To trigger these you usually have to be aware of them and write your code in a certain way. Compiler writers also look for common patterns in people's code and

To trigger these you usually have to be aware of them and write your code in a certain way. Compiler writers also look for common patterns in people's code and figure out how to optimize them. when you have both years (decades) of legacy code and developers who don't even know what patterns are optimized, you as a compiler writer need to optimize the code that is being written.