[llvm] [LV] Vectorize selecting last IV of min/max element. (PR #141431)

[Florian Hahn via llvm-commits]

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@@ -965,3 +965,101 @@ bool VPlanTransforms::handleMaxMinNumReductions(VPlan &Plan) {
   MiddleTerm->setOperand(0, NewCond);
   return true;
 }
+
+bool VPlanTransforms::legalizeMultiUseReductions(VPlan &Plan) {
+  for (auto &PhiR : make_early_inc_range(
+           Plan.getVectorLoopRegion()->getEntryBasicBlock()->phis())) {
+    auto *MinMaxPhiR = dyn_cast<VPReductionPHIRecipe>(&PhiR);
+    if (!MinMaxPhiR)
+      continue;
+
+    RecurKind RdxKind = MinMaxPhiR->getRecurrenceKind();
+    // TODO: check for multi-uses in VPlan directly.
+    if (!RecurrenceDescriptor::isIntMinMaxRecurrenceKind(RdxKind) ||
+        !MinMaxPhiR->isPhiMultiUse())
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fhahn wrote:

yes that should be sufficient. Update to check for the latter, assert to former

https://github.com/llvm/llvm-project/pull/141431