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Rollup merge of #148054 - nnethercote:chain, r=saethlin

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Streamline iterator chaining when computing successors.

There are numerous unnecessary `into_iter` calls.

Also add a comment explaining why the code looks like this, because it's non-obvious at first glance.

r? `@saethlin`
This commit is contained in:
Stuart Cook
2025-10-24 14:53:48 +11:00
committed by GitHub
parent 195815583d 3d951598b2
commit 7141a0f634
1 changed files with 12 additions and 12 deletions
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24
compiler/rustc_middle/src/mir/terminator.rs
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@@ -501,6 +501,8 @@ pub use helper::*;
mod helper {
use super::*;
// Note: the methods below use a `slice.chain(Option).chain(Option)` pattern so that all paths
// produce an iterator with the same concrete type.
pub type Successors<'a> = impl DoubleEndedIterator<Item = BasicBlock> + 'a;
impl SwitchTargets {
@@ -510,7 +512,7 @@ mod helper {
#[define_opaque(Successors)]
pub fn successors_for_value(&self, value: u128) -> Successors<'_> {
let target = self.target_for_value(value);
(&[]).into_iter().copied().chain(Some(target).into_iter().chain(None))
(&[]).into_iter().copied().chain(Some(target)).chain(None)
}
}
@@ -522,10 +524,7 @@ mod helper {
match *self {
// 3-successors for async drop: target, unwind, dropline (parent coroutine drop)
Drop { target: ref t, unwind: UnwindAction::Cleanup(u), drop: Some(d), .. } => {
slice::from_ref(t)
.into_iter()
.copied()
.chain(Some(u).into_iter().chain(Some(d)))
slice::from_ref(t).into_iter().copied().chain(Some(u)).chain(Some(d))
}
// 2-successors
Call { target: Some(ref t), unwind: UnwindAction::Cleanup(u), .. }
@@ -534,7 +533,7 @@ mod helper {
| Drop { target: ref t, unwind: _, drop: Some(u), .. }
| Assert { target: ref t, unwind: UnwindAction::Cleanup(u), .. }
| FalseUnwind { real_target: ref t, unwind: UnwindAction::Cleanup(u) } => {
slice::from_ref(t).into_iter().copied().chain(Some(u).into_iter().chain(None))
slice::from_ref(t).into_iter().copied().chain(Some(u)).chain(None)
}
// single successor
Goto { target: ref t }
@@ -544,7 +543,7 @@ mod helper {
| Drop { target: ref t, unwind: _, .. }
| Assert { target: ref t, unwind: _, .. }
| FalseUnwind { real_target: ref t, unwind: _ } => {
slice::from_ref(t).into_iter().copied().chain(None.into_iter().chain(None))
slice::from_ref(t).into_iter().copied().chain(None).chain(None)
}
// No successors
UnwindResume
@@ -554,23 +553,24 @@ mod helper {
| Unreachable
| TailCall { .. }
| Call { target: None, unwind: _, .. } => {
(&[]).into_iter().copied().chain(None.into_iter().chain(None))
(&[]).into_iter().copied().chain(None).chain(None)
}
// Multiple successors
InlineAsm { ref targets, unwind: UnwindAction::Cleanup(u), .. } => {
targets.iter().copied().chain(Some(u).into_iter().chain(None))
targets.iter().copied().chain(Some(u)).chain(None)
}
InlineAsm { ref targets, unwind: _, .. } => {
targets.iter().copied().chain(None.into_iter().chain(None))
targets.iter().copied().chain(None).chain(None)
}
SwitchInt { ref targets, .. } => {
targets.targets.iter().copied().chain(None.into_iter().chain(None))
targets.targets.iter().copied().chain(None).chain(None)
}
// FalseEdge
FalseEdge { ref real_target, imaginary_target } => slice::from_ref(real_target)
.into_iter()
.copied()
.chain(Some(imaginary_target).into_iter().chain(None)),
.chain(Some(imaginary_target))
.chain(None),
}
}