Getting InternalError with a combination of compute_with, and reductions that use functions with update definitions

[sakehl]

This example program

#include "Halide.h"

using namespace Halide;

int main(int argc, char **argv){
  Func denominator_inter("denominator_inter");
  Func numerator("numerator"), denominator("denominator");
  Var i("i"), si("si"), vis("vis");

  numerator(si) = 0;
  denominator(si) = 0;
  RDom rv(0, 10, "rv");

  denominator_inter(i, vis) = 0;
  denominator_inter(0, vis) = 1 + vis;
  denominator(rv) += denominator_inter(0, rv);

  numerator(rv) += rv;
  numerator.compute_root();
  denominator.compute_root();
  denominator.update().compute_with(numerator.update(), rv);

  Func next("next");
  next(si) = numerator(si) / denominator(si);

  try{
    Target target = get_target_from_environment();
    target.set_feature(Target::Debug);
    next.compile_to_static_library("TestHalide.c", {}, "Test", target);
  } catch (Halide::Error &e){
    std::cerr << "Halide Error: " << e.what() << std::endl;
    __throw_exception_again;
  } 
}

throws an internal error:

Halide Error: Internal Error at /home/halidenightly/build_bot/worker/halide-nightly-release_17-x86-64-linux-cmake/halide-source/src/CodeGen_LLVM.cpp:1293 triggered by user code at : Symbol not found: denominator.s1.rv$x
The following names are in scope:
{
  ::Test
  denominator
  next
  next.buffer
  next.device_dirty
  next.dimensions
  next.extent.0
  next.min.0
  next.stride.0
  next.type
  numerator
  numerator.s1.rv$x
  numerator.si.extent_realized
  t12
}

whilst I believe this would be a valid program.

I've attached the output when running this with HL_DEBUG_CODEGEN=2

out.txt

I'm using the latest released version 17.0.1.

[abadams]

Thanks for the simple repro. I found that it's really not possible to simplify this one much more. It looks like the bug is specifically caused by a compute_with on an RVar where there's a producer stage whose bounds will depend on that RVar, because it's scheduled inside the loop over the RVar.

[sakehl]

Yes I had the same observation. It came from a more complex program, where even without an intermediate function like denominator_inter this occurred. Let me know if you need more information.