[llvm] [VPlan] Rewrite sinkScalarOperands (NFC) (PR #151696)

[Ramkumar Ramachandra via llvm-commits]

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@@ -151,59 +151,65 @@ static bool cannotHoistOrSinkRecipe(const VPRecipeBase &R) {
 
 static bool sinkScalarOperands(VPlan &Plan) {
   auto Iter = vp_depth_first_deep(Plan.getEntry());
+  bool ScalarVFOnly = Plan.hasScalarVFOnly();
   bool Changed = false;
+
+  auto IsValidSinkCandidate = [ScalarVFOnly](VPBasicBlock *SinkTo,
+                                             VPSingleDefRecipe *Candidate) {
+    // We only know how to duplicate VPReplicateRecipes and
+    // VPScalarIVStepsRecipes for now.
+    if (!isa<VPReplicateRecipe, VPScalarIVStepsRecipe>(Candidate))
+      return false;
+
+    if (Candidate->getParent() == SinkTo || Candidate->mayHaveSideEffects() ||
+        Candidate->mayReadOrWriteMemory())
+      return false;
+
+    if (auto *RepR = dyn_cast<VPReplicateRecipe>(Candidate))
+      if (!ScalarVFOnly && RepR->isSingleScalar())
+        return false;
+
+    return true;
+  };
+
   // First, collect the operands of all recipes in replicate blocks as seeds for
   // sinking.
   SetVector<std::pair<VPBasicBlock *, VPSingleDefRecipe *>> WorkList;
   for (VPRegionBlock *VPR : VPBlockUtils::blocksOnly<VPRegionBlock>(Iter)) {
     VPBasicBlock *EntryVPBB = VPR->getEntryBasicBlock();
     if (!VPR->isReplicator() || EntryVPBB->getSuccessors().size() != 2)
       continue;
-    VPBasicBlock *VPBB = dyn_cast<VPBasicBlock>(EntryVPBB->getSuccessors()[0]);
-    if (!VPBB || VPBB->getSingleSuccessor() != VPR->getExitingBasicBlock())
+    VPBasicBlock *VPBB = cast<VPBasicBlock>(EntryVPBB->getSuccessors().front());
+    if (VPBB->getSingleSuccessor() != VPR->getExitingBasicBlock())
       continue;
     for (auto &Recipe : *VPBB) {
-      for (VPValue *Op : Recipe.operands())
+      for (VPValue *Op : Recipe.operands()) {
         if (auto *Def =
                 dyn_cast_or_null<VPSingleDefRecipe>(Op->getDefiningRecipe()))
-          WorkList.insert({VPBB, Def});
+          if (IsValidSinkCandidate(VPBB, Def))
+            WorkList.insert({VPBB, Def});
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artagnon wrote:

This is a good idea! Will follow-up soon.

https://github.com/llvm/llvm-project/pull/151696