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Change SymbolName::name to a &str. #74214

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merged 2 commits into from
Jul 15, 2020

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nnethercote
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This eliminates a bunch of Symbol::intern() and Symbol::as_str()
calls, which is good, because they require locking the interner.

Note that the unsafety in from_cycle_error() is identical to the
unsafety on other adjacent impls.

r? @eddyb

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 10, 2020
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This gives some very small perf wins. At least they're mostly on the real-world benchmarks. Here is a subset of results:

clap-rs-debug
        avg: -0.4%      min: -0.4%      max: -0.4%
webrender-debug
        avg: -0.4%      min: -0.4%      max: -0.4%
cranelift-codegen-debug
        avg: -0.4%      min: -0.4%      max: -0.4%
piston-image-debug
        avg: -0.3%      min: -0.3%      max: -0.3%
webrender-wrench-debug
        avg: -0.3%      min: -0.3%      max: -0.3%
hyper-2-debug
        avg: -0.3%      min: -0.3%      max: -0.3%
tokio-webpush-simple-debug
        avg: -0.2%      min: -0.2%      max: -0.2%
deep-vector-debug
        avg: -0.2%      min: -0.2%      max: -0.2%
cargo-debug
        avg: -0.2%      min: -0.2%      max: -0.2%
ripgrep-debug
        avg: -0.2%      min: -0.2%      max: -0.2%
regression-31157-debug
        avg: -0.2%      min: -0.2%      max: -0.2%
regex-debug
        avg: -0.2%      min: -0.2%      max: -0.2%
syn-debug
        avg: -0.1%      min: -0.1%      max: -0.1%
encoding-debug
        avg: -0.1%      min: -0.1%      max: -0.1%
issue-46449-debug
        avg: -0.1%      min: -0.1%      max: -0.1%
inflate-debug
        avg: -0.1%      min: -0.1%      max: -0.1% 
futures-debug
        avg: -0.1%      min: -0.1%      max: -0.1%
html5ever-debug
        avg: -0.1%      min: -0.1%      max: -0.1%

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@bors try @rust-timer queue

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Awaiting bors try build completion

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bors commented Jul 10, 2020

⌛ Trying commit 61e2a3949b118fd04592e73c8ca4ef4b805076a2 with merge 28b4962ee286e2682945dd2a9b3dec058d518ec7...

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bors commented Jul 10, 2020

☀️ Try build successful - checks-actions, checks-azure
Build commit: 28b4962ee286e2682945dd2a9b3dec058d518ec7 (28b4962ee286e2682945dd2a9b3dec058d518ec7)

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Queued 28b4962ee286e2682945dd2a9b3dec058d518ec7 with parent e59b08e, future comparison URL.

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Finished benchmarking try commit (28b4962ee286e2682945dd2a9b3dec058d518ec7): comparison url.

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I only measured check-full and debug-full runs locally, and the best improvement was 0.4%. But this change helps incremental runs more, and when all runs are done (as on CI) we see improvements of up to 2.5%.

@bors rollup=never

Comment on lines +22 to +25
impl<'tcx> Value<'tcx> for ty::SymbolName<'_> {
fn from_cycle_error(tcx: TyCtxt<'tcx>) -> Self {
// SAFETY: This is never called when `Self` is not `SymbolName<'tcx>`.
// FIXME: Represent the above fact in the trait system somehow.
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Why can't you write ty::SymbolName<'tcx>? That's why Value has a 'tcx parameter.

Oh this is a specialization issue. IMO it should be noted as such rather then left as a vague FIXME (cc @matthewjasper).

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What exactly would you like me to write in the comment?

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I hope @matthewjasper can come up with a better comment. Otherwise it's probably fine as-is.
Although I kind of doubt this from_cycle_error implementation is needed at all.

@eddyb eddyb 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 Jul 15, 2020
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bors commented Jul 15, 2020

☔ The latest upstream changes (presumably #74175) made this pull request unmergeable. Please resolve the merge conflicts.

This eliminates a bunch of `Symbol::intern()` and `Symbol::as_str()`
calls, which is good, because they require locking the interner.

Note that the unsafety in `from_cycle_error()` is identical to the
unsafety on other adjacent impls.
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eddyb commented Jul 15, 2020

@bors r+

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bors commented Jul 15, 2020

📌 Commit a1b8540 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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jul 15, 2020
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bors commented Jul 15, 2020

⌛ Testing commit a1b8540 with merge d9e8d62...

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bors commented Jul 15, 2020

☀️ Test successful - checks-actions, checks-azure
Approved by: eddyb
Pushing d9e8d62 to master...

@bors bors added the merged-by-bors This PR was explicitly merged by bors. label Jul 15, 2020
@bors bors merged commit d9e8d62 into rust-lang:master Jul 15, 2020
@nnethercote nnethercote deleted the change-SymbolName-name branch July 16, 2020 00:12
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nnethercote commented Jul 20, 2020

This was a perf win upon landing, as expected.

@rust-lang rust-lang deleted a comment from alex Jul 20, 2020
@cuviper cuviper added this to the 1.47.0 milestone May 2, 2024
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7 participants