On Wed, 23 Mar 2022 12:25:08 GMT, Magnus Ihse Bursie <i...@openjdk.org> wrote:
> [JDK-8247872](https://bugs.openjdk.java.net/browse/JDK-8247872) (upgrade > HarfBuzz to 2.7.2) caused build time to go up with 24 seconds on my reference > linux machine. This was one of the four culprits that caused a 25-30% build > time regression over the last two years. > > The problem here was that the new HarfBuzz code caught really bad behaviour > from gcc when compiling with optimizations. The official HarfBuzz build does > not use any -O flags at all for gcc, so presumably the HarfBuzz team is: > > a) not thinking compiler optimization is important for the performance of > this library, and > b) unaware that their code causes such a headache for gcc. > > (Other compilers fare much better: visual studio makes no difference at all, > and for clang just a small regression was observed.) > > The current optimization level was introduced by > [JDK-8255790](https://bugs.openjdk.java.net/browse/JDK-8255790), which were > really about moving libharfbuzz compilation back into libfontmanager. I could > find no comments/discussion relating to the change of optimization level, so > I assume it was incidental, and just seemed good at the time. > > This patch changes the optimization level to `SIZE` (which is the closest > thing we have to no optimization level) on gcc. I have a question, though, because I suppose font rendering engine is performance sensitive. AFAICS, the `LIBFONTMANAGER_OPTIMIZATION` was changed from `HIGH` to `HIGHEST` here: https://github.com/openjdk/jdk/commit/05fe06a6#diff-c75e2d581b3730cf900075cedb66ac72eaba40fbbd92eaac5710161830b572b4L534-R491 Does it mean we should instead downgrade to `HIGH`, not `SIZE`? Would that recover the build times? ------------- PR: https://git.openjdk.java.net/jdk/pull/7919
