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

[Florian Hahn via llvm-commits]

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@@ -8856,21 +8852,9 @@ static void addLiveOutsForFirstOrderRecurrences(
   // Start by finding out if middle block branches to scalar preheader, which is
   // not a VPIRBasicBlock, unlike Exit block - the other possible successor of
   // middle block.
-  // TODO: Should be replaced by
-  // Plan->getScalarLoopRegion()->getSinglePredecessor() in the future once the
-  // scalar region is modeled as well.
-  auto *MiddleVPBB = cast<VPBasicBlock>(VectorRegion->getSingleSuccessor());
-  VPBasicBlock *ScalarPHVPBB = nullptr;
-  if (MiddleVPBB->getNumSuccessors() == 2) {
-    // Order is strict: first is the exit block, second is the scalar preheader.
-    ScalarPHVPBB = cast<VPBasicBlock>(MiddleVPBB->getSuccessors()[1]);
-  } else if (ExitUsersToFix.empty()) {
-    ScalarPHVPBB = cast<VPBasicBlock>(MiddleVPBB->getSingleSuccessor());
-  } else {
-    llvm_unreachable("unsupported CFG in VPlan");
-  }
-
+  VPBasicBlock *ScalarPHVPBB = Plan.getScalarPreheader();
   VPBuilder ScalarPHBuilder(ScalarPHVPBB);
+  auto *MiddleVPBB = cast<VPBasicBlock>(VectorRegion->getSingleSuccessor());
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fhahn wrote:

Done, thanks!

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