I bet Google Benchmark will have what you want.
As a first guess, maybe this?
https://github.com/google/benchmark/blob/master/include/benchmark/benchmark.h#L297
(And if godbolt says they are wrong, please send them a PR :))
On Fri, Oct 6, 2017 at 9:16 AM, Gabriele Svelto <gsve...@mozilla.com> wrote:
> On 06/10/2017 11:00, Henri Sivonen wrote:
> > Do we already have a C++ analog of Rust's test::black_box() function?
> > I.e. a function that just passes through a value but taints it in such
> > a way that the optimizer can't figure out that there are no side
> > effects. (For the purpose of ensuring that the compiler can't
> > eliminate computation that's being benchmarked.)
> >
> > If we don't have one, how should one be written so that it works in
> > GCC, clang and MSVC?
> >
> > It's surprisingly hard to find an answer to this on Google or
> > StackOverflow, and experimentation on godbolt.org suggests that easy
> > answers that are found are also wrong.
> >
> > Specifically, this isn't the answer for GCC:
> > void* black_box(void* foo) {
> > asm ("":"=r" (foo): "r" (foo):"memory");
> > return foo;
> > }
>
> IIUC what you are looking for is the '+' constraint which implies the
> parameter is both read and written in the asm statement, e.g.:
>
> void* black_box(void* foo) {
> asm ("":"+r" (foo): "r" (foo):"memory");
> return foo;
> }
>
> Gabriele
>
>
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