Rename _match to usefulness

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -1,5 +1,5 @@
-use super::_match::Usefulness::*;
-use super::_match::{
+use super::usefulness::Usefulness::*;
+use super::usefulness::{
     compute_match_usefulness, expand_pattern, MatchArm, MatchCheckCtxt, UsefulnessReport,
 };
 use super::{PatCtxt, PatKind, PatternError};

compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs

@@ -4,8 +4,8 @@
 use self::Constructor::*;
 use self::SliceKind::*;
 
-use super::_match::{MatchCheckCtxt, PatCtxt};
 use super::compare_const_vals;
+use super::usefulness::{MatchCheckCtxt, PatCtxt};
 use super::{FieldPat, Pat, PatKind, PatRange};
 
 use rustc_data_structures::captures::Captures;

compiler/rustc_mir_build/src/thir/pattern/mod.rs

@@ -1,9 +1,9 @@
 //! Validation of patterns/matches.
 
-mod _match;
 mod check_match;
 mod const_to_pat;
 mod deconstruct_pat;
+mod usefulness;
 
 pub(crate) use self::check_match::check_match;