[llvm] [VPlan] Make canonical IV part of the region (PR #156262)

[Florian Hahn via llvm-commits]

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@@ -406,13 +406,23 @@ static void createLoopRegion(VPlan &Plan, VPBlockBase *HeaderVPB) {
   // LatchExitVPB, taking care to preserve the original predecessor & successor
   // order of blocks. Set region entry and exiting after both HeaderVPB and
   // LatchVPBB have been disconnected from their predecessors/successors.
-  auto *R = Plan.createVPRegionBlock();
+  VPPhi *ScalarCanIV = nullptr;
+  if (PreheaderVPBB->getSinglePredecessor() == Plan.getEntry())
+    ScalarCanIV = cast<VPPhi>(&*cast<VPBasicBlock>(HeaderVPB)->begin());
+  auto *R = Plan.createVPRegionBlock(
+      ScalarCanIV->getOperand(0)->getLiveInIRValue()->getType(),
+      ScalarCanIV ? ScalarCanIV->getDebugLoc()
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fhahn wrote:

We currently only create a canonical IV in the outermost loop. when vectorizing an inner loop, we won't have a scalar phi for the canonical induction. In that case, it won't be used currently.

https://github.com/llvm/llvm-project/pull/156262