[PATCH] D62783: [DAG] isBitwiseNot / isConstOrConstSplat - add support for build vector undefs + truncation (PR41020)

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: lebedev.ri, nikic, spatel, craig.topper, t.p.northover, efriedma.
Herald added a subscriber: javed.absar.
Herald added a project: LLVM.

Add (opt-in) support for implicit truncation to isConstOrConstSplat, which allows us to match truncated 'all ones' cases in isBitwiseNot.

PR41020 compares against using ISD::isBuildVectorAllOnes() instead, but that predicate silently accepts any UNDEF elements in the build vector which might not be what we want in isBitwiseNot - so I've added an opt-in 'AllowUndefs' flag that is set to false by default but will allow us to enable it on individual cases where its safe.


Repository:
  rL LLVM

https://reviews.llvm.org/D62783

Files:
  include/llvm/CodeGen/SelectionDAGNodes.h
  lib/CodeGen/SelectionDAG/SelectionDAG.cpp
  test/CodeGen/AArch64/sat-add.ll

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