Python: cache shared SSA liveness across staged consumers (DCA) - #22465

Flips the Python dataflow trunk from the legacy CFG (semmle/python/Flow.qll)
and legacy ESSA SSA (semmle/python/essa/*) to the new shared CFG facade
(semmle.python.controlflow.internal.Cfg) and the new SSA adapter
(semmle.python.dataflow.new.internal.SsaImpl), both introduced
additively in the preceding PRs in this stack.

This is the trunk-flip equivalent of the original draft PR github#21894 (kept
around as documentation), rebased on top of the four preparatory PRs:

  P1: Remove AstNode.getAFlowNode() and rewrite callers (github#21919).
  P2: Qualify Flow.qll's AST references with Py:: prefix (github#21920).
  P3: Add new shared-CFG-backed control flow graph (github#21921).
  P4: Add new shared-SSA-backed SSA adapter (github#21923).

The Python dataflow library (semmle/python/dataflow/new/) now imports
the new CFG facade and SSA adapter. All CFG-typed predicates
(ControlFlowNode, CallNode, BasicBlock, NameNode, AttrNode, ...) are
qualified with the Cfg:: prefix; SSA references switch from
EssaVariable/EssaDefinition to SsaImpl::Definition/SourceVariable.

GuardNode is redesigned to use the new CFG's outcome-node model
(isAfterTrue / isAfterFalse) instead of the legacy ConditionBlock +
flipped indirection. Only BarrierGuard<...> is preserved as public
API.

Framework files (Bottle, FastApi, Django, Tornado, Pyramid, Stdlib,
...) are updated to take CFG nodes from the new facade.

A handful of dataflow consistency tweaks for the new CFG:
- Augmented-assignment targets are treated as both load and store.
- 'from X import *' produces uncertain SSA writes for unknown names.
- CFG nodes are canonicalised so dataflow does not see equivalent
  pre/post-order pairs as distinct nodes.

Two AST tweaks for the new CFG:
- AstNodeImpl: omit PEP 695 type-parameter names from
  FunctionDefExpr / ClassDefExpr children.
- ImportResolution: drop the legacy essa import.

Test churn (~175 files): reblessed library- and query-test .expected
files reflect slightly different CFG granularity, different toString
output, and a handful of true alert deltas in security queries.

Verification: all 367 lib + src + consistency-queries compile clean.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

The `Cfg::ControlFlowNode` facade re-exports the shared CFG library's
`dominates`/`strictlyDominates` predicates, which are declared
`bindingset[this, that]` + `pragma[inline_late]` and are meant to be used
as bound-pair membership checks. The facade wrappers dropped these
annotations (using plain `pragma[inline]`), so even though the only
callers — the `with` / `async with` taint steps in DataFlowPrivate.qll
and TaintTrackingPrivate.qll — bind both endpoints, the optimizer was
free to materialise `Cfg::ControlFlowNode.strictlyDominates/1` as a full
O(nodes^2) relation over the (larger) shared-CFG node set.

On some projects this dominated analysis time entirely (DCA showed e.g.
ICTU/quality-time and biosimulations regressing ~75-160x). Restoring
`bindingset[this, other]` + `pragma[inline_late]` on the wrappers turns
the predicate back into a bound-pair check and is result-preserving (only
binding annotations change, the predicate body is unchanged).

Reproduced on ICTU/quality-time: full python-security-extended suite went
from stalling >20min on `strictlyDominates` to completing in ~6min; all
ControlFlow and dataflow/coverage library tests pass.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Document the public expression adapter and apply the canonical QL annotation ordering required by the formatter.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 529363f5-bc7d-4f0b-9f47-e03ba9aa0cdf

The legacy CFG (`Flow.qll`) and legacy ESSA (`Essa`/`SsaCompute`/
`SsaDefinitions`) were pinned into the always-on `Stages::AST` cached stage
via `Stages::AST::ref()` and the matching `backref()` disjuncts. Because a
cached stage is materialized as a unit once any of its predicates is demanded
(and every query demands e.g. `Expr.toString()`), this forced the legacy
CFG/ESSA to be computed for *every* query -- including the security/dataflow
queries, which after the shared-CFG dataflow flip no longer depend on the
legacy CFG at all.

Since `Stages::AST::ref()` is `1 = 1`, removing it is result-preserving; it
only changes stage scheduling. After this change the legacy CFG/ESSA is no
longer materialised for queries that do not genuinely reference it. Verified
on the full `python-security-extended` suite and on django: legacy CFG/ESSA
families materialised drop from ~165 to 0 with byte-identical results.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

The previous capturedJumpStep shape introduced an independent
Cfg::DefinitionNode and related it to the captured variable before nodeTo
bound the relevant scope-entry definition. On substantial databases, the
evaluator chose a plan that materialized a high-duplication store/variable
join before applying the target entry and source-node constraints.

Bind the scope-entry definition from nodeTo first, derive its source variable,
and then match nodeFrom's DefinitionNode directly to that variable's store.
This is relation-equivalent existential elimination: the old
nodeFrom.asCfgNode() = def and def.getNode() = store constraints become
nodeFrom.asCfgNode().(Cfg::DefinitionNode).getNode() = store, preserving the
DefinitionNode type restriction and the unchanged enclosing-scope condition.

