Extend and backport SubNode peephole (#254)

* Extend and backport SubNode peephole

* Add tests

* Restrict subtraction zero peepholes to integer operands

Require resolved integer mode in chapter 25 so zero subtraction preserves floating-point signed zero. Keep nonnumeric operands in the graph for subtraction diagnostics.

Add signed-zero coverage from chapter 12 and null-subtraction diagnostics from chapter 22. Confirmed the regressions fail on the original PR. Full Make suites pass in chapters 4-25 (5462 tests), including fresh chapter 25 sys.o compilation.

---------

Co-authored-by: Cliff Click <cliffc@acm.org>

2 files changed, 35 insertions, 0 deletions

diff --git a/chapter15/src/test/java/com/seaofnodes/simple/Chapter04Test.java b/chapter15/src/test/java/com/seaofnodes/simple/Chapter04Test.java
index 80cdb3f2..a3109ff7 100644
--- a/chapter15/src/test/java/com/seaofnodes/simple/Chapter04Test.java
+++ b/chapter15/src/test/java/com/seaofnodes/simple/Chapter04Test.java
@@ -51,6 +51,34 @@ public class Chapter04Test {
     }
 
     @Test
+    public void testSub0() {
+        Parser parser = new Parser("return arg-0;");
+        StopNode ret = parser.parse();
+        assertEquals("return arg;", ret.print());
+    }
+
+    @Test
+    public void test0Sub() {
+        Parser parser = new Parser("return 0-arg;");
+        StopNode ret = parser.parse();
+        assertEquals("return (-arg);", ret.print());
+    }
+
+    @Test
+    public void testSubNeg() {
+        Parser parser = new Parser("return 3--arg;");
+        StopNode ret = parser.parse();
+        assertEquals("return (arg+3);", ret.print());
+    }
+
+    @Test
+    public void testNegSub() {
+        Parser parser = new Parser("return -arg-3;");
+        StopNode ret = parser.parse();
+        assertEquals("return (-(arg+3));", ret.print());
+    }
+
+    @Test
     public void testVarArg() {
         Parser parser = new Parser("return arg; ");
         StopNode stop = parser.parse();
diff --git a/chapter15/src/test/java/com/seaofnodes/simple/Chapter12Test.java b/chapter15/src/test/java/com/seaofnodes/simple/Chapter12Test.java
index c8802f4c..4eaf81df 100644
--- a/chapter15/src/test/java/com/seaofnodes/simple/Chapter12Test.java
+++ b/chapter15/src/test/java/com/seaofnodes/simple/Chapter12Test.java
@@ -8,6 +8,13 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.fail;
 
 public class Chapter12Test {
+    @Test public void testSubZeroFloat() {
+        var stop = new Parser("flt x = arg; return 0-x;").parse().iterate();
+        // Compare strings so +0.0 and -0.0 remain distinct.
+        assertEquals("0.0", Evaluator.evaluate(stop,0).toString());
+        assertEquals("-1.0", Evaluator.evaluate(stop,1).toString());
+    }
+
     @Test public void testDeadNumericReturns() {
         for( String[] test : new String[][] {
             {"if(1) return 7; else return 2.5;", "7"},