WASM Size Optimization Trick

[SaumitraLohokare]

TLDR;

• Updated build script to perform the following commands:
  • $ wasm2wat client.wasm > client.wat
  • $ wat2wasm client.wat -o client.wasm
  • $ wasm2wat server.wasm > server.wat
  • $ wat2wasm server.wat -o server.wasm
• Updated README to add dependency on wabt.

Problem

LLVM bloats the generated wasm binary.

Solution

While learning about WASM and WAT I noticed that if you disassemble the wasm binary using wasm2wat, then compile it again using wat2wasm, it significantly reduces the size of the generated wasm binary.
This is important for online games as smaller binaries take less time to load.

Results

# Before
$ ls -alh *wasm
-rwxr-xr-x 1 saumi saumi 172K Jan 17 00:21 client.wasm
-rwxr-xr-x 1 saumi saumi  82K Jan 17 00:21 server.wasm

# After
$ ls -alh *wasm
-rwxr-xr-x 1 saumi saumi 162K Jan 17 00:43 client.wasm
-rwxr-xr-x 1 saumi saumi  70K Jan 17 00:43 server.wasm

On running the game no issues were noticed.

[nikpivkin]

Hi @SaumitraLohokare ! Have you considered using wasm-opt? This tool is specifically designed for WASM optimization.

[SaumitraLohokare]

Thanks for the link! I did not know about this! I'll definitely check this out @nikpivkin

[nikpivkin]

@SaumitraLohokare using wasm-opt with optimization flag O4 I got a file which is 2 times smaller than the original one:

❯ wasm-opt -O4 client.wasm -o client-opt.wasm
❯ du -sh *.wasm
 96K    client-opt.wasm
184K    client.wasm