Create master equality engine at context level 0

Fixes #4077. The master equality engine in `TheoryEngine` was being
created at SAT context level 1. If the context was popped to level zero
by `(reset-assertions)`, `true` and `false` were removed from the master
equality engine, which lead for example to `(= ((_ extract 3 3) x) (_
bv1 1))` and `(_ bv1 4)` being merged (this can be gathered from looking
at `-t equality`). This commit fixes the issue by postponing the global
context pushes until after the theory engine has been initialized.

4 files changed, 22 insertions, 5 deletions

diff --git a/src/smt/smt_engine.cpp b/src/smt/smt_engine.cpp
index 5fc0189c3..d2919143b 100644
--- a/src/smt/smt_engine.cpp
+++ b/src/smt/smt_engine.cpp
@@ -925,11 +925,6 @@ void SmtEngine::finishInit()
 
   d_private->addUseTheoryListListener(d_theoryEngine);
 
-  // global push/pop around everything, to ensure proper destruction
-  // of context-dependent data structures
-  d_userContext->push();
-  d_context->push();
-
   // ensure that our heuristics are properly set up
   setDefaults();
 
@@ -951,6 +946,11 @@ void SmtEngine::finishInit()
   Trace("smt-debug") << "Finishing init for theory engine..." << std::endl;
   d_theoryEngine->finishInit();
 
+  // global push/pop around everything, to ensure proper destruction
+  // of context-dependent data structures
+  d_userContext->push();
+  d_context->push();
+
   Trace("smt-debug") << "Set up assertion list..." << std::endl;
   // [MGD 10/20/2011] keep around in incremental mode, due to a
   // cleanup ordering issue and Nodes/TNodes.  If SAT is popped
diff --git a/src/theory/uf/equality_engine.cpp b/src/theory/uf/equality_engine.cpp
index 693b7bd66..b6896e45d 100644
--- a/src/theory/uf/equality_engine.cpp
+++ b/src/theory/uf/equality_engine.cpp
@@ -81,6 +81,11 @@ void EqualityEngine::init() {
   Debug("equality") << "EqualityEdge::EqualityEngine(): edge_null = " << +null_edge << std::endl;
   Debug("equality") << "EqualityEdge::EqualityEngine(): trigger_null = " << +null_trigger << std::endl;
 
+  // If we are not at level zero when we initialize this equality engine, we
+  // may remove true/false from the equality engine when we pop to level zero,
+  // which leads to issues.
+  Assert(d_context->getLevel() == 0);
+
   d_true = NodeManager::currentNM()->mkConst<bool>(true);
   d_false = NodeManager::currentNM()->mkConst<bool>(false);
 
diff --git a/test/regress/CMakeLists.txt b/test/regress/CMakeLists.txt
index a68c31441..d822ce157 100644
--- a/test/regress/CMakeLists.txt
+++ b/test/regress/CMakeLists.txt
@@ -898,6 +898,7 @@ set(regress_0_tests
   regress0/smtlib/get-unsat-assumptions.smt2
   regress0/smtlib/global-decls.smt2
   regress0/smtlib/issue4028.smt2
+  regress0/smtlib/issue4077.smt2
   regress0/smtlib/reason-unknown.smt2
   regress0/smtlib/reset.smt2
   regress0/smtlib/reset-assertions1.smt2
diff --git a/test/regress/regress0/smtlib/issue4077.smt2 b/test/regress/regress0/smtlib/issue4077.smt2
new file mode 100644
index 000000000..76a37886b
--- /dev/null
+++ b/test/regress/regress0/smtlib/issue4077.smt2
@@ -0,0 +1,11 @@
+; COMMAND-LINE: --incremental
+; EXPECT: sat
+
+; Use a quantified logic to make sure that TheoryEngine creates a master
+; equality engine
+(set-logic BV)
+(declare-const x (_ BitVec 4))
+(push)
+(reset-assertions)
+(assert (bvslt (bvsrem (_ bv1 4) x) (_ bv1 4)))
+(check-sat)