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

[via llvm-commits]

================
@@ -74,8 +74,11 @@ class VPlanTestIRBase : public testing::Test {
     PredicatedScalarEvolution PSE(*SE, *L);
     auto Plan = VPlanTransforms::buildPlainCFG(L, *LI);
     VFRange R(ElementCount::getFixed(1), ElementCount::getFixed(2));
-    VPlanTransforms::prepareForVectorization(*Plan, IntegerType::get(*Ctx, 64),
-                                             PSE, true, false, L, {}, false, R);
+    VPlanTransforms::addInitialSkeleton(*Plan, IntegerType::get(*Ctx, 64), {},
+                                        PSE, L);
----------------
ayalz wrote:

addInitialSkeleton() complements buildPlainCFG() in constructing the common VF-agnostic VPlan0 base, so best appear together, if not fused:
```suggestion
    VPlanTransforms::addInitialSkeleton(*Plan, IntegerType::get(*Ctx, 64), {},
                                        PSE, L);
    Range R(ElementCount::getFixed(1), ElementCount::getFixed(2));
```

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