[llvm] [VPlan] Rewrite sinkScalarOperands in preparation to extend (PR #151696)

[Florian Hahn via llvm-commits]

================
@@ -131,60 +131,63 @@ bool VPlanTransforms::tryToConvertVPInstructionsToVPRecipes(
 }
 
 static bool sinkScalarOperands(VPlan &Plan) {
-  auto Iter = vp_depth_first_deep(Plan.getEntry());
+  bool ScalarVFOnly = Plan.hasScalarVFOnly();
   bool Changed = false;
   // 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)) {
+  for (VPRegionBlock *VPR : VPBlockUtils::blocksOnly<VPRegionBlock>(
+           vp_depth_first_deep(Plan.getEntry()))) {
     VPBasicBlock *EntryVPBB = VPR->getEntryBasicBlock();
     if (!VPR->isReplicator() || EntryVPBB->getSuccessors().size() != 2)
       continue;
-    VPBasicBlock *VPBB = dyn_cast<VPBasicBlock>(EntryVPBB->getSuccessors()[0]);
+    VPBasicBlock *VPBB =
+        dyn_cast<VPBasicBlock>(EntryVPBB->getSuccessors().front());
     if (!VPBB || VPBB->getSingleSuccessor() != VPR->getExitingBasicBlock())
       continue;
     for (auto &Recipe : *VPBB) {
-      for (VPValue *Op : Recipe.operands())
-        if (auto *Def =
-                dyn_cast_or_null<VPSingleDefRecipe>(Op->getDefiningRecipe()))
-          WorkList.insert({VPBB, Def});
+      for (VPValue *Op : Recipe.operands()) {
+        auto *Def =
+            dyn_cast_or_null<VPSingleDefRecipe>(Op->getDefiningRecipe());
+        if (!Def)
+          continue;
+
+        // We only know how to duplicate VPReplicateRecipes and
+        // VPScalarIVStepsRecipes for now.
+        if (!isa<VPReplicateRecipe, VPScalarIVStepsRecipe>(Def))
+          continue;
+
+        if (Def->getParent() == VPBB || Def->mayHaveSideEffects() ||
+            Def->mayReadOrWriteMemory())
+          continue;
+
+        if (auto *RepR = dyn_cast<VPReplicateRecipe>(Op))
+          if (!ScalarVFOnly && RepR->isSingleScalar())
+            continue;
+
+        WorkList.insert({VPBB, Def});
+      }
     }
   }
 
-  bool ScalarVFOnly = Plan.hasScalarVFOnly();
   // Try to sink each replicate or scalar IV steps recipe in the worklist.
-  for (unsigned I = 0; I != WorkList.size(); ++I) {
+  for (const auto &Item : WorkList) {
----------------
fhahn wrote:

```suggestion
  for (const auto &[SinkTo, SinkCandidate]: WorkList) {
```

does this work instead of using `std::tie`?

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