Rollup merge of #136307 - WaffleLapkin:minminmin, r=scottmcm

Implement all mix/max functions in a (hopefully) more optimization amendable way

Previously the graph was like this:

```
min -> Ord::min -> min_by -> match on compare() (in these cases compare = Ord::cmp)
                                      ^
                                      |
                                 min_by_key
```
now it looks like this:
```
min -> Ord::min -> `<=` <- min_by_key

min_by -> `Ordering::is_le` of `compare()`
```
(`max*` and `minmax*` are the exact same, i.e. they also use `<=` and `is_le`)

I'm not sure how to test this, but it should probably be easier for the backend to optimize.

r? `@scottmcm`
cc #115939 (comment)

Author: matthiaskrgr

library/core/src/cmp.rs

@@ -973,6 +973,24 @@ pub trait Ord: Eq + PartialOrd<Self> {
     /// assert_eq!(1.max(2), 2);
     /// assert_eq!(2.max(2), 2);
     /// ```
+    /// ```
+    /// use std::cmp::Ordering;
+    ///
+    /// #[derive(Eq)]
+    /// struct Equal(&'static str);
+    ///
+    /// impl PartialEq for Equal {
+    ///     fn eq(&self, other: &Self) -> bool { true }
+    /// }
+    /// impl PartialOrd for Equal {
+    ///     fn partial_cmp(&self, other: &Self) -> Option<Ordering> { Some(Ordering::Equal) }
+    /// }
+    /// impl Ord for Equal {
+    ///     fn cmp(&self, other: &Self) -> Ordering { Ordering::Equal }
+    /// }
+    ///
+    /// assert_eq!(Equal("self").max(Equal("other")).0, "other");
+    /// ```
     #[stable(feature = "ord_max_min", since = "1.21.0")]
     #[inline]
     #[must_use]
@@ -981,7 +999,7 @@ pub trait Ord: Eq + PartialOrd<Self> {
     where
         Self: Sized,
     {
-        max_by(self, other, Ord::cmp)
+        if other < self { self } else { other }
     }
 
     /// Compares and returns the minimum of two values.
@@ -994,6 +1012,24 @@ pub trait Ord: Eq + PartialOrd<Self> {
     /// assert_eq!(1.min(2), 1);
     /// assert_eq!(2.min(2), 2);
     /// ```
+    /// ```
+    /// use std::cmp::Ordering;
+    ///
+    /// #[derive(Eq)]
+    /// struct Equal(&'static str);
+    ///
+    /// impl PartialEq for Equal {
+    ///     fn eq(&self, other: &Self) -> bool { true }
+    /// }
+    /// impl PartialOrd for Equal {
+    ///     fn partial_cmp(&self, other: &Self) -> Option<Ordering> { Some(Ordering::Equal) }
+    /// }
+    /// impl Ord for Equal {
+    ///     fn cmp(&self, other: &Self) -> Ordering { Ordering::Equal }
+    /// }
+    ///
+    /// assert_eq!(Equal("self").min(Equal("other")).0, "self");
+    /// ```
     #[stable(feature = "ord_max_min", since = "1.21.0")]
     #[inline]
     #[must_use]
@@ -1002,7 +1038,7 @@ pub trait Ord: Eq + PartialOrd<Self> {
     where
         Self: Sized,
     {
-        min_by(self, other, Ord::cmp)
+        if other < self { other } else { self }
     }
 
     /// Restrict a value to a certain interval.
@@ -1414,6 +1450,24 @@ pub macro PartialOrd($item:item) {
 /// assert_eq!(cmp::min(1, 2), 1);
 /// assert_eq!(cmp::min(2, 2), 2);
 /// ```
+/// ```
+/// use std::cmp::{self, Ordering};
+///
+/// #[derive(Eq)]
+/// struct Equal(&'static str);
+///
+/// impl PartialEq for Equal {
+///     fn eq(&self, other: &Self) -> bool { true }
+/// }
+/// impl PartialOrd for Equal {
+///     fn partial_cmp(&self, other: &Self) -> Option<Ordering> { Some(Ordering::Equal) }
+/// }
+/// impl Ord for Equal {
+///     fn cmp(&self, other: &Self) -> Ordering { Ordering::Equal }
+/// }
+///
+/// assert_eq!(cmp::min(Equal("v1"), Equal("v2")).0, "v1");
+/// ```
 #[inline]
 #[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -1431,20 +1485,22 @@ pub fn min<T: Ord>(v1: T, v2: T) -> T {
 /// ```
 /// use std::cmp;
 ///
-/// let result = cmp::min_by(-2, 1, |x: &i32, y: &i32| x.abs().cmp(&y.abs()));
-/// assert_eq!(result, 1);
+/// let abs_cmp = |x: &i32, y: &i32| x.abs().cmp(&y.abs());
 ///
-/// let result = cmp::min_by(-2, 3, |x: &i32, y: &i32| x.abs().cmp(&y.abs()));
-/// assert_eq!(result, -2);
+/// let result = cmp::min_by(2, -1, abs_cmp);
+/// assert_eq!(result, -1);
+///
+/// let result = cmp::min_by(2, -3, abs_cmp);
+/// assert_eq!(result, 2);
+///
+/// let result = cmp::min_by(1, -1, abs_cmp);
+/// assert_eq!(result, 1);
 /// ```
 #[inline]
 #[must_use]
 #[stable(feature = "cmp_min_max_by", since = "1.53.0")]
 pub fn min_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
-    match compare(&v1, &v2) {
-        Ordering::Less | Ordering::Equal => v1,
-        Ordering::Greater => v2,
-    }
+    if compare(&v2, &v1).is_lt() { v2 } else { v1 }
 }
 
