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  1. JDK
  2. JDK-8153837

AArch64: Handle special cases for MaxINode & MinINode

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    • 9
    • b06
    • aarch64
    • linux

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        I witnessed some code sequence like the following in specjbb2005 and other benchmarks:
          61976 0x0000007f7e17ff44: mov w13, wzr
          61977 0x0000007f7e17ff48: cmp w12, w13
          61978 0x0000007f7e17ff4c: csel w11, w12, w13, gt ;*iinc {reexecute=0 rethrow=0 return_oop=0}
          61979 ; - jdk.internal.org.objectweb.asm.Type::getArgumentsAndReturnSizes@103 (line 451)
        ......
         123349 0x0000007f7e1db660: mov w16, wzr
         123350 0x0000007f7e1db664: sub w10, w19, w23 ;*iload {reexecute=0 rethrow=0 return_oop=0}
         123351 ; - java.math.MutableBigInteger::divideMagnitude@182 (line 1503)
         123352
         123353 0x0000007f7e1db668: cmp w15, w16
         123354 0x0000007f7e1db66c: csel w18, w15, w16, gt
         123355 0x0000007f7e1db670: mov w25, wzr ;*iastore {reexecute=0 rethrow=0 return_oop=0}
         123356 ; - java.math.MutableBigInteger::divideMagnitude@221 (line 1506)
        ......
         187167 0x0000007f7e23a6f0: mov w12, wzr
         187168 0x0000007f7e23a6f4: cmp w11, w12
         187169 0x0000007f7e23a6f8: csel w10, w11, w12, gt
        ......
          17114 0x0000007f7e124058: orr w14, wzr, #0x1
          17115
          17116 0x0000007f7e12405c: mov w10, wzr
          17117 0x0000007f7e124060: cmp w13, w14
          17118 0x0000007f7e124064: csel w12, w13, w14, gt
        ......
          61072 0x0000007f7e179450: orr w11, wzr, #0x1
          61073 0x0000007f7e179454: cmp w10, w11
          61074 0x0000007f7e179458: csel w12, w10, w11, gt

        For the aarch64 port, we have csel/csinc/csinv instructions which can be applied for these cases eliminating one extra mov instruction here.

        I mean something like this:
        min(x, 1) which becomes

        cmp x, 0
        csinc x, x, zr, le

        min(x, -1) which becomes

        cmp x, 0
        csinv x, x, zr, lt

        max(x, 1)

        cmp x, 0
        csinc x, x, zr, gt

        max(x, -1)

        cmp x, 0
        csinv x, x, zr, ge

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                dchuyko Dmitry Chuyko
                fyang Fei Yang
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                  Created:
                  Updated:
                  Resolved: