[DAG, X86] Revert r327197 "Revert r327170, r327171, r327172"

Reland ISel cycle checking improvements after simplifying node id
invariant traversal and correcting typo.

llvm-svn: 327898

1 files changed, 152 insertions, 227 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index 2724480e03e..406e253fe4c 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -960,6 +960,43 @@ public:
 
 } // end anonymous namespace
 
+// This function is used to enforce the topological node id property
+// property leveraged during Instruction selection. Before selection all
+// nodes are given a non-negative id such that all nodes have a larger id than
+// their operands. As this holds transitively we can prune checks that a node N
+// is a predecessor of M another by not recursively checking through M's
+// operands if N's ID is larger than M's ID. This is significantly improves
+// performance of for various legality checks (e.g. IsLegalToFold /
+// UpdateChains).
+
+// However, when we fuse multiple nodes into a single node
+// during selection we may induce a predecessor relationship between inputs and
+// outputs of distinct nodes being merged violating the topological property.
+// Should a fused node have a successor which has yet to be selected, our
+// legality checks would be incorrect. To avoid this we mark all unselected
+// sucessor nodes, i.e. id != -1 as invalid for pruning by bit-negating (x =>
+// (-(x+1))) the ids and modify our pruning check to ignore negative Ids of M.
+// We use bit-negation to more clearly enforce that node id -1 can only be
+// achieved by selected nodes). As the conversion is reversable the original Id,
+// topological pruning can still be leveraged when looking for unselected nodes.
+// This method is call internally in all ISel replacement calls.
+void SelectionDAGISel::EnforceNodeIdInvariant(SDNode *Node) {
+  SmallVector<SDNode *, 4> Nodes;
+  Nodes.push_back(Node);
+
+  while (!Nodes.empty()) {
+    SDNode *N = Nodes.pop_back_val();
+    for (auto *U : N->uses()) {
+      auto UId = U->getNodeId();
+      if (UId > 0) {
+        int InvalidatedUId = -UId + 1;
+        U->setNodeId(InvalidatedUId);
+        Nodes.push_back(U);
+      }
+    }
+  }
+}
+
 void SelectionDAGISel::DoInstructionSelection() {
   DEBUG(dbgs() << "===== Instruction selection begins: "
                << printMBBReference(*FuncInfo->MBB) << " '"
@@ -995,6 +1032,33 @@ void SelectionDAGISel::DoInstructionSelection() {
       if (Node->use_empty())
         continue;
 
+#ifndef NDEBUG
+      SmallVector<SDNode *, 4> Nodes;
+      Nodes.push_back(Node);
+
+      while (!Nodes.empty()) {
+        auto N = Nodes.pop_back_val();
+        if (N->getOpcode() == ISD::TokenFactor || N->getNodeId() < 0)
+          continue;
+        for (const SDValue &Op : N->op_values()) {
+          if (Op->getOpcode() == ISD::TokenFactor)
+            Nodes.push_back(Op.getNode());
+          else {
+            // We rely on topological ordering of node ids for checking for
+            // cycles when fusing nodes during selection. All unselected nodes
+            // successors of an already selected node should have a negative id.
+            // This assertion will catch such cases. If this assertion triggers
+            // it is likely you using DAG-level Value/Node replacement functions
+            // (versus equivalent ISEL replacement) in backend-specific
+            // selections. See comment in EnforceNodeIdInvariant for more
+            // details.
+            assert(Op->getNodeId() != -1 &&
+                   "Node has already selected predecessor node");
+          }
+        }
+      }
+#endif
+
       // When we are using non-default rounding modes or FP exception behavior
       // FP operations are represented by StrictFP pseudo-operations.  They
       // need to be simplified here so that the target-specific instruction
@@ -2164,54 +2228,44 @@ static SDNode *findGlueUse(SDNode *N) {
   return nullptr;
 }
 
