fast-path for try_eval_scalar (instead of try_eval_scalar_int)

Author: RalfJung

compiler/rustc_middle/src/mir/consts.rs

@@ -279,7 +279,14 @@ impl<'tcx> Const<'tcx> {
         tcx: TyCtxt<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
     ) -> Option<Scalar> {
-        self.eval(tcx, param_env, None).ok()?.try_to_scalar()
+        match self {
+            Const::Ty(c) => {
+                // Avoid the `valtree_to_const_val` query.
+                let val = c.eval(tcx, param_env, None).ok()?;
+                val.try_to_scalar()
+            }
+            _ => self.eval(tcx, param_env, None).ok()?.try_to_scalar(),
+        }
     }
 
     #[inline]
@@ -288,16 +295,7 @@ impl<'tcx> Const<'tcx> {
         tcx: TyCtxt<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
     ) -> Option<ScalarInt> {
-        match self {
-            // If the constant is already evaluated, we shortcut here.
-            Const::Ty(c) if let ty::ConstKind::Value(valtree) = c.kind() => {
-                valtree.try_to_scalar_int()
-            },
-            // This is a more general form of the previous case.
-            _ => {
-                self.try_eval_scalar(tcx, param_env)?.try_to_int().ok()
-            },
-        }
+        self.try_eval_scalar(tcx, param_env)?.try_to_int().ok()
     }
 
     #[inline]