message: Allow phi in entry block
diff: @@ -647,7 +647,8 @@ function evalInstr(instr: bril.Instruction, state: State): Action {
  throw error(`phi node has unequal numbers of labels and args`);
  }
  if (!state.lastlabel) {
  - throw error(`phi node executed with no last label`);
  + state.env.delete(instr.dest);
  + return NEXT;
  }
  let idx = labels.indexOf(state.lastlabel);
  if (idx === -1) {
  