On 2015.05.27 at 10:14 +0200, Martin Liška wrote: > I would like to ask folks what is their opinion about support of > precompiled headers for future releases of GCC. From my point of view, > the feature brings some speed-up, but question is if it's worth for? > > Last time I hit precompiled headers was when I was rewriting memory > allocation statistics infrastructure, where GGC memory is 'streamed' > and loaded afterwards in usage of precompiled headers. Because of > that I was unable to track some pointers that were allocated in the > first phase of compilation. > > There are numbers related to --disable-libstdcxx-pch option: > > Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz: > Boostrap time w/ precompiled headers enabled: 35m47s (100.00%) > Boostrap time w/ precompiled headers disabled: 36m27s (101.86%) > > make -j9 check-target-libstdc++-v3 -k time: > precompiled headers enabled: 8m11s (100.00%) > precompiled headers disabled: 8m42s (106.31%) > > Intel(R) Core(TM) i5-3320M CPU @ 2.60GHz: > Boostrap time w/ precompiled headers enabled: 57m35s (100.00%) > Boostrap time w/ precompiled headers disabled: 57m12s (99.33%)
Measuring the impact on bigger projects that use pch like QT or Boost would be more informative perhaps. And until C++ modules are implemented (unfortunately nobody is working on this AFAIK) pch is still the only option left. So deprecating them now seem premature. -- Markus
