Integrated: 8345110: RISC-V: Optimize and and clean up byte reverse assembler routines

[Fei Yang]

On Wed, 27 Nov 2024 12:28:40 GMT, Fei Yang <fyang at openjdk.org> wrote:

> Hi, Could you please help review this change?
> 
> MacroAssembler routines `revb_w` and `revb_w_w` will emit 32 and 17 instructions respectively without Zbb.
> 
> Major changes:
> 1. There is no need for `revb_w` to reverse bytes for each 32-bit word in the 64-bit register.
>    All the callers only care about the lower 32-bit word. This reimplement `revb_w` so that it only
>    reverses bytes in lower 32-bit word and sign-extends the result (14 instructions). This makes `revb_w_w` duplicate.
> 2. Removed some assembler routines that are unused or become unnecessary (`revb_h`, `revb_h_helper`, `revb_h_h`, `revb_w_w`).
> 3. Adapted callers of these removed assembler routines in file `riscv_b.ad` to emit Zbb instructions directly.
> 
> Will look into `revb_h_h_u` and `revb_h_w_u` after this change. Seems to me they could be factored out as well.
> 
> Testing on linux-riscv64 platform:
> - [x] tier1 (release)
> - [x] hotspot:tier1 (fastdebug)
> - [x] non-trivial benchmark workloads like Dacapo, SpecJBB, Renaissance (release)

This pull request has now been integrated.

Changeset: 08d563ba
Author:    Fei Yang <fyang at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/08d563ba15047020fd5f5fea80547e18898bbab2
Stats:     128 lines in 4 files changed: 28 ins; 77 del; 23 mod

8345110: RISC-V: Optimize and and clean up byte reverse assembler routines

Reviewed-by: mli, rehn

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PR: https://git.openjdk.org/jdk/pull/22410