RFR: 8319197: Exclude hb-subset and hb-style from compilation

[Phil Race]

On Wed, 1 Nov 2023 18:51:26 GMT, Phil Race <prr at openjdk.org> wrote:

>> hb-subset and hb-style APIs are not used and not exported by libfontmanger. We can cut the compilation time by not compiling the unused files.
>> 
>> The added exclusions reduce the build time by ~1 minute (~8%) on my machine. This is with harfbuzz 8, with harfbuzz 7 the improvement was ~30 seconds.
>> 
>> Client libs tests continue to pass.
>
> make/modules/java.desktop/lib/Awt2dLibraries.gmk line 499:
> 
>> 497:    LIBFONTMANAGER_EXCLUDE_FILES += hb-ft.cc hb-subset-cff-common.cc \
>> 498:        hb-subset-cff1.cc hb-subset-cff2.cc hb-subset-input.cc hb-subset-plan.cc \
>> 499:        hb-subset.cc hb-subset-instancer-solver.cc gsubgpos-context.cc hb-style.cc
> 
> I'm quite confused from where you got gsubgpos-context.cc. I don't see any file of that name.
> Also I just realised that since the Nov 2020 import of freetype it has a bunch of handly ifdefs that
> you can see in hb-config.h
> And so probably a better way of doing this, even if it means one of these files (the instance-solver one) doesn't seem to get the ifdef treatment is to use the specific defines passed to the build.
> Then I'd expect harfbuzz to apply the same ifdef even if these files got refactored.
> I further noticed that the same 2020 update adds HAVE_FREETYPE and hb-ft.cc isn't compiled unless you actually set that. Which we don't
> So this whole exclude can go away and be replaced by a few -D defines.
> You could probably go overboard and experiment with all sorts of combinations from hb-config.h but I recommend you just apply the minimal set that makes your build time happier.
> hb-style.cc isn't one I'd have realised we don't currently need .. and for many of them it isn't clear to me without research what the consequences would be of excluding it. Without that support would something non-optimal happen in some cases - you can't trust the tests we have to come near proving it.
> I know we don't subset, and that's the only one I consider "safe" to use here without actual research.

These two
#define HB_NO_SUBSET_LAYOUT
#define HB_NO_SUBSET_CFF

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PR Review Comment: https://git.openjdk.org/jdk/pull/16440#discussion_r1379184282