Uploaded image for project: 'JDK'
  1. JDK
  2. JDK-8173470

C2: Mask shift operands in ideal graph

    Details

    • Subcomponent:
    • Resolved In Build:
      b21

      Description

      Constant shift operand > 31 (int) or > 63 (long) are pointless. Mask them in the ideal graph.

      From the standard:
      https://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.19
      If the promoted type of the left-hand operand is int, only the five lowest-order bits of the right-hand operand are used as the shift distance. It is as if the right-hand operand were subjected to a bitwise logical AND operator & (§15.22.1) with the mask value 0x1f (0b11111). The shift distance actually used is therefore always in the range 0 to 31, inclusive.

      If the promoted type of the left-hand operand is long, then only the six lowest-order bits of the right-hand operand are used as the shift distance. It is as if the right-hand operand were subjected to a bitwise logical AND operator & (§15.22.1) with the mask value 0x3f (0b111111). The shift distance actually used is therefore always in the range 0 to 63, inclusive.

        Attachments

          Issue Links

            Activity

              People

              • Assignee:
                goetz Goetz Lindenmaier
                Reporter:
                goetz Goetz Lindenmaier
              • Votes:
                0 Vote for this issue
                Watchers:
                3 Start watching this issue

                Dates

                • Created:
                  Updated:
                  Resolved: