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-rw-r--r--compiler/rustc_attr_data_structures/src/attributes.rs6
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs40
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/mod.rs1
-rw-r--r--compiler/rustc_attr_parsing/src/context.rs2
-rw-r--r--compiler/rustc_codegen_gcc/messages.ftl16
-rw-r--r--compiler/rustc_codegen_gcc/src/errors.rs26
-rw-r--r--compiler/rustc_codegen_gcc/src/gcc_util.rs123
-rw-r--r--compiler/rustc_codegen_gcc/src/lib.rs52
-rw-r--r--compiler/rustc_codegen_llvm/messages.ftl10
-rw-r--r--compiler/rustc_codegen_llvm/src/errors.rs26
-rw-r--r--compiler/rustc_codegen_llvm/src/llvm_util.rs279
-rw-r--r--compiler/rustc_codegen_ssa/messages.ftl24
-rw-r--r--compiler/rustc_codegen_ssa/src/codegen_attrs.rs55
-rw-r--r--compiler/rustc_codegen_ssa/src/errors.rs103
-rw-r--r--compiler/rustc_codegen_ssa/src/target_features.rs284
-rw-r--r--compiler/rustc_const_eval/src/check_consts/check.rs8
-rw-r--r--compiler/rustc_const_eval/src/check_consts/ops.rs22
-rw-r--r--compiler/rustc_const_eval/src/errors.rs4
-rw-r--r--compiler/rustc_driver_impl/src/pretty.rs6
-rw-r--r--compiler/rustc_error_codes/src/error_codes/E0722.md8
-rw-r--r--compiler/rustc_error_codes/src/lib.rs1
-rw-r--r--compiler/rustc_hir_analysis/src/check/mod.rs4
-rw-r--r--compiler/rustc_hir_analysis/src/check/wfcheck.rs2
-rw-r--r--compiler/rustc_hir_typeck/src/errors.rs6
-rw-r--r--compiler/rustc_hir_typeck/src/expr.rs21
-rw-r--r--compiler/rustc_hir_typeck/src/method/probe.rs1
-rw-r--r--compiler/rustc_interface/src/passes.rs4
-rw-r--r--compiler/rustc_lint/src/expect.rs3
-rw-r--r--compiler/rustc_middle/src/hir/map.rs16
-rw-r--r--compiler/rustc_middle/src/hir/mod.rs10
-rw-r--r--compiler/rustc_middle/src/ty/context.rs35
-rw-r--r--compiler/rustc_parse/src/validate_attr.rs1
-rw-r--r--compiler/rustc_passes/src/check_attr.rs8
-rw-r--r--compiler/rustc_session/messages.ftl8
-rw-r--r--compiler/rustc_session/src/errors.rs17
-rw-r--r--compiler/rustc_session/src/features.rs59
-rw-r--r--compiler/rustc_session/src/lib.rs1
-rw-r--r--compiler/rustc_session/src/options.rs8
-rw-r--r--compiler/rustc_target/src/target_features.rs45
-rw-r--r--compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs6
40 files changed, 597 insertions, 754 deletions
diff --git a/compiler/rustc_attr_data_structures/src/attributes.rs b/compiler/rustc_attr_data_structures/src/attributes.rs
index cdc01dc6c91..65061059a02 100644
--- a/compiler/rustc_attr_data_structures/src/attributes.rs
+++ b/compiler/rustc_attr_data_structures/src/attributes.rs
@@ -38,7 +38,8 @@ pub enum InstructionSetAttr {
     ArmT32,
 }
 
-#[derive(Clone, Encodable, Decodable, Debug, PartialEq, Eq, HashStable_Generic, Default)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Default, PrintAttribute)]
+#[derive(Encodable, Decodable, HashStable_Generic)]
 pub enum OptimizeAttr {
     /// No `#[optimize(..)]` attribute
     #[default]
@@ -229,7 +230,8 @@ pub enum AttributeKind {
 
     /// Represents `#[rustc_macro_transparency]`.
     MacroTransparency(Transparency),
-
+    /// Represents `#[optimize(size|speed)]`
+    Optimize(OptimizeAttr, Span),
     /// Represents [`#[repr]`](https://doc.rust-lang.org/stable/reference/type-layout.html#representations).
     Repr(ThinVec<(ReprAttr, Span)>),
 
diff --git a/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs b/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs
new file mode 100644
index 00000000000..ddcf82cbf7c
--- /dev/null
+++ b/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs
@@ -0,0 +1,40 @@
+use rustc_attr_data_structures::{AttributeKind, OptimizeAttr};
+use rustc_feature::{AttributeTemplate, template};
+use rustc_span::sym;
+
+use super::{AttributeOrder, OnDuplicate, SingleAttributeParser};
+use crate::context::{AcceptContext, Stage};
+use crate::parser::ArgParser;
+
+pub(crate) struct OptimizeParser;
+
+impl<S: Stage> SingleAttributeParser<S> for OptimizeParser {
+    const PATH: &[rustc_span::Symbol] = &[sym::optimize];
+    const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepLast;
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::WarnButFutureError;
+    const TEMPLATE: AttributeTemplate = template!(List: "size|speed|none");
+
+    fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
+        let Some(list) = args.list() else {
+            cx.expected_list(cx.attr_span);
+            return None;
+        };
+
+        let Some(single) = list.single() else {
+            cx.expected_single_argument(list.span);
+            return None;
+        };
+
+        let res = match single.meta_item().and_then(|i| i.path().word().map(|i| i.name)) {
+            Some(sym::size) => OptimizeAttr::Size,
+            Some(sym::speed) => OptimizeAttr::Speed,
+            Some(sym::none) => OptimizeAttr::DoNotOptimize,
+            _ => {
+                cx.expected_specific_argument(single.span(), vec!["size", "speed", "none"]);
+                OptimizeAttr::Default
+            }
+        };
+
+        Some(AttributeKind::Optimize(res, cx.attr_span))
+    }
+}
diff --git a/compiler/rustc_attr_parsing/src/attributes/mod.rs b/compiler/rustc_attr_parsing/src/attributes/mod.rs
index fa2a6087506..3bb4c163d32 100644
--- a/compiler/rustc_attr_parsing/src/attributes/mod.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/mod.rs
@@ -28,6 +28,7 @@ use crate::session_diagnostics::UnusedMultiple;
 
 pub(crate) mod allow_unstable;
 pub(crate) mod cfg;
+pub(crate) mod codegen_attrs;
 pub(crate) mod confusables;
 pub(crate) mod deprecation;
 pub(crate) mod inline;
diff --git a/compiler/rustc_attr_parsing/src/context.rs b/compiler/rustc_attr_parsing/src/context.rs
index d7570634c1f..1708fd72e58 100644
--- a/compiler/rustc_attr_parsing/src/context.rs
+++ b/compiler/rustc_attr_parsing/src/context.rs
@@ -15,6 +15,7 @@ use rustc_session::Session;
 use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span, Symbol, sym};
 
 use crate::attributes::allow_unstable::{AllowConstFnUnstableParser, AllowInternalUnstableParser};
+use crate::attributes::codegen_attrs::OptimizeParser;
 use crate::attributes::confusables::ConfusablesParser;
 use crate::attributes::deprecation::DeprecationParser;
 use crate::attributes::inline::{InlineParser, RustcForceInlineParser};
@@ -108,6 +109,7 @@ attribute_parsers!(
         Single<ConstStabilityIndirectParser>,
         Single<DeprecationParser>,
         Single<InlineParser>,
+        Single<OptimizeParser>,
         Single<RustcForceInlineParser>,
         Single<TransparencyParser>,
         // tidy-alphabetical-end
diff --git a/compiler/rustc_codegen_gcc/messages.ftl b/compiler/rustc_codegen_gcc/messages.ftl
index 18a8a5a1e04..55a28bc9493 100644
--- a/compiler/rustc_codegen_gcc/messages.ftl
+++ b/compiler/rustc_codegen_gcc/messages.ftl
@@ -1,7 +1,3 @@
-codegen_gcc_unknown_ctarget_feature_prefix =
-    unknown feature specified for `-Ctarget-feature`: `{$feature}`
-    .note = features must begin with a `+` to enable or `-` to disable it
-
 codegen_gcc_unwinding_inline_asm =
     GCC backend does not support unwinding from inline asm
 
@@ -16,15 +12,3 @@ codegen_gcc_lto_disallowed = lto can only be run for executables, cdylibs and st
 codegen_gcc_lto_dylib = lto cannot be used for `dylib` crate type without `-Zdylib-lto`
 
 codegen_gcc_lto_bitcode_from_rlib = failed to get bitcode from object file for LTO ({$gcc_err})
-
-codegen_gcc_unknown_ctarget_feature =
-    unknown and unstable feature specified for `-Ctarget-feature`: `{$feature}`
-    .note = it is still passed through to the codegen backend, but use of this feature might be unsound and the behavior of this feature can change in the future
-    .possible_feature = you might have meant: `{$rust_feature}`
-    .consider_filing_feature_request = consider filing a feature request
-
-codegen_gcc_missing_features =
-    add the missing features in a `target_feature` attribute
-
-codegen_gcc_target_feature_disable_or_enable =
-    the target features {$features} must all be either enabled or disabled together
diff --git a/compiler/rustc_codegen_gcc/src/errors.rs b/compiler/rustc_codegen_gcc/src/errors.rs
index 7786be9ae5d..b7e7343460f 100644
--- a/compiler/rustc_codegen_gcc/src/errors.rs
+++ b/compiler/rustc_codegen_gcc/src/errors.rs
@@ -1,31 +1,7 @@
-use rustc_macros::{Diagnostic, Subdiagnostic};
+use rustc_macros::Diagnostic;
 use rustc_span::Span;
 
 #[derive(Diagnostic)]
-#[diag(codegen_gcc_unknown_ctarget_feature_prefix)]
-#[note]
-pub(crate) struct UnknownCTargetFeaturePrefix<'a> {
-    pub feature: &'a str,
-}
-
-#[derive(Diagnostic)]
-#[diag(codegen_gcc_unknown_ctarget_feature)]
-#[note]
-pub(crate) struct UnknownCTargetFeature<'a> {
-    pub feature: &'a str,
-    #[subdiagnostic]
-    pub rust_feature: PossibleFeature<'a>,
-}
-
-#[derive(Subdiagnostic)]
-pub(crate) enum PossibleFeature<'a> {
-    #[help(codegen_gcc_possible_feature)]
-    Some { rust_feature: &'a str },
-    #[help(codegen_gcc_consider_filing_feature_request)]
-    None,
-}
-
-#[derive(Diagnostic)]
 #[diag(codegen_gcc_unwinding_inline_asm)]
 pub(crate) struct UnwindingInlineAsm {
     #[primary_span]
diff --git a/compiler/rustc_codegen_gcc/src/gcc_util.rs b/compiler/rustc_codegen_gcc/src/gcc_util.rs
index 2e00d5fcb61..42ba40692b7 100644
--- a/compiler/rustc_codegen_gcc/src/gcc_util.rs
+++ b/compiler/rustc_codegen_gcc/src/gcc_util.rs
@@ -1,20 +1,12 @@
 #[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_data_structures::unord::UnordSet;
+use rustc_codegen_ssa::target_features;
 use rustc_session::Session;
-use rustc_session::features::{StabilityExt, retpoline_features_by_flags};
-use rustc_target::target_features::RUSTC_SPECIFIC_FEATURES;
 use smallvec::{SmallVec, smallvec};
 
-use crate::errors::{PossibleFeature, UnknownCTargetFeature, UnknownCTargetFeaturePrefix};
-
-fn gcc_features_by_flags(sess: &Session) -> Vec<&str> {
-    let mut features: Vec<&str> = Vec::new();
-    retpoline_features_by_flags(sess, &mut features);
-    features
+fn gcc_features_by_flags(sess: &Session, features: &mut Vec<String>) {
+    target_features::retpoline_features_by_flags(sess, features);
+    // FIXME: LLVM also sets +reserve-x18 here under some conditions.
 }
 
