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explain why we dont skip some of this work when there are field projections #151902

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Merged
rust-bors merged 1 commit into from
Feb 3, 2026
Merged

explain why we dont skip some of this work when there are field projections #151902

rust-bors merged 1 commit into from
Feb 3, 2026
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@RalfJung RalfJung commented Jan 31, 2026 •
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Perf says it doesn't help 🤷

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jan 31, 2026
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rustbot commented Jan 31, 2026

r? @madsmtm

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RalfJung commented Jan 31, 2026

@bors try
@rust-timer queue

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rust-bors bot pushed a commit that referenced this pull request Jan 31, 2026
@bors
Auto merge of #151902 - RalfJung:place-ty-opt, r=<try>
5e48880 
Place::ty: avoid iterating the entire chain when the type can be read from a field projection
@rustbot rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jan 31, 2026
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rust-bors bot commented Jan 31, 2026

☀️ Try build successful (CI)
Build commit: 5e48880 (5e488805d36baf5169ae11fb20c4efe7a707964d, parent: 1e9be1b77fe89d9757d6179973b2fc970c6e83b7)

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rust-timer commented Jan 31, 2026

Finished benchmarking commit (5e48880): comparison URL.

Overall result: ❌✅ regressions and improvements - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

mean range count
Regressions ❌
(primary)		 - - 0
Regressions ❌
(secondary)		 0.2% [0.0%, 0.4%] 4
Improvements ✅
(primary)		 - - 0
Improvements ✅
(secondary)		 -0.1% [-0.2%, -0.0%] 2
All ❌✅ (primary) - - 0

Max RSS (memory usage)

Results (primary 1.2%, secondary 2.2%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

mean range count
Regressions ❌
(primary)		 2.4% [2.1%, 2.8%] 3
Regressions ❌
(secondary)		 2.2% [2.2%, 2.2%] 1
Improvements ✅
(primary)		 -2.4% [-2.4%, -2.4%] 1
Improvements ✅
(secondary)		 - - 0
All ❌✅ (primary) 1.2% [-2.4%, 2.8%] 4

Cycles

Results (secondary -0.3%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

mean range count
Regressions ❌
(primary)		 - - 0
Regressions ❌
(secondary)		 9.0% [2.5%, 15.5%] 2
Improvements ✅
(primary)		 - - 0
Improvements ✅
(secondary)		 -6.5% [-7.0%, -6.0%] 3
All ❌✅ (primary) - - 0

Binary size

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

Bootstrap: 474.929s -> 475.237s (0.06%)
Artifact size: 397.85 MiB -> 397.65 MiB (-0.05%)

@rustbot rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jan 31, 2026
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RalfJung commented Jan 31, 2026

This does not seem worth it...

... I'll add a comment instead saying that we tried the "obvious" perf improvement here and it didn't help.

@RalfJung RalfJung changed the title Place::ty: avoid iterating the entire chain when the type can be read from a field projection explain why we dont skip some of this work when there are field projections Feb 2, 2026
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Kobzol commented Feb 2, 2026

@bors r+ rollup

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rust-bors bot commented Feb 2, 2026

📌 Commit c725637 has been approved by Kobzol

It is now in the queue for this repository.

@rust-bors rust-bors bot 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 Feb 2, 2026
JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request Feb 2, 2026
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Rollup merge of rust-lang#151902 - RalfJung:place-ty-opt, r=Kobzol
b05a0f6 
explain why we dont skip some of this work when there are field projections

Perf says it doesn't help 🤷
@JonathanBrouwer JonathanBrouwer mentioned this pull request Feb 2, 2026
Closed
rust-bors bot pushed a commit that referenced this pull request Feb 2, 2026
@bors
Auto merge of #151997 - JonathanBrouwer:rollup-txk7tC8, r=JonathanBro…
6ad3d3d 
…uwer

Rollup of 11 pull requests

Successful merges:

