[sv-ec] Covergroup fixed-size vector bin creation

Hi all:

In the meeting yesterday we discussed the order in which the bin distribution and with expression application should be done when creating fixed-size vector bins. Below is an example of where this would matter.

bit [3:0] coverpoint b {
  bins onehot[4] = b with $onehot(item);
}

If we apply the with function and then distribute to the bins we get what is probably the intended result of one item/bin. If we distribute then apply the with function we end up with three bins, <0001,0010>,<0100>,<1000>. The fourth bin is emptied by the application of the with expression and is excluded from coverage.

In the meeting, I had stated that I thought the application of the with expression should apply after the distribution of bins. This would be in line with how ignore bins are handled (see 19.5.4). Based on the above example it seems like that is the wrong thing to do. Do folks recall how the decision was made regarding ordering between applying ignore bins and distribution? Is there another example that shows why distribution before application of the with expression is desirable?

Thanks,
Scott

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