[llvm] [AArch64] Improve index selection for histograms (PR #111150)

[Sander de Smalen via llvm-commits]

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@@ -24079,12 +24079,42 @@ static bool findMoreOptimalIndexType(const MaskedGatherScatterSDNode *N,
 
 static SDValue performMaskedGatherScatterCombine(
     SDNode *N, TargetLowering::DAGCombinerInfo &DCI, SelectionDAG &DAG) {
-  MaskedGatherScatterSDNode *MGS = cast<MaskedGatherScatterSDNode>(N);
-  assert(MGS && "Can only combine gather load or scatter store nodes");
+  MaskedHistogramSDNode *HG;
+  MaskedGatherScatterSDNode *MGS;
+  if (N->getOpcode() == ISD::EXPERIMENTAL_VECTOR_HISTOGRAM) {
+    HG = cast<MaskedHistogramSDNode>(N);
+  } else {
+    MGS = cast<MaskedGatherScatterSDNode>(N);
+  }
+  assert((HG || MGS) &&
+         "Can only combine gather load, scatter store or histogram nodes");
 
   if (!DCI.isBeforeLegalize())
     return SDValue();
 
+  if (N->getOpcode() == ISD::EXPERIMENTAL_VECTOR_HISTOGRAM) {
+    SDLoc DL(HG);
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sdesmalen-arm wrote:

Given that HG is only used inside this condition, I'd suggest removing the code above where it conditionally defines either `HG` or` MGS`, and just define `HG` here, and define `MGS` below in the original code.

https://github.com/llvm/llvm-project/pull/111150