From 9acaa4890c7e336020ebe3eafcb061b1d3b9c1c9 Mon Sep 17 00:00:00 2001
From: Josh Davies <jodavies@users.noreply.github.com>
Date: Mon, 25 Nov 2024 12:49:17 +0000
Subject: [PATCH 1/2] Add documentation for UNCHANGED_ and ZERO_

---
 doc/manual/prepro.tex | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/doc/manual/prepro.tex b/doc/manual/prepro.tex
index 5a7e5ba32..44d3f523d 100644
--- a/doc/manual/prepro.tex
+++ b/doc/manual/prepro.tex
@@ -108,6 +108,14 @@ \section{The preprocessor variables}
         #endif
     #enddo
 \end{verbatim}
+\item[UNCHANGED\_] Takes the value 1 if all active expressions were unchanged in the
+                   previous module, and 0 otherwise. `UNCHANGED\_exprname' is 1 if the
+                   expression ``exprname'' was unchanged in the previous module, and
+                   0 otherwise.
+\item[ZERO\_] Takes the value 1 if all active expressions were zero in the
+                   previous module, and 0 otherwise. `ZERO\_exprname' is 1 if the
+                   expression ``exprname'' was zero in the previous module, and
+                   0 otherwise.
 \end{description}
 
 \noindent If \FORM\ cannot find a preprocessor variable, because it has 

From 4c8d47e305b06aa92a79b7b7822940305a35ed7b Mon Sep 17 00:00:00 2001
From: Josh Davies <jodavies@users.noreply.github.com>
Date: Fri, 23 May 2025 16:34:06 +0100
Subject: [PATCH 2/2] Add a simple test for UNCHANGED_ and ZERO_

Currently, UNCHANGED_ is not always "correct", for example when an expression
becomes zero due to Multiply 0;
---
 check/features.frm | 90 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)

diff --git a/check/features.frm b/check/features.frm
index 5a1ff3c8c..fbdd33de1 100644
--- a/check/features.frm
+++ b/check/features.frm
@@ -1187,3 +1187,93 @@ else
   assert runtime_error?('Could not create sort file: bad_path\xformxxx.sor')
 end
 *--#] TempSortDir_windows :
+*--#[ ZeroUnchanged :
+#-
+
+#procedure exprinfo
+	#message Module `CMODULE_':
+	#do e = {`activeexprnames_'}
+		#if `ZERO_`e''
+			#message zero `e': `ZERO_`e''
+		#endif
+		#if `UNCHANGED_`e''
+			#message unchanged `e': `UNCHANGED_`e''
+		#endif
+	#enddo
+	#if `ZERO_'
+		#message All zero: `ZERO_'
+	#endif
+	#if `UNCHANGED_'
+		#message All unchanged: `UNCHANGED_'
+	#endif
+	#message
+#endprocedure
+
+
+Off stats;
+
+Symbol x,y;
+
+Local test1 = x;
+Local test2 = y;
+Local test3 = 1;
+.sort:1;
+
+#call exprinfo
+Identify x = 0;
+.sort:2;
+
+#call exprinfo
+Identify y = 0;
+.sort:3;
+
+#call exprinfo
+.sort:4;
+
+#call exprinfo
+Multiply 0;
+.sort:5;
+
+#message Here, test3 is incorrectly flagged as unchanged:
+#call exprinfo
+Print;
+.end
+assert succeeded?
+assert result("test1") =~ expr("0")
+assert result("test2") =~ expr("0")
+assert result("test3") =~ expr("0")
+assert stdout =~ exact_pattern(<<'EOF')
+~~~Module 2:
+~~~
+~~~Module 3:
+~~~zero test1: 1
+~~~unchanged test2: 1
+~~~unchanged test3: 1
+~~~
+~~~Module 4:
+~~~zero test1: 1
+~~~unchanged test1: 1
+~~~zero test2: 1
+~~~unchanged test3: 1
+~~~
+~~~Module 5:
+~~~zero test1: 1
+~~~unchanged test1: 1
+~~~zero test2: 1
+~~~unchanged test2: 1
+~~~unchanged test3: 1
+~~~All unchanged: 1
+~~~
+~~~Here, test3 is incorrectly flagged as unchanged:
+~~~Module 6:
+~~~zero test1: 1
+~~~unchanged test1: 1
+~~~zero test2: 1
+~~~unchanged test2: 1
+~~~zero test3: 1
+~~~unchanged test3: 1
+~~~All zero: 1
+~~~All unchanged: 1
+~~~
+EOF
+*--#] ZeroUnchanged :