stabilize s390x specific target-feature backchain

compiler/rustc_codegen_llvm/src/attributes.rs

@@ -384,9 +384,9 @@ fn packed_stack_attr<'ll>(
         return None;
     }
 
-    // The backchain and softfloat flags can be set via -Ctarget-features=...
+    // The backchain and softfloat flags can be set via -Ctarget-feature=...
     // or via #[target_features(enable = ...)] so we have to check both possibilities
-    let have_backchain = sess.unstable_target_features.contains(&sym::backchain)
+    let have_backchain = sess.target_features.contains(&sym::backchain)
         || function_attributes.iter().any(|feature| feature.name == sym::backchain);
     let have_softfloat = sess.unstable_target_features.contains(&sym::soft_float)
         || function_attributes.iter().any(|feature| feature.name == sym::soft_float);

compiler/rustc_target/src/target_features.rs

@@ -904,8 +904,7 @@ static LOONGARCH_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
 #[rustfmt::skip]
 const IBMZ_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     // tidy-alphabetical-start
-    // For "backchain", https://github.com/rust-lang/rust/issues/142412 is a stabilization blocker
-    ("backchain", Unstable(sym::s390x_target_feature), &[]),
+    ("backchain", Stable, &[]),
     ("concurrent-functions", Unstable(sym::s390x_target_feature), &[]),
     ("deflate-conversion", Unstable(sym::s390x_target_feature), &[]),
     ("enhanced-sort", Unstable(sym::s390x_target_feature), &[]),

tests/codegen-llvm/packedstack.rs

@@ -1,7 +1,6 @@
 //@ add-minicore
 //@ compile-flags: -Copt-level=3 --crate-type=lib --target=s390x-unknown-none-softfloat -Zpacked-stack
 //@ needs-llvm-components: systemz
-#![feature(s390x_target_feature)]
 #![crate_type = "lib"]
 #![feature(no_core, lang_items)]
 #![no_core]

tests/ui/target-feature/packedstack-combinations.rs

@@ -24,21 +24,17 @@
 //@ [with_softfloat] build-pass
 //@ [with_softfloat] needs-llvm-components: systemz
 
-#![feature(s390x_target_feature)]
 #![crate_type = "rlib"]
-#![feature(no_core,lang_items)]
+#![feature(no_core, lang_items)]
 #![no_core]
 
 extern crate minicore;
 use minicore::*;
 
 #[no_mangle]
-#[cfg_attr(backchain_attr,target_feature(enable = "backchain"))]
-pub fn test() {
-}
+#[cfg_attr(backchain_attr, target_feature(enable = "backchain"))]
+pub fn test() {}
 
 //[wrong_arch]~? ERROR `-Zpacked-stack` is only supported on s390x
-//[backchain_cli]~? WARN unstable feature specified for `-Ctarget-feature`: `backchain`
 //[backchain_cli]~? ERROR `-Zpacked-stack` is incompatible with `backchain` target feature
 //[backchain_attr]~? ERROR `-Zpacked-stack` is incompatible with `backchain` target feature
-//[with_softfloat]~? WARN unstable feature specified for `-Ctarget-feature`: `backchain`