Deep DRC can miss violations when a cell has many shapes

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  • #2547 by @nikosavola — closed without merging

Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
52/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
cpp
Domain
computer-graphics, testing

Research direction

Read the box_scanner2 sweep and the instance to shape interaction scan in dbHierProcessor.cc, focusing on how reported pairs are keyed and how layer ids enter the scan. Reproduce the issue with the small box_scanner2 test described in the report, using duplicate insertions with different properties and enough boxes to cross the threshold. Done means the sweep reports both pairs and the deep DRC result retains all 4296 markers.

Written by the indexing model from the issue text.

Description

On a clipped deep DRC run of the vexriscv layout, a via1 in metal1 enclosure check loses 2127 of its 4296 markers. Forcing the brute force path everywhere gives all 4296. Almost every via either keeps all of its markers or loses all of them.

The cause is in the box_scanner2 sweep. It remembers the pairs it has already reported in a set, and that set is keyed on the two object pointers only. In the instance to shape interaction scan in dbHierProcessor.cc the same shape can be inserted twice with two different intruder layer ids. The second pair then looks like a duplicate and is dropped. Small cells don't use the sweep, so there both pairs are reported and the result depends on how many shapes a cell has. A small box_scanner2 test shows the same thing when one object is inserted twice with different properties and there are enough other boxes to go over the threshold.

Dominant language
C++
Stars
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Forks
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Avg merge
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Merged PRs (30d)
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