New hotspot build only builds "PRODUCT"

[Volker Simonis]

On Wed, May 6, 2015 at 10:24 AM, Erik Joelsson <erik.joelsson at oracle.com> wrote:
>
> On 2015-05-05 18:12, Volker Simonis wrote:
>>
>> On Tue, May 5, 2015 at 3:31 PM, Magnus Ihse Bursie
>> <magnus.ihse.bursie at oracle.com> wrote:
>> OK, I see so I won't mess with debug builds then:)
>
> I think leaving debug builds until we are at the stage of organizing flags
> better is OK. Some flags will come from configure, some are based on debug
> level etc.
>>
>> But another question: I just compared the dependencies compiler flags
>> of the old and the new build and realized that for the old build we
>> use '-MMD -MP -MF -fpch-deps' but in the new build we only use '-MMD
>> -MF' (except for x86 which is the only platform in the new build where
>> we still use -fpch-deps). Is this intentional as well?
>>
>> I think the omission of -MP may be related to "8072106: Properly
>> handle dependencies for deleted header files" which created the
>> corresponding targets manually. But what about '-fpch-deps', shouldn't
>> we always use it?
>
> As Magnus said, -MP is more efficient, but we have a general solution that
> achieves the same thing for all platforms already.
>
> Regarding -fpch-deps, I think we should not use it if we declare proper
> dependencies from header files to precompiled header and from precompiled
> header to object files using it. It would just be redundant and with the
> amount of header files being included everywhere in hotspot, redundancy in
> dependency file generation is not something we need. I think the current
> dependency makefiles are already around 50MB!

Hi Erik,

I thought about '-fpch-deps' and I think you're absolutely right! Its
usage is counter-productive.
We should really have every .cpp file include all the headers it
depends on. Using '-fpch-deps' would unnecessarily and drastically
increase the number of files a compilation unit depends on. And now
when I think about it this may also be one of the reasons why in the
old build we actually recompile most of the .ccp files once we change
a single .hpp file which is included in the .pch file (this was
recently discussed in another thread).

So if we're lucky, removing '-fpch-deps' may even increase the speed
of incremental PCH builds.

Regards,
Volker


> /Erik
>