[SLP]Fix/improve getSpillCost analysis

Previous implementation may took some extra time, when walked over the
same instructions several times. And also it did not include proper
analysis for cross-basic-block use of the vectorized values. This
version fixes it.

It walks over the tree and checks the deps between entries and their
operands. If there are non-vectorized calls in between, it adds
a single(!) spill cost, because the vector value should be
spilled/reloaded only once.

Also, this version caches analysis for each entries, which are detected,
and do not repeats it, uses data, found during previous analysis for
previous nodes.

Also, it has the internal limit. If the number of instructions
between nodes and their operands is too big (> than ScheduleRegionSizeBudget / VectorizableTree.size()), it is considered that the spill is required. It allows to improve compile time.

Reviewers: preames, RKSimon, mikhailramalho

Reviewed By: preames

Pull Request: llvm/llvm-project#129258

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -12165,118 +12165,224 @@ InstructionCost BoUpSLP::getSpillCost() {
   // live. When we see a call instruction that is not part of our tree,
   // query TTI to see if there is a cost to keeping values live over it
   // (for example, if spills and fills are required).
-  InstructionCost Cost = 0;
 
-  SmallPtrSet<const TreeEntry *, 4> LiveEntries;
-  const TreeEntry *Prev = nullptr;
+  const TreeEntry *Root = VectorizableTree.front().get();
+  if (Root->isGather())
+    return 0;
 
-  // The entries in VectorizableTree are not necessarily ordered by their
-  // position in basic blocks. Collect them and order them by dominance so later
-  // instructions are guaranteed to be visited first. For instructions in
-  // different basic blocks, we only scan to the beginning of the block, so
-  // their order does not matter, as long as all instructions in a basic block
-  // are grouped together. Using dominance ensures a deterministic order.
-  SmallVector<TreeEntry *, 16> OrderedEntries;
+  InstructionCost Cost = 0;
+  SmallDenseMap<const TreeEntry *, SmallVector<const TreeEntry *>>
+      EntriesToOperands;
+  SmallDenseMap<const TreeEntry *, Instruction *> EntriesToLastInstruction;
+  SmallPtrSet<const Instruction *, 8> LastInstructions;
   for (const auto &TEPtr : VectorizableTree) {
-    if (TEPtr->isGather())
-      continue;
-    OrderedEntries.push_back(TEPtr.get());
-  }
-  llvm::stable_sort(OrderedEntries, [&](const TreeEntry *TA,
-                                        const TreeEntry *TB) {
-    Instruction &A = getLastInstructionInBundle(TA);
-    Instruction &B = getLastInstructionInBundle(TB);
-    auto *NodeA = DT->getNode(A.getParent());
-    auto *NodeB = DT->getNode(B.getParent());
-    assert(NodeA && "Should only process reachable instructions");
-    assert(NodeB && "Should only process reachable instructions");
-    assert((NodeA == NodeB) == (NodeA->getDFSNumIn() == NodeB->getDFSNumIn()) &&
-           "Different nodes should have different DFS numbers");
-    if (NodeA != NodeB)
-      return NodeA->getDFSNumIn() > NodeB->getDFSNumIn();
-    return B.comesBefore(&A);
-  });
-
-  for (const TreeEntry *TE : OrderedEntries) {
-    if (!Prev) {
-      Prev = TE;
-      continue;
+    if (!TEPtr->isGather()) {
+      Instruction *LastInst = &getLastInstructionInBundle(TEPtr.get());
+      EntriesToLastInstruction.try_emplace(TEPtr.get(), LastInst);
+      LastInstructions.insert(LastInst);
     }
+    if (TEPtr->UserTreeIndex)
+      EntriesToOperands[TEPtr->UserTreeIndex.UserTE].push_back(TEPtr.get());
+  }
 
