[lworld] RFR: 8311219: [lworld] VM option "InlineFieldMaxFlatSize" cannot work well [v4]

[Jatin Bhateja]

On Thu, 7 Sep 2023 08:16:43 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

>> The main problem for me is how to check the flatten status for an `InlineTypeNode`. Maybe we can check the decode operation generated by the field accessing (or loading) to an primitive class field. Any better idea for this?
>
> Couldn't you just check that there is no oop load for that particular field, i.e., no indirection to load the fields from a heap buffer?

If a primitive class field is flattened, then compiler will not be creating an InlineTypeNode for field access, sub-field will be part of container, isn't that sufficient to make the check, e.g.


primitive class ABC {
   int f1;
   long f2;
   ABC (int f1, long f2) {
      this.f1 = f1;
      this.f2 = f2;
   }
}


public class flatten {
   public final ABC field;

   public flatten(int val) {
     this.field = new ABC(val, (long)val);
   }

   public static long micro(int val) {
      flatten obj =  new flatten(val);
      return obj.field.f1 + obj.field.f2;
   }

   public static void main(String [] args) {
      long res = 0;
      for (int i = 0; i < 10000; i++) {
          res += micro(i);
      }
      System.out.println(res);
   }
}



We see no InlineTypeNode in post parse IR with following command line:-

-XX:CompileCommand=compileonly,flatten::micro -XX:+EnablePrimitiveClasses -cp . flatten

But, field access does generate InlineTypeNode if flatten size explicitly set as 0 with following options.

-XX:InlineFieldMaxFlatSize=0  -XX:CompileCommand=compileonly,flatten::micro -XX:+EnablePrimitiveClasses -cp . flatten

EA will anyways remove non-escapable allocation, but post parse IR verification should be good enough to test your changes ?

-------------

PR Review Comment: https://git.openjdk.org/valhalla/pull/888#discussion_r1318305754