On 4/11/2018 5:27 PM, Magnus Ihse Bursie wrote:
3 nov. 2018 kl. 23:24 skrev David Holmes <david.hol...@oracle.com>:
On 3/11/2018 10:09 PM, David Holmes wrote:
Looks okay - thanks for doing all the experiments! (Though I'm still curious
what happens if you recompile individual header files :) ).
s/recompile/precompile/ :)
What do you mean? To have more than one set of PCH? As far as I know, all
compilers we use only support a single PCH per source file to compile. So while
you could have a PCH tailored per source file, that would only make sense in a
scenario were you recompile all source files (but no header files) often.
The GCC description for PCH describes it as a per-file header file
optimization. You can precompile each .hpp file and if it is located in
the same directory as the .hpp (or is on an include directory ahead of
the .hpp) then the PCH file will be used instead. So rather than
precompiling precompiled.hpp and having source files include it, you
would precompile each individual (chosen) header file and have that in
the special PCH include directory, and they would then be included where
a source file asked for the corresponding .hpp file.
That would also remove the problem of things not compiling with PCH
disabled as a single set of includes would be used for both PCH and
non-PCH building.
I don't know if the other compilers support PCH in a similar manner to gcc.
Cheers,
David
/Magnus
David
25 // Precompiled headers are turned off for Sun Studio,
May as well change to Solaris Studio if you're going to fix the typo :)
Thanks.
David
On 3/11/2018 7:06 PM, Magnus Ihse Bursie wrote:
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
