Add #[cfg(target_has_atomic)] to get atomic support for the current target

45 files changed, 90 insertions, 10 deletions

diff --git a/src/doc/reference.md b/src/doc/reference.md
index 397abfe563c..ebb111a2e2e 100644
--- a/src/doc/reference.md
+++ b/src/doc/reference.md
@@ -2091,6 +2091,8 @@ The following configurations must be defined by the implementation:
 * `target_pointer_width = "..."` - Target pointer width in bits. This is set
   to `"32"` for targets with 32-bit pointers, and likewise set to `"64"` for
   64-bit pointers.
+* `target_has_atomic = "..."` - Set of integer sizes on which the target can perform
+  atomic operations. Values are `"8"`, `"16"`, `"32"`, `"64"` and `"ptr"`.
 * `target_vendor = "..."` - Vendor of the target, for example `apple`, `pc`, or
   simply `"unknown"`.
 * `test` - Enabled when compiling the test harness (using the `--test` flag).
@@ -2295,6 +2297,9 @@ The currently implemented features of the reference compiler are:
 * `cfg_target_vendor` - Allows conditional compilation using the `target_vendor`
                         matcher which is subject to change.
 
+* `cfg_target_has_atomic` - Allows conditional compilation using the `target_has_atomic`
+                            matcher which is subject to change.
+
 * `concat_idents` - Allows use of the `concat_idents` macro, which is in many
                     ways insufficient for concatenating identifiers, and may be
                     removed entirely for something more wholesome.
diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs
index fa5e90562d8..873059d3ccc 100644
--- a/src/libcore/lib.rs
+++ b/src/libcore/lib.rs
@@ -63,6 +63,7 @@
 #![feature(associated_type_defaults)]
 #![feature(concat_idents)]
 #![feature(const_fn)]
+#![feature(cfg_target_has_atomic)]
 #![feature(custom_attribute)]
 #![feature(fundamental)]
 #![feature(inclusive_range_syntax)]
diff --git a/src/librustc/session/config.rs b/src/librustc/session/config.rs
index 1a2c1b9a095..82237e0abb7 100644
--- a/src/librustc/session/config.rs
+++ b/src/librustc/session/config.rs
@@ -695,6 +695,7 @@ pub fn default_configuration(sess: &Session) -> ast::CrateConfig {
     let os = &sess.target.target.target_os;
     let env = &sess.target.target.target_env;
     let vendor = &sess.target.target.target_vendor;
+    let max_atomic_width = sess.target.target.options.max_atomic_width;
 
     let fam = if let Some(ref fam) = sess.target.target.options.target_family {
         intern(fam)
@@ -721,6 +722,15 @@ pub fn default_configuration(sess: &Session) -> ast::CrateConfig {
     if sess.target.target.options.has_elf_tls {
         ret.push(attr::mk_word_item(InternedString::new("target_thread_local")));
     }
+    for &i in &[8, 16, 32, 64, 128] {
+        if i <= max_atomic_width {
+            let s = i.to_string();
+            ret.push(mk(InternedString::new("target_has_atomic"), intern(&s)));
+            if &s == wordsz {
+                ret.push(mk(InternedString::new("target_has_atomic"), intern("ptr")));
+            }
+        }
+    }
     if sess.opts.debug_assertions {
         ret.push(attr::mk_word_item(InternedString::new("debug_assertions")));
     }
diff --git a/src/librustc_back/target/aarch64_apple_ios.rs b/src/librustc_back/target/aarch64_apple_ios.rs
index 2f0a043f9a7..481338d1cee 100644
--- a/src/librustc_back/target/aarch64_apple_ios.rs
+++ b/src/librustc_back/target/aarch64_apple_ios.rs
@@ -24,6 +24,7 @@ pub fn target() -> Target {
         options: TargetOptions {
             features: "+neon,+fp-armv8,+cyclone".to_string(),
             eliminate_frame_pointer: false,
+            max_atomic_width: 128,
             .. opts(Arch::Arm64)
         },
     }
diff --git a/src/librustc_back/target/aarch64_linux_android.rs b/src/librustc_back/target/aarch64_linux_android.rs
index c4212e70212..ed171822464 100644
--- a/src/librustc_back/target/aarch64_linux_android.rs
+++ b/src/librustc_back/target/aarch64_linux_android.rs
@@ -11,6 +11,8 @@
 use target::Target;
 
