[llvm] [InstCombine] Do not simplify lshr/shl arg if it is part of fshl rotate pattern. (PR #73441)

[Yingwei Zheng via llvm-commits]

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@@ -2874,11 +2873,22 @@ static Instruction *matchFunnelShift(Instruction &Or, InstCombinerImpl &IC,
   }
 
   if (FShiftArgs.empty())
-    return nullptr;
+    return std::nullopt;
 
   Intrinsic::ID IID = IsFshl ? Intrinsic::fshl : Intrinsic::fshr;
-  Function *F = Intrinsic::getDeclaration(Or.getModule(), IID, Or.getType());
-  return CallInst::Create(F, FShiftArgs);
+  return std::make_tuple(IID, FShiftArgs);
+}
+
+/// Match UB-safe variants of the funnel shift intrinsic.
+static Instruction *matchFunnelShift(Instruction &Or, InstCombinerImpl &IC,
+                                     const DominatorTree &DT) {
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dtcxzyw wrote:

`DT` is unused now. Looks like it was introduced to pass the DomTree info to `computeKnownBits`.

https://github.com/llvm/llvm-project/pull/73441