Stabilize x86/x86_64 SIMD

This commit stabilizes the SIMD in Rust for the x86/x86_64 platforms. Notably
this commit is stabilizing:

* The `std::arch::{x86, x86_64}` modules and the intrinsics contained inside.
* The `is_x86_feature_detected!` macro in the standard library
* The `#[target_feature(enable = "...")]` attribute
* The `#[cfg(target_feature = "...")]` matcher

Stabilization of the module and intrinsics were primarily done in
rust-lang/stdarch#414 and the two attribute stabilizations are done in
this commit. The standard library is also tweaked a bit with the new way that
stdsimd is integrated.

Note that other architectures like `std::arch::arm` are not stabilized as part
of this commit, they will likely stabilize in the future after they've been
implemented and fleshed out. Similarly the `std::simd` module is also not being
stabilized in this commit, only `std::arch`. Finally, nothing related to `__m64`
is stabilized in this commit either (MMX), only SSE and up types and intrinsics
are stabilized.

Closes #29717
Closes #44839
Closes #48556

.gitmodules

@@ -49,7 +49,7 @@
 	url = https://github.com/rust-lang/llvm
 [submodule "src/stdsimd"]
 	path = src/stdsimd
-	url = https://github.com/rust-lang-nursery/stdsimd
+	url = https://github.com/alexcrichton/stdsimd
 [submodule "src/tools/lld"]
 	path = src/tools/lld
 	url = https://github.com/rust-lang/lld.git

src/libcore/lib.rs

@@ -68,7 +68,6 @@
 #![feature(asm)]
 #![feature(associated_type_defaults)]
 #![feature(attr_literals)]
-#![feature(cfg_target_feature)]
 #![feature(cfg_target_has_atomic)]
 #![feature(concat_idents)]
 #![feature(const_fn)]
@@ -96,11 +95,13 @@
 #![feature(specialization)]
 #![feature(staged_api)]
 #![feature(stmt_expr_attributes)]
-#![feature(target_feature)]
 #![feature(unboxed_closures)]
 #![feature(untagged_unions)]
 #![feature(unwind_attributes)]
 
+#![cfg_attr(stage0, feature(target_feature))]
+#![cfg_attr(stage0, feature(cfg_target_feature))]
+
 #[prelude_import]
 #[allow(unused)]
 use prelude::v1::*;
@@ -204,6 +205,20 @@ mod unit;
 // things like SIMD and such. Note that the actual source for all this lies in a
 // different repository, rust-lang-nursery/stdsimd. That's why the setup here is
 // a bit wonky.
+#[allow(unused_macros)]
+macro_rules! test_v16 { ($item:item) => {}; }
+#[allow(unused_macros)]
+macro_rules! test_v32 { ($item:item) => {}; }
+#[allow(unused_macros)]
+macro_rules! test_v64 { ($item:item) => {}; }
+#[allow(unused_macros)]
+macro_rules! test_v128 { ($item:item) => {}; }
+#[allow(unused_macros)]
+macro_rules! test_v256 { ($item:item) => {}; }
+#[allow(unused_macros)]
+macro_rules! test_v512 { ($item:item) => {}; }
+#[allow(unused_macros)]
+macro_rules! vector_impl { ($([$f:ident, $($args:tt)*]),*) => { $($f!($($args)*);)* } }
 #[path = "../stdsimd/coresimd/mod.rs"]
 #[allow(missing_docs, missing_debug_implementations, dead_code)]
 #[unstable(feature = "stdsimd", issue = "48556")]
@@ -213,6 +228,6 @@ mod coresimd;
 #[unstable(feature = "stdsimd", issue = "48556")]
 #[cfg(not(stage0))]
 pub use coresimd::simd;
-#[unstable(feature = "stdsimd", issue = "48556")]
+#[stable(feature = "simd_arch", since = "1.27.0")]
 #[cfg(not(stage0))]
 pub use coresimd::arch;

src/libstd/lib.rs

@@ -525,7 +525,7 @@ mod coresimd {
 #[unstable(feature = "stdsimd", issue = "48556")]
 #[cfg(all(not(stage0), not(test)))]
 pub use stdsimd::simd;
-#[unstable(feature = "stdsimd", issue = "48556")]
+#[stable(feature = "simd_arch", since = "1.27.0")]
 #[cfg(all(not(stage0), not(test)))]
 pub use stdsimd::arch;
 

src/libsyntax/feature_gate.rs

@@ -231,9 +231,6 @@ declare_features! (
     // allow `repr(simd)`, and importing the various simd intrinsics
     (active, repr_simd, "1.4.0", Some(27731), None),
 
-    // Allows cfg(target_feature = "...").
-    (active, cfg_target_feature, "1.4.0", Some(29717), None),
-
     // allow `extern "platform-intrinsic" { ... }`
     (active, platform_intrinsics, "1.4.0", Some(27731), None),
 
@@ -293,9 +290,6 @@ declare_features! (
 
     (active, use_extern_macros, "1.15.0", Some(35896), None),
 
-    // Allows #[target_feature(...)]
-    (active, target_feature, "1.15.0", None, None),
-
     // `extern "ptx-*" fn()`
     (active, abi_ptx, "1.15.0", None, None),
 
@@ -574,6 +568,10 @@ declare_features! (
     (accepted, underscore_lifetimes, "1.26.0", Some(44524), None),
     // Allows attributes on lifetime/type formal parameters in generics (RFC 1327)
     (accepted, generic_param_attrs, "1.26.0", Some(48848), None),
+    // Allows cfg(target_feature = "...").
+    (accepted, cfg_target_feature, "1.27.0", Some(29717), None),
+    // Allows #[target_feature(...)]
+    (accepted, target_feature, "1.27.0", None, None),
 );
 
 // If you change this, please modify src/doc/unstable-book as well. You must
@@ -918,10 +916,7 @@ pub const BUILTIN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeG
                                  "the `#[naked]` attribute \
                                   is an experimental feature",
                                  cfg_fn!(naked_functions))),
-    ("target_feature", Whitelisted, Gated(
-        Stability::Unstable, "target_feature",
-        "the `#[target_feature]` attribute is an experimental feature",
-        cfg_fn!(target_feature))),
+    ("target_feature", Normal, Ungated),
     ("export_name", Whitelisted, Ungated),
     ("inline", Whitelisted, Ungated),
     ("link", Whitelisted, Ungated),
@@ -1052,7 +1047,6 @@ pub const BUILTIN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeG
 // cfg(...)'s that are feature gated
 const GATED_CFGS: &[(&str, &str, fn(&Features) -> bool)] = &[
     // (name in cfg, feature, function to check if the feature is enabled)
-    ("target_feature", "cfg_target_feature", cfg_fn!(cfg_target_feature)),
     ("target_vendor", "cfg_target_vendor", cfg_fn!(cfg_target_vendor)),
     ("target_thread_local", "cfg_target_thread_local", cfg_fn!(cfg_target_thread_local)),
     ("target_has_atomic", "cfg_target_has_atomic", cfg_fn!(cfg_target_has_atomic)),