Querify global_backend_features

At the very least this serves to deduplicate the diagnostics that are
output about unknown target features provided via CLI.

compiler/rustc_codegen_gcc/src/lib.rs

@@ -132,7 +132,7 @@ impl ExtraBackendMethods for GccCodegenBackend {
         base::compile_codegen_unit(tcx, cgu_name)
     }
 
-    fn target_machine_factory(&self, _sess: &Session, _opt_level: OptLevel) -> TargetMachineFactoryFn<Self> {
+    fn target_machine_factory(&self, _sess: &Session, _opt_level: OptLevel, _features: &[String]) -> TargetMachineFactoryFn<Self> {
         // TODO(antoyo): set opt level.
         Arc::new(|_| {
             Ok(())

compiler/rustc_codegen_llvm/src/attributes.rs

@@ -79,13 +79,11 @@ pub fn sanitize_attrs<'ll>(
     }
     if enabled.contains(SanitizerSet::MEMTAG) {
         // Check to make sure the mte target feature is actually enabled.
-        let sess = cx.tcx.sess;
+        let features = cx.tcx.global_backend_features(());
-        let features = llvm_util::llvm_global_features(sess).join(",");
+        let mte_feature =
-        let mte_feature_enabled = features.rfind("+mte");
+            features.iter().map(|s| &s[..]).rfind(|n| ["+mte", "-mte"].contains(&&n[..]));
-        let mte_feature_disabled = features.rfind("-mte");
+        if let None | Some("-mte") = mte_feature {
-
+            cx.tcx.sess.err("`-Zsanitizer=memtag` requires `-Ctarget-feature=+mte`");
-        if mte_feature_enabled.is_none() || (mte_feature_disabled > mte_feature_enabled) {
-            sess.err("`-Zsanitizer=memtag` requires `-Ctarget-feature=+mte`");
         }
 
         attrs.push(llvm::AttributeKind::SanitizeMemTag.create_attr(cx.llcx));
@@ -415,10 +413,11 @@ pub fn from_fn_attrs<'ll, 'tcx>(
     }
 
     if !function_features.is_empty() {
-        let mut global_features = llvm_util::llvm_global_features(cx.tcx.sess);
+        let global_features = cx.tcx.global_backend_features(()).iter().map(|s| &s[..]);
-        global_features.extend(function_features.into_iter());
+        let val = global_features
-        let features = global_features.join(",");
+            .chain(function_features.iter().map(|s| &s[..]))
-        let val = CString::new(features).unwrap();
+            .intersperse(",")
+            .collect::<SmallCStr>();
         to_add.push(llvm::CreateAttrStringValue(cx.llcx, cstr!("target-features"), &val));
     }
 

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -100,7 +100,10 @@ pub fn write_output_file<'ll>(
 
 pub fn create_informational_target_machine(sess: &Session) -> &'static mut llvm::TargetMachine {
     let config = TargetMachineFactoryConfig { split_dwarf_file: None };
-    target_machine_factory(sess, config::OptLevel::No)(config)
+    // Can't use query system here quite yet because this function is invoked before the query
+    // system/tcx is set up.
+    let features = llvm_util::global_llvm_features(sess, false);
+    target_machine_factory(sess, config::OptLevel::No, &features)(config)
         .unwrap_or_else(|err| llvm_err(sess.diagnostic(), &err).raise())
 }
 
@@ -115,8 +118,12 @@ pub fn create_target_machine(tcx: TyCtxt<'_>, mod_name: &str) -> &'static mut ll
         None
     };
     let config = TargetMachineFactoryConfig { split_dwarf_file };
-    target_machine_factory(tcx.sess, tcx.backend_optimization_level(()))(config)
+    target_machine_factory(
-        .unwrap_or_else(|err| llvm_err(tcx.sess.diagnostic(), &err).raise())
+        &tcx.sess,
+        tcx.backend_optimization_level(()),
+        tcx.global_backend_features(()),
+    )(config)
+    .unwrap_or_else(|err| llvm_err(tcx.sess.diagnostic(), &err).raise())
 }
 
 pub fn to_llvm_opt_settings(
@@ -171,6 +178,7 @@ pub(crate) fn to_llvm_code_model(code_model: Option<CodeModel>) -> llvm::CodeMod
 pub fn target_machine_factory(
     sess: &Session,
     optlvl: config::OptLevel,
+    target_features: &[String],
 ) -> TargetMachineFactoryFn<LlvmCodegenBackend> {
     let reloc_model = to_llvm_relocation_model(sess.relocation_model());
 
@@ -195,8 +203,7 @@ pub fn target_machine_factory(
 
     let triple = SmallCStr::new(&sess.target.llvm_target);
     let cpu = SmallCStr::new(llvm_util::target_cpu(sess));
-    let features = llvm_util::llvm_global_features(sess).join(",");
+    let features = CString::new(target_features.join(",")).unwrap();
-    let features = CString::new(features).unwrap();
     let abi = SmallCStr::new(&sess.target.llvm_abiname);
     let trap_unreachable =
         sess.opts.debugging_opts.trap_unreachable.unwrap_or(sess.target.trap_unreachable);

compiler/rustc_codegen_llvm/src/lib.rs

@@ -11,6 +11,7 @@
 #![feature(extern_types)]
 #![feature(once_cell)]
 #![feature(nll)]
+#![feature(iter_intersperse)]
 #![recursion_limit = "256"]
 #![allow(rustc::potential_query_instability)]
 
