Presentation at the London Open Source Meetup for RISC-V, hosted by BCS Open Source Specialist Group

1. WD RISCV inliner work effort
Nidal Faour – toolchain engineer
Western Digital
April 19, 2021

2. Agenda
London Open Source Meetup for RISC-V
• Introduction
• LLVM inliner
• New approach
• SuggestedSolution

3. Introduction
• Decrease code size
• Compare with other target
• Compare with other compilers
• Finding weak points in the assembly
• Tweak the compiler passes to fix the weak points

4. • One of the weak points we found was in
the LLVM inliner, where other compilers
found more inlining opportunities and
made the code size smaller.
• The major limitation is the way the inliner
works
• We need another approach to solve this.
LLVM inliner

5. • Credits for MI – (mutual inliner) goes to
Phd. Yosi Ben Asher
• Look at the whole picture
• Include the whole call-graph effect in the
inlining decisions
New approach - MI
B Saving C Saving
D Saving D Saving
E Saving F Saving

6. • Integrate the MI inside the LLVM inliner
• Replace the LLVM inliner
• Use the inliner adviser to give the LLVM
more insight using the MI algorithm
Suggested solution

7. Q&A

8. Thanks