 pub fn target() -> Target {
+    let mut base = super::android_base::opts();
+    base.max_atomic_width = 128;
     Target {
         llvm_target: "aarch64-linux-android".to_string(),
         target_endian: "little".to_string(),
@@ -20,6 +22,6 @@ pub fn target() -> Target {
         target_os: "android".to_string(),
         target_env: "".to_string(),
         target_vendor: "unknown".to_string(),
-        options: super::android_base::opts(),
+        options: base,
     }
 }
diff --git a/src/librustc_back/target/aarch64_unknown_linux_gnu.rs b/src/librustc_back/target/aarch64_unknown_linux_gnu.rs
index 3bf4e92fb6a..aec1bae60c8 100644
--- a/src/librustc_back/target/aarch64_unknown_linux_gnu.rs
+++ b/src/librustc_back/target/aarch64_unknown_linux_gnu.rs
@@ -11,7 +11,8 @@
 use target::Target;
 
 pub fn target() -> Target {
-    let base = super::linux_base::opts();
+    let mut base = super::linux_base::opts();
+    base.max_atomic_width = 128;
     Target {
         llvm_target: "aarch64-unknown-linux-gnu".to_string(),
         target_endian: "little".to_string(),
diff --git a/src/librustc_back/target/arm_linux_androideabi.rs b/src/librustc_back/target/arm_linux_androideabi.rs
index 5be78595138..ab662a97dc2 100644
--- a/src/librustc_back/target/arm_linux_androideabi.rs
+++ b/src/librustc_back/target/arm_linux_androideabi.rs
@@ -13,6 +13,7 @@ use target::Target;
 pub fn target() -> Target {
     let mut base = super::android_base::opts();
     base.features = "+v7,+vfp3,+d16".to_string();
+    base.max_atomic_width = 64;
 
     Target {
         llvm_target: "arm-linux-androideabi".to_string(),
diff --git a/src/librustc_back/target/arm_unknown_linux_gnueabi.rs b/src/librustc_back/target/arm_unknown_linux_gnueabi.rs
index 29ab7120389..60c4a7c3c90 100644
--- a/src/librustc_back/target/arm_unknown_linux_gnueabi.rs
+++ b/src/librustc_back/target/arm_unknown_linux_gnueabi.rs
@@ -11,7 +11,8 @@
 use target::{Target, TargetOptions};
 
 pub fn target() -> Target {
-    let base = super::linux_base::opts();
+    let mut base = super::linux_base::opts();
+    base.max_atomic_width = 64;
     Target {
         llvm_target: "arm-unknown-linux-gnueabi".to_string(),
         target_endian: "little".to_string(),
diff --git a/src/librustc_back/target/arm_unknown_linux_gnueabihf.rs b/src/librustc_back/target/arm_unknown_linux_gnueabihf.rs
index 8ca7c23eb55..72128e30641 100644
--- a/src/librustc_back/target/arm_unknown_linux_gnueabihf.rs
+++ b/src/librustc_back/target/arm_unknown_linux_gnueabihf.rs
@@ -11,7 +11,8 @@
 use target::{Target, TargetOptions};
 
