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elaborate_drop: Avoid as_mut.unwrap dance, empty vectors are cheap. #157162

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Merged
rust-bors merged 1 commit into from
May 31, 2026
+7 −14
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elaborate_drop: Avoid as_mut.unwrap dance, empty vectors are cheap. #157162

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21 changes: 7 additions & 14 deletions compiler/rustc_mir_transform/src/elaborate_drop.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -842,9 +842,9 @@ where
let mut values = Vec::with_capacity(adt.variants().len());
let mut normal_blocks = Vec::with_capacity(adt.variants().len());
let mut unwind_blocks =
if unwind.is_cleanup() { None } else { Some(Vec::with_capacity(adt.variants().len())) };
Vec::with_capacity(if unwind.is_cleanup() { 0 } else { adt.variants().len() });
let mut dropline_blocks =
if dropline.is_none() { None } else { Some(Vec::with_capacity(adt.variants().len())) };
Vec::with_capacity(if dropline.is_none() { 0 } else { adt.variants().len() });

let mut have_otherwise_with_drop_glue = false;
let mut have_otherwise = false;
Expand Down Expand Up @@ -880,7 +880,6 @@ where
// I want to minimize the divergence between MSVC
// and non-MSVC.

let unwind_blocks = unwind_blocks.as_mut().unwrap();
let unwind_ladder = vec![Unwind::InCleanup; fields.len() + 1];
let dropline_ladder: Vec<Option<BasicBlock>> = vec![None; fields.len() + 1];
let halfladder =
Expand All @@ -890,7 +889,7 @@ where
let (normal, _, drop_bb) = self.drop_ladder(fields, succ, unwind, dropline);
normal_blocks.push(normal);
if dropline.is_some() {
dropline_blocks.as_mut().unwrap().push(drop_bb.unwrap());
dropline_blocks.push(drop_bb.unwrap());
}
} else {
have_otherwise = true;
Expand All @@ -911,28 +910,22 @@ where
} else if !have_otherwise_with_drop_glue {
normal_blocks.push(self.goto_block(succ, unwind));
if let Unwind::To(unwind) = unwind {
unwind_blocks.as_mut().unwrap().push(self.goto_block(unwind, Unwind::InCleanup));
unwind_blocks.push(self.goto_block(unwind, Unwind::InCleanup));
}
} else {
normal_blocks.push(self.drop_block(succ, unwind));
if let Unwind::To(unwind) = unwind {
unwind_blocks.as_mut().unwrap().push(self.drop_block(unwind, Unwind::InCleanup));
unwind_blocks.push(self.drop_block(unwind, Unwind::InCleanup));
}
}

(
self.adt_switch_block(adt, normal_blocks, &values, succ, unwind),
unwind.map(|unwind| {
self.adt_switch_block(
adt,
unwind_blocks.unwrap(),
&values,
unwind,
Unwind::InCleanup,
)
self.adt_switch_block(adt, unwind_blocks, &values, unwind, Unwind::InCleanup)
}),
dropline.map(|dropline| {
self.adt_switch_block(adt, dropline_blocks.unwrap(), &values, dropline, unwind)
self.adt_switch_block(adt, dropline_blocks, &values, dropline, unwind)
}),
)
}
Expand Down
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