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java-topology/tools/tickets/defects/ghc-0001.md
russell@unturf.com db29a08762 undefect. CWE-407 — 92 sites, 42 ecosystems 
B&W print-friendly diagrams + tinkerpop-0001 + wave-3 proof sections.
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2026-03-26 19:48:18 -04:00

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id repo severity status created patched patch
ghc-0001 ghc HIGH PATCHED 2026-03-23 2026-03-23 defects/ghc/patch/ghc-cwe407-set-membership.patch

Defect

File: compiler/GHC/Data/Graph/Directed/Internal.hs:78 Pattern: v `elem` adjacency_list in SCC decode Complexity: O(V×degree) Language: Haskell

Description

During SCC decoding, GHC checks edge membership using elem on an adjacency list represented as a plain Haskell list. For each vertex V being decoded, every neighbor lookup scans up to degree entries linearly. With V vertices each having up to degree neighbors, the aggregate cost across the full SCC decode is O(V×degree), which degrades to O(V²) for dense graphs.

Fix

Replace: v `elem` adjacency_list With: v `S.member` adjacency_set Data structure change: adjacency_list: [Vertex] → adjacency_set: Set Vertex

Work required

  • Patch in defects/ghc/patch/
  • Unit test — asserts exact operation counts before/after (in defects/ghc/unit/)
  • Integration test (in defects/ghc/integration/)
  • Benchmark — before/after on V=100,200,400,800 (in defects/ghc/bench/)
  • White paper section