Diamond: How to add falling clock to INPUT_SETUP constraint/preference in Diamond?
1. Try using Synplify Pro as the synthesis tool and migrate your LDC file to an SDC file (please put the correct names of the clock, ports, nets, and pins as these might change when changing synthesis tool.)
2. Use INPUT_SETUP preference. This has the CLK_OFFSET option of which you can set to 0.5 X equivalent to the -clock_fall option on constraints. This will work regardless of synthesis tool.