Verilator is the fastest free Verilog HDL simulator, and beats most commercial
simulators. It compiles synthesizable Verilog (not test-bench code!), plus some
PSL, SystemVerilog and Synthesis assertions into C++ or SystemC code. It is
designed for large projects where fast simulation performance is of primary
concern, and is especially well suited to generate executable models of CPUs
for embedded software design teams.