-/// findNonImmUse - Return true if "Use" is a non-immediate use of "Def".
-/// This function iteratively traverses up the operand chain, ignoring
-/// certain nodes.
-static bool findNonImmUse(SDNode *Use, SDNode* Def, SDNode *ImmedUse,
-                          SDNode *Root, SmallPtrSetImpl<SDNode*> &Visited,
+/// findNonImmUse - Return true if "Def" is a predecessor of "Root" via a path
+/// beyond "ImmedUse".  We may ignore chains as they are checked separately.
+static bool findNonImmUse(SDNode *Root, SDNode *Def, SDNode *ImmedUse,
                           bool IgnoreChains) {
-  // The NodeID's are given uniques ID's where a node ID is guaranteed to be
-  // greater than all of its (recursive) operands.  If we scan to a point where
-  // 'use' is smaller than the node we're scanning for, then we know we will
-  // never find it.
-  //
-  // The Use may be -1 (unassigned) if it is a newly allocated node.  This can
-  // happen because we scan down to newly selected nodes in the case of glue
-  // uses.
-  std::vector<SDNode *> WorkList;
-  WorkList.push_back(Use);
-
-  while (!WorkList.empty()) {
-    Use = WorkList.back();
-    WorkList.pop_back();
-    // NodeId topological order of TokenFactors is not guaranteed. Do not skip.
-    if (Use->getOpcode() != ISD::TokenFactor &&
-        Use->getNodeId() < Def->getNodeId() && Use->getNodeId() != -1)
-      continue;
+  SmallPtrSet<const SDNode *, 16> Visited;
+  SmallVector<const SDNode *, 16> WorkList;
+  // Only check if we have non-immediate uses of Def.
+  if (ImmedUse->isOnlyUserOf(Def))
+    return false;
 
-    // Don't revisit nodes if we already scanned it and didn't fail, we know we
-    // won't fail if we scan it again.
-    if (!Visited.insert(Use).second)
+  // We don't care about paths to Def that go through ImmedUse so mark it
+  // visited and mark non-def operands as used.
+  Visited.insert(ImmedUse);
+  for (const SDValue &Op : ImmedUse->op_values()) {
+    SDNode *N = Op.getNode();
+    // Ignore chain deps (they are validated by
+    // HandleMergeInputChains) and immediate uses
+    if ((Op.getValueType() == MVT::Other && IgnoreChains) || N == Def)
       continue;
+    if (!Visited.insert(N).second)
+      continue;
+    WorkList.push_back(N);
+  }
 
-    for (const SDValue &Op : Use->op_values()) {
-      // Ignore chain uses, they are validated by HandleMergeInputChains.
-      if (Op.getValueType() == MVT::Other && IgnoreChains)
-        continue;
-
+  // Initialize worklist to operands of Root.
+  if (Root != ImmedUse) {
+    for (const SDValue &Op : Root->op_values()) {
       SDNode *N = Op.getNode();
-      if (N == Def) {
-        if (Use == ImmedUse || Use == Root)
-          continue;  // We are not looking for immediate use.
-        assert(N != Root);
-        return true;
-      }
-
-      // Traverse up the operand chain.
+      // Ignore chains (they are validated by HandleMergeInputChains)
+      if ((Op.getValueType() == MVT::Other && IgnoreChains) || N == Def)
+        continue;
+      if (!Visited.insert(N).second)
+        continue;
       WorkList.push_back(N);
     }
   }
-  return false;
+
+  return SDNode::hasPredecessorHelper(Def, Visited, WorkList, 0, true);
 }
 
 /// IsProfitableToFold - Returns true if it's profitable to fold the specific
@@ -2283,13 +2337,12 @@ bool SelectionDAGISel::IsLegalToFold(SDValue N, SDNode *U, SDNode *Root,
 
     // If our query node has a glue result with a use, we've walked up it.  If
     // the user (which has already been selected) has a chain or indirectly uses
-    // the chain, our WalkChainUsers predicate will not consider it.  Because of
+    // the chain, HandleMergeInputChains will not consider it.  Because of
     // this, we cannot ignore chains in this predicate.
     IgnoreChains = false;
   }
 
-  SmallPtrSet<SDNode*, 16> Visited;
-  return !findNonImmUse(Root, N.getNode(), U, Root, Visited, IgnoreChains);
+  return !findNonImmUse(Root, N.getNode(), U, IgnoreChains);
 }
 
 void SelectionDAGISel::Select_INLINEASM(SDNode *N) {
@@ -2393,7 +2446,7 @@ void SelectionDAGISel::UpdateChains(
                          static_cast<SDNode *>(nullptr));
           });
       if (ChainNode->getOpcode() != ISD::TokenFactor)
-        CurDAG->ReplaceAllUsesOfValueWith(ChainVal, InputChain);
+        ReplaceUses(ChainVal, InputChain);
 
       // If the node became dead and we haven't already seen it, delete it.
       if (ChainNode != NodeToMatch && ChainNode->use_empty() &&
@@ -2408,143 +2461,6 @@ void SelectionDAGISel::UpdateChains(
   DEBUG(dbgs() << "ISEL: Match complete!\n");
 }
 
