Zhongyunde 7203286329 [LangRef] vscale_range implies the vscale is power-of-two ...

According the discuss on D154953, we need to make the LangRef change
before the optimization relied on the new behaviour:
      vscale_range implies vscale is a power-of-two value, parse of the
  attribute to reject values that are not a power-of-two.

Thanks nikic for the wonderful summary of discussing on D154953:
To provide a bit more context here. We would like to have power of two vscale exposed in a target-independent way, so we can make use of this in places like ValueTracking, just like we currently do the vscale range. Some options that have been discussed are:
  - Remove support for non-power-of-two vscales entirely. (This is my personal preference, but this is hard to undo if it turns out someone does need them.)
  - Add an extra attribute vscale_pow2, or a data layout property.
  - Make vscale_range imply power-of-two vscale, as a compromise solution (what this patch does). This would be relatively easy to turn into one of the two above at a later point.

Reviewed By: paulwalker-arm, nikic, efriedma
Differential Revision: https://reviews.llvm.org/D155193

2023-07-15 09:13:48 +08:00

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