wasm-opt flags -Os vs. -Oz

[webmaster128]

Locally I'm testing the two optimization modes with wasm-opt version 110:

$ wasm-opt --help
  …
   -Os                                          execute default optimization 
                                                passes, focusing on code size 

   -Oz                                          execute default optimization 
                                                passes, super-focusing on code 
                                                size 
  …

For my tests, there is a difference in the order of magnitute of 1-2%:

# -Os

-rwxr-xr-x  1 me  staff  192130 16 Okt 17:27 nois_demo.wasm
-rwxr-xr-x  1 me  staff  480903 16 Okt 17:27 nois_oracle.wasm
-rwxr-xr-x  1 me  staff  225705 16 Okt 17:27 nois_proxy.wasm

# -Oz

-rwxr-xr-x  1 me  staff  189263 16 Okt 17:29 nois_demo.wasm
-rwxr-xr-x  1 me  staff  472586 16 Okt 17:29 nois_oracle.wasm
-rwxr-xr-x  1 me  staff  223632 16 Okt 17:29 nois_proxy.wasm

So for now I don't see a strong need to move away from the well established -Os.

[webmaster128]

Some more example numbers from https://twitter.com/const_amit/status/1752210883156062660:

[maurolacy]

Running both in sequence gives the (very slightly) best results, AFAIK.