[PATCH] D35381: [DAGCombiner] Recognise vector rotations with non-splat constants

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


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Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:4672
       if (LHSMask.getNode()) {
-        APInt RHSBits = APInt::getLowBitsSet(EltSizeInBits, LShVal);
+        SDValue RHSBits = buildLoHiRotateVecBitmask(RHSShiftAmt, true, DL, VT);
         Mask = DAG.getNode(ISD::AND, DL, VT, Mask,
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RKSimon wrote:
> This can be done with
> ```
> SDValue RHSBits = DAG.getNode(ISD::SRL, DL, VT, AllOnes, RHSShiftAmt);
> ```
> (Taking AllOnes from the value initially assigned to Mask).
Probably safer to use getNode instead of FoldConstantArithmetic, same for below


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Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:4591
+// if Left + Right == Sum (constant or constant splat vector)
+bool DAGCombiner::sumMatchConstant(SDValue Left, SDValue Right, unsigned Sum,
+                                   const SDLoc &DL) {
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There's no need for this to be part of DAGCombiner - just make it static and pass SelectionDAG& as an argument


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Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:4655
     if (LHSMask.getNode() || RHSMask.getNode()) {
-      SDValue Mask = DAG.getAllOnesConstant(DL, VT);
+      SDValue One = DAG.getAllOnesConstant(DL, VT);
+      SDValue Mask = One;
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Probably better to call this AllOnes not One


https://reviews.llvm.org/D35381