WASM: complex numbers

[certik]

Add complex numbers and operations on them.

[certik]

There are several ways to implement it.

In the backend

Just create a WASM function complex_add(), which accepts the two operands a,b on stack and returns the result on stack (this function is implemented in asr_to_wasm directly using wasm instructions). Each complex number is represented by two floating point numbers on stack.

Using ASR->ASR pass

This pass would work similarly to pass_compare.cpp which inserts new ASR functions (to global scope) to implement a given operation (and only inserts it once and reuses it everywhere).

Surface language

The code for complex operations can also be implemented in the surface language. This approach is almost equivalent to the previous ASR->ASR pass approach, except that the operations are not implemented directly in ASR but rather in the surface language and compiled to ASR. We can for example maintain a precompiled version of such functions in the .mod file format that is just serialized ASR.