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Auto merge of #127560 - oli-obk:safe_clobber, r=nnethercote

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Make `visit_clobber`'s impl safe

This was originally introduced in #58061 but I didn't see any perf discussion about it, so let's see what perf says.

r? `@nnethercote`
This commit is contained in:
bors 2024-07-10 22:01:02 +00:00
commit 3ad5f459b3
1 changed files with 3 additions and 14 deletions
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17
compiler/rustc_ast/src/mut_visit.rs
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@ -20,7 +20,7 @@
use rustc_span::Span;
use smallvec::{smallvec, Array, SmallVec};
use std::ops::DerefMut;
use std::{panic, ptr};
use std::panic;
use thin_vec::ThinVec;
pub trait ExpectOne<A: Array> {
@ -318,19 +318,8 @@ fn visit_capture_by(&mut self, capture_by: &mut CaptureBy) {
//
// No `noop_` prefix because there isn't a corresponding method in `MutVisitor`.
pub fn visit_clobber<T: DummyAstNode>(t: &mut T, f: impl FnOnce(T) -> T) {
unsafe {
// Safe because `t` is used in a read-only fashion by `read()` before
// being overwritten by `write()`.
let old_t = ptr::read(t);
let new_t =
panic::catch_unwind(panic::AssertUnwindSafe(|| f(old_t))).unwrap_or_else(|err| {
// Set `t` to some valid but possible meaningless value,
// and pass the fatal error further.
ptr::write(t, T::dummy());
panic::resume_unwind(err);
});
ptr::write(t, new_t);
}
let old_t = std::mem::replace(t, T::dummy());
*t = f(old_t);
}
// No `noop_` prefix because there isn't a corresponding method in `MutVisitor`.