Auto merge of #57234 - Centril:const-stabilizations-2, r=oli-obk

Const-stabilize `const_int_ops` + `const_ip`

r? @oli-obk

## Note for relnotes: This PR includes https://github.com/rust-lang/rust/pull/57105.

I've added T-lang since this affects intrinsics and the operational semantics of Rust's `const fn` fragment.

## Stable APIs proposed for constification

+ `const_int_ops`:
    + `count_ones`
    + `count_zeros`
    + `leading_zeros`
    + `trailing_zeros`
    + `swap_bytes`
    + `from_be`
    + `from_le`
    + `to_be`
    + `to_le`
+ `const_ip`
    + `Ipv4Addr::new`

## Unstable APIs constified

+ `const_int_conversion`:
    + `reverse_bits`

3 files changed, 78 insertions, 43 deletions

diff --git a/src/libcore/intrinsics.rs b/src/libcore/intrinsics.rs
index 4f5310f5285..db19baf7a2c 100644
--- a/src/libcore/intrinsics.rs
+++ b/src/libcore/intrinsics.rs
@@ -1348,7 +1348,7 @@ extern "rust-intrinsic" {
     /// use std::intrinsics::ctlz;
     ///
     /// let x = 0b0001_1100_u8;
-    /// let num_leading = unsafe { ctlz(x) };
+    /// let num_leading = ctlz(x);
     /// assert_eq!(num_leading, 3);
     /// ```
     ///
@@ -1360,7 +1360,7 @@ extern "rust-intrinsic" {
     /// use std::intrinsics::ctlz;
     ///
     /// let x = 0u16;
-    /// let num_leading = unsafe { ctlz(x) };
+    /// let num_leading = ctlz(x);
     /// assert_eq!(num_leading, 16);
     /// ```
     pub fn ctlz<T>(x: T) -> T;
@@ -1391,7 +1391,7 @@ extern "rust-intrinsic" {
     /// use std::intrinsics::cttz;
     ///
     /// let x = 0b0011_1000_u8;
-    /// let num_trailing = unsafe { cttz(x) };
+    /// let num_trailing = cttz(x);
     /// assert_eq!(num_trailing, 3);
     /// ```
     ///
@@ -1403,7 +1403,7 @@ extern "rust-intrinsic" {
     /// use std::intrinsics::cttz;
     ///
     /// let x = 0u16;
-    /// let num_trailing = unsafe { cttz(x) };
+    /// let num_trailing = cttz(x);
     /// assert_eq!(num_trailing, 16);
     /// ```
     pub fn cttz<T>(x: T) -> T;
diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs
index b2cafc4cede..a5f20d08e47 100644
--- a/src/libcore/lib.rs
+++ b/src/libcore/lib.rs
@@ -71,7 +71,7 @@
 #![feature(cfg_target_has_atomic)]
 #![feature(concat_idents)]
 #![feature(const_fn)]
-#![feature(const_int_ops)]
+#![cfg_attr(stage0, feature(const_int_ops))]
 #![feature(const_fn_union)]
 #![feature(custom_attribute)]
 #![feature(doc_cfg)]
@@ -114,9 +114,7 @@
 #![feature(const_slice_len)]
 #![feature(const_str_as_bytes)]
 #![feature(const_str_len)]
-#![feature(const_int_rotate)]
-#![feature(const_int_wrapping)]
-#![feature(const_int_sign)]
+#![cfg_attr(stage0, feature(const_int_rotate))]
 #![feature(const_int_conversion)]
 #![feature(const_transmute)]
 #![feature(reverse_bits)]
diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs
index 97bf582df5a..7ff04410516 100644
--- a/src/libcore/num/mod.rs
+++ b/src/libcore/num/mod.rs
@@ -275,7 +275,7 @@ $EndFeature, "
 ```
 "),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_ops")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_ops"))]
             #[inline]
             pub const fn count_ones(self) -> u32 { (self as $UnsignedT).count_ones() }
         }
@@ -291,7 +291,7 @@ Basic usage:
 ", $Feature, "assert_eq!(", stringify!($SelfT), "::max_value().count_zeros(), 1);", $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_ops")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_ops"))]
             #[inline]
             pub const fn count_zeros(self) -> u32 {
                 (!self).count_ones()
@@ -312,7 +312,7 @@ assert_eq!(n.leading_zeros(), 0);",
 $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_ops")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_ops"))]
             #[inline]
             pub const fn leading_zeros(self) -> u32 {
                 (self as $UnsignedT).leading_zeros()
@@ -333,7 +333,7 @@ assert_eq!(n.trailing_zeros(), 2);",
 $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_ops")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_ops"))]
             #[inline]
             pub const fn trailing_zeros(self) -> u32 {
                 (self as $UnsignedT).trailing_zeros()
@@ -357,7 +357,7 @@ let m = ", $rot_result, ";
 assert_eq!(n.rotate_left(", $rot, "), m);
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_rotate")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_rotate"))]
             #[inline]
             pub const fn rotate_left(self, n: u32) -> Self {
                 (self as $UnsignedT).rotate_left(n) as Self
@@ -382,7 +382,7 @@ let m = ", $rot_op, ";
 assert_eq!(n.rotate_right(", $rot, "), m);
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_rotate")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_rotate"))]
             #[inline]
             pub const fn rotate_right(self, n: u32) -> Self {
                 (self as $UnsignedT).rotate_right(n) as Self
@@ -404,7 +404,7 @@ let m = n.swap_bytes();
 assert_eq!(m, ", $swapped, ");
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_ops")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_ops"))]
             #[inline]
             pub const fn swap_bytes(self) -> Self {
                 (self as $UnsignedT).swap_bytes() as Self
@@ -454,7 +454,7 @@ if cfg!(target_endian = \"big\") {
 $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_ops")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_ops"))]
             #[inline]
             pub const fn from_be(x: Self) -> Self {
                 #[cfg(target_endian = "big")]
@@ -488,7 +488,7 @@ if cfg!(target_endian = \"little\") {
 $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_ops")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_ops"))]
             #[inline]
             pub const fn from_le(x: Self) -> Self {
                 #[cfg(target_endian = "little")]
@@ -522,7 +522,7 @@ if cfg!(target_endian = \"big\") {
 $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_ops")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_ops"))]
             #[inline]
             pub const fn to_be(self) -> Self { // or not to be?
                 #[cfg(target_endian = "big")]
@@ -556,7 +556,7 @@ if cfg!(target_endian = \"little\") {
 $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_ops")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_ops"))]
             #[inline]
             pub const fn to_le(self) -> Self {
                 #[cfg(target_endian = "little")]
@@ -994,12 +994,15 @@ assert_eq!(", stringify!($SelfT), "::max_value().wrapping_add(2), ", stringify!(
 $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_wrapping")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_wrapping"))]
             #[inline]
             pub const fn wrapping_add(self, rhs: Self) -> Self {
