Handle double-negation preserving not-null knowledge

2 files changed, 62 insertions, 1 deletions

diff --git a/chapter24/src/test/java/com/seaofnodes/simple/Chapter10Test.java b/chapter24/src/test/java/com/seaofnodes/simple/Chapter10Test.java
index ec363239..c1b5e3a8 100644
--- a/chapter24/src/test/java/com/seaofnodes/simple/Chapter10Test.java
+++ b/chapter24/src/test/java/com/seaofnodes/simple/Chapter10Test.java
@@ -7,6 +7,61 @@ import static org.junit.Assert.fail;
 
 public class Chapter10Test {
 
+    // Issue #246: null-check guards start in Chapter 10; arrays arrive in Chapter 15.
+    private static final String NULLABLE_POINT_SOURCE = """
+        struct Point { int x; };
+        Point?[] !points = new Point?[2];
+        points[arg] = new Point { x = 42; };
+        Point? p = points[1];
+        """;
+
+    @Test
+    public void testNullGuards() {
+        for( String body : new String[] {
+            "if (p != null) return p.x; return -1;",
+            "if (null != p) return p.x; return -1;",
+            "if (!!!!p) return p.x; return -1;",
+            "if (!!!p) return -1; return p.x;",
+            "int b = !!p; if (b) return p.x + b - 1; return -1;",
+            "if (!(p == null || arg == 0)) return p.x; return -1;"
+        } ) {
+            CodeGen code = new CodeGen(NULLABLE_POINT_SOURCE+body).parse().opto().typeCheck();
+            assertEquals(body,"-1",Eval2.eval(code,0));
+            assertEquals(body,"42",Eval2.eval(code,1));
+        }
+    }
+
+    @Test
+    public void testShortCircuitGuardScheduling() {
+        // The call result exists only on the RHS path, not above the merge.
+        CodeGen code = new CodeGen("""
+            val f = { int n -> (n+1)&7; };
+            int x = 0;
+            if (!!(arg && (x=f(arg)))) return x;
+            return -1;
+            """).driver(CodeGen.Phase.TypeCheck);
+        assertEquals("-1",Eval2.eval(code,0));
+        assertEquals("2",Eval2.eval(code,1));
+        assertEquals("-1",Eval2.eval(code,7));
+        code.driver(CodeGen.Phase.LocalSched);
+    }
+
+    @Test
+    public void testNullGuardErrors() {
+        for( String body : new String[] {
+            "return p.x;",
+            "if (!!points) return p.x; return -1;",
+            "if (!!p) { int x = p.x; } return p.x;"
+        } ) {
+            try {
+                new CodeGen(NULLABLE_POINT_SOURCE+body).parse().opto().typeCheck();
+                fail(body);
+            } catch( RuntimeException e ) {
+                assertEquals(body,"Might be null accessing 'x'",e.getMessage());
+            }
+        }
+    }
+
     @Test
     public void testFuzzer() {
         CodeGen code = new CodeGen(
diff --git a/chapter24/src/test/java/com/seaofnodes/simple/Eval2.java b/chapter24/src/test/java/com/seaofnodes/simple/Eval2.java
index 5994e7e1..770f8351 100644
--- a/chapter24/src/test/java/com/seaofnodes/simple/Eval2.java
+++ b/chapter24/src/test/java/com/seaofnodes/simple/Eval2.java
@@ -271,7 +271,7 @@ public abstract class Eval2 {
         case MulFNode     mlf  -> d(mlf.in(1)) *  d(mlf.in(2));
         case MulNode      mul  -> x(mul.in(1)) *  x(mul.in(2));
         case NewNode      alloc-> alloc(alloc);
-        case NotNode      not  -> x(not.in(1)) == 0 ? 1L : 0L;
+        case NotNode      not  -> not(not);
         case OrNode       or   -> x(or .in(1)) |  x(or .in(2));
         case ProjNode     proj -> proj._type instanceof TypeMem ? "$mem" : val(proj.in(0));
         case ReadOnlyNode read -> val(read.in(1));
@@ -288,6 +288,12 @@ public abstract class Eval2 {
         };
     }
 
+    private static Object not( NotNode not ) {
+        Object n = val(not.in(1));
+        return ( n==null || (n instanceof Double D && D==0.0) || n instanceof Long L && L==0 )
+            ? 1L : 0L;
+    }
+
     // Fetch without unboxing, searching up-Frame
     static Object val( Node n ) { return F.get(n); }
     // Fetch and unbox as primitive long