[llvm] [LV][VPlan] Add initial support for CSA vectorization (PR #121222)

[Michael Maitland via llvm-commits]

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@@ -7580,9 +7585,18 @@ InstructionCost LoopVectorizationPlanner::cost(VPlan &Plan,
 /// not have corresponding recipes in \p Plan and are not marked to be ignored
 /// in \p CostCtx. This means the VPlan contains simplification that the legacy
 /// cost-model did not account for.
-static bool planContainsAdditionalSimplifications(VPlan &Plan,
-                                                  VPCostContext &CostCtx,
-                                                  Loop *TheLoop) {
+static bool
+planContainsAdditionalSimplifications(VPlan &Plan, VPCostContext &CostCtx,
+                                      Loop *TheLoop,
+                                      LoopVectorizationLegality &Legal) {
+
+  // CSA cost is more complicated since there is significant overhead in the
+  // preheader and middle block. It also contains recipes that are not backed by
+  // underlying instructions in the original loop. This makes it difficult to
+  // model in the legacy cost model.
+  if (!Legal.getConditionalScalarAssignments().empty())
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michaelmaitland wrote:

@fhahn 

You said:

> Better check for the CSA recipes?

What is the reason to walk all recipes in the plan looking for CSA recipes when we can do this check in O(1) like this?

https://github.com/llvm/llvm-project/pull/121222