[PATCH] D143283: [AArch64][SVE]: custom lower AVGFloor/AVGCeil.

[Sander de Smalen via Phabricator via llvm-commits]

sdesmalen added inline comments.


================
Comment at: llvm/lib/Target/AArch64/AArch64ISelLowering.cpp:13391
+    if (ISD::isConstantSplatVector(Node.getOperand(1).getNode(), SplatVal))
+      if (SplatVal.isMask() && SplatVal.countPopulation() <
+                                   Node->getValueType(0).getScalarSizeInBits())
----------------
hassnaa-arm wrote:
> dmgreen wrote:
> > Can it use countTrailingOnes as opposed to countPopulation? Although I think these functions might be better removed and use computeKnownBits checks instead.
> I think using countTrailingOnes is much simpler than computeKnownBits  because the operand and its value are already known.
I presume that @dmgreen meant using `computeKnownBits` on `Node` as a whole, not specifically on the splatted value so that you don't need to check for the opcode explicitly.

See for example `checkZExtBool`, where it does:

    APInt RequredZero(SizeInBits, 0xFE);
    KnownBits Bits = DAG.computeKnownBits(Arg, 4);
    bool ZExtBool = (Bits.Zero & RequredZero) == RequredZero;

You can probably do a similar thing for `IsSignExtended`, but then looking at the `Bits.One` instead of  `Bits.Zero`.


Repository:
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  https://reviews.llvm.org/D143283/new/

https://reviews.llvm.org/D143283