huge object file / compile time

[hiokazaki]

I have a function with the following signature:

double F(double, double, double, std::array<double, 100>)

and contains about 3000 lines of code, each of which has a few (on average, close to 1) arithmetic operations (only + and *) which take some mix of one of the 103 arguments, one of about 80 temporary (stack) variables, and floating point constants.

In forward mode, the file compiles in a second or two and creates a 50kB object (including debug info etc.)

However, templating the function and attempting to compute its adjoint took clang ~25 minutes to compile (at -O2), and resulted in a 55MB object. Adding #undef XAD_USE_STRONG_INLINE reduced the compile time to ~23 minutes, and the resulting object to ~30MB.

In any case, it seems that both the compile time and object size have increased by about 1000x - is that expected?

I am able to manually break up this function into about 12 smaller functions each emitting a scalar, which are then assembled by another ~100 or so operations into the final scalar. Would that help?

To Reproduce
I think that any (non-degenerate) random with this signature and this number of intermediate operations will experience the same issue.

Perhaps a test to validate compile time, object size, and runtime performance scaling as a function of input function size/complexity is worth writing?

Expected behaviour
I was expecting compile and runtime to increase by 10x or so, not 1000x.

Environment (please complete the following information):

• OS: Ubuntu 24.04 LTS
• Compiler: Clang 20, -O2 -g
• CMake Configuration (if not default): Not using CMake (just including/linking to xad separately); xad was built with the default CMake configuration.

[boring-cyborg]

Thanks for opening your first issue here. We'll look into it and get back in due time.