constify pointer::is_aligned{,_to}

Author: Lukas Markeffsky

library/core/src/lib.rs

@@ -130,6 +130,7 @@
 #![feature(const_option)]
 #![feature(const_option_ext)]
 #![feature(const_pin)]
+#![feature(const_pointer_is_aligned)]
 #![feature(const_ptr_sub_ptr)]
 #![feature(const_replace)]
 #![feature(const_result_drop)]

library/core/src/ptr/const_ptr.rs

@@ -1363,10 +1363,13 @@ impl<T: ?Sized> *const T {
     }
 
     /// Returns whether the pointer is properly aligned for `T`.
+    // #[cfg(not(bootstrap))] -- Calling this function in a const context from the bootstrap
+    // compiler will always return false.
     #[must_use]
     #[inline]
     #[unstable(feature = "pointer_is_aligned", issue = "96284")]
-    pub fn is_aligned(self) -> bool
+    #[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "none")]
+    pub const fn is_aligned(self) -> bool
     where
         T: Sized,
     {
@@ -1381,16 +1384,26 @@ impl<T: ?Sized> *const T {
     /// # Panics
     ///
     /// The function panics if `align` is not a power-of-two (this includes 0).
+    // #[cfg(not(bootstrap))] -- Calling this function in a const context from the bootstrap
+    // compiler will always return false.
     #[must_use]
     #[inline]
     #[unstable(feature = "pointer_is_aligned", issue = "96284")]
-    pub fn is_aligned_to(self, align: usize) -> bool {
-        if !align.is_power_of_two() {
-            panic!("is_aligned_to: align is not a power-of-two");
+    #[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "none")]
+    pub const fn is_aligned_to(self, align: usize) -> bool {
+        assert!(align.is_power_of_two(), "is_aligned_to: align is not a power-of-two");
+
+        #[inline]
+        fn runtime(ptr: *const u8, align: usize) -> bool {
+            ptr.addr() & (align - 1) == 0
+        }
+
+        const fn comptime(ptr: *const u8, align: usize) -> bool {
+            ptr.align_offset(align) == 0
         }
 
-        // Cast is needed for `T: !Sized`
-        self.cast::<u8>().addr() & align - 1 == 0
+        // SAFETY: `ptr.align_offset(align)` returns 0 if and only if the pointer is already aligned.
+        unsafe { intrinsics::const_eval_select((self.cast::<u8>(), align), comptime, runtime) }
     }
 }
 

library/core/src/ptr/mut_ptr.rs

@@ -1631,10 +1631,13 @@ impl<T: ?Sized> *mut T {
     }
 
     /// Returns whether the pointer is properly aligned for `T`.
+    // #[cfg(not(bootstrap))] -- Calling this function in a const context from the bootstrap
+    // compiler will always return false.
     #[must_use]
     #[inline]
     #[unstable(feature = "pointer_is_aligned", issue = "96284")]
-    pub fn is_aligned(self) -> bool
+    #[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "none")]
+    pub const fn is_aligned(self) -> bool
     where
         T: Sized,
     {
@@ -1649,16 +1652,26 @@ impl<T: ?Sized> *mut T {
     /// # Panics
     ///
     /// The function panics if `align` is not a power-of-two (this includes 0).
+    // #[cfg(not(bootstrap))] -- Calling this function in a const context from the bootstrap
+    // compiler will always return false.
     #[must_use]
     #[inline]
     #[unstable(feature = "pointer_is_aligned", issue = "96284")]
-    pub fn is_aligned_to(self, align: usize) -> bool {
-        if !align.is_power_of_two() {
-            panic!("is_aligned_to: align is not a power-of-two");
+    #[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "none")]
+    pub const fn is_aligned_to(self, align: usize) -> bool {
+        assert!(align.is_power_of_two(), "is_aligned_to: align is not a power-of-two");
+
+        #[inline]
+        fn runtime(ptr: *mut u8, align: usize) -> bool {
+            ptr.addr() & (align - 1) == 0
+        }
+
+        const fn comptime(ptr: *mut u8, align: usize) -> bool {
+            ptr.align_offset(align) == 0
         }
 
-        // Cast is needed for `T: !Sized`
-        self.cast::<u8>().addr() & align - 1 == 0
+        // SAFETY: `ptr.align_offset(align)` returns 0 if and only if the pointer is already aligned.
+        unsafe { intrinsics::const_eval_select((self.cast::<u8>(), align), comptime, runtime) }
     }
 }