Allow the optimizer to elide bounds checks when enumerating IndexSlice/IndecVec.

Author: Jarcho

compiler/rustc_index/src/slice.rs

@@ -65,13 +65,17 @@ impl<I: Idx, T> IndexSlice<I, T> {
 
 #[inline]
 pubfniter_enumerated(&self) -> implDoubleEndedIterator<Item = (I,&T)> + ExactSizeIterator{
+// Allow the optimizer to elide the bounds checking when creating each index.
+let _ = I::new(self.len());
 self.raw.iter().enumerate().map(|(n, t)| (I::new(n), t))
 }
 
 #[inline]
 pubfnindices(
 &self,
 ) -> implDoubleEndedIterator<Item = I> + ExactSizeIterator + Clone + 'static{
+// Allow the optimizer to elide the bounds checking when creating each index.
+let _ = I::new(self.len());
 (0..self.len()).map(|n| I::new(n))
 }
 
@@ -84,6 +88,8 @@ impl<I: Idx, T> IndexSlice<I, T> {
 pubfniter_enumerated_mut(
 &mutself,
 ) -> implDoubleEndedIterator<Item = (I,&mutT)> + ExactSizeIterator{
+// Allow the optimizer to elide the bounds checking when creating each index.
+let _ = I::new(self.len());
 self.raw.iter_mut().enumerate().map(|(n, t)| (I::new(n), t))
 }
 

compiler/rustc_index/src/vec.rs

@@ -93,6 +93,8 @@ impl<I: Idx, T> IndexVec<I, T> {
 /// be allocated only once, with a capacity of at least `n`.)
 #[inline]
 pubfnfrom_fn_n(func:implFnMut(I) -> T,n:usize) -> Self{
+// Allow the optimizer to elide the bounds checking when creating each index.
+let _ = I::new(n);
 IndexVec::from_raw((0..n).map(I::new).map(func).collect())
 }
 
@@ -128,6 +130,8 @@ impl<I: Idx, T> IndexVec<I, T> {
 pubfninto_iter_enumerated(
 self,
 ) -> implDoubleEndedIterator<Item = (I,T)> + ExactSizeIterator{
+// Allow the optimizer to elide the bounds checking when creating each index.
+let _ = I::new(self.len());
 self.raw.into_iter().enumerate().map(|(n, t)| (I::new(n), t))
 }