you mean can be seen instead of cant be seen ?
I just explained the meaning of the message;
this is a different story - why ?
to answer it one needs to study logs and/or the rtl itself;
if you believe synplify did a good job switch off optimization in quartus;
could be that synplify added some redundant logic to meet speed
requirements, could be that quartus found a way, overlooked by synplify,
to reduce further logic usage;
and of course could be something else ...
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