About

Instruction fusion is an important technique to improve performance of RISC-V systems.  While GCC has support for a common set of instruction fusions, it's believed that additional cases will become more important as new designs come to market. 

1. Synopsys engineers have changes which change GCC's model from "these are fusible, keep them consecutive" to "find fusible cases, bring them together and keep them together".  Maybe as much as a 10% increase in real fusion opportunities.

   1. New pass for discovery

   2. Adjust register allocator to avoid spoiling fusion opportunities

   3. Adjust software register renaming to avoid spoiling fusion opportunities

2. Tests to verify basic fusion behavior, realistically this can't be upstreamed without a target that enables those fusions.

Ventana has code to support these cases using the general infrastructure already in the RISC-V GCC backend.  This code just needs to be benchmarked and upstreamed once gcc-16 is open for development.

Stakeholders/Partners

                     Synopsys: Artemiy Volkov

Dependencies

Status

Updates

Jul 16, 2025 

• Unfinished items broken out into a new project