check - check for obvious problems in the design

    check [options] [selection]

This pass identifies the following problems in the current design:

 - combinatorial loops

 - two or more conflicting drivers for one wire

 - used wires that do not have a driver

When called with -noinit then this command also checks for wires which have
the 'init' attribute set.

When called with -initdrv then this command also checks for wires which have
the 'init' attribute set and aren't driven by a FF cell type.

When called with -assert then the command will produce an error if any
problems are found in the current design.