move cfg(target_feature) computation into shared place

RalfJung · RalfJung · commit 75d8b1e7a123 · 2025-06-13T23:46:08.000+02:00
diff --git a/compiler/rustc_codegen_gcc/src/lib.rs b/compiler/rustc_codegen_gcc/src/lib.rs
@@ -102,7 +102,9 @@ use rustc_codegen_ssa::back::write::{
 };
 use rustc_codegen_ssa::base::codegen_crate;
 use rustc_codegen_ssa::traits::{CodegenBackend, ExtraBackendMethods, WriteBackendMethods};
-use rustc_codegen_ssa::{CodegenResults, CompiledModule, ModuleCodegen, TargetConfig};
+use rustc_codegen_ssa::{
+    CodegenResults, CompiledModule, ModuleCodegen, TargetConfig, target_features,
+};
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::sync::IntoDynSyncSend;
 use rustc_errors::DiagCtxtHandle;
@@ -486,40 +488,23 @@ 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)
-                /*
-                  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
-                */
-            })
-            .map(Symbol::intern)
-            .collect()
-    };
-
-    let target_features = f(false);
-    let unstable_target_features = f(true);
+    let (unstable_target_features, target_features) = target_features::cfg_target_feature(
+        sess,
+        /* FIXME: we ignore `-Ctarget-feature` */ "",
+        |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)
+            /*
+              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
+            */
+        },
+    );
 
     TargetConfig {
         target_features,
diff --git a/compiler/rustc_codegen_llvm/src/llvm_util.rs b/compiler/rustc_codegen_llvm/src/llvm_util.rs
@@ -6,9 +6,9 @@ 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_codegen_ssa::{TargetConfig, target_features};
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::small_c_str::SmallCStr;
 use rustc_data_structures::unord::UnordSet;
@@ -17,9 +17,8 @@ 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 rustc_target::target_features::RUSTC_SPECIFIC_FEATURES;
 use smallvec::{SmallVec, smallvec};
 
 use crate::back::write::create_informational_target_machine;
@@ -343,18 +342,11 @@ 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;
-            }
+
+    let (unstable_target_features, target_features) =
+        target_features::cfg_target_feature(sess, &sess.opts.cg.target_feature, |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
@@ -368,73 +360,8 @@ pub(crate) fn target_config(sess: &Session) -> TargetConfig {
             } 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)),
-            );
-        } 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
-                }
-            });
-        }
-    }
-
-    // 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,
diff --git 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::{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::Session;
 use rustc_session::features::StabilityExt;
 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_SPECIAL_FEATURES, Stability};
 
 use crate::errors;
 
@@ -156,6 +157,100 @@ pub(crate) fn check_target_feature_trait_unsafe(tcx: TyCtxt<'_>, id: LocalDefId,
     }
 }
 
+/// 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_feature_flag` is the value of `-Ctarget-feature` (giving the caller a chance to override it).
+/// `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,
+    target_feature_flag: &str,
+    mut is_feature_enabled: 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: FxHashSet<Symbol> = sess
+        .target
+        .rust_target_features()
+        .iter()
+        .filter(|(feature, _, _)| {
+            // Skip checking special features, those are not known to the backend.
+            if RUSTC_SPECIAL_FEATURES.contains(feature) {
+                return true;
+            }
+            is_feature_enabled(feature)
+        })
+        .map(|(feature, _, _)| Symbol::intern(feature))
+        .collect();
+
+    // Add enabled and remove disabled features.
+    for (enabled, feature) in
+        target_feature_flag.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)),
+            );
+        } 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
+                }
+            });
+        }
+    }
+
+    // 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))
+}
+
 pub(crate) fn provide(providers: &mut Providers) {
     *providers = Providers {
         rust_target_features: |tcx, cnum| {
