[PATCH] D137140: [SDAG] Allow scalable vectors in ComputeKnownBits

[Philip Reames via Phabricator via llvm-commits]

reames added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:2982-2984
+    // TODO: Support zeroinitializer pattern
+    if (Op.getValueType().isScalableVector())
+      break;
----------------
paulwalker-arm wrote:
> I don't believe this is possible because `ISD::VECTOR_SHUFFLE` only supports fixed length vectors.  The zeroinitializer pattern you mention should be covered by `ISD::SPLAT_VECTOR`?
> 
> So I guess thus can be an assert like with the `ISD::BUILD_VECTOR` case.  Although both those ISD nodes are baked by a SDNode classes that should have asserts within their constructors and so we should have failed long before we get to this code.
I'm happy to turn this into an assert if desired.  I see value in making it locally obvious that a code path is dead.  This was not obvious to me.  

You mention an assert in the constructor.  Glancing at ShuffleVectorSDNode constructor, I do not see such a thing.  Am I missing something obvious?


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D137140/new/

https://reviews.llvm.org/D137140