@@ -32,6 +33,7 @@ use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::{ErrorReported, FatalError, Handler};
 use rustc_metadata::EncodedMetadata;
 use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
+use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::config::{OptLevel, OutputFilenames, PrintRequest};
 use rustc_session::Session;
@@ -126,8 +128,9 @@ impl ExtraBackendMethods for LlvmCodegenBackend {
         &self,
         sess: &Session,
         optlvl: OptLevel,
+        target_features: &[String],
     ) -> TargetMachineFactoryFn<Self> {
-        back::write::target_machine_factory(sess, optlvl)
+        back::write::target_machine_factory(sess, optlvl, target_features)
     }
     fn target_cpu<'b>(&self, sess: &'b Session) -> &'b str {
         llvm_util::target_cpu(sess)
@@ -251,6 +254,11 @@ impl CodegenBackend for LlvmCodegenBackend {
         llvm_util::init(sess); // Make sure llvm is inited
     }
 
+    fn provide(&self, providers: &mut Providers) {
+        providers.global_backend_features =
+            |tcx, ()| llvm_util::global_llvm_features(tcx.sess, true)
+    }
+
     fn print(&self, req: PrintRequest, sess: &Session) {
         match req {
             PrintRequest::RelocationModels => {

compiler/rustc_codegen_ssa/src/back/write.rs

@@ -1033,6 +1033,7 @@ fn start_executing_work<B: ExtraBackendMethods>(
     } else {
         tcx.backend_optimization_level(())
     };
+    let backend_features = tcx.global_backend_features(());
     let cgcx = CodegenContext::<B> {
         backend: backend.clone(),
         crate_types: sess.crate_types().to_vec(),
@@ -1054,7 +1055,7 @@ fn start_executing_work<B: ExtraBackendMethods>(
         regular_module_config: regular_config,
         metadata_module_config: metadata_config,
         allocator_module_config: allocator_config,
-        tm_factory: backend.target_machine_factory(tcx.sess, ol),
+        tm_factory: backend.target_machine_factory(tcx.sess, ol, backend_features),
         total_cgus,
         msvc_imps_needed: msvc_imps_needed(tcx),
         is_pe_coff: tcx.sess.target.is_like_windows,

compiler/rustc_codegen_ssa/src/traits/backend.rs

@@ -134,6 +134,7 @@ pub trait ExtraBackendMethods: CodegenBackend + WriteBackendMethods + Sized + Se
         &self,
         sess: &Session,
         opt_level: config::OptLevel,
+        target_features: &[String],
     ) -> TargetMachineFactoryFn<Self>;
     fn target_cpu<'b>(&self, sess: &'b Session) -> &'b str;
     fn tune_cpu<'b>(&self, sess: &'b Session) -> Option<&'b str>;

compiler/rustc_data_structures/src/small_c_str.rs

@@ -66,3 +66,15 @@ impl Deref for SmallCStr {
         self.as_c_str()
     }
 }
+
+impl<'a> FromIterator<&'a str> for SmallCStr {
+    fn from_iter<T: IntoIterator<Item = &'a str>>(iter: T) -> Self {
+        let mut data =
+            iter.into_iter().flat_map(|s| s.as_bytes()).copied().collect::<SmallVec<_>>();
+        data.push(0);
+        if let Err(e) = ffi::CStr::from_bytes_with_nul(&data) {
+            panic!("The iterator {:?} cannot be converted into a CStr: {}", data, e);
+        }
+        Self { data }
+    }
+}

compiler/rustc_middle/src/query/mod.rs

@@ -1944,4 +1944,13 @@ rustc_queries! {
         no_hash
         desc { "performing HIR wf-checking for predicate {:?} at item {:?}", key.0, key.1 }
     }
+
+
+    /// The list of backend features computed from CLI flags (`-Ctarget-cpu`, `-Ctarget-feature`,
+    /// `--target` and similar).
+    query global_backend_features(_: ()) -> Vec<String> {
+        storage(ArenaCacheSelector<'tcx>)
+        eval_always
+        desc { "computing the backend features for CLI flags" }
+    }
 }

src/test/ui/target-feature/missing-plusminus.stderr

@@ -2,17 +2,5 @@ warning: unknown feature specified for `-Ctarget-feature`: `banana`
    |
    = note: features must begin with a `+` to enable or `-` to disable it
 
-warning: unknown feature specified for `-Ctarget-feature`: `banana`
+warning: 1 warning emitted
-   |
-   = note: features must begin with a `+` to enable or `-` to disable it
-
-warning: unknown feature specified for `-Ctarget-feature`: `banana`
-   |
-   = note: features must begin with a `+` to enable or `-` to disable it
-
-warning: unknown feature specified for `-Ctarget-feature`: `banana`
-   |
-   = note: features must begin with a `+` to enable or `-` to disable it
-
-warning: 4 warnings emitted
 

src/test/ui/target-feature/similar-feature-suggestion.stderr

@@ -3,20 +3,5 @@ warning: unknown feature specified for `-Ctarget-feature`: `rdrnd`
    = note: it is still passed through to the codegen backend
    = help: you might have meant: `rdrand`
 
-warning: unknown feature specified for `-Ctarget-feature`: `rdrnd`
+warning: 1 warning emitted
-   |
-   = note: it is still passed through to the codegen backend
-   = help: did you mean: `rdrand`
-
-warning: unknown feature specified for `-Ctarget-feature`: `rdrnd`
-   |
-   = note: it is still passed through to the codegen backend
-   = help: did you mean: `rdrand`
-
-warning: unknown feature specified for `-Ctarget-feature`: `rdrnd`
-   |
-   = note: it is still passed through to the codegen backend
-   = help: did you mean: `rdrand`
-
-warning: 4 warnings emitted