RFR: 8362504: AArch64: Replace MOVZ+MOVK+MOVK with ADRP+ADD

[Andrew Haley]

On Fri, 8 Aug 2025 08:08:36 GMT, Fei Gao <fgao at openjdk.org> wrote:

> > I've done some modelling using llvm-mca and it looks like `adrp; add` is a win on recent Apple processors as well as on Arm processors, so go ahead with making this the default.
> 
> Thanks for testing that — really great to hear! I’ll update the patch with a constraint for AOT cache shortly.

Correction: I'm afraid that the llvm-mca results are nonsense. It says that this sequence


  movk w0, #0x1234, lsl 16
  movk w1, #0x1234, lsl 16
  movk w2, #0x1234, lsl 16
  movk w3, #0x1234, lsl 16
  movk w4, #0x1234, lsl 16
  movk w5, #0x1234, lsl 16
  movk w6, #0x1234, lsl 16
  movk w7, #0x1234, lsl 16

takes 2 clock cycles on Apple M1, but Dougall Johnson measured real hardware executing this at 1 clock cycle.

I'm not going to believe any more without numbers we can trust.

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PR Comment: https://git.openjdk.org/jdk/pull/26653#issuecomment-3167078839