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  1. JDK
  2. JDK-8279607

Existing optimization "~x+1" -> "-x" can be generalized to "~x+c" -> "(c-1)-x".

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    • Subcomponent:
    • Resolved In Build:
      b07
    • CPU:
      generic
    • OS:
      generic

      Description

      A DESCRIPTION OF THE PROBLEM :
      Existing optimization `~x+1 -> -x` can be generalized to `~x+c -> (c-1)-x`. I included both microbenchmark and jtreg tests.

      ```cpp
      // Convert (~x+c) into (c-1)-x. Note there isn't a bitwise not
      // bytecode, "~x" would typically represented as "x^(-1)", so (~x+c)
      // will be (x^(-1))+c.
      if (op1 == Op_Xor(bt) &&
          (in2->Opcode() == Op_ConI || in2->Opcode() == Op_ConL) &&
          phase->type(in1->in(2)) == TypeInteger::minus_1(bt)) {
        Node* c_minus_one = phase->makecon(add_ring(phase->type(in(2)), TypeInteger::minus_1(bt)));
        return SubNode::make(c_minus_one, in1->in(1), bt);
      }
      ```

      I have submitted a pull request https://github.com/openjdk/jdk/pull/6858


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              Reporter:
              webbuggrp Webbug Group
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