To reproduce, please have Verilator installed (tested with Verilator 5.021 devel rev v5.020-31-g54922c036) and run:
bash run.sh
The bug is corrected by enabling traces.
Expected output:
Output[32] 0
-fno-assemble
Output[32] 0
-fno-case
Output[32] 0
-fno-combine
Output[32] 0
-fno-const
Output[32] 0
-fno-const-bit-op-tree
Output[32] 0
-fno-dedup
Output[32] 0
-fno-dfg
Output[32] 0
-fno-dfg-peephole
Output[32] 0
-fno-dfg-pre-inline
Output[32] 0
-fno-dfg-post-inline
Output[32] 0
-fno-expand
Output[32] 0
-fno-gate
Output[32] 0
-fno-inline
Output[32] 0
-fno-life
Output[32] 0
-fno-life-post
Output[32] 0
-fno-localize
Output[32] 0
-fno-merge-cond
Output[32] 0
-fno-merge-cond-motion
Output[32] 0
-fno-merge-const-pool
Output[32] 0
-fno-reloop
Output[32] 0
-fno-reorder
Output[32] 0
-fno-split
Output[32] 0
-fno-subst
Output[32] 0
-fno-subst-const
Output[32] 0
-fno-table
Output[32] 0
Actual output:
Output[32] 1
-fno-assemble
Output[32] 1
-fno-case
Output[32] 1
-fno-combine
Output[32] 1
-fno-const
Output[32] 1
-fno-const-bit-op-tree
Output[32] 0
-fno-dedup
Output[32] 1
-fno-dfg
Output[32] 1
-fno-dfg-peephole
Output[32] 1
-fno-dfg-pre-inline
Output[32] 1
-fno-dfg-post-inline
Output[32] 1
-fno-expand
Output[32] 0
-fno-gate
Output[32] 0
-fno-inline
Output[32] 1
-fno-life
Output[32] 1
-fno-life-post
Output[32] 1
-fno-localize
Output[32] 1
-fno-merge-cond
Output[32] 1
-fno-merge-cond-motion
Output[32] 1
-fno-merge-const-pool
Output[32] 1
-fno-reloop
Output[32] 1
-fno-reorder
Output[32] 1
-fno-split
Output[32] 1
-fno-subst
Output[32] 1
-fno-subst-const
Output[32] 1
-fno-table
Output[32] 1
In summary, the following individual flags correct the bug:
-fno-const-bit-op-tree
-fno-expand
-fno-gate