From 27d4d51670710aa44a73baf04130bc262b8de244 Mon Sep 17 00:00:00 2001
From: Scott McMurray <scottmcm@users.noreply.github.com>
Date: Wed, 7 Feb 2018 11:11:54 -0800
Subject: [PATCH] Simplify RangeInclusive::next[_back]

`match`ing on an `Option<Ordering>` seems cause some confusion for LLVM; switching to just using comparison operators removes a few jumps from the simple `for` loops I was trying.
---
 src/libcore/iter/range.rs | 28 ++++++++++++----------------
 src/libcore/tests/iter.rs | 19 +++++++++++++++++++
 2 files changed, 31 insertions(+), 16 deletions(-)

diff --git a/src/libcore/iter/range.rs b/src/libcore/iter/range.rs
index 3b034efcce14c..6d582b9a721fe 100644
--- a/src/libcore/iter/range.rs
+++ b/src/libcore/iter/range.rs
@@ -331,19 +331,17 @@ impl<A: Step> Iterator for ops::RangeInclusive<A> {
 
     #[inline]
     fn next(&mut self) -> Option<A> {
-        use cmp::Ordering::*;
-
-        match self.start.partial_cmp(&self.end) {
-            Some(Less) => {
+        if self.start <= self.end {
+            if self.start < self.end {
                 let n = self.start.add_one();
                 Some(mem::replace(&mut self.start, n))
-            },
-            Some(Equal) => {
+            } else {
                 let last = self.start.replace_one();
                 self.end.replace_zero();
                 Some(last)
-            },
-            _ => None,
+            }
+        } else {
+            None
         }
     }
 
@@ -425,19 +423,17 @@ impl<A: Step> Iterator for ops::RangeInclusive<A> {
 impl<A: Step> DoubleEndedIterator for ops::RangeInclusive<A> {
     #[inline]
     fn next_back(&mut self) -> Option<A> {
-        use cmp::Ordering::*;
-
-        match self.start.partial_cmp(&self.end) {
-            Some(Less) => {
+        if self.start <= self.end {
+            if self.start < self.end {
                 let n = self.end.sub_one();
                 Some(mem::replace(&mut self.end, n))
-            },
-            Some(Equal) => {
+            } else {
                 let last = self.end.replace_zero();
                 self.start.replace_one();
                 Some(last)
-            },
-            _ => None,
+            }
+        } else {
+            None
         }
     }
 
diff --git a/src/libcore/tests/iter.rs b/src/libcore/tests/iter.rs
index dc866d180bfa0..c742a1d8048fc 100644
--- a/src/libcore/tests/iter.rs
+++ b/src/libcore/tests/iter.rs
@@ -1332,6 +1332,18 @@ fn test_range_inclusive_exhaustion() {
     assert_eq!(r.next_back(), Some(10));
     assert_eq!(r, 1..=0);
 
+    let mut r = 10..=12;
+    assert_eq!(r.next(), Some(10));
+    assert_eq!(r.next(), Some(11));
+    assert_eq!(r.next(), Some(12));
+    assert_eq!(r, 1..=0);
+
+    let mut r = 10..=12;
+    assert_eq!(r.next_back(), Some(12));
+    assert_eq!(r.next_back(), Some(11));
+    assert_eq!(r.next_back(), Some(10));
+    assert_eq!(r, 1..=0);
+
     let mut r = 10..=12;
     assert_eq!(r.nth(2), Some(12));
     assert_eq!(r, 1..=0);
@@ -1340,6 +1352,13 @@ fn test_range_inclusive_exhaustion() {
     assert_eq!(r.nth(5), None);
     assert_eq!(r, 1..=0);
 
+    let mut r = 100..=10;
+    assert_eq!(r.next(), None);
+    assert_eq!(r, 100..=10);
+
+    let mut r = 100..=10;
+    assert_eq!(r.next_back(), None);
+    assert_eq!(r, 100..=10);
 }
 
 #[test]