Implement a discriminant_value intrinsic

src/libcore/intrinsics.rs

@@ -545,6 +545,11 @@ extern "rust-intrinsic" {
     pub fn u32_mul_with_overflow(x: u32, y: u32) -> (u32, bool);
     /// Performs checked `u64` multiplication.
     pub fn u64_mul_with_overflow(x: u64, y: u64) -> (u64, bool);
+
+    /// Returns the value of the discriminant for the variant in 'v'. If there is no discriminant
+    /// for the type, zero is returned
+    #[cfg(not(stage0))]
+    pub fn discriminant_value<T>(v: &T) -> u64;
 }
 
 

src/librustc_trans/trans/intrinsic.rs

@@ -14,6 +14,7 @@ use llvm;
 use llvm::{SequentiallyConsistent, Acquire, Release, AtomicXchg, ValueRef, TypeKind};
 use middle::subst;
 use middle::subst::FnSpace;
+use trans::adt;
 use trans::base::*;
 use trans::build::*;
 use trans::callee;
@@ -517,6 +518,17 @@ pub fn trans_intrinsic_call<'a, 'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
             }
         }
 
+        (_, "discriminant_value") => {
+            let val_ty = substs.types.get(FnSpace, 0);
+            match val_ty.sty {
+                ty::ty_enum(..) => {
+                    let repr = adt::represent_type(ccx, *val_ty);
+                    adt::trans_get_discr(bcx, &*repr, llargs[0], Some(llret_ty))
+                }
+                _ => C_null(llret_ty)
+            }
+        }
+
         // This requires that atomic intrinsics follow a specific naming pattern:
         // "atomic_<operation>[_<ordering>]", and no ordering means SeqCst
         (_, name) if name.starts_with("atomic_") => {

src/librustc_typeck/check/mod.rs

@@ -5767,6 +5767,12 @@ pub fn check_intrinsic_type(ccx: &CrateCtxt, it: &ast::ForeignItem) {
 
             "assume" => (0, vec![tcx.types.bool], ty::mk_nil(tcx)),
 
+            "discriminant_value" => (1, vec![
+                    ty::mk_imm_rptr(tcx,
+                                    tcx.mk_region(ty::ReLateBound(ty::DebruijnIndex::new(1),
+                                                                  ty::BrAnon(0))),
+                                    param(ccx, 0))], tcx.types.u64),
+
             ref other => {
                 span_err!(tcx.sess, it.span, E0093,
                     "unrecognized intrinsic function: `{}`", *other);

src/test/run-pass/discriminant_value.rs

@@ -0,0 +1,62 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+extern crate core;
+use core::intrinsics::discriminant_value;
+
+enum CLike1 {
+    A,
+    B,
+    C,
+    D
+}
+
+enum CLike2 {
+    A = 5,
+    B = 2,
+    C = 19,
+    D
+}
+
+enum ADT {
+    First(u32, u32),
+    Second(u64)
+}
+
+enum NullablePointer {
+    Something(&'static u32),
+    Nothing
+}
+
+static CONST : u32 = 0xBEEF;
+
+pub fn main() {
+    unsafe {
+
+        assert_eq!(discriminant_value(&CLike1::A), 0);
+        assert_eq!(discriminant_value(&CLike1::B), 1);
+        assert_eq!(discriminant_value(&CLike1::C), 2);
+        assert_eq!(discriminant_value(&CLike1::D), 3);
+
+        assert_eq!(discriminant_value(&CLike2::A), 5);
+        assert_eq!(discriminant_value(&CLike2::B), 2);
+        assert_eq!(discriminant_value(&CLike2::C), 19);
+        assert_eq!(discriminant_value(&CLike2::D), 20);
+
+        assert_eq!(discriminant_value(&ADT::First(0,0)), 0);
+        assert_eq!(discriminant_value(&ADT::Second(5)), 1);
+
+        assert_eq!(discriminant_value(&NullablePointer::Nothing), 1);
+        assert_eq!(discriminant_value(&NullablePointer::Something(&CONST)), 0);
+
+        assert_eq!(discriminant_value(&10), 0);
+        assert_eq!(discriminant_value(&"test"), 0);
+    }
+}