remove buggy code, close, fix #5825

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
Z3Prover · Mar 20, 2022 · f1806d3 · f1806d3
1 parent 1e8bae0
commit f1806d3
Showing 1 changed file with 5 additions and 14 deletions.
diff --git a/src/ast/rewriter/seq_rewriter.cpp b/src/ast/rewriter/seq_rewriter.cpp
@@ -936,22 +936,13 @@ expr_ref seq_rewriter::mk_seq_last(expr* t) {
 }
 
 /*
-*  In general constructs substring(t,0,|t|-1) but if t = substring(s,0,k) then simplifies to substring(s,0,k-1) 
-*  This method assumes that |t| > 0, thus, if t = substring(s,0,k) then k > 0 so substring(s,0,k-1) is correct.
+*  In general constructs substring(t,0,|t|-1) 
+*  Incorrect comment: "but if t = substring(s,0,k) then simplifies to substring(s,0,k-1). 
+*     This method assumes that |t| > 0, thus, if t = substring(s,0,k) then k > 0 so substring(s,0,k-1) is correct."
+*  No: if k > |s| then substring(s,0,k) = substring(s,0,k-1)
 */
 expr_ref seq_rewriter::mk_seq_butlast(expr* t) {
-    expr_ref result(m());
-    expr* s, * j, * k;
-    rational v;
-    if (false && str().is_extract(t, s, j, k) && m_autil.is_numeral(j, v) && v.is_zero()) {
-        expr_ref_vector k_min_1(m());
-        k_min_1.push_back(k);
-        k_min_1.push_back(minus_one());
-        result = str().mk_substr(s, j, m_autil.mk_add_simplify(k_min_1));
-    }
-    else
-        result = str().mk_substr(t, zero(), m_autil.mk_sub(str().mk_length(t), one()));
-    return result;
+    return expr_ref(str().mk_substr(t, zero(), m_autil.mk_sub(str().mk_length(t), one())), m());
 }
 
 /*