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

[Daniel Jeliński]

On Mon, 6 Nov 2023 12:26:58 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> FWIW, I compiled the code without this PR, but with `HARFBUZZ_CFLAGS += -DHB_NO_SUBSET_LAYOUT -DHB_NO_SUBSET_CFF` instead, and checked `make LOG=profile` output. Results:
>> - without this change, compiling `hb-subset.cc` took 56 seconds, and `hb-subset-plan.cc` took 33 seconds
>> - with this change, compiling `hb-subset.cc` took 33 seconds, and `hb-subset-plan.cc` took 22 seconds
>> 
>> It's a nice improvement, but not compiling these files at all is still much better.
>
> @djelinski Just curious; what would the effect be to both include this change and setting the NO_* defines?
> 
> If all the references to these defines are made in the excluded files then the only reason for doing that would be some kind of information to subsequent readers of the code, but they might also be checked elsewhere, and thus give an additional speedup.

HB_NO_SUBSET_CFF is indeed referenced in 2 header files, which are in turn included somewhere else.
I added the defines on top of the excludes, but this resulted in no measurable build time difference.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16440#discussion_r1383306726