Stream: wasm

Topic: Creating small call indirect examples

view this post on Zulip Jannik Schütz (Jan 04 2024 at 23:11):

Hi, I am trying to understand why and where the compiler creates the specific patterns ahead of a call indirect, determining its index
I analyzed the WasmBench dataset and looked for pattern ahead of a call indirect and it turns out, that there are basically two patterns determining over 87% the index.
The first one is the Add Case and the second one the Load Offset Case:

ADD CASE
i32.add
i32.const
i32.and
i32.const
load offset
call_indirect (type x)

LOAD OFFSET CASE I
local.get
load offset
local.get
load offset
call_indirect (type x)

LOAD OFFSET CASE II
local.get
local.get
load offset
load offset
call_indirect (type x)

I mainly want to focus on C++ and Rust, as there these patterns occurred the most in the dataset, with the Add Case being dominant withing C++ and the Load Offset Case being dominant within Rust (but both cases occur in both languages).
I am trying to recreate those patterns by manually writing minimum viable programs. For example if you look at this small C Code. I do so, as i already know that a lot of call_indirects come from libraries, for example in Rust a program with a std lib creates over 76 call_indirects, whereas a #![no_std] program, doesn't.

int add(int a, int b) { return a+b; }
static int sub(int a, int b) { return a-b; }

int main(int argc) {
    int (*functionPtr)(int, int);
    if (argc)
        functionPtr = add;
    else
        functionPtr = sub;

    int a = functionPtr(2, 3);
    return a;
}

This creates a small wat File, that is still readable and has a call_indirect instruction in it, as i want. But it does not yet have one of the patterns above
It would be nice to know and thus i am asking if anyone knows the section, where the compiler creates these snippets?
Or could help me manually creating these patterns.

Thank you in advance, Jannik

GitHub - sola-st/WasmBench: A large dataset of real-world WebAssembly binaries, collected from the Web, GitHub, NPM and other sources. Useful as test data, to study WebAssembly, for training machine learning models, and much more.
A large dataset of real-world WebAssembly binaries, collected from the Web, GitHub, NPM and other sources. Useful as test data, to study WebAssembly, for training machine learning models, and much ...
Compiler Explorer - C (WebAssembly clang (trunk))
int add(int a, int b) { return a+b; } static int sub(int a, int b) { return a-b; } int main(int argc) { int (*functionPtr)(int, int); if (argc) functionPtr = add; else functionPtr = sub; int a = functionPtr(2, 3); return a; }

Last updated: Nov 22 2024 at 16:03 UTC