[llvm] [VPlan] Model FOR resume value extraction in VPlan. (PR #93396)

[via llvm-commits]

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@@ -3391,16 +3390,16 @@ void InnerLoopVectorizer::fixVectorizedLoop(VPTransformState &State,
     fixNonInductionPHIs(Plan, State);
 
   // At this point every instruction in the original loop is widened to a
-  // vector form. Now we need to fix the recurrences in the loop. These PHI
-  // nodes are currently empty because we did not want to introduce cycles.
-  // This is the second stage of vectorizing recurrences. Note that fixing
-  // reduction phis are already modeled in VPlan.
-  // TODO: Also model fixing fixed-order recurrence phis in VPlan.
-  VPRegionBlock *VectorRegion = State.Plan->getVectorLoopRegion();
-  VPBasicBlock *HeaderVPBB = VectorRegion->getEntryBasicBlock();
-  for (VPRecipeBase &R : HeaderVPBB->phis()) {
-    if (auto *FOR = dyn_cast<VPFirstOrderRecurrencePHIRecipe>(&R))
-      fixFixedOrderRecurrence(FOR, State);
+  // vector form. Note that fixing reduction phis, as well as extracting the
+  // exit and resume values for fixed-order recurrences are already modeled in
+  // VPlan. All that remains to do here is creating a phi in the scalar
+  // pre-header for each fixed-rder recurrence resume value.
+  // TODO: Also model creating phis in the scalar pre-header in VPlan.
+  for (const auto &[_, LO] : to_vector(Plan.getLiveOuts())) {
+    if (!Legal->isFixedOrderRecurrence(LO->getPhi()))
+      continue;
+    fixFixedOrderRecurrence(LO, State);
+    Plan.removeLiveOut(LO->getPhi());
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ayalz wrote:

Worth a comment, somewhere. Plan holds LO's that need fixing, any LO that is fixed is removed from Plan, remaining LO's receive a default LO->fixPhi() fix below.

https://github.com/llvm/llvm-project/pull/93396