 /// The list of GCC features computed from CLI flags (`-Ctarget-cpu`, `-Ctarget-feature`,
@@ -44,98 +36,29 @@ pub(crate) fn global_gcc_features(sess: &Session, diagnostics: bool) -> Vec<Stri
     features.extend(sess.target.features.split(',').filter(|v| !v.is_empty()).map(String::from));
 
     // -Ctarget-features
-    let known_features = sess.target.rust_target_features();
-    let mut featsmap = FxHashMap::default();
-
-    // Compute implied features
-    let mut all_rust_features = vec![];
-    for feature in sess.opts.cg.target_feature.split(',').chain(gcc_features_by_flags(sess)) {
-        if let Some(feature) = feature.strip_prefix('+') {
-            all_rust_features.extend(
-                UnordSet::from(sess.target.implied_target_features(feature))
-                    .to_sorted_stable_ord()
-                    .iter()
-                    .map(|&&s| (true, s)),
-            )
-        } else if let Some(feature) = feature.strip_prefix('-') {
-            // FIXME: Why do we not remove implied features on "-" here?
-            // We do the equivalent above in `target_config`.
-            // See <https://github.com/rust-lang/rust/issues/134792>.
-            all_rust_features.push((false, feature));
-        } else if !feature.is_empty() && diagnostics {
-            sess.dcx().emit_warn(UnknownCTargetFeaturePrefix { feature });
-        }
-    }
-    // Remove features that are meant for rustc, not codegen.
-    all_rust_features.retain(|&(_, feature)| {
-        // Retain if it is not a rustc feature
-        !RUSTC_SPECIFIC_FEATURES.contains(&feature)
-    });
-
-    // Check feature validity.
-    if diagnostics {
-        for &(enable, feature) in &all_rust_features {
-            let feature_state = known_features.iter().find(|&&(v, _, _)| v == feature);
-            match feature_state {
-                None => {
-                    let rust_feature = known_features.iter().find_map(|&(rust_feature, _, _)| {
-                        let gcc_features = to_gcc_features(sess, rust_feature);
-                        if gcc_features.contains(&feature) && !gcc_features.contains(&rust_feature)
-                        {
-                            Some(rust_feature)
-                        } else {
-                            None
-                        }
-                    });
-                    let unknown_feature = if let Some(rust_feature) = rust_feature {
-                        UnknownCTargetFeature {
-                            feature,
-                            rust_feature: PossibleFeature::Some { rust_feature },
-                        }
-                    } else {
-                        UnknownCTargetFeature { feature, rust_feature: PossibleFeature::None }
-                    };
-                    sess.dcx().emit_warn(unknown_feature);
-                }
-                Some(&(_, stability, _)) => {
-                    stability.verify_feature_enabled_by_flag(sess, enable, feature);
-                }
-            }
-
-            // FIXME(nagisa): figure out how to not allocate a full hashset here.
-            featsmap.insert(feature, enable);
-        }
-    }
-
-    // Translate this into GCC features.
-    let feats =
-        all_rust_features.iter().flat_map(|&(enable, feature)| {
-            let enable_disable = if enable { '+' } else { '-' };
+    target_features::flag_to_backend_features(
+        sess,
+        diagnostics,
+        |feature| to_gcc_features(sess, feature),
+        |feature, enable| {
             // We run through `to_gcc_features` when
             // passing requests down to GCC. This means that all in-language
             // features also work on the command line instead of having two
             // different names when the GCC name and the Rust name differ.
-            to_gcc_features(sess, feature)
-                .iter()
-                .flat_map(|feat| to_gcc_features(sess, feat).into_iter())
-                .map(|feature| {
-                    if enable_disable == '-' {
-                        format!("-{}", feature)
-                    } else {
-                        feature.to_string()
-                    }
-                })
-                .collect::<Vec<_>>()
-        });
-    features.extend(feats);
-
-    if diagnostics && let Some(f) = check_tied_features(sess, &featsmap) {
-        sess.dcx().emit_err(TargetFeatureDisableOrEnable {
-            features: f,
-            span: None,
-            missing_features: None,
-        });
-    }
+            features.extend(
+                to_gcc_features(sess, feature)
+                    .iter()
+                    .flat_map(|feat| to_gcc_features(sess, feat).into_iter())
+                    .map(
+                        |feature| {
+                            if !enable { format!("-{}", feature) } else { feature.to_string() }
+                        },
+                    ),
+            );
+        },
+    );
+
+    gcc_features_by_flags(sess, &mut features);
 
     features
 }
diff --git a/compiler/rustc_codegen_gcc/src/lib.rs b/compiler/rustc_codegen_gcc/src/lib.rs
index aa57655921d..a912678ef2a 100644
--- a/compiler/rustc_codegen_gcc/src/lib.rs
+++ b/compiler/rustc_codegen_gcc/src/lib.rs
@@ -102,6 +102,7 @@ use rustc_codegen_ssa::back::write::{
     CodegenContext, FatLtoInput, ModuleConfig, TargetMachineFactoryFn,
 };
 use rustc_codegen_ssa::base::codegen_crate;
+use rustc_codegen_ssa::target_features::cfg_target_feature;
 use rustc_codegen_ssa::traits::{CodegenBackend, ExtraBackendMethods, WriteBackendMethods};
 use rustc_codegen_ssa::{CodegenResults, CompiledModule, ModuleCodegen, TargetConfig};
 use rustc_data_structures::fx::FxIndexMap;
@@ -476,42 +477,21 @@ fn to_gcc_opt_level(optlevel: Option<OptLevel>) -> OptimizationLevel {
 
 /// Returns the features that should be set in `cfg(target_feature)`.
 fn target_config(sess: &Session, target_info: &LockedTargetInfo) -> TargetConfig {
-    // TODO(antoyo): use global_gcc_features.
-    let f = |allow_unstable| {
-        sess.target
-            .rust_target_features()
-            .iter()
-            .filter_map(|&(feature, gate, _)| {
-                if allow_unstable
-                    || (gate.in_cfg()
-                        && (sess.is_nightly_build() || gate.requires_nightly().is_none()))
-                {
-                    Some(feature)
-                } else {
-                    None
-                }
-            })
-            .filter(|feature| {
-                // TODO: we disable Neon for now since we don't support the LLVM intrinsics for it.
-                if *feature == "neon" {
-                    return false;
-                }
-                target_info.cpu_supports(feature)
-                // cSpell:disable
-                /*
-                  adx, aes, avx, avx2, avx512bf16, avx512bitalg, avx512bw, avx512cd, avx512dq, avx512er, avx512f, avx512fp16, avx512ifma,
-                  avx512pf, avx512vbmi, avx512vbmi2, avx512vl, avx512vnni, avx512vp2intersect, avx512vpopcntdq,
-                  bmi1, bmi2, cmpxchg16b, ermsb, f16c, fma, fxsr, gfni, lzcnt, movbe, pclmulqdq, popcnt, rdrand, rdseed, rtm,
-                  sha, sse, sse2, sse3, sse4.1, sse4.2, sse4a, ssse3, tbm, vaes, vpclmulqdq, xsave, xsavec, xsaveopt, xsaves
-                */
-                // cSpell:enable
-            })
-            .map(Symbol::intern)
-            .collect()
-    };
-
-    let target_features = f(false);
-    let unstable_target_features = f(true);
+    let (unstable_target_features, target_features) = cfg_target_feature(sess, |feature| {
+        // TODO: we disable Neon for now since we don't support the LLVM intrinsics for it.
+        if feature == "neon" {
+            return false;
+        }
+        target_info.cpu_supports(feature)
+        // cSpell:disable
+        /*
+          adx, aes, avx, avx2, avx512bf16, avx512bitalg, avx512bw, avx512cd, avx512dq, avx512er, avx512f, avx512fp16, avx512ifma,
+          avx512pf, avx512vbmi, avx512vbmi2, avx512vl, avx512vnni, avx512vp2intersect, avx512vpopcntdq,
+          bmi1, bmi2, cmpxchg16b, ermsb, f16c, fma, fxsr, gfni, lzcnt, movbe, pclmulqdq, popcnt, rdrand, rdseed, rtm,
+          sha, sse, sse2, sse3, sse4.1, sse4.2, sse4a, ssse3, tbm, vaes, vpclmulqdq, xsave, xsavec, xsaveopt, xsaves
+        */
+        // cSpell:enable
+    });
 
     let has_reliable_f16 = target_info.supports_target_dependent_type(CType::Float16);
     let has_reliable_f128 = target_info.supports_target_dependent_type(CType::Float128);
diff --git a/compiler/rustc_codegen_llvm/messages.ftl b/compiler/rustc_codegen_llvm/messages.ftl
index 3faeb9b3b22..3885f18271f 100644
--- a/compiler/rustc_codegen_llvm/messages.ftl
+++ b/compiler/rustc_codegen_llvm/messages.ftl
@@ -59,16 +59,6 @@ codegen_llvm_symbol_already_defined =
 codegen_llvm_target_machine = could not create LLVM TargetMachine for triple: {$triple}
 codegen_llvm_target_machine_with_llvm_err = could not create LLVM TargetMachine for triple: {$triple}: {$llvm_err}
 
-codegen_llvm_unknown_ctarget_feature =
-    unknown and unstable feature specified for `-Ctarget-feature`: `{$feature}`
-    .note = it is still passed through to the codegen backend, but use of this feature might be unsound and the behavior of this feature can change in the future
-    .possible_feature = you might have meant: `{$rust_feature}`
-    .consider_filing_feature_request = consider filing a feature request
-
-codegen_llvm_unknown_ctarget_feature_prefix =
-    unknown feature specified for `-Ctarget-feature`: `{$feature}`
-    .note = features must begin with a `+` to enable or `-` to disable it
-
 codegen_llvm_unknown_debuginfo_compression = unknown debuginfo compression algorithm {$algorithm} - will fall back to uncompressed debuginfo
 
 codegen_llvm_write_bytecode = failed to write bytecode to {$path}: {$err}
diff --git a/compiler/rustc_codegen_llvm/src/errors.rs b/compiler/rustc_codegen_llvm/src/errors.rs
index 8bc74fbec7e..d50ad8a1a9c 100644
--- a/compiler/rustc_codegen_llvm/src/errors.rs
+++ b/compiler/rustc_codegen_llvm/src/errors.rs
@@ -3,36 +3,12 @@ use std::path::Path;
 
 use rustc_data_structures::small_c_str::SmallCStr;
 use rustc_errors::{Diag, DiagCtxtHandle, Diagnostic, EmissionGuarantee, Level};
-use rustc_macros::{Diagnostic, Subdiagnostic};
+use rustc_macros::Diagnostic;
 use rustc_span::Span;
 
 use crate::fluent_generated as fluent;
 
 #[derive(Diagnostic)]
-#[diag(codegen_llvm_unknown_ctarget_feature_prefix)]
-#[note]
-pub(crate) struct UnknownCTargetFeaturePrefix<'a> {
-    pub feature: &'a str,
-}
-
-#[derive(Diagnostic)]
-#[diag(codegen_llvm_unknown_ctarget_feature)]
-#[note]
-pub(crate) struct UnknownCTargetFeature<'a> {
-    pub feature: &'a str,
-    #[subdiagnostic]
-    pub rust_feature: PossibleFeature<'a>,
-}
-
-#[derive(Subdiagnostic)]
-pub(crate) enum PossibleFeature<'a> {
-    #[help(codegen_llvm_possible_feature)]
-    Some { rust_feature: &'a str },
-    #[help(codegen_llvm_consider_filing_feature_request)]
-    None,
-}
-
-#[derive(Diagnostic)]
 #[diag(codegen_llvm_symbol_already_defined)]
 pub(crate) struct SymbolAlreadyDefined<'a> {
     #[primary_span]
diff --git a/compiler/rustc_codegen_llvm/src/llvm_util.rs b/compiler/rustc_codegen_llvm/src/llvm_util.rs
index 0e77bc43df8..6fd07d562af 100644
--- a/compiler/rustc_codegen_llvm/src/llvm_util.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm_util.rs
@@ -6,27 +6,20 @@ use std::sync::Once;
 use std::{ptr, slice, str};
 
 use libc::c_int;
-use rustc_codegen_ssa::TargetConfig;
 use rustc_codegen_ssa::base::wants_wasm_eh;
-use rustc_codegen_ssa::codegen_attrs::check_tied_features;
-use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_codegen_ssa::target_features::cfg_target_feature;
+use rustc_codegen_ssa::{TargetConfig, target_features};
+use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::small_c_str::SmallCStr;
-use rustc_data_structures::unord::UnordSet;
 use rustc_fs_util::path_to_c_string;
 use rustc_middle::bug;
 use rustc_session::Session;
 use rustc_session::config::{PrintKind, PrintRequest};
-use rustc_session::features::{StabilityExt, retpoline_features_by_flags};
-use rustc_span::Symbol;
 use rustc_target::spec::{MergeFunctions, PanicStrategy, SmallDataThresholdSupport};
-use rustc_target::target_features::{RUSTC_SPECIAL_FEATURES, RUSTC_SPECIFIC_FEATURES};
 use smallvec::{SmallVec, smallvec};
 
 use crate::back::write::create_informational_target_machine;
-use crate::errors::{
-    FixedX18InvalidArch, PossibleFeature, UnknownCTargetFeature, UnknownCTargetFeaturePrefix,
-};
-use crate::llvm;
+use crate::{errors, llvm};
 
 static INIT: Once = Once::new();
 
