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Allow to disable thinLTO buffer to support lto-embed-bitcode lld feature #98162

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merged 1 commit into from
Jul 21, 2022
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Allow to disable thinLTO buffer to support lto-embed-bitcode lld feature #98162

merged 1 commit into from
Jul 21, 2022

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@darkness-ai darkness-ai commented Jun 16, 2022 •
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Hello
This change is to fix issue (#84395) in which passing "-lto-embed-bitcode=optimized" to lld when linking rust code via linker-plugin-lto doesn't produce the expected result.

Instead of emitting a single unified module into a llvmbc section of the linked elf, it emits multiple submodules.
This is caused because rustc emits the BC modules after running llvm createWriteThinLTOBitcodePass pass.
Which in turn triggers a thinLTO linkage and causes the said issue.

This patch allows via compiler flag (-Cemit-thin-lto=) to select between running createWriteThinLTOBitcodePass and createBitcodeWriterPass.
Note this pattern of selecting between those 2 passes is common inside of LLVM code.
The default is to match the old behavior.

@rustbot rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Jun 16, 2022
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Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @lcnr (or someone else) soon.

Please see the contribution instructions for more information.

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jun 16, 2022
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lcnr commented Jun 28, 2022

seems like i missed the notification for this PR 😅 sorry

r? rust-lang/compiler

@rust-highfive rust-highfive assigned davidtwco and unassigned lcnr Jun 28, 2022
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@davidtwco davidtwco 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 28, 2022
@darkness-ai darkness-ai force-pushed the support_lto_embed_bitcode branch from 4cb2088 to cb61ea9 Compare July 3, 2022 08:06
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@darkness-ai darkness-ai force-pushed the support_lto_embed_bitcode branch from cb61ea9 to 725971a Compare July 3, 2022 08:35
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@rustbot label -S-waiting-on-author +S-waiting-on-review

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jul 3, 2022
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@rustbot label -S-waiting-on-review +S-waiting-on-author

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@darkness-ai darkness-ai force-pushed the support_lto_embed_bitcode branch from 725971a to d6ac2b6 Compare July 3, 2022 10:54
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@darkness-ai darkness-ai force-pushed the support_lto_embed_bitcode branch from d6ac2b6 to 87967e8 Compare July 3, 2022 12:59
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@rustbot label -S-waiting-on-author +S-waiting-on-review

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jul 3, 2022
@darkness-ai darkness-ai requested a review from davidtwco July 3, 2022 13:39
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@darkness-ai darkness-ai force-pushed the support_lto_embed_bitcode branch from 87967e8 to f9c1459 Compare July 4, 2022 06:51
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Do you think you could add a test case that uses this and -lto-embed-bitcode=optimized to confirm that it fixes the issue?

@davidtwco davidtwco removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 4, 2022
@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 Jul 6, 2022
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@darkness-ai darkness-ai force-pushed the support_lto_embed_bitcode branch from 28b6f43 to 3858cdd Compare July 9, 2022 11:33
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bors commented Jul 10, 2022

@darkness-ai: 🔑 Insufficient privileges: Not in reviewers

@darkness-ai darkness-ai requested a review from davidtwco July 10, 2022 13:27
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@bors r+

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bors commented Jul 11, 2022

📌 Commit 3858cddaec9a7480b94bfa8432c9ed4df13b0478 has been approved by davidtwco

It is now in the queue for this repository.

@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 Jul 11, 2022
@darkness-ai
rustc: add ability to output regular LTO bitcode modules
724c912 
Adding the option to control from rustc CLI
if the resulted ".o" bitcode module files are with
thinLTO info or regular LTO info.

Allows using "-lto-embed-bitcode=optimized" during linkage
correctly.

Signed-off-by: Ziv Dunkelman <[email protected]>
@darkness-ai darkness-ai force-pushed the support_lto_embed_bitcode branch from 3858cdd to 724c912 Compare July 14, 2022 19:22
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@davidtwco saw PRs conflicting with this one got merged into master.
Pushed fixes for the mismatch.

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bors commented Jul 15, 2022

📌 Commit 724c912 has been approved by davidtwco

It is now in the queue for this repository.

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bors commented Jul 21, 2022

⌛ Testing commit 724c912 with merge 74f600b...

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bors commented Jul 21, 2022

☀️ Test successful - checks-actions
Approved by: davidtwco
Pushing 74f600b to master...

@bors bors added the merged-by-bors This PR was explicitly merged by bors. label Jul 21, 2022
@bors bors merged commit 74f600b into rust-lang:master Jul 21, 2022
@rustbot rustbot added this to the 1.64.0 milestone Jul 21, 2022
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Finished benchmarking commit (74f600b): comparison url.

Instruction count

  • Primary benchmarks: 🎉 relevant improvements found
  • Secondary benchmarks: no relevant changes found
mean1 max count2
Regressions 😿
(primary)		 N/A N/A 0
Regressions 😿
(secondary)		 N/A N/A 0
Improvements 🎉
(primary)		 -0.4% -0.4% 2
Improvements 🎉
(secondary)		 N/A N/A 0
All 😿🎉 (primary) -0.4% -0.4% 2

Max RSS (memory usage)

Results
  • Primary benchmarks: 🎉 relevant improvement found
  • Secondary benchmarks: 😿 relevant regression found
mean1 max count2
Regressions 😿
(primary)		 N/A N/A 0
Regressions 😿
(secondary)		 5.7% 5.7% 1
Improvements 🎉
(primary)		 -2.2% -2.2% 1
Improvements 🎉
(secondary)		 N/A N/A 0
All 😿🎉 (primary) -2.2% -2.2% 1

Cycles

Results
  • Primary benchmarks: 😿 relevant regression found
  • Secondary benchmarks: 🎉 relevant improvement found
mean1 max count2
Regressions 😿
(primary)		 1.8% 1.8% 1
Regressions 😿
(secondary)		 N/A N/A 0
Improvements 🎉
(primary)		 N/A N/A 0
Improvements 🎉
(secondary)		 -2.5% -2.5% 1
All 😿🎉 (primary) 1.8% 1.8% 1

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

@rustbot label: -perf-regression

Footnotes

  1. the arithmetic mean of the percent change ↩ ↩2 ↩3

  2. number of relevant changes ↩ ↩2 ↩3

@darkness-ai darkness-ai deleted the support_lto_embed_bitcode branch July 26, 2022 07:51
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