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Why does the x86 not have an instruction to obtain its instruction pointer?

A readable PC may require extra hardware resources, perhaps a dedicated set of unidirectional wires from the PC to some write Dest reg data path. Fetching instructions and pushing the PC only requires ...
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What motivated the weird boolean instruction repertoire of the PDP-11?

What am I missing? You are missing that in really the majority of real-world cases, and, or and not are used for bitmasks. And you need bitmasks all the time, in particular if you don't have that ...
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What motivated the weird boolean instruction repertoire of the PDP-11?

I'm not sure what motivated this instruction selection, beyond that it is sufficient, but you may be overestimating the pessimization caused by not having the full repertoire of Boolean instructions. ...
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11 votes

What motivated the weird boolean instruction repertoire of the PDP-11?

The functions AND and BIC together provide a means of partitioning the bits of a byte into two sets: those that match a mask and those that don't. Some instruction sets usefully include both (and ...
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