Constify `core::intrinsics::black_box`

diff --git a/library/core/src/hint.rs b/library/core/src/hint.rs
index f49aefea81bacb3302d806830cb5888743e2c53d..003391e52be6b93aae3c7004beb8981def8142c1 100644 (file)
--- a/library/core/src/hint.rs
+++ b/library/core/src/hint.rs
@@ -159,6 +159,7 @@ pub fn spin_loop() {
 /// [`std::convert::identity`]: crate::convert::identity
 #[inline]
 #[unstable(feature = "bench_black_box", issue = "64102")]
-pub fn black_box<T>(dummy: T) -> T {
+#[rustc_const_unstable(feature = "const_black_box", issue = "none")]
+pub const fn black_box<T>(dummy: T) -> T {
     crate::intrinsics::black_box(dummy)
 }

diff --git a/library/core/src/intrinsics.rs b/library/core/src/intrinsics.rs
index 46370f76e7ced48d5c89c0c4376587b63d89b3f3..4ecc3b0c7f8e1ad4b174dd261adf93b6ed801eff 100644 (file)
--- a/library/core/src/intrinsics.rs
+++ b/library/core/src/intrinsics.rs
@@ -1940,6 +1940,7 @@ pub unsafe fn drop_in_place<T: ?Sized>(to_drop: *mut T) {
     /// See documentation of [`std::hint::black_box`] for details.
     ///
     /// [`std::hint::black_box`]: crate::hint::black_box
+    #[rustc_const_unstable(feature = "const_black_box", issue = "none")]
     pub fn black_box<T>(dummy: T) -> T;
 }
 

diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs
index 32a5fd9c4811a7f092ae56644d70f1d6dda453dd..4bd94e3ce39152e166af71825d4fb3901b109079 100644 (file)
--- a/library/core/src/lib.rs
+++ b/library/core/src/lib.rs
@@ -103,6 +103,7 @@
 #![feature(const_arguments_as_str)]
 #![feature(const_array_into_iter_constructors)]
 #![feature(const_bigint_helper_methods)]
+#![feature(const_black_box)]
 #![feature(const_caller_location)]
 #![feature(const_cell_into_inner)]
 #![feature(const_char_convert)]

diff --git a/library/core/tests/intrinsics.rs b/library/core/tests/intrinsics.rs
index 84cef53b3584b091da23e53c58688c48fad3d201..7a2e4e290655743ce958eafe5eb76c7698d96725 100644 (file)
--- a/library/core/tests/intrinsics.rs
+++ b/library/core/tests/intrinsics.rs
@@ -65,3 +65,18 @@ const fn test_write_bytes_in_const_contexts() {
     assert!(TEST2[1] == 16843009);
     assert!(TEST2[2] == 3);
 }
+
+#[test]
+fn test_hints_in_const_contexts() {
+    use core::intrinsics::{likely, unlikely};
+
+    // In const contexts, they just return their argument.
+    const {
+        assert!(true == likely(true));
+        assert!(false == likely(false));
+        assert!(true == unlikely(true));
+        assert!(false == unlikely(false));
+        assert!(42u32 == core::intrinsics::black_box(42u32));
+        assert!(42u32 == core::hint::black_box(42u32));
+    }
+}

diff --git a/library/core/tests/lib.rs b/library/core/tests/lib.rs
index 21562acf3d766cad63cc648c08f0f907ad34e4c7..ec700346ac91d2f6e2433e8ce620b78868b01f18 100644 (file)
--- a/library/core/tests/lib.rs
+++ b/library/core/tests/lib.rs
@@ -2,12 +2,14 @@
 #![feature(array_chunks)]
 #![feature(array_methods)]
 #![feature(array_windows)]
+#![feature(bench_black_box)]
 #![feature(bool_to_option)]
 #![feature(box_syntax)]
 #![feature(cell_update)]
 #![feature(cfg_panic)]
 #![feature(cfg_target_has_atomic)]
 #![feature(const_assume)]
+#![feature(const_black_box)]
 #![feature(const_bool_to_option)]
 #![feature(const_cell_into_inner)]
 #![feature(const_convert)]
@@ -18,6 +20,7 @@
 #![feature(const_ptr_write)]
 #![feature(const_ptr_offset)]
 #![feature(const_trait_impl)]
+#![feature(const_likely)]
 #![feature(core_intrinsics)]
 #![feature(core_private_bignum)]
 #![feature(core_private_diy_float)]
@@ -35,6 +38,7 @@
 #![feature(array_from_fn)]
 #![feature(hashmap_internals)]
 #![feature(try_find)]
+#![feature(inline_const)]
 #![feature(is_sorted)]
 #![feature(pattern)]
 #![feature(sort_internals)]