1 files changed, 68 insertions, 0 deletions
diff --git a/src/main/java/com/seaofnodes/simple/node/GuardNode.java b/src/main/java/com/seaofnodes/simple/node/GuardNode.java
new file mode 100644
index 00000000..0ce504d9
--- /dev/null
+++ b/src/main/java/com/seaofnodes/simple/node/GuardNode.java
@@ -0,0 +1,68 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.print.ExprPrinter;
+
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeScalar;
+import com.seaofnodes.simple.util.BAOS;
+import com.seaofnodes.simple.util.Utils;
+
+import java.util.HashMap;
+import java.util.IdentityHashMap;
+
+// A branch-proven refinement to zero/null or non-zero/non-null.  The value
+// family is deliberately taken from the input when it becomes known.
+public class GuardNode extends Node {
+    public final boolean _nonZero;
+
+    public GuardNode(boolean nonZero, Node ctrl, Node val) {
+        super(ctrl,val);
+        _nonZero = nonZero;
+    }
+
+    public GuardNode(GuardNode guard) {
+        super(guard);
+        _nonZero = guard._nonZero;
+    }
+
+    @Override public Tag serialTag() { return Tag.Guard; }
+    @Override public void packed(BAOS baos, HashMap<String,Integer> strs, HashMap<Type,Integer> types, IdentityHashMap<Node,Integer> anodes) {
+        baos.write(_nonZero ? 1 : 0);
+    }
+    static Node make(BAOS bais) { return new GuardNode(bais.read()!=0,null,null); }
+
+    @Override public String label() { return _nonZero ? "(!=0)" : "(==0)"; }
+
+    @Override protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
+        return p.p(label()).n(in(1));
+    }
+
+    @Override public Type compute() {
+        // Guard is a pinned, path-local fact.  If its control path is not
+        // executable, the fact is not executable either, regardless of how the
+        // value input sharpens later.
+        Type c = in(0)._type;
+        if( c != Type.CONTROL && c != Type.BOTTOM )
+            return Type.TOP;
+        Type t = in(1)._type;
+        if( t==Type.BOTTOM || t==Type.TOP ) return t;
+        // The scalar envelope does not identify a value family.  Preserve it
+        // until SCCP learns whether this is an int, float, pointer, or fptr;
+        // choosing generic ptr here can be weaker than a later concrete type.
+        if( t==TypeScalar.BOT || t==TypeScalar.TOP ) return t;
+        Type t2 = _nonZero ? t.nonZero() : t.makeZero();
+        return t2==null ? (_type==null ? Type.TOP : _type) : t2; // No sane answer for e.g. not-zero of a zero
+    }
+
+    @Override public Node idealize() {
+        if( in(0)._type != Type.CONTROL && in(0)._type != Type.BOTTOM )
+            return null;
+        if( in(1)._type==Type.BOTTOM || in(1)._type==Type.TOP ) return null;
+        if( _type.isHighOrConst() && in(1)._type.isa(_type) )
+            return in(1);
+        return null;
+    }
+
+    @Override public boolean eq(Node n) { return _nonZero==((GuardNode)n)._nonZero; }
+    @Override int hash() { return _nonZero ? 1 : 0; }
+}