cg_gcc: properly populate cfg(target_features) with -Ctarget-features

Author: RalfJung

compiler/rustc_codegen_gcc/src/lib.rs

@@ -101,10 +101,9 @@ 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, target_features,
-};
+use rustc_codegen_ssa::{CodegenResults, CompiledModule, ModuleCodegen, TargetConfig};
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::sync::IntoDynSyncSend;
 use rustc_errors::DiagCtxtHandle;
@@ -488,23 +487,19 @@ 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 {
-    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
-            */
-        },
-    );
+    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)
+        /*
+          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,

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -7,6 +7,7 @@ use std::{ptr, slice, str};
 
 use libc::c_int;
 use rustc_codegen_ssa::base::wants_wasm_eh;
+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;
@@ -331,24 +332,23 @@ pub(crate) fn target_config(sess: &Session) -> TargetConfig {
     // by LLVM.
     let target_machine = create_informational_target_machine(sess, 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
-                    // 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
             }
-        });
+            true
+        } else {
+            false
+        }
+    });
 
     let mut cfg = TargetConfig {
         target_features,

compiler/rustc_codegen_ssa/src/target_features.rs

@@ -163,8 +163,7 @@ pub(crate) fn check_target_feature_trait_unsafe(tcx: TyCtxt<'_>, id: LocalDefId,
 /// 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: &Session,
-    target_feature_flag: &'a str,
+    sess: &'a Session,
     err_callback: impl Fn(&'a str),
     mut callback: impl FnMut(
         /* base_feature */ &'a str,
@@ -175,7 +174,7 @@ fn parse_rust_feature_flag<'a>(
     // A cache for the backwards implication map.
     let mut inverse_implied_features: Option<FxHashMap<&str, FxHashSet<&str>>> = None;
 
-    for feature in target_feature_flag.split(',') {
+    for feature in sess.opts.cg.target_feature.split(',') {
         if let Some(base_feature) = feature.strip_prefix('+') {
             callback(base_feature, sess.target.implied_target_features(base_feature), true)
         } else if let Some(base_feature) = feature.strip_prefix('-') {
@@ -215,15 +214,13 @@ fn parse_rust_feature_flag<'a>(
 /// 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,
+    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.
@@ -236,15 +233,14 @@ pub fn cfg_target_feature(
             if RUSTC_SPECIAL_FEATURES.contains(feature) {
                 return true;
             }
-            is_feature_enabled(feature)
+            target_base_has_feature(feature)
         })
         .map(|(feature, _, _)| Symbol::intern(feature))
         .collect();
 
     // Add enabled and remove disabled features.
     parse_rust_feature_flag(
         sess,
-        target_feature_flag,
         /* err_callback */ |_| {},
         |_base_feature, new_features, enabled| {
             // Iteration order is irrelevant since this only influences an `UnordSet`.
@@ -323,7 +319,6 @@ pub fn flag_to_backend_features<'a, const N: usize>(
     let mut rust_features = vec![];
     parse_rust_feature_flag(
         sess,
-        &sess.opts.cg.target_feature,
         /* err_callback */
         |feature| {
             if diagnostics {