Re: Improve CRC32C performance on SSE4.2

On 6/14/25 15:56, Nathan Bossart wrote:
> On Sat, Jun 14, 2025 at 03:47:33PM +0200, Tomas Vondra wrote:
>> I suggest you try with a newer gcc, perhaps 13.4. There's been a bunch
>> of fixes related to AVX512 since 13.0, chances are this was already
>> fixed. I don't see this failure on 14.3.1.
> 
> From the config.log, it looks like Andy is using clang:
> 
>     configure:3998: clang --version >&5
>     clang version 18.1.6 (https://gitee.com/mirrors/llvm-project.git 1118c2e05e67a36ed8ca250524525cdb66a55256)
> 
> And I see -O0 used, too, which would match the existing report [0],
> although that report is for clang 19.1.7.
> 

Ah, I got confused by this:

-----------------
Found candidate GCC installation:
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/13.3.0
Selected GCC installation:
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/13.3.0
-----------------

> I'm also genuinely curious why folks are using -O0...
> 
> [0] https://postgr.es/m/CAE-ML%2B-OV6p9uvCFBcSQjZUEh__y0h-KjN%2BBseyGJHt7u8EP%2Bw%40mail.gmail.com
> 

I personally use -O0 to get better backtraces (without values optimized
out), better valgrind reports, etc.


-- 
Tomas Vondra