1. Critical Warning (332012): Synopsys Design Constraints File file not found: 'led_test.sdc'. A Synopsys Design Constraints File is required by the TimeQuest Timing Analyzer to get proper timing constraints. Without it, the Compiler will not properly optimize the design.

这个问题，一般情况下可以忽略，但是当你设置Tools 选项中的Options中的Massage中的Promote critical warning messages to error messages，打勾后，综合编译就会一直提示错误，使得编译无法通过，无法往下进行。