Replace Parser scopes with ScopeNode (#14)

Fixes #12 
* Replace Parser scopes with ScopeNode

Basically move the Stack of HashMaps to a ScopeNode, with wrappers.
The HashMap maps String names to Integer indices; inputs to the ScopeNode.
This way, the ScopeNode keeps alive Nodes that are only alive because they are alive in the HashMap.

Fix bug isDead -> isUnused in deadCodeElim.
Support routines for adding/removing edges in ScopeNode.
Set $ctrl to null after a Return; there is no control.
Regression tests.

* One more test case

1 files changed, 21 insertions, 0 deletions

diff --git a/chapter04/src/test/java/com/seaofnodes/simple/Chapter04Test.java b/chapter04/src/test/java/com/seaofnodes/simple/Chapter04Test.java
index 988e3608..8cc78af0 100644
--- a/chapter04/src/test/java/com/seaofnodes/simple/Chapter04Test.java
+++ b/chapter04/src/test/java/com/seaofnodes/simple/Chapter04Test.java
@@ -99,6 +99,20 @@ public class Chapter04Test {
     }
 
     @Test
+    public void testChapter4Bug1() {
+        Parser parser = new Parser("int a=arg+1; int b=a; b=1; return a+2; #showGraph;", TypeInteger.BOT);
+        ReturnNode ret = parser.parse();
+        assertEquals("return (Proj_3+3);", ret.print());
+    }
+
+    @Test
+    public void testChapter4Bug2() {
+        Parser parser = new Parser("int a=arg+1; a=a; return a; #showGraph;", TypeInteger.BOT);
+        ReturnNode ret = parser.parse();
+        assertEquals("return (Proj_3+1);", ret.print());
+    }
+
+    @Test
     public void testVarDecl() {
         Parser parser = new Parser("int a=1; return a;");
         ReturnNode ret = parser.parse();
@@ -135,6 +149,13 @@ public class Chapter04Test {
         assertEquals("return 8;", ret.print());
     }
 
+    @Test
+    public void testSelfAssign() {
+        exceptionRule.expect(RuntimeException.class);
+        exceptionRule.expectMessage("Undefined name 'a'");
+        new Parser("int a=a; return a;").parse();
+    }
+
 
     @Test
     public void testChapter2ParseGrammar() {