After PR #150846 changed MCFragment to use fixed 16KB blocks, large
sections like .debug_names produce thousands of fragments. The
DW_IDX_parent emission called emitLabelDifference(ParentSymbol,
EntryPool, 4) per entry, which fell through to
attemptToFoldSymbolOffsetDifference's O(n) fragment walk when symbols
were in different fragments. This caused O(entries * fragments)
quadratic behavior, regressing dsymutil on large binaries like clang.
Fix by pre-computing byte offsets from EntryPool for each entry in a
first pass, then emitting emitInt32(offset) directly for DW_IDX_parent
instead of symbol differences. This also eliminates per-entry MCSymbol
allocation that was only needed for parent references.
Fix#188376
0f63c0a3a5