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Originally Posted by meynaf
The only possibility i can see, is extra programming flexibility.
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Do not understand what that would be.
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Nobody would want to code on that monster.
Beware, too, of 64 bit immediates. Simple move of a full sized data to a linear address would be a monster instruction of at least 18 bytes !
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Yes while doing the work of two instructions together being 24 bytes. Guess what's smaller, easier to support in hardware, faster?
64 bit values are very rarely needed but not supporting them would make the processor less orthogonal and harder to use. The same hardware that extracts them from the instruction stream also makes 64 bit branch and address displacements trivial. Compared to CISC instructions decoding is easy.
What exactly makes this look monstrous to you? Minimum instruction size?