The reasons for the current set of files included in precompiled.hpp is
somewhat lost in the mists of history. However, it is clear that it is
not optimal.
This patch replaces the current set with a new set, based on how often a
header file is included in a C++ file. This selection contains all
header files that are included by at least 130 C++ files. Testing has
shown that this is around the optimal value -- include many more, and
too many "innocent" files get hurt by unneeded work, leave out many
more, and we miss out on optimization possibilities.
The same set turned out to work well for both clang and gcc. However,
files named "*.inline.hpp" did hurt rather than help performance, so
those have been left out. For visual studio, the same set was also
optimal, as long as the inline files were included. Presumably, visual
studio is better than gcc/clang on handling precompiled headers
containing inlined code.
Here are some rough comparisons from our internal CI system, for
building the target "hotspot" from scratch.
macosx-x64:
old: 00:05:00
new: 00:03:47
linux-x64:
old: 00:05:43
new: 00:04:51
windows-x64:
old: 00:05:18
new: 00:04:33
linux-aarch64:
old: 00:07:57
new: 00:03:48
Bug: https://bugs.openjdk.java.net/browse/JDK-8213339
WebRev:
http://cr.openjdk.java.net/~ihse/JDK-8213339-update-precompiled-headers/webrev.01
/Magnus
