Replace const_hint! helper with full const evaluation helper

Author: taiki-e

build.rs

@@ -39,7 +39,7 @@ fn main() {
         // Custom cfgs set by build script. Not public API.
         // grep -F 'cargo:rustc-cfg=' build.rs | grep -Ev '^ *//' | sed -E 's/^.*cargo:rustc-cfg=//; s/(=\\)?".*$//' | LC_ALL=C sort -u | tr '\n' ',' | sed -E 's/,$/\n/'
         println!(
-            "cargo:rustc-check-cfg=cfg(atomic_maybe_uninit_no_asm,atomic_maybe_uninit_no_cmpxchg,atomic_maybe_uninit_no_cmpxchg8b,atomic_maybe_uninit_no_const_mut_refs,atomic_maybe_uninit_no_diagnostic_namespace,atomic_maybe_uninit_no_inline_const,atomic_maybe_uninit_no_strict_provenance,atomic_maybe_uninit_no_sync,atomic_maybe_uninit_pre_llvm_20,atomic_maybe_uninit_target_feature,atomic_maybe_uninit_unstable_asm_experimental_arch)"
+            "cargo:rustc-check-cfg=cfg(atomic_maybe_uninit_no_asm,atomic_maybe_uninit_no_cmpxchg,atomic_maybe_uninit_no_cmpxchg8b,atomic_maybe_uninit_no_const_mut_refs,atomic_maybe_uninit_no_diagnostic_namespace,atomic_maybe_uninit_no_strict_provenance,atomic_maybe_uninit_no_sync,atomic_maybe_uninit_pre_llvm_20,atomic_maybe_uninit_target_feature,atomic_maybe_uninit_unstable_asm_experimental_arch)"
         );
         // TODO: handle multi-line target_feature_fallback
         // grep -F 'target_feature_fallback("' build.rs | grep -Ev '^ *//' | sed -E 's/^.*target_feature_fallback\(//; s/",.*$/"/' | LC_ALL=C sort -u | tr '\n' ',' | sed -E 's/,$/\n/'
@@ -72,10 +72,6 @@ fn main() {
     if !version.probe(78, 2024, 3, 8) {
         println!("cargo:rustc-cfg=atomic_maybe_uninit_no_diagnostic_namespace");
     }
-    // inline_const stabilized in Rust 1.79 (nightly-2024-04-25): https://github.com/rust-lang/rust/pull/104087
-    if !version.probe(79, 2024, 4, 24) {
-        println!("cargo:rustc-cfg=atomic_maybe_uninit_no_inline_const");
-    }
     // const_mut_refs/const_refs_to_cell stabilized in Rust 1.83 (nightly-2024-09-16): https://github.com/rust-lang/rust/pull/129195
     if !version.probe(83, 2024, 9, 15) {
         println!("cargo:rustc-cfg=atomic_maybe_uninit_no_const_mut_refs");

src/arch/s390x.rs

@@ -49,7 +49,8 @@ macro_rules! serialization {
 // Extracts and checks condition code.
 #[inline(always)]
 const fn extract_cc(r: i64) -> bool {
-    r.wrapping_add(-268435456) & const_hint!({ 1 << 31 }) != 0
+    const BIT: i64 = 1 << 31;
+    r.wrapping_add(-268435456) & BIT != 0
 }
 
 macro_rules! atomic_load_store {

src/utils.rs

@@ -13,33 +13,48 @@ use core::{
 
 /// Static assertion without depending on const block which requires Rust 1.79.
 macro_rules! static_assert {
-    ($($ty:ident),+ => $($tt:tt)*) => {{
-        // Inspired by https://github.com/nvzqz/static-assertions/issues/40#issuecomment-1458897730.
-        struct _Assert<$($ty),+>($($ty),+);
-        impl<$($ty),+> _Assert<$($ty,)*> {
-            const _CHECK: () = assert!($($tt)*);
-        }
-        _Assert::<$($ty,)*>::_CHECK
+    ($(const $consts:ident: $ty:ty),+ => $($tt:tt)*) => {{
+        const_eval!($(const $consts: $ty),+ => () { assert!($($tt)*) })
+    }};
+    ($($ty_params:ident $(: ?Sized $(+ $bounds:path)?)?),+ => $($tt:tt)*) => {{
+        const_eval!($($ty_params $(: ?Sized $(+ $bounds)?)?),+ => () { assert!($($tt)*) })
     }};
+    ($($ty_params:ident $(: $bounds:path)?),+ => $($tt:tt)*) => {{
+        const_eval!($($ty_params $(: $bounds)?),+ => () { assert!($($tt)*) })
+    }};
+    // Use const _: () = assert!(..) for no parameter cases instead.
 }
 