-enum ChainResult {
-  CR_Simple,
-  CR_InducesCycle,
-  CR_LeadsToInteriorNode
-};
-
-/// WalkChainUsers - Walk down the users of the specified chained node that is
-/// part of the pattern we're matching, looking at all of the users we find.
-/// This determines whether something is an interior node, whether we have a
-/// non-pattern node in between two pattern nodes (which prevent folding because
-/// it would induce a cycle) and whether we have a TokenFactor node sandwiched
-/// between pattern nodes (in which case the TF becomes part of the pattern).
-///
-/// The walk we do here is guaranteed to be small because we quickly get down to
-/// already selected nodes "below" us.
-static ChainResult
-WalkChainUsers(const SDNode *ChainedNode,
-               SmallVectorImpl<SDNode *> &ChainedNodesInPattern,
-               DenseMap<const SDNode *, ChainResult> &TokenFactorResult,
-               SmallVectorImpl<SDNode *> &InteriorChainedNodes) {
-  ChainResult Result = CR_Simple;
-
-  for (SDNode::use_iterator UI = ChainedNode->use_begin(),
-         E = ChainedNode->use_end(); UI != E; ++UI) {
-    // Make sure the use is of the chain, not some other value we produce.
-    if (UI.getUse().getValueType() != MVT::Other) continue;
-
-    SDNode *User = *UI;
-
-    if (User->getOpcode() == ISD::HANDLENODE)  // Root of the graph.
-      continue;
-
-    // If we see an already-selected machine node, then we've gone beyond the
-    // pattern that we're selecting down into the already selected chunk of the
-    // DAG.
-    unsigned UserOpcode = User->getOpcode();
-    if (User->isMachineOpcode() ||
-        UserOpcode == ISD::CopyToReg ||
-        UserOpcode == ISD::CopyFromReg ||
-        UserOpcode == ISD::INLINEASM ||
-        UserOpcode == ISD::EH_LABEL ||
-        UserOpcode == ISD::LIFETIME_START ||
-        UserOpcode == ISD::LIFETIME_END) {
-      // If their node ID got reset to -1 then they've already been selected.
-      // Treat them like a MachineOpcode.
-      if (User->getNodeId() == -1)
-        continue;
-    }
-
-    // If we have a TokenFactor, we handle it specially.
-    if (User->getOpcode() != ISD::TokenFactor) {
-      // If the node isn't a token factor and isn't part of our pattern, then it
-      // must be a random chained node in between two nodes we're selecting.
-      // This happens when we have something like:
-      //   x = load ptr
-      //   call
-      //   y = x+4
-      //   store y -> ptr
-      // Because we structurally match the load/store as a read/modify/write,
-      // but the call is chained between them.  We cannot fold in this case
-      // because it would induce a cycle in the graph.
-      if (!std::count(ChainedNodesInPattern.begin(),
-                      ChainedNodesInPattern.end(), User))
-        return CR_InducesCycle;
-
-      // Otherwise we found a node that is part of our pattern.  For example in:
-      //   x = load ptr
-      //   y = x+4
-      //   store y -> ptr
-      // This would happen when we're scanning down from the load and see the
-      // store as a user.  Record that there is a use of ChainedNode that is
-      // part of the pattern and keep scanning uses.
-      Result = CR_LeadsToInteriorNode;
-      InteriorChainedNodes.push_back(User);
-      continue;
-    }
-
-    // If we found a TokenFactor, there are two cases to consider: first if the
-    // TokenFactor is just hanging "below" the pattern we're matching (i.e. no
-    // uses of the TF are in our pattern) we just want to ignore it.  Second,
-    // the TokenFactor can be sandwiched in between two chained nodes, like so:
-    //     [Load chain]
-    //         ^
-    //         |
-    //       [Load]
-    //       ^    ^
-    //       |    \                    DAG's like cheese
-    //      /       \                       do you?
-    //     /         |
-    // [TokenFactor] [Op]
-    //     ^          ^
-    //     |          |
-    //      \        /
-    //       \      /
-    //       [Store]
-    //
-    // In this case, the TokenFactor becomes part of our match and we rewrite it
-    // as a new TokenFactor.
-    //
-    // To distinguish these two cases, do a recursive walk down the uses.
-    auto MemoizeResult = TokenFactorResult.find(User);
-    bool Visited = MemoizeResult != TokenFactorResult.end();
-    // Recursively walk chain users only if the result is not memoized.
-    if (!Visited) {
-      auto Res = WalkChainUsers(User, ChainedNodesInPattern, TokenFactorResult,
-                                InteriorChainedNodes);
-      MemoizeResult = TokenFactorResult.insert(std::make_pair(User, Res)).first;
-    }
-    switch (MemoizeResult->second) {
-    case CR_Simple:
-      // If the uses of the TokenFactor are just already-selected nodes, ignore
-      // it, it is "below" our pattern.
-      continue;
-    case CR_InducesCycle:
-      // If the uses of the TokenFactor lead to nodes that are not part of our
-      // pattern that are not selected, folding would turn this into a cycle,
-      // bail out now.
-      return CR_InducesCycle;
-    case CR_LeadsToInteriorNode:
-      break;  // Otherwise, keep processing.
-    }
-
-    // Okay, we know we're in the interesting interior case.  The TokenFactor
-    // is now going to be considered part of the pattern so that we rewrite its
-    // uses (it may have uses that are not part of the pattern) with the
-    // ultimate chain result of the generated code.  We will also add its chain
-    // inputs as inputs to the ultimate TokenFactor we create.
-    Result = CR_LeadsToInteriorNode;
-    if (!Visited) {
-      ChainedNodesInPattern.push_back(User);
-      InteriorChainedNodes.push_back(User);
-    }
-  }
-
-  return Result;
-}
-
 /// HandleMergeInputChains - This implements the OPC_EmitMergeInputChains
 /// operation for when the pattern matched at least one node with a chains.  The
 /// input vector contains a list of all of the chained nodes that we match.  We
@@ -2554,47 +2470,56 @@ WalkChainUsers(const SDNode *ChainedNode,
 static SDValue
 HandleMergeInputChains(SmallVectorImpl<SDNode*> &ChainNodesMatched,
                        SelectionDAG *CurDAG) {
-  // Used for memoization. Without it WalkChainUsers could take exponential
-  // time to run.
-  DenseMap<const SDNode *, ChainResult> TokenFactorResult;
-  // Walk all of the chained nodes we've matched, recursively scanning down the
-  // users of the chain result. This adds any TokenFactor nodes that are caught
-  // in between chained nodes to the chained and interior nodes list.
-  SmallVector<SDNode*, 3> InteriorChainedNodes;
-  for (unsigned i = 0, e = ChainNodesMatched.size(); i != e; ++i) {
-    if (WalkChainUsers(ChainNodesMatched[i], ChainNodesMatched,
-                       TokenFactorResult,
-                       InteriorChainedNodes) == CR_InducesCycle)
-      return SDValue(); // Would induce a cycle.
-  }
 
