Eliminate some rare occurrences of redundant PHIs.

src/lj_opt_loop.c

@@ -159,11 +159,15 @@ static void loop_emit_phi(jit_State *J, IRRef1 *subst, IRRef1 *phi, IRRef nphi,
   for (i = 0; i < nphi; i++) {
     IRRef lref = phi[i];
     IRIns *ir = IR(lref);
-    if (!irt_ismarked(ir->t)) {  /* Emit PHI if not marked. */
+    if (!irt_ismarked(ir->t)) {  /* Emit PHI if not marked and not redundant. */
       IRRef rref = subst[lref];
-      if (rref > invar)
-	irt_setphi(IR(rref)->t);
-      emitir_raw(IRT(IR_PHI, irt_type(ir->t)), lref, rref);
+      if (lref == rref) {
+	irt_clearphi(ir->t);
+      } else {
+	if (rref > invar)
+	  irt_setphi(IR(rref)->t);
+	emitir_raw(IRT(IR_PHI, irt_type(ir->t)), lref, rref);
+      }
     } else {  /* Otherwise eliminate PHI. */
       irt_clearmark(ir->t);
       irt_clearphi(ir->t);