Mark instruction helpers appropriately as constexpr

[axic]

Pulled out of #562.

[axic]

Both fmin and fmax use std::signbit which is not constexpr: https://en.cppreference.com/w/cpp/numeric/math/signbit

[axic]

@chfast could you benchmark this?

[chfast]

@chfast could you benchmark this?

Check assembly output first.

[axic]

I don't see any change in any of the functions touched by this. Some stuff is moved around, so can't tell much with benchmarking.

[codecov]

Codecov Report

Merging #567 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #567   +/-   ##
=======================================
  Coverage   98.24%   98.24%           
=======================================
  Files          62       62           
  Lines        9048     9048           
=======================================
  Hits         8889     8889           
  Misses        159      159           

[chfast]

I don't see any change in any of the functions touched by this. Some stuff is moved around, so can't tell much with benchmarking.

The execute.cpp.s is identical in both cases. As it should be.

[axic]

I don't see any change in any of the functions touched by this. Some stuff is moved around, so can't tell much with benchmarking.

The execute.cpp.s is identical in both cases. As it should be.

It wasn't identical for me. Let me check again.

Still not identical, interestingly the resulting .S is the same number of characters, but the content is different.

[axic]

I don't see any change in any of the functions touched by this. Some stuff is moved around, so can't tell much with benchmarking.

The execute.cpp.s is identical in both cases. As it should be.

It wasn't identical for me. Let me check again.

Still not identical, interestingly the resulting .S is the same number of characters, but the content is different.

I totally forgot to consider optimiser settings when comparing the output. With the settings of the release build indeed it is identical.