RFR: 8247396: PCH should be disabled for opt-size feature with clang after JDK-8246751

[Magnus Ihse Bursie]

On 2020-06-11 14:34, Erik Joelsson wrote:
> I agree with the assessment, but I think the disabling should happen 
> in configure. That way the configure log can accurately tell the user 
> why it was disabled. This can be done by just adding another elif in 
> BPERF_SETUP_PRECOMPILED_HEADERS. To check for a jvm feature in 
> configure, you can use JVM_FEATURES_IS_ACTIVE(opt-size).
Actually, I'm not sure I agree with the assessment. Why does this only 
happen for clang? Is it a problem when building with opt-size and pch 
for other compilers?

If not, that's likely due to the problematic files being excluded from 
PCH (if I remember correctly). I believe a better way forward would be 
to make sure that files that are compiled with a different optimization 
level should be excluded from PCH for clang as well.

/Magnus
>
> /Erik
>
> On 2020-06-11 02:25, jiefu(傅杰) wrote:
>> Hi all,
>>
>> JBS:    https://bugs.openjdk.java.net/browse/JDK-8247396
>> Webrev: http://cr.openjdk.java.net/~jiefu/8247396/webrev.00/
>>
>> -O3 is used for clang on MacOS after JDK-8246751.
>> But it breaks the builds of VMs with opt-size feature when PCH is 
>> enabled.
>>
>> The reason is that the PCH was built with -Os while some other files 
>> were built with -O3, which causes an error with clang.
>> It would be better to disable the PCH for opt-size builds.
>>
>> Thanks a lot.
>> Best regards,
>> Jie