Eliminate COPY of CONST

COPY is opaque for tiling, so the COPY of CONST values disables tiles
that operate on a const directly. This allows us to use the CONST
value directly which should help us pick better tiles.

src/jit/optimize.c

@@ -136,6 +136,15 @@ static void optimize_postorder(MVMThreadContext *tc, MVMJitTreeTraverser *traver
         }
         break;
     }
+    case MVM_JIT_COPY:
+    {
+        MVMint32 child = MVM_JIT_EXPR_LINKS(tree, node)[0];
+        if (tree->nodes[child] == MVM_JIT_CONST) {
+            _DEBUG("Elinimating COPY of CONST (%d)", tree->nodes[child+1]);
+            replacement = child;
+        }
+        break;
+    }
     }
 
     if (replacement > 0) {