-    LiveEntries.erase(Prev);
-    for (unsigned I : seq<unsigned>(Prev->getNumOperands())) {
-      const TreeEntry *Op = getVectorizedOperand(Prev, I);
-      if (!Op)
-        continue;
-      assert(!Op->isGather() && "Expected vectorized operand.");
-      LiveEntries.insert(Op);
-    }
-
-    LLVM_DEBUG({
-      dbgs() << "SLP: #LV: " << LiveEntries.size();
-      for (auto *X : LiveEntries)
-        X->dump();
-      dbgs() << ", Looking at ";
-      TE->dump();
-    });
-
-    // Now find the sequence of instructions between PrevInst and Inst.
-    unsigned NumCalls = 0;
-    const Instruction *PrevInst = &getLastInstructionInBundle(Prev);
-    BasicBlock::const_reverse_iterator
-        InstIt = ++getLastInstructionInBundle(TE).getIterator().getReverse(),
-        PrevInstIt = PrevInst->getIterator().getReverse();
-    while (InstIt != PrevInstIt) {
-      if (PrevInstIt == PrevInst->getParent()->rend()) {
-        PrevInstIt = getLastInstructionInBundle(TE).getParent()->rbegin();
-        continue;
-      }
-
-      auto NoCallIntrinsic = [this](const Instruction *I) {
-        const auto *II = dyn_cast<IntrinsicInst>(I);
-        if (!II)
-          return false;
-        if (II->isAssumeLikeIntrinsic())
-          return true;
-        FastMathFlags FMF;
-        SmallVector<Type *, 4> Tys;
-        for (auto &ArgOp : II->args())
-          Tys.push_back(ArgOp->getType());
-        if (auto *FPMO = dyn_cast<FPMathOperator>(II))
-          FMF = FPMO->getFastMathFlags();
-        IntrinsicCostAttributes ICA(II->getIntrinsicID(), II->getType(), Tys,
-                                    FMF);
-        InstructionCost IntrCost =
-            TTI->getIntrinsicInstrCost(ICA, TTI::TCK_RecipThroughput);
-        InstructionCost CallCost = TTI->getCallInstrCost(
-            nullptr, II->getType(), Tys, TTI::TCK_RecipThroughput);
-        return IntrCost < CallCost;
-      };
+  auto NoCallIntrinsic = [this](const Instruction *I) {
+    const auto *II = dyn_cast<IntrinsicInst>(I);
+    if (!II)
+      return false;
+    if (II->isAssumeLikeIntrinsic())
+      return true;
+    IntrinsicCostAttributes ICA(II->getIntrinsicID(), *II);
+    InstructionCost IntrCost =
+        TTI->getIntrinsicInstrCost(ICA, TTI::TCK_RecipThroughput);
+    InstructionCost CallCost = TTI->getCallInstrCost(
+        nullptr, II->getType(), ICA.getArgTypes(), TTI::TCK_RecipThroughput);
+    return IntrCost < CallCost;
+  };
 
+  // Maps last instruction in the entry to the last instruction for the one of
+  // operand entries and the flag. If the flag is true, there are no calls in
+  // between these instructions.
+  SmallDenseMap<const Instruction *, PointerIntPair<const Instruction *, 1>>
+      CheckedInstructions;
+  unsigned Budget = 0;
+  const unsigned BudgetLimit =
+      ScheduleRegionSizeBudget / VectorizableTree.size();
+  auto CheckForNonVecCallsInSameBlock = [&](Instruction *First,
+                                            const Instruction *Last) {
+    assert(First->getParent() == Last->getParent() &&
+           "Expected instructions in same block.");
+    if (auto It = CheckedInstructions.find(Last);
+        It != CheckedInstructions.end()) {
+      const Instruction *Checked = It->second.getPointer();
+      if (Checked == First || Checked->comesBefore(First))
+        return It->second.getInt() != 0;
+      Last = Checked;
+    } else if (Last == First || Last->comesBefore(First)) {
+      return true;
+    }
+    BasicBlock::const_reverse_iterator InstIt =
+                                           ++First->getIterator().getReverse(),
+                                       PrevInstIt =
+                                           Last->getIterator().getReverse();
+    SmallVector<const Instruction *> LastInstsInRange;
+    while (InstIt != PrevInstIt && Budget <= BudgetLimit) {
       // Debug information does not impact spill cost.
       // Vectorized calls, represented as vector intrinsics, do not impact spill
       // cost.
       if (const auto *CB = dyn_cast<CallBase>(&*PrevInstIt);
-          CB && !NoCallIntrinsic(CB) && !isVectorized(CB))
-        NumCalls++;
+          CB && !NoCallIntrinsic(CB) && !isVectorized(CB)) {
+        for (const Instruction *LastInst : LastInstsInRange)
+          CheckedInstructions.try_emplace(LastInst, &*PrevInstIt, 0);
+        return false;
+      }
+      if (LastInstructions.contains(&*PrevInstIt))
+        LastInstsInRange.push_back(&*PrevInstIt);
 
