Fix SSE flags for Clang / AppleClang and Cross Compile

[svenevs]

1. Addition of -march=native is currently skipped for all clang.
2. Cross compiling should never include -march=native for any compiler, currently only excluded for GCC.

Will fix after #2100. (Assign to: @svenevs) 😄

[SergioRAgostinho]

@svenevs You can fire up the "oven" for this one. #2100 should be merged in the next few days. 👍

[svenevs]

Oven is at temperature ;)

[SergioRAgostinho]

I went ahead of myself and actually submitted the PR #2416 as you can see 😅 . Can you review it (last commit only) just to guaranteed I covered all points you mentioned in this Issue?

[svenevs]

Ok I'll take a closer look this weekend when I'm back at a Linux box. From the other PR it sounded like you all are pushing for more modern cmake. Generally speaking, tinkering with CMAKE_CXX_FLAGS is discouraged in favor of doing everything target based (target_compile_{features,options}). It keeps things cleaner / makes the targets easier to export assuming you're doing PUBLIC|PRIVATE|INTERFACE appropriately.

You can also then safely use the CheckCXXCompilerFlag module (still guarded underneath checks for cross compiling in this specific case). That makes it so you don't need to worry about clang vs AppleClang vs gcc. You could also then check -xHost for Intel without actually needing to check the compiler ids.

Anyway I'll provide feedback on the PR validating when I can check on both Linux and OSX this weekend. I don't really have time to help with a more thorough removal of CMAKE_CXX_FLAGS but I can definitely check the PR adds the flags for clang so they get in there for what sounds like an imminent release 😄

[SergioRAgostinho]

Ok I'll take a closer look this weekend when I'm back at a Linux box. From the other PR it sounded like you all are pushing for more modern cmake.

Slowly. The change was still driven by a problematic bug with the flags.

It keeps things cleaner / makes the targets easier to export assuming you're doing PUBLIC|PRIVATE|INTERFACE appropriately.

It isn't being done appropriately. The CMake definitely needs revamping but there are more important (project level) short terms goals.

Anyway I'll provide feedback on the PR validating when I can check on both Linux and OSX this weekend. I don't really have time to help with a more thorough removal of CMAKE_CXX_FLAGS but I can definitely check the PR adds the flags for clang so they get in there for what sounds like an imminent release smile.

I tried OS X with Apple's Clang already. I assume Linux will work ok as well but give it a try if you get the chance. There is indeed an imminent release. We've been working over the past months on different items to speed up our release process. Hopefully the changes in our release cycle will be noteworthy.