Upstream fast path

Author: Nadrieril

compiler/rustc_middle/src/mir/consts.rs

@@ -297,7 +297,15 @@ impl<'tcx> Const<'tcx> {
         tcx: TyCtxt<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
     ) -> Option<ScalarInt> {
-        self.try_eval_scalar(tcx, param_env)?.try_to_int().ok()
+        match self {
+            // Fast path for already evaluated constants.
+            Const::Val(ConstValue::Scalar(Scalar::Int(scalar_int)), _) => Some(scalar_int),
+            Const::Ty(c)
+                if let ty::ConstKind::Value(ty::ValTree::Leaf(scalar_int)) = c.kind()
+                   && c.ty().is_primitive()
+                   => Some(scalar_int),
+            _ => self.try_eval_scalar(tcx, param_env)?.try_to_int().ok(),
+        }
     }
 
     #[inline]

compiler/rustc_middle/src/thir.rs

@@ -941,13 +941,6 @@ impl<'tcx> PatRangeBoundary<'tcx> {
         param_env: ty::ParamEnv<'tcx>,
     ) -> u128 {
         match self {
-            Self::Finite {
-                value: mir::Const::Val(mir::ConstValue::Scalar(Scalar::Int(scalar_int)), _),
-            } => scalar_int.assert_bits(scalar_int.size()),
-            Self::Finite {
-                value: mir::Const::Ty(c),
-            } if let ty::ConstKind::Value(ty::ValTree::Leaf(scalar_int)) = c.kind()
-              => scalar_int.assert_bits(scalar_int.size()),
             Self::Finite { value } => value.eval_bits(tcx, param_env),
             // Self::NegInfinity => {
             //     // Unwrap is ok because the type is known to be numeric.