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

[Florian Hahn via llvm-commits]

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@@ -8173,6 +8202,36 @@ VPWidenRecipe *VPRecipeBuilder::tryToWiden(Instruction *I,
   };
 }
 
+VPHistogramRecipe *
+VPRecipeBuilder::tryToWidenHistogram(const HistogramInfo *HI,
+                                     ArrayRef<VPValue *> Operands) {
+  // FIXME: Support other operations.
+  unsigned Opcode = HI->Update->getOpcode();
+  assert((Opcode == Instruction::Add || Opcode == Instruction::Sub) &&
+         "Histogram update operation must be an Add or Sub");
+
+  SmallVector<VPValue *, 3> HGramOps;
+  // Bucket address.
+  HGramOps.push_back(Operands[1]);
+  // Increment value.
+  HGramOps.push_back(getVPValueOrAddLiveIn(HI->Update->getOperand(1), Plan));
+
+  // In case of predicated execution (due to tail-folding, or conditional
+  // execution, or both), pass the relevant mask. When there is no such mask,
+  // generate an all-true mask.
+  VPValue *Mask = nullptr;
+  if (Legal->isMaskRequired(HI->Store))
+    Mask = getBlockInMask(HI->Store->getParent());
+  else
+    Mask = Plan.getOrAddLiveIn(
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fhahn wrote:

For loads/stores the mask is optional, instead of providing an all true mask can we instead not add a mask if there's no mask needed?

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