[llvm] [VPlan] Explicitly reassociate header mask in logical and (PR #180898)

[Florian Hahn via llvm-commits]

================
@@ -1614,6 +1605,31 @@ void VPlanTransforms::simplifyRecipes(VPlan &Plan) {
   }
 }
 
+/// Reassociate (headermask && x) && y -> headermask && (x && y) to allow the
+/// header mask to be simplified further, e.g. in optimizeEVLMasks.
+static void reassociateHeaderMask(VPlan &Plan) {
+  VPValue *HeaderMask = vputils::findHeaderMask(Plan);
+  if (!HeaderMask)
+    return;
+  SmallSetVector<VPUser *, 8> Worklist(HeaderMask->user_begin(),
+                                       HeaderMask->user_end());
+  while (!Worklist.empty()) {
----------------
fhahn wrote:

> I tried iterating with an index but it runs into problems, it looks like insert_range can invalidate the iterator? i.e. this ends up crashing trying to dereference what I presume is the end of an old iterator.

Yeah I think that would need accessing via an index instead.

https://github.com/llvm/llvm-project/pull/180898