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

[jiefu(傅杰)]

Hi Erik and Magnus,

Thanks for your help.

Updated: http://cr.openjdk.java.net/~jiefu/8247396/webrev.02/
Also I've changed the JBS title to 'Exclude PCH for files in $(OPT_SPEED_SRC) with clang after JDK-8246751'.

Please review it and give me some adviece.

Thanks a lot.
Best regards,
Jie

On 2020/6/11, 9:54 PM, "Erik Joelsson" <erik.joelsson at oracle.com> wrote:

    On 2020-06-11 06:41, Magnus Ihse Bursie wrote:
    > 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.
    >
    Right, I just took a look and in JvmOverrideFiles.gmk we build a list of 
    files to exclude from precompiled header. We could just add 
    $(OPT_SPEED_SRC) to this list (as that variable is defined earlier in 
    JvmFeatures.gmk). OPT_SPEED_SRC is empty unless opt-size is true, so 
    just adding it to the list should be fine.
    
    /Erik
    
    > /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
    >