 pub fn target() -> Target {
-    let base = super::linux_base::opts();
+    let mut base = super::linux_base::opts();
+    base.max_atomic_width = 64;
     Target {
         llvm_target: "arm-unknown-linux-gnueabihf".to_string(),
         target_endian: "little".to_string(),
diff --git a/src/librustc_back/target/armv7_apple_ios.rs b/src/librustc_back/target/armv7_apple_ios.rs
index d131f8b2ef0..a2486a1330a 100644
--- a/src/librustc_back/target/armv7_apple_ios.rs
+++ b/src/librustc_back/target/armv7_apple_ios.rs
@@ -23,6 +23,7 @@ pub fn target() -> Target {
         target_vendor: "apple".to_string(),
         options: TargetOptions {
             features: "+v7,+vfp3,+neon".to_string(),
+            max_atomic_width: 64,
             .. opts(Arch::Armv7)
         }
     }
diff --git a/src/librustc_back/target/armv7_unknown_linux_gnueabihf.rs b/src/librustc_back/target/armv7_unknown_linux_gnueabihf.rs
index 549da058d51..7bcca3a3934 100644
--- a/src/librustc_back/target/armv7_unknown_linux_gnueabihf.rs
+++ b/src/librustc_back/target/armv7_unknown_linux_gnueabihf.rs
@@ -25,6 +25,7 @@ pub fn target() -> Target {
         options: TargetOptions {
             features: "+v7,+vfp3,+neon".to_string(),
             cpu: "cortex-a8".to_string(),
+            max_atomic_width: 64,
             .. base
         }
     }
diff --git a/src/librustc_back/target/armv7s_apple_ios.rs b/src/librustc_back/target/armv7s_apple_ios.rs
index d317589bf36..e5379aa1b42 100644
--- a/src/librustc_back/target/armv7s_apple_ios.rs
+++ b/src/librustc_back/target/armv7s_apple_ios.rs
@@ -23,6 +23,7 @@ pub fn target() -> Target {
         target_vendor: "apple".to_string(),
         options: TargetOptions {
             features: "+v7,+vfp4,+neon".to_string(),
+            max_atomic_width: 64,
             .. opts(Arch::Armv7s)
         }
     }
diff --git a/src/librustc_back/target/asmjs_unknown_emscripten.rs b/src/librustc_back/target/asmjs_unknown_emscripten.rs
index 546f9df605b..e6200177944 100644
--- a/src/librustc_back/target/asmjs_unknown_emscripten.rs
+++ b/src/librustc_back/target/asmjs_unknown_emscripten.rs
@@ -22,6 +22,7 @@ pub fn target() -> Target {
         linker_is_gnu: true,
         allow_asm: false,
         obj_is_bitcode: true,
+        max_atomic_width: 32,
         .. Default::default()
     };
     Target {
diff --git a/src/librustc_back/target/i386_apple_ios.rs b/src/librustc_back/target/i386_apple_ios.rs
index d149d4bbdc2..cf4020eeb58 100644
--- a/src/librustc_back/target/i386_apple_ios.rs
+++ b/src/librustc_back/target/i386_apple_ios.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use target::Target;
+use target::{Target, TargetOptions};
 use super::apple_ios_base::{opts, Arch};
 
 pub fn target() -> Target {
@@ -21,6 +21,9 @@ pub fn target() -> Target {
         target_os: "ios".to_string(),
         target_env: "".to_string(),
         target_vendor: "apple".to_string(),
-        options: opts(Arch::I386)
+        options: TargetOptions {
+            max_atomic_width: 64,
+            .. opts(Arch::I386)
+        }
     }
 }
diff --git a/src/librustc_back/target/i686_apple_darwin.rs b/src/librustc_back/target/i686_apple_darwin.rs
index b6e2f4d8e8a..302691e9a59 100644
--- a/src/librustc_back/target/i686_apple_darwin.rs
+++ b/src/librustc_back/target/i686_apple_darwin.rs
@@ -13,6 +13,7 @@ use target::Target;
 pub fn target() -> Target {
     let mut base = super::apple_base::opts();
     base.cpu = "yonah".to_string();
+    base.max_atomic_width = 64;
     base.pre_link_args.push("-m32".to_string());
 
     Target {
diff --git a/src/librustc_back/target/i686_linux_android.rs b/src/librustc_back/target/i686_linux_android.rs
index b338a971ff7..426be63cf21 100644
--- a/src/librustc_back/target/i686_linux_android.rs
+++ b/src/librustc_back/target/i686_linux_android.rs
@@ -13,6 +13,7 @@ use target::Target;
 pub fn target() -> Target {
     let mut base = super::android_base::opts();
     base.cpu = "pentium4".to_string();
+    base.max_atomic_width = 64;
 
     Target {
         llvm_target: "i686-linux-android".to_string(),
diff --git a/src/librustc_back/target/i686_pc_windows_gnu.rs b/src/librustc_back/target/i686_pc_windows_gnu.rs
index 48203cc74d6..c2cc624c9f9 100644
--- a/src/librustc_back/target/i686_pc_windows_gnu.rs
+++ b/src/librustc_back/target/i686_pc_windows_gnu.rs
@@ -13,6 +13,7 @@ use target::Target;
 pub fn target() -> Target {
     let mut base = super::windows_base::opts();
     base.cpu = "pentium4".to_string();
+    base.max_atomic_width = 64;
 
