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Auto merge of #77755 - bugadani:perf-calc-dtor, r=ecstatic-morse

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Monomorphize `calculate_dtor` instead of using function pointers

Change `calculate_dtor` to avoid dynamic dispatching. This change allows the empty functions to be optimized away.

Based on the discussion in https://github.com/rust-lang/rust/pull/77754#discussion_r502498970, the performance impact of this change was measured.

Perf run results: https://perf.rust-lang.org/compare.html?start=7bc5839e99411aad9061a632b62075d1346cbb3b&end=ffec759ae9bbc4d6d2235ff40ade6723a85bc7cc
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bors 2020-10-13 10:19:30 +00:00
commit 2d6eccdb67
4 changed files with 4 additions and 4 deletions
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compiler/rustc_mir/src/transform/check_const_item_mutation.rs
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@ -53,7 +53,7 @@ impl<'a, 'tcx> ConstMutationChecker<'a, 'tcx> {
//
// #[const_mutation_allowed]
// pub const LOG: Log = Log { msg: "" };
match self.tcx.calculate_dtor(def_id, &mut |_, _| Ok(())) {
match self.tcx.calculate_dtor(def_id, |_, _| Ok(())) {
Some(_) => None,
None => Some(def_id),
}