A method for supporting the register-transfer-level (RTL) design of a
semiconductor integrated circuit, includes reading an RTL description
related to the semiconductor integrated circuit into a first memory, the
RTL description including a description of a compound block containing a
mixture of combinational and non-combinational circuits, analyzing the
RTL description, extracting a description of the non-combinational
circuit from the compound block description, reading an RTL library into
a second memory, comparing the logic of the extracted non-combinational
circuit description with the logic of each cell of the RTL library, and
in accordance with to a result of the comparison, replacing the extracted
non-combinational circuit description with a cell of the RTL library
having the same logic as the logic of the extracted non-combinational
circuit description. The method may further includes comparing the logics
of combinational circuits described in the RTL description with one
another and rewriting the RTL description if there are a plurality of
combinational circuits of the same logic.