int2bv: Fix conversion of signed bit-vector values. (#7061)

This commit fixes the conversion of signed bit-vector values to integers in the int-to-bv preprocessing pass.

1 files changed, 14 insertions, 2 deletions

diff --git a/src/preprocessing/passes/int_to_bv.cpp b/src/preprocessing/passes/int_to_bv.cpp
index 8c18ccf54..41d52d1ae 100644
--- a/src/preprocessing/passes/int_to_bv.cpp
+++ b/src/preprocessing/passes/int_to_bv.cpp
@@ -217,8 +217,20 @@ Node IntToBV::intToBV(TNode n, NodeMap& cache)
           result = sm->mkDummySkolem("__intToBV_var",
                                      nm->mkBitVectorType(size),
                                      "Variable introduced in intToBV pass");
-          Node bv2nat = nm->mkNode(kind::BITVECTOR_TO_NAT, result);
-          d_preprocContext->addSubstitution(current, bv2nat);
+          /**
+           * Correctly convert signed/unsigned BV values to Integers as follows
+           * x < 0 ? -nat(-x) : nat(x)
+           * where x refers to the bit-vector term `result`.
+           */
+          BitVector bvzero(size, Integer(0));
+          Node negResult = nm->mkNode(kind::BITVECTOR_TO_NAT,
+                                      nm->mkNode(kind::BITVECTOR_NEG, result));
+          Node bv2int = nm->mkNode(
+              kind::ITE,
+              nm->mkNode(kind::BITVECTOR_SLT, result, nm->mkConst(bvzero)),
+              nm->mkNode(kind::UMINUS, negResult),
+              nm->mkNode(kind::BITVECTOR_TO_NAT, result));
+          d_preprocContext->addSubstitution(current, bv2int);
         }
       }
       else if (current.isConst())