[llvm] [VPlan] Add new VPInstruction ocpode for header mask. (PR #89603)

[via llvm-commits]

================
@@ -1258,30 +1199,23 @@ void VPlanTransforms::addActiveLaneMask(
           UseActiveLaneMaskForControlFlow) &&
          "DataAndControlFlowWithoutRuntimeCheck implies "
          "UseActiveLaneMaskForControlFlow");
-
-  auto FoundWidenCanonicalIVUser =
-      find_if(Plan.getCanonicalIV()->users(),
-              [](VPUser *U) { return isa<VPWidenCanonicalIVRecipe>(U); });
-  assert(FoundWidenCanonicalIVUser &&
-         "Must have widened canonical IV when tail folding!");
-  auto *WideCanonicalIV =
-      cast<VPWidenCanonicalIVRecipe>(*FoundWidenCanonicalIVUser);
+  VPValue *HeaderMask = getHeaderMask(Plan);
+  assert(HeaderMask && "Active-lane-mask not needed?");
   VPSingleDefRecipe *LaneMask;
   if (UseActiveLaneMaskForControlFlow) {
     LaneMask = addVPLaneMaskPhiAndUpdateExitBranch(
         Plan, DataAndControlFlowWithoutRuntimeCheck);
   } else {
-    VPBuilder B = VPBuilder::getToInsertAfter(WideCanonicalIV);
-    LaneMask = B.createNaryOp(VPInstruction::ActiveLaneMask,
-                              {WideCanonicalIV, Plan.getTripCount()}, nullptr,
-                              "active.lane.mask");
+    VPBasicBlock *HeaderVPBB = Plan.getVectorLoopRegion()->getEntryBasicBlock();
+    VPBuilder B;
+    B.setInsertPoint(HeaderVPBB, HeaderVPBB->getFirstNonPhi());
----------------
ayalz wrote:

```suggestion
    VPBuilder B(HeaderVPBB->getFirstNonPhi());
```

https://github.com/llvm/llvm-project/pull/89603