Give const_deallocate a default body

Author: oli-obk

Diff for: compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs

@@ -1229,11 +1229,6 @@ fn codegen_regular_intrinsic_call<'tcx>(
             ret.write_cvalue(fx, CValue::by_val(cmp, ret.layout()));
         }
 
-        sym::const_deallocate => {
-            intrinsic_args!(fx, args => (_ptr, _size, _align); intrinsic);
-            // nop at runtime.
-        }
-
         sym::black_box => {
             intrinsic_args!(fx, args => (a); intrinsic);
 

Diff for: compiler/rustc_codegen_ssa/src/mir/intrinsic.rs

@@ -281,11 +281,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 }
             }
 
-            sym::const_deallocate => {
-                // nop at runtime.
-                return Ok(());
-            }
-
             // This requires that atomic intrinsics follow a specific naming pattern:
             // "atomic_<operation>[_<ordering>]"
             name if let Some(atomic) = name_str.strip_prefix("atomic_") => {

Diff for: compiler/rustc_hir_analysis/src/check/intrinsic.rs

@@ -367,7 +367,7 @@ pub fn check_intrinsic_type(
             }
             sym::const_deallocate => (
                 0,
-                0,
+                1,
                 vec![Ty::new_mut_ptr(tcx, tcx.types.u8), tcx.types.usize, tcx.types.usize],
                 Ty::new_unit(tcx),
             ),

Diff for: library/core/src/intrinsics.rs

@@ -2368,20 +2368,6 @@ extern "rust-intrinsic" {
     #[rustc_nounwind]
     pub fn ptr_guaranteed_cmp<T>(ptr: *const T, other: *const T) -> u8;
 
-    /// Deallocates a memory which allocated by `intrinsics::const_allocate` at compile time.
-    /// At runtime, does nothing.
-    ///
-    /// # Safety
-    ///
-    /// - The `align` argument must be a power of two.
-    ///    - At compile time, a compile error occurs if this constraint is violated.
-    ///    - At runtime, it is not checked.
-    /// - If the `ptr` is created in an another const, this intrinsic doesn't deallocate it.
-    /// - If the `ptr` is pointing to a local variable, this intrinsic doesn't deallocate it.
-    #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
-    #[rustc_nounwind]
-    pub fn const_deallocate(ptr: *mut u8, size: usize, align: usize);
-
     /// Determines whether the raw bytes of the two values are equal.
     ///
     /// This is particularly handy for arrays, since it allows things like just
@@ -2591,13 +2577,30 @@ pub(crate) const unsafe fn debug_assertions() -> bool {
 ///    - At compile time, a compile error occurs if this constraint is violated.
 ///    - At runtime, it is not checked.
 #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
+#[unstable(feature = "core_intrinsics", issue = "none")]
 #[rustc_nounwind]
 #[cfg_attr(not(bootstrap), rustc_intrinsic)]
 pub const unsafe fn const_allocate(_size: usize, _align: usize) -> *mut u8 {
     // const eval overrides this function, but runtime code should always just return null pointers.
     crate::ptr::null_mut()
 }
 
+/// Deallocates a memory which allocated by `intrinsics::const_allocate` at compile time.
+/// At runtime, does nothing.
+///
+/// # Safety
+///
+/// - The `align` argument must be a power of two.
+///    - At compile time, a compile error occurs if this constraint is violated.
+///    - At runtime, it is not checked.
+/// - If the `ptr` is created in an another const, this intrinsic doesn't deallocate it.
+/// - If the `ptr` is pointing to a local variable, this intrinsic doesn't deallocate it.
+#[rustc_const_unstable(feature = "const_heap", issue = "79597")]
+#[unstable(feature = "core_intrinsics", issue = "none")]
+#[rustc_nounwind]
+#[cfg_attr(not(bootstrap), rustc_intrinsic)]
+pub const unsafe fn const_deallocate(_ptr: *mut u8, _size: usize, _align: usize) {}
+
 // Some functions are defined here because they accidentally got made
 // available in this module on stable. See <https://github.com/rust-lang/rust/issues/15702>.
 // (`transmute` also falls into this category, but it cannot be wrapped due to the