Build not fully optimized? about cib HOT 17 OPEN

@kripken that fixed it. Nice branch name :)

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Oh wait, is this using emscripten with the LLVM wasm backend, and not fastcomp/asm2wasm? Seems so from the list of repos in build.py. If so, then the 15-20% size difference is not that surprising, as the wasm backend tends to emit larger code. Might be worth adding a build step to run binaryen's optimizer, then.

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is this using emscripten with the LLVM wasm backend

Yes.

Might be worth adding a build step to run binaryen's optimizer, then.

Sounds good.

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If using CMake and e.g. Unix Makefiles generator, then one should pass -DCMAKE_BUILD_TYPE=Release to the build if not otherwise specified, as CMake defaults to building Debug build type, which is unoptimized. emcmake does not reach the linking phase to do any adjustments.

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Here's what it currently uses:

• -DCMAKE_BUILD_TYPE=Release to build llvm's *.a
• -DCMAKE_BUILD_TYPE=Debug to build the final executable. Release crashes during build.

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It's now down to 43M.

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I'm a little confused by

@juj: emcmake does not reach the linking phase to do any adjustments.

@tbfleming -DCMAKE_BUILD_TYPE=Debug to build the final executable.

Is cmake issuing the final emcc command to link and generate the executable? I don't see an emcc command in the build script, so it seems like that's the case, but if I understand you @juj that shouldn't be possible?

Release crashes during build.

Oh, do you have an error message or stack trace from that? EMCC_DEBUG=1 in the env could give more info.

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Is cmake issuing the final emcc command to link and generate the executable?

Yes. Here's the commands which create the app. I'm running it through release to give you a log.

cd /mnt/cib/build/clang-browser-Release/ && emcmake cmake -G "Ninja" -DCMAKE_BUILD_TYPE=Release -DLLVM_BUILD=/mnt/cib/build/llvm-browser-Release/ -DEMSCRIPTEN=on ../../src

cd /mnt/cib/build/clang-browser-Release/ && ninja clang

-DLLVM_BUILD=... and -DEMSCRIPTEN=on are variables in my CMakeLists.txt.

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Oops. Sorry; I remembered wrong. It builds but hits this at runtime:

stackAlloc is not defined

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1: That stackAlloc issue might be fixed by emscripten-core/emscripten#5986 (Please let me know either way if you check.)

2: Is the relevant CMakeLists.txt this one? https://github.com/tbfleming/cib/blob/master/src/CMakeLists.txt#L105

If so then it looks like cmake is picking the -Ox optimization level for the final link stage. (@juj, is that odd?) Some notes on the flags:

• Looks like it's using SAFE_HEAP? That can increase size a lot. https://github.com/tbfleming/cib/blob/master/src/CMakeLists.txt#L73
• I think cmake will emit -O2 for a release build. -O3 could be faster, and -Os could be smaller.
• NO_EXIT_RUNTIME is now the default, can remove that (unless using an older version).

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1: I'll try it
2: Yes

I forgot to remove the SAFE_HEAP after debugging.

This reminds me of an issue: NO_EXIT_RUNTIME doesn't stop it from closing stdio. I had to do this instead: https://github.com/tbfleming/cib/blob/master/src/process.js#L137

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emscripten-core/emscripten#5986 fixed the stackAlloc issue. I also removed SAFE_HEAP, ASSERTIONS, DEMANGLE_SUPPORT, and NO_EXIT_RUNTIME.

Step 3 is because the builds sometimes produce around 130,000 data segments, which exceed Firefox's and Chrome's 100,000 limit. I combine them into a single segment.

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Is that stdio issue fixed by emscripten-core/emscripten#6038 ?

About wasm having a 100,000 segment limitation, I wasn't aware of that limit. @lukewagner , is that a temporary thing, or should binaryen work around it?

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emscripten-core/emscripten#6038 fixed it.

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It's a permanent limit and should be the same across browsers since it is in the list of constant limits. If there was a hard reason to relax it, it could be relaxed.

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Ok, thanks for the info, I'll handle it in binaryen.

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@tbfleming WebAssembly/binaryen#1350 should work around the 100K segment limit, please verify it works if you can.

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