Merge ref '125ff8a788c5' from rust-lang/rust

Pull recent changes from https://github.com/rust-lang/rust via Josh.

Upstream ref: 125ff8a788c5d6a66917f499abdc00051afe6886
Filtered ref: bcbe2eb

This merge was created using https://github.com/rust-lang/josh-sync.

Author: The Miri Cronjob Bot

tests/pass/prefetch.rs

@@ -0,0 +1,23 @@
+#![feature(core_intrinsics)]
+
+// Test that these intrinsics work. Their behavior should be a no-op.
+
+fn main() {
+    static X: [u8; 8] = [0; 8];
+
+    ::std::intrinsics::prefetch_read_data::<_, 1>(::std::ptr::null::<u8>());
+    ::std::intrinsics::prefetch_read_data::<_, 2>(::std::ptr::dangling::<u8>());
+    ::std::intrinsics::prefetch_read_data::<_, 3>(X.as_ptr());
+
+    ::std::intrinsics::prefetch_write_data::<_, 1>(::std::ptr::null::<u8>());
+    ::std::intrinsics::prefetch_write_data::<_, 2>(::std::ptr::dangling::<u8>());
+    ::std::intrinsics::prefetch_write_data::<_, 3>(X.as_ptr());
+
+    ::std::intrinsics::prefetch_read_instruction::<_, 1>(::std::ptr::null::<u8>());
+    ::std::intrinsics::prefetch_read_instruction::<_, 2>(::std::ptr::dangling::<u8>());
+    ::std::intrinsics::prefetch_read_instruction::<_, 3>(X.as_ptr());
+
+    ::std::intrinsics::prefetch_write_instruction::<_, 1>(::std::ptr::null::<u8>());
+    ::std::intrinsics::prefetch_write_instruction::<_, 2>(::std::ptr::dangling::<u8>());
+    ::std::intrinsics::prefetch_write_instruction::<_, 3>(X.as_ptr());
+}