TYPE name issue in coverage report for inherited covergroups

[hodjat91]

Hi Matthew,

I'm showing two testcases here, I believe the issue for both originates from the same place. Say that I have these three covergroups where two of them are extending the first one:

@vsc.covergroup
class main_cg(object):
    def __init__(self, it):
        super().__init__()

        self.cp1 = vsc.coverpoint(it, bins={
            "a": vsc.bin(5)
        })


@vsc.covergroup
class first_extended_cg(main_cg):
    def __init__(self, it):
        super().__init__(it)

        self.cp2 = vsc.coverpoint(it, bins={
            "a": vsc.bin(7)
        })


@vsc.covergroup
class second_extended_cg(main_cg):
    def __init__(self, it):
        super().__init__(it)

        self.cp3 = vsc.coverpoint(it, bins={
            "a": vsc.bin(9)
        })


a = 5
cg1 = first_extended_cg(lambda: a)
cg1.sample()

b = 8
cg2 = second_extended_cg(lambda: b)
cg2.sample()

report = vsc.get_coverage_report()
print("Report:\n" + report)

The issue is with the TYPE names: It seems like the inherited covergroups TYPE first_extended_cg and TYPE second_extended_cg are mistakenly get their names and are mapped to TYPE main_cg: So in the below results you see TYPE main_cg and TYPE main_cg2:

TYPE main_cg : 50.000000%
    CVP cp1 : 100.000000%
    CVP cp2 : 0.000000%
    INST main_cg : 50.000000%
        CVP cp1 : 100.000000%
        CVP cp2 : 0.000000%
TYPE main_cg_2 : 0.000000%
    CVP cp1 : 0.000000%
    CVP cp3 : 0.000000%
    INST main_cg_1 : 0.000000%
        CVP cp1 : 0.000000%
        CVP cp3 : 0.000000%

This could be really problematic in the final coverage results.

Here is another testcase (as I said, I think it originates from the same naming issue discussed above):

@vsc.covergroup
class main_cg(object):
    def __init__(self, it):
        super().__init__()

        self.cp1 = vsc.coverpoint(it, bins={
            "a": vsc.bin(5)
        })


@vsc.covergroup
class first_extended_cg(main_cg):
    def __init__(self, it):
        super().__init__(it)


@vsc.covergroup
class second_extended_cg(main_cg):
    def __init__(self, it):
        super().__init__(it)


a = 5
cg1 = first_extended_cg(lambda: a)
cg1.sample()

b = 8
cg2 = second_extended_cg(lambda: b)
cg2.sample()


report = vsc.get_coverage_report()
print("Report:\n" + report)

It's very similar to the previous example with one small difference: first_extended_cg and second_extended_cg just inherit from the main_cg without adding additional coverpoints. As you can see in the results below, both types are considered as two instances to a single TYPE main_cg while they should actually be two different TYPEs (TYPE first_extended_cg and second_extended_cg):

Report:
TYPE main_cg : 100.000000%
    CVP cp1 : 100.000000%
    INST main_cg : 100.000000%
        CVP cp1 : 100.000000%
    INST main_cg_1 : 0.000000%
        CVP cp1 : 0.000000%

Thanks beforehand for fixing this!

Best, Hodjat

[mballance]

Hi Hodjat, Yes, covergroups and inheritance isn't implemented at the moment. Perhaps the library should trap inheritance and error out for now... That said, the ability to have inheritance is a very attractive aspect of using Python. What priority would you place on having this feature? Just trying to ensure I direct effort in the right direction short and long-term.

Best Regards, Matthew

[hodjat91]

Hi Matthew,

Thanks for your confirmation, the library actually doesn't trap/raise error, it finishes the execution but like I said, the report isn't correct. As you said, having several covergroups inherit from a base covergroup is a very attractive feature that could be enabled in Python while SV side doesn't have such feature. Speaking of priorities, I guess this feature would have a high priority as we're building lots of covergroups (say for add, sub, branch, etc riscv instructions) which all extend an r_type_covergroup (although for the time being I'm moving forward with a workaround).

Cheers, Hodjat

[mballance]

Okay, I've add a check for inheritance for now. I've also kept this issue open as an enhancement