Use #[rustc_inherit_overflow_checks] instead of Add::add etc.

Author: m-ou-se

library/core/src/iter/adapters/enumerate.rs

@@ -1,6 +1,6 @@
 use crate::iter::adapters::{zip::try_get_unchecked, SourceIter, TrustedRandomAccess};
 use crate::iter::{FusedIterator, InPlaceIterable, TrustedLen};
-use crate::ops::{Add, AddAssign, Try};
+use crate::ops::Try;
 
 /// An iterator that yields the current count and the element during iteration.
 ///
@@ -39,11 +39,11 @@ where
     ///
     /// Might panic if the index of the element overflows a `usize`.
     #[inline]
+    #[rustc_inherit_overflow_checks]
     fn next(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
         let a = self.iter.next()?;
         let i = self.count;
-        // Possible undefined overflow.
-        AddAssign::add_assign(&mut self.count, 1);
+        self.count += 1;
         Some((i, a))
     }
 
@@ -53,11 +53,11 @@ where
     }
 
     #[inline]
+    #[rustc_inherit_overflow_checks]
     fn nth(&mut self, n: usize) -> Option<(usize, I::Item)> {
         let a = self.iter.nth(n)?;
-        // Possible undefined overflow.
-        let i = Add::add(self.count, n);
-        self.count = Add::add(i, 1);
+        let i = self.count + n;
+        self.count = i + 1;
         Some((i, a))
     }
 
@@ -78,10 +78,10 @@ where
             count: &'a mut usize,
             mut fold: impl FnMut(Acc, (usize, T)) -> R + 'a,
         ) -> impl FnMut(Acc, T) -> R + 'a {
+            #[rustc_inherit_overflow_checks]
             move |acc, item| {
                 let acc = fold(acc, (*count, item));
-                // Possible undefined overflow.
-                AddAssign::add_assign(count, 1);
+                *count += 1;
                 acc
             }
         }
@@ -99,25 +99,26 @@ where
             mut count: usize,
             mut fold: impl FnMut(Acc, (usize, T)) -> Acc,
         ) -> impl FnMut(Acc, T) -> Acc {
+            #[rustc_inherit_overflow_checks]
             move |acc, item| {
                 let acc = fold(acc, (count, item));
-                // Possible undefined overflow.
-                AddAssign::add_assign(&mut count, 1);
+                count += 1;
                 acc
             }
         }
 
         self.iter.fold(init, enumerate(self.count, fold))
     }
 
+    #[rustc_inherit_overflow_checks]
     unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> <Self as Iterator>::Item
     where
         Self: TrustedRandomAccess,
     {
         // SAFETY: the caller must uphold the contract for
         // `Iterator::__iterator_get_unchecked`.
         let value = unsafe { try_get_unchecked(&mut self.iter, idx) };
-        (Add::add(self.count, idx), value)
+        (self.count + idx, value)
     }
 }
 

library/core/src/iter/range.rs

@@ -1,7 +1,7 @@
 use crate::char;
 use crate::convert::TryFrom;
 use crate::mem;
-use crate::ops::{self, Add, Sub, Try};
+use crate::ops::{self, Try};
 
 use super::{FusedIterator, TrustedLen};
 
@@ -201,23 +201,25 @@ macro_rules! step_identical_methods {
 
         #[inline]
         #[allow(arithmetic_overflow)]
+        #[rustc_inherit_overflow_checks]
         fn forward(start: Self, n: usize) -> Self {
             // In debug builds, trigger a panic on overflow.
             // This should optimize completely out in release builds.
             if Self::forward_checked(start, n).is_none() {
-                let _ = Add::add(Self::MAX, 1);
+                let _ = Self::MAX + 1;
             }
             // Do wrapping math to allow e.g. `Step::forward(-128i8, 255)`.
             start.wrapping_add(n as Self)
         }
 
         #[inline]
         #[allow(arithmetic_overflow)]
+        #[rustc_inherit_overflow_checks]
         fn backward(start: Self, n: usize) -> Self {
             // In debug builds, trigger a panic on overflow.
             // This should optimize completely out in release builds.
             if Self::backward_checked(start, n).is_none() {
-                let _ = Sub::sub(Self::MIN, 1);
+                let _ = Self::MIN - 1;
             }
             // Do wrapping math to allow e.g. `Step::backward(127i8, 255)`.
             start.wrapping_sub(n as Self)

library/core/src/iter/traits/accum.rs

@@ -1,6 +1,5 @@
 use crate::iter;
 use crate::num::Wrapping;
-use crate::ops::{Add, Mul};
 
 /// Trait to represent types that can be created by summing up an iterator.
 ///
@@ -37,34 +36,49 @@ pub trait Product<A = Self>: Sized {
     fn product<I: Iterator<Item = A>>(iter: I) -> Self;
 }
 
