diff --git a/src/jse/org/luaj/vm2/luajc/ProtoInfo.java b/src/jse/org/luaj/vm2/luajc/ProtoInfo.java
index df0ca683..1adf41c1 100644
--- a/src/jse/org/luaj/vm2/luajc/ProtoInfo.java
+++ b/src/jse/org/luaj/vm2/luajc/ProtoInfo.java
@@ -18,6 +18,7 @@ public class ProtoInfo {
 	public final BasicBlock[] blocks;     // basic block analysis of code branching
 	public final BasicBlock[] blocklist;  // blocks in breadhth-first order
 	public final VarInfo[][] vars;        // Each variable
+	public final VarInfo[] params;        // Parameters and initial values of stack variables
 	public final UpvalInfo[] upvals;      // from outer scope
 	public final UpvalInfo[][] openups;   // per slot, upvalues allocated by this prototype
 
@@ -35,6 +36,15 @@ public class ProtoInfo {
 		// find basic blocks
 		this.blocks = BasicBlock.findBasicBlocks(p);
 		this.blocklist = BasicBlock.sortDepthFirst(blocks);
+
+		
+		// params are inputs to first block
+		this.params = new VarInfo[p.maxstacksize];
+		for ( int slot=0; slot<p.maxstacksize; slot++ ) {
+			VarInfo v = VarInfo.PARAM(slot);
+			params[slot] = v;
+			this.blocklist[0].mergeSlotInput(slot, v);
+		}
 		
 		// find variables and block inputs
 		this.vars = findVariables();
@@ -295,23 +305,20 @@ public class ProtoInfo {
 	}
 
 	public boolean isUpvalueAssign(int pc, int slot) {
-		if ( pc < 0 ) pc = 0;
-		VarInfo v = vars[slot][pc];
+		VarInfo v = pc<0? params[slot]: vars[slot][pc];
 //		return v.upvalue != null && v.upvalue.rw;
 		return v != null && v.upvalue != null;
 	}
 
 	public boolean isUpvalueCreate(int pc, int slot) {
-		if ( pc < 0 ) pc = 0;
-		VarInfo v = vars[slot][pc];
+		VarInfo v = pc<0? params[slot]: vars[slot][pc];
 //		return v.upvalue != null && v.upvalue.rw && v.allocupvalue && pc == v.pc;
 		return v != null && v.upvalue != null && v.allocupvalue && pc == v.pc;
 	}
 
 	public boolean isUpvalueRefer(int pc, int slot) {
 		// TODO: when it is a CALL
-		if ( pc < 0 ) pc = 0;
-		VarInfo v = vars[slot][pc];
+		VarInfo v = pc<0? params[slot]: vars[slot][pc];
 //		return v.upvalue != null && v.upvalue.rw;
 		return v != null && v.upvalue != null;
 	}
diff --git a/src/jse/org/luaj/vm2/luajc/UpvalInfo.java b/src/jse/org/luaj/vm2/luajc/UpvalInfo.java
index 12ab3567..94b64b06 100644
--- a/src/jse/org/luaj/vm2/luajc/UpvalInfo.java
+++ b/src/jse/org/luaj/vm2/luajc/UpvalInfo.java
@@ -63,13 +63,12 @@ public class UpvalInfo {
 			// invalid values terminate search
 			if ( v == VarInfo.INVALID )
 				return;
-			// nil values also terminate (TODO: mark as unintialized upvalue)
-			if ( v.pc == -1 )
-				return;
+
+			// basic block for nil values is initial block
+			BasicBlock b = pi.blocks[v.pc<0? 0: v.pc];
 			
-			BasicBlock b = pi.blocks[v.pc];
+			// look for loops
 			if ( v.upvalue == this ) {
-				// loop detected, include previous values
 				for ( int i=0, n=b.ninputs[slot]; i<n; i++ ) {
 					v = b.inputs[slot][i];
 					if ( v.upvalue != this )
@@ -77,7 +76,7 @@ public class UpvalInfo {
 				}
 				return;
 			}
-			
+
 			// check for assignment to 2 upvalues at once
 			if ( v.upvalue != null ) 
 				throw new IllegalArgumentException("upvalue collision detected between "+v.upvalue+" and "+this);
@@ -86,6 +85,10 @@ public class UpvalInfo {
 			v.upvalue = this;
 			this.includeVar(v);
 
+			// nil values also terminate
+			if ( v.pc == -1 )
+				return;
+			
 			// find next variable within the basic block
 			for ( int i=v.pc; i<=b.pc1; i++ ) {
 				if ( pi.vars[slot][i] != v ) {
@@ -102,6 +105,8 @@ public class UpvalInfo {
 	}
 	
 	private boolean testIsAllocUpvalue(VarInfo v) {
+		if ( v.pc < 0 )
+			return true;
 		BasicBlock b = pi.blocks[v.pc];
 		if ( v.pc > b.pc0 )
 			return pi.vars[slot][v.pc-1].upvalue != this;
diff --git a/src/jse/org/luaj/vm2/luajc/VarInfo.java b/src/jse/org/luaj/vm2/luajc/VarInfo.java
index 0ab7e4c8..06078db9 100644
--- a/src/jse/org/luaj/vm2/luajc/VarInfo.java
+++ b/src/jse/org/luaj/vm2/luajc/VarInfo.java
@@ -7,14 +7,26 @@ public class VarInfo {
 	
 	public static VarInfo INVALID = new VarInfo(-1,-1);
 	
-	public static VarInfo NIL(int slot) {
-		return new VarInfo(slot,-1);
+	public static VarInfo PARAM(int slot) {
+		return new VarInfo(slot,-1) {
+			public String toString() {
+				return slot+".p";
+			}
+		};
 	}
 	
+	public static VarInfo NIL(final int slot) {
+		return new VarInfo(slot,-1) {
+			public String toString() {
+				return "nil";
+			}
+		};
+	}
+
 	public static VarInfo PHI(int slot, int pc) {
 		return new VarInfo(slot,pc) {
 			public String toString() {
-				return super.toString()+"p";
+				return super.toString()+"{}";
 			}
 		};
 	}
@@ -23,7 +35,7 @@ public class VarInfo {
 	public final int pc;   // where assigned, or -1 if for block inputs
 	
 	public UpvalInfo upvalue;    // not null if this var is an upvalue
-	public boolean allocupvalue; // true if this variable allocations r/w upvalue storage
+	public boolean allocupvalue; // true if this variable allocates r/w upvalue storage
 	
 	public VarInfo(int slot, int pc) {
 		this.slot = slot;
@@ -32,7 +44,6 @@ public class VarInfo {
 
 	public String toString() {
 		return slot<0? "x.x": 
-			pc<0? "nil":
 			(slot+"."+pc);
 	}
 }
\ No newline at end of file