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codeql/python/ql/lib/change-notes/2026-05-19-add-shared-ssa.md
Copilot b7f79f2d34 Python: add new shared-SSA-backed SSA adapter 
Preparatory refactor for the shared-CFG dataflow migration. Adds the
new Python SSA adapter additively, without changing any production
behaviour.

Library additions:

- semmle.python.dataflow.new.internal.SsaImpl — Python SSA
  implementation built on the new (shared) CFG. Mirrors the Java SSA
  adapter (java/ql/lib/semmle/code/java/dataflow/internal/SsaImpl.qll):
  an InputSig is defined in terms of positional (BasicBlock, int)
  variable references, and the shared
  codeql.ssa.Ssa::Make<Location, Cfg, Input> module is then
  instantiated.

  SourceVariable is the AST-level Py::Variable. Variable references
  are looked up via the new CFG facade's NameNode.defines/uses/deletes
  predicates (added in the preceding PR), which themselves are
  one-line bridges to AST-level Name.defines/uses/deletes.

  Implicit-entry definitions are inserted for non-local/global/builtin
  reads, captured variables, and (when needed) parameters.

Test additions:

- library-tests/dataflow-new-ssa/ — exercises the new SSA over a
  representative test corpus and checks expected def/use chains.

- library-tests/dataflow-new-ssa-vs-legacy/ — runs both new SSA and
  legacy ESSA over the same corpus and diffs the results, so any
  semantic divergence shows up as a test failure.

Production impact:

None. The new SSA adapter has zero callers in lib/ and src/ — the
legacy ESSA SSA (semmle/python/essa/*) remains the default. The
dataflow library is not migrated yet; that lands in a follow-up PR.

Verified by:
- All 367 lib + src + consistency-queries compile clean.
- All 641 ControlFlow + PointsTo + dataflow + essa + consistency
  library-tests pass.
- Both new dataflow-new-ssa[/vs-legacy] test packs pass.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
2026-06-22 13:38:40 +00:00

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  • A new SSA adapter has been added under semmle.python.dataflow.new.internal.SsaImpl, built on the shared codeql.ssa.Ssa library and the new shared CFG (semmle.python.controlflow.internal.Cfg). It is not yet used by the dataflow library or any production query; the legacy ESSA SSA in semmle/python/essa/* remains the default. The new SSA adapter is exposed for tests and for the upcoming dataflow migration.