[llvm] [RISCV] computeKnownBits - add support for RISCVISD::VECREDUCE_ADD_VL (PR #210493)

[Craig Topper via llvm-commits]

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@@ -24096,6 +24108,28 @@ void RISCVTargetLowering::computeKnownBitsForTargetNode(const SDValue Op,
     Known.Zero.setBitsFrom(Known2.countMaxActiveBits());
     break;
   }
+  case RISCVISD::VECREDUCE_ADD_VL: {
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topperc wrote:

VECREDUCE_ADD_VL result is a vector and the KnownBits result must be accurate for all elements. The result here is only accurate for element 0.

Maybe we need to handle VECREDUCE_ADD_VL+VMV_S_X together so we know only element 0 is used?

https://github.com/llvm/llvm-project/pull/210493