MirPass: make name more const

compiler/rustc_middle/src/util/common.rs

@@ -65,3 +65,19 @@ pub fn indenter() -> Indenter {
     debug!(">>");
     Indenter { _cannot_construct_outside_of_this_module: () }
 }
+
+// const wrapper for `if let Some((_, tail)) = name.rsplit_once(':') { tail } else { name }`
+pub const fn c_name(name: &'static str) -> &'static str {
+    // FIXME Simplify the implementation once more `str` methods get const-stable.
+    // and inline into call site
+    let bytes = name.as_bytes();
+    let mut i = bytes.len();
+    while i > 0 && bytes[i - 1] != b':' {
+        i = i - 1;
+    }
+    let (_, bytes) = bytes.split_at(i);
+    match std::str::from_utf8(bytes) {
+        Ok(name) => name,
+        Err(_) => name,
+    }
+}