[fpc-devel] Attn: J. Gareth // 3.3.1 opt = slower // Fwd: [Lazarus] Faster than popcnt

Jonas Maebe jonas at freepascal.org
Tue Jan 4 18:43:21 CET 2022

On 03/01/2022 12:54, Martin Frb via fpc-devel wrote:
> not sure if this is of interest to you, but I see you do a lot on the 
> optimizer....

It's very likely unrelated to anything the optimiser does or does not 
do, and more regarding random differences in code layout. Charlie posted 
the following video on core just yesterday, and it touches on exactly 
this subject: https://www.youtube.com/watch?v=r-TLSBdHe1A

Choice quote: code layout and environment variables can produce up to 
40% differences in performance, which is more than what even the best 
optimizing compilers can achieve do in most cases.


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