@@ -195,15 +188,6 @@ impl<'a> LLVMFeature<'a> {
     ) -> Self {
         Self { llvm_feature_name, dependencies }
     }
-
-    fn contains(&'a self, feat: &str) -> bool {
-        self.iter().any(|dep| dep == feat)
-    }
-
-    fn iter(&'a self) -> impl Iterator<Item = &'a str> {
-        let dependencies = self.dependencies.iter().map(|feat| feat.as_str());
-        std::iter::once(self.llvm_feature_name).chain(dependencies)
-    }
 }
 
 impl<'a> IntoIterator for LLVMFeature<'a> {
@@ -216,18 +200,22 @@ impl<'a> IntoIterator for LLVMFeature<'a> {
     }
 }
 
-// WARNING: the features after applying `to_llvm_features` must be known
-// to LLVM or the feature detection code will walk past the end of the feature
-// array, leading to crashes.
-//
-// To find a list of LLVM's names, see llvm-project/llvm/lib/Target/{ARCH}/*.td
-// where `{ARCH}` is the architecture name. Look for instances of `SubtargetFeature`.
-//
-// Check the current rustc fork of LLVM in the repo at https://github.com/rust-lang/llvm-project/.
-// The commit in use can be found via the `llvm-project` submodule in
-// https://github.com/rust-lang/rust/tree/master/src Though note that Rust can also be build with
-// an external precompiled version of LLVM which might lead to failures if the oldest tested /
-// supported LLVM version doesn't yet support the relevant intrinsics.
+/// Convert a Rust feature name to an LLVM feature name. Returning `None` means the
+/// feature should be skipped, usually because it is not supported by the current
+/// LLVM version.
+///
+/// WARNING: the features after applying `to_llvm_features` must be known
+/// to LLVM or the feature detection code will walk past the end of the feature
+/// array, leading to crashes.
+///
+/// To find a list of LLVM's names, see llvm-project/llvm/lib/Target/{ARCH}/*.td
+/// where `{ARCH}` is the architecture name. Look for instances of `SubtargetFeature`.
+///
+/// Check the current rustc fork of LLVM in the repo at
+/// <https://github.com/rust-lang/llvm-project/>. The commit in use can be found via the
+/// `llvm-project` submodule in <https://github.com/rust-lang/rust/tree/master/src> Though note that
+/// Rust can also be build with an external precompiled version of LLVM which might lead to failures
+/// if the oldest tested / supported LLVM version doesn't yet support the relevant intrinsics.
 pub(crate) fn to_llvm_features<'a>(sess: &Session, s: &'a str) -> Option<LLVMFeature<'a>> {
     let arch = if sess.target.arch == "x86_64" {
         "x86"
@@ -343,98 +331,25 @@ pub(crate) fn target_config(sess: &Session) -> TargetConfig {
     // the target CPU, that is still expanded to target features (with all their implied features)
     // by LLVM.
     let target_machine = create_informational_target_machine(sess, true);
-    // Compute which of the known target features are enabled in the 'base' target machine. We only
-    // consider "supported" features; "forbidden" features are not reflected in `cfg` as of now.
-    let mut features: FxHashSet<Symbol> = sess
-        .target
-        .rust_target_features()
-        .iter()
-        .filter(|(feature, _, _)| {
-            // skip checking special features, as LLVM may not understand them
-            if RUSTC_SPECIAL_FEATURES.contains(feature) {
-                return true;
-            }
-            if let Some(feat) = to_llvm_features(sess, feature) {
-                for llvm_feature in feat {
-                    let cstr = SmallCStr::new(llvm_feature);
-                    // `LLVMRustHasFeature` is moderately expensive. On targets with many
-                    // features (e.g. x86) these calls take a non-trivial fraction of runtime
-                    // when compiling very small programs.
-                    if !unsafe { llvm::LLVMRustHasFeature(target_machine.raw(), cstr.as_ptr()) } {
-                        return false;
-                    }
+
+    let (unstable_target_features, target_features) = cfg_target_feature(sess, |feature| {
+        if let Some(feat) = to_llvm_features(sess, feature) {
+            // All the LLVM features this expands to must be enabled.
+            for llvm_feature in feat {
+                let cstr = SmallCStr::new(llvm_feature);
+                // `LLVMRustHasFeature` is moderately expensive. On targets with many
+                // features (e.g. x86) these calls take a non-trivial fraction of runtime
+                // when compiling very small programs.
+                if !unsafe { llvm::LLVMRustHasFeature(target_machine.raw(), cstr.as_ptr()) } {
+                    return false;
                 }
-                true
-            } else {
-                false
             }
-        })
-        .map(|(feature, _, _)| Symbol::intern(feature))
-        .collect();
-
-    // Add enabled and remove disabled features.
-    for (enabled, feature) in
-        sess.opts.cg.target_feature.split(',').filter_map(|s| match s.chars().next() {
-            Some('+') => Some((true, Symbol::intern(&s[1..]))),
-            Some('-') => Some((false, Symbol::intern(&s[1..]))),
-            _ => None,
-        })
-    {
-        if enabled {
-            // Also add all transitively implied features.
-
-            // We don't care about the order in `features` since the only thing we use it for is the
-            // `features.contains` below.
-            #[allow(rustc::potential_query_instability)]
-            features.extend(
-                sess.target
-                    .implied_target_features(feature.as_str())
-                    .iter()
-                    .map(|s| Symbol::intern(s)),
-            );
+            true
         } else {
-            // Remove transitively reverse-implied features.
-
-            // We don't care about the order in `features` since the only thing we use it for is the
-            // `features.contains` below.
-            #[allow(rustc::potential_query_instability)]
-            features.retain(|f| {
-                if sess.target.implied_target_features(f.as_str()).contains(&feature.as_str()) {
-                    // If `f` if implies `feature`, then `!feature` implies `!f`, so we have to
-                    // remove `f`. (This is the standard logical contraposition principle.)
-                    false
-                } else {
-                    // We can keep `f`.
-                    true
-                }
-            });
+            false
         }
-    }
-
-    // Filter enabled features based on feature gates.
-    let f = |allow_unstable| {
-        sess.target
-            .rust_target_features()
-            .iter()
-            .filter_map(|(feature, gate, _)| {
-                // The `allow_unstable` set is used by rustc internally to determined which target
-                // features are truly available, so we want to return even perma-unstable
-                // "forbidden" features.
-                if allow_unstable
-                    || (gate.in_cfg()
-                        && (sess.is_nightly_build() || gate.requires_nightly().is_none()))
-                {
-                    Some(Symbol::intern(feature))
-                } else {
-                    None
-                }
-            })
-            .filter(|feature| features.contains(&feature))
-            .collect()
-    };
+    });
 
-    let target_features = f(false);
-    let unstable_target_features = f(true);
     let mut cfg = TargetConfig {
         target_features,
         unstable_target_features,
@@ -707,10 +622,18 @@ pub(crate) fn target_cpu(sess: &Session) -> &str {
     handle_native(cpu_name)
 }
 
-fn llvm_features_by_flags(sess: &Session) -> Vec<&str> {
-    let mut features: Vec<&str> = Vec::new();
-    retpoline_features_by_flags(sess, &mut features);
-    features
+/// The target features for compiler flags other than `-Ctarget-features`.
+fn llvm_features_by_flags(sess: &Session, features: &mut Vec<String>) {
+    target_features::retpoline_features_by_flags(sess, features);
+
+    // -Zfixed-x18
+    if sess.opts.unstable_opts.fixed_x18 {
+        if sess.target.arch != "aarch64" {
+            sess.dcx().emit_fatal(errors::FixedX18InvalidArch { arch: &sess.target.arch });
+        } else {
+            features.push("+reserve-x18".into());
+        }
+    }
 }
 
 /// The list of LLVM features computed from CLI flags (`-Ctarget-cpu`, `-Ctarget-feature`,
@@ -777,6 +700,8 @@ pub(crate) fn global_llvm_features(
             .split(',')
             .filter(|v| !v.is_empty())
             // Drop +v8plus feature introduced in LLVM 20.
+            // (Hard-coded target features do not go through `to_llvm_feature` since they already
+            // are LLVM feature names, hence we need a special case here.)
             .filter(|v| *v != "+v8plus" || get_version() >= (20, 0, 0))
             .map(String::from),
     );
@@ -787,86 +712,23 @@ pub(crate) fn global_llvm_features(
 
     // -Ctarget-features
     if !only_base_features {
-        let known_features = sess.target.rust_target_features();
-        // Will only be filled when `diagnostics` is set!
-        let mut featsmap = FxHashMap::default();
-
-        // Compute implied features
-        let mut all_rust_features = vec![];
-        for feature in sess.opts.cg.target_feature.split(',').chain(llvm_features_by_flags(sess)) {
-            if let Some(feature) = feature.strip_prefix('+') {
-                all_rust_features.extend(
-                    UnordSet::from(sess.target.implied_target_features(feature))
-                        .to_sorted_stable_ord()
-                        .iter()
-                        .map(|&&s| (true, s)),
-                )
-            } else if let Some(feature) = feature.strip_prefix('-') {
-                // FIXME: Why do we not remove implied features on "-" here?
-                // We do the equivalent above in `target_config`.
-                // See <https://github.com/rust-lang/rust/issues/134792>.
-                all_rust_features.push((false, feature));
-            } else if !feature.is_empty() {
-                if diagnostics {
-                    sess.dcx().emit_warn(UnknownCTargetFeaturePrefix { feature });
-                }
-            }
-        }
-        // Remove features that are meant for rustc, not LLVM.
-        all_rust_features.retain(|(_, feature)| {
-            // Retain if it is not a rustc feature
-            !RUSTC_SPECIFIC_FEATURES.contains(feature)
-        });
-
-        // Check feature validity.
-        if diagnostics {
-            for &(enable, feature) in &all_rust_features {
-                let feature_state = known_features.iter().find(|&&(v, _, _)| v == feature);
-                match feature_state {
-                    None => {
-                        let rust_feature =
-                            known_features.iter().find_map(|&(rust_feature, _, _)| {
-                                let llvm_features = to_llvm_features(sess, rust_feature)?;
-                                if llvm_features.contains(feature)
-                                    && !llvm_features.contains(rust_feature)
-                                {
-                                    Some(rust_feature)
-                                } else {
-                                    None
-                                }
-                            });
-                        let unknown_feature = if let Some(rust_feature) = rust_feature {
-                            UnknownCTargetFeature {
-                                feature,
-                                rust_feature: PossibleFeature::Some { rust_feature },
-                            }
-                        } else {
-                            UnknownCTargetFeature { feature, rust_feature: PossibleFeature::None }
-                        };
-                        sess.dcx().emit_warn(unknown_feature);
-                    }
-                    Some((_, stability, _)) => {
-                        stability.verify_feature_enabled_by_flag(sess, enable, feature);
-                    }
-                }
-
-                // FIXME(nagisa): figure out how to not allocate a full hashset here.
-                featsmap.insert(feature, enable);
-            }
-        }
-
-        // Translate this into LLVM features.
-        let feats = all_rust_features
-            .iter()
-            .filter_map(|&(enable, feature)| {
+        target_features::flag_to_backend_features(
+            sess,
+            diagnostics,
+            |feature| {
+                to_llvm_features(sess, feature)
+                    .map(|f| SmallVec::<[&str; 2]>::from_iter(f.into_iter()))
+                    .unwrap_or_default()
+            },
+            |feature, enable| {
                 let enable_disable = if enable { '+' } else { '-' };
                 // We run through `to_llvm_features` when
                 // passing requests down to LLVM. This means that all in-language
                 // features also work on the command line instead of having two
                 // different names when the LLVM name and the Rust name differ.
-                let llvm_feature = to_llvm_features(sess, feature)?;
+                let Some(llvm_feature) = to_llvm_features(sess, feature) else { return };
 
