Half of Serde compile time is spent in ElaborateDrops #37106
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P-high
High priority
T-compiler
Relevant to the compiler team, which will review and decide on the PR/issue.
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Looks like this is largely explained by array and tuple Deserialize impls. We have impls for arrays sized 1 through 32 and tuples sized 1 through 16 that look like this: $(
let $name = match try!(visitor.visit()) {
Some(value) => value,
None => { return Err(Error::end_of_stream()); }
};
)+;
try!(visitor.end());
Ok(($($name,)+))Without the array and tuple impls the total compile time is 4.35 seconds with 1.370 in ElaborateDrops. I will look into using a loop for the larger array impls. On the Rust side is there maybe an optimization that would handle this pattern better? |
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cc @rust-lang/compiler |
alexcrichton
added
I-nominated
T-compiler
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callgrind does not show ElaborateDrops as hot (but it does take 10 minutes to run). Odd. |
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triage: P-high |
arielb1
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Oct 13, 2016
There used to be only a global cache, which led to uncached calls to trait selection when there were type parameters. I'm running a check that there are no adverse performance effects. Fixes rust-lang#37106 (drop elaboration times are now ~half of borrow checking, so might still be worthy of optimization, but not critical).
bors
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Oct 15, 2016
add a per-param-env cache to `impls_bound` There used to be only a global cache, which led to uncached calls to trait selection when there were type parameters. This causes a 20% decrease in borrow-checking time and an overall 0.5% performance increase during bootstrapping (as borrow-checking tends to be a tiny part of compilation time). Fixes #37106 (drop elaboration times are now ~half of borrow checking, so might still be worthy of optimization, but not critical). r? @pnkfelix
brson
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Nov 3, 2016
There used to be only a global cache, which led to uncached calls to trait selection when there were type parameters. I'm running a check that there are no adverse performance effects. Fixes rust-lang#37106 (drop elaboration times are now ~half of borrow checking, so might still be worthy of optimization, but not critical).
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The main
serdecrate compiles in 10 seconds, 5 of which is ElaborateDrops. Is this expected? Is there anything we can do on our end to reduce this? I don't see any other tickets about this pass in particular.https://github.com/serde-rs/serde/tree/v0.8.12/serde
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