RFR: 8375536: PPC64: Implement special MachNodes for floating point CMove [v5]

[Martin Doerr]

On Fri, 30 Jan 2026 15:01:11 GMT, Richard Reingruber <rrich at openjdk.org> wrote:

> > That was also wrong, but an additional problem was the wrong handling of NaN: C2 requires unordered to get treated like less
> 
> The requirement is to implement `op1 cond op2 ? src1 : src2`. For NaN this means the result has to be `src2` except for `!=`. And that's it, isn't it?
> 
> It might have helped to implement `op1 < op2` as `op2 > op1` using xscmpgtdp. The chosen implementation is also good.

We had tried. The following example can show that it's wrong:

class test {
  static double cmovf_ge(double op1, double op2, double src1, double src2) {
    return op1 >= op2 ? src1 : src2;
  }

  static void main(String[] args) {
    double result = 0.0;
    System.out.println(cmovf_ge(Double.NaN, Double.NaN, 1.0, 2.0));
    for (int i = 0; i < 100_000; ++i) {
      result += cmovf_ge((double) (i / 2), (double) ((i + 1) / 2), 1.0, 2.0);
    }
    System.out.println("result = " + result);
    System.out.println(cmovf_ge(Double.NaN, Double.NaN, 1.0, 2.0));
  }
}

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PR Comment: https://git.openjdk.org/jdk/pull/29281#issuecomment-3824211983