Speed up obligation forest code #51411
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`process_predicates` returns a `Result<Option<Vec<PredicateObligation>>>`. `process_obligation` calls it and then fiddles with the output (using `map`, `map`, `into_iter`, `collect`) to produce a a `Result<Option<Vec<PendingPredicateObligation>>>`. This function is sufficiently hot that the fiddling is expensive. It's much better for `process_predicate` to directly return a `Result<Option<Vec<PendingPredicateObligation>>>` because `Ok(None)` accounts for ~90% of the results, and `Ok(vec![])` accounts for another ~5%.
Because it has a single callsite. This patch is large but trivial, doing the minimal amount of work (mostly `self.` insertions) necessary.
It's very hot, and this speeds things up.
A tri-valued enum is nicer than Result<Option<T>>, and it's slightly faster.
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@bors r+ |
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📌 Commit c83d152 has been approved by |
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⌛ Testing commit c83d152 with merge b541bf54dca84e576bb481a6992bf743dcebf8bd... |
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💔 Test failed - status-travis |
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This is clearly an infra failure. |
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@bors retry |
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Jun 16, 2018
Speed up obligation forest code
Here are the rustc-perf benchmarks that get at least a 1% speedup on one or more of their runs with these patches applied:
```
inflate-check
avg: -8.7% min: -12.1% max: 0.0%
inflate
avg: -5.9% min: -8.6% max: 1.1%
inflate-opt
avg: -1.5% min: -2.0% max: -0.3%
clap-rs-check
avg: -0.6% min: -1.9% max: 0.5%
coercions
avg: -0.2%? min: -1.3%? max: 0.6%?
serde-opt
avg: -0.6% min: -1.0% max: 0.1%
coercions-check
avg: -0.4%? min: -1.0%? max: -0.0%?
```
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☀️ Test successful - status-appveyor, status-travis |
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Here are the rustc-perf benchmarks that get at least a 1% speedup on one or more of their runs with these patches applied: