Questions Related to Adding Local Variables to Functions in C API

[mobsceneZ]

Hey developers, I try to rewrite Wasm modules using the Binaryen C API, and the rewriting process may introduce new local variables to the function, however I could not find a way to append newly-introduced locals to the function via C API. Either there is one C API that serves this purpose and I do not recognize that (in this case could anyone point that out for me?), or it doesn't exist yet.

In the latter case, I manually add one such API called BinaryenFunctionAppendVar to binaryen-c.h/cpp, whose source code can be inspected in pull request #6213 . A sample code using such API may look like this:

#include <stdio.h>
#include <binaryen-c.h>

int main(void) {

    BinaryenType par = BinaryenTypeNone();
    BinaryenType res = BinaryenTypeInt32();
    BinaryenModuleRef mod = BinaryenModuleCreate();

    BinaryenExpressionRef local_get = BinaryenLocalGet(mod, 0, BinaryenTypeInt32());
    BinaryenFunctionRef new_func = BinaryenAddFunction(mod, "test", par, res, NULL, 0, local_get);
    printf("new local idx: %u\n", BinaryenFunctionAppendVar(new_func, BinaryenTypeInt32()));
    printf("%d\n", BinaryenModuleValidate(mod));
    
    BinaryenModulePrint(mod);
    BinaryenModuleDispose(mod);
    return 0;

}

Compiling above code with following command:

clang test.c -o test -L/usr/local/lib -lbinaryen -Wl,-rpath,/usr/local/lib

The terminal output looks like this, here the local index is counted from the function's local variables instead of parameters:

new local idx: 0
1
(module
 (type $0 (func (result i32)))
 (func $test (result i32)
  (local $0 i32)
  (local.get $0)
)

If we could not find an off-the-shelf C API, maybe above API can be a possible solution.

[kripken]

Fixed by #6213