From 7d1c5cbef46f316d044a73ad11fac8a64c864f2c Mon Sep 17 00:00:00 2001
From: Andrew Reynolds <andrew.j.reynolds@gmail.com>
Date: Mon, 12 Jul 2021 14:18:17 -0500
Subject: [PATCH] Fix for learned rewrite pass, add regression (#6850)

Fixes #4791.
---
 src/preprocessing/passes/learned_rewrite.cpp |  2 +-
 test/regress/CMakeLists.txt                  |  1 +
 test/regress/regress1/nl/issue4791-llr.smt2  | 21 ++++++++++++++++++++
 3 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 test/regress/regress1/nl/issue4791-llr.smt2

diff --git a/src/preprocessing/passes/learned_rewrite.cpp b/src/preprocessing/passes/learned_rewrite.cpp
index fd3cf832b..81fbf1ea1 100644
--- a/src/preprocessing/passes/learned_rewrite.cpp
+++ b/src/preprocessing/passes/learned_rewrite.cpp
@@ -293,7 +293,7 @@ Node LearnedRewrite::rewriteLearned(Node n,
         || (!db.upper_value.isNull()
             && db.upper_value.getConst<Rational>().sgn() == -1))
     {
-      Rational bden = db.lower_value.isNull()
+      Rational bden = db.upper_value.isNull()
                           ? db.lower_value.getConst<Rational>()
                           : db.upper_value.getConst<Rational>().abs();
       // if 0 <= UB(num) < LB(den) or 0 <= UB(num) < -UB(den)
diff --git a/test/regress/CMakeLists.txt b/test/regress/CMakeLists.txt
index cdc77c980..be0815668 100644
--- a/test/regress/CMakeLists.txt
+++ b/test/regress/CMakeLists.txt
@@ -1676,6 +1676,7 @@ set(regress_1_tests
   regress1/nl/issue3656.smt2
   regress1/nl/issue3803-nl-check-model.smt2
   regress1/nl/issue3955-ee-double-notify.smt2
+  regress1/nl/issue4791-llr.smt2
   regress1/nl/issue5372-2-no-m-presolve.smt2
   regress1/nl/issue5662-nl-tc.smt2
   regress1/nl/issue5662-nl-tc-min.smt2
diff --git a/test/regress/regress1/nl/issue4791-llr.smt2 b/test/regress/regress1/nl/issue4791-llr.smt2
new file mode 100644
index 000000000..d29a16313
--- /dev/null
+++ b/test/regress/regress1/nl/issue4791-llr.smt2
@@ -0,0 +1,21 @@
+; COMMAND-LINE: --learned-rewrite --no-check-unsat-cores
+; EXPECT: unsat
+;
+;!(a,b,c).( 0<=b & 1<=c & 0<=a & 1<=c
+;               =>
+;               (a+(b mod c)) mod c = (a+b) mod c)
+;
+(set-logic QF_NIA)
+(set-option :print-success false)
+
+(declare-fun a () Int)
+(declare-fun b () Int)
+(declare-fun c () Int)
+
+(assert (<= 0 a))
+(assert (<= 1 c))
+(assert (<= 0 b))
+
+(assert (! (not (= (mod (+ a (mod b c)) c) (mod (+ a b) c))) :named goal))
+(check-sat)
+(exit)
-- 
2.30.2