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>

3 files changed, 44 insertions, 0 deletions

diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter04Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter04Test.java
index eaa959cb..1132375e 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter04Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter04Test.java
@@ -53,6 +53,34 @@ public class Chapter04Test {
     }
 
     @Test
+    public void testSub0() {
+        CodeGen code = new CodeGen("return arg-0;");
+        code.parse();
+        assertEquals("return arg;", code.print());
+    }
+
+    @Test
+    public void test0Sub() {
+        CodeGen code = new CodeGen("return 0-arg;");
+        code.parse();
+        assertEquals("return (-arg);", code.print());
+    }
+
+    @Test
+    public void testSubNeg() {
+        CodeGen code = new CodeGen("return 3--arg;");
+        code.parse();
+        assertEquals("return (arg+3);", code.print());
+    }
+
+    @Test
+    public void testNegSub() {
+        CodeGen code = new CodeGen("return -arg-3;");
+        code.parse();
+        assertEquals("return (-(arg+3));", code.print());
+    }
+
+    @Test
     public void testVarArg() {
         CodeGen code = new CodeGen("return arg; ");
         code.parse();
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter12Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter12Test.java
index 4b2d48d8..0f4bb0b4 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter12Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter12Test.java
@@ -5,6 +5,13 @@ import org.junit.Test;
 import static org.junit.Assert.assertEquals;
 
 public class Chapter12Test {
+    @Test public void testSubZeroFloat() {
+        var code = new CodeGen("flt x = arg; return 0-x;").parse().opto().typeCheck();
+        // Compare strings so +0.0 and -0.0 remain distinct.
+        assertEquals("0.0", Eval2.eval(code,0));
+        assertEquals("-1.0", Eval2.eval(code,1));
+    }
+
     @Test public void testDeadNumericReturns() {
         for( String[] test : new String[][] {
             {"if(1) return 7; else return 2.5;", "7"},
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter22Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter22Test.java
index fde523cf..4b036e62 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter22Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter22Test.java
@@ -11,6 +11,15 @@ import org.junit.Test;
 import static org.junit.Assert.*;
 
 public class Chapter22Test {
+    @Test public void testSubZeroTypeError() {
+        try {
+            new CodeGen("return null-0;").parse().opto().typeCheck();
+            fail("Subtraction must reject null even when the other operand is zero");
+        } catch( Parser.ParseException e ) {
+            assertEquals("Cannot null - 0",e.getMessage());
+        }
+    }
+
 
     @Test
     public void testJig() throws IOException {