     // Mark all dynamic libraries and executables as compatible with the larger 4GiB address
     // space available to x86 Windows binaries on x86_64.
diff --git a/src/librustc_back/target/i686_pc_windows_msvc.rs b/src/librustc_back/target/i686_pc_windows_msvc.rs
index 501219ad607..8c1bacc2807 100644
--- a/src/librustc_back/target/i686_pc_windows_msvc.rs
+++ b/src/librustc_back/target/i686_pc_windows_msvc.rs
@@ -13,6 +13,7 @@ use target::Target;
 pub fn target() -> Target {
     let mut base = super::windows_msvc_base::opts();
     base.cpu = "pentium4".to_string();
+    base.max_atomic_width = 64;
 
     // Mark all dynamic libraries and executables as compatible with the larger 4GiB address
     // space available to x86 Windows binaries on x86_64.
diff --git a/src/librustc_back/target/i686_unknown_dragonfly.rs b/src/librustc_back/target/i686_unknown_dragonfly.rs
index cdbbd5eafdd..6446ac45f7d 100644
--- a/src/librustc_back/target/i686_unknown_dragonfly.rs
+++ b/src/librustc_back/target/i686_unknown_dragonfly.rs
@@ -13,6 +13,7 @@ use target::Target;
 pub fn target() -> Target {
     let mut base = super::dragonfly_base::opts();
     base.cpu = "pentium4".to_string();
+    base.max_atomic_width = 64;
     base.pre_link_args.push("-m32".to_string());
 
     Target {
diff --git a/src/librustc_back/target/i686_unknown_freebsd.rs b/src/librustc_back/target/i686_unknown_freebsd.rs
index fadedc24149..a7903d5db64 100644
--- a/src/librustc_back/target/i686_unknown_freebsd.rs
+++ b/src/librustc_back/target/i686_unknown_freebsd.rs
@@ -13,6 +13,7 @@ use target::Target;
 pub fn target() -> Target {
     let mut base = super::freebsd_base::opts();
     base.cpu = "pentium4".to_string();
+    base.max_atomic_width = 64;
     base.pre_link_args.push("-m32".to_string());
 
     Target {
diff --git a/src/librustc_back/target/i686_unknown_linux_gnu.rs b/src/librustc_back/target/i686_unknown_linux_gnu.rs
index a1f3ab76907..7813d557076 100644
--- a/src/librustc_back/target/i686_unknown_linux_gnu.rs
+++ b/src/librustc_back/target/i686_unknown_linux_gnu.rs
@@ -13,6 +13,7 @@ use target::Target;
 pub fn target() -> Target {
     let mut base = super::linux_base::opts();
     base.cpu = "pentium4".to_string();
+    base.max_atomic_width = 64;
     base.pre_link_args.push("-m32".to_string());
 
     Target {
diff --git a/src/librustc_back/target/i686_unknown_linux_musl.rs b/src/librustc_back/target/i686_unknown_linux_musl.rs
index 95fc0abece0..52744295837 100644
--- a/src/librustc_back/target/i686_unknown_linux_musl.rs
+++ b/src/librustc_back/target/i686_unknown_linux_musl.rs
@@ -13,6 +13,7 @@ use target::Target;
 pub fn target() -> Target {
     let mut base = super::linux_musl_base::opts();
     base.cpu = "pentium4".to_string();
+    base.max_atomic_width = 64;
     base.pre_link_args.push("-m32".to_string());
     base.pre_link_args.push("-Wl,-melf_i386".to_string());
 
