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Less cloning in early otherwise branch #77472

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simonvandel wants to merge 8 commits into from
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Less cloning in early otherwise branch #77472

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e7811f9
Do not clone vec and bail early
simonvandel Oct 2, 2020
7a8c277
less clone
simonvandel Oct 2, 2020
62b6896
Remove duplicated check
simonvandel Oct 2, 2020
4784a5c
reorder checks from (intuitively) cheapest to most expensive
simonvandel Oct 2, 2020
586ba9d
Restructure data such that data about the first switch is not duplicated
simonvandel Oct 2, 2020
b4e144e
Move helper creation out of loop
simonvandel Oct 3, 2020
bd56b11
Use SwitchTargets instead of storing in Vec
simonvandel Oct 14, 2020
1a8d28a
Use otherwise from switchTargets
simonvandel Oct 14, 2020
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24 changes: 12 additions & 12 deletions compiler/rustc_mir/src/transform/early_otherwise_branch.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -234,23 +234,13 @@ impl<'a, 'tcx> Helper<'a, 'tcx> {
if is_switch(terminator) {
let this_bb_discr_info = self.find_switch_discriminant_info(bb, terminator)?;

// the types of the two adts matched on have to be equalfor this optimization to apply
if discr_info.type_adt_matched_on != this_bb_discr_info.type_adt_matched_on {
trace!(
"NO: types do not match. LHS: {:?}, RHS: {:?}",
discr_info.type_adt_matched_on,
this_bb_discr_info.type_adt_matched_on
);
return None;
}

// the otherwise branch of the two switches have to point to the same bb
// The otherwise branch of the two switches have to point to the same bb
if discr_info.otherwise_bb != this_bb_discr_info.otherwise_bb {
trace!("NO: otherwise target is not the same");
return None;
}

// only allow optimization if the left and right of the tuple being matched are the same variants.
// Only allow optimization if the left and right of the tuple being matched are the same variants.
// so the following should not optimize
// ```rust
// let x: Option<()>;
Expand All @@ -270,6 +260,16 @@ impl<'a, 'tcx> Helper<'a, 'tcx> {
return None;
}

// The types of the two adts matched on have to be equal for this optimization to apply
if discr_info.type_adt_matched_on != this_bb_discr_info.type_adt_matched_on {
trace!(
"NO: types do not match. LHS: {:?}, RHS: {:?}",
discr_info.type_adt_matched_on,
this_bb_discr_info.type_adt_matched_on
);
return None;
}
Comment on lines +261 to +269
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@jyn514 jyn514 Oct 30, 2020

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There doesn't seem to be much point to this change without benchmarks. Personally I would expect a simple != to be faster than two conditionals.


// if we reach this point, the optimization applies, and we should be able to optimize this case
// store the info that is needed to apply the optimization

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