+                #[cfg(stage0)]
                 unsafe {
                     intrinsics::overflowing_add(self, rhs)
                 }
+                #[cfg(not(stage0))]
+                intrinsics::overflowing_add(self, rhs)
             }
         }
 
@@ -1018,12 +1021,15 @@ stringify!($SelfT), "::max_value());",
 $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_wrapping")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_wrapping"))]
             #[inline]
             pub const fn wrapping_sub(self, rhs: Self) -> Self {
+                #[cfg(stage0)]
                 unsafe {
                     intrinsics::overflowing_sub(self, rhs)
                 }
+                #[cfg(not(stage0))]
+                intrinsics::overflowing_sub(self, rhs)
             }
         }
 
@@ -1041,12 +1047,15 @@ assert_eq!(11i8.wrapping_mul(12), -124);",
 $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_wrapping")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_wrapping"))]
             #[inline]
             pub const fn wrapping_mul(self, rhs: Self) -> Self {
+                #[cfg(stage0)]
                 unsafe {
                     intrinsics::overflowing_mul(self, rhs)
                 }
+                #[cfg(not(stage0))]
+                intrinsics::overflowing_mul(self, rhs)
             }
         }
 
@@ -1205,7 +1214,7 @@ assert_eq!((-1", stringify!($SelfT), ").wrapping_shl(128), -1);",
 $EndFeature, "
 ```"),
             #[stable(feature = "num_wrapping", since = "1.2.0")]
-            #[rustc_const_unstable(feature = "const_int_wrapping")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_wrapping"))]
             #[inline]
             pub const fn wrapping_shl(self, rhs: u32) -> Self {
                 unsafe {
@@ -1233,7 +1242,7 @@ assert_eq!((-128i16).wrapping_shr(64), -128);",
 $EndFeature, "
 ```"),
             #[stable(feature = "num_wrapping", since = "1.2.0")]
-            #[rustc_const_unstable(feature = "const_int_wrapping")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_wrapping"))]
             #[inline]
             pub const fn wrapping_shr(self, rhs: u32) -> Self {
                 unsafe {
@@ -1886,7 +1895,6 @@ assert!(!(-10", stringify!($SelfT), ").is_positive());",
 $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_sign")]
             #[inline]
             pub const fn is_positive(self) -> bool { self > 0 }
         }
@@ -1905,7 +1913,6 @@ assert!(!10", stringify!($SelfT), ".is_negative());",
 $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_sign")]
             #[inline]
             pub const fn is_negative(self) -> bool { self < 0 }
         }
@@ -2227,10 +2234,13 @@ Basic usage:
 assert_eq!(n.count_ones(), 3);", $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_ops")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_ops"))]
             #[inline]
             pub const fn count_ones(self) -> u32 {
+                #[cfg(stage0)]
                 unsafe { intrinsics::ctpop(self as $ActualT) as u32 }
+                #[cfg(not(stage0))]
+                { intrinsics::ctpop(self as $ActualT) as u32 }
             }
         }
 
@@ -2245,7 +2255,7 @@ Basic usage:
 ", $Feature, "assert_eq!(", stringify!($SelfT), "::max_value().count_zeros(), 0);", $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_ops")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_ops"))]
             #[inline]
             pub const fn count_zeros(self) -> u32 {
                 (!self).count_ones()
@@ -2265,10 +2275,13 @@ Basic usage:
 assert_eq!(n.leading_zeros(), 2);", $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_ops")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_ops"))]
             #[inline]
             pub const fn leading_zeros(self) -> u32 {
+                #[cfg(stage0)]
                 unsafe { intrinsics::ctlz(self as $ActualT) as u32 }
+                #[cfg(not(stage0))]
+                { intrinsics::ctlz(self as $ActualT) as u32 }
             }
         }
 
@@ -2286,10 +2299,13 @@ Basic usage:
 assert_eq!(n.trailing_zeros(), 3);", $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_ops")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_ops"))]
             #[inline]
             pub const fn trailing_zeros(self) -> u32 {
+                #[cfg(stage0)]
                 unsafe { intrinsics::cttz(self) as u32 }
+                #[cfg(not(stage0))]
+                { intrinsics::cttz(self) as u32 }
             }
         }
 
@@ -2310,10 +2326,13 @@ let m = ", $rot_result, ";
 assert_eq!(n.rotate_left(", $rot, "), m);
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_rotate")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_rotate"))]
             #[inline]
             pub const fn rotate_left(self, n: u32) -> Self {
+                #[cfg(stage0)]
                 unsafe { intrinsics::rotate_left(self, n as $SelfT) }
+                #[cfg(not(stage0))]
+                intrinsics::rotate_left(self, n as $SelfT)
             }
         }
 
@@ -2335,10 +2354,13 @@ let m = ", $rot_op, ";
 assert_eq!(n.rotate_right(", $rot, "), m);
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_rotate")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_rotate"))]
             #[inline]
             pub const fn rotate_right(self, n: u32) -> Self {
+                #[cfg(stage0)]
                 unsafe { intrinsics::rotate_right(self, n as $SelfT) }
+                #[cfg(not(stage0))]
+                intrinsics::rotate_right(self, n as $SelfT)
             }
         }
 
@@ -2357,10 +2379,13 @@ let m = n.swap_bytes();
 assert_eq!(m, ", $swapped, ");
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_ops")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_ops"))]
             #[inline]
             pub const fn swap_bytes(self) -> Self {
+                #[cfg(stage0)]
                 unsafe { intrinsics::bswap(self as $ActualT) as Self }
+                #[cfg(not(stage0))]
+                { intrinsics::bswap(self as $ActualT) as Self }
             }
         }
 
@@ -2380,10 +2405,13 @@ let m = n.reverse_bits();
 assert_eq!(m, ", $reversed, ");
 ```"),
             #[unstable(feature = "reverse_bits", issue = "48763")]
-            #[rustc_const_unstable(feature = "const_int_conversion")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_conversion"))]
             #[inline]
             pub const fn reverse_bits(self) -> Self {
+                #[cfg(stage0)]
                 unsafe { intrinsics::bitreverse(self as $ActualT) as Self }
+                #[cfg(not(stage0))]
+                { intrinsics::bitreverse(self as $ActualT) as Self }
             }
         }
 
