QCX not activating with optimized UVM testbench (qsim only, no qopt -qcx license)

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Hi,

I’m trying to use QCX (-qcx flag in qsim) to accelerate functional coverage closure on a UVM testbench running on Questa One Sim 2025.3.

My setup:

  • UVM 1.1d testbench with a Coverage collector class (uvm_subscriber) containing a functional covergroup connected to the Monitor via analysis port
  • Dut written in VHDL and compiled in DUT library
  • Tetbench top is called Top_TB, compiled in TB library
  • License available: QoneSim, msimhdlsim, msimhdlmix, svverification, msimcoverage
  • Note: -qcx in qopt fails with ICVS_LIMITED_FEATURES_KEY error, so I can only use -qcx in qsim

Current flow:

  1. vlog (TB files, no -cover flag yet)
  2. qopt -work TB -L DUT TB.Top_TB -o TB_opt (TB fully optimized)
  3. qsim TB.TB_opt -coverage -qcx …

Problem:
No QCX messages appear in the transcript after elaboration.
The covergroups ARE visible in the UCDB after simulation, but QCX shows no activity — no mapping messages, no acceleration.

Questions:

  1. Does QCX work with a fully optimized UVM testbench (TB_opt),
    or does it require the TB to be unoptimized to inspect
    dynamic class objects?
  2. Should I optimize only the DUT and run qsim on TB.Top_TB
    directly?
  3. Is -cover sbcfu required on vlog for QCX to map covergroups,
    or is -coverage on qsim sufficient?
  4. Are there any known limitations with QCX and uvm_subscriber
    based coverage collectors?

Any guidance would be greatly appreciated.

Thank you

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