diff --git a/src/librustc_back/target/le32_unknown_nacl.rs b/src/librustc_back/target/le32_unknown_nacl.rs
index 472b73302a3..f4f0262d476 100644
--- a/src/librustc_back/target/le32_unknown_nacl.rs
+++ b/src/librustc_back/target/le32_unknown_nacl.rs
@@ -25,6 +25,7 @@ pub fn target() -> Target {
         no_compiler_rt: false,
         linker_is_gnu: true,
         allow_asm: false,
+        max_atomic_width: 32,
         .. Default::default()
     };
     Target {
diff --git a/src/librustc_back/target/mips_unknown_linux_gnu.rs b/src/librustc_back/target/mips_unknown_linux_gnu.rs
index 863f5ceab0a..794e4d4996c 100644
--- a/src/librustc_back/target/mips_unknown_linux_gnu.rs
+++ b/src/librustc_back/target/mips_unknown_linux_gnu.rs
@@ -23,6 +23,7 @@ pub fn target() -> Target {
         options: TargetOptions {
             cpu: "mips32r2".to_string(),
             features: "+mips32r2,+soft-float".to_string(),
+            max_atomic_width: 32,
             ..super::linux_base::opts()
         },
     }
diff --git a/src/librustc_back/target/mips_unknown_linux_musl.rs b/src/librustc_back/target/mips_unknown_linux_musl.rs
index ac0fde5449f..35366659d58 100644
--- a/src/librustc_back/target/mips_unknown_linux_musl.rs
+++ b/src/librustc_back/target/mips_unknown_linux_musl.rs
@@ -23,6 +23,7 @@ pub fn target() -> Target {
         options: TargetOptions {
             cpu: "mips32r2".to_string(),
             features: "+mips32r2,+soft-float".to_string(),
+            max_atomic_width: 32,
             ..super::linux_base::opts()
         }
     }
diff --git a/src/librustc_back/target/mipsel_unknown_linux_gnu.rs b/src/librustc_back/target/mipsel_unknown_linux_gnu.rs
index ff33effa3e7..ac1536b3d00 100644
--- a/src/librustc_back/target/mipsel_unknown_linux_gnu.rs
+++ b/src/librustc_back/target/mipsel_unknown_linux_gnu.rs
@@ -24,6 +24,7 @@ pub fn target() -> Target {
         options: TargetOptions {
             cpu: "mips32".to_string(),
             features: "+mips32".to_string(),
+            max_atomic_width: 32,
             ..super::linux_base::opts()
         },
     }
diff --git a/src/librustc_back/target/mipsel_unknown_linux_musl.rs b/src/librustc_back/target/mipsel_unknown_linux_musl.rs
index d9fb1405036..a9ea52c4278 100644
--- a/src/librustc_back/target/mipsel_unknown_linux_musl.rs
+++ b/src/librustc_back/target/mipsel_unknown_linux_musl.rs
@@ -23,6 +23,7 @@ pub fn target() -> Target {
         options: TargetOptions {
             cpu: "mips32".to_string(),
             features: "+mips32".to_string(),
+            max_atomic_width: 32,
             ..super::linux_base::opts()
         }
     }
diff --git a/src/librustc_back/target/mod.rs b/src/librustc_back/target/mod.rs
index 30d0b47029d..2163a8a1689 100644
--- a/src/librustc_back/target/mod.rs
+++ b/src/librustc_back/target/mod.rs
@@ -292,6 +292,10 @@ pub struct TargetOptions {
     // If we give emcc .o files that are actually .bc files it
     // will 'just work'.
     pub obj_is_bitcode: bool,
+
+    /// Maximum integer size in bits that this target can perform atomic
+    /// operations on.
+    pub max_atomic_width: u64,
 }
 
 impl Default for TargetOptions {
@@ -340,6 +344,7 @@ impl Default for TargetOptions {
             allow_asm: true,
             has_elf_tls: false,
             obj_is_bitcode: false,
+            max_atomic_width: 0,
         }
     }
 }
@@ -392,6 +397,9 @@ impl Target {
             options: Default::default(),
         };
 
