GSIM: A Fast RTL Simulator for Large-Scale Designs

GSIM accepts chirrtl, and compiles it to C++

Prerequisites

• Install GMP, clang 19(+).

Quike Start

• GSIM provides 4 RISC-V cores ready for simulation: ysyx3, Rocket, BOOM, XiangShan.

• To try GSIM, using

  $ make init
  $ make run dutName=core
  

• Set core to ysyx3, rocket, small-boom, large-boom, minimal-xiangshan or default-xiangshan

Usage

• Run make build-gsim to build GSIM
• Build a static binary locally with make STATIC=1 build-gsim (CI artifacts are built statically).
• Run build/gsim/gsim $(chirrtl-file) to compile chirrtl to C++
• Refer to build/gsim/gsim --help for more information
• See C++ harness example to know how it interacts with the emitted C++ code.

Debug logs & dumps

• By default gsim runs quietly (LogLevel=0, dump disabled). Enable lightweight stage logs with --log-level=1 (prints pass begin/end). Use --log-level=2 for verbose constant-analysis traces; expect a lot more stderr.
• Graph dumps: --dump turns on both DOT and JSON dumps for every stage; --dump-json / --dump-dot turn on a single format. Combine with --dump-stages=a,b,c to limit which stages emit (e.g., AfterSplitNodes,ConstantAnalysis). Set --dir=tmp-out/gsim-dumps to choose the output directory.
• Extra debugging artifacts: --dump-assign-tree includes assignTree structure in JSON dumps; --dump-const-status writes <name>_<stage>_ConstStatus.json with per-node constant-analysis status.
• Example: build/gsim/gsim --dir tmp-out/gsim-dumps --dump --dump-stages=AfterSplitNodes,ConstantAnalysis --dump-assign-tree --log-level=1 ready-to-run/TestHarness-rocket.fir

Papers and Presentations

GSIM: Accelerating RTL Simulation for Large-Scale Design

Lu Chen, Dingyi Zhao, Zihao Yu, Ninghui Sun, Yungang Bao

Design Automation Conference (DAC), 2025

Paper PDF | Slides | Chinese Slides