-                Some(
+                features.extend(
                     std::iter::once(format!(
                         "{}{}",
                         enable_disable, llvm_feature.llvm_feature_name
@@ -881,27 +743,12 @@ pub(crate) fn global_llvm_features(
                         },
                     )),
                 )
-            })
-            .flatten();
-        features.extend(feats);
-
-        if diagnostics && let Some(f) = check_tied_features(sess, &featsmap) {
-            sess.dcx().emit_err(rustc_codegen_ssa::errors::TargetFeatureDisableOrEnable {
-                features: f,
-                span: None,
-                missing_features: None,
-            });
-        }
+            },
+        );
     }
 
-    // -Zfixed-x18
-    if sess.opts.unstable_opts.fixed_x18 {
-        if sess.target.arch != "aarch64" {
-            sess.dcx().emit_fatal(FixedX18InvalidArch { arch: &sess.target.arch });
-        } else {
-            features.push("+reserve-x18".into());
-        }
-    }
+    // We add this in the "base target" so that these show up in `sess.unstable_target_features`.
+    llvm_features_by_flags(sess, &mut features);
 
     features
 }
diff --git a/compiler/rustc_codegen_ssa/messages.ftl b/compiler/rustc_codegen_ssa/messages.ftl
index 5322fe58cf3..2bd8644e0d7 100644
--- a/compiler/rustc_codegen_ssa/messages.ftl
+++ b/compiler/rustc_codegen_ssa/messages.ftl
@@ -48,8 +48,6 @@ codegen_ssa_error_writing_def_file =
 
 codegen_ssa_expected_name_value_pair = expected name value pair
 
-codegen_ssa_expected_one_argument = expected one argument
-
 codegen_ssa_expected_used_symbol = expected `used`, `used(compiler)` or `used(linker)`
 
 codegen_ssa_extern_funcs_not_found = some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
@@ -68,6 +66,11 @@ codegen_ssa_failed_to_write = failed to write {$path}: {$error}
 
 codegen_ssa_field_associated_value_expected = associated value expected for `{$name}`
 
+codegen_ssa_forbidden_ctarget_feature =
+    target feature `{$feature}` cannot be {$enabled} with `-Ctarget-feature`: {$reason}
+    .note = this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+codegen_ssa_forbidden_ctarget_feature_issue = for more information, see issue #116344 <https://github.com/rust-lang/rust/issues/116344>
+
 codegen_ssa_forbidden_target_feature_attr =
     target feature `{$feature}` cannot be enabled with `#[target_feature]`: {$reason}
 
@@ -86,9 +89,6 @@ codegen_ssa_incorrect_cgu_reuse_type =
 
 codegen_ssa_insufficient_vs_code_product = VS Code is a different product, and is not sufficient.
 
-codegen_ssa_invalid_argument = invalid argument
-    .help = valid inline arguments are `always` and `never`
-
 codegen_ssa_invalid_instruction_set = invalid instruction set specified
 
 codegen_ssa_invalid_link_ordinal_nargs = incorrect number of arguments to `#[link_ordinal]`
@@ -368,8 +368,22 @@ codegen_ssa_unexpected_parameter_name = unexpected parameter name
 codegen_ssa_unknown_archive_kind =
     Don't know how to build archive of type: {$kind}
 
+codegen_ssa_unknown_ctarget_feature =
+    unknown and unstable feature specified for `-Ctarget-feature`: `{$feature}`
+    .note = it is still passed through to the codegen backend, but use of this feature might be unsound and the behavior of this feature can change in the future
+    .possible_feature = you might have meant: `{$rust_feature}`
+    .consider_filing_feature_request = consider filing a feature request
+
+codegen_ssa_unknown_ctarget_feature_prefix =
+    unknown feature specified for `-Ctarget-feature`: `{$feature}`
+    .note = features must begin with a `+` to enable or `-` to disable it
+
 codegen_ssa_unknown_reuse_kind = unknown cgu-reuse-kind `{$kind}` specified
 
+codegen_ssa_unstable_ctarget_feature =
+    unstable feature specified for `-Ctarget-feature`: `{$feature}`
+    .note = this feature is not stably supported; its behavior can change in the future
+
 codegen_ssa_unsupported_instruction_set = target does not support `#[instruction_set]`
 
 codegen_ssa_unsupported_link_self_contained = option `-C link-self-contained` is not supported on this target
diff --git a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
index 98742255063..e855f1d3558 100644
--- a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
+++ b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
@@ -6,7 +6,6 @@ use rustc_ast::{LitKind, MetaItem, MetaItemInner, attr};
 use rustc_attr_data_structures::{
     AttributeKind, InlineAttr, InstructionSetAttr, OptimizeAttr, find_attr,
 };
-use rustc_data_structures::fx::FxHashMap;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE, LocalDefId};
 use rustc_hir::weak_lang_items::WEAK_LANG_ITEMS;
@@ -18,13 +17,15 @@ use rustc_middle::mir::mono::Linkage;
 use rustc_middle::query::Providers;
 use rustc_middle::span_bug;
 use rustc_middle::ty::{self as ty, TyCtxt};
+use rustc_session::lint;
 use rustc_session::parse::feature_err;
-use rustc_session::{Session, lint};
 use rustc_span::{Ident, Span, sym};
 use rustc_target::spec::SanitizerSet;
 
 use crate::errors;
-use crate::target_features::{check_target_feature_trait_unsafe, from_target_feature_attr};
+use crate::target_features::{
+    check_target_feature_trait_unsafe, check_tied_features, from_target_feature_attr,
+};
 
 fn linkage_by_name(tcx: TyCtxt<'_>, def_id: LocalDefId, name: &str) -> Linkage {
     use rustc_middle::mir::mono::Linkage::*;
@@ -455,33 +456,8 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
         codegen_fn_attrs.inline = InlineAttr::Never;
     }
 
-    codegen_fn_attrs.optimize = attrs.iter().fold(OptimizeAttr::Default, |ia, attr| {
-        if !attr.has_name(sym::optimize) {
-            return ia;
-        }
-        if attr.is_word() {
-            tcx.dcx().emit_err(errors::ExpectedOneArgumentOptimize { span: attr.span() });
-            return ia;
-        }
-        let Some(ref items) = attr.meta_item_list() else {
-            return OptimizeAttr::Default;
-        };
-
-        let [item] = &items[..] else {
-            tcx.dcx().emit_err(errors::ExpectedOneArgumentOptimize { span: attr.span() });
-            return OptimizeAttr::Default;
-        };
-        if item.has_name(sym::size) {
-            OptimizeAttr::Size
-        } else if item.has_name(sym::speed) {
-            OptimizeAttr::Speed
-        } else if item.has_name(sym::none) {
-            OptimizeAttr::DoNotOptimize
-        } else {
-            tcx.dcx().emit_err(errors::InvalidArgumentOptimize { span: item.span() });
-            OptimizeAttr::Default
-        }
-    });
+    codegen_fn_attrs.optimize =
+        find_attr!(attrs, AttributeKind::Optimize(i, _) => *i).unwrap_or(OptimizeAttr::Default);
 
     // #73631: closures inherit `#[target_feature]` annotations
     //
@@ -615,25 +591,6 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
     codegen_fn_attrs
 }
 
-/// 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]> {
-    if !features.is_empty() {
-        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(|f| enabled != features.get(f)) {
-                return Some(tied);
-            }
-        }
-    }
-    None
-}
-
 /// Checks if the provided DefId is a method in a trait impl for a trait which has track_caller
 /// applied to the method prototype.
 fn should_inherit_track_caller(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
diff --git a/compiler/rustc_codegen_ssa/src/errors.rs b/compiler/rustc_codegen_ssa/src/errors.rs
index 5387b2a7f81..72e71b97a17 100644
--- a/compiler/rustc_codegen_ssa/src/errors.rs
+++ b/compiler/rustc_codegen_ssa/src/errors.rs
@@ -209,20 +209,6 @@ pub(crate) struct OutOfRangeInteger {
 }
 
 #[derive(Diagnostic)]
-#[diag(codegen_ssa_expected_one_argument, code = E0722)]
-pub(crate) struct ExpectedOneArgumentOptimize {
-    #[primary_span]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(codegen_ssa_invalid_argument, code = E0722)]
-pub(crate) struct InvalidArgumentOptimize {
-    #[primary_span]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
 #[diag(codegen_ssa_copy_path_buf)]
 pub(crate) struct CopyPathBuf {
     pub source_file: PathBuf,
@@ -1217,30 +1203,6 @@ pub(crate) struct ErrorCreatingImportLibrary<'a> {
     pub error: String,
 }
 
-pub struct TargetFeatureDisableOrEnable<'a> {
-    pub features: &'a [&'a str],
-    pub span: Option<Span>,
-    pub missing_features: Option<MissingFeatures>,
-}
-
-#[derive(Subdiagnostic)]
-#[help(codegen_ssa_missing_features)]
-pub 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_ssa_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
-    }
-}
-
 #[derive(Diagnostic)]
 #[diag(codegen_ssa_aix_strip_not_used)]
 pub(crate) struct AixStripNotUsed;
@@ -1283,3 +1245,68 @@ pub(crate) struct XcrunSdkPathWarning {
 #[derive(LintDiagnostic)]
 #[diag(codegen_ssa_aarch64_softfloat_neon)]
 pub(crate) struct Aarch64SoftfloatNeon;
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_unknown_ctarget_feature_prefix)]
+#[note]
+pub(crate) struct UnknownCTargetFeaturePrefix<'a> {
+    pub feature: &'a str,
+}
+
+#[derive(Subdiagnostic)]
+pub(crate) enum PossibleFeature<'a> {
+    #[help(codegen_ssa_possible_feature)]
+    Some { rust_feature: &'a str },
+    #[help(codegen_ssa_consider_filing_feature_request)]
+    None,
+}
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_unknown_ctarget_feature)]
+#[note]
+pub(crate) struct UnknownCTargetFeature<'a> {
+    pub feature: &'a str,
+    #[subdiagnostic]
+    pub rust_feature: PossibleFeature<'a>,
+}
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_unstable_ctarget_feature)]
+#[note]
+pub(crate) struct UnstableCTargetFeature<'a> {
+    pub feature: &'a str,
+}
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_forbidden_ctarget_feature)]
+#[note]
+#[note(codegen_ssa_forbidden_ctarget_feature_issue)]
+pub(crate) struct ForbiddenCTargetFeature<'a> {
+    pub feature: &'a str,
+    pub enabled: &'a str,
+    pub reason: &'a str,
+}
+
+pub struct TargetFeatureDisableOrEnable<'a> {
+    pub features: &'a [&'a str],
+    pub span: Option<Span>,
+    pub missing_features: Option<MissingFeatures>,
+}
+
+#[derive(Subdiagnostic)]
+#[help(codegen_ssa_missing_features)]
+pub 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_ssa_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
+    }
+}
diff --git a/compiler/rustc_codegen_ssa/src/target_features.rs b/compiler/rustc_codegen_ssa/src/target_features.rs
index 640d197c219..67ac619091b 100644
--- a/compiler/rustc_codegen_ssa/src/target_features.rs
+++ b/compiler/rustc_codegen_ssa/src/target_features.rs
@@ -1,5 +1,5 @@
 use rustc_attr_data_structures::InstructionSetAttr;
-use rustc_data_structures::fx::FxIndexSet;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
 use rustc_data_structures::unord::{UnordMap, UnordSet};
 use rustc_errors::Applicability;
 use rustc_hir as hir;
@@ -8,11 +8,12 @@ use rustc_hir::def_id::{DefId, LOCAL_CRATE, LocalDefId};
 use rustc_middle::middle::codegen_fn_attrs::TargetFeature;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::TyCtxt;
-use rustc_session::features::StabilityExt;
+use rustc_session::Session;
 use rustc_session::lint::builtin::AARCH64_SOFTFLOAT_NEON;
 use rustc_session::parse::feature_err;
 use rustc_span::{Span, Symbol, sym};
-use rustc_target::target_features::{self, Stability};
+use rustc_target::target_features::{self, RUSTC_SPECIFIC_FEATURES, Stability};
+use smallvec::SmallVec;
 
 use crate::errors;
 
