Readme.md

Mis-optimization of wide shifts

Tested with Yosys 0.37+29 (git sha1 3c3788ee2, clang 10.0.0-4ubuntu1 -fPIC -Os). The mismatch is confirmed by Icarus Verilog. No x or z values are involved.

How to reproduce:

bash run.sh

This will:

1. Create top_opt.sv, the optimized version of top_noopt.sv.
2. Run a simple simulation of top_opt.sv and top_noopt.sv with Icarus Verilog.
3. Report a mismatch.

Expected output (the output should not be affected by the optimizations):

no optimization
Output: 00000000
with optimization
Output: 00000000

Actual output:

no optimization
Output: 00000000
with optimization
Output: ffffffff