 - #150992 (link modifier `export-symbols`: export all global symbols from selected uptream c static libraries)
 - #151695 (compiletest: Support `--extern` modifiers with `proc-macro` directive)
 - #151938 (Use `#![feature(adt_const_params)]` for static query flags)
 - #151172 (Use default field values in a few more cases)
 - #151825 (more float constants)
 - #151870 (regression test for alias-relate changes in lub)
 - #151902 (explain why we dont skip some of this work when there are field projections)
 - #151974 (Update documentation for `Result::ok()`)
 - #151978 (Query cleanups)
 - #151979 (Fix uninitialized UEFI globals in tests)
 - #151992 (Port `#[rustc_hidden_type_of_opaque]` to attribute parser)
JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request Feb 2, 2026
@JonathanBrouwer
Rollup merge of rust-lang#151902 - RalfJung:place-ty-opt, r=Kobzol
d856522 
explain why we dont skip some of this work when there are field projections

Perf says it doesn't help 🤷
This was referenced Feb 2, 2026
Closed
Merged
rust-bors bot pushed a commit that referenced this pull request Feb 2, 2026
@bors
Auto merge of #152006 - JonathanBrouwer:rollup-TXHXPNU, r=JonathanBro…
6c828e5 
…uwer

Rollup of 12 pull requests

Successful merges:

 - #149596 (resolve: Report more visibility-related early resolution ambiguities for imports)
 - #151695 (compiletest: Support `--extern` modifiers with `proc-macro` directive)
 - #151938 (Use `#![feature(adt_const_params)]` for static query flags)
 - #151172 (Use default field values in a few more cases)
 - #151825 (more float constants)
 - #151870 (regression test for alias-relate changes in lub)
 - #151872 (Add inline syntax for diagnostic messages)
 - #151902 (explain why we dont skip some of this work when there are field projections)
 - #151909 (Skip overlapping spans in argument error suggestions)
 - #151978 (Query cleanups)
 - #151979 (Fix uninitialized UEFI globals in tests)
 - #151992 (Port `#[rustc_hidden_type_of_opaque]` to attribute parser)
rust-bors bot pushed a commit that referenced this pull request Feb 2, 2026
@bors
Auto merge of #152006 - JonathanBrouwer:rollup-TXHXPNU, r=JonathanBro…
fc8438a 
…uwer

Rollup of 12 pull requests

Successful merges:

 - #149596 (resolve: Report more visibility-related early resolution ambiguities for imports)
 - #151695 (compiletest: Support `--extern` modifiers with `proc-macro` directive)
 - #151938 (Use `#![feature(adt_const_params)]` for static query flags)
 - #151172 (Use default field values in a few more cases)
 - #151825 (more float constants)
 - #151870 (regression test for alias-relate changes in lub)
 - #151872 (Add inline syntax for diagnostic messages)
 - #151902 (explain why we dont skip some of this work when there are field projections)
 - #151909 (Skip overlapping spans in argument error suggestions)
 - #151978 (Query cleanups)
 - #151979 (Fix uninitialized UEFI globals in tests)
 - #151992 (Port `#[rustc_hidden_type_of_opaque]` to attribute parser)
rust-bors bot pushed a commit that referenced this pull request Feb 3, 2026
@bors
Auto merge of #152006 - JonathanBrouwer:rollup-TXHXPNU, r=JonathanBro…
5ac8ece 
…uwer

Rollup of 12 pull requests

Successful merges:

 - #149596 (resolve: Report more visibility-related early resolution ambiguities for imports)
 - #151695 (compiletest: Support `--extern` modifiers with `proc-macro` directive)
 - #151938 (Use `#![feature(adt_const_params)]` for static query flags)
 - #151172 (Use default field values in a few more cases)
 - #151825 (more float constants)
 - #151870 (regression test for alias-relate changes in lub)
 - #151872 (Add inline syntax for diagnostic messages)
 - #151902 (explain why we dont skip some of this work when there are field projections)
 - #151909 (Skip overlapping spans in argument error suggestions)
 - #151978 (Query cleanups)
 - #151979 (Fix uninitialized UEFI globals in tests)
 - #151992 (Port `#[rustc_hidden_type_of_opaque]` to attribute parser)
@rust-bors rust-bors bot merged commit 382c889 into rust-lang:main Feb 3, 2026
11 checks passed
@rustbot rustbot added this to the 1.95.0 milestone Feb 3, 2026
rust-timer added a commit that referenced this pull request Feb 3, 2026
@rust-timer
Unrolled build for #151902
80fc3d8 
Rollup merge of #151902 - RalfJung:place-ty-opt, r=Kobzol

explain why we dont skip some of this work when there are field projections

Perf says it doesn't help 🤷
@RalfJung RalfJung deleted the place-ty-opt branch February 3, 2026 07:50
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