Cannot call C++ __qpu__ function from within another kernel if parameters contain vector of cudaq::measure_results

[bmhowe23]

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Describe the bug

Calling a function with const std::vector<cudaq::measure_result> &result_vec parameters seems to not work when running with --enable-mlir.

Steps to reproduce the bug

Consider the following file:

#include "cudaq.h"

bool xor_result(const std::vector<cudaq::measure_result> &result_vec) __qpu__ {
  bool result = false;
  for (auto x : result_vec)
    result ^= x;
  return result;
}

bool kernel() __qpu__ {
  cudaq::qvector q(7);
  std::vector<cudaq::measure_result> mz_res = mz(q);
  bool res = xor_result(mz_res);
  return res;
}

int main(int argc, char *argv[]) {
  printf("Result: %d\n", static_cast<int>(kernel()));
  return 0;
}

That produces the following compilation error:

$ nvq++ --enable-mlir issue.cpp
issue.cpp:21:14: error: 'func.call' op kernel call was not inlined, possible recursion in call tree
issue.cpp:21:14: note: see current operation: %3 = "func.call"(%2) {callee = @__nvqpp__mlirgen__function_xor_result._Z10xor_resultRKSt6vectorIbSaIbEE} : (!cc.stdvec<i1>) -> i1
failed: "/workspaces/cuda-quantum/build/bin/cudaq-opt --pass-pipeline=builtin.module(func.func(unwind-lowering),canonicalize,lambda-lifting,func.func(memtoreg{quantum=0}),canonicalize,apply-op-specialization,kernel-execution,aggressive-early-inlining,func.func(quake-add-metadata),device-code-loader{use-quake=1},expand-measurements,func.func(lower-to-cfg),canonicalize,cse) issue.qke -o issue.qke.v8G01q"

There is no recursion in the call tree.

Also, interestingly enough, if one were to remove the __qpu__ attribute on the xor_result function, the program compiles but produces a Segmentation fault, which is undesirable. We should throw a cleaner error message in that case.

Expected behavior

The program provide in the above section should compile and run.

Is this a regression? If it is, put the last known working version (or commit) here.

Not a regression

Environment

• CUDA Quantum version: latest (f798375)
• Python version:
• C++ compiler:
• Operating system:

Suggestions

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