[llvm] [VPlan] Introduce scalar loop header in plan, remove VPLiveOut. (PR #109975)

[via llvm-commits]

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@@ -9166,11 +9174,11 @@ LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(VFRange &Range) {
          "VPBasicBlock");
   RecipeBuilder.fixHeaderPhis();
 
+  addScalarResumePhis(RecipeBuilder, *Plan);
   SetVector<VPIRInstruction *> ExitUsersToFix = collectUsersInExitBlock(
       OrigLoop, RecipeBuilder, *Plan, Legal->getInductionVars());
   addLiveOutsForFirstOrderRecurrences(*Plan, ExitUsersToFix);
   addUsersInExitBlock(*Plan, ExitUsersToFix);
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ayalz wrote:

Perhaps first collecting ExitUsersToFix, then searching for to handle and remove the FOR ones, and finally handling all remaining ones, can now be simplified and fused, to be more consistent with how addScalarResumePhis() handles scalar preheader phis. WDYT?

https://github.com/llvm/llvm-project/pull/109975