 /// Returns the element that gives the minimum value from the specified function.
@@ -1456,17 +1512,20 @@ pub fn min_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
 /// ```
 /// use std::cmp;
 ///
-/// let result = cmp::min_by_key(-2, 1, |x: &i32| x.abs());
-/// assert_eq!(result, 1);
+/// let result = cmp::min_by_key(2, -1, |x: &i32| x.abs());
+/// assert_eq!(result, -1);
 ///
-/// let result = cmp::min_by_key(-2, 2, |x: &i32| x.abs());
-/// assert_eq!(result, -2);
+/// let result = cmp::min_by_key(2, -3, |x: &i32| x.abs());
+/// assert_eq!(result, 2);
+///
+/// let result = cmp::min_by_key(1, -1, |x: &i32| x.abs());
+/// assert_eq!(result, 1);
 /// ```
 #[inline]
 #[must_use]
 #[stable(feature = "cmp_min_max_by", since = "1.53.0")]
 pub fn min_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
-    min_by(v1, v2, |v1, v2| f(v1).cmp(&f(v2)))
+    if f(&v2) < f(&v1) { v2 } else { v1 }
 }
 
 /// Compares and returns the maximum of two values.
@@ -1483,6 +1542,24 @@ pub fn min_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
 /// assert_eq!(cmp::max(1, 2), 2);
 /// assert_eq!(cmp::max(2, 2), 2);
 /// ```
+/// ```
+/// use std::cmp::{self, Ordering};
+///
+/// #[derive(Eq)]
+/// struct Equal(&'static str);
+///
+/// impl PartialEq for Equal {
+///     fn eq(&self, other: &Self) -> bool { true }
+/// }
+/// impl PartialOrd for Equal {
+///     fn partial_cmp(&self, other: &Self) -> Option<Ordering> { Some(Ordering::Equal) }
+/// }
+/// impl Ord for Equal {
+///     fn cmp(&self, other: &Self) -> Ordering { Ordering::Equal }
+/// }
+///
+/// assert_eq!(cmp::max(Equal("v1"), Equal("v2")).0, "v2");
+/// ```
 #[inline]
 #[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -1500,20 +1577,22 @@ pub fn max<T: Ord>(v1: T, v2: T) -> T {
 /// ```
 /// use std::cmp;
 ///
-/// let result = cmp::max_by(-2, 1, |x: &i32, y: &i32| x.abs().cmp(&y.abs()));
+/// let abs_cmp = |x: &i32, y: &i32| x.abs().cmp(&y.abs());
+///
+/// let result = cmp::max_by(3, -2, abs_cmp) ;
+/// assert_eq!(result, 3);
+///
+/// let result = cmp::max_by(1, -2, abs_cmp);
 /// assert_eq!(result, -2);
 ///
-/// let result = cmp::max_by(-2, 2, |x: &i32, y: &i32| x.abs().cmp(&y.abs())) ;
-/// assert_eq!(result, 2);
+/// let result = cmp::max_by(1, -1, abs_cmp);
+/// assert_eq!(result, -1);
 /// ```
 #[inline]
 #[must_use]
 #[stable(feature = "cmp_min_max_by", since = "1.53.0")]
 pub fn max_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
-    match compare(&v1, &v2) {
-        Ordering::Less | Ordering::Equal => v2,
-        Ordering::Greater => v1,
-    }
+    if compare(&v2, &v1).is_lt() { v1 } else { v2 }
 }
 
