Rollup merge of rust-lang#124896 - RalfJung:miri-intrinsic-fallback, r=oli-obk

miri: rename intrinsic_fallback_checks_ub to intrinsic_fallback_is_spec

Checking UB is not the only concern, we also have to make sure we are not losing out on non-determinism.

r? ``@oli-obk`` (not urgent, take your time)

Author: fmease

core/src/intrinsics.rs

@@ -987,7 +987,7 @@ pub const unsafe fn assume(b: bool) {
 #[unstable(feature = "core_intrinsics", issue = "none")]
 #[rustc_intrinsic]
 #[rustc_nounwind]
-#[cfg_attr(not(bootstrap), miri::intrinsic_fallback_checks_ub)]
+#[cfg_attr(not(bootstrap), miri::intrinsic_fallback_is_spec)]
 pub const fn likely(b: bool) -> bool {
     b
 }
@@ -1007,7 +1007,7 @@ pub const fn likely(b: bool) -> bool {
 #[unstable(feature = "core_intrinsics", issue = "none")]
 #[rustc_intrinsic]
 #[rustc_nounwind]
-#[cfg_attr(not(bootstrap), miri::intrinsic_fallback_checks_ub)]
+#[cfg_attr(not(bootstrap), miri::intrinsic_fallback_is_spec)]
 pub const fn unlikely(b: bool) -> bool {
     b
 }
@@ -2483,7 +2483,7 @@ extern "rust-intrinsic" {
 #[rustc_nounwind]
 #[rustc_do_not_const_check]
 #[inline]
-#[cfg_attr(not(bootstrap), miri::intrinsic_fallback_checks_ub)]
+#[cfg_attr(not(bootstrap), miri::intrinsic_fallback_is_spec)]
 pub const fn ptr_guaranteed_cmp<T>(ptr: *const T, other: *const T) -> u8 {
     (ptr == other) as u8
 }
@@ -2748,7 +2748,7 @@ pub const fn ub_checks() -> bool {
 #[unstable(feature = "core_intrinsics", issue = "none")]
 #[rustc_nounwind]
 #[rustc_intrinsic]
-#[cfg_attr(not(bootstrap), miri::intrinsic_fallback_checks_ub)]
+#[cfg_attr(not(bootstrap), miri::intrinsic_fallback_is_spec)]
 pub const unsafe fn const_allocate(_size: usize, _align: usize) -> *mut u8 {
     // const eval overrides this function, but runtime code for now just returns null pointers.
     // See <https://github.com/rust-lang/rust/issues/93935>.
@@ -2769,7 +2769,7 @@ pub const unsafe fn const_allocate(_size: usize, _align: usize) -> *mut u8 {
 #[unstable(feature = "core_intrinsics", issue = "none")]
 #[rustc_nounwind]
 #[rustc_intrinsic]
-#[cfg_attr(not(bootstrap), miri::intrinsic_fallback_checks_ub)]
+#[cfg_attr(not(bootstrap), miri::intrinsic_fallback_is_spec)]
 pub const unsafe fn const_deallocate(_ptr: *mut u8, _size: usize, _align: usize) {
     // Runtime NOP
 }