codegen_ssa: consolidate tied feature checking

`rustc_codegen_llvm` and `rustc_codegen_gcc` duplicated logic for
checking if tied target features were partially enabled. This commit
consolidates these checks into `rustc_codegen_ssa` in the
`codegen_fn_attrs` query, which also is run pre-monomorphisation for
each function, which ensures that this check is run for unused functions,
as would be expected.

compiler/rustc_codegen_gcc/src/attributes.rs

@@ -7,11 +7,9 @@ use rustc_attr::InstructionSetAttr;
 #[cfg(feature = "master")]
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::ty;
-use rustc_span::symbol::sym;
 
 use crate::context::CodegenCx;
-use crate::errors::TiedTargetFeatures;
-use crate::gcc_util::{check_tied_features, to_gcc_features};
+use crate::gcc_util::to_gcc_features;
 
 /// Get GCC attribute for the provided inline heuristic.
 #[cfg(feature = "master")]
@@ -72,26 +70,10 @@ pub fn from_fn_attrs<'gcc, 'tcx>(
         }
     }
 
-    let function_features = codegen_fn_attrs
+    let mut function_features = codegen_fn_attrs
         .target_features
         .iter()
         .map(|features| features.name.as_str())
-        .collect::<Vec<&str>>();
-
-    if let Some(features) = check_tied_features(
-        cx.tcx.sess,
-        &function_features.iter().map(|features| (*features, true)).collect(),
-    ) {
-        let span = cx
-            .tcx
-            .get_attr(instance.def_id(), sym::target_feature)
-            .map_or_else(|| cx.tcx.def_span(instance.def_id()), |a| a.span);
-        cx.tcx.dcx().create_err(TiedTargetFeatures { features: features.join(", "), span }).emit();
-        return;
-    }
-
-    let mut function_features = function_features
-        .iter()
         .flat_map(|feat| to_gcc_features(cx.tcx.sess, feat).into_iter())
         .chain(codegen_fn_attrs.instruction_set.iter().map(|x| match *x {
             InstructionSetAttr::ArmA32 => "-thumb-mode", // TODO(antoyo): support removing feature.

compiler/rustc_codegen_gcc/src/errors.rs

@@ -1,9 +1,6 @@
-use rustc_errors::{Diag, DiagCtxtHandle, Diagnostic, EmissionGuarantee, Level};
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_span::Span;
 
-use crate::fluent_generated as fluent;
-
 #[derive(Diagnostic)]
 #[diag(codegen_gcc_unknown_ctarget_feature_prefix)]
 #[note]
@@ -45,15 +42,6 @@ pub(crate) struct InvalidMinimumAlignment {
     pub err: String,
 }
 
-#[derive(Diagnostic)]
-#[diag(codegen_gcc_tied_target_features)]
-#[help]
-pub(crate) struct TiedTargetFeatures {
-    #[primary_span]
-    pub span: Span,
-    pub features: String,
-}
-
 #[derive(Diagnostic)]
 #[diag(codegen_gcc_copy_bitcode)]
 pub(crate) struct CopyBitcode {
@@ -78,27 +66,3 @@ pub(crate) struct LtoDylib;
 pub(crate) struct LtoBitcodeFromRlib {
     pub gcc_err: String,
 }
-
-pub(crate) struct TargetFeatureDisableOrEnable<'a> {
-    pub features: &'a [&'a str],
-    pub span: Option<Span>,
-    pub missing_features: Option<MissingFeatures>,
-}
-
-#[derive(Subdiagnostic)]
-#[help(codegen_gcc_missing_features)]
-pub(crate) struct MissingFeatures;
-
-impl<G: EmissionGuarantee> Diagnostic<'_, G> for TargetFeatureDisableOrEnable<'_> {
-    fn into_diag(self, dcx: DiagCtxtHandle<'_>, level: Level) -> Diag<'_, G> {
-        let mut diag = Diag::new(dcx, level, fluent::codegen_gcc_target_feature_disable_or_enable);
-        if let Some(span) = self.span {
-            diag.span(span);
-        };
-        if let Some(missing_features) = self.missing_features {
-            diag.subdiagnostic(missing_features);
-        }
-        diag.arg("features", self.features.join(", "));
-        diag
-    }
-}

compiler/rustc_codegen_gcc/src/gcc_util.rs

@@ -1,15 +1,14 @@
 #[cfg(feature = "master")]
 use gccjit::Context;
+use rustc_codegen_ssa::codegen_attrs::check_tied_features;
+use rustc_codegen_ssa::errors::TargetFeatureDisableOrEnable;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_middle::bug;
 use rustc_session::Session;
 use rustc_target::target_features::RUSTC_SPECIFIC_FEATURES;
 use smallvec::{SmallVec, smallvec};
 
-use crate::errors::{
-    PossibleFeature, TargetFeatureDisableOrEnable, UnknownCTargetFeature,
-    UnknownCTargetFeaturePrefix,
-};
+use crate::errors::{PossibleFeature, UnknownCTargetFeature, UnknownCTargetFeaturePrefix};
 
 /// The list of GCC features computed from CLI flags (`-Ctarget-cpu`, `-Ctarget-feature`,
 /// `--target` and similar).
@@ -185,23 +184,6 @@ pub fn to_gcc_features<'a>(sess: &Session, s: &'a str) -> SmallVec<[&'a str; 2]>
     }
 }
 
-// Given a map from target_features to whether they are enabled or disabled,
-// ensure only valid combinations are allowed.
-pub fn check_tied_features(
-    sess: &Session,
-    features: &FxHashMap<&str, bool>,
-) -> Option<&'static [&'static str]> {
-    for tied in sess.target.tied_target_features() {
-        // Tied features must be set to the same value, or not set at all
-        let mut tied_iter = tied.iter();
-        let enabled = features.get(tied_iter.next().unwrap());
-        if tied_iter.any(|feature| enabled != features.get(feature)) {
-            return Some(tied);
-        }
-    }
-    None
-}
-
 fn arch_to_gcc(name: &str) -> &str {
     match name {
         "M68020" => "68020",