Avoid creating SmallVecs in global_llvm_features
#97579
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| @@ -218,6 +218,9 @@ pub fn check_tied_features( | |||
| sess: &Session, | |||
| features: &FxHashMap<&str, bool>, | |||
| ) -> Option<&'static [&'static str]> { | |||
| if features.len() == 0 { | |||
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Nit: this is probably better written as something like:
if !features.is_empty() {
for tied in ... {
...
}
}
return None;
The code isn't particularly deeply nested here and avoids having to specify None as a return twice.
| @@ -485,35 +490,35 @@ pub(crate) fn global_llvm_features(sess: &Session, diagnostics: bool) -> Vec<Str | |||
| } | |||
| diag.emit(); | |||
| } | |||
| Some((enable_disable, feature)) | |||
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| if diagnostics && tied_features.iter().any(|tied| tied.contains(&feature)) { | |||
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This is doing a second linear lookup through the tied_features list (in addition to the one that will happen later in the check_tied_features.
Ignoring entirely the fact that what's going on here is an exercise in micro-optimization, and the overall performance of the compiler is likely going to stay pretty much the same, I feel like such double lookup is probably defeating any improvements gained here by all the other changes.
It would seem to me that we'd be better off by just not checking this here (while leaving everything else intact):
| if diagnostics && tied_features.iter().any(|tied| tied.contains(&feature)) { | |
| if diagnostics { |
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Thanks for pointing out! That makes sense and I think we can keep the FIXME here
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Thanks for reviewing! I made the corresponding corrections |
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@bors r+ thanks! |
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📌 Commit b3cd892 has been approved by |
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Rollup of 5 pull requests Successful merges: - rust-lang#97312 (Compute lifetimes in scope at diagnostic time) - rust-lang#97495 (Add E0788 for improper #[no_coverage] usage) - rust-lang#97579 (Avoid creating `SmallVec`s in `global_llvm_features`) - rust-lang#97767 (interpret: do not claim UB until we looked more into variadic functions) - rust-lang#97787 (E0432: rust 2018 -> rust 2018 or later in --explain message) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
This PR made a simple optimization to avoid creating extra
SmallVecs by adjusting the use of iterator statements.Also, given the very small size of
tied_target_features, there is no need to insert each feature into the FxHashMap.