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[ARM][MVE] Tail-predication: remove the BTC + 1 overflow checks

Authored by SjoerdMeijer on Aug 25 2020, 5:53 AM.

Description

[ARM][MVE] Tail-predication: remove the BTC + 1 overflow checks

This adapts tail-predication to the new semantics of get.active.lane.mask as
defined in D86147. This means that:

  • we can remove the BTC + 1 overflow checks because now the loop tripcount is passed in to the intrinsic,
  • we can immediately use that value to setup a counter for the number of elements processed by the loop and don't need to materialize BTC + 1.

Differential Revision: https://reviews.llvm.org/D86303