Implement the fast float math intrinsics.

src/terminator/intrinsic.rs

@@ -217,12 +217,20 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
                 self.write_primval(dest, PrimVal::from_f64(f.abs()), dest_ty)?;
             }
 
-            "fadd_fast" => {
+            "fadd_fast" | "fsub_fast" | "fmul_fast" | "fdiv_fast" | "frem_fast" => {
                 let ty = substs.type_at(0);
                 let kind = self.ty_to_primval_kind(ty)?;
                 let a = self.value_to_primval(arg_vals[0], ty)?;
-                let b = self.value_to_primval(arg_vals[0], ty)?;
-                let result = operator::binary_op(mir::BinOp::Add, a, kind, b, kind)?;
+                let b = self.value_to_primval(arg_vals[1], ty)?;
+                let op = match intrinsic_name {
+                    "fadd_fast" => mir::BinOp::Add,
+                    "fsub_fast" => mir::BinOp::Sub,
+                    "fmul_fast" => mir::BinOp::Mul,
+                    "fdiv_fast" => mir::BinOp::Div,
+                    "frem_fast" => mir::BinOp::Rem,
+                    _ => bug!(),
+                };
+                let result = operator::binary_op(op, a, kind, b, kind)?;
                 self.write_primval(dest, result.0, dest_ty)?;
             }
 

tests/run-pass/float_fast_math.rs

@@ -0,0 +1,30 @@
+// Copyright 2016 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.
+
+#![feature(core_intrinsics)]
+
+use std::intrinsics::{fadd_fast, fsub_fast, fmul_fast, fdiv_fast, frem_fast};
+
+#[inline(never)]
+pub fn test_operations(a: f64, b: f64) {
+    // make sure they all map to the correct operation
+    unsafe {
+        assert_eq!(fadd_fast(a, b), a + b);
+        assert_eq!(fsub_fast(a, b), a - b);
+        assert_eq!(fmul_fast(a, b), a * b);
+        assert_eq!(fdiv_fast(a, b), a / b);
+        assert_eq!(frem_fast(a, b), a % b);
+    }
+}
+
+fn main() {
+    test_operations(1., 2.);
+    test_operations(10., 5.);
+}