reduce RPC overhead for common proc_macro operations

Cargo.lock

@@ -3886,6 +3886,7 @@ dependencies = [
  "rustc_span",
  "smallvec",
  "tracing",
+ "unicode-normalization",
 ]
 
 [[package]]

compiler/rustc_expand/Cargo.toml

@@ -24,3 +24,4 @@ rustc_parse = { path = "../rustc_parse" }
 rustc_session = { path = "../rustc_session" }
 smallvec = { version = "1.6.1", features = ["union", "may_dangle"] }
 rustc_ast = { path = "../rustc_ast" }
+unicode-normalization = "0.1.11"

library/proc_macro/src/bridge/buffer.rs

@@ -1,10 +1,41 @@
 //! Buffer management for same-process client<->server communication.
 
 use std::io::{self, Write};
+use std::marker::PhantomData;
 use std::mem;
 use std::ops::{Deref, DerefMut};
 use std::slice;
 
+#[repr(C)]
+pub struct Slice<'a> {
+    data: *const u8,
+    len: usize,
+    _marker: PhantomData<&'a [u8]>,
+}
+
+unsafe impl<'a> Send for Slice<'a> {}
+unsafe impl<'a> Sync for Slice<'a> {}
+
+impl<'a> Copy for Slice<'a> {}
+impl<'a> Clone for Slice<'a> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl<'a> From<&'a [u8]> for Slice<'a> {
+    fn from(xs: &'a [u8]) -> Self {
+        Slice { data: xs.as_ptr(), len: xs.len(), _marker: PhantomData }
+    }
+}
+
+impl<'a> Deref for Slice<'a> {
+    type Target = [u8];
+    fn deref(&self) -> &[u8] {
+        unsafe { slice::from_raw_parts(self.data, self.len) }
+    }
+}
+
 #[repr(C)]
 pub struct Buffer {
     data: *mut u8,