[llvm] [VPlan] Create header phi recipes after initial scalar optimizations. (PR #200920)

[Luke Lau via llvm-commits]

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@@ -6517,8 +6523,6 @@ VPlanPtr LoopVectorizationPlanner::tryToBuildVPlan1() {
   if (const LoopAccessInfo *LAI = Legal->getLAI())
     RUN_VPLAN_PASS(VPlanTransforms::replaceSymbolicStrides, *VPlan0, PSE,
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lukel97 wrote:

Nothing modifies the CFG between the first replaceSymbolicStrides and the second does it? Might be good to share the VPDominatorTree to avoid recomputing it the second time round, but doesn't need to be done this PR. (Premature optimisation is the root of all evil etc.)

https://github.com/llvm/llvm-project/pull/200920