       ++PrevInstIt;
       ++Budget;
     }
-
-    if (NumCalls) {
-      SmallVector<Type *, 4> EntriesTypes;
-      for (const TreeEntry *TE : LiveEntries) {
-        auto *ScalarTy = TE->getMainOp()->getType();
-        auto It = MinBWs.find(TE);
-        if (It != MinBWs.end())
-          ScalarTy = IntegerType::get(ScalarTy->getContext(), It->second.first);
-        EntriesTypes.push_back(getWidenedType(ScalarTy, TE->getVectorFactor()));
+    for (const Instruction *LastInst : LastInstsInRange)
+      CheckedInstructions.try_emplace(
+          LastInst, PrevInstIt == InstIt ? First : &*PrevInstIt,
+          Budget <= BudgetLimit ? 1 : 0);
+    return Budget <= BudgetLimit;
+  };
+  auto AddCosts = [&](const TreeEntry *Op) {
+    Type *ScalarTy = Op->Scalars.front()->getType();
+    auto It = MinBWs.find(Op);
+    if (It != MinBWs.end())
+      ScalarTy = IntegerType::get(ScalarTy->getContext(), It->second.first);
+    auto *VecTy = getWidenedType(ScalarTy, Op->getVectorFactor());
+    Cost += TTI->getCostOfKeepingLiveOverCall(VecTy);
+    if (ScalarTy->isVectorTy()) {
+      // Handle revec dead vector instructions.
+      Cost -= Op->Scalars.size() * TTI->getCostOfKeepingLiveOverCall(ScalarTy);
+    }
+  };
+  // Memoize the relationship between blocks, i.e. if there is (at least one)
+  // non-vectorized call between the blocks. This allows to skip the analysis of
+  // the same block paths multiple times.
+  SmallDenseMap<std::pair<const BasicBlock *, const BasicBlock *>, bool>
+      ParentOpParentToPreds;
+  auto CheckPredecessors = [&](BasicBlock *Root, BasicBlock *Pred,
+                               BasicBlock *OpParent) {
+    auto Key = std::make_pair(Root, OpParent);
+    if (auto It = ParentOpParentToPreds.find(Key);
+        It != ParentOpParentToPreds.end())
+      return It->second;
+    SmallVector<BasicBlock *> Worklist;
+    if (Pred)
+      Worklist.push_back(Pred);
+    else
+      Worklist.append(pred_begin(Root), pred_end(Root));
+    SmallPtrSet<const BasicBlock *, 16> Visited;
+    SmallDenseSet<std::pair<const BasicBlock *, const BasicBlock *>>
+        ParentsPairsToAdd;
+    bool Res = false;
+    auto Cleanup = make_scope_exit([&]() {
+      for (const auto &KeyPair : ParentsPairsToAdd) {
+        assert(!ParentOpParentToPreds.contains(KeyPair) &&
+               "Should not have been added before.");
+        ParentOpParentToPreds.try_emplace(KeyPair, Res);
+      }
+    });
+    while (!Worklist.empty()) {
+      BasicBlock *BB = Worklist.pop_back_val();
+      if (BB == OpParent || !Visited.insert(BB).second)
+        continue;
+      auto Pair = std::make_pair(BB, OpParent);
+      if (auto It = ParentOpParentToPreds.find(Pair);
+          It != ParentOpParentToPreds.end()) {
+        Res = It->second;
+        return Res;
+      }
+      ParentsPairsToAdd.insert(Pair);
+      unsigned BlockSize = BB->size();
+      if (BlockSize > static_cast<unsigned>(ScheduleRegionSizeBudget))
+        return Res;
+      Budget += BlockSize;
+      if (Budget > BudgetLimit)
+        return Res;
