From 50bc72df448dc284e4ffdc296a85aad3282dc99e Mon Sep 17 00:00:00 2001
From: kennytm <kennytm@gmail.com>
Date: Thu, 17 May 2018 04:24:10 +0800
Subject: [PATCH] Make sure the float comparison output is consistent with the
 expected behavior when NaN is involved.

---
 src/librustc_mir/interpret/operator.rs | 13 +++---
 src/test/run-pass/issue-50811.rs       | 65 ++++++++++++++++++++++++++
 2 files changed, 71 insertions(+), 7 deletions(-)
 create mode 100644 src/test/run-pass/issue-50811.rs

diff --git a/src/librustc_mir/interpret/operator.rs b/src/librustc_mir/interpret/operator.rs
index ef6deab047750..a4a36b0b35581 100644
--- a/src/librustc_mir/interpret/operator.rs
+++ b/src/librustc_mir/interpret/operator.rs
@@ -1,7 +1,6 @@
 use rustc::mir;
 use rustc::ty::{self, Ty};
 use syntax::ast::FloatTy;
-use std::cmp::Ordering;
 use rustc::ty::layout::LayoutOf;
 use rustc_apfloat::ieee::{Double, Single};
 use rustc_apfloat::Float;
@@ -181,12 +180,12 @@ impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M> {
                     let l = <$ty>::from_bits(l);
                     let r = <$ty>::from_bits(r);
                     let val = match bin_op {
-                        Eq => PrimVal::from_bool(l.partial_cmp(&r).unwrap_or(Ordering::Greater) == Ordering::Equal),
-                        Ne => PrimVal::from_bool(l.partial_cmp(&r).unwrap_or(Ordering::Greater) != Ordering::Equal),
-                        Lt => PrimVal::from_bool(l.partial_cmp(&r).unwrap_or(Ordering::Greater) == Ordering::Less),
-                        Le => PrimVal::from_bool(l.partial_cmp(&r).unwrap_or(Ordering::Greater) != Ordering::Greater),
-                        Gt => PrimVal::from_bool(l.partial_cmp(&r).unwrap_or(Ordering::Greater) == Ordering::Greater),
-                        Ge => PrimVal::from_bool(l.partial_cmp(&r).unwrap_or(Ordering::Greater) != Ordering::Less),
+                        Eq => PrimVal::from_bool(l == r),
+                        Ne => PrimVal::from_bool(l != r),
+                        Lt => PrimVal::from_bool(l < r),
+                        Le => PrimVal::from_bool(l <= r),
+                        Gt => PrimVal::from_bool(l > r),
+                        Ge => PrimVal::from_bool(l >= r),
                         Add => PrimVal::Bytes((l + r).value.to_bits()),
                         Sub => PrimVal::Bytes((l - r).value.to_bits()),
                         Mul => PrimVal::Bytes((l * r).value.to_bits()),
diff --git a/src/test/run-pass/issue-50811.rs b/src/test/run-pass/issue-50811.rs
new file mode 100644
index 0000000000000..05b168d98f1f2
--- /dev/null
+++ b/src/test/run-pass/issue-50811.rs
@@ -0,0 +1,65 @@
+// Copyright 2018 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(test)]
+
+extern crate test;
+
+use std::f64::{NAN, NEG_INFINITY, INFINITY, MAX};
+use std::mem::size_of;
+use test::black_box;
+
+// Ensure the const-eval result and runtime result of float comparison are equivalent.
+
+macro_rules! compare {
+    ($op:tt) => {
+        compare!(
+            [NEG_INFINITY, -MAX, -1.0, -0.0, 0.0, 1.0, MAX, INFINITY, NAN],
+            $op
+        );
+    };
+    ([$($lhs:expr),+], $op:tt) => {
+        $(compare!(
+            $lhs,
+            $op,
+            [NEG_INFINITY, -MAX, -1.0, -0.0, 0.0, 1.0, MAX, INFINITY, NAN]
+        );)+
+    };
+    ($lhs:expr, $op:tt, [$($rhs:expr),+]) => {
+        $({
+            // Wrap the check in its own function to reduce time needed to borrowck.
+            fn check() {
+                static CONST_EVAL: bool = $lhs $op $rhs;
+                let runtime_eval = black_box($lhs) $op black_box($rhs);
+                assert_eq!(CONST_EVAL, runtime_eval, stringify!($lhs $op $rhs));
+                assert_eq!(
+                    size_of::<[u8; ($lhs $op $rhs) as usize]>(),
+                    runtime_eval as usize,
+                    stringify!($lhs $op $rhs (forced const eval))
+                );
+            }
+            check();
+        })+
+    };
+}
+
+fn main() {
+    assert_eq!(0.0/0.0 < 0.0/0.0, false);
+    assert_eq!(0.0/0.0 > 0.0/0.0, false);
+    assert_eq!(NAN < NAN, false);
+    assert_eq!(NAN > NAN, false);
+
+    compare!(==);
+    compare!(!=);
+    compare!(<);
+    compare!(<=);
+    compare!(>);
+    compare!(>=);
+}