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

[David Sherwood via llvm-commits]

================
@@ -1432,6 +1434,91 @@ static bool isConditionTrueViaVFAndUF(VPValue *Cond, VPlan &Plan,
   return SE.isKnownPredicate(CmpInst::ICMP_EQ, TripCount, C);
 }
 
+static bool useWideActiveLaneMask(VPlan &Plan, ElementCount VF, unsigned UF) {
+  VPRegionBlock *VectorRegion = Plan.getVectorLoopRegion();
+  VPBasicBlock *ExitingVPBB = VectorRegion->getExitingBasicBlock();
+  auto *Term = &ExitingVPBB->back();
+
+  using namespace llvm::VPlanPatternMatch;
+  if (!EnableWideActiveLaneMask || !VF.isVector() || UF == 1 ||
+      !match(Term, m_BranchOnCond(m_Not(m_ActiveLaneMask(
+                       m_VPValue(), m_VPValue(), m_VPValue())))))
+    return false;
+
+  auto *Header = cast<VPBasicBlock>(VectorRegion->getEntry());
+  VPCanonicalIVPHIRecipe *CanonicalIV = Plan.getCanonicalIV();
----------------
david-arm wrote:

I think you can avoid this extra variable and just do:

```
  auto *Header = cast<VPBasicBlock>(VectorRegion->getEntry());
  LLVMContext &Ctx = Plan.getContext();
```

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