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Fix coverpoint sampling for nested rand_attr fields (#265)
* Initial plan * Add test cases for nested rand_attr coverpoint issue Co-authored-by: mballance <1340805+mballance@users.noreply.github.com> * Fix nested rand_attr coverpoint sampling by enabling indexed field references Co-authored-by: mballance <1340805+mballance@users.noreply.github.com> * Update test documentation to reflect that the fix is now implemented Co-authored-by: mballance <1340805+mballance@users.noreply.github.com> --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: mballance <1340805+mballance@users.noreply.github.com>
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‎src/vsc/rand_obj.py‎

Lines changed: 7 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -179,6 +179,8 @@ def build_field_model(self, name):
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model = FieldCompositeModel(name, self._int_field_info.is_rand, self)
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model.typename = T.__qualname__
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self._int_field_info.model = model
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# Mark this field as composite so nested fields can be indexed correctly
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self._int_field_info.is_composite = True
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# Iterate through the fields and constraints
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# First, assign IDs to each of the randomized fields
@@ -310,7 +312,9 @@ def _id_fields(self, it, parent):
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fid += 1
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if fi.is_composite:
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self._id_fields(fo, fi)
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# Recursively process composite fields
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# Pass it._int_field_info as the parent, not fi
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self._id_fields(fo, it._int_field_info)
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setattr(T, "__getattribute__", __getattribute__)
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setattr(T, "__setattr__", __setattr__)
@@ -407,6 +411,8 @@ def build_field_model(self, name):
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model = FieldCompositeModel(name, self._int_field_info.is_rand, self)
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model.typename = T.__name__
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self._int_field_info.model = model
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# Mark this field as composite so nested fields can be indexed correctly
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self._int_field_info.is_composite = True
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# Iterate through the fields and constraints
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# First, assign IDs to each of the randomized fields

