Add the movrs target feature and movrs_target_feature feature gate

Author: sayantn

Diff for: compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -304,6 +304,7 @@ pub(crate) fn to_llvm_features<'a>(sess: &Session, s: &'a str) -> Option<LLVMFea
         {
             None
         }
+        ("x86", "movrs") if get_version().0 < 20 => None,
         (_, s) => Some(LLVMFeature::new(s)),
     }
 }

Diff for: compiler/rustc_feature/src/unstable.rs

@@ -323,6 +323,7 @@ declare_features! (
     (unstable, loongarch_target_feature, "1.73.0", Some(44839)),
     (unstable, m68k_target_feature, "1.85.0", Some(134328)),
     (unstable, mips_target_feature, "1.27.0", Some(44839)),
+    (unstable, movrs_target_feature, "CURRENT_RUSTC_VERSION", Some(137976)),
     (unstable, powerpc_target_feature, "1.27.0", Some(44839)),
     (unstable, prfchw_target_feature, "1.78.0", Some(44839)),
     (unstable, riscv_target_feature, "1.45.0", Some(44839)),

Diff for: compiler/rustc_span/src/symbol.rs

@@ -1348,6 +1348,7 @@ symbols! {
         movbe_target_feature,
         move_ref_pattern,
         move_size_limit,
+        movrs_target_feature,
         mul,
         mul_assign,
         mul_with_overflow,

Diff for: compiler/rustc_target/src/target_features.rs

@@ -423,6 +423,7 @@ static X86_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     ("lahfsahf", Unstable(sym::lahfsahf_target_feature), &[]),
     ("lzcnt", Stable, &[]),
     ("movbe", Stable, &[]),
+    ("movrs", Unstable(sym::movrs_target_feature), &[]),
     ("pclmulqdq", Stable, &["sse2"]),
     ("popcnt", Stable, &[]),
     ("prfchw", Unstable(sym::prfchw_target_feature), &[]),

Diff for: tests/ui/check-cfg/target_feature.stderr

@@ -153,6 +153,7 @@ LL |     cfg!(target_feature = "_UNEXPECTED_VALUE");
 `mclass`
 `mops`
 `movbe`
+`movrs`
 `mp`
 `mp1e2`
 `msa`

Diff for: tests/ui/feature-gates/feature-gate-movrs_target_feature.rs

@@ -0,0 +1,6 @@
+//@ only-x86_64
+#[target_feature(enable = "movrs")]
+//~^ ERROR: currently unstable
+unsafe fn foo() {}
+
+fn main() {}

Diff for: tests/ui/feature-gates/feature-gate-movrs_target_feature.stderr

@@ -0,0 +1,13 @@
+error[E0658]: the target feature `movrs` is currently unstable
+  --> $DIR/feature-gate-movrs_target_feature.rs:2:18
+   |
+LL | #[target_feature(enable = "movrs")]
+   |                  ^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #137976 <https://github.com/rust-lang/rust/issues/137976> for more information
+   = help: add `#![feature(movrs_target_feature)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0658`.