@@ -2407,7 +2435,7 @@ if cfg!(target_endian = \"big\") {
 }", $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_ops")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_ops"))]
             #[inline]
             pub const fn from_be(x: Self) -> Self {
                 #[cfg(target_endian = "big")]
@@ -2441,7 +2469,7 @@ if cfg!(target_endian = \"little\") {
 }", $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_ops")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_ops"))]
             #[inline]
             pub const fn from_le(x: Self) -> Self {
                 #[cfg(target_endian = "little")]
@@ -2475,7 +2503,7 @@ if cfg!(target_endian = \"big\") {
 }", $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_ops")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_ops"))]
             #[inline]
             pub const fn to_be(self) -> Self { // or not to be?
                 #[cfg(target_endian = "big")]
@@ -2509,7 +2537,7 @@ if cfg!(target_endian = \"little\") {
 }", $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_ops")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_ops"))]
             #[inline]
             pub const fn to_le(self) -> Self {
                 #[cfg(target_endian = "little")]
@@ -2884,12 +2912,15 @@ assert_eq!(200", stringify!($SelfT), ".wrapping_add(", stringify!($SelfT), "::ma
 $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_wrapping")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_wrapping"))]
             #[inline]
             pub const fn wrapping_add(self, rhs: Self) -> Self {
+                #[cfg(stage0)]
                 unsafe {
                     intrinsics::overflowing_add(self, rhs)
                 }
+                #[cfg(not(stage0))]
+                intrinsics::overflowing_add(self, rhs)
             }
         }
 
