const_deallocate: Don't deallocate memory allocated in an another const. Does nothing at runtime.

`const_allocate`:  Returns a null pointer at runtime.

Author: lilasta

core/src/intrinsics.rs

@@ -1914,12 +1914,13 @@ extern "rust-intrinsic" {
     #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
     pub fn ptr_guaranteed_ne<T>(ptr: *const T, other: *const T) -> bool;
 
-    /// Allocate at compile time. Should not be called at runtime.
+    /// Allocate at compile time.
+    /// Returns a null pointer at runtime.
     #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
     pub fn const_allocate(size: usize, align: usize) -> *mut u8;
 
     /// Deallocate a memory which allocated by `intrinsics::const_allocate` at compile time.
-    /// Should not be called at runtime.
+    /// Does nothing at runtime.
     #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
     #[cfg(not(bootstrap))]
     pub fn const_deallocate(ptr: *mut u8, size: usize, align: usize);

core/tests/intrinsics.rs

@@ -80,3 +80,16 @@ fn test_hints_in_const_contexts() {
         assert!(42u32 == core::hint::black_box(42u32));
     }
 }
+
+#[cfg(not(bootstrap))]
+#[test]
+fn test_const_dealocate_at_runtime() {
+    use core::intrinsics::const_deallocate;
+    const X: &u32 = &42u32;
+    let x = &0u32;
+    unsafe {
+        const_deallocate(X as *const _ as *mut u8, 4, 4); // nop
+        const_deallocate(x as *const _ as *mut u8, 4, 4); // nop
+        const_deallocate(core::ptr::null_mut(), 1, 1); // nop
+    }
+}

core/tests/lib.rs

@@ -13,6 +13,7 @@
 #![feature(const_bool_to_option)]
 #![feature(const_cell_into_inner)]
 #![feature(const_convert)]
+#![feature(const_heap)]
 #![feature(const_maybe_uninit_as_mut_ptr)]
 #![feature(const_maybe_uninit_assume_init)]
 #![feature(const_maybe_uninit_assume_init_read)]