[utils] Fix DenseMap debugger printers for the packed used-bit array#201755
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DenseMap no longer use in-band sentinel keys. (llvm#200595 and llvm#201281). Update the GDB pretty printer and LLDB data formatters to test the used bit rather than comparing keys. GDB: advancePastEmptyBuckets relied on DenseMapInfo::getEmptyKey(), which could not be evaluated in GDB and so was disabled, leaving the printer to emit empty and erased buckets. It now walks bucket indices and skips any whose used bit is clear. LLDB: DenseMapSynthetic used a key-uniqueness heuristic to guess which buckets were live, which mishandled a lone erased bucket (hence the former tombstones=1 summary note). It now reads the used array directly, so erased entries are skipped exactly. NumTombstones no longer exists, so drop it from the summary. Written by Claude Opus 4.8
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test scripts |
aengelke
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Jun 5, 2026
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Looks ok? I never used these (and also never wrote debugger printers myself), so I'm probably not the best person to review this...
kastiglione
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Jun 7, 2026
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| for index in range(num_buckets): | ||
| bucket = buckets.GetValueForExpressionPath(f"[{index}]") | ||
| key = bucket.GetChildAtIndex(0) | ||
| key_buckets[str(key.data)].append(index) | ||
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| # Heuristic: This is not a multi-map, any repeated (non-unique) keys are | ||
| # either the the empty key or the tombstone key. Populate child_buckets | ||
| # with the indexes of entries containing unique keys. | ||
| for indexes in key_buckets.values(): | ||
| if len(indexes) == 1: | ||
| self.child_buckets.append(indexes[0]) | ||
| word = used.GetValueForExpressionPath(f"[{index >> 5}]").unsigned | ||
| if (word >> (index & 31)) & 1: | ||
| self.child_buckets.append(index) |
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I haven't tested it with the updated DenseMap, but I suggest avoiding calling GetValueForExpressionPath("[N]") 32 times for each N, by doing something like:
used_data = used.GetPointeeData(0, num_buckets // 32)
for word_idx, word in enumerate(used_data.uint32):
for bit in range(32):
if (word >> bit) & 1:
self.child_buckets.append(word_idx * 32 + bit)
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Thx for the suggestion! Changed num_buckets // 32 to (N+31)//32, since the number of buckets can be 4/8/16, smaller than 32.
kastiglione
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Jun 8, 2026
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Approving the lldb formatter. Thank you.
Co-authored-by: Dave Lee <[email protected]>
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DenseMap no longer use in-band sentinel keys. (#200595 and #201281).
Update the GDB pretty printer and LLDB data formatters to test the used
bit rather than comparing keys.
GDB: advancePastEmptyBuckets relied on DenseMapInfo::getEmptyKey(), which
could not be evaluated in GDB and so was disabled, leaving the printer to
emit empty and erased buckets. It now walks bucket indices and skips any
whose used bit is clear.
LLDB: DenseMapSynthetic used a key-uniqueness heuristic to guess which
buckets were live, which mishandled a lone erased bucket (hence the
former tombstones=1 summary note). It now reads the used array directly,
so erased entries are skipped exactly. NumTombstones no longer exists, so
drop it from the summary.
Written by Claude Opus 4.8