Custom `sinc` path not working

[ax3l]

Hi @wsmoses,

Thank you for the guidance today!

Pre-Defined sinc paths

I was trying if a self-defined function called sinc is picked up and replaced with the pre-defined custom paths, and it does not seem to work as expected: https://fwd.gymni.ch/DdjNuM

#include <cmath>
#include <stdio.h>

double sinc (double x) {
    return std::sin(x) / x;
}

double __enzyme_autodiff(void*, double);
int main() {
    double x = 3.14;

    double grad_x = __enzyme_autodiff((void*)sinc, x);
    printf("sinc'(%f) = %f\n", x,  grad_x);  // -0.318632

    x = 0;
    double grad_x00 = __enzyme_autodiff((void*)sinc, x);
    printf("sinc'(%f) = %f\n", x,  grad_x00);  // 0.0

    return 0;
}

sinc'(3.140000) = -0.318632
sinc'(0.000000) = -5486124068873210445588960243682892870359454172549082081269977249875439498450530608481829736532482212550881929053150599861406478595121674729324160965665746675952409952613381490567235017715679668230311379032918639874384375900517443469363980679948746539362679355976183938475470978590331407354983321197084672.000000

Enzyme Function-Like "sinc"

I then tried enzyme_function_like but that does not do the trick either: https://fwd.gymni.ch/DHb8VC

#include <cmath>
#include <stdio.h>

__attribute__((enzyme_function_like("sinc")))
double my_sinc (double x) {
    return std::sin(x) / x;
}

double __enzyme_autodiff(void*, double);
int main() {
    double x = 3.14;

    double grad_x = __enzyme_autodiff((void*)my_sinc, x);
    printf("sinc'(%f) = %f\n", x,  grad_x);  // -0.318632

    x = 0;
    double grad_x0 = __enzyme_autodiff((void*)my_sinc, x);
    printf("my_sinc'(%f) = %f\n", x,  grad_x0);  // 0.0

    return 0;
}

sinc'(3.140000) = -0.318632
my_sinc'(0.000000) = -nan

What am I missing? :)

[ax3l]

1st example

The 1st example also does not work if declared extern "C": https://fwd.gymni.ch/whurNe No work-around

Explored today: 2nd example posted above

This is a bug that is already fixed in the Julia version but not yet in the C++ version (@wsmoses knows what the fix).

Work-around: The issue only appears if the attributed function is directly called from enzyme autodiff. Using it in a lower layer of the call stack, or wrapping it in an extra function, works: https://fwd.gymni.ch/8PBXdM