@@ -67,7 +68,7 @@ pub(crate) fn from_target_feature_attr(
 
             // Only allow target features whose feature gates have been enabled
             // and which are permitted to be toggled.
-            if let Err(reason) = stability.is_toggle_permitted(tcx.sess) {
+            if let Err(reason) = stability.toggle_allowed() {
                 tcx.dcx().emit_err(errors::ForbiddenTargetFeatureAttr {
                     span: item.span(),
                     feature,
@@ -88,7 +89,7 @@ pub(crate) fn from_target_feature_attr(
                 let feature_sym = Symbol::intern(feature);
                 for &name in tcx.implied_target_features(feature_sym) {
                     // But ensure the ABI does not forbid enabling this.
-                    // Here we do assume that LLVM doesn't add even more implied features
+                    // Here we do assume that the backend doesn't add even more implied features
                     // we don't know about, at least no features that would have ABI effects!
                     // We skip this logic in rustdoc, where we want to allow all target features of
                     // all targets, so we can't check their ABI compatibility and anyway we are not
@@ -156,6 +157,276 @@ pub(crate) fn check_target_feature_trait_unsafe(tcx: TyCtxt<'_>, id: LocalDefId,
     }
 }
 
+/// Parse the value of `-Ctarget-feature`, also expanding implied features,
+/// and call the closure for each (expanded) Rust feature. If the list contains
+/// a syntactically invalid item (not starting with `+`/`-`), the error callback is invoked.
+fn parse_rust_feature_flag<'a>(
+    sess: &'a Session,
+    err_callback: impl Fn(&'a str),
+    mut callback: impl FnMut(
+        /* base_feature */ &'a str,
+        /* with_implied */ FxHashSet<&'a str>,
+        /* enable */ bool,
+    ),
+) {
+    // A cache for the backwards implication map.
+    let mut inverse_implied_features: Option<FxHashMap<&str, FxHashSet<&str>>> = None;
+
+    for feature in sess.opts.cg.target_feature.split(',') {
+        if let Some(base_feature) = feature.strip_prefix('+') {
+            // Skip features that are not target features, but rustc features.
+            if RUSTC_SPECIFIC_FEATURES.contains(&base_feature) {
+                return;
+            }
+
+            callback(base_feature, sess.target.implied_target_features(base_feature), true)
+        } else if let Some(base_feature) = feature.strip_prefix('-') {
+            // Skip features that are not target features, but rustc features.
+            if RUSTC_SPECIFIC_FEATURES.contains(&base_feature) {
+                return;
+            }
+
+            // If `f1` implies `f2`, then `!f2` implies `!f1` -- this is standard logical
+            // contraposition. So we have to find all the reverse implications of `base_feature` and
+            // disable them, too.
+
+            let inverse_implied_features = inverse_implied_features.get_or_insert_with(|| {
+                let mut set: FxHashMap<&str, FxHashSet<&str>> = FxHashMap::default();
+                for (f, _, is) in sess.target.rust_target_features() {
+                    for i in is.iter() {
+                        set.entry(i).or_default().insert(f);
+                    }
+                }
+                set
+            });
+
+            // Inverse implied target features have their own inverse implied target features, so we
+            // traverse the map until there are no more features to add.
+            let mut features = FxHashSet::default();
+            let mut new_features = vec![base_feature];
+            while let Some(new_feature) = new_features.pop() {
+                if features.insert(new_feature) {
+                    if let Some(implied_features) = inverse_implied_features.get(&new_feature) {
+                        new_features.extend(implied_features)
+                    }
+                }
+            }
+
+            callback(base_feature, features, false)
+        } else if !feature.is_empty() {
+            err_callback(feature)
+        }
+    }
+}
+
+/// Utility function for a codegen backend to compute `cfg(target_feature)`, or more specifically,
+/// to populate `sess.unstable_target_features` and `sess.target_features` (these are the first and
+/// 2nd component of the return value, respectively).
+///
+/// `target_base_has_feature` should check whether the given feature (a Rust feature name!) is
+/// enabled in the "base" target machine, i.e., without applying `-Ctarget-feature`.
+///
+/// We do not have to worry about RUSTC_SPECIFIC_FEATURES here, those are handled elsewhere.
+pub fn cfg_target_feature(
+    sess: &Session,
+    mut target_base_has_feature: impl FnMut(&str) -> bool,
+) -> (Vec<Symbol>, Vec<Symbol>) {
+    // Compute which of the known target features are enabled in the 'base' target machine. We only
+    // consider "supported" features; "forbidden" features are not reflected in `cfg` as of now.
+    let mut features: UnordSet<Symbol> = sess
+        .target
+        .rust_target_features()
+        .iter()
+        .filter(|(feature, _, _)| target_base_has_feature(feature))
+        .map(|(feature, _, _)| Symbol::intern(feature))
+        .collect();
+
+    // Add enabled and remove disabled features.
+    parse_rust_feature_flag(
+        sess,
+        /* err_callback */
+        |_| {
+            // Errors are already emitted in `flag_to_backend_features`; avoid duplicates.
+        },
+        |_base_feature, new_features, enabled| {
+            // Iteration order is irrelevant since this only influences an `UnordSet`.
+            #[allow(rustc::potential_query_instability)]
+            if enabled {
+                features.extend(new_features.into_iter().map(|f| Symbol::intern(f)));
+            } else {
+                // Remove `new_features` from `features`.
+                for new in new_features {
+                    features.remove(&Symbol::intern(new));
+                }
+            }
+        },
+    );
+
+    // Filter enabled features based on feature gates.
+    let f = |allow_unstable| {
+        sess.target
+            .rust_target_features()
+            .iter()
+            .filter_map(|(feature, gate, _)| {
+                // The `allow_unstable` set is used by rustc internally to determine which target
+                // features are truly available, so we want to return even perma-unstable
+                // "forbidden" features.
+                if allow_unstable
+                    || (gate.in_cfg()
+                        && (sess.is_nightly_build() || gate.requires_nightly().is_none()))
+                {
+                    Some(Symbol::intern(feature))
+                } else {
+                    None
+                }
+            })
+            .filter(|feature| features.contains(&feature))
+            .collect()
+    };
+
+    (f(true), f(false))
+}
+
+/// 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]> {
+    if !features.is_empty() {
+        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(|f| enabled != features.get(f)) {
+                return Some(tied);
+            }
+        }
+    }
+    None
+}
+
+/// Translates the `-Ctarget-feature` flag into a backend target feature list.
+///
+/// `to_backend_features` converts a Rust feature name into a list of backend feature names; this is
+/// used for diagnostic purposes only.
+///
+/// `extend_backend_features` extends the set of backend features (assumed to be in mutable state
+/// accessible by that closure) to enable/disable the given Rust feature name.
+pub fn flag_to_backend_features<'a, const N: usize>(
+    sess: &'a Session,
+    diagnostics: bool,
+    to_backend_features: impl Fn(&'a str) -> SmallVec<[&'a str; N]>,
+    mut extend_backend_features: impl FnMut(&'a str, /* enable */ bool),
+) {
+    let known_features = sess.target.rust_target_features();
+
+    // Compute implied features
+    let mut rust_features = vec![];
+    parse_rust_feature_flag(
+        sess,
+        /* err_callback */
+        |feature| {
+            if diagnostics {
+                sess.dcx().emit_warn(errors::UnknownCTargetFeaturePrefix { feature });
+            }
+        },
+        |base_feature, new_features, enable| {
+            rust_features.extend(
+                UnordSet::from(new_features).to_sorted_stable_ord().iter().map(|&&s| (enable, s)),
+            );
+            // Check feature validity.
+            if diagnostics {
+                let feature_state = known_features.iter().find(|&&(v, _, _)| v == base_feature);
+                match feature_state {
+                    None => {
+                        // This is definitely not a valid Rust feature name. Maybe it is a backend
+                        // feature name? If so, give a better error message.
+                        let rust_feature =
+                            known_features.iter().find_map(|&(rust_feature, _, _)| {
+                                let backend_features = to_backend_features(rust_feature);
+                                if backend_features.contains(&base_feature)
+                                    && !backend_features.contains(&rust_feature)
+                                {
+                                    Some(rust_feature)
+                                } else {
+                                    None
+                                }
+                            });
+                        let unknown_feature = if let Some(rust_feature) = rust_feature {
+                            errors::UnknownCTargetFeature {
+                                feature: base_feature,
+                                rust_feature: errors::PossibleFeature::Some { rust_feature },
+                            }
+                        } else {
+                            errors::UnknownCTargetFeature {
+                                feature: base_feature,
+                                rust_feature: errors::PossibleFeature::None,
+                            }
+                        };
+                        sess.dcx().emit_warn(unknown_feature);
+                    }
+                    Some((_, stability, _)) => {
+                        if let Err(reason) = stability.toggle_allowed() {
+                            sess.dcx().emit_warn(errors::ForbiddenCTargetFeature {
+                                feature: base_feature,
+                                enabled: if enable { "enabled" } else { "disabled" },
+                                reason,
+                            });
+                        } else if stability.requires_nightly().is_some() {
+                            // An unstable feature. Warn about using it. It makes little sense
+                            // to hard-error here since we just warn about fully unknown
+                            // features above.
+                            sess.dcx().emit_warn(errors::UnstableCTargetFeature {
+                                feature: base_feature,
+                            });
+                        }
+                    }
+                }
+            }
+        },
+    );
+
+    if diagnostics {
+        // FIXME(nagisa): figure out how to not allocate a full hashmap here.
+        if let Some(f) = check_tied_features(
+            sess,
+            &FxHashMap::from_iter(rust_features.iter().map(|&(enable, feature)| (feature, enable))),
+        ) {
+            sess.dcx().emit_err(errors::TargetFeatureDisableOrEnable {
+                features: f,
+                span: None,
+                missing_features: None,
+            });
+        }
+    }
+
+    // Add this to the backend features.
+    for (enable, feature) in rust_features {
+        extend_backend_features(feature, enable);
+    }
+}
+
+/// Computes the backend target features to be added to account for retpoline flags.
+/// Used by both LLVM and GCC since their target features are, conveniently, the same.
+pub fn retpoline_features_by_flags(sess: &Session, features: &mut Vec<String>) {
+    // -Zretpoline without -Zretpoline-external-thunk enables
+    // retpoline-indirect-branches and retpoline-indirect-calls target features
+    let unstable_opts = &sess.opts.unstable_opts;
+    if unstable_opts.retpoline && !unstable_opts.retpoline_external_thunk {
+        features.push("+retpoline-indirect-branches".into());
+        features.push("+retpoline-indirect-calls".into());
+    }
+    // -Zretpoline-external-thunk (maybe, with -Zretpoline too) enables
+    // retpoline-external-thunk, retpoline-indirect-branches and
+    // retpoline-indirect-calls target features
+    if unstable_opts.retpoline_external_thunk {
+        features.push("+retpoline-external-thunk".into());
+        features.push("+retpoline-indirect-branches".into());
+        features.push("+retpoline-indirect-calls".into());
+    }
+}
+
 pub(crate) fn provide(providers: &mut Providers) {
     *providers = Providers {
         rust_target_features: |tcx, cnum| {
@@ -182,7 +453,8 @@ pub(crate) fn provide(providers: &mut Providers) {
                                     Stability::Unstable { .. } | Stability::Forbidden { .. },
                                 )
                                 | (Stability::Forbidden { .. }, Stability::Forbidden { .. }) => {
-                                    // The stability in the entry is at least as good as the new one, just keep it.
+                                    // The stability in the entry is at least as good as the new
+                                    // one, just keep it.
                                 }
                                 _ => {
                                     // Overwrite stabilite.
diff --git a/compiler/rustc_const_eval/src/check_consts/check.rs b/compiler/rustc_const_eval/src/check_consts/check.rs
index 4f252f3ccd4..576b174369d 100644
--- a/compiler/rustc_const_eval/src/check_consts/check.rs
+++ b/compiler/rustc_const_eval/src/check_consts/check.rs
@@ -463,12 +463,6 @@ impl<'mir, 'tcx> Checker<'mir, 'tcx> {
         );
     }
 
