[PATCH] D119629: [DAG] computeKnownBits - add ISD::AVGCEILU handling

[Jay Foad via Phabricator via llvm-commits]

foad added a comment.

I guess this method can calculate some low bits of the result, but is that actually useful? If you're only interested in the high bits you can just say that the result is known to be >= the smaller operand and <= the larger one, which would work for all four avg variants (floor/ceil, signed/unsigned).



================
Comment at: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:3135
+    Known2 = computeKnownBits(Op.getOperand(1), DemandedElts, Depth + 1);
+    Known = Known.zext(BitWidth * 2);
+    Known2 = Known2.zext(BitWidth * 2);
----------------
BitWidth+1 is enough.


Repository:
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  https://reviews.llvm.org/D119629/new/

https://reviews.llvm.org/D119629