+      if (!CheckForNonVecCallsInSameBlock(&*BB->getFirstNonPHIOrDbgOrAlloca(),
+                                          BB->getTerminator()))
+        return Res;
+      Worklist.append(pred_begin(BB), pred_end(BB));
+    }
+    Res = true;
+    return Res;
+  };
+  SmallVector<const TreeEntry *> LiveEntries(1, Root);
+  while (!LiveEntries.empty()) {
+    const TreeEntry *Entry = LiveEntries.pop_back_val();
+    SmallVector<const TreeEntry *> Operands = EntriesToOperands.lookup(Entry);
+    if (Operands.empty())
+      continue;
+    Instruction *LastInst = EntriesToLastInstruction.at(Entry);
+    BasicBlock *Parent = LastInst->getParent();
+    for (const TreeEntry *Op : Operands) {
+      if (!Op->isGather())
+        LiveEntries.push_back(Op);
+      if ((Entry->getOpcode() != Instruction::PHI && Op->isGather()) ||
+          (Op->isGather() && allConstant(Op->Scalars)))
+        continue;
+      Budget = 0;
+      BasicBlock *Pred = nullptr;
+      if (auto *Phi = dyn_cast<PHINode>(Entry->getMainOp()))
+        Pred = Phi->getIncomingBlock(Op->UserTreeIndex.EdgeIdx);
+      BasicBlock *OpParent;
+      Instruction *OpLastInst;
+      if (Op->isGather()) {
+        assert(Entry->getOpcode() == Instruction::PHI &&
+               "Expected phi node only.");
+        OpParent = cast<PHINode>(Entry->getMainOp())
+                       ->getIncomingBlock(Op->UserTreeIndex.EdgeIdx);
+        OpLastInst = OpParent->getTerminator();
+        for (Value *V : Op->Scalars) {
+          auto *Inst = dyn_cast<Instruction>(V);
+          if (!Inst)
+            continue;
+          if (isVectorized(V)) {
+            OpParent = Inst->getParent();
+            OpLastInst = Inst;
+            break;
+          }
+        }
+      } else {
+        OpLastInst = EntriesToLastInstruction.at(Op);
+        OpParent = OpLastInst->getParent();
+      }
+      // Check the call instructions within the same basic blocks.
+      if (OpParent == Parent) {
+        if (Entry->getOpcode() == Instruction::PHI) {
+          if (!CheckForNonVecCallsInSameBlock(LastInst, OpLastInst))
+            AddCosts(Op);
+          continue;
+        }
+        if (!CheckForNonVecCallsInSameBlock(OpLastInst, LastInst))
+          AddCosts(Op);
+        continue;
+      }
+      // Check for call instruction in between blocks.
+      // 1. Check entry's block to the head.
+      if (Entry->getOpcode() != Instruction::PHI &&
+          !CheckForNonVecCallsInSameBlock(
+              &*LastInst->getParent()->getFirstNonPHIOrDbgOrAlloca(),
+              LastInst)) {
+        AddCosts(Op);
+        continue;
+      }
+      // 2. Check op's block from the end.
+      if (!CheckForNonVecCallsInSameBlock(OpLastInst,
+                                          OpParent->getTerminator())) {
+        AddCosts(Op);
+        continue;
+      }
+      // 3. Check the predecessors of entry's block till op's block.
+      if (!CheckPredecessors(Parent, Pred, OpParent)) {
+        AddCosts(Op);
+        continue;
       }
-      Cost += NumCalls * TTI->getCostOfKeepingLiveOverCall(EntriesTypes);
     }
-
-    Prev = TE;
   }
 
   return Cost;