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  1. JDK
  2. JDK-8153713

aarch64: improve short array clearing using store pair

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    Details

    • Type: Enhancement
    • Status: Resolved
    • Priority: P4
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 9
    • Component/s: hotspot
    • Labels:
    • Subcomponent:
    • Introduced In Version:
      9
    • Resolved In Build:
      b120
    • CPU:
      aarch64
    • OS:
      linux

      Backports

        Description

        Currently, C2 compiler generate independent stores to clear short arrays whose size is no bigger than parameter InitArrayShortSize (refer to ClearArrayNode::Ideal function). For the aarch64 port, we have store pair instruction which can zero two memory words at a time and this will be good for code size and maybe performance for some micro-archs.

        Example C2 JIT code snippet:

          0x0000007fa85c03a8: cmp x11, x10
          0x0000007fa85c03ac: b.cs 0x0000007fa85c0474
          0x0000007fa85c03b0: orr x10, xzr, #0x1
          0x0000007fa85c03b4: str x11, [x28,#96]
          0x0000007fa85c03b8: str x10, [x12]
          0x0000007fa85c03bc: mov x10, #0x10000 // #65536
                                                        ; {metadata('java/lang/Object'[])}
          0x0000007fa85c03c0: movk x10, #0x1080
          0x0000007fa85c03c4: str w10, [x12,#8]
          0x0000007fa85c03c8: str w2, [x12,#12]
          0x0000007fa85c03cc: str xzr, [x12,#16]
          0x0000007fa85c03d0: str xzr, [x12,#24]
          0x0000007fa85c03d4: str xzr, [x12,#32]
          0x0000007fa85c03d8: str xzr, [x12,#40]
          0x0000007fa85c03dc: str xzr, [x12,#48]
          0x0000007fa85c03e0: prfm pstl1keep, [x11,#256]
          0x0000007fa85c03e4: str xzr, [x12,#56]
          0x0000007fa85c03e8: prfm pstl1keep, [x11,#320]
          0x0000007fa85c03ec: str xzr, [x12,#64]
          0x0000007fa85c03f0: prfm pstl1keep, [x11,#384]
          0x0000007fa85c03f4: str xzr, [x12,#72]
          0x0000007fa85c03f8: dmb ishst ;*anewarray
                                                        ; - scala.collection.mutable.ResizableArray$class::$init$@14 (line 32)
                                                        ; - scala.collection.mutable.ArrayBuffer::<init>@34 (line 47)
                                                        ; - scala.collection.mutable.ArrayBuffer::<init>@3 (line 62)
                                                        ; - scala.collection.mutable.ArrayBuffer$::newBuilder@4 (line 189)
                                                        ; - scala.collection.generic.GenericTraversableTemplate$class::genericBuilder@6 (line 69)
                                                        ; - scala.collection.AbstractTraversable::genericBuilder@1 (line 105)

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                Assignee:
                fyang Fei Yang
                Reporter:
                fyang Fei Yang
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                  Created:
                  Updated:
                  Resolved: