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

[Luke Lau via llvm-commits]

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@@ -2758,12 +2770,14 @@ void VPlanTransforms::optimize(VPlan &Plan) {
   RUN_VPLAN_PASS(removeRedundantCanonicalIVs, Plan);
   RUN_VPLAN_PASS(removeRedundantInductionCasts, Plan);
 
+  RUN_VPLAN_PASS(reassociateHeaderMask, Plan);
   RUN_VPLAN_PASS(simplifyRecipes, Plan);
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lukel97 wrote:

I think it's the other way around, where we want to run reassociateHeaderMask beforehand so we still unlock the same simplification opportunities. I.e. reassociateHeaderMask allows simplifyRecipes to kick in more, not the other way round. 

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