[llvm] [GlobalISel] Add G_ROTL/G_ROTR to computeNumSignBits (PR #213364)

[Simon Pilgrim via llvm-commits]

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@@ -590,6 +590,11 @@ struct KnownBits {
   static KnownBits remGetLowBits(const KnownBits &LHS, const KnownBits &RHS);
 };
 
+/// Compute the number of sign bits after rotating a value.
+LLVM_ABI unsigned rotateNumSignBits(unsigned SrcSignBits, unsigned BitWidth,
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RKSimon wrote:

can we put this in a llvm::SignBitsOps namespace and just call this rot() ?

https://github.com/llvm/llvm-project/pull/213364