To reproduce, please have Verilator installed and run:
bash run.sh
Tested with Verilator 5.021 devel rev v5.020-31-g54922c036.
Expected output:
Noflag
Output: 18
-fno-expand
Output: 18
Actual output:
Noflag
Output: 19
-fno-expand
Output: 18
Please note the bug is corrected by enabling any of these flags:
-fno-expand
-fno-const-bit-op-tree.
Any other unique flag, as well as traces, will preserve this bug.