-// N.B., explicitly use Add and Mul here to inherit overflow checks
 macro_rules! integer_sum_product {
     (@impls $zero:expr, $one:expr, #[$attr:meta], $($a:ty)*) => ($(
         #[$attr]
         impl Sum for $a {
             fn sum<I: Iterator<Item=Self>>(iter: I) -> Self {
-                iter.fold($zero, Add::add)
+                iter.fold(
+                    $zero,
+                    #[rustc_inherit_overflow_checks]
+                    |a, b| a + b,
+                )
             }
         }
 
         #[$attr]
         impl Product for $a {
             fn product<I: Iterator<Item=Self>>(iter: I) -> Self {
-                iter.fold($one, Mul::mul)
+                iter.fold(
+                    $one,
+                    #[rustc_inherit_overflow_checks]
+                    |a, b| a * b,
+                )
             }
         }
 
         #[$attr]
         impl<'a> Sum<&'a $a> for $a {
             fn sum<I: Iterator<Item=&'a Self>>(iter: I) -> Self {
-                iter.fold($zero, Add::add)
+                iter.fold(
+                    $zero,
+                    #[rustc_inherit_overflow_checks]
+                    |a, b| a + b,
+                )
             }
         }
 
         #[$attr]
         impl<'a> Product<&'a $a> for $a {
             fn product<I: Iterator<Item=&'a Self>>(iter: I) -> Self {
-                iter.fold($one, Mul::mul)
+                iter.fold(
+                    $one,
+                    #[rustc_inherit_overflow_checks]
+                    |a, b| a * b,
+                )
             }
         }
     )*);
@@ -83,28 +97,44 @@ macro_rules! float_sum_product {
         #[stable(feature = "iter_arith_traits", since = "1.12.0")]
         impl Sum for $a {
             fn sum<I: Iterator<Item=Self>>(iter: I) -> Self {
-                iter.fold(0.0, Add::add)
+                iter.fold(
+                    0.0,
+                    #[rustc_inherit_overflow_checks]
+                    |a, b| a + b,
+                )
             }
         }
 
         #[stable(feature = "iter_arith_traits", since = "1.12.0")]
         impl Product for $a {
             fn product<I: Iterator<Item=Self>>(iter: I) -> Self {
-                iter.fold(1.0, Mul::mul)
+                iter.fold(
+                    1.0,
+                    #[rustc_inherit_overflow_checks]
+                    |a, b| a * b,
+                )
             }
         }
 
         #[stable(feature = "iter_arith_traits", since = "1.12.0")]
         impl<'a> Sum<&'a $a> for $a {
             fn sum<I: Iterator<Item=&'a Self>>(iter: I) -> Self {
-                iter.fold(0.0, Add::add)
+                iter.fold(
+                    0.0,
+                    #[rustc_inherit_overflow_checks]
+                    |a, b| a + b,
+                )
             }
         }
 
         #[stable(feature = "iter_arith_traits", since = "1.12.0")]
         impl<'a> Product<&'a $a> for $a {
             fn product<I: Iterator<Item=&'a Self>>(iter: I) -> Self {
-                iter.fold(1.0, Mul::mul)
+                iter.fold(
+                    1.0,
+                    #[rustc_inherit_overflow_checks]
+                    |a, b| a * b,
+                )
             }
         }
     )*)

library/core/src/iter/traits/iterator.rs

@@ -3,7 +3,7 @@
 // can't split that into multiple files.
 
 use crate::cmp::{self, Ordering};
-use crate::ops::{Add, ControlFlow, Try};
+use crate::ops::{ControlFlow, Try};
 
 use super::super::TrustedRandomAccess;
 use super::super::{Chain, Cloned, Copied, Cycle, Enumerate, Filter, FilterMap, Fuse};
@@ -242,13 +242,11 @@ pub trait Iterator {
     where
         Self: Sized,
     {
-        #[inline]
-        fn add1<T>(count: usize, _: T) -> usize {
-            // Might overflow.
-            Add::add(count, 1)
-        }
-
-        self.fold(0, add1)
+        self.fold(
+            0,
+            #[rustc_inherit_overflow_checks]
+            |count, _| count + 1,
+        )
     }
 
     /// Consumes the iterator, returning the last element.
@@ -2475,13 +2473,9 @@ pub trait Iterator {
         fn check<T>(
             mut predicate: impl FnMut(T) -> bool,
         ) -> impl FnMut(usize, T) -> ControlFlow<usize, usize> {
-            // The addition might panic on overflow
+            #[rustc_inherit_overflow_checks]
             move |i, x| {
-                if predicate(x) {
-                    ControlFlow::Break(i)
-                } else {
-                    ControlFlow::Continue(Add::add(i, 1))
-                }
+                if predicate(x) { ControlFlow::Break(i) } else { ControlFlow::Continue(i + 1) }
             }
         }