RFR: 8348207: Linux PPC64 PCH build broken after JDK-8347909

[Magnus Ihse Bursie]

On Fri, 24 Jan 2025 08:10:21 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

>> I agree with Magnus the files should only be excluded where there is a problem and for PPC the problem can be fixed by using the same `-m` flag (or else fixing the build logic to check for PPC as Magnus has).
>> 
>> As far as I can see PCH has been used with these files on Linux and gcc with no problem for other architectures. I'm still unclear exactly what changed for PPC.
>
>> Note that OPT_SPEED_SRC contains a rather large set of files. They have previously been compiling using PCH just fine with gcc. I don't think it is motivated to exclude them everywhere, just because gcc on ppc64 has a problem.
> 
> It seems usually it is empty, because in 99% of cases  people will not set the opt-size jvm feature 
> 
> 
> 193 ifeq ($(call check-jvm-feature, opt-size), true)
> 194   JVM_OPTIMIZATION := SIZE
> 195   OPT_SPEED_SRC := \
> 196       allocation.cpp \
> 
> 
> I haven't checked what happens with those recent PCH changes, when opt-size is configured.  If it works I am fine with your approach too that does not  add those to  JVM_PRECOMPILED_HEADER_EXCLUDE .

I must admit I did not realize this list was dependent on the `opt-size` feature, so I cannot say if my patch really works with that enabled. Maybe the OPT_SPEED_SRC list is needed then, after all.

Nevertheless, I think we can limit the change for ppc on gcc. When I added the -W flag for more detailed warnings, I was taught that it was the value of some -mpower-..somethingsomething flag that was problematic for PCHs. So it seems like it could be a very much PPC specific problem.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/23268#discussion_r1928318138