[llvm] [VPlan] Move initial skeleton construction earlier (NFC). (PR #150848)

[Florian Hahn via llvm-commits]

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@@ -516,35 +552,11 @@ void VPlanTransforms::prepareForVectorization(
   assert((!HasUncountableEarlyExit || HandledUncountableEarlyExit) &&
          "missed an uncountable exit that must be handled");
 
-  // Create SCEV and VPValue for the trip count.
-  // We use the symbolic max backedge-taken-count, which works also when
-  // vectorizing loops with uncountable early exits.
-  const SCEV *BackedgeTakenCountSCEV = PSE.getSymbolicMaxBackedgeTakenCount();
-  assert(!isa<SCEVCouldNotCompute>(BackedgeTakenCountSCEV) &&
-         "Invalid loop count");
-  ScalarEvolution &SE = *PSE.getSE();
-  const SCEV *TripCount = SE.getTripCountFromExitCount(BackedgeTakenCountSCEV,
-                                                       InductionTy, TheLoop);
-  Plan.setTripCount(
-      vputils::getOrCreateVPValueForSCEVExpr(Plan, TripCount, SE));
-
-  VPBasicBlock *ScalarPH = Plan.createVPBasicBlock("scalar.ph");
-  VPBlockUtils::connectBlocks(ScalarPH, Plan.getScalarHeader());
-
-  // The connection order corresponds to the operands of the conditional branch,
-  // with the middle block already connected to the exit block.
-  VPBlockUtils::connectBlocks(MiddleVPBB, ScalarPH);
-  // Also connect the entry block to the scalar preheader.
-  // TODO: Also introduce a branch recipe together with the minimum trip count
-  // check.
-  VPBlockUtils::connectBlocks(Plan.getEntry(), ScalarPH);
-  Plan.getEntry()->swapSuccessors();
-
   // If MiddleVPBB has a single successor then the original loop does not exit
   // via the latch and the single successor must be the scalar preheader.
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fhahn wrote:

Yep, this should be taken care of by consistently emitting a check if VectorTC == TC. This is the most general, the others are optimizations of cases where we know the check is either always false or true.

https://github.com/llvm/llvm-project/pull/150848