--- a/graal/com.oracle.graal.lir/src/com/oracle/graal/lir/alloc/trace/lsra/TraceLinearScanEliminateSpillMovePhase.java	Mon Nov 30 17:38:22 2015 +0100
+++ b/graal/com.oracle.graal.lir/src/com/oracle/graal/lir/alloc/trace/lsra/TraceLinearScanEliminateSpillMovePhase.java	Tue Dec 01 16:14:17 2015 +0100
@@ -193,21 +193,33 @@
      *            no valid opId but -1.)
      */
     private static boolean canEliminateSpillMove(TraceLinearScan allocator, AbstractBlockBase<?> block, MoveOp move, int lastOpId) {
+        assert ((LIRInstruction) move).id() == -1 : "Not a spill move: " + move;
         assert isVariable(move.getResult()) : "LinearScan inserts only moves to variables: " + move;
         assert lastOpId >= 0 : "Invalid lastOpId: " + lastOpId;
 
         TraceInterval curInterval = allocator.intervalFor(move.getResult());
 
-        if (!isRegister(curInterval.location()) && curInterval.inMemoryAt(lastOpId) && isPhiResolutionMove(allocator, move)) {
+        if (!isRegister(curInterval.location()) && curInterval.inMemoryAt(lastOpId) && !isPhiResolutionMove(allocator, move)) {
+            /* Phi resolution moves cannot be removed because they define the value. */
+            // TODO (je) check if the comment is still valid!
             assert isStackSlotValue(curInterval.location()) : "Not a stack slot: " + curInterval.location();
             return true;
         }
         return false;
     }
 
+    /**
+     * Checks if a (spill or split) move is a Phi resolution move.
+     *
+     * A spill or split move connects a split parent or a split child with another split child.
+     * Therefore the destination of the move is always a split child. Phi resolution moves look like
+     * spill moves (i.e. {@link LIRInstruction#id() id} is {@code 0}, but they define a new
+     * variable. As a result the destination interval is a split parent.
+     */
     private static boolean isPhiResolutionMove(TraceLinearScan allocator, MoveOp move) {
+        assert ((LIRInstruction) move).id() == -1 : "Not a spill move: " + move;
         TraceInterval curInterval = allocator.intervalFor(move.getResult());
-        return !curInterval.isSplitParent();
+        return curInterval.isSplitParent();
     }
 
     private static void checkIntervals(TraceInterval interval) {