+        // Default max-atomic-width to target-pointer-width
+        base.options.max_atomic_width = base.target_pointer_width.parse().unwrap();
+
         macro_rules! key {
             ($key_name:ident) => ( {
                 let name = (stringify!($key_name)).replace("_", "-");
@@ -404,6 +412,12 @@ impl Target {
                     .map(|o| o.as_boolean()
                          .map(|s| base.options.$key_name = s));
             } );
+            ($key_name:ident, u64) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                obj.find(&name[..])
+                    .map(|o| o.as_u64()
+                         .map(|s| base.options.$key_name = s));
+            } );
             ($key_name:ident, list) => ( {
                 let name = (stringify!($key_name)).replace("_", "-");
                 obj.find(&name[..]).map(|o| o.as_array()
@@ -451,6 +465,7 @@ impl Target {
         key!(archive_format);
         key!(allow_asm, bool);
         key!(custom_unwind_resume, bool);
+        key!(max_atomic_width, u64);
 
         base
     }
diff --git a/src/librustc_back/target/powerpc64_unknown_linux_gnu.rs b/src/librustc_back/target/powerpc64_unknown_linux_gnu.rs
index fe7daaec1cd..be4be8e6fc9 100644
--- a/src/librustc_back/target/powerpc64_unknown_linux_gnu.rs
+++ b/src/librustc_back/target/powerpc64_unknown_linux_gnu.rs
@@ -14,6 +14,7 @@ pub fn target() -> Target {
     let mut base = super::linux_base::opts();
     base.cpu = "ppc64".to_string();
     base.pre_link_args.push("-m64".to_string());
+    base.max_atomic_width = 64;
 
     Target {
         llvm_target: "powerpc64-unknown-linux-gnu".to_string(),
diff --git a/src/librustc_back/target/powerpc64le_unknown_linux_gnu.rs b/src/librustc_back/target/powerpc64le_unknown_linux_gnu.rs
index 4aab2b1802c..b0a81ce7ec5 100644
--- a/src/librustc_back/target/powerpc64le_unknown_linux_gnu.rs
+++ b/src/librustc_back/target/powerpc64le_unknown_linux_gnu.rs
@@ -14,6 +14,7 @@ pub fn target() -> Target {
     let mut base = super::linux_base::opts();
     base.cpu = "ppc64le".to_string();
     base.pre_link_args.push("-m64".to_string());
+    base.max_atomic_width = 64;
 
     Target {
         llvm_target: "powerpc64le-unknown-linux-gnu".to_string(),
diff --git a/src/librustc_back/target/powerpc_unknown_linux_gnu.rs b/src/librustc_back/target/powerpc_unknown_linux_gnu.rs
index 1df36442c06..aea57dc4b7f 100644
--- a/src/librustc_back/target/powerpc_unknown_linux_gnu.rs
+++ b/src/librustc_back/target/powerpc_unknown_linux_gnu.rs
@@ -13,6 +13,7 @@ use target::Target;
 pub fn target() -> Target {
     let mut base = super::linux_base::opts();
     base.pre_link_args.push("-m32".to_string());
+    base.max_atomic_width = 32;
 
     Target {
         llvm_target: "powerpc-unknown-linux-gnu".to_string(),
diff --git a/src/librustc_back/target/x86_64_apple_darwin.rs b/src/librustc_back/target/x86_64_apple_darwin.rs
index c8b5dd0eccc..5542c9120a4 100644
--- a/src/librustc_back/target/x86_64_apple_darwin.rs
+++ b/src/librustc_back/target/x86_64_apple_darwin.rs
@@ -13,6 +13,7 @@ use target::Target;
 pub fn target() -> Target {
     let mut base = super::apple_base::opts();
     base.cpu = "core2".to_string();
+    base.max_atomic_width = 128; // core2 support cmpxchg16b
     base.eliminate_frame_pointer = false;
     base.pre_link_args.push("-m64".to_string());
 
diff --git a/src/librustc_back/target/x86_64_apple_ios.rs b/src/librustc_back/target/x86_64_apple_ios.rs
index d038e88f2b4..8638241f861 100644
--- a/src/librustc_back/target/x86_64_apple_ios.rs
+++ b/src/librustc_back/target/x86_64_apple_ios.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use target::Target;
+use target::{Target, TargetOptions};
 use super::apple_ios_base::{opts, Arch};
 
