riscv_CMOs_with_paren

Extension: Zicbom, Zicbop and Zicboz

• Status: Merged for 2.39
• Branch: riscv-CMOs-with-paren
• Tracking PR: none
• Mailing List:
  • PATCH v1 (without paren) (2021-12-16)
    • PATCH v1 0/5
    • PATCH v1 1/5
    • PATCH v1 2/5
    • PATCH v1 3/5
    • PATCH v1 4/5
    • PATCH v1 5/5
  • PATCH v2 (without paren) (2022-01-11)
  • PATCH v1 (effectively PATCH v2 with paren) (2022-02-09)

Feature Description

General

This patchset adds support for three recently ratified RISC-V extensions:

• Zicbom (Cache-Block Management Instructions)
• Zicbop (Cache-Block Prefetch hint instructions)
• Zicboz (Cache-Block Zero Instructions)

prefetch.[irw] hint instructions in Zicbop extension require new operand type which is pseudo S-type immediate with low 5-bits set to zero (32-byte aligned). So, Zicbop changes are separate from Zicbom/Zicboz.

With or Without Paren

In the original RISC-V CMO document (v1.0), it had no paren in an operand.

cbo.zero    a0

However, there seems a proposal to change operand of cbo.* instructions on https://github.com/riscv/riscv-CMOs/issues/47.

cbo.zero    (a0)
cbo.zero    0(a0)    # only zero is allowed

I proposed both options on the GNU Binutils mailing list and ...surprisingly, a patchset with paren is merged without this change is approved in riscv-CMOs.

Some RISC-V folks including me worked to resolve the situation and the RISC-V CMO document is changed to have a paren (in v1.0.1).