@@ -2907,12 +2938,15 @@ assert_eq!(100", stringify!($SelfT), ".wrapping_sub(", stringify!($SelfT), "::ma
 $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
-            #[rustc_const_unstable(feature = "const_int_wrapping")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_wrapping"))]
             #[inline]
             pub const fn wrapping_sub(self, rhs: Self) -> Self {
+                #[cfg(stage0)]
                 unsafe {
                     intrinsics::overflowing_sub(self, rhs)
                 }
+                #[cfg(not(stage0))]
+                intrinsics::overflowing_sub(self, rhs)
             }
         }
 
@@ -2931,12 +2965,15 @@ $EndFeature, "
         /// assert_eq!(25u8.wrapping_mul(12), 44);
         /// ```
         #[stable(feature = "rust1", since = "1.0.0")]
-        #[rustc_const_unstable(feature = "const_int_wrapping")]
+        #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_wrapping"))]
         #[inline]
         pub const fn wrapping_mul(self, rhs: Self) -> Self {
+            #[cfg(stage0)]
             unsafe {
                 intrinsics::overflowing_mul(self, rhs)
             }
+            #[cfg(not(stage0))]
+            intrinsics::overflowing_mul(self, rhs)
         }
 
         doc_comment! {
@@ -3081,7 +3118,7 @@ Basic usage:
 assert_eq!(1", stringify!($SelfT), ".wrapping_shl(128), 1);", $EndFeature, "
 ```"),
             #[stable(feature = "num_wrapping", since = "1.2.0")]
-            #[rustc_const_unstable(feature = "const_int_wrapping")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_wrapping"))]
             #[inline]
             pub const fn wrapping_shl(self, rhs: u32) -> Self {
                 unsafe {
@@ -3111,7 +3148,7 @@ Basic usage:
 assert_eq!(128", stringify!($SelfT), ".wrapping_shr(128), 128);", $EndFeature, "
 ```"),
             #[stable(feature = "num_wrapping", since = "1.2.0")]
-            #[rustc_const_unstable(feature = "const_int_wrapping")]
+            #[cfg_attr(stage0, rustc_const_unstable(feature = "const_int_wrapping"))]
             #[inline]
             pub const fn wrapping_shr(self, rhs: u32) -> Self {
                 unsafe {