-    fn crate_inject_span(&self) -> Option<Span> {
-        self.tcx.hir_crate_items(()).definitions().next().and_then(|id| {
-            self.tcx.crate_level_attribute_injection_span(self.tcx.local_def_id_to_hir_id(id))
-        })
-    }
-
     /// Check the const stability of the given item (fn or trait).
     fn check_callee_stability(&mut self, def_id: DefId) {
         match self.tcx.lookup_const_stability(def_id) {
@@ -543,7 +537,6 @@ impl<'mir, 'tcx> Checker<'mir, 'tcx> {
                         feature,
                         feature_enabled,
                         safe_to_expose_on_stable: callee_safe_to_expose_on_stable,
-                        suggestion_span: self.crate_inject_span(),
                         is_function_call: self.tcx.def_kind(def_id) != DefKind::Trait,
                     });
                 }
@@ -919,7 +912,6 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                                 name: intrinsic.name,
                                 feature,
                                 const_stable_indirect: is_const_stable,
-                                suggestion: self.crate_inject_span(),
                             });
                         }
                         Some(attrs::ConstStability {
diff --git a/compiler/rustc_const_eval/src/check_consts/ops.rs b/compiler/rustc_const_eval/src/check_consts/ops.rs
index 9c30dbff99e..887275e7294 100644
--- a/compiler/rustc_const_eval/src/check_consts/ops.rs
+++ b/compiler/rustc_const_eval/src/check_consts/ops.rs
@@ -1,8 +1,8 @@
 //! Concrete error types for all operations which may be invalid in a certain const context.
 
 use hir::{ConstContext, LangItem};
+use rustc_errors::Diag;
 use rustc_errors::codes::*;
-use rustc_errors::{Applicability, Diag};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::TyCtxtInferExt;
@@ -384,7 +384,6 @@ pub(crate) struct CallUnstable {
     /// expose on stable.
     pub feature_enabled: bool,
     pub safe_to_expose_on_stable: bool,
-    pub suggestion_span: Option<Span>,
     /// true if `def_id` is the function we are calling, false if `def_id` is an unstable trait.
     pub is_function_call: bool,
 }
@@ -412,20 +411,7 @@ impl<'tcx> NonConstOp<'tcx> for CallUnstable {
                 def_path: ccx.tcx.def_path_str(self.def_id),
             })
         };
-        // FIXME: make this translatable
-        let msg = format!("add `#![feature({})]` to the crate attributes to enable", self.feature);
-        #[allow(rustc::untranslatable_diagnostic)]
-        if let Some(span) = self.suggestion_span {
-            err.span_suggestion_verbose(
-                span,
-                msg,
-                format!("#![feature({})]\n", self.feature),
-                Applicability::MachineApplicable,
-            );
-        } else {
-            err.help(msg);
-        }
-
+        ccx.tcx.disabled_nightly_features(&mut err, [(String::new(), self.feature)]);
         err
     }
 }
@@ -452,7 +438,6 @@ pub(crate) struct IntrinsicUnstable {
     pub name: Symbol,
     pub feature: Symbol,
     pub const_stable_indirect: bool,
-    pub suggestion: Option<Span>,
 }
 
 impl<'tcx> NonConstOp<'tcx> for IntrinsicUnstable {
@@ -472,8 +457,7 @@ impl<'tcx> NonConstOp<'tcx> for IntrinsicUnstable {
             span,
             name: self.name,
             feature: self.feature,
-            suggestion: self.suggestion,
-            help: self.suggestion.is_none(),
+            suggestion: ccx.tcx.crate_level_attribute_injection_span(),
         })
     }
 }
diff --git a/compiler/rustc_const_eval/src/errors.rs b/compiler/rustc_const_eval/src/errors.rs
index 037cbf777e7..69c71aef9f3 100644
--- a/compiler/rustc_const_eval/src/errors.rs
+++ b/compiler/rustc_const_eval/src/errors.rs
@@ -136,9 +136,7 @@ pub(crate) struct UnstableIntrinsic {
         code = "#![feature({feature})]\n",
         applicability = "machine-applicable"
     )]
-    pub suggestion: Option<Span>,
-    #[help(const_eval_unstable_intrinsic_suggestion)]
-    pub help: bool,
+    pub suggestion: Span,
 }
 
 #[derive(Diagnostic)]
diff --git a/compiler/rustc_driver_impl/src/pretty.rs b/compiler/rustc_driver_impl/src/pretty.rs
index ec77043cd12..688307a941f 100644
--- a/compiler/rustc_driver_impl/src/pretty.rs
+++ b/compiler/rustc_driver_impl/src/pretty.rs
@@ -292,7 +292,11 @@ pub fn print<'tcx>(sess: &Session, ppm: PpMode, ex: PrintExtra<'tcx>) {
         }
         HirTree => {
             debug!("pretty printing HIR tree");
-            format!("{:#?}", ex.tcx().hir_crate(()))
+            ex.tcx()
+                .hir_crate_items(())
+                .owners()
+                .map(|owner| format!("{:#?} => {:#?}\n", owner, ex.tcx().hir_owner_nodes(owner)))
+                .collect()
         }
         Mir => {
             let mut out = Vec::new();
diff --git a/compiler/rustc_error_codes/src/error_codes/E0722.md b/compiler/rustc_error_codes/src/error_codes/E0722.md
index 570717a92bd..1799458d46c 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0722.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0722.md
@@ -1,8 +1,14 @@
+#### Note: this error code is no longer emitted by the compiler
+
+This is because it was too specific to the `optimize` attribute.
+Similar diagnostics occur for other attributes too.
+The example here will now emit `E0539`
+
 The `optimize` attribute was malformed.
 
 Erroneous code example:
 
-```compile_fail,E0722
+```compile_fail,E0539
 #![feature(optimize_attribute)]
 
 #[optimize(something)] // error: invalid argument
diff --git a/compiler/rustc_error_codes/src/lib.rs b/compiler/rustc_error_codes/src/lib.rs
index 6f5e4829802..22cc1e894da 100644
--- a/compiler/rustc_error_codes/src/lib.rs
+++ b/compiler/rustc_error_codes/src/lib.rs
@@ -686,6 +686,7 @@ E0805: 0805,
 //  E0707, // multiple elided lifetimes used in arguments of `async fn`
 //  E0709, // multiple different lifetimes used in arguments of `async fn`
 //  E0721, // `await` keyword
+//  E0722, // replaced with a generic attribute input check
 //  E0723, // unstable feature in `const` context
 //  E0738, // Removed; errored on `#[track_caller] fn`s in `extern "Rust" { ... }`.
 //  E0744, // merged into E0728
diff --git a/compiler/rustc_hir_analysis/src/check/mod.rs b/compiler/rustc_hir_analysis/src/check/mod.rs
index ca24d5a6424..bf2d4f662ef 100644
--- a/compiler/rustc_hir_analysis/src/check/mod.rs
+++ b/compiler/rustc_hir_analysis/src/check/mod.rs
@@ -311,9 +311,7 @@ fn default_body_is_unstable(
         reason: reason_str,
     });
 
-    let inject_span = item_did
-        .as_local()
-        .and_then(|id| tcx.crate_level_attribute_injection_span(tcx.local_def_id_to_hir_id(id)));
+    let inject_span = item_did.is_local().then(|| tcx.crate_level_attribute_injection_span());
     rustc_session::parse::add_feature_diagnostics_for_issue(
         &mut err,
         &tcx.sess,
diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
index 20d0e87b7a7..13f95024e5a 100644
--- a/compiler/rustc_hir_analysis/src/check/wfcheck.rs
+++ b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
@@ -1064,7 +1064,7 @@ fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) -> Result<(),
                     Ok(..) => Some(vec![(adt_const_params_feature_string, sym::adt_const_params)]),
                 };
                 if let Some(features) = may_suggest_feature {
-                    tcx.disabled_nightly_features(&mut diag, Some(param.hir_id), features);
+                    tcx.disabled_nightly_features(&mut diag, features);
                 }
 
                 Err(diag.emit())
diff --git a/compiler/rustc_hir_typeck/src/errors.rs b/compiler/rustc_hir_typeck/src/errors.rs
index abb8cdc1cdf..5f59b3ad96e 100644
--- a/compiler/rustc_hir_typeck/src/errors.rs
+++ b/compiler/rustc_hir_typeck/src/errors.rs
@@ -30,8 +30,6 @@ pub(crate) struct BaseExpressionDoubleDot {
     )]
     pub default_field_values_suggestion: Option<Span>,
     #[subdiagnostic]
-    pub default_field_values_help: Option<BaseExpressionDoubleDotEnableDefaultFieldValues>,
-    #[subdiagnostic]
     pub add_expr: Option<BaseExpressionDoubleDotAddExpr>,
     #[subdiagnostic]
     pub remove_dots: Option<BaseExpressionDoubleDotRemove>,
@@ -61,10 +59,6 @@ pub(crate) struct BaseExpressionDoubleDotAddExpr {
     pub span: Span,
 }
 
-#[derive(Subdiagnostic)]
-#[help(hir_typeck_base_expression_double_dot_enable_default_field_values)]
-pub(crate) struct BaseExpressionDoubleDotEnableDefaultFieldValues;
-
 #[derive(Diagnostic)]
 #[diag(hir_typeck_field_multiply_specified_in_initializer, code = E0062)]
 pub(crate) struct FieldMultiplySpecifiedInInitializer {
diff --git a/compiler/rustc_hir_typeck/src/expr.rs b/compiler/rustc_hir_typeck/src/expr.rs
index 55c39d960e7..eca9c5faa32 100644
--- a/compiler/rustc_hir_typeck/src/expr.rs
+++ b/compiler/rustc_hir_typeck/src/expr.rs
@@ -43,10 +43,9 @@ use crate::Expectation::{self, ExpectCastableToType, ExpectHasType, NoExpectatio
 use crate::coercion::{CoerceMany, DynamicCoerceMany};
 use crate::errors::{
     AddressOfTemporaryTaken, BaseExpressionDoubleDot, BaseExpressionDoubleDotAddExpr,
-    BaseExpressionDoubleDotEnableDefaultFieldValues, BaseExpressionDoubleDotRemove,
-    CantDereference, FieldMultiplySpecifiedInInitializer, FunctionalRecordUpdateOnNonStruct,
-    HelpUseLatestEdition, NakedAsmOutsideNakedFn, NoFieldOnType, NoFieldOnVariant,
-    ReturnLikeStatementKind, ReturnStmtOutsideOfFnBody, StructExprNonExhaustive,
+    BaseExpressionDoubleDotRemove, CantDereference, FieldMultiplySpecifiedInInitializer,
+    FunctionalRecordUpdateOnNonStruct, HelpUseLatestEdition, NakedAsmOutsideNakedFn, NoFieldOnType,
+    NoFieldOnVariant, ReturnLikeStatementKind, ReturnStmtOutsideOfFnBody, StructExprNonExhaustive,
     TypeMismatchFruTypo, YieldExprOutsideOfCoroutine,
 };
 use crate::{
@@ -2158,7 +2157,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 }
             }
             if !self.tcx.features().default_field_values() {
-                let sugg = self.tcx.crate_level_attribute_injection_span(expr.hir_id);
+                let sugg = self.tcx.crate_level_attribute_injection_span();
                 self.dcx().emit_err(BaseExpressionDoubleDot {
                     span: span.shrink_to_hi(),
                     // We only mention enabling the feature if this is a nightly rustc *and* the
@@ -2166,18 +2165,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     default_field_values_suggestion: if self.tcx.sess.is_nightly_build()
                         && missing_mandatory_fields.is_empty()
                         && !missing_optional_fields.is_empty()
-                        && sugg.is_some()
                     {
-                        sugg
-                    } else {
-                        None
-                    },
-                    default_field_values_help: if self.tcx.sess.is_nightly_build()
-                        && missing_mandatory_fields.is_empty()
-                        && !missing_optional_fields.is_empty()
-                        && sugg.is_none()
-                    {
-                        Some(BaseExpressionDoubleDotEnableDefaultFieldValues)
+                        Some(sugg)
                     } else {
                         None
                     },
diff --git a/compiler/rustc_hir_typeck/src/method/probe.rs b/compiler/rustc_hir_typeck/src/method/probe.rs
index a3fdf200c8e..589dbb53116 100644
--- a/compiler/rustc_hir_typeck/src/method/probe.rs
+++ b/compiler/rustc_hir_typeck/src/method/probe.rs
@@ -1727,7 +1727,6 @@ impl<'tcx> Pick<'tcx> {
             }
             tcx.disabled_nightly_features(
                 lint,
-                Some(scope_expr_id),
                 self.unstable_candidates.iter().map(|(candidate, feature)| {
                     (format!(" `{}`", tcx.def_path_str(candidate.item.def_id)), *feature)
                 }),
diff --git a/compiler/rustc_interface/src/passes.rs b/compiler/rustc_interface/src/passes.rs
index 02d1ebdb31a..70ae9147fb1 100644
--- a/compiler/rustc_interface/src/passes.rs
+++ b/compiler/rustc_interface/src/passes.rs
@@ -1011,8 +1011,8 @@ fn run_required_analyses(tcx: TyCtxt<'_>) {
 
