DONT_TOUCH - DONT_TOUCH - 2026.1 English - UG903

Set DONT_TOUCH on a leaf cell, hierarchical cell, or net object to preserve it during netlist optimizations. The DONT_TOUCH property is most commonly used for the following purposes:

• Prevent a net from optimizing away.

  A net with DONT_TOUCH cannot be absorbed by synthesis or implementation. This helps with logic probing or debugging that is unexpected optimized. To preserve a net with multiple hierarchical segments, place DONT_TOUCH on the net PARENT (get_property PARENT $net), the segment closest to its driver.

• Prevent merging of manually replicated logic.

  Sometimes you manually replicate logic, such as a high-fanout driver that spans a wide area. Add DONT_TOUCH to the manually replicated drivers and the original to prevent synthesis and implementation from optimizing these cells.