From 736713253104bcc5c3c0e19b0abcda4d20c68ab7 Mon Sep 17 00:00:00 2001
From: Andrew Reynolds <andrew.j.reynolds@gmail.com>
Date: Mon, 10 Jun 2019 15:51:21 -0500
Subject: [PATCH] Optimization for strings normalize disequalities (#3047)

---
 src/theory/strings/theory_strings.cpp | 34 +++++++++++++++++----------
 1 file changed, 22 insertions(+), 12 deletions(-)

diff --git a/src/theory/strings/theory_strings.cpp b/src/theory/strings/theory_strings.cpp
index 1947f1730..67f032193 100644
--- a/src/theory/strings/theory_strings.cpp
+++ b/src/theory/strings/theory_strings.cpp
@@ -4468,19 +4468,29 @@ void TheoryStrings::checkNormalFormsDeq()
         for( unsigned j=0; j<cols[i].size(); j++ ){
           for( unsigned k=(j+1); k<cols[i].size(); k++ ){
             //for strings that are disequal, but have the same length
-            if( areDisequal( cols[i][j], cols[i][k] ) ){
-              Assert( !d_conflict );
-              if (Trace.isOn("strings-solve"))
+            if (cols[i][j].isConst() && cols[i][k].isConst())
+            {
+              // if both are constants, they should be distinct, and its trivial
+              Assert(cols[i][j] != cols[i][k]);
+            }
+            else
+            {
+              if (areDisequal(cols[i][j], cols[i][k]))
               {
-                Trace("strings-solve") << "- Compare " << cols[i][j] << " ";
-                printConcat(getNormalForm(cols[i][j]).d_nf, "strings-solve");
-                Trace("strings-solve") << " against " << cols[i][k] << " ";
-                printConcat(getNormalForm(cols[i][k]).d_nf, "strings-solve");
-                Trace("strings-solve") << "..." << std::endl;
-              }
-              processDeq( cols[i][j], cols[i][k] );
-              if( hasProcessed() ){
-                return;
+                Assert(!d_conflict);
+                if (Trace.isOn("strings-solve"))
+                {
+                  Trace("strings-solve") << "- Compare " << cols[i][j] << " ";
+                  printConcat(getNormalForm(cols[i][j]).d_nf, "strings-solve");
+                  Trace("strings-solve") << " against " << cols[i][k] << " ";
+                  printConcat(getNormalForm(cols[i][k]).d_nf, "strings-solve");
+                  Trace("strings-solve") << "..." << std::endl;
+                }
+                processDeq(cols[i][j], cols[i][k]);
+                if (hasProcessed())
+                {
+                  return;
+                }
               }
             }
           }
-- 
2.30.2