Make ptr_guaranteed_cmp a rustc_intrinsic and favor its body over backends implementing it

compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs

@@ -757,13 +757,6 @@ fn codegen_regular_intrinsic_call<'tcx>(
             ret.write_cvalue(fx, val);
         }
 
-        sym::ptr_guaranteed_cmp => {
-            intrinsic_args!(fx, args => (a, b); intrinsic);
-
-            let val = crate::num::codegen_ptr_binop(fx, BinOp::Eq, a, b).load_scalar(fx);
-            ret.write_cvalue(fx, CValue::by_val(val, fx.layout_of(fx.tcx.types.u8)));
-        }
-
         sym::caller_location => {
             intrinsic_args!(fx, args => (); intrinsic);
 

compiler/rustc_codegen_ssa/src/mir/intrinsic.rs

@@ -1,7 +1,6 @@
 use super::operand::{OperandRef, OperandValue};
 use super::place::PlaceRef;
 use super::FunctionCx;
-use crate::common::IntPredicate;
 use crate::errors;
 use crate::errors::InvalidMonomorphization;
 use crate::meth;
@@ -456,12 +455,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 return Ok(());
             }
 
-            sym::ptr_guaranteed_cmp => {
-                let a = args[0].immediate();
-                let b = args[1].immediate();
-                bx.icmp(IntPredicate::IntEQ, a, b)
-            }
-
             sym::ptr_offset_from | sym::ptr_offset_from_unsigned => {
                 let ty = fn_args.type_at(0);
                 let pointee_size = bx.layout_of(ty).size;

compiler/rustc_hir_analysis/src/check/intrinsic.rs

@@ -441,7 +441,7 @@ pub fn check_intrinsic_type(
 
             sym::ptr_guaranteed_cmp => (
                 1,
-                0,
+                1,
                 vec![Ty::new_imm_ptr(tcx, param(0)), Ty::new_imm_ptr(tcx, param(0))],
                 tcx.types.u8,
             ),

library/core/src/intrinsics.rs

@@ -2434,20 +2434,29 @@ extern "rust-intrinsic" {
     #[rustc_nounwind]
     pub fn ptr_offset_from_unsigned<T>(ptr: *const T, base: *const T) -> usize;
 
+    #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
+    #[rustc_safe_intrinsic]
+    #[rustc_nounwind]
+    #[cfg(bootstrap)]
+    pub fn ptr_guaranteed_cmp<T>(ptr: *const T, other: *const T) -> u8;
+}
+
 /// See documentation of `<*const T>::guaranteed_eq` for details.
 /// Returns `2` if the result is unknown.
 /// Returns `1` if the pointers are guaranteed equal
 /// Returns `0` if the pointers are guaranteed inequal
-    ///
-    /// Note that, unlike most intrinsics, this is safe to call;
-    /// it does not require an `unsafe` block.
-    /// Therefore, implementations must not require the user to uphold
-    /// any safety invariants.
 #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
-    #[rustc_safe_intrinsic]
+#[unstable(feature = "core_intrinsics", issue = "none")]
+#[rustc_intrinsic]
+#[cfg(not(bootstrap))]
 #[rustc_nounwind]
-    pub fn ptr_guaranteed_cmp<T>(ptr: *const T, other: *const T) -> u8;
+#[rustc_do_not_const_check]
+#[inline]
+pub const fn ptr_guaranteed_cmp<T>(ptr: *const T, other: *const T) -> u8 {
+    (ptr == other) as u8
+}
 
+extern "rust-intrinsic" {
     /// Determines whether the raw bytes of the two values are equal.
     ///
     /// This is particularly handy for arrays, since it allows things like just