SOFT Primitive

The SOFT buffer specifies that a logic cell may be needed in the project. During project processing, Analysis & Synthesis examines the logic feeding the primitive and determines whether a logic cell is needed. If it is needed, the SOFT buffer is converted into an LCELL; if not, the SOFT buffer is removed.

If the Compiler indicates that the project is too complex, you can edit the project by inserting SOFT buffers to prevent logic expansion. For example, you can add a SOFT buffer at the combinational output of a logic function to decouple two combinational circuits.

Note:

When you turn on the Ignore SOFT Buffers logic option, the Compiler automatically converts all SOFT buffers to WIRE primitives. For newer device families, the Ignore SOFT Buffers logic option is turned on by default.
For information about Quartus^® Prime Standard Edition primitive instantiation, go to Using a Quartus^® Prime Standard Edition Logic Function.
The SOFT primitive is not recommended for newer device families.