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  2. Slidedown overlapping of dest and source regsiters

Re: Slidedown overlapping of dest and source regsiters

Andrew Waterman
 

It's important that the slidedown instruction can overwrite its source operand.  Debuggers will use this feature to populate a vector register in-place without clobbering other architectural state.

On Tue, Jan 28, 2020 at 10:59 AM Thang Tran <thang@...> wrote:
The slideup instruction has this restriction:

The destination vector register group for vslideup cannot overlap the source vector register group or the mask register, otherwise an illegal instruction exception is raised.

The slidedown instruction has different restriction:

The destination vector register group cannot overlap the mask register if LMUL>1, otherwise an illegal instruction exception is raised.

The overlapping of the source and destination registers assumes the implementation to be in a certain way which is inflexible. I think that the slidedown instruction should have the same restriction of non-overlapping of source and destination registers.

Thanks, Thang
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