     // Prefetch this to prevent multiple threads from blocking on it later.
     // This is needed since the `hir_id_validator::check_crate` call above is not guaranteed
-    // to use `hir_crate`.
-    tcx.ensure_done().hir_crate(());
+    // to use `hir_crate_items`.
+    tcx.ensure_done().hir_crate_items(());
 
     let sess = tcx.sess;
     sess.time("misc_checking_1", || {
diff --git a/compiler/rustc_lint/src/expect.rs b/compiler/rustc_lint/src/expect.rs
index 4c2b82a9a23..481e116d06e 100644
--- a/compiler/rustc_lint/src/expect.rs
+++ b/compiler/rustc_lint/src/expect.rs
@@ -1,5 +1,4 @@
 use rustc_data_structures::fx::FxHashSet;
-use rustc_hir::CRATE_OWNER_ID;
 use rustc_middle::lint::LintExpectation;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::TyCtxt;
@@ -18,7 +17,7 @@ fn lint_expectations(tcx: TyCtxt<'_>, (): ()) -> Vec<(LintExpectationId, LintExp
 
     let mut expectations = Vec::new();
 
-    for owner in std::iter::once(CRATE_OWNER_ID).chain(krate.owners()) {
+    for owner in krate.owners() {
         let lints = tcx.shallow_lint_levels_on(owner);
         expectations.extend_from_slice(&lints.expectations);
     }
diff --git a/compiler/rustc_middle/src/hir/map.rs b/compiler/rustc_middle/src/hir/map.rs
index e5e1ae508ed..03bb97095a4 100644
--- a/compiler/rustc_middle/src/hir/map.rs
+++ b/compiler/rustc_middle/src/hir/map.rs
@@ -328,8 +328,7 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 
     /// Returns an iterator of the `DefId`s for all body-owners in this
-    /// crate. If you would prefer to iterate over the bodies
-    /// themselves, you can do `self.hir_crate(()).body_ids.iter()`.
+    /// crate.
     #[inline]
     pub fn hir_body_owners(self) -> impl Iterator<Item = LocalDefId> {
         self.hir_crate_items(()).body_owners.iter().copied()
@@ -396,12 +395,11 @@ impl<'tcx> TyCtxt<'tcx> {
     where
         V: Visitor<'tcx>,
     {
-        let krate = self.hir_crate(());
-        for info in krate.owners.iter() {
-            if let MaybeOwner::Owner(info) = info {
-                for attrs in info.attrs.map.values() {
-                    walk_list!(visitor, visit_attribute, *attrs);
-                }
+        let krate = self.hir_crate_items(());
+        for owner in krate.owners() {
+            let attrs = self.hir_attr_map(owner);
+            for attrs in attrs.map.values() {
+                walk_list!(visitor, visit_attribute, *attrs);
             }
         }
         V::Result::output()
@@ -1225,6 +1223,7 @@ pub(super) fn hir_module_items(tcx: TyCtxt<'_>, module_id: LocalModDefId) -> Mod
         ..
     } = collector;
     ModuleItems {
+        add_root: false,
         submodules: submodules.into_boxed_slice(),
         free_items: items.into_boxed_slice(),
         trait_items: trait_items.into_boxed_slice(),
@@ -1260,6 +1259,7 @@ pub(crate) fn hir_crate_items(tcx: TyCtxt<'_>, _: ()) -> ModuleItems {
     } = collector;
 
     ModuleItems {
+        add_root: true,
         submodules: submodules.into_boxed_slice(),
         free_items: items.into_boxed_slice(),
         trait_items: trait_items.into_boxed_slice(),
diff --git a/compiler/rustc_middle/src/hir/mod.rs b/compiler/rustc_middle/src/hir/mod.rs
index 9f79ed4b5a5..d7a8dce0536 100644
--- a/compiler/rustc_middle/src/hir/mod.rs
+++ b/compiler/rustc_middle/src/hir/mod.rs
@@ -24,6 +24,9 @@ use crate::ty::{EarlyBinder, ImplSubject, TyCtxt};
 /// bodies. The Ids are in visitor order. This is used to partition a pass between modules.
 #[derive(Debug, HashStable, Encodable, Decodable)]
 pub struct ModuleItems {
+    /// Whether this represents the whole crate, in which case we need to add `CRATE_OWNER_ID` to
+    /// the iterators if we want to account for the crate root.
+    add_root: bool,
     submodules: Box<[OwnerId]>,
     free_items: Box<[ItemId]>,
     trait_items: Box<[TraitItemId]>,
@@ -66,9 +69,10 @@ impl ModuleItems {
     }
 
     pub fn owners(&self) -> impl Iterator<Item = OwnerId> {
-        self.free_items
-            .iter()
-            .map(|id| id.owner_id)
+        self.add_root
+            .then_some(CRATE_OWNER_ID)
+            .into_iter()
+            .chain(self.free_items.iter().map(|id| id.owner_id))
             .chain(self.trait_items.iter().map(|id| id.owner_id))
             .chain(self.impl_items.iter().map(|id| id.owner_id))
             .chain(self.foreign_items.iter().map(|id| id.owner_id))
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index f1395c242f2..82825b9b38e 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -2113,7 +2113,7 @@ impl<'tcx> TyCtxt<'tcx> {
     ) -> &'tcx rustc_hir::def_path_hash_map::DefPathHashMap {
         // Create a dependency to the crate to be sure we re-execute this when the amount of
         // definitions change.
-        self.ensure_ok().hir_crate(());
+        self.ensure_ok().hir_crate_items(());
         // Freeze definitions once we start iterating on them, to prevent adding new ones
         // while iterating. If some query needs to add definitions, it should be `ensure`d above.
         self.untracked.definitions.freeze().def_path_hash_to_def_index_map()
@@ -3160,42 +3160,33 @@ impl<'tcx> TyCtxt<'tcx> {
         lint_level(self.sess, lint, level, Some(span.into()), decorate);
     }
 
-    /// Find the crate root and the appropriate span where `use` and outer attributes can be
-    /// inserted at.
-    pub fn crate_level_attribute_injection_span(self, hir_id: HirId) -> Option<Span> {
-        for (_hir_id, node) in self.hir_parent_iter(hir_id) {
-            if let hir::Node::Crate(m) = node {
-                return Some(m.spans.inject_use_span.shrink_to_lo());
-            }
-        }
-        None
+    /// Find the appropriate span where `use` and outer attributes can be inserted at.
+    pub fn crate_level_attribute_injection_span(self) -> Span {
+        let node = self.hir_node(hir::CRATE_HIR_ID);
+        let hir::Node::Crate(m) = node else { bug!() };
+        m.spans.inject_use_span.shrink_to_lo()
     }
 
     pub fn disabled_nightly_features<E: rustc_errors::EmissionGuarantee>(
         self,
         diag: &mut Diag<'_, E>,
-        hir_id: Option<HirId>,
         features: impl IntoIterator<Item = (String, Symbol)>,
     ) {
         if !self.sess.is_nightly_build() {
             return;
         }
 
-        let span = hir_id.and_then(|id| self.crate_level_attribute_injection_span(id));
+        let span = self.crate_level_attribute_injection_span();
         for (desc, feature) in features {
             // FIXME: make this string translatable
             let msg =
                 format!("add `#![feature({feature})]` to the crate attributes to enable{desc}");
-            if let Some(span) = span {
-                diag.span_suggestion_verbose(
-                    span,
-                    msg,
-                    format!("#![feature({feature})]\n"),
-                    Applicability::MaybeIncorrect,
-                );
-            } else {
-                diag.help(msg);
-            }
+            diag.span_suggestion_verbose(
+                span,
+                msg,
+                format!("#![feature({feature})]\n"),
+                Applicability::MaybeIncorrect,
+            );
         }
     }
 
diff --git a/compiler/rustc_parse/src/validate_attr.rs b/compiler/rustc_parse/src/validate_attr.rs
index a12215a44f9..646e996ff30 100644
--- a/compiler/rustc_parse/src/validate_attr.rs
+++ b/compiler/rustc_parse/src/validate_attr.rs
@@ -291,6 +291,7 @@ fn emit_malformed_attribute(
             | sym::repr
             | sym::align
             | sym::deprecated
+            | sym::optimize
     ) {
         return;
     }
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index 50d6c5d9764..a5d2ad4dc20 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -128,6 +128,9 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 Attribute::Parsed(AttributeKind::Inline(kind, attr_span)) => {
                     self.check_inline(hir_id, *attr_span, span, kind, target)
                 }
+                Attribute::Parsed(AttributeKind::Optimize(_, attr_span)) => {
+                    self.check_optimize(hir_id, *attr_span, span, target)
+                }
                 Attribute::Parsed(AttributeKind::AllowInternalUnstable(syms)) => self
                     .check_allow_internal_unstable(
                         hir_id,
@@ -167,7 +170,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                             self.check_diagnostic_on_unimplemented(attr.span(), hir_id, target)
                         }
                         [sym::coverage, ..] => self.check_coverage(attr, span, target),
-                        [sym::optimize, ..] => self.check_optimize(hir_id, attr, span, target),
                         [sym::no_sanitize, ..] => {
                             self.check_no_sanitize(attr, span, target)
                         }
@@ -529,7 +531,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
 