 pub fn target() -> Target {
@@ -21,6 +21,9 @@ pub fn target() -> Target {
         target_os: "ios".to_string(),
         target_env: "".to_string(),
         target_vendor: "apple".to_string(),
-        options: opts(Arch::X86_64)
+        options: TargetOptions {
+            max_atomic_width: 64,
+            .. opts(Arch::X86_64)
+        }
     }
 }
diff --git a/src/librustc_back/target/x86_64_pc_windows_gnu.rs b/src/librustc_back/target/x86_64_pc_windows_gnu.rs
index f0a09ae71ef..e243054d023 100644
--- a/src/librustc_back/target/x86_64_pc_windows_gnu.rs
+++ b/src/librustc_back/target/x86_64_pc_windows_gnu.rs
@@ -14,6 +14,7 @@ pub fn target() -> Target {
     let mut base = super::windows_base::opts();
     base.cpu = "x86-64".to_string();
     base.pre_link_args.push("-m64".to_string());
+    base.max_atomic_width = 64;
 
     Target {
         llvm_target: "x86_64-pc-windows-gnu".to_string(),
diff --git a/src/librustc_back/target/x86_64_pc_windows_msvc.rs b/src/librustc_back/target/x86_64_pc_windows_msvc.rs
index b3fbd6ef051..a23a807a025 100644
--- a/src/librustc_back/target/x86_64_pc_windows_msvc.rs
+++ b/src/librustc_back/target/x86_64_pc_windows_msvc.rs
@@ -13,6 +13,7 @@ use target::Target;
 pub fn target() -> Target {
     let mut base = super::windows_msvc_base::opts();
     base.cpu = "x86-64".to_string();
+    base.max_atomic_width = 64;
 
     Target {
         llvm_target: "x86_64-pc-windows-msvc".to_string(),
diff --git a/src/librustc_back/target/x86_64_rumprun_netbsd.rs b/src/librustc_back/target/x86_64_rumprun_netbsd.rs
index 652159d10fd..af5d21c4d93 100644
--- a/src/librustc_back/target/x86_64_rumprun_netbsd.rs
+++ b/src/librustc_back/target/x86_64_rumprun_netbsd.rs
@@ -15,6 +15,7 @@ pub fn target() -> Target {
     base.pre_link_args.push("-m64".to_string());
     base.linker = "x86_64-rumprun-netbsd-gcc".to_string();
     base.ar = "x86_64-rumprun-netbsd-ar".to_string();
+    base.max_atomic_width = 64;
 
     base.dynamic_linking = false;
     base.has_rpath = false;
diff --git a/src/librustc_back/target/x86_64_sun_solaris.rs b/src/librustc_back/target/x86_64_sun_solaris.rs
index 5aa08ea9c8c..8f2c905cf2e 100644
--- a/src/librustc_back/target/x86_64_sun_solaris.rs
+++ b/src/librustc_back/target/x86_64_sun_solaris.rs
@@ -14,6 +14,7 @@ pub fn target() -> Target {
     let mut base = super::solaris_base::opts();
     base.pre_link_args.push("-m64".to_string());
     base.cpu = "x86-64".to_string();
+    base.max_atomic_width = 64;
 
     Target {
         llvm_target: "x86_64-pc-solaris".to_string(),
diff --git a/src/librustc_back/target/x86_64_unknown_bitrig.rs b/src/librustc_back/target/x86_64_unknown_bitrig.rs
index e8b95ed80d9..87753da540a 100644
--- a/src/librustc_back/target/x86_64_unknown_bitrig.rs
+++ b/src/librustc_back/target/x86_64_unknown_bitrig.rs
@@ -12,6 +12,7 @@ use target::Target;
 
 pub fn target() -> Target {
     let mut base = super::bitrig_base::opts();
+    base.max_atomic_width = 64;
     base.pre_link_args.push("-m64".to_string());
 
     Target {
diff --git a/src/librustc_back/target/x86_64_unknown_dragonfly.rs b/src/librustc_back/target/x86_64_unknown_dragonfly.rs
index 3fa46c31a5e..2535071f308 100644
--- a/src/librustc_back/target/x86_64_unknown_dragonfly.rs
+++ b/src/librustc_back/target/x86_64_unknown_dragonfly.rs
@@ -13,6 +13,7 @@ use target::Target;
 pub fn target() -> Target {
     let mut base = super::dragonfly_base::opts();
     base.cpu = "x86-64".to_string();
+    base.max_atomic_width = 64;
     base.pre_link_args.push("-m64".to_string());
 
