Auto merge of rust-lang#106774 - Nugine:master, r=Amanieu

Stabilize cmpxchg16b_target_feature

Tracking issue for target features
+ rust-lang#44839

stdarch issue
+ rust-lang/stdarch#827

stdarch PR
+ rust-lang/stdarch#1358

reference PR
+ rust-lang/reference#1331

It's my first time contributing to rust-lang/rust. Please tell me if I missed something.

compiler/rustc_codegen_ssa/src/target_features.rs

@@ -185,7 +185,7 @@ const X86_ALLOWED_FEATURES: &[(&str, Option<Symbol>)] = &[
     ("avx512vpopcntdq", Some(sym::avx512_target_feature)),
     ("bmi1", None),
     ("bmi2", None),
-    ("cmpxchg16b", Some(sym::cmpxchg16b_target_feature)),
+    ("cmpxchg16b", None),
     ("ermsb", Some(sym::ermsb_target_feature)),
     ("f16c", None),
     ("fma", None),
@@ -394,7 +394,6 @@ pub fn from_target_feature(
                 Some(sym::sse4a_target_feature) => rust_features.sse4a_target_feature,
                 Some(sym::tbm_target_feature) => rust_features.tbm_target_feature,
                 Some(sym::wasm_target_feature) => rust_features.wasm_target_feature,
-                Some(sym::cmpxchg16b_target_feature) => rust_features.cmpxchg16b_target_feature,
                 Some(sym::movbe_target_feature) => rust_features.movbe_target_feature,
                 Some(sym::rtm_target_feature) => rust_features.rtm_target_feature,
                 Some(sym::ermsb_target_feature) => rust_features.ermsb_target_feature,

compiler/rustc_feature/src/accepted.rs

@@ -90,6 +90,8 @@ declare_features! (
     (accepted, clone_closures, "1.26.0", Some(44490), None),
     /// Allows coercing non capturing closures to function pointers.
     (accepted, closure_to_fn_coercion, "1.19.0", Some(39817), None),
+    /// Allows using `cmpxchg16b` from `core::arch::x86_64`.
+    (accepted, cmpxchg16b_target_feature, "CURRENT_RUSTC_VERSION", Some(44839), None),
     /// Allows usage of the `compile_error!` macro.
     (accepted, compile_error, "1.20.0", Some(40872), None),
     /// Allows `impl Trait` in function return types.

compiler/rustc_feature/src/active.rs

@@ -256,7 +256,6 @@ declare_features! (
     (active, arm_target_feature, "1.27.0", Some(44839), None),
     (active, avx512_target_feature, "1.27.0", Some(44839), None),
     (active, bpf_target_feature, "1.54.0", Some(44839), None),
-    (active, cmpxchg16b_target_feature, "1.32.0", Some(44839), None),
     (active, ermsb_target_feature, "1.49.0", Some(44839), None),
     (active, hexagon_target_feature, "1.27.0", Some(44839), None),
     (active, mips_target_feature, "1.27.0", Some(44839), None),

library/core/src/lib.rs

@@ -244,7 +244,6 @@
 // Target features:
 #![feature(arm_target_feature)]
 #![feature(avx512_target_feature)]
-#![feature(cmpxchg16b_target_feature)]
 #![feature(hexagon_target_feature)]
 #![feature(mips_target_feature)]
 #![feature(powerpc_target_feature)]
@@ -253,6 +252,7 @@
 #![feature(sse4a_target_feature)]
 #![feature(tbm_target_feature)]
 #![feature(wasm_target_feature)]
+#![cfg_attr(bootstrap, feature(cmpxchg16b_target_feature))]
 
 // allow using `core::` in intra-doc links
 #[allow(unused_extern_crates)]