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theory_lra: eagerly propagate offset equalities x=y (fixes #10065)

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When a term column x - y is fixed to 0 (e.g. from t <= ca and t >= ca),
theory_lra previously discovered the implied equality x = y only lazily via
assume_eqs() during final_check. On the FP fuel-recursive axiom in issue #10065
this discovery is starved by E-matching, which unfolds the recursion and
bit-blasts an exploding FP subproblem before the branch closes.

Add propagate_offset_eq() to detect a fixed 2-variable offset term with opposite
unit-scaled coefficients and propagate the operand equality x = y directly to the
core, so congruence closure merges dependent terms immediately. This mirrors the
offset-row propagation performed by theory_arith (propagate_cheap_eq) and matches
its behavior on this benchmark (timeout -> unsat 0.06s, 2 quant-instantiations).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 726c4e71-03ff-45f6-8322-5253254e1d7e
This commit is contained in:
Nikolaj Bjorner 2026-07-14 22:46:06 -07:00
parent 7c8c6a4df0
commit ad063580dc
2 changed files with 50 additions and 0 deletions
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2
src/math/lp/lp_api.h
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@ -108,6 +108,7 @@ namespace lp_api {
unsigned m_num_iterations_with_no_progress;
unsigned m_need_to_solve_inf;
unsigned m_fixed_eqs;
unsigned m_offset_eqs;
unsigned m_conflicts;
unsigned m_bound_propagations1;
unsigned m_bound_propagations2;
@ -129,6 +130,7 @@ namespace lp_api {
st.update("arith-pivots", m_need_to_solve_inf);
st.update("arith-plateau-iterations", m_num_iterations_with_no_progress);
st.update("arith-fixed-eqs", m_fixed_eqs);
st.update("arith-offset-eqs", m_offset_eqs);
st.update("arith-conflicts", m_conflicts);
st.update("arith-bound-propagations-lp", m_bound_propagations1);
st.update("arith-bound-propagations-cheap", m_bound_propagations2);