---

yaml
---
r: 169908
b: refs/heads/auto
c: cd85f0a
h: refs/heads/master
v: v3

Author: steveklabnik

[refs]

@@ -10,7 +10,7 @@ refs/tags/release-0.3: b5f0d0f648d9a6153664837026ba1be43d3e2503
 refs/tags/release-0.3.1: 495bae036dfe5ec6ceafd3312b4dca48741e845b
 refs/tags/release-0.4: e828ea2080499553b97dfe33b3f4d472b4562ad7
 refs/tags/release-0.5: 7e3bcfbf21278251ee936ad53e92e9b719702d73
-refs/heads/auto: 20fa7cbfc0b5143f6c88e288772fc0f65610c2ec
+refs/heads/auto: cd85f0a56a790f24bb1c1928fbc37c9d24dd2937
 refs/heads/servo: af82457af293e2a842ba6b7759b70288da276167
 refs/tags/release-0.6: b4ebcfa1812664df5e142f0134a5faea3918544c
 refs/tags/0.1: b19db808c2793fe2976759b85a355c3ad8c8b336

branches/auto/src/doc/guide-testing.md

@@ -556,8 +556,12 @@ extern crate test;
 # fn main() {
 # struct X; impl X { fn iter<T>(&self, _: || -> T) {} } let b = X;
 b.iter(|| {
-    test::black_box(range(0u, 1000).fold(0, |old, new| old ^ new));
-});
+    let mut n = 1000_u32;
+
+    test::black_box(&mut n); // pretend to modify `n`
+
+    range(0, n).fold(0, |a, b| a ^ b)
+})
 # }
 ```
 
@@ -573,3 +577,6 @@ test bench_xor_1000_ints ... bench:       1 ns/iter (+/- 0)
 
 test result: ok. 0 passed; 0 failed; 0 ignored; 1 measured
 ```
+
+However, the optimizer can still modify a testcase in an undesirable manner
+even when using either of the above.