precompiled header rule misses build type flags

[nbuwe]

add_pch_rule in vm/cmake/functions.cmake doesn't correctly add build type specific flags to the rule that produces the precompiled header. this makes the compiler complain later on, when the precompiled header is used, that the flags used to create the header and the flags it is used with are different and that the precompiled header will be ignored.

The flags that are missing are stuff from COMPILE_DEFINITIONS_RELEASE and friends set in vm/cmake/configurations.cmake (like GENERATE_DEBUGGING_AIDS, etc)

I don't have any cmake-fu to fix this. I figure it needs gather_flags but my naive attemtps fail with "get_property could not find TARGET .../self/vm. Perhaps it has not yet been created."

[nbuwe]

As a side note, precompiled header that is forced to be included with -include on the command line makes #pragma interface in the source files invalid (hence the ifdef around them). this makes all inline functions from the headers to be emitted in every object file. For the RelWithDebInfo (i.e. optimized) this gives about 4MB Self binary, but the object files total 83MB of code, i.e. about 95% is duplicates.

If I don't fix up the precompiled header rule manually and so the precompiled header is not used, the slowdown is not too bad - about 4% user time (1% wall time in my -j4 build).

Would be interesting to test with proper include hygiene, but that requires a lot of menial changes, so not a quick test to try.

[nbuwe]

I have tried to compile with #pragma implementation in effect and it reduces object file sizes and compilation time quite a bit. On Linux with -j4 a RelWithDebInfo build with manually fixed pch rule goes:

$ tail -3 build-reldbg/.log
real	20m35.995s
user	72m48.945s
sys	2m45.777s

$ size build-reldbg/vm/Self
   text	   data	    bss	    dec	    hex	filename
4287395	  38344	 151148	4476887	 444fd7	build-reldbg/vm/Self

$ ll build-reldbg/vm/Self
-rwxrwxr-x 1 uwe uwe 373488596 Aug 12 01:54 build-reldbg/vm/Self*

$ find build-reldbg/vm/CMakeFiles/Self.dir -name '*.o' | xargs size -t | tail -1
87429670	  36053	 150638	87616361	538eb69	(TOTALS)

vs.

$ tail -3 build-reldbg-pragma/.log
real	6m18.492s
user	21m9.525s
sys	1m5.130s

$ size build-reldbg-pragma/vm/Self
   text	   data	    bss	    dec	    hex	filename
4397634	  38344	 151148	4587126	 45fe76	build-reldbg-pragma/vm/Self

$ ll build-reldbg-pragma/vm/Self
-rwxrwxr-x 1 uwe uwe 91423604 Aug 12 23:55 build-reldbg-pragma/vm/Self*

$ find build-reldbg-pragma/vm/CMakeFiles/Self.dir -name '*.o' | xargs size -t | tail -1
21322576	  36053	 150638	21509267	1483493	(TOTALS)

To do this test I have added a bunch of #include "_precompiled.hh" to the cpp files and dropped -include for it from the command line. This might be easier to do by including _precompiled.hh in the generated _<file>.cpp.incl files, but it would have taken me longer to figure out how to do that.

I haven't yet checked where the 110K text size increase comes from. But otherwise this looks like something worth pursuing.

[nbuwe]

Ah, the build sets -fkeep-inline-functions for gcc. And I used to wonder, why clang was so lightning fast... Dropping that flag brings the build time down to just a few minutes

real	1m49.889s
user	5m48.046s
sys	0m34.977s

and object files are now tiny.