Remove one use of compare_const_vals.

A direct comparison has the same effect. This also avoids the need for a
type test within `compare_const_vals`.

Author: nnethercote

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

@@ -848,16 +848,7 @@ impl<'tcx> Constructor<'tcx> {
             (Str(self_val), Str(other_val)) => {
                 // FIXME Once valtrees are available we can directly use the bytes
                 // in the `Str` variant of the valtree for the comparison here.
-                match compare_const_vals(
-                    pcx.cx.tcx,
-                    *self_val,
-                    *other_val,
-                    pcx.cx.param_env,
-                    pcx.ty,
-                ) {
-                    Some(comparison) => comparison == Ordering::Equal,
-                    None => false,
-                }
+                self_val == other_val
             }
             (Slice(self_slice), Slice(other_slice)) => self_slice.is_covered_by(*other_slice),
 

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

@@ -755,16 +755,12 @@ pub(crate) fn compare_const_vals<'tcx>(
     ty: Ty<'tcx>,
 ) -> Option<Ordering> {
     assert_eq!(a.ty(), b.ty());
+    assert_eq!(a.ty(), ty);
 
     let from_bool = |v: bool| v.then_some(Ordering::Equal);
 
     let fallback = || from_bool(a == b);
 
-    // Use the fallback if any type differs
-    if a.ty() != ty {
-        return fallback();
-    }
-
     if a == b {
         return from_bool(true);
     }