RFR : 8218965: aix: support xlclang++ in the compiler detection

[Magnus Ihse Bursie]

On 2019-02-14 15:44, Baesken, Matthias wrote:
> Hello,
>
> please review this small  change .
>
> On AIX,   it adds   detection  of xlc16 /  clang    to the  build environment.
>
> The xlc16  package contains   2 compiler frontends :
>
>
>    *   The legacy  xlc
>    *   The new clang-based  xlclang++
>
> For older xlc (12 / 13)  we should for now still support the "legacy"  xlc .
> For  xlc16    the usage  of   xlclang++    is desired , because  it  promises better C++11/14   support  (important for the coming JEPs dealing with C++11/14 features)  .
>
> Additionally to the compiler detection , the  debug-flag is changed to -g1  when xlclang++ is used  (because of issues with -g) ;    thanks to Steven for providing the info.
>
>
>
> Bug/webrev :
>
> https://bugs.openjdk.java.net/browse/JDK-8218965
>
> http://cr.openjdk.java.net/~mbaesken/webrevs/8218965.0/
Hi Matthias,

I have several doubts about this patch.

Let me start at the highest level before dwelling on details.

Is this really the right way to handle this? Maybe we should either 
treat xlclang as a new, separate toolchain, or we should treat xlclang 
as a variant of the clang toolchain.

If xlclang is very similar to clang (same compilation behavior, same 
compiler flags), then I believe the latter way is the proper way forward.

If xlclang is -- even though the change of frontend -- mostly similar to 
the traditional xlc, then the path chosen by you might be the best way 
forward after all.

If xlclang is different enought from both the traditional xlc, and from 
clang, we might want to treat it like an entirely new toolchain. We can 
of course share code with the existing xlc and clang toolchains. I think 
this is the best way if e.g. compiler flags are still shared with xlc, 
but source code defines etc is shared with clang. That way we can test 
for "xlc or xlclang" when setting up flags, but "clang or xlclang" in 
the #ifdefs.

---

If we should go forward with your patch, please note the following:

We try to use "true" and "false" as values for boolean variable, so 
"AIX_USE_CLANG=1" should be "AIX_USE_CLANG=true".

The test to determine if we're using xlclang seem to happen in the wrong 
location. It also calls the bare "xlclang++" from the path, without any 
consideration if the user has specified a toolchain path, etc.

I won't go into more details on the patch until we've determined if this 
is the solution we should pursue.

/Magnus
>
>
>
> Thanks, Matthias