[llvm] [LV] Vectorize histogram operations (PR #99851)

[Graham Hunter via llvm-commits]

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@@ -1575,6 +1577,52 @@ class VPWidenCallRecipe : public VPSingleDefRecipe {
 #endif
 };
 
+/// A recipe representing a sequence of load -> update -> store as part of
+/// a histogram operation. This means there may be aliasing between vector
+/// lanes, which is handled by the llvm.experimental.vector.histogram family
+/// of intrinsics. The only update operations currently supported are
+/// 'add' and 'sub' where the other term is loop-invariant.
+class VPHistogramRecipe : public VPRecipeBase {
+  const HistogramInfo &Info;
+  unsigned Opcode;
+
+public:
+  template <typename IterT>
+  VPHistogramRecipe(const HistogramInfo &HI, unsigned Opcode,
+                    iterator_range<IterT> Operands, DebugLoc DL = {})
+      : VPRecipeBase(VPDef::VPHistogramSC, Operands, DL), Info(HI),
+        Opcode(Opcode) {}
+
+  ~VPHistogramRecipe() override = default;
+
+  VPHistogramRecipe *clone() override {
+    llvm_unreachable("cloning not supported");
+  }
+
+  VP_CLASSOF_IMPL(VPDef::VPHistogramSC);
+
+  /// Produce a vectorized histogram operation.
+  void execute(VPTransformState &State) override;
+
+  unsigned getOpcode() const { return Opcode; }
+
+  const HistogramInfo &getHistogramInfo() const { return Info; }
+
+  /// Return the mask operand if one was provided, or a null pointer if all
+  /// lanes should be executed unconditionally.
+  VPValue *getMask() const {
+    if (getNumOperands() == 3)
+      return getOperand(2);
+    return nullptr;
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huntergr-arm wrote:

done.

https://github.com/llvm/llvm-project/pull/99851