Remove some -O3 optimization flags to improve performance from 20% ~ …

[ChihMin]

…60 speed up while decoding the most expensive frame

[DavidLvSinonet]

Hi @ChihMin ,
I have tested your branch in emscripten v1.35.0, there have some error:
Unknown command line argument '-demanded-bits'.
Unknown command line argument '-elim-avail-extern'
Unknown command line argument '-demanded-bits'.
Traceback (most recent call last):
File "/Users/david/Documents/DevTools/emsdk/emscripten/1.35.0/emcc", line 1283, in
final = shared.Building.llvm_opt(final, llvm_opts, DEFAULT_FINAL)
File "/Users/david/Documents/DevTools/emsdk/emscripten/1.35.0/tools/shared.py", line 1471, in llvm_opt
assert os.path.exists(target), 'Failed to run llvm optimizations: ' + output
AssertionError: Failed to run llvm optimizations:
Traceback (most recent call last):
File "make.py", line 134, in
emscripten.Building.emcc('avc.bc', link_args, os.path.join(JS_DIR, 'avc.js'))
File "/Users/david/Documents/DevTools/emsdk/emscripten/1.35.0/tools/shared.py", line 1548, in emcc
assert os.path.exists(output_filename), 'emcc could not create output file: ' + output_filename
AssertionError: emcc could not create output file: js/avc.js

[ChihMin]

Hi @DavidLvSinonet,

I faced the same problem while building this project with emscripten 1.36.
Maybe there are some bugs in emscripten python building wrapper script, and optimization parameters passed to shared.py will cause errors while calling LLVM optimizer(opt).
So currently my solution is wrapping the opt executable file. For instance:

• Backup origin LLVM opt executable file and touch new opt shell script

mv ${YOUR_PATH}/opt ${YOUR_PATH}/opt.bak
touch ${YOUR_PATH}/opt
chmod +x ${YOUR_PATH}/opt

• Edit new opt shell script

#!/bin/bash
${ABSOLUTE_PATH}/opt.bak $@

[DavidLvSinonet]

Hi @ChihMin ,

There have the some problems.

opt.bak: Unknown command line argument '-demanded-bits'.  Try: '/Users/david/Documents/DevTools/emsdk/clang/e1.35.0_64bit/opt.bak -help'
opt.bak: Did you mean '-delinearize'?

[ChihMin]

Hi @DavidLvSinonet,
Oh, maybe our LLVM version is not the same, so some flags are NOT supported in your LLVM optimizer.
My emscripten version is 1.36.0, and LLVM version is 3.9.0.
Maybe you should try to build emscripten & emscripten-fastcom 1.36.0?

[soliton4]

i was running my tests with emscripten 1.36.9

[DavidLvSinonet]

OK, I will update my emscripten.
Thanks @ChihMin , @soliton4 .

[luopingkklp]

Thank you for this project,it is very good.