-/// Uses inline const if available.
-///
-/// As the name implies, this is intended as a hint. Do not use this for use case
-/// that relies on this being computed in a const context (use static_assert instead).
-#[cfg(not(atomic_maybe_uninit_no_inline_const))]
-#[allow(unused_macros)]
-macro_rules! const_hint {
-    ({$($tt:tt)*}) => {
-        const { $($tt)* }
-    }
-}
-#[cfg(atomic_maybe_uninit_no_inline_const)]
-#[allow(unused_macros)]
-macro_rules! const_hint {
-    ({$($tt:tt)*}) => {
-        { $($tt)* }
-    }
+/// Const block emulation without depending on real const block which requires Rust 1.79.
+// Inspired by https://github.com/nvzqz/static-assertions/issues/40#issuecomment-1458897730.
+macro_rules! const_eval {
+    ($(const $const_params:ident: $ty:ty),+ => $ret:ty { $($tt:tt)* }) => {{
+        struct _Tmp<$(const $const_params: $ty,)*>;
+        impl<$(const $const_params: $ty,)*> _Tmp<$($const_params,)*> {
+            const _VAL: $ret = { $($tt)* };
+        }
+        _Tmp::<$($const_params,)*>::_VAL
+    }};
+    ($($ty_params:ident $(: ?Sized $(+ $bounds:path)?)?),+ => $ret:ty { $($tt:tt)* }) => {{
+        struct _Tmp<$($ty_params $(: ?Sized $(+ $bounds)?)?),+>(
+            $(::core::marker::PhantomData<$ty_params>),+
+        );
+        impl<$($ty_params $(: ?Sized $(+ $bounds)?)?),+> _Tmp<$($ty_params,)*> {
+            const _VAL: $ret = { $($tt)* };
+        }
+        _Tmp::<$($ty_params,)*>::_VAL
+    }};
+    ($($ty_params:ident $(: $bounds:path)?),+ => $ret:ty { $($tt:tt)* }) => {{
+        struct _Tmp<$($ty_params $(: $bounds)?),+>($(::core::marker::PhantomData<$ty_params>),+);
+        impl<$($ty_params $(: $bounds)?),+> _Tmp<$($ty_params,)*> {
+            const _VAL: $ret = { $($tt)* };
+        }
+        _Tmp::<$($ty_params,)*>::_VAL
+    }};
+    (=> $ret:ty { $($tt:tt)* }) => {{
+        const _VAL: $ret = { $($tt)* };
+        _VAL
+    }};
 }
 
 /// Make the given function const if the given condition is true.
@@ -152,7 +167,9 @@ macro_rules! debug_assert_atomic_unsafe_precondition {
         #[allow(clippy::arithmetic_side_effects)]
         {
             // Using const block here improves codegen on opt-level=0 https://godbolt.org/z/vrrvTqGda
-            debug_assert!($ptr.addr() & const_hint!({ core::mem::size_of::<$ty>() - 1 }) == 0);
+            debug_assert!(
+                $ptr.addr() & const_eval!(=> usize { core::mem::size_of::<$ty>() - 1 }) == 0
+            );
         }
     }};
 }
@@ -496,7 +513,8 @@ pub(crate) fn create_sub_word_mask_values<T>(ptr: *mut T) -> (*mut MinWord, RetI
         target_arch = "xtensa",
     ));
     const PTR_MASK: usize = mem::size_of::<MinWord>() - 1;
-    let aligned_ptr = ptr.with_addr(ptr.addr() & const_hint!({ !PTR_MASK })).cast::<MinWord>();
+    const PTR_INV_MASK: usize = !PTR_MASK;
+    let aligned_ptr = ptr.with_addr(ptr.addr() & PTR_INV_MASK).cast::<MinWord>();
     let ptr_lsb = if SHIFT_MASK {
         ptr.addr() & PTR_MASK
     } else {
@@ -507,10 +525,10 @@ pub(crate) fn create_sub_word_mask_values<T>(ptr: *mut T) -> (*mut MinWord, RetI
     let shift = if cfg!(any(target_endian = "little", target_arch = "s390x")) {
         ptr_lsb << 3
     } else {
-        (ptr_lsb ^ const_hint!({ mem::size_of::<MinWord>() - mem::size_of::<T>() })) << 3
+        (ptr_lsb ^ const_eval!(T => usize { mem::size_of::<MinWord>() - mem::size_of::<T>() })) << 3
     };
     #[allow(clippy::arithmetic_side_effects)]
-    let mut mask: RetInt = const_hint!({ (1 << (mem::size_of::<T>() << 3)) - 1 }); // !(0 as T) as RetInt
+    let mut mask = const_eval!(T => RetInt { (1 << (mem::size_of::<T>() << 3)) - 1 }); // !(0 as T) as RetInt
     if SHIFT_MASK {
         mask <<= shift;
     }