Add some SIMD target_feature cfg's when appropriate.

NB. this may not be 100% perfect.

src/librustc_driver/lib.rs

@@ -89,6 +89,7 @@ pub mod test;
 
 pub mod driver;
 pub mod pretty;
+pub mod target_features;
 
 
 const BUG_REPORT_URL: &'static str =
@@ -136,7 +137,8 @@ pub fn run_compiler<'a>(args: &[String],
     if sess.unstable_options() {
         sess.opts.show_span = matches.opt_str("show-span");
     }
-    let cfg = config::build_configuration(&sess);
+    let mut cfg = config::build_configuration(&sess);
+    target_features::add_configuration(&mut cfg, &sess);
 
     do_or_return!(callbacks.late_callback(&matches, &sess, &input, &odir, &ofile));
 

src/librustc_driver/target_features.rs

@@ -0,0 +1,98 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use syntax::{ast, attr};
+use rustc::session::Session;
+use syntax::parse::token::InternedString;
+use syntax::parse::token::intern_and_get_ident as intern;
+
+/// Add `target_feature = "..."` cfgs for a variety of platform
+/// specific features (SSE, NEON etc.).
+///
+/// This uses a scheme similar to that employed by clang: reimplement
+/// the target feature knowledge. *Theoretically* we could query LLVM
+/// since that has perfect knowledge about what things are enabled in
+/// code-generation, however, it is extremely non-obvious how to do
+/// this successfully. Each platform defines a subclass of a
+/// SubtargetInfo, which knows all this information, but the ways to
+/// query them do not seem to be public.
+pub fn add_configuration(cfg: &mut ast::CrateConfig, sess: &Session) {
+    let tf = InternedString::new("target_feature");
+    macro_rules! fillout {
+        ($($func: ident, $name: expr;)*) => {{
+            $(if $func(sess) {
+                cfg.push(attr::mk_name_value_item_str(tf.clone(), intern($name)))
+            })*
+        }}
+    }
+    fillout! {
+        has_sse, "sse";
+        has_sse2, "sse2";
+        has_sse3, "sse3";
+        has_ssse3, "ssse3";
+        has_sse41, "sse4.1";
+        has_sse42, "sse4.2";
+        has_avx, "avx";
+        has_avx2, "avx2";
+        has_neon, "neon";
+        has_vfp, "vfp";
+    }
+}
+
+
+fn features_contain(sess: &Session, s: &str) -> bool {
+    sess.target.target.options.features.contains(s) ||
+        sess.opts.cg.target_feature.contains(s)
+}
+
+pub fn has_sse(sess: &Session) -> bool {
+    features_contain(sess, "+sse") ||
+        has_sse2(sess)
+}
+pub fn has_sse2(sess: &Session) -> bool {
+    // x86-64 requires at least SSE2 support
+    sess.target.target.arch == "x86_64" ||
+        features_contain(sess, "+sse2") ||
+        has_sse3(sess)
+}
+pub fn has_sse3(sess: &Session) -> bool {
+    features_contain(sess, "+sse3") ||
+        has_ssse3(sess)
+}
+pub fn has_ssse3(sess: &Session) -> bool {
+    features_contain(sess, "+ssse3") ||
+        has_sse41(sess)
+}
+pub fn has_sse41(sess: &Session) -> bool {
+    features_contain(sess, "+sse4.1") ||
+        has_sse42(sess)
+}
+pub fn has_sse42(sess: &Session) -> bool {
+    features_contain(sess, "+sse4.2") ||
+        has_avx(sess)
+}
+pub fn has_avx(sess: &Session) -> bool {
+    features_contain(sess, "+avx") ||
+        has_avx2(sess)
+}
+pub fn has_avx2(sess: &Session) -> bool {
+    features_contain(sess, "+avx2")
+}
+
+pub fn has_neon(sess: &Session) -> bool {
+    // AArch64 requires NEON support
+    sess.target.target.arch == "aarch64" ||
+        features_contain(sess, "+neon")
+}
+pub fn has_vfp(sess: &Session) -> bool {
+    // AArch64 requires VFP support
+    sess.target.target.arch == "aarch64" ||
+        features_contain(sess, "+vfp")
+}

src/librustdoc/core.rs

@@ -10,7 +10,7 @@
 pub use self::MaybeTyped::*;
 
 use rustc_lint;
-use rustc_driver::driver;
+use rustc_driver::{driver, target_features};
 use rustc::session::{self, config};
 use rustc::middle::{privacy, ty};
 use rustc::ast_map;
@@ -119,7 +119,8 @@ pub fn run_core(search_paths: SearchPaths, cfgs: Vec<String>, externs: Externs,
                                        span_diagnostic_handler);
     rustc_lint::register_builtins(&mut sess.lint_store.borrow_mut(), Some(&sess));
 
-    let cfg = config::build_configuration(&sess);
+    let mut cfg = config::build_configuration(&sess);
+    target_features::add_configuration(&mut cfg, &sess);
 
     let krate = driver::phase_1_parse_input(&sess, cfg, &input);