[llvm] [DAGCombiner] Attempt to fold 'add' nodes to funnel-shift or rotate (PR #125612)

[Alex MacLean via llvm-commits]

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@@ -8340,7 +8344,7 @@ static SDValue extractShiftForRotate(SelectionDAG &DAG, SDValue OppShift,
 // The IsRotate flag should be set when the LHS of both shifts is the same.
 // Otherwise if matching a general funnel shift, it should be clear.
 static bool matchRotateSub(SDValue Pos, SDValue Neg, unsigned EltSize,
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AlexMaclean wrote:

I don't think this rename makes sense. The `Sub` here reflects how the shift amounts are related to each-other not something about the combining operation. The fact that we can now handle ADD cases in this function doesn't mean we should have an `Add` suffix on the function, just as the fact that we already handle OR cases doesn't mean we should have an `Or` suffix. 

https://github.com/llvm/llvm-project/pull/125612