Mel Chen 4480a22c2b [LV][EVL] Emit vp.merge intrinsic to enable out-loop reduction in EVL vectorization. (#101641) ...

Following #90184, this patch emits vp.merge intrinsic, which is used to
set the inactive lanes in a select operation to the RHS instead of
undef. Currently, it is applied to out-loop reduction for EVL
vectorization.

This patch performs transformation to convert 
  select(header_mask, LHS, RHS)
into
  vp.merge(all-true, LHS, RHS, EVL) 
And always use the predicated reduction select to set the incoming value
of the reduction phi to support out-loop reduction when using tail
folding with EVL.

TODO: Postpone the adjustment of the predicated reduction select to
VPlanTransform. The current adjustment might be too early, which could
lead to a situation where the predicated reduction select is adjusted,
but the EVL recipes cannot be successfully generated during
VPlanTransform.

2024-11-06 14:53:49 +08:00

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