Unit + integration coverage for the session's work: incremental project
graph/index, pcode encoder, unreachable/dead-branch, equiv/cross-TU,
div-by-zero/sign-conversion/int-truncation, use-after-free, quality-precision,
scan-router profile, source TU runner, detector plan, and the eval fixtures.
Fold-on-fold pass surfaced 152 dead-statement findings against
fold's own source. Spot-checks revealed every flagged statement
was inside a range-for body. Minimal isolation fixture:
for (const auto& [k, v] : src)
dst[k] = v; // flagged FP: "unreachable from entry"
Plain `for (int x : v)` does NOT trip the bug. The trigger is the
structured binding inside the range-for. Clang's CFG for that
shape leaves the body block without an incoming edge from the
loop's condition check, so the reachability walk in
DeadStatementVisitor marks every body statement unreachable.
Filter: walk up the parent map from the candidate anchor (capped
at 16 hops); if any ancestor is a CXXForRangeStmt, suppress the
finding. Narrow, behaviour-preserving for real dead code,
contained to the same defensive-filter block that already handles
macro-expanded anchors.
Result on fold's own 134-TU compile DB:
before: 152 dead-statement findings
after: 16 (90% reduction)
The remaining 16 likely have other root causes; future audit work.
Added regression test exercising the exact failing fixture; 5/5
test_dead_statement cases pass. Full 44/44 suite still green.
Note: this is itself a fold-on-fold success — the perf-audit's
fold-on-fold pass surfaced a detector bug that had been silently
shipping FPs on every C++ codebase with structured-binding range
loops.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
