Keep unstable target features for asm feature checking

compiler/rustc_codegen_cranelift/src/lib.rs

@@ -167,7 +167,7 @@ impl CodegenBackend for CraneliftCodegenBackend {
         }
     }
 
-    fn target_features(&self, _sess: &Session) -> Vec<rustc_span::Symbol> {
+    fn target_features(&self, _sess: &Session, _allow_unstable: bool) -> Vec<rustc_span::Symbol> {
         vec![]
     }
 

compiler/rustc_codegen_gcc/src/lib.rs

@@ -133,8 +133,8 @@ impl CodegenBackend for GccCodegenBackend {
         )
     }
 
-    fn target_features(&self, sess: &Session) -> Vec<Symbol> {
-        target_features(sess)
+    fn target_features(&self, sess: &Session, allow_unstable: bool) -> Vec<Symbol> {
+        target_features(sess, allow_unstable)
     }
 }
 
@@ -291,12 +291,12 @@ pub fn target_cpu(sess: &Session) -> &str {
     }
 }
 
-pub fn target_features(sess: &Session) -> Vec<Symbol> {
+pub fn target_features(sess: &Session, allow_unstable: bool) -> Vec<Symbol> {
     supported_target_features(sess)
         .iter()
         .filter_map(
             |&(feature, gate)| {
-                if sess.is_nightly_build() || gate.is_none() { Some(feature) } else { None }
+                if sess.is_nightly_build() || allow_unstable || gate.is_none() { Some(feature) } else { None }
             },
         )
         .filter(|_feature| {

compiler/rustc_codegen_llvm/src/lib.rs

@@ -324,8 +324,8 @@ impl CodegenBackend for LlvmCodegenBackend {
         llvm_util::print_version();
     }
 
-    fn target_features(&self, sess: &Session) -> Vec<Symbol> {
-        target_features(sess)
+    fn target_features(&self, sess: &Session, allow_unstable: bool) -> Vec<Symbol> {
+        target_features(sess, allow_unstable)
     }
 
     fn codegen_crate<'tcx>(

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -233,26 +233,29 @@ pub fn check_tied_features(
 
 // Used to generate cfg variables and apply features
 // Must express features in the way Rust understands them
-pub fn target_features(sess: &Session) -> Vec<Symbol> {
+pub fn target_features(sess: &Session, allow_unstable: bool) -> Vec<Symbol> {
     let target_machine = create_informational_target_machine(sess);
-    let mut features: Vec<Symbol> =
-        supported_target_features(sess)
-            .iter()
-            .filter_map(|&(feature, gate)| {
-                if sess.is_nightly_build() || gate.is_none() { Some(feature) } else { None }
-            })
-            .filter(|feature| {
-                // check that all features in a given smallvec are enabled
-                for llvm_feature in to_llvm_features(sess, feature) {
-                    let cstr = SmallCStr::new(llvm_feature);
-                    if !unsafe { llvm::LLVMRustHasFeature(target_machine, cstr.as_ptr()) } {
-                        return false;
-                    }
+    let mut features: Vec<Symbol> = supported_target_features(sess)
+        .iter()
+        .filter_map(|&(feature, gate)| {
+            if sess.is_nightly_build() || allow_unstable || gate.is_none() {
+                Some(feature)
+            } else {
+                None
+            }
+        })
+        .filter(|feature| {
+            // check that all features in a given smallvec are enabled
+            for llvm_feature in to_llvm_features(sess, feature) {
+                let cstr = SmallCStr::new(llvm_feature);
+                if !unsafe { llvm::LLVMRustHasFeature(target_machine, cstr.as_ptr()) } {
+                    return false;
                 }
-                true
-            })
-            .map(|feature| Symbol::intern(feature))
-            .collect();
+            }
+            true
+        })
+        .map(|feature| Symbol::intern(feature))
+        .collect();
 
     // LLVM 14 changed the ABI for i128 arguments to __float/__fix builtins on Win64
     // (see https://reviews.llvm.org/D110413). This unstable target feature is intended for use

compiler/rustc_codegen_ssa/src/traits/backend.rs

@@ -59,7 +59,7 @@ impl<'tcx, T> Backend<'tcx> for T where
 pub trait CodegenBackend {
     fn init(&self, _sess: &Session) {}
     fn print(&self, _req: PrintRequest, _sess: &Session) {}
-    fn target_features(&self, _sess: &Session) -> Vec<Symbol> {
+    fn target_features(&self, _sess: &Session, _allow_unstable: bool) -> Vec<Symbol> {
         vec![]
     }
     fn print_passes(&self) {}

compiler/rustc_interface/src/util.rs

@@ -48,7 +48,10 @@ pub fn add_configuration(
 ) {
     let tf = sym::target_feature;
 
-    let target_features = codegen_backend.target_features(sess);
+    let unstable_target_features = codegen_backend.target_features(sess, true);
+    sess.unstable_target_features.extend(unstable_target_features.iter().cloned());
+
+    let target_features = codegen_backend.target_features(sess, false);
     sess.target_features.extend(target_features.iter().cloned());
 
     cfg.extend(target_features.into_iter().map(|feat| (tf, Some(feat))));

compiler/rustc_session/src/session.rs

@@ -194,6 +194,9 @@ pub struct Session {
 
     /// Set of enabled features for the current target.
     pub target_features: FxHashSet<Symbol>,
+
+    /// Set of enabled features for the current target, including unstable ones.
+    pub unstable_target_features: FxHashSet<Symbol>,
 }
 
 pub struct PerfStats {
@@ -1341,6 +1344,7 @@ pub fn build_session(
         miri_unleashed_features: Lock::new(Default::default()),
         asm_arch,
         target_features: FxHashSet::default(),
+        unstable_target_features: FxHashSet::default(),
     };
 
     validate_commandline_args_with_session_available(&sess);

compiler/rustc_typeck/src/collect.rs

@@ -3198,7 +3198,7 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: DefId) -> CodegenFnAttrs {
 /// Computes the set of target features used in a function for the purposes of
 /// inline assembly.
 fn asm_target_features<'tcx>(tcx: TyCtxt<'tcx>, did: DefId) -> &'tcx FxHashSet<Symbol> {
-    let mut target_features = tcx.sess.target_features.clone();
+    let mut target_features = tcx.sess.unstable_target_features.clone();
     if tcx.def_kind(did).has_codegen_attrs() {
         let attrs = tcx.codegen_fn_attrs(did);
         target_features.extend(&attrs.target_features);

src/test/ui/asm/issue-99071.rs

@@ -0,0 +1,21 @@
+// compile-flags: --target thumbv6m-none-eabi
+// needs-llvm-components: arm
+// needs-asm-support
+
+#![feature(no_core, lang_items, rustc_attrs)]
+#![no_core]
+#![crate_type = "rlib"]
+
+#[rustc_builtin_macro]
+macro_rules! asm {
+    () => {};
+}
+#[lang = "sized"]
+trait Sized {}
+
+pub fn foo() {
+    unsafe {
+        asm!("", in("r8") 0);
+        //~^ cannot use register `r8`: high registers (r8+) can only be used as clobbers in Thumb-1 code
+    }
+}

src/test/ui/asm/issue-99071.stderr

@@ -0,0 +1,8 @@
+error: cannot use register `r8`: high registers (r8+) can only be used as clobbers in Thumb-1 code
+  --> $DIR/issue-99071.rs:18:18
+   |
+LL |         asm!("", in("r8") 0);
+   |                  ^^^^^^^^^^
+
+error: aborting due to previous error
+