[llvm] [VPlan] Introduce explicit ExtractFromEnd recipes for live-outs. (PR #100658)

[via llvm-commits]

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@@ -8660,6 +8757,14 @@ LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(VFRange &Range) {
   // After here, VPBB should not be used.
   VPBB = nullptr;
 
+  assert(isa<VPRegionBlock>(Plan->getVectorLoopRegion()) &&
+         !Plan->getVectorLoopRegion()->getEntryBasicBlock()->empty() &&
+         "entry block must be set to a VPRegionBlock having a non-empty entry "
+         "VPBasicBlock");
+  RecipeBuilder.fixHeaderPhis();
+
+  addLiveOutsForFirstOrderRecurrences(*Plan);
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ayalz wrote:

Now that addLiveOutsForFirstOrderRecurrences() moves to be ahead of addUsersInExitBlock() - could the former add *all* live-outs of FORs, both those in scalar header and those in exit block (when scalar epilog isn't required)?

Independent, while we're here: name should be `addLiveOutsForFixedOrderRecurrences()` - as it deals with FOR's of distance >= 1, right? May be a bit confusing, along with "optimizing" the extract of v2's penultimate value instead of v3's last value.

https://github.com/llvm/llvm-project/pull/100658