[llvm] [LoopVectorize] Generate wide active lane masks (PR #147535)

[Kerry McLaughlin via llvm-commits]

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@@ -1432,20 +1433,93 @@ static bool isConditionTrueViaVFAndUF(VPValue *Cond, VPlan &Plan,
   return SE.isKnownPredicate(CmpInst::ICMP_EQ, TripCount, C);
 }
 
+static void extractFromWideActiveLaneMask(VPlan &Plan, ElementCount VF,
+                                          unsigned UF) {
+  VPRegionBlock *VectorRegion = Plan.getVectorLoopRegion();
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kmclaughlin-arm wrote:

Yes, to enable this without passing the extra flag we will need to decide whether it's profitable based on the cost of the wider mask, taking into account the features available on the target.

https://github.com/llvm/llvm-project/pull/147535