[llvm] [InstCombine] Refactoring matchFunnelShift (NFC) (PR #73390)

[via llvm-commits]

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@@ -2810,7 +2809,7 @@ static Instruction *matchFunnelShift(Instruction &Or, InstCombinerImpl &IC,
       IsFshl = false; // Sub on SHL.
     }
     if (!ShAmt)
-      return nullptr;
+      return std::nullopt;
 
     FShiftArgs = {ShVal0, ShVal1, ShAmt};
   } else if (isa<ZExtInst>(Or0) || isa<ZExtInst>(Or1)) {
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goldsteinn wrote:

not really sure what @nikic means. Do you mean these ops wont match `shl`/`lshr` anyways so its unnecessary? But then what would be alternative?

https://github.com/llvm/llvm-project/pull/73390