__cxa_throw performance issue


Bugzilla Link	PR51037
Status	NEW
Importance	P enhancement
Reported by	glibcxx.chrono@gmail.com (glibcxx.chrono@gmail.com)
Reported on	2021-07-09 04:20:16 -0700
Last modified on	2021-07-09 04:20:16 -0700
Version	12.0
Hardware	PC Linux
CC	llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
Fixed by commit(s)
Attachments	`clang_expensive_error_handling.cpp` (5974 bytes, text/x-c++src)
Blocks
Blocked by
See also

Created attachment 25012 File with code in issue

Hi, i noticed this unusual behaviour of exception-throwing system.

This is small analysis of Storage::StorageRecord* Storage::find function most expensive operations from my project (full code available in file below):

flags:      -std=c++1z -O1 -fno-stack-protector
ldflags:    <none>

сlang++ -   QtCreator profiler:
             __cxa_throw                 cost (instruction read access):  171,241,920
            |__ _Unwind_RaiseException   cost (instruction read access):  170,541,920

 g++ -      QtCreator profiler:
             __cxa_throw                 cost (instruction read access):  133,161,906
            |__ _Unwind_RaiseException:  cost (instruction read access):  132,541,906

You can see, that performance difference between GCC and Clang almost 30%.

I think, for same optimization level Clang's exception-throwing costs are too high compared to GCC.

Thank you for your attention.

Quuxplusone / LLVMBugzillaTest

__cxa_throw performance issue #50005