[PATCH] D107883: [DAGCombiner] Teach isKnownToBeAPowerOfTwo handle SPLAT_VECTOR.

[Fraser Cormack via Phabricator via llvm-commits]

frasercrmck added a comment.

Now that the scope of this has increased, I think we should try and add scalable-vector tests for all of the DAGCombines which use `isKnownToBeAPowerOfTwo`.



================
Comment at: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:3654
+      return C->getAPIntValue().zextOrTrunc(BitWidth).isPowerOf2();
+  return false;
+
----------------
This `return false` isn't doing the right thing and is skipping the `computeKnownBits` stuff below. I'm surprised the tests are still passing! Are we missing coverage?

I think this should simply be `if (C->getAPIntValue().zextOrTrunc(BitWidth).isPowerOf2()) return true`, allowing it to fall through to the next checks.


Repository:
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  https://reviews.llvm.org/D107883/new/

https://reviews.llvm.org/D107883