manmanren added a comment.
Bruno helped on collecting performance data for this patch:
$ cat cocoa-test.h
#import <Cocoa/Cocoa.h>
$ rm -rf tmp; clang -x objective-c -isysroot `xcrun --sdk macosx
--show-sdk-path` -fblocks -fmodules -fmodules-cache-path=tmp cocoa-test.h
-fsyntax-only
clang-release (10 runs)
-----------------------
name avg min med max SD SD% total
user 2.0023 1.9804 1.9994 2.0408 0.0149 0.74 20.0225
sys 0.3601 0.3547 0.3505 0.4454 0.0287 7.98 3.6007
wall 2.5432 2.4291 2.4264 3.3604 0.2737 10.76 25.4324
clang-modhash-release (10 runs)
-------------------------------
name avg min med max SD SD% total
user 2.1101 2.0935 2.1095 2.1274 0.0112 0.53 21.1012
sys 0.3485 0.3462 0.3556 0.3476 0.0052 1.50 3.4854
wall 2.5614 2.5163 2.5605 2.6657 0.0419 1.63 25.6138
This ~5% slowdown for the total time of compiling all the modules (30+ modules).
A similar test for one object file in selfhost clang:
[TemplateName.cpp.o] clang-release (10 runs)
--------------------------------------------
name avg min med max SD SD% total
user 7.4332 7.3716 7.4369 7.4976 0.0444 0.60 74.3318
sys 0.5646 0.5512 0.5688 0.5570 0.0161 2.86 5.6464
wall 8.3357 8.1675 8.2991 8.2570 0.3240 3.89 83.3568
[TemplateName.cpp.o] clang-modhash-release (10 runs)
----------------------------------------------------
name avg min med max SD SD% total
user 7.6911 7.6202 7.6979 7.7779 0.0418 0.54 76.9114
sys 0.5531 0.5437 0.5520 0.5622 0.0105 1.89 5.5315
wall 8.4598 8.3868 8.4839 8.5497 0.0455 0.54 84.5977
~3.5% slowdown for total of modules:
$ ls module.cache/1UKP65OUKXURH/
Clang_AST-1XMT5DOVQWGLJ.pcm LLVM_C-2WKTHJHA6SDF0.pcm
LLVM_Pass-HNKP05GYNHFQ.pcm
_Builtin_stddef_max_align_t-2T552E4NSAIDI.pcm
Clang_Basic-1XMT5DOVQWGLJ.pcm
LLVM_Config_ABI_Breaking-2FT1AFJTZ51QZ.pcm
LLVM_Support_DataTypes-2FT1AFJTZ51QZ.pcm modules.idx
Darwin-399Z2LWDSMSTV.pcm LLVM_IR-HNKP05GYNHFQ.pcm
LLVM_Utils-HNKP05GYNHFQ.pcm std-1337JMP4UGPIP.pcm
Note that the cache was wiped out right before every tests instance.
--------------------------------------------------------------------
Thanks Bruno. I am going to guard the hashing with a CC1 option (something like
fmodules-hash-content) and force that flag to be enabled when the frontend
implicitly builds a module. We will try to improve the hashing performance
later (either improving SHA1 or using MD5 instead of SHA1).
Manman
https://reviews.llvm.org/D27689
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