Take a look at
https://www.veripool.com/verilator.html
Summary
Verilator is the fastest free Verilog HDL simulator. 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 create executable models of CPUs for embedded software design teams.
Do not download this program if you are expecting a full featured replacement for NC-Verilog, VCS or another commercial Verilog simulator for a little project! Don't get it if you expect a corporate support organization. However, if you are looking for a path to migrate synthesizable Verilog to C++ or SystemC, and writing just a touch of C code and Makefiles doesn't scare you off, this is the free Verilog compiler for you.
Verilator supports the synthesis subset of Verilog, plus initial statements, proper blocking/non-blocking assignments, functions, tasks, multi-dimensional arrays, and signed numbers. It also supports very simple assertions and coverage analysis. Verilator supports the more important Verilog 2001 constructs, with additional constructs and Verilog 2005 support added as users request them. Verilator has been used to simulate for many very large multi-million gate designs with thousands of modules.
Performance
Verilator does not simply convert Verilog HDL to C++ or SystemC. Doing so is fairly easy (and was what Verilator did over 5 years ago). Instead, Verilator compiles your code into a much faster optimized model, which is in turn wrapped inside a SystemC module. The results are a model that executes over 10x faster then standalone SystemC.
Verilator is about 100 times faster then interpreted Verilog simulators such as Icarus Verilog. Verilator has about the same performance as the leading commercial Verilog simulators including Modelsim, NC-Verilog, VCS and VTOC, but is free, so you can spend on computes rather then licenses. Thus Verilator gives you more cycles/dollar then anything else available. (If you benchmark Verilator, please see the notes in 'bin/verilator' and also let the author know the results; there may be additional tweaks possible.)