[llvm] [VPlan] Run initial recipe simplification on VPlan0. (PR #176828)

[Ramkumar Ramachandra via llvm-commits]

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@@ -3414,8 +3432,13 @@ void VPlanTransforms::replaceSymbolicStrides(
   // evolution.
   auto CanUseVersionedStride = [&Plan](VPUser &U, unsigned) {
     auto *R = cast<VPRecipeBase>(&U);
-    return R->getRegion() ||
-           R->getParent() == Plan.getVectorLoopRegion()->getSinglePredecessor();
+    if (R->getRegion())
+      return true;
+    // For VPlan0 (no VectorLoopRegion yet), allow replacement in the loop body.
+    auto *VectorLoopRegion = Plan.getVectorLoopRegion();
+    if (!VectorLoopRegion)
+      return !isa<VPIRBasicBlock>(R->getParent());
+    return R->getParent() == VectorLoopRegion->getSinglePredecessor();
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artagnon wrote:

Confused: do we call replaceSymbolicStrides on VPlan0 currently? Why is this change required?

https://github.com/llvm/llvm-project/pull/176828