[llvm] [LV] Don't vectorize epilogue with scalable VF if no iterations remain. (PR #149789)

[Paul Walker via llvm-commits]

================
@@ -4496,24 +4518,7 @@ VectorizationFactor LoopVectorizationPlanner::selectEpilogueVectorizationFactor(
 
     // If NextVF is greater than the number of remaining iterations, the
     // epilogue loop would be dead. Skip such factors.
-    if (!MainLoopVF.isScalable() && !NextVF.Width.isScalable()) {
-      // TODO: extend to support scalable VFs.
-      if (!RemainingIterations) {
-        const SCEV *TC = vputils::getSCEVExprForVPValue(
-            getPlanFor(NextVF.Width).getTripCount(), SE);
-        assert(!isa<SCEVCouldNotCompute>(TC) &&
-               "Trip count SCEV must be computable");
-        RemainingIterations = SE.getURemExpr(
-            TC, SE.getConstant(TCType, MainLoopVF.getFixedValue() * IC));
-        MaxTripCount = MainLoopVF.getFixedValue() * IC - 1;
-        if (SE.isKnownPredicate(CmpInst::ICMP_ULT, RemainingIterations,
-                                SE.getConstant(TCType, MaxTripCount))) {
-          MaxTripCount =
-              SE.getUnsignedRangeMax(RemainingIterations).getZExtValue();
-        }
-        LLVM_DEBUG(dbgs() << "LEV: Maximum Trip Count for Epilogue: "
-                          << MaxTripCount << "\n");
-      }
+    if (RemainingIterations && !NextVF.Width.isScalable()) {
----------------
paulwalker-arm wrote:

The `!isScalable()` check looks unnecessary because the call to `SE.isKnownPredicate()` can use `SE.getElementCount(TCType, NextVF.Width)`.

https://github.com/llvm/llvm-project/pull/149789