gcc-10 optimizer issue about mp-units HOT 9 CLOSED

What does "self contained" mean?

Like a repo which has a 1 line main() and which submodule includes mp-units@trunk and its dependencies?

It's sort of just a cut down version of trunk, really? ie trunk minus tests and other examples?

Or do they mean, actually cut down the code to a "minimal example" which produces the same symptom? Something less than 100 lines of code in a single file.

The latter would make more sense to me.

from mp-units.

from mp-units.

Taken some baby steps and reduced the above example to the below:

1. it's not about int casting
2. it's not about quantity casting either
3. a single calculation won't do it, you need 2 calculations using exactly the same units. The second one breaks.
4. a single dimension/unit won't do it, you need a combination in each calculation

Wild guess: Compiler does the "eval" of the units string for the display of the first value. And thinks it's "cached / already eval'd" for the second one...except it isn't.

[thoughtful face]

https://godbolt.org/z/mYFohP

#include <units/physical/si/velocity.h>
#include <iostream>

using namespace units;

int main()
{
  using namespace si::literals;
  Velocity auto v1 = 100km/2h;
  Velocity auto v4 = 220.1km/3h;

  std::cout << v1 << '\n';    // 50 km/h
  std::cout << v4 << '\n';    // 73.3667  (missing units)
}

from mp-units.

What does "self contained" mean?
It means that all the sample is in a single file without any external headers and ideally no C++ headers.

from mp-units.

If you moved this to "in progress" does that mean you are working on it?
I don't want to double up.
It "might" pop-out quickly, but this could also be a black hole, I fear?

from mp-units.

No, I actually thought that you work on it ;-)

from mp-units.

OK, that's fine. I will let you know how I get on. As I said, I might get stuck...

from mp-units.

It seems that the problem was caused by gcc and was fixed on master: https://godbolt.org/z/pJ7fC_.

from mp-units.

Phew..I was dreading this one!

from mp-units.