-  // Okay, we have walked all the matched nodes and collected TokenFactor nodes
-  // that we are interested in.  Form our input TokenFactor node.
+  SmallPtrSet<const SDNode *, 16> Visited;
+  SmallVector<const SDNode *, 8> Worklist;
   SmallVector<SDValue, 3> InputChains;
-  for (unsigned i = 0, e = ChainNodesMatched.size(); i != e; ++i) {
-    // Add the input chain of this node to the InputChains list (which will be
-    // the operands of the generated TokenFactor) if it's not an interior node.
-    SDNode *N = ChainNodesMatched[i];
-    if (N->getOpcode() != ISD::TokenFactor) {
-      if (std::count(InteriorChainedNodes.begin(),InteriorChainedNodes.end(),N))
-        continue;
+  unsigned int Max = 8192;
 
-      // Otherwise, add the input chain.
-      SDValue InChain = ChainNodesMatched[i]->getOperand(0);
-      assert(InChain.getValueType() == MVT::Other && "Not a chain");
-      InputChains.push_back(InChain);
-      continue;
-    }
+  // Quick exit on trivial merge.
+  if (ChainNodesMatched.size() == 1)
+    return ChainNodesMatched[0]->getOperand(0);
 
-    // If we have a token factor, we want to add all inputs of the token factor
-    // that are not part of the pattern we're matching.
-    for (const SDValue &Op : N->op_values()) {
-      if (!std::count(ChainNodesMatched.begin(), ChainNodesMatched.end(),
-                      Op.getNode()))
-        InputChains.push_back(Op);
-    }
+  // Add chains that aren't already added (internal). Peek through
+  // token factors.
+  std::function<void(const SDValue)> AddChains = [&](const SDValue V) {
+    if (V.getValueType() != MVT::Other)
+      return;
+    if (V->getOpcode() == ISD::EntryToken)
+      return;
+    if (!Visited.insert(V.getNode()).second)
+      return;
+    if (V->getOpcode() == ISD::TokenFactor) {
+      for (const SDValue &Op : V->op_values())
+        AddChains(Op);
+    } else
+      InputChains.push_back(V);
+  };
+
+  for (auto *N : ChainNodesMatched) {
+    Worklist.push_back(N);
+    Visited.insert(N);
   }
 
