Rollup merge of #138372 - Eclips4:issue-138196, r=scottmcm

Refactor `pick2_mut` & `pick3_mut` to use `get_disjoint_mut`
Closes#138196

Author: matthiaskrgr

compiler/rustc_index/src/slice.rs

@@ -1,6 +1,7 @@
 use std::fmt;
 use std::marker::PhantomData;
 use std::ops::{Index,IndexMut};
+use std::slice::GetDisjointMutError::*;
 use std::slice::{self,SliceIndex};
 
 usecrate::{Idx,IndexVec,IntoSliceIdx};
@@ -121,32 +122,36 @@ impl<I: Idx, T> IndexSlice<I, T> {
 
 /// Returns mutable references to two distinct elements, `a` and `b`.
 ///
-/// Panics if `a == b`.
+/// Panics if `a == b` or if some of them are out of bounds.
 #[inline]
 pubfnpick2_mut(&mutself,a:I,b:I) -> (&mutT,&mutT){
 let(ai, bi) = (a.index(), b.index());
-assert!(ai != bi);
-
-if ai < bi {
-let(c1, c2) = self.raw.split_at_mut(bi);
-(&mut c1[ai],&mut c2[0])
-}else{
-let(c2, c1) = self.pick2_mut(b, a);
-(c1, c2)
+
+matchself.raw.get_disjoint_mut([ai, bi]){
+Ok([a, b]) => (a, b),
+Err(OverlappingIndices) => panic!("Indices {ai:?} and {bi:?} are not disjoint!"),
+Err(IndexOutOfBounds) => {
+panic!("Some indices among ({ai:?}, {bi:?}) are out of bounds")
+}
 }
 }
 
 /// Returns mutable references to three distinct elements.
 ///
-/// Panics if the elements are not distinct.
+/// Panics if the elements are not distinct or if some of them are out of bounds.
 #[inline]
 pubfnpick3_mut(&mutself,a:I,b:I,c:I) -> (&mutT,&mutT,&mutT){
 let(ai, bi, ci) = (a.index(), b.index(), c.index());
-assert!(ai != bi && bi != ci && ci != ai);
-let len = self.raw.len();
-assert!(ai < len && bi < len && ci < len);
-let ptr = self.raw.as_mut_ptr();
-unsafe{(&mut*ptr.add(ai),&mut*ptr.add(bi),&mut*ptr.add(ci))}
+
+matchself.raw.get_disjoint_mut([ai, bi, ci]){
+Ok([a, b, c]) => (a, b, c),
+Err(OverlappingIndices) => {
+panic!("Indices {ai:?}, {bi:?} and {ci:?} are not disjoint!")
+}
+Err(IndexOutOfBounds) => {
+panic!("Some indices among ({ai:?}, {bi:?}, {ci:?}) are out of bounds")
+}
+}
 }
 
 #[inline]