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Move promotion into its own pass #65949

Merged
merged 5 commits into from
Nov 9, 2019
Merged

Move promotion into its own pass #65949

merged 5 commits into from
Nov 9, 2019

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ecstatic-morse
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@ecstatic-morse ecstatic-morse commented Oct 29, 2019 •
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This adds a PromoteTemps pass, which runs after the old QualifyAndPromoteConsts pass, that only does promotion (no const-checking). Everything related to promotion has been removed from QualifyAndPromoteConstants: it no longer even visits the body of a non-const fn.

As a result we no longer need to keep the BitSet of promotable locals that was returned by mir_const_qualif. Rvalue-static promotion in a const is now done in promote_consts, and it operates on a set of Candidates instead. This will allow me–in a later PR–to create promoted MIR fragments for consts when necessary, which could resolve some shortcomings of the current approach (removing StorageDead).

r? @eddyb

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Oct 29, 2019
@ecstatic-morse ecstatic-morse changed the title Move promotion into its own pass [WIP] Move promotion into its own pass Oct 29, 2019
@ecstatic-morse ecstatic-morse changed the title [WIP] Move promotion into its own pass [DO NOT MERGE] Move promotion into its own pass Oct 29, 2019
@ecstatic-morse ecstatic-morse mentioned this pull request Oct 29, 2019
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eddyb commented Oct 30, 2019

I would prefer to remove the minimum possible (maybe just number two?) to avoid needless work

Is popping bubble wrap needless work 😁? I can do some of it if you want.

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ecstatic-morse commented Oct 30, 2019 •
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Is popping bubble wrap needless work grin? I can do some of it if you want.

I actually laughed out loud at this.

Sorry, my post reads as a bit petulant to me today. The last time I did a major change to qualify_consts it didn't turn out very well (#63860). I was secretly hoping the next major change to it would be made with rm 😄.

I didn't want to waste time removing stuff that you didn't really want removed, so if you tell me you want all dead code (including the full checklist) gone I can do that. Alternatively, if it really is like popping bubble wrap for you, have at it.

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eddyb commented Oct 31, 2019

Just remembered I saw somewhere someone point out that beta branches on November 5th.

I'd suggest we remove the old promotion logic from qualify_consts just after that, to make sure the comparison trickles into beta and stable.

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ecstatic-morse commented Oct 31, 2019 •
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I'd suggest we remove the old promotion logic from qualify_consts just after that, to make sure the comparison trickles into beta and stable.

Agreed. This would be ideal.

@ecstatic-morse ecstatic-morse mentioned this pull request Nov 5, 2019
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bors commented Nov 6, 2019

☔ The latest upstream changes (presumably #65728) made this pull request unmergeable. Please resolve the merge conflicts.

@ecstatic-morse ecstatic-morse changed the title [DO NOT MERGE] Move promotion into its own pass Move promotion into its own pass Nov 6, 2019
@ecstatic-morse
Stop returning promotables from mir_const_qualif
3783ef6
@ecstatic-morse
Add a PromoteTemps pass
170272b 
`remove_storage_dead_and_drop` has been copied to `promote_temps` and
now operates on an array of `Candidate`s instead of a bitset.
@ecstatic-morse
Use new PromoteTemps for promotion
b316384
@ecstatic-morse
Bless tests now that we do promotion if min_const_fn fails
b13c2c3 
We bailed out of `QualifyAndPromoteConsts` immediately if the
`min_const_fn` checks failed, which sometimes resulted in additional,
spurious errors since promotion was skipped.

We now do promotion in a completely separate pass, so this is no longer
an issue.
@ecstatic-morse
Clean up dead code in qualify_consts
a3b0369 
We don't do promotion here anymore, so `Checker` will never even visit
the body of a non-const `fn`.
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@eddyb This is ready for review now that #66066 has been merged.

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eddyb reviewed Nov 9, 2019
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src/test/ui/consts/min_const_fn/min_const_fn.stderr
| ^--
| ||
| |temporary value created here
| returns a reference to data owned by the current function
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What was this bug, looks confusing, maybe related to min_const_fn checks? cc @oli-obk

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Nevermind, there's a commit that explains this!

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eddyb commented Nov 9, 2019

@bors r+

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bors commented Nov 9, 2019

📌 Commit a3b0369 has been approved by eddyb

@bors 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 9, 2019
Centril added a commit to Centril/rust that referenced this pull request Nov 9, 2019
@Centril
Rollup merge of rust-lang#65949 - ecstatic-morse:promote-only-pass, r…
aaceede 
…=eddyb

Move promotion into its own pass

**edited**

This adds a `PromoteTemps` pass, which runs after the old `QualifyAndPromoteConsts` pass, that *only* does promotion (no const-checking). Everything related to promotion has been removed from `QualifyAndPromoteConstants`: it no longer even visits the body of a non-const `fn`.

As a result we no longer need to keep the `BitSet` of promotable locals that was returned by `mir_const_qualif`. Rvalue-static promotion in a `const` is now done in `promote_consts`, and it operates on a set of `Candidate`s instead. This will allow me–in a later PR–to create promoted MIR fragments for `const`s when necessary, which could resolve some shortcomings of the current approach (removing `StorageDead`).

r? @eddyb
@Centril Centril mentioned this pull request Nov 9, 2019
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bors added a commit that referenced this pull request Nov 9, 2019
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Auto merge of #66242 - Centril:rollup-h73ztr1, r=Centril
5a50275 
Rollup of 6 pull requests

Successful merges:

 - #65949 (Move promotion into its own pass)
 - #65994 (Point at where clauses where the associated item was restricted)
 - #66050 (Fix C aggregate-passing ABI on powerpc)
 - #66134 (Point at formatting descriptor string when it is invalid)
 - #66172 (Stabilize @file command line arguments)
 - #66226 (add link to unstable book for asm! macro)

Failed merges:

r? @ghost
@bors bors merged commit a3b0369 into rust-lang:master Nov 9, 2019
@ecstatic-morse ecstatic-morse deleted the promote-only-pass branch October 6, 2020 01:42
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