[llvm] [VPlan] Add VPInstruction to unpack vector values to scalars. (PR #155670)

[Florian Hahn via llvm-commits]

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@@ -466,25 +466,40 @@ void VPlanTransforms::unrollByUF(VPlan &Plan, unsigned UF) {
 /// Create a single-scalar clone of \p DefR (must be a VPReplicateRecipe or
 /// VPInstruction) for lane \p Lane. Use \p Def2LaneDefs to look up scalar
 /// definitions for operands of \DefR.
-static VPRecipeWithIRFlags *
+static VPValue *
 cloneForLane(VPlan &Plan, VPBuilder &Builder, Type *IdxTy,
              VPRecipeWithIRFlags *DefR, VPLane Lane,
              const DenseMap<VPValue *, SmallVector<VPValue *>> &Def2LaneDefs) {
+
+  VPValue *Op;
+  if (match(DefR,
+            m_VPInstruction<VPInstruction::UnpackVector>(m_VPValue(Op)))) {
+    auto LaneDefs = Def2LaneDefs.find(Op);
+    if (LaneDefs != Def2LaneDefs.end())
+      return LaneDefs->second[Lane.getKnownLane()];
+
+    VPValue *Idx =
+        Plan.getOrAddLiveIn(ConstantInt::get(IdxTy, Lane.getKnownLane()));
+    return Builder.createNaryOp(Instruction::ExtractElement, {Op, Idx});
+  }
+
   // Collect the operands at Lane, creating extracts as needed.
   SmallVector<VPValue *> NewOps;
   for (VPValue *Op : DefR->operands()) {
+    if (Lane.getKind() == VPLane::Kind::ScalableLast) {
+      match(Op, m_VPInstruction<VPInstruction::UnpackVector>(m_VPValue(Op)));
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fhahn wrote:

Added a comment, thanks. 

It can stay at the original position in the latest version, moved back, thanks

https://github.com/llvm/llvm-project/pull/155670