[llvm] [RISCV][GISel] Use maskedValueIsZero in RISCVInstructionSelector::selectZExtBits. (PR #115244)

[Matt Arsenault via llvm-commits]

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@@ -261,7 +261,9 @@ RISCVInstructionSelector::selectZExtBits(MachineOperand &Root,
     return {{[=](MachineInstrBuilder &MIB) { MIB.addReg(RegX); }}};
   }
 
-  // TODO: Use computeKnownBits.
+  unsigned Size = MRI->getType(RootReg).getSizeInBits();
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arsenm wrote:

scalar size? 

https://github.com/llvm/llvm-project/pull/115244