Auto merge of #51828 - kennytm:no-simd-swap-for-mac, r=<try>

[DO NOT MERGE] Disable SIMD in mem::swap on macOS

Tries to address the various TLS segfault on macOS 10.10.

.travis.yml

@@ -16,13 +16,13 @@ matrix:
       if: type = pull_request OR branch = auto
 
     - env: IMAGE=dist-x86_64-linux DEPLOY=1
-      if: branch = try OR branch = auto
+      if: branch = auto
 
     # "alternate" deployments, these are "nightlies" but have LLVM assertions
     # turned on, they're deployed to a different location primarily for
     # additional testing.
     - env: IMAGE=dist-x86_64-linux DEPLOY_ALT=1 CI_JOB_NAME=dist-x86_64-linux-alt
-      if: branch = try OR branch = auto
+      if: branch = auto
 
     - env: >
         RUST_CHECK_TARGET=dist
@@ -105,7 +105,7 @@ matrix:
         CI_JOB_NAME=dist-x86_64-apple
       os: osx
       osx_image: xcode9.3-moar
-      if: branch = auto
+      if: branch = try OR branch = auto
 
     # Linux builders, remaining docker images
     - env: IMAGE=arm-android

src/libcore/ptr.rs

@@ -194,9 +194,11 @@ unsafe fn swap_nonoverlapping_bytes(x: *mut u8, y: *mut u8, len: usize) {
     // Haswell E processors. LLVM is more able to optimize if we give a struct a
     // #[repr(simd)], even if we don't actually use this struct directly.
     //
-    // FIXME repr(simd) broken on emscripten and redox
+    // FIXME repr(simd) broken on emscripten and redox and macOS
     // It's also broken on big-endian powerpc64 and s390x.  #42778
+    // It's also broken on macOS 10.10.  #51794/#51758/#48866/#44056
     #[cfg_attr(not(any(target_os = "emscripten", target_os = "redox",
+                       target_os = "macos",
                        target_endian = "big")),
                repr(simd))]
     struct Block(u64, u64, u64, u64);