+  while (!Worklist.empty())
+    AddChains(Worklist.pop_back_val()->getOperand(0));
+
+  // Skip the search if there are no chain dependencies.
+  if (InputChains.size() == 0)
+    return CurDAG->getEntryNode();
+
+  // If one of these chains is a successor of input, we must have a
+  // node that is both the predecessor and successor of the
+  // to-be-merged nodes. Fail.
+  Visited.clear();
+  for (SDValue V : InputChains)
+    Worklist.push_back(V.getNode());
+
+  for (auto *N : ChainNodesMatched)
+    if (SDNode::hasPredecessorHelper(N, Visited, Worklist, Max, true))
+      return SDValue();
+
+  // Return merged chain.
   if (InputChains.size() == 1)
     return InputChains[0];
   return CurDAG->getNode(ISD::TokenFactor, SDLoc(ChainNodesMatched[0]),
@@ -2639,8 +2564,8 @@ MorphNode(SDNode *Node, unsigned TargetOpc, SDVTList VTList,
   // Move the glue if needed.
   if ((EmitNodeInfo & OPFL_GlueOutput) && OldGlueResultNo != -1 &&
       (unsigned)OldGlueResultNo != ResNumResults-1)
-    CurDAG->ReplaceAllUsesOfValueWith(SDValue(Node, OldGlueResultNo),
-                                      SDValue(Res, ResNumResults-1));
+    ReplaceUses(SDValue(Node, OldGlueResultNo),
+                SDValue(Res, ResNumResults - 1));
 
   if ((EmitNodeInfo & OPFL_GlueOutput) != 0)
     --ResNumResults;
@@ -2648,14 +2573,15 @@ MorphNode(SDNode *Node, unsigned TargetOpc, SDVTList VTList,
   // Move the chain reference if needed.
   if ((EmitNodeInfo & OPFL_Chain) && OldChainResultNo != -1 &&
       (unsigned)OldChainResultNo != ResNumResults-1)
-    CurDAG->ReplaceAllUsesOfValueWith(SDValue(Node, OldChainResultNo),
-                                      SDValue(Res, ResNumResults-1));
+    ReplaceUses(SDValue(Node, OldChainResultNo),
+                SDValue(Res, ResNumResults - 1));
 
   // Otherwise, no replacement happened because the node already exists. Replace
   // Uses of the old node with the new one.
   if (Res != Node) {
-    CurDAG->ReplaceAllUsesWith(Node, Res);
-    CurDAG->RemoveDeadNode(Node);
+    ReplaceNode(Node, Res);
+  } else {
+    EnforceNodeIdInvariant(Res);
   }
 
   return Res;
@@ -2972,8 +2898,7 @@ void SelectionDAGISel::SelectCodeCommon(SDNode *NodeToMatch,
     return;
   case ISD::AssertSext:
   case ISD::AssertZext:
-    CurDAG->ReplaceAllUsesOfValueWith(SDValue(NodeToMatch, 0),
-                                      NodeToMatch->getOperand(0));
+    ReplaceUses(SDValue(NodeToMatch, 0), NodeToMatch->getOperand(0));
     CurDAG->RemoveDeadNode(NodeToMatch);
     return;
   case ISD::INLINEASM:
@@ -3731,7 +3656,7 @@ void SelectionDAGISel::SelectCodeCommon(SDNode *NodeToMatch,
                 NodeToMatch->getValueType(i).getSizeInBits() ==
                     Res.getValueSizeInBits()) &&
                "invalid replacement");
-        CurDAG->ReplaceAllUsesOfValueWith(SDValue(NodeToMatch, i), Res);
+        ReplaceUses(SDValue(NodeToMatch, i), Res);
       }
 
       // Update chain uses.
@@ -3744,8 +3669,8 @@ void SelectionDAGISel::SelectCodeCommon(SDNode *NodeToMatch,
       if (NodeToMatch->getValueType(NodeToMatch->getNumValues() - 1) ==
               MVT::Glue &&
           InputGlue.getNode())
-        CurDAG->ReplaceAllUsesOfValueWith(
-            SDValue(NodeToMatch, NodeToMatch->getNumValues() - 1), InputGlue);
+        ReplaceUses(SDValue(NodeToMatch, NodeToMatch->getNumValues() - 1),
+                    InputGlue);
 
       assert(NodeToMatch->use_empty() &&
              "Didn't replace all uses of the node?");