lto optimization not usable for wasm

[KaruroChori]

Somehow, the lto optimizations are breaking the wasm build.
This might be related to limits of the stack being reached.

RuntimeError: Out of bounds memory access (evaluating 'instance.exports')
      at vs.templ.js.wasm-function[_GLOBAL__sub_I_pugixml.cpp]
      at vs.templ.js.wasm-function[__wasm_call_ctors]
      at vs.templ.js.wasm-function[_start]
      at start (node:wasi:1023:26)
      at /archive/shared/projects/vs.templ/build/vs.templ.js:49:11

The solution would be to ask for a bigger stack, but I don't know how to do that in zig cc and the usual -stack-size=xxxx is not working.
If implemented, lto optimization would result in a blob going from 6.5MB to 4.4MB which is very substantial.

[KaruroChori]

For context:

meson setup --reconfigure build/ -Db_lto=true --buildtype=release --cross-file ./platforms/zig-wasm32.ini -Ddefault_library=static
meson compile vs.templ:executable -C build

builds without issues, but the resulting vs.templ.js when run has the issue I reported before. Removing -Db_lto=true works as expected.

[built-in options]
c_args = ['--target=wasm32-wasi','-fno-exceptions']
c_link_args = ['--target=wasm32-wasi','-fno-exceptions']
cpp_args = ['--target=wasm32-wasi','-fno-exceptions']
cpp_link_args = ['--target=wasm32-wasi','-fno-exceptions']

are being passed, but I was unable to find a way to increase the stack size and see if that was the cause.

[KaruroChori]

Just tested the same setup without linking anything from my code or the upstream libraries of this project. So, just the basic libraries linked by default.
Just tring a simple printf, the result is not even deterministic:

$ bun run ./build/vs.test.js
RuntimeError: Out of bounds memory access (evaluating 'instance.exports')
      at vs.test.js.wasm-function[__wasm_call_dtors]
      at vs.test.js.wasm-function[_start]
      at start (node:wasi:1023:26)
      at /archive/shared/projects/vs.templ/build/vs.test.js:49:11

Bun v1.1.37 (Linux x64)
$ bun run ./build/vs.test.js
RuntimeError: Out of bounds memory access (evaluating 'instance.exports')
      at vs.test.js.wasm-function[memmove]
      at vs.test.js.wasm-function[memcpy]
      at vs.test.js.wasm-function[__fwritex]
      at vs.test.js.wasm-function[printf_core]
      at vs.test.js.wasm-function[printf]
      at vs.test.js.wasm-function[__main_void]
      at vs.test.js.wasm-function[_start]
      at start (node:wasi:1023:26)
      at /archive/shared/projects/vs.templ/build/vs.test.js:49:11

[KaruroChori]

Well, I am really failing to make it work as I would expect. I made few tests using zig 14-dev standalone, without meson, just the command to compile and link.

Very simple c++ file:

#include <iostream>

int main(){
	std::cout<<"hello\n";
	return 0;
}

And a c one:

#include <stdio.h>

int main(){
	printf("hello\n");
	return 0;
}

zig c++ --target=wasm32-wasi main.cpp -flto -> fail to run
zig c++ --target=wasm32-wasi main.cpp -> fail, surprisingly as from meson it works.
zig cc --target=wasm32-wasi main.c -flto -> fail to run
zig cc --target=wasm32-wasi main.c -> working

I also tested C++ using the C code, no libc++ and it works without -flto.

I also noticed that the -static attribute does not work, so zig cc main.c -static does not generate a static build, but clang would.

[KaruroChori]

Issues notified upstream @ ziglang/zig#22629