RFR: 8336245: AArch64: remove extra register copy when converting from long to pointer

[Fei Gao]

In the cases like:

  UNSAFE.putLong(address + off1 + 1030, lseed);
  UNSAFE.putLong(address + 1023, lseed);
  UNSAFE.putLong(address + off2 + 1001, lseed);


Unsafe intrinsifies direct memory access using a long as the base address, generating a `CastX2P` node converting long to pointer in C2. Then we get optoassembly code like:

  ldr  R10, [R15, #120]    # int ! Field: address
  ldr  R11, [R16, #136]    # int ! Field: off1
  ldr  R12, [R16, #144]    # int ! Field: off2
  add  R11, R11, R10
  mov R11, R11    # long -> ptr
  add  R12, R12, R10
  mov R10, R10    # long -> ptr
  add R11, R11, #1030    # ptr
  str  R17, [R11]    # int
  add R10, R10, #1023    # ptr
  str  R17, [R10]    # int
  mov R10, R12    # long -> ptr
  add R10, R10, #1001    # ptr
  str  R17, [R10]    # int


In aarch64, the conversion from long to pointer could be a nop but C2 doesn't know it. On the existing code, we do nothing for `mov dst src` only when `dst` == `src` [1], then we have assembly:

  ldr    x10, [x15,#120]
  ldp    x11, x12, [x16,#136]
  add    x11, x11, x10
  add    x12, x12, x10
  add    x11, x11, #0x406
  str    x17, [x11]
  add    x10, x10, #0x3ff
  str    x17, [x10]
  mov    x10, x12  <--- extra register copy
  add    x10, x10, #0x3e9
  str    x17, [x10]


There is still one extra register copy, which we're trying to remove in this patch.

This patch folds `CastX2P` into memory operands by introducing `indirectX2P` and `indOffX2P`. We also create a new opclass `iRegPorL2P` to remove extra copies from `CastX2P` in pointer addition.

Tier 1~3 passed on aarch64. No obvious change in size of libjvm.so

[1] https://github.com/openjdk/jdk/blob/5c612c230b0a852aed5fd36e58b82ebf2e1838af/src/hotspot/cpu/aarch64/aarch64.ad#L7906

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Commit messages:
 - 8336245: AArch64: remove extra register copy when converting from long to pointer

Changes: https://git.openjdk.org/jdk/pull/20157/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20157&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336245
  Stats: 320 lines in 5 files changed: 297 ins; 3 del; 20 mod
  Patch: https://git.openjdk.org/jdk/pull/20157.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20157/head:pull/20157

PR: https://git.openjdk.org/jdk/pull/20157