New Issue: proposal: @aligned N attribute

Notifications Issues
1

20945, "mppf", "proposal: @aligned N attribute", "2022-11-01T15:13:30Z"

Related to:

Over on issue #14141 we have some agreement to use an attribute to request particular alignment of a field.

This issue proposes a specific way of doing so.

Here is a sketch:

record R {
  @aligned 64
  var x: int;
  var y: int;
}

@aligned 64 just before the x field indicates that the x field should always be allocated with 64 byte alignment. As a result, the whole R record will also need 64 byte alignment.

To implement the alignment:

  • Compute the maximum alignment of any field. That is the alignment for the aggregate.
  • Add padding so that, assuming the aggregate is aligned (as above step would suggest), each field is aligned as requested

Design Questions:

  • Should alignment for class fields cause the new on the class to do an aligned allocation?
  • Is the syntax OK here?