‎ve/unit/test_coverage_nested_randattr.py‎

Lines changed: 194 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,194 @@
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'''
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Test for coverage sampling on nested rand_attr objects
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This test verifies that coverpoints correctly sample nested fields
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that are included via vsc.rand_attr in a parent object.
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Issue: When a coverpoint targets fields within a nested object decorated with
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@vsc.randobj and included via vsc.rand_attr in the item, functional coverage
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is not correctly sampled when using direct field references (without lambda).
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'''
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import enum
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import vsc
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from vsc_test_case import VscTestCase
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@enum.unique
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class Security(enum.IntEnum):
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SEC = 0
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NONSEC = 1
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ROOT = 2
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class TestCoverageNestedRandAttr(VscTestCase):
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def test_nested_randattr_direct_reference_issue(self):
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"""
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Test that verifies direct field references on nested rand_attr objects
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now work correctly after the fix. Before the fix, direct references would
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bind to the initial value and only hit the first bin.
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"""
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@vsc.randobj
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class Protection:
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def __init__(self):
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self.security = vsc.rand_enum_t(Security)
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@vsc.randobj
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class MyItem:
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def __init__(self):
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self.protection = vsc.rand_attr(Protection())
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@vsc.covergroup
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class simple_covergroup:
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def __init__(self):
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self.with_sample(dict(it=MyItem()))
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# Direct reference - now works correctly after the fix
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self.security_cp_direct = vsc.coverpoint(
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self.it.protection.security,
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bins={s.name: vsc.bin(s.value) for s in Security}
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)
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# Create covergroup and sample multiple times
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cg = simple_covergroup()
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item = MyItem()
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# Track which values we've seen during randomization
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seen_values = set()
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# Sample many times to ensure we hit all values
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for _ in range(100):
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item.randomize()
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cg.sample(item)
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seen_values.add(item.protection.security)
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# We should have seen all three security values
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self.assertEqual(len(seen_values), 3,
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f"Expected to see all 3 Security values, but only saw: {seen_values}")
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# Check coverage - each bin should have been hit
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model = cg.security_cp_direct.get_model()
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# Get hit counts for each bin using the hit_l list
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bins_hit = 0
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for hit_count in model.hit_l:
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if hit_count > 0:
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bins_hit += 1
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# All 3 bins should be hit with the fix
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self.assertEqual(bins_hit, 3,
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f"Expected all 3 bins to be hit, but only {bins_hit} were hit")
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def test_nested_randattr_lambda_workaround(self):
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"""
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Test that verifies lambda expressions continue to work correctly
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for nested rand_attr coverpoints. Lambda expressions were the
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workaround before the fix and should continue to work after the fix.
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"""
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@vsc.randobj
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class Protection:
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def __init__(self):
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self.security = vsc.rand_enum_t(Security)
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@vsc.randobj
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class MyItem:
98+
def __init__(self):
99+
self.protection = vsc.rand_attr(Protection())
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@vsc.covergroup
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class simple_covergroup:
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def __init__(self):
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self.with_sample(dict(it=MyItem()))
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# Lambda reference - continues to work after the fix
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self.security_cp_lambda = vsc.coverpoint(
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lambda: self.it.protection.security,
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cp_t=vsc.enum_t(Security),
110+
bins={s.name: vsc.bin(s.value) for s in Security}
111+
)
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# Create covergroup and sample multiple times
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cg = simple_covergroup()
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item = MyItem()
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# Track which values we've seen during randomization
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seen_values = set()
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# Sample many times to ensure we hit all values
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for _ in range(100):
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item.randomize()
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cg.sample(item)
124+
seen_values.add(item.protection.security)
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# We should have seen all three security values
127+
self.assertEqual(len(seen_values), 3,
128+
f"Expected to see all 3 Security values, but only saw: {seen_values}")
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# Check coverage - each bin should have been hit
131+
model = cg.security_cp_lambda.get_model()
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# Get hit counts for each bin using the hit_l list
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bins_hit = 0
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for hit_count in model.hit_l:
136+
if hit_count > 0:
137+
bins_hit += 1
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# All 3 bins should be hit with lambda
140+
self.assertEqual(bins_hit, 3,
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f"Expected all 3 bins to be hit, but only {bins_hit} were hit")
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def test_non_nested_direct_reference_works(self):
144+
"""
145+
Test that direct references work correctly for non-nested fields.
146+
This should PASS and demonstrates that the issue is specific to nested fields.
147+
"""
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149+
@vsc.randobj
150+
class MyItem:
151+
def __init__(self):
152+
self.security = vsc.rand_enum_t(Security)
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@vsc.covergroup
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class simple_covergroup:
156+
def __init__(self):
157+
self.with_sample(dict(it=MyItem()))
158+
159+
# Direct reference to non-nested field - works correctly
160+
self.security_cp = vsc.coverpoint(
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self.it.security,
162+
bins={s.name: vsc.bin(s.value) for s in Security}
163+
)
164+
165+
# Create covergroup and sample multiple times
166+
cg = simple_covergroup()
167+
item = MyItem()
168+
169+
# Track which values we've seen during randomization
170+
seen_values = set()
171+
172+
# Sample many times to ensure we hit all values
173+
for _ in range(100):
174+
item.randomize()
175+
cg.sample(item)
176+
# item.security is directly the Security enum value
177+
seen_values.add(item.security)
178+
179+
# We should have seen all three security values
180+
self.assertEqual(len(seen_values), 3,
181+
f"Expected to see all 3 Security values, but only saw: {seen_values}")
182+
183+
# Check coverage - each bin should have been hit
184+
model = cg.security_cp.get_model()
185+
186+
# Get hit counts for each bin using the hit_l list
187+
bins_hit = 0
188+
for hit_count in model.hit_l:
189+
if hit_count > 0:
190+
bins_hit += 1
191+
192+
# All 3 bins should be hit for non-nested fields
193+
self.assertEqual(bins_hit, 3,
194+
f"Expected all 3 bins to be hit, but only {bins_hit} were hit")

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