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[mir-opt] Allow debuginfo to be generated for a constant or a Place #73210

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merged 2 commits into from
Dec 15, 2020
Merged

[mir-opt] Allow debuginfo to be generated for a constant or a Place #73210

merged 2 commits into from
Dec 15, 2020

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wesleywiser
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Prior to this commit, debuginfo was always generated by mapping a name
to a Place. This has the side-effect that SimplifyLocals cannot remove
locals that are only used for debuginfo because their other uses have
been const-propagated.

To allow these locals to be removed, we now allow debuginfo to point to
a constant value. The ConstProp pass detects when debuginfo points to
a local with a known constant value and replaces it with the value. This
allows the later SimplifyLocals pass to remove the local.

@wesleywiser wesleywiser added the A-mir-opt Area: MIR optimizations label Jun 10, 2020
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r? @estebank

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@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jun 10, 2020
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@bors try @rust-timer queue

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Awaiting bors try build completion

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bors commented Jun 10, 2020

⌛ Trying commit e36759f0f6501606e036c97a84f80294e2f6bd3a with merge 25e92ddd8e4c25f9882f1f4d1822f1b860b3788a...

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bors commented Jun 10, 2020

☀️ Try build successful - checks-azure
Build commit: 25e92ddd8e4c25f9882f1f4d1822f1b860b3788a (25e92ddd8e4c25f9882f1f4d1822f1b860b3788a)

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Queued 25e92ddd8e4c25f9882f1f4d1822f1b860b3788a with parent bb86748, future comparison URL.

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Finished benchmarking try commit (25e92ddd8e4c25f9882f1f4d1822f1b860b3788a): comparison url.

@wesleywiser wesleywiser force-pushed the consts_in_debuginfo branch from e36759f to 0cf171c Compare June 11, 2020 00:28
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@JohnCSimon JohnCSimon added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 23, 2020
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triage: assigning back to author to address merge conflicts.

@wesleywiser wesleywiser force-pushed the consts_in_debuginfo branch from 0cf171c to 232f6c7 Compare June 30, 2020 01:31
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Rebased

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@JohnTitor JohnTitor mentioned this pull request Jul 1, 2020
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@wesleywiser wesleywiser force-pushed the consts_in_debuginfo branch from 232f6c7 to 77f5128 Compare July 2, 2020 03:32
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Rebased and CI is passing.

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eddyb approved these changes Jul 6, 2020
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r=me but maybe @oli-obk should take a look at the const-prop changes, I'm not sure what "only within the same block" propagation does.

@wesleywiser wesleywiser force-pushed the consts_in_debuginfo branch from 77f5128 to 7493d7c Compare July 6, 2020 01:35
@bors bors added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Oct 25, 2020
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oli-obk commented Oct 26, 2020

The debuginfo tests need updating now, too

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bors commented Oct 26, 2020

☔ The latest upstream changes (presumably #68965) made this pull request unmergeable. Please resolve the merge conflicts.

Note that reviewers usually do not review pull requests until merge conflicts are resolved! Once you resolve the conflicts, you should change the labels applied by bors to indicate that your PR is ready for review. Post this as a comment to change the labels:

@rustbot modify labels: +S-waiting-on-review -S-waiting-on-author

@oli-obk oli-obk added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 3, 2020
@crlf0710 crlf0710 added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Nov 20, 2020
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@wesleywiser any updates?

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I still can't repro this locally but I'm starting to wonder if this has something to do with the version of gdb being tested. My local version of gdb is quite a bit newer than the one being tested on the failing platform (7.10). I'm trying to see if I can get that version from my distro to test with.

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[mir-opt] Allow debuginfo to be generated for a constant or a Place
01aec8d 
Prior to this commit, debuginfo was always generated by mapping a name
to a Place. This has the side-effect that `SimplifyLocals` cannot remove
locals that are only used for debuginfo because their other uses have
been const-propagated.

To allow these locals to be removed, we now allow debuginfo to point to
a constant value. The `ConstProp` pass detects when debuginfo points to
a local with a known constant value and replaces it with the value. This
allows the later `SimplifyLocals` pass to remove the local.
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It doesn't seem the issue is merely the version of gdb as a similarly old version works fine on Linux. I will still try to get a repro on Windows but in the meantime I'd like to go ahead and merge this with the pass disabled by default. I've had to rebase this a few times now and the PR is just large enough to be a bit unpleasant when rebasing. Once the windows-gnu issue is resolved, I'll open another PR to enable this by default.

@oli-obk does that seem fine to you?

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oli-obk commented Dec 14, 2020

yes that seems perfectly reasonable to me

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Disable the constant debuginfo promotion pass by default
0b18ed8 
It doesn't work correctly on *-pc-windows-gnu
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Tests are blessed.

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oli-obk commented Dec 15, 2020

@bors r+

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bors commented Dec 15, 2020

📌 Commit 0b18ed8 has been approved by oli-obk

@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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Dec 15, 2020
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bors commented Dec 15, 2020

⌛ Testing commit 0b18ed8 with merge e99a89c...

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bors commented Dec 15, 2020

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing e99a89c to master...

@bors bors added the merged-by-bors This PR was explicitly merged by bors. label Dec 15, 2020
@bors bors merged commit e99a89c into rust-lang:master Dec 15, 2020
@rustbot rustbot added this to the 1.50.0 milestone Dec 15, 2020
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@wesleywiser wesleywiser mentioned this pull request Oct 27, 2022
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