Why fixing hold first?
Setup is much more difficult to fix. There are limited techniques to fix setup.
Hold is a lot easier to fix. If there is enough setup slack in the path, you can always fix hold by inserting buffer(s).
If there are both setup hold violations at the same end point (e.g., D input), the design is in trouble. This is often caused by poor CTS quality, constraints issue, or poor design to start with.
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