-ffast-math trick is not working

[RJ Skerry-Ryan]

Bug #1524561 introduced a dedicated object in our binary that is built without -ffast-math.

Our header macro tricks are causing failing builds on some systems.

https://github.com/mixxxdj/mixxx/commit/7e9bba7e88842b5bbb5e7b4ee602b410c455892d#commitcomment-17448450

And:

m0r13 (IRC)
hey guys, I'm having a problem building mixxx on arch linux
got the error output and gcc version (6.1.1) here: https://gist.github.com/m0r13/daea7e93ab04b349039a5acb12472972
M
I was able to build mixxx from sources until I got gcc 6 I think, unfortunately I can't try it again with gcc 5 or 4, as I'm getting errors too building those from aur

[Daniel Schürmann (daschuer)]

> Changing that cmath to #include "/usr/include/c++/6.1.1/math.h"
did the trick.

We may also move verify that we include util/math.h before all external include files that
use fpclassify and friends.

[RJ Skerry-Ryan (rryan)]

> Changing that cmath to #include "/usr/include/c++/6.1.1/math.h"
did the trick.

That's just a workaround though -- not a real fix.

> We may also move verify that we include util/math.h before all external include files that
use fpclassify and friends.

Correct me if I'm wrong -- but if we include util/math.h and a file we include afterwards includes cmath, then we will see the same problem, right? What about headers outside of our control?

[Daniel Schürmann (daschuer)]

>> Changing that cmath to #include "/usr/include/c++/6.1.1/math.h"
did the trick.

> That's just a workaround though -- not a real fix.

IMHO that is the fix for all plain fpclassify calls nim Mixxx and in external headers.
I have no solution for explicit "std::fclassify" calls or "using" statements in external code though.

Do you think we should prepare defines for that or just ignore that case?
For now I am not aware of a single fclassify call in any header. So the issue might be only a hypothetical one.

> Correct me if I'm wrong -- but if we include util/math.h and a file we include afterwards includes cmath, then we will see the same problem, right? What about headers outside of our control?

From gcc version 6.1.1 <math.h> includes <cmath> and the include guards will prevent the issues.
In previous gcc version math.h cmath seams to be independent. So i am not sure if it works on all compilers versions and targets, hopefully it will not reintroduce other math header issues. So I am afraid we can just do try and error.

[RJ Skerry-Ryan (rryan)]

> IMHO that is the fix for all plain fpclassify calls nim Mixxx and in external headers.

I was responding to the "/usr/include" and "6.6.1" in the path -- that's definitely not going to work on systems that don't locate the library in /usr/include or don't have version 6.6.1 of libc++/libstdc++, right?

[Daniel Schürmann (daschuer)]

Oh, I had missed that.
Just #include <math.h> should work as well.

[Daniel Schürmann (daschuer)]

Trying at https://github.com/mixxxdj/mixxx/pull/957

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/8562