 /// Returns the element that gives the maximum value from the specified function.
@@ -1525,17 +1604,20 @@ pub fn max_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
 /// ```
 /// use std::cmp;
 ///
-/// let result = cmp::max_by_key(-2, 1, |x: &i32| x.abs());
+/// let result = cmp::max_by_key(3, -2, |x: &i32| x.abs());
+/// assert_eq!(result, 3);
+///
+/// let result = cmp::max_by_key(1, -2, |x: &i32| x.abs());
 /// assert_eq!(result, -2);
 ///
-/// let result = cmp::max_by_key(-2, 2, |x: &i32| x.abs());
-/// assert_eq!(result, 2);
+/// let result = cmp::max_by_key(1, -1, |x: &i32| x.abs());
+/// assert_eq!(result, -1);
 /// ```
 #[inline]
 #[must_use]
 #[stable(feature = "cmp_min_max_by", since = "1.53.0")]
 pub fn max_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
-    max_by(v1, v2, |v1, v2| f(v1).cmp(&f(v2)))
+    if f(&v2) < f(&v1) { v1 } else { v2 }
 }
 
 /// Compares and sorts two values, returning minimum and maximum.
@@ -1549,21 +1631,40 @@ pub fn max_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
 /// use std::cmp;
 ///
 /// assert_eq!(cmp::minmax(1, 2), [1, 2]);
-/// assert_eq!(cmp::minmax(2, 2), [2, 2]);
+/// assert_eq!(cmp::minmax(2, 1), [1, 2]);
 ///
 /// // You can destructure the result using array patterns
 /// let [min, max] = cmp::minmax(42, 17);
 /// assert_eq!(min, 17);
 /// assert_eq!(max, 42);
 /// ```
+/// ```
+/// #![feature(cmp_minmax)]
+/// use std::cmp::{self, Ordering};
+///
+/// #[derive(Eq)]
+/// struct Equal(&'static str);
+///
+/// impl PartialEq for Equal {
+///     fn eq(&self, other: &Self) -> bool { true }
+/// }
+/// impl PartialOrd for Equal {
+///     fn partial_cmp(&self, other: &Self) -> Option<Ordering> { Some(Ordering::Equal) }
+/// }
+/// impl Ord for Equal {
+///     fn cmp(&self, other: &Self) -> Ordering { Ordering::Equal }
+/// }
+///
+/// assert_eq!(cmp::minmax(Equal("v1"), Equal("v2")).map(|v| v.0), ["v1", "v2"]);
+/// ```
 #[inline]
 #[must_use]
 #[unstable(feature = "cmp_minmax", issue = "115939")]
 pub fn minmax<T>(v1: T, v2: T) -> [T; 2]
 where
     T: Ord,
 {
-    if v1 <= v2 { [v1, v2] } else { [v2, v1] }
+    if v2 < v1 { [v2, v1] } else { [v1, v2] }
 }
 
 /// Returns minimum and maximum values with respect to the specified comparison function.
@@ -1576,11 +1677,14 @@ where
 /// #![feature(cmp_minmax)]
 /// use std::cmp;
 ///
-/// assert_eq!(cmp::minmax_by(-2, 1, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), [1, -2]);
-/// assert_eq!(cmp::minmax_by(-2, 2, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), [-2, 2]);
+/// let abs_cmp = |x: &i32, y: &i32| x.abs().cmp(&y.abs());
+///
+/// assert_eq!(cmp::minmax_by(-2, 1, abs_cmp), [1, -2]);
+/// assert_eq!(cmp::minmax_by(-1, 2, abs_cmp), [-1, 2]);
+/// assert_eq!(cmp::minmax_by(-2, 2, abs_cmp), [-2, 2]);
 ///
 /// // You can destructure the result using array patterns
-/// let [min, max] = cmp::minmax_by(-42, 17, |x: &i32, y: &i32| x.abs().cmp(&y.abs()));
+/// let [min, max] = cmp::minmax_by(-42, 17, abs_cmp);
 /// assert_eq!(min, 17);
 /// assert_eq!(max, -42);
 /// ```
@@ -1591,7 +1695,7 @@ pub fn minmax_by<T, F>(v1: T, v2: T, compare: F) -> [T; 2]
 where
     F: FnOnce(&T, &T) -> Ordering,
 {
-    if compare(&v1, &v2).is_le() { [v1, v2] } else { [v2, v1] }
+    if compare(&v2, &v1).is_lt() { [v2, v1] } else { [v1, v2] }
 }
 
 /// Returns minimum and maximum values with respect to the specified key function.
@@ -1620,7 +1724,7 @@ where
     F: FnMut(&T) -> K,
     K: Ord,
 {
-    minmax_by(v1, v2, |v1, v2| f(v1).cmp(&f(v2)))
+    if f(&v2) < f(&v1) { [v2, v1] } else { [v1, v2] }
 }
 
 // Implementation of PartialEq, Eq, PartialOrd and Ord for primitive types