[llvm] [LV] Vectorize conditional scalar assignments (PR #158088)

[Florian Hahn via llvm-commits]

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@@ -4593,3 +4594,80 @@ void VPlanTransforms::addExitUsersForFirstOrderRecurrences(VPlan &Plan,
     }
   }
 }
+
+void VPlanTransforms::convertFindLastRecurrences(
+    VPlan &Plan, VPRecipeBuilder &RecipeBuilder,
+    LoopVectorizationLegality *Legal) {
+  assert(Legal && "Need valid LoopVecLegality");
+
+  // May need to do something better than this?
+  if (Plan.hasScalarVFOnly())
+    return;
+
+  // We want to create the following nodes:
+  // vec.body:
+  //   mask.phi = phi <VF x i1> [ all.false, vec.ph ], [ new.mask, vec.body ]
+  //   ...data.phi already exists, but needs updating...
+  //   data.phi = phi <VF x Ty> [ default.val, vec.ph ], [ new.data, vec.body ]
+  //
+  //   ...'data' and 'compare' created by existing nodes...
+  //
+  //   any_active = i1 any_of_reduction(compare)
+  //   new.mask = select any_active, compare, mask.phi
+  //   new.data = select any_active, data, data.phi
+  //
+  // middle.block:
+  //   result = extract-last-active new.data, new.mask, default.val
+
+  for (const auto &[Phi, RdxDesc] : Legal->getReductionVars()) {
+    if (RecurrenceDescriptor::isFindLastRecurrenceKind(
+            RdxDesc.getRecurrenceKind())) {
+      VPRecipeBase *PhiR = RecipeBuilder.getRecipe(Phi);
----------------
fhahn wrote:

Please avoid going through Legal/RecipeBuilder here if possible and instead use the information directly available in VPlan. 

https://github.com/llvm/llvm-project/pull/158088