On Airflow a9da0f7 with CodeQL 2.26.2, against exact github#21925 head
1a8e317:

* The call-target diagnostic retains the identical 59,732-edge set while
  tuples joined fall from 1,032,403,207 to 66,969,953 (-93.5%), maximum
  duplication falls from 1,473,981 to 4,053, and evaluator wall time falls
  from 59.9s to 6.2s.
* py/clear-text-logging-sensitive-data retains every result tuple (130 alerts,
  256,708 path edges, 102,385 path nodes, and 116,976 subpaths) while tuples
  joined fall from 1,329,594,809 to 242,111,554 (-81.8%) and evaluator wall
  time falls from 94s to 14.4s.

The preceding commit is intentionally a semantic call-target invariant
diagnostic that passes on the unoptimized relation and after this rewrite. An
inline MISSING/SPURIOUS red-state would assert an artificial semantic delta;
this optimization must preserve every valid captured call target.

These measurements cover one exact substantial Airflow database and two query
shapes. No DCA was run, the fix does not reduce legitimate call-graph or path
growth, and broader fleet performance remains to be confirmed separately.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 5dfda5f5-08c8-481b-9ecb-299018701497

Exercise the three public AdjacentUses relations and compare them with their internal projection or recursive expansion contracts. The cache-placement defect changes evaluator specialization and work rather than semantic results, so a semantic contract snapshot is the stable red-state equivalent; wall-time assertions would be machine-dependent and flaky.

This intentionally records no MISSING or SPURIOUS rows: the expected invariant is exact relation equality before and after cache placement changes.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 21ab8585-861f-42c9-a834-451604646c6b

The shared SSA module requires language adapters to cache predicates that they expose. The Python adapter exposed firstUse, adjacentUseUse, and useOfDef without restoring that cache boundary, unlike the legacy AdjacentUses implementation.

On exact historical Salt, the missing boundary caused the same 6,313,793-row liveAtExit fixed point to be evaluated twice. The equivalent plans received distinct RA hashes (c6bc8xgji0uv6seurbhesjqd315 versus fabf1xs3jb6t67a2buq2iv8iof4 for unsafe deserialization, and c6bc8xgji0uv6seurbhesjqd315 versus 8270excv27ldlfrtk19ou81d206 for modification-of-default-value) because one inherited an unrelated cached-empty sentinel while the other used a literal empty base.

Cache the three Python adapter relations rather than generic liveness. This restores the documented shared-SSA contract at the narrow language boundary and avoids imposing a 6.31M-row generic cache on every language instantiation.

On current head 1a8e317 with exact saltstack/salt@d036b117, three matched prewarmed -j1 repeats reduced median evaluator time from 51.294s to 45.103s for unsafe deserialization and from 42.377s to 34.238s for modification-of-default-value. Median paired reductions were 6.428s and 8.247s. Joined tuples fell by 58,255,670 and 85,664,313; recursive pipeline runs fell by 1,999 and 3,015. Both queries retained the identical empty endpoint hash 2a514e093aae140a14f6bf77beebe1ad in every repeat.

Historical exact controls also retained 483,922 definitions, 169,921 phi inputs, 390,548 first uses, 475,226 adjacent uses, and 123,231 semantic call edges with zero left-only or right-only rows. Historical Salt evaluator recovery was 16.5% and 19.9%. Cold prewarm evaluator time was neutral (106.609s to 106.620s), so this is a warm-query optimization rather than a claimed cold-cache speedup.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 21ab8585-861f-42c9-a834-451604646c6b

Prove that the query-shaped shared-SSA relation for direct truthiness guards is equivalent to the generic BarrierGuard abstraction on the modification-of-default-value regression corpus. This guards the performance specialization against semantic drift before changing production code.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 07c775e7-cd7c-4e1c-8d97-5194ffd43e1a

Keep the modification-of-default-value query on shared SSA while expressing its two direct truthiness checks in a query-shaped predicate. The generic BarrierGuard abstraction causes the evaluator to materialize and rescan a 1,579,772,664-row def-use pair relation before applying branch control. Binding both concrete NameNode uses in one predicate lets the optimizer fuse the same joins with controlsBlock and persist only the 4,992 guarded uses.

On FreeCAD@0def330, three prewarmed evaluator runs improve from 309.159-329.621s to 77.781-81.349s with byte-identical query results. A direct symmetric-difference evaluation returns zero rows, and the CommandInjection path-query control retains identical results, work, and plan hashes.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 07c775e7-cd7c-4e1c-8d97-5194ffd43e1a

Allow language adapters that expose one SSA instantiation through multiple
cached API stages to persist the complete liveness fixed point once. Keep
the existing demand-specialized factory as the default.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 07c775e7-cd7c-4e1c-8d97-5194ffd43e1a

Use the opt-in shared SSA factory so Python reuses the same complete
liveness relation across its staged public SSA and data-flow consumers.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 07c775e7-cd7c-4e1c-8d97-5194ffd43e1a