 27, 2022

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Nov 27, 2022

JakobDegen force-pushed the custom_mir_let branch from 0d2d784 to 58f39b3 Compare November 27, 2022 11:16

JakobDegen mentioned this pull request Nov 28, 2022

Support most consts in custom mir #105000

Closed

JakobDegen force-pushed the custom_mir_let branch from 58f39b3 to 885250b Compare November 28, 2022 05:26

JakobDegen changed the title ~~Support arbitrary let statements in custom mir~~ #![custom_mir]: Various improvements Nov 28, 2022

oli-obk reviewed Nov 28, 2022

View reviewed changes

JakobDegen force-pushed the custom_mir_let branch from 885250b to 30e0f8a Compare November 28, 2022 11:08

JakobDegen added 4 commits November 29, 2022 19:19

Support arbitrary let statements in custom mir

a982541

Support most constant kinds in custom mir

7578100

Support statics in custom mir

52ce1f7

Improve spans in custom mir

5a34dbf

JakobDegen force-pushed the custom_mir_let branch from 30e0f8a to 5a34dbf Compare November 30, 2022 03:27

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 30, 2022

Dylan-DPC mentioned this pull request Dec 1, 2022

Rollup of 6 pull requests #105122

Closed

bors added the merged-by-bors This PR was explicitly merged by bors. label Dec 1, 2022

bors merged commit 9c0bc30 into rust-lang:master Dec 1, 2022

rustbot added this to the 1.67.0 milestone Dec 1, 2022

bors mentioned this pull request Dec 1, 2022

Add a note about implicit temporaries on &mut (fn or const) #104857

Closed

JakobDegen deleted the custom_mir_let branch December 4, 2022 01:43

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`#![custom_mir]`: Various improvements #104975

`#![custom_mir]`: Various improvements #104975

JakobDegen commented Nov 27, 2022 •

edited

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rustbot commented Nov 27, 2022

oli-obk Nov 28, 2022

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JakobDegen Nov 28, 2022

oli-obk Nov 28, 2022

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rust-timer commented Dec 1, 2022

#![custom_mir]: Various improvements #104975

#![custom_mir]: Various improvements #104975

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JakobDegen commented Nov 27, 2022 • edited Loading

Commit 1: Support arbitrary let

Commit 2: Parse consts

Commit 3: Parse statics

Commit 4: Fix some spans

rustbot commented Nov 27, 2022

oli-obk Nov 28, 2022

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oli-obk commented Nov 28, 2022

bors commented Nov 28, 2022

bors commented Nov 29, 2022

JakobDegen commented Nov 30, 2022

bors commented Nov 30, 2022

bors commented Dec 1, 2022

bors commented Dec 1, 2022

rust-timer commented Dec 1, 2022

Overall result: no relevant changes - no action needed

Instruction count

Max RSS (memory usage)

Cycles

`#![custom_mir]`: Various improvements #104975

`#![custom_mir]`: Various improvements #104975

JakobDegen commented Nov 27, 2022 •

edited

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Commit 1: Support arbitrary `let`