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hi,

i tested your code and it works fine here (quartus 8.1).
I guess your are using this code in a bigger project and the rest of the project only uses 32 bit of this registers. That would explain why xst says that the bits 32 to 63 are constant.

hi,

no, there is no such option as it doesn't make sense to do it.
There is a bug in your design which makes these registers useless. Remove this bug, and the registers will stay.

Basically - you have inputs that are stuck at '0'. Therefore xilinx sees no use for the registers.

Find the error that is causing the inputs to be stuck at '0'.