Bug fix loop depth on infinite split-tail loops

3 files changed, 9 insertions, 73 deletions

diff --git a/chapter17/README.md b/chapter17/README.md
index bf998ab8..1bac940b 100644
--- a/chapter17/README.md
+++ b/chapter17/README.md
@@ -125,7 +125,6 @@ return i; // ERROR: Undefined name 'i'
 
 
 
-finalize final
 oper-assign +=, -=
 TODO
 switch
@@ -134,65 +133,3 @@ switch
 
 
 
-# Chapter 18: Functions
-
-Some thinking on function syntax:
-
-Function Types:
-```
-{ argtype, argtype, ... -> rettype }
-```
-
-Leading `{` character denotes the start of a function or function type.
-
-Functions are normal variables and assigned the same way:
-
-```functiontype var = function-typed-expr```
-
-Functions themselves using the same syntax with as types, but filled in:
-
-```
-{ int x, int y ->
-  sqrt(x*x+y*y);
-}
-```
-
-Used in a declaration statement:
-```
-// TYPE        VAR  =   EXPR
-{flt,flt->flt} dist = { flt x, flt y ->
-  sqrt(x*x+y*y);
-}
-```
-
-Because it gets clunky to write the function type, and because it can be
-directly inferred from forwards-flow analysis (not even HM) which we're already
-doing at parse-time, we add a new variable declaration syntax: "var" - for
-auto-inferring variable types.  Not allowed in function headers.
-```
-var dist = { flt x, flt y -> sqrt(x*x*,y*y); }
-```
-
-`var` can be used for normal variables as well:
-
-```
-// Newtons approximation to the square root
-var sqrt = { flt x ->
-    var guess = x*x/2;
-    while( 1 ) {
-        var next = (x/guess + guess)/2;
-        if( next == guess ) break;
-        guess = next;
-    }
-    guess;
-}
-```
-
-When inferring pointer types, it will use the `glb` of the initial expression
-type, which may not be what you want:
-
-```
-struct LLI { LLI? next; int i; };
-var head = LLI(); // Want this declared not-null, but GLB will allow null
-head = null;      // Allowed
-```
\ No newline at end of file
diff --git a/chapter17/src/main/java/com/seaofnodes/simple/node/IfNode.java b/chapter17/src/main/java/com/seaofnodes/simple/node/IfNode.java
index 41de4c82..2f3798d7 100644
--- a/chapter17/src/main/java/com/seaofnodes/simple/node/IfNode.java
+++ b/chapter17/src/main/java/com/seaofnodes/simple/node/IfNode.java
@@ -43,6 +43,9 @@ public class IfNode extends CFGNode implements MultiNode {
         // Else true branch is reachable
         if( t.isConstant() )
             return t.makeInit()==t ? TypeTuple.IF_FALSE : TypeTuple.IF_TRUE;
+        // Integers allow non-zero ranges: "1-65535"
+        if( t.makeZero().meet(t) != t )
+            return TypeTuple.IF_TRUE;
 
         return TypeTuple.IF_BOTH;
     }
diff --git a/chapter17/src/main/java/com/seaofnodes/simple/node/LoopNode.java b/chapter17/src/main/java/com/seaofnodes/simple/node/LoopNode.java
index 27134420..e5f34833 100644
--- a/chapter17/src/main/java/com/seaofnodes/simple/node/LoopNode.java
+++ b/chapter17/src/main/java/com/seaofnodes/simple/node/LoopNode.java
@@ -39,15 +39,12 @@ public class LoopNode extends RegionNode {
         for( CFGNode idom = back(); idom!=this; idom = idom.idom() ) {
             // Walk idom in loop, setting depth
             idom._loopDepth = _loopDepth;
-            // Loop exit hits the CProj before the If, instead of jumping from
-            // Region directly to If.
-            if( idom instanceof CProjNode proj ) {
-                assert proj.in(0) instanceof IfNode; // Loop exit test
-                // Find the loop exit CProj, and set loop_depth
-                for( Node use : proj.in(0)._outputs )
-                    if( use instanceof CProjNode proj2 && proj2 != idom )
-                        proj2._loopDepth = _loopDepth-1;
-            }
+            // Mark backedge loop depth.  The loop exit hits the CProj before the
+            // If, instead of jumping from Region directly to If.  The other
+            // arm is either a loop exit OR if this is a split tail the other
+            // arm leads to a inner loop.
+            if( idom instanceof CProjNode cproj )
+                break;
         }
         return _loopDepth;
     }
@@ -62,7 +59,6 @@ public class LoopNode extends RegionNode {
         while( x != this ) {
             if( x instanceof CProjNode exit && exit.in(0) instanceof IfNode iff ) {
                 CFGNode other = iff.cproj(1-exit._idx);
-                //if( !(other.out(0) instanceof LoopNode loop) || loop.entry()==exit )
                 if( other.loopDepth() < loopDepth() )
                     return;         // Found an exit, not an infinite loop
             }