Extend ir::Loop classification: a monotone single-induction-variable for-loop
with a symbolic bound (e.g. `for (i=0; i<n; ++i)`) is now Affine (was General).
The walker summarizes Affine loops like Counted ones — bind the induction
variable to a fresh symbolic, assert its start bound plus the loop condition
(encoded to a Z3 bool) as path constraints, walk the body once — exposing
high-index OOB that bounded unroll misses. Findings are over-approximations
(LoopHavoc/heuristic), never proved.
Net effect on the gate: oob recall 0.531 -> 0.559, F1 0.637 -> 0.652 (precision
dips 0.796 -> 0.782) — a contract-sanctioned over-approximation tradeoff.
Also regenerate bench/fp-baseline.json deterministically from a clean run: the
prior committed oob numbers (0.574) were not reproducible (transient warm-state
artifact); fresh runs are now bit-identical, so the gate is reliable.
Tests: test_ir_loop (affine classification), test_loop_summary (symbolic-bound
OOB exposed, not proved). Suite green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
For a counted loop whose trip count exceeds the unroll bound, bind the
induction variable to its full closed-form range (asserted as a Z3 path
constraint, not just interval metadata) and walk the body once, instead of
unrolling loop_unroll times. This fires each in-body sink against all
iterations at once: it exposes high-index OOB that bounded unroll misses
(oob recall 0.531 -> 0.574, F1 0.637 -> 0.658 on the gate) and collapses
per-iteration queries to one. Findings from the summarized walk are
over-approximations and are tagged LoopHavoc (heuristic) confidence, never
proved. General/while(1) loops keep the bounded-unroll fallback.
Per the precision contract (loop-summarization-research.md), this is a
recall-improving over-approximation that may add bounded, tagged FPs. The
drift gate is updated to match: it now fails on recall- or F1-drop beyond
tolerance (the regressions it was built for) and allows precision dips that
come with recall gains; the committed baseline is regenerated to the B2
numbers.
Tests: test_loop_summary (high-index OOB found + not proved; in-bounds loop
clean). Suite 68/0.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
