wasmblr
A single header file WebAssembly assembler.
This library makes it easier to generate web assembly binaries directly from C++.
Useful for JIT compilation from within projects compiled with Emscripten.
For examples see below, or read the test.cc file.
Some benchmarks:
- Measure Bandwidth (cache not flushed): https://bwasti.github.io/wasmblr
- Measure Peak Theoretical FLOPs: https://bwasti.github.io/wasmblr/flops
- Measure Matrix Multiplication Performance (GFLOPs): https://bwasti.github.io/wasmblr/matmul/
Contributions welcome!
Usage
#include "wasmblr.h" and compile with -std=c++11 or higher.
In C++:
struct Code : wasmblr::CodeGenerator {
Code() : wasmblr::CodeGenerator() {
auto add_func = function({f32, f32}, {f32}, [&]() {
local.get(0);
local.get(1);
f32.add();
});
export_(add_func, "add");
}
};
Code c;
auto bytes = c.emit();
std::ofstream wasm("add.wasm", std::ios::binary);
wasm.write((char*)bytes.data(), bytes.size());If you'd prefer to avoid inheritance, you can use the code generator directly:
wasmblr::CodeGenerator cg;
auto add_func = cg.function({cg.f32, cg.f32}, {cg.f32}, [&]() {
cg.local.get(0);
cg.local.get(1);
cg.f32.add();
});
cg.export_(add_func, "add");
auto bytes = cg.emit();
std::ofstream wasm("add.wasm", std::ios::binary);
wasm.write((char*)bytes.data(), bytes.size());And then, in JavaScript:
const wasm = fs.readFileSync('add.wasm'); // or however you'd like to load it
const m = new WebAssembly.Module(wasm);
const instance = new WebAssembly.Instance(m, {});
// use the function
console.log(instance.exports.add(8, 9));Test
With node.js installed,
g++ test.cc -std=c++11 -o test
./test
Supported Features
The semantics of the assembler attempt to mimic the WebAssembly standard closely.
In the case of reserved keywords in C++ (such as export, xor, etc.), the mnemonic has an underscore appended (e.g. export_, i32.xor_).
A couple of example uses follow:
Recursion
struct Code : wasmblr::CodeGenerator {
// NB: Needs to be a class variable; the function body is evaluated later
uint32_t factorial;
Code() : wasmblr::CodeGenerator() {
factorial = function({f32}, {f32}, [&]() {
local.get(0);
f32.const_(1.0f);
f32.lt();
// base case
if_(f32);
{
f32.const_(1.0f);
}
else_();
{
local.get(0);
local.get(0);
f32.const_(1.0f);
f32.sub();
call(factorial);
f32.mul();
}
end();
});
export_(factorial, "factorial");
}
};Blocks
If-statements
struct Code : wasmblr::CodeGenerator {
Code() : wasmblr::CodeGenerator() {
auto if_func = function({f32}, {f32}, [&]() {
f32.const_(0.0f);
local.get(0);
f32.gt();
if_(f32);
f32.const_(0.0f);
else_();
local.get(0);
end();
});
export_(if_func, "relu");
}
};Loops
struct Code : wasmblr::CodeGenerator {
Code() : wasmblr::CodeGenerator() {
auto loop_fn = function({}, {i32}, [&]() {
auto i = local(i32);
loop(void_);
{
local.get(i);
i32.const_(1);
i32.add();
local.set(i);
local.get(i);
i32.const_(10);
i32.lt_s();
br_if(0);
}
end();
local.get(i);
});
export_(loop_fn, "loop");
}
};Memory
struct Code : wasmblr::CodeGenerator {
Code() : wasmblr::CodeGenerator() {
memory(1, 10).export_("mem");
auto store = function({}, {}, [&]() {
i32.const_(0); // index 0
i32.const_(1337); // value 1337
i32.store(0, 0); // align 0, offset 0
});
export_(store, "store");
}
};SIMD (32-bit lanes for now)
struct Code : wasmblr::CodeGenerator {
Code() : wasmblr::CodeGenerator() {
memory(1, 10).export_("mem");
auto square = function({}, {}, [&]() {
auto vec = local(v128);
i32.const_(0);
v128.load();
local.set(vec);
local.get(vec);
local.get(vec);
v128.f32x4_mul();
local.set(vec);
i32.const_(0);
local.get(vec);
v128.store();
});
export_(square, "simd_square");
}
};TODO
Many things. I would appreciate any help filing issues for missing things!