RFR: 8329257: AIX: Switch HOTSPOT_TOOLCHAIN_TYPE from xlc to gcc [v3]

[Magnus Ihse Bursie]

On Wed, 17 Apr 2024 11:52:42 GMT, Julian Waters <jwaters at openjdk.org> wrote:

>> @magicus @TheShermanTanker @TheRealMDoerr @kimbarrett 
>> Let me summarize the choices we have and ask for your vote.
>> Julian dislikes the `-Dalloca'(size)'=__builtin_alloca'(size)'` in `flags-cflags.m4` I introduced to get rid of 
>> 
>> #if defined(_AIX)
>> #include <alloca.h>
>> #endif
>> 
>> in `globalDefinitions_gcc.hpp`. 
>> 
>> We have three possible solutions
>> 
>> 1. Reintroduce
>> 
>> #if defined(_AIX)
>> #include <alloca.h>
>> #endif
>> 
>> in `globalDefinitions_gcc.hpp`. 
>> 
>> 2. Unconditionally introduce only `#include <alloca.h>` in `globalDefinitions_gcc.hpp`. This should work for all platforms using this header including the unofficial Windows/gcc Port, although only AIX needs it. 
>> 
>> 3. Add 
>> 
>> #if defined(_AIX)
>> #include <alloca.h>
>> #endif
>> 
>> to the sources using alloca(). These are
>> /hotspot/share/runtime/os.cpp
>> /hotspot/share/runtime/javaThread.cpp
>> /hotspot/share/utilities/vmError.cpp
>> Here we need the AIX condition, because otherwise the classic Windows Build (NTAMD64) fails.
>> 
>> I will implement the solution with the most likes and having no dislike.
>
> I don't mind all 3, though I certainly prefer 1 and 3 over 2 (The way I see it, the AIX macro check is more of a message to the programmer than it is important to the compiler, so I prefer the options that have it. However, I also don't mind if we were to go the way of option 2, this is more of a preference thing). The fact that only 3 files need it is also surprising to me, and makes option 3 seem like a good fit (Again, personal preference)
> 
> Magnus and Kim, what do you guys think?

If there are just 3 files using alloca, I strongly prefer solution 3. I think solution 1 has already been rejected by Kim.

(Also, for the record, it was me, not Julian, who expressed dislike about the `-Dalloca'(size)'=__builtin_alloca'(size)'` change)

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/18536#discussion_r1568754458