     /// Checks that `#[optimize(..)]` is applied to a function/closure/method,
     /// or to an impl block or module.
-    fn check_optimize(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) {
+    fn check_optimize(&self, hir_id: HirId, attr_span: Span, span: Span, target: Target) {
         let is_valid = matches!(
             target,
             Target::Fn
@@ -538,7 +540,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         );
         if !is_valid {
             self.dcx().emit_err(errors::OptimizeInvalidTarget {
-                attr_span: attr.span(),
+                attr_span,
                 defn_span: span,
                 on_crate: hir_id == CRATE_HIR_ID,
             });
diff --git a/compiler/rustc_session/messages.ftl b/compiler/rustc_session/messages.ftl
index 61953614c77..528c52eace7 100644
--- a/compiler/rustc_session/messages.ftl
+++ b/compiler/rustc_session/messages.ftl
@@ -40,11 +40,6 @@ session_file_is_not_writeable = output file {$file} is not writeable -- check it
 
 session_file_write_fail = failed to write `{$path}` due to error `{$err}`
 
-session_forbidden_ctarget_feature =
-    target feature `{$feature}` cannot be {$enabled} with `-Ctarget-feature`: {$reason}
-    .note = this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-session_forbidden_ctarget_feature_issue = for more information, see issue #116344 <https://github.com/rust-lang/rust/issues/116344>
-
 session_function_return_requires_x86_or_x86_64 = `-Zfunction-return` (except `keep`) is only supported on x86 and x86_64
 
 session_function_return_thunk_extern_requires_non_large_code_model = `-Zfunction-return=thunk-extern` is only supported on non-large code models
@@ -137,9 +132,6 @@ session_target_stack_protector_not_supported = `-Z stack-protector={$stack_prote
 session_unleashed_feature_help_named = skipping check for `{$gate}` feature
 session_unleashed_feature_help_unnamed = skipping check that does not even have a feature gate
 
-session_unstable_ctarget_feature =
-    unstable feature specified for `-Ctarget-feature`: `{$feature}`
-    .note = this feature is not stably supported; its behavior can change in the future
 session_unstable_virtual_function_elimination = `-Zvirtual-function-elimination` requires `-Clto`
 
 session_unsupported_crate_type_for_target =
diff --git a/compiler/rustc_session/src/errors.rs b/compiler/rustc_session/src/errors.rs
index 9c591dcf619..bf95014843d 100644
--- a/compiler/rustc_session/src/errors.rs
+++ b/compiler/rustc_session/src/errors.rs
@@ -501,20 +501,3 @@ pub(crate) struct SoftFloatIgnored;
 #[note]
 #[note(session_soft_float_deprecated_issue)]
 pub(crate) struct SoftFloatDeprecated;
-
-#[derive(Diagnostic)]
-#[diag(session_forbidden_ctarget_feature)]
-#[note]
-#[note(session_forbidden_ctarget_feature_issue)]
-pub(crate) struct ForbiddenCTargetFeature<'a> {
-    pub feature: &'a str,
-    pub enabled: &'a str,
-    pub reason: &'a str,
-}
-
-#[derive(Diagnostic)]
-#[diag(session_unstable_ctarget_feature)]
-#[note]
-pub(crate) struct UnstableCTargetFeature<'a> {
-    pub feature: &'a str,
-}
diff --git a/compiler/rustc_session/src/features.rs b/compiler/rustc_session/src/features.rs
deleted file mode 100644
index 70a088a236f..00000000000
--- a/compiler/rustc_session/src/features.rs
+++ /dev/null
@@ -1,59 +0,0 @@
-use rustc_target::target_features::Stability;
-
-use crate::Session;
-use crate::errors::{ForbiddenCTargetFeature, UnstableCTargetFeature};
-
-pub trait StabilityExt {
-    /// Returns whether the feature may be toggled via `#[target_feature]` or `-Ctarget-feature`.
-    /// Otherwise, some features also may only be enabled by flag (target modifier).
-    /// (It might still be nightly-only even if this returns `true`, so make sure to also check
-    /// `requires_nightly`.)
-    fn is_toggle_permitted(&self, sess: &Session) -> Result<(), &'static str>;
-
-    /// Check that feature is correctly enabled/disabled by command line flag (emits warnings)
-    fn verify_feature_enabled_by_flag(&self, sess: &Session, enable: bool, feature: &str);
-}
-
-impl StabilityExt for Stability {
-    fn is_toggle_permitted(&self, sess: &Session) -> Result<(), &'static str> {
-        match self {
-            Stability::Forbidden { reason } => Err(reason),
-            Stability::TargetModifierOnly { reason, flag } => {
-                if !sess.opts.target_feature_flag_enabled(*flag) { Err(reason) } else { Ok(()) }
-            }
-            _ => Ok(()),
-        }
-    }
-    fn verify_feature_enabled_by_flag(&self, sess: &Session, enable: bool, feature: &str) {
-        if let Err(reason) = self.is_toggle_permitted(sess) {
-            sess.dcx().emit_warn(ForbiddenCTargetFeature {
-                feature,
-                enabled: if enable { "enabled" } else { "disabled" },
-                reason,
-            });
-        } else if self.requires_nightly().is_some() {
-            // An unstable feature. Warn about using it. It makes little sense
-            // to hard-error here since we just warn about fully unknown
-            // features above.
-            sess.dcx().emit_warn(UnstableCTargetFeature { feature });
-        }
-    }
-}
-
-pub fn retpoline_features_by_flags(sess: &Session, features: &mut Vec<&str>) {
-    // -Zretpoline without -Zretpoline-external-thunk enables
-    // retpoline-indirect-branches and retpoline-indirect-calls target features
-    let unstable_opts = &sess.opts.unstable_opts;
-    if unstable_opts.retpoline && !unstable_opts.retpoline_external_thunk {
-        features.push("+retpoline-indirect-branches");
-        features.push("+retpoline-indirect-calls");
-    }
-    // -Zretpoline-external-thunk (maybe, with -Zretpoline too) enables
-    // retpoline-external-thunk, retpoline-indirect-branches and
-    // retpoline-indirect-calls target features
-    if unstable_opts.retpoline_external_thunk {
-        features.push("+retpoline-external-thunk");
-        features.push("+retpoline-indirect-branches");
-        features.push("+retpoline-indirect-calls");
-    }
-}
diff --git a/compiler/rustc_session/src/lib.rs b/compiler/rustc_session/src/lib.rs
index 4added19e56..5e5872ee068 100644
--- a/compiler/rustc_session/src/lib.rs
+++ b/compiler/rustc_session/src/lib.rs
@@ -29,7 +29,6 @@ pub use session::*;
 pub mod output;
 
 pub use getopts;
-pub mod features;
 
 rustc_fluent_macro::fluent_messages! { "../messages.ftl" }
 
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 31b4237d3b2..7fef942525b 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -290,14 +290,6 @@ macro_rules! top_level_options {
                 mods.sort_by(|a, b| a.opt.cmp(&b.opt));
                 mods
             }
-
-            pub fn target_feature_flag_enabled(&self, flag: &str) -> bool {
-                match flag {
-                    "retpoline" => self.unstable_opts.retpoline,
-                    "retpoline-external-thunk" => self.unstable_opts.retpoline_external_thunk,
-                    _ => false,
-                }
-            }
         }
     );
 }
diff --git a/compiler/rustc_target/src/target_features.rs b/compiler/rustc_target/src/target_features.rs
index a1eac1fba25..3eea1e070a6 100644
--- a/compiler/rustc_target/src/target_features.rs
+++ b/compiler/rustc_target/src/target_features.rs
@@ -11,11 +11,6 @@ use crate::spec::{FloatAbi, RustcAbi, Target};
 /// These exist globally and are not in the target-specific lists below.
 pub const RUSTC_SPECIFIC_FEATURES: &[&str] = &["crt-static"];
 
-/// Features that require special handling when passing to LLVM:
-/// these are target-specific (i.e., must also be listed in the target-specific list below)
-/// but do not correspond to an LLVM target feature.
-pub const RUSTC_SPECIAL_FEATURES: &[&str] = &["backchain"];
-
 /// Stability information for target features.
 #[derive(Debug, Copy, Clone)]
 pub enum Stability {
@@ -34,9 +29,6 @@ pub enum Stability {
     /// particular for features are actually ABI configuration flags (not all targets are as nice as
     /// RISC-V and have an explicit way to set the ABI separate from target features).
     Forbidden { reason: &'static str },
-    /// This feature can not be set via `-Ctarget-feature` or `#[target_feature]`, it can only be set
-    /// by target modifier flag. Target modifier flags are tracked to be consistent in linked modules.
-    TargetModifierOnly { reason: &'static str, flag: &'static str },
 }
 use Stability::*;
 
@@ -52,7 +44,6 @@ impl<CTX> HashStable<CTX> for Stability {
             Stability::Forbidden { reason } => {
                 reason.hash_stable(hcx, hasher);
             }
-            Stability::TargetModifierOnly { .. } => {}
         }
     }
 }
@@ -62,7 +53,7 @@ impl Stability {
     /// (It might still be nightly-only even if this returns `true`, so make sure to also check
     /// `requires_nightly`.)
     pub fn in_cfg(&self) -> bool {
-        !matches!(self, Stability::Forbidden { .. })
+        matches!(self, Stability::Stable | Stability::Unstable { .. })
     }
 
     /// Returns the nightly feature that is required to toggle this target feature via
@@ -78,7 +69,16 @@ impl Stability {
             Stability::Unstable(nightly_feature) => Some(nightly_feature),
             Stability::Stable { .. } => None,
             Stability::Forbidden { .. } => panic!("forbidden features should not reach this far"),
-            Stability::TargetModifierOnly { .. } => None,
+        }
+    }
+
+    /// Returns whether the feature may be toggled via `#[target_feature]` or `-Ctarget-feature`.
+    /// (It might still be nightly-only even if this returns `true`, so make sure to also check
+    /// `requires_nightly`.)
+    pub fn toggle_allowed(&self) -> Result<(), &'static str> {
+        match self {
+            Stability::Unstable(_) | Stability::Stable { .. } => Ok(()),
+            Stability::Forbidden { reason } => Err(reason),
         }
     }
 }
@@ -270,12 +270,7 @@ static AARCH64_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     ("rcpc3", Unstable(sym::aarch64_unstable_target_feature), &["rcpc2"]),
     // FEAT_RDM
     ("rdm", Stable, &["neon"]),
-    // This is needed for inline assembly, but shouldn't be stabilized as-is
-    // since it should be enabled globally using -Zfixed-x18, not
-    // #[target_feature].
-    // Note that cfg(target_feature = "reserve-x18") is currently not set for
-    // targets that reserve x18 by default.
-    ("reserve-x18", Unstable(sym::aarch64_unstable_target_feature), &[]),
+    ("reserve-x18", Forbidden { reason: "use `-Zfixed-x18` compiler flag instead" }, &[]),
     // FEAT_SB
     ("sb", Stable, &[]),
     // FEAT_SHA1 & FEAT_SHA256
@@ -450,26 +445,17 @@ static X86_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     ("rdseed", Stable, &[]),
     (
         "retpoline-external-thunk",
-        Stability::TargetModifierOnly {
-            reason: "use `retpoline-external-thunk` target modifier flag instead",
-            flag: "retpoline-external-thunk",
-        },
+        Stability::Forbidden { reason: "use `-Zretpoline-external-thunk` compiler flag instead" },
         &[],
     ),
     (
         "retpoline-indirect-branches",
-        Stability::TargetModifierOnly {
-            reason: "use `retpoline` target modifier flag instead",
-            flag: "retpoline",
-        },
+        Stability::Forbidden { reason: "use `-Zretpoline` compiler flag instead" },
         &[],
     ),
     (
         "retpoline-indirect-calls",
-        Stability::TargetModifierOnly {
-            reason: "use `retpoline` target modifier flag instead",
-            flag: "retpoline",
-        },
+        Stability::Forbidden { reason: "use `-Zretpoline` compiler flag instead" },
         &[],
     ),
     ("rtm", Unstable(sym::rtm_target_feature), &[]),
@@ -732,6 +718,7 @@ 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), &[]),
     ("concurrent-functions", Unstable(sym::s390x_target_feature), &[]),
     ("deflate-conversion", Unstable(sym::s390x_target_feature), &[]),
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
index ee5a5b247ce..6d07ae021ae 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
@@ -3575,11 +3575,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             }
             ObligationCauseCode::TrivialBound => {
                 err.help("see issue #48214");
-                tcx.disabled_nightly_features(
-                    err,
-                    Some(tcx.local_def_id_to_hir_id(body_id)),
-                    [(String::new(), sym::trivial_bounds)],
-                );
+                tcx.disabled_nightly_features(err, [(String::new(), sym::trivial_bounds)]);
             }
             ObligationCauseCode::OpaqueReturnType(expr_info) => {
                 let (expr_ty, expr) = if let Some((expr_ty, hir_id)) = expr_info {