We REALLY nead a NON-PCH build in JPRT NOW!

Coleen Phillimore coleen.phillimore at oracle.com
Tue Apr 21 18:08:47 UTC 2015

On 4/20/15, 9:31 PM, David Holmes wrote:
> On 21/04/2015 10:14 AM, Volker Simonis wrote:
>> Hi Coleen,
>> the default is not to use PCH and I think that's probably OK for most
>> people. If somebody plays with the include files, he should use the
>> '--disable-precompiled-headers' configure option.
> The default depends on platform. For solaris we never use PCH. For the 
> other platforms I think we always do.

Yes, my motivation with this comment is that instead of adding JPRT 
targets or more work to do in JPRT is to simply make linux x64 at least 
default to non-PCH.  It would break less frequently because that's the 
default and the side benefit is that when you're working and editing a 
header file, you don't get the whole JVM recompiled. IE. I would prefer 
if this were the default so I don't have to add yet another option to my 
configure script.

> Simply switching the default just creates a different problem. 
> Engineers will use PCH locally and so may encounter issues if PCH has 
> not been tested at integration time.

It seems that the converse is more likely though.  If something compiles 
without PCH it's very likely to compile with PCH.

I'd prefer the default changed and not find whether I broke PCH with JPRT.


> I plan to fix this in JPRT by making a few configurations non-PCH.
> David
> -----
>> Making this option the default for the JPRT builds only will guard
>> against the build errors described before while it still allows
>> everybody to do local builds at full speed.
>> Regards,
>> Volker
>> On 4/21/15, Coleen Phillimore <coleen.phillimore at oracle.com> wrote:
>>> Can we just switch the default instead?  Is that a simple makefile 
>>> change?
>>> Coleen
>>> On 4/17/15, 6:35 AM, Lindenmaier, Goetz wrote:
>>>> That would be great!!
>>>> Thanks David,
>>>> Goetz.
>>>> -----Original Message-----
>>>> From: David Holmes [mailto:david.holmes at oracle.com]
>>>> Sent: Freitag, 17. April 2015 12:23
>>>> To: Lindenmaier, Goetz; Volker Simonis; Andrew Dinn
>>>> Cc: HotSpot Open Source Developers
>>>> Subject: Re: We REALLY nead a NON-PCH build in JPRT NOW!
>>>> On 17/04/2015 7:58 PM, Lindenmaier, Goetz wrote:
>>>>> Hi,
>>>>> another occurance of this ...  please, please add a non-pch build to
>>>>> jprt!
>>>>> https://bugs.openjdk.java.net/browse/JDK-8078048
>>>> I will. Unfortunately first I have some no-PCH issues to address. And
>>>> unfortunately they are not top of my priority list right now. 
>>>> Hopefully
>>>> next week sometime.
>>>> David
>>>>> Best regards,
>>>>>      Goetz.
>>>>> -----Original Message-----
>>>>> From: hotspot-dev [mailto:hotspot-dev-bounces at openjdk.java.net] On 
>>>>> Behalf
>>>>> Of Volker Simonis
>>>>> Sent: Donnerstag, 9. April 2015 11:35
>>>>> To: Andrew Dinn
>>>>> Cc: HotSpot Open Source Developers
>>>>> Subject: Re: We REALLY nead a NON-PCH build in JPRT NOW!
>>>>> On Thu, Apr 9, 2015 at 10:10 AM, Andrew Dinn <adinn at redhat.com> 
>>>>> wrote:
>>>>>> On 09/04/15 09:02, Erik Joelsson wrote:
>>>>>>> I think that as long as we claim to support building both with and
>>>>>>> without PCH, the automatic testing should test both with and 
>>>>>>> without
>>>>>>> PCH. By adding one or two build targets, or perhaps change an 
>>>>>>> existing
>>>>>>> target, we could increase our test matrix to cover this easily.
>>>>>> I think this restates Volker's original remarks in redux.
>>>>> No, not at all! I don't necessarily want to test more build
>>>>> configurations (that's another topic).
>>>>> My point is that PCH changes the compilation semantics and can hide
>>>>> real program errors. That's because with PCHs, every compilation unit
>>>>> sees the full precompiled header database (i.e. all the headers which
>>>>> are included in the "precompiled.hpp" PCH file). So if somebody
>>>>> forgets to include a dependency X.hpp in A.cpp, A.cpp may still
>>>>> compile with PCH because it includes the precompiled header file
>>>>> "precompiled.hpp" which in turn includes X.hpp. But the 
>>>>> compilation of
>>>>> A.cpp will fail on platforms/configurations where we do not use
>>>>> precompiled headers. The two references I gave in my original mail 
>>>>> are
>>>>> bugs that resulted from this problem.
>>>>> Besides program errors, the use of PCH can also lead to behavioral
>>>>> changes in the created binary when it comes to inlining. Because of
>>>>> PCHs some compilation units may be able to inline methods even if 
>>>>> they
>>>>> do not explicitly include the files which contain the corresponding
>>>>> implementations because the implementation files are included in the
>>>>> PCH file. Without PCHs the compilers will simply emit calls to these
>>>>> functions (and, depending on the toolchain, emit a warning).
>>>>> I'm not familiar with ccache so I can not say if it has similar 
>>>>> effects.
>>>>>> So, given that we do need this (NOW! :-) is anyone able and 
>>>>>> willing to
>>>>>> sponsor this?
>>>>> Yes, this question remains to be answered :)
>>>>> Regards,
>>>>> Volker
>>>>>> regards,
>>>>>> Andrew Dinn
>>>>>> -----------

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