[all-commits] [llvm/llvm-project] 06e2b4: [RISCV] Optimize scalable frame setup when VLEN is...

[Philip Reames via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 06e2b44c46243a74ba5682aa3225d79e45038651
      https://github.com/llvm/llvm-project/commit/06e2b44c46243a74ba5682aa3225d79e45038651
  Author: Philip Reames <preames at rivosinc.com>
  Date:   2022-11-18 (Fri, 18 Nov 2022)

  Changed paths:
    M llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
    M llvm/test/CodeGen/RISCV/rvv/rv64-spill-vector-csr.ll

  Log Message:
  -----------
  [RISCV] Optimize scalable frame setup when VLEN is precisely known

If we know the exact value of VLEN, the frame offset adjustment for scalable stack slots becomes a fixed constant. This avoids the need to read vlenb, and may allow the offset to be folded into the immediate field of an add/sub.

We could go further here, and fold the offset into a single larger frame adjustment - instead of having a separate scalable adjustment step - but that requires a bit more code reorganization. I may (or may not) return to that in a future patch.

Differential Revision: https://reviews.llvm.org/D137593