RFR: 8256956: RegisterImpl::max_slots_per_register is incorrect on AMD64

[Jie Fu]

Hi all,

The bug was found while I was learning @iwanowww 's patch [1].

As we know, the slot-size is 32-bit and the registers are 64-bit on AMD64.
So RegisterImpl::max_slots_per_register [2] should be 2 on AMD64.

It would be better to fix it.

Testing:
  - tier1~3 on Linux/x64

Thanks.
Best regards,
Jie

[1] https://github.com/openjdk/jdk/pull/1132
[2] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/register_x86.hpp#L53

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Commit messages:
 - 8256956: RegisterImpl::max_slots_per_register is incorrect on AMD64

Changes: https://git.openjdk.java.net/jdk/pull/1413/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1413&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256956
  Stats: 5 lines in 1 file changed: 0 ins; 3 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1413.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1413/head:pull/1413

PR: https://git.openjdk.java.net/jdk/pull/1413