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

[via llvm-commits]

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@@ -8615,22 +8625,14 @@ VPlanPtr LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(
   // visit each basic block after having visited its predecessor basic blocks.
   // ---------------------------------------------------------------------------
 
-  // Create initial VPlan skeleton, having a basic block for the pre-header
-  // which contains SCEV expansions that need to happen before the CFG is
-  // modified; a basic block for the vector pre-header, followed by a region for
-  // the vector loop, followed by the middle basic block. The skeleton vector
-  // loop region contains a header and latch basic blocks.
-
   bool RequiresScalarEpilogueCheck =
       LoopVectorizationPlanner::getDecisionAndClampRange(
           [this](ElementCount VF) {
             return !CM.requiresScalarEpilogue(VF.isVector());
           },
           Range);
-  VPlanTransforms::prepareForVectorization(
-      *Plan, Legal->getWidestInductionType(), PSE, RequiresScalarEpilogueCheck,
-      CM.foldTailByMasking(), OrigLoop,
-      getDebugLocFromInstOrOperands(Legal->getPrimaryInduction()),
+  VPlanTransforms::handleEarlyExitsAndAddMiddleCheck(
+      *Plan, RequiresScalarEpilogueCheck, CM.foldTailByMasking(),
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ayalz wrote:

Potential follow-up: would be good to complete the common skeleton with a canonical representation of early exits and middle check, to be specialized per each VF range according to its RequiresScalarEpilogueCheck (fold tail is currently also common?).

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