update codegen of discriminant_value

src/librustc_codegen_llvm/intrinsic.rs

@@ -188,11 +188,11 @@ impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
             }
             "size_of" | "pref_align_of" | "min_align_of" | "needs_drop" | "type_id"
             | "type_name" => {
-                let ty_name = self
+                let value = self
                     .tcx
                     .const_eval_instance(ty::ParamEnv::reveal_all(), instance, None)
                     .unwrap();
-                OperandRef::from_const(self, ty_name, ret_ty).immediate_or_packed_pair(self)
+                OperandRef::from_const(self, value, ret_ty).immediate_or_packed_pair(self)
             }
             // Effectively no-op
             "forget" => {
@@ -549,7 +549,13 @@ impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
                 }
             }
 
-            "discriminant_value" => args[0].deref(self.cx()).codegen_get_discr(self, ret_ty),
+            "discriminant_value" => {
+                if ret_ty.is_integral() {
+                    args[0].deref(self.cx()).codegen_get_discr(self, ret_ty)
+                } else {
+                    span_bug!(span, "Invalid discriminant type for `{:?}`", arg_tys[0])
+                }
+            }
 
             name if name.starts_with("simd_") => {
                 match generic_simd_intrinsic(self, name, callee_ty, args, ret_ty, llret_ty, span) {

src/librustc_mir/interpret/intrinsics.rs

@@ -2,8 +2,6 @@
 //! looking at their MIR. Intrinsics/functions supported here are shared by CTFE
 //! and miri.
 
-use std::convert::TryFrom;
-
 use rustc_hir::def_id::DefId;
 use rustc_middle::mir::{
     self,
@@ -220,7 +218,12 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             sym::discriminant_value => {
                 let place = self.deref_operand(args[0])?;
                 let discr_val = self.read_discriminant(place.into())?.0;
-                self.write_scalar(Scalar::from_u64(u64::try_from(discr_val).unwrap()), dest)?;
+                let scalar = match dest.layout.ty.kind {
+                    ty::Int(_) => Scalar::from_int(discr_val as i128, dest.layout.size),
+                    ty::Uint(_) => Scalar::from_uint(discr_val, dest.layout.size),
+                    _ => bug!("invalid `discriminant_value` return layout: {:?}", dest.layout),
+                };
+                self.write_scalar(scalar, dest)?;
             }
             sym::unchecked_shl
             | sym::unchecked_shr

src/librustc_typeck/check/intrinsic.rs

@@ -8,7 +8,7 @@ use rustc_hir as hir;
 use rustc_middle::traits::{ObligationCause, ObligationCauseCode};
 use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::{self, Ty, TyCtxt};
-use rustc_span::symbol::{Ident, Symbol};
+use rustc_span::symbol::Symbol;
 use rustc_target::spec::abi::Abi;
 
 use std::iter;