I see the following failure on auto-tester:
---
****** FAIL debug32 std.datetime.stopwatch
core.exception.AssertError@std/datetime/stopwatch.d(452): unittest failure
----------------
gmake[1]: *** [posix.mak:380: unittest/std/datetime/stopwatch.run] Error 1
gmake[1]: *** Waiting for unfinished jobs....
---
https://auto-tester.puremagic.com/show-run.ghtml?projectid=1&runid=3102407&isPull=true
```
void f0() nothrow {}
void f1() nothrow { auto b = to!string(a); }
auto r = benchmark!(f0, f1)(1000);
assert(r[0] >= Duration.zero);
assert(r[1] > Duration.zero);
assert(r[1] > r[0]);
```
It looks like we need to disable optimization of f1.