[llvm] [LV] Support tail-folded epilogue loops (PR #208764)

[Florian Hahn via llvm-commits]

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@@ -5401,22 +5414,30 @@ void LoopVectorizationPlanner::plan(ElementCount UserVF, unsigned UserIC) {
       // Collect the instructions (and their associated costs) that will be more
       // profitable to scalarize.
       CM->collectNonVectorizedAndSetWideningDecisions(UserVF);
-      buildVPlans(*VPlan1, UserVF, UserVF);
-      ElementCount EpilogueUserVF = EpilogueVectorizationForceVF;
-      if (EpilogueUserVF.isVector() &&
-          ElementCount::isKnownLT(EpilogueUserVF, UserVF)) {
-        CM->collectNonVectorizedAndSetWideningDecisions(EpilogueUserVF);
-        buildVPlans(*VPlan1, EpilogueUserVF, EpilogueUserVF);
-      }
-      if (!VPlans.empty() && VPlans.front()->getSingleVF() == UserVF) {
-        // For scalar VF, skip VPlan cost check as VPlan cost is designed for
-        // vector VFs only.
-        if (UserVF.isScalar() ||
-            cost(*VPlans.front(), UserVF, /*RU=*/nullptr).isValid()) {
-          LLVM_DEBUG(dbgs() << "LV: Using user VF " << UserVF << ".\n");
-          LLVM_DEBUG(printPlans(dbgs()));
-          return;
+      // Build the main-loop VPlan firstly because if epilogue tail-folding is
+      // enabled, it will be built later, so we keep the epilogue vplans at the
+      // end.
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fhahn wrote:

nit: I think this can be removed.

```suggestion
```

https://github.com/llvm/llvm-project/pull/208764