Function call support

[georgemitenkov]

Support function calls in NMODL

• locally defined functions
• mathematical built-ins

Question: can we call function external to the current mod file?
Question: does ordering of functions matter? (do we need declarations?)

[pramodk]

can we call function external to the current mod file?

In theory yes but for what would like to do here, we can assume all functions are defined in the mod file.

does ordering of functions matter? (do we need declarations?)

IIRC, I read somewhere in language reference guide that order of method definitions doesn’t matter in the same modules. So prototype declaration is not required (?)

[georgemitenkov]

1. Cool, thanks!
2. Here I mean if we are allowed to have this in NMODL

FUNCTION bar() {bar = foo()}
FUNCTION foo() {foo = 2}

Because traversing AST first meets bar, we need to create call instruction to foo. We pass foo to builder.CreateCall() as a llvm::Function* variable, that in this case hasn't been created.

If NMODL takes care of these cases already, then we can assume all functions in calls have been processed beforehand.

[pramodk]

Here I mean if we are allowed to have this in NMODL
FUNCTION bar() {bar = foo()}
FUNCTION foo() {foo = 2}

Understood now! NMODL doesn't handle this i.e. order in the AST is same as how user write. For this reason, C++ code generation backend does emit prototype declarations for all functions and procedure at the beginning.

IIRC, prototype declaration is straightforward in LLVM IR, right? In that case it would be safe to emit them at the beginning.

I suggest two options:

• if you see issues or complications to implement next option then assume that procedures or functions are in the "right" order and continue implementation.
• get list of functions + procedures and emit declarations at the beginning. For this, we can use CodegenHelperVisitor. As name suggest, this visitor is used to traverse AST and "collect" necessary information to help code generation passes. It's used in

  nmodl/src/codegen/codegen_c_visitor.cpp

  Line 4375 in ab27595

  CodegenHelperVisitor v;

Basically, in visit_program, we can run CodegenHelperVisitor to populate CodegenInfo structure which collect lot of information including list of functions and procedures:

visit_program(const Program& node) {
    CodegenHelperVisitor v;
    auto& info = v.analyze(node);

    for (const auto& node: info.functions) {
        // emit declaration
    }
    for (const auto& node: info.procedures) {
         // emit declaration
    }
....
}

We do the same in C++ backend here

nmodl/src/codegen/codegen_c_visitor.cpp

Line 1416 in ab27595

void CodegenCVisitor::print_function_prototypes() {

[georgemitenkov]

Thanks! Yes, I just wanted to clarify before implementing these. I think that emitting declarations is a good and rather straightforward approach.