Rollup merge of #120733 - klensy:trait-const-fn, r=oli-obk

MirPass: make name more const

Continues #120161, this time applied to `MirPass` instead of `MirLint`, locally shaves few (very few) instructions off.

r? ``@cjgillot``

compiler/rustc_middle/src/lib.rs

@@ -30,6 +30,7 @@
 #![feature(assert_matches)]
 #![feature(box_patterns)]
 #![feature(core_intrinsics)]
+#![feature(const_type_name)]
 #![feature(discriminant_kind)]
 #![feature(exhaustive_patterns)]
 #![feature(coroutines)]

compiler/rustc_middle/src/mir/mod.rs

@@ -140,8 +140,12 @@ fn to_profiler_name(type_name: &'static str) -> &'static str {
 /// loop that goes over each available MIR and applies `run_pass`.
 pub trait MirPass<'tcx> {
     fn name(&self) -> &'static str {
-        let name = std::any::type_name::<Self>();
-        if let Some((_, tail)) = name.rsplit_once(':') { tail } else { name }
+        // FIXME Simplify the implementation once more `str` methods get const-stable.
+        // See copypaste in `MirLint`
+        const {
+            let name = std::any::type_name::<Self>();
+            crate::util::common::c_name(name)
+        }
     }
 
     fn profiler_name(&self) -> &'static str {

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,
+    }
+}

compiler/rustc_mir_transform/src/pass_manager.rs

@@ -8,18 +8,10 @@
 pub trait MirLint<'tcx> {
     fn name(&self) -> &'static str {
         // FIXME Simplify the implementation once more `str` methods get const-stable.
+        // See copypaste in `MirPass`
         const {
             let name = std::any::type_name::<Self>();
-            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,
-            }
+            rustc_middle::util::common::c_name(name)
         }
     }