     Target {
diff --git a/src/librustc_back/target/x86_64_unknown_freebsd.rs b/src/librustc_back/target/x86_64_unknown_freebsd.rs
index d345a321794..d3ad0578aeb 100644
--- a/src/librustc_back/target/x86_64_unknown_freebsd.rs
+++ b/src/librustc_back/target/x86_64_unknown_freebsd.rs
@@ -13,6 +13,7 @@ use target::Target;
 pub fn target() -> Target {
     let mut base = super::freebsd_base::opts();
     base.cpu = "x86-64".to_string();
+    base.max_atomic_width = 64;
     base.pre_link_args.push("-m64".to_string());
 
     Target {
diff --git a/src/librustc_back/target/x86_64_unknown_linux_gnu.rs b/src/librustc_back/target/x86_64_unknown_linux_gnu.rs
index 69e333a1350..7908e0d581b 100644
--- a/src/librustc_back/target/x86_64_unknown_linux_gnu.rs
+++ b/src/librustc_back/target/x86_64_unknown_linux_gnu.rs
@@ -13,6 +13,7 @@ use target::Target;
 pub fn target() -> Target {
     let mut base = super::linux_base::opts();
     base.cpu = "x86-64".to_string();
+    base.max_atomic_width = 64;
     base.pre_link_args.push("-m64".to_string());
 
     Target {
diff --git a/src/librustc_back/target/x86_64_unknown_linux_musl.rs b/src/librustc_back/target/x86_64_unknown_linux_musl.rs
index f8f85e5c066..3301e0e0dc9 100644
--- a/src/librustc_back/target/x86_64_unknown_linux_musl.rs
+++ b/src/librustc_back/target/x86_64_unknown_linux_musl.rs
@@ -13,6 +13,7 @@ use target::Target;
 pub fn target() -> Target {
     let mut base = super::linux_musl_base::opts();
     base.cpu = "x86-64".to_string();
+    base.max_atomic_width = 64;
     base.pre_link_args.push("-m64".to_string());
 
     Target {
diff --git a/src/librustc_back/target/x86_64_unknown_netbsd.rs b/src/librustc_back/target/x86_64_unknown_netbsd.rs
index 74bf7189119..7e6d1b78469 100644
--- a/src/librustc_back/target/x86_64_unknown_netbsd.rs
+++ b/src/librustc_back/target/x86_64_unknown_netbsd.rs
@@ -12,6 +12,7 @@ use target::Target;
 
 pub fn target() -> Target {
     let mut base = super::netbsd_base::opts();
+    base.max_atomic_width = 64;
     base.pre_link_args.push("-m64".to_string());
 
     Target {
diff --git a/src/librustc_back/target/x86_64_unknown_openbsd.rs b/src/librustc_back/target/x86_64_unknown_openbsd.rs
index 521de5373d0..823b0994b0a 100644
--- a/src/librustc_back/target/x86_64_unknown_openbsd.rs
+++ b/src/librustc_back/target/x86_64_unknown_openbsd.rs
@@ -13,6 +13,7 @@ use target::Target;
 pub fn target() -> Target {
     let mut base = super::openbsd_base::opts();
     base.cpu = "x86-64".to_string();
+    base.max_atomic_width = 64;
     base.pre_link_args.push("-m64".to_string());
 
     Target {
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 7f01821b004..cf797b85f54 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -268,8 +268,11 @@ declare_features! (
     // pub(restricted) visibilities (RFC 1422)
     (active, pub_restricted, "1.9.0", Some(32409)),
 
-     // Allow Drop types in statics/const functions (RFC 1440)
-    (active, drop_types_in_const, "1.9.0", Some(33156))
+    // Allow Drop types in statics/const functions (RFC 1440)
+    (active, drop_types_in_const, "1.9.0", Some(33156)),
+
+    // Allows cfg(target_has_atomic = "...").
+    (active, cfg_target_has_atomic, "1.9.0", Some(32976))
 );
 
 declare_features! (
@@ -577,6 +580,7 @@ const GATED_CFGS: &'static [(&'static str, &'static str, fn(&Features) -> bool)]
     ("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)),
 ];
 
 #[derive(Debug, Eq, PartialEq)]