Combine the implementations of the core part of the SSAUpdater and

MachineSSAUpdater to avoid duplicating all the code.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@103060 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 463 insertions, 0 deletions

diff --git a/include/llvm/Transforms/Utils/SSAUpdaterImpl.h b/include/llvm/Transforms/Utils/SSAUpdaterImpl.h
new file mode 100644
index 0000000..8253796
--- /dev/null
+++ b/include/llvm/Transforms/Utils/SSAUpdaterImpl.h
@@ -0,0 +1,463 @@
+//===-- SSAUpdaterImpl.h - SSA Updater Implementation -----------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file provides a template that implements the core algorithm for the
+// SSAUpdater and MachineSSAUpdater.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_UTILS_SSAUPDATERIMPL_H
+#define LLVM_TRANSFORMS_UTILS_SSAUPDATERIMPL_H
+
+namespace llvm {
+
+template<typename T> class SSAUpdaterTraits;
+
+template<typename UpdaterT>
+class SSAUpdaterImpl {
+private:
+  UpdaterT *Updater;
+
+  typedef SSAUpdaterTraits<UpdaterT> Traits;
+  typedef typename Traits::BlkT BlkT;
+  typedef typename Traits::ValT ValT;
+  typedef typename Traits::PhiT PhiT;
+
+  /// BBInfo - Per-basic block information used internally by SSAUpdaterImpl.
+  /// The predecessors of each block are cached here since pred_iterator is
+  /// slow and we need to iterate over the blocks at least a few times.
+  class BBInfo {
+  public:
+    BlkT *BB;          // Back-pointer to the corresponding block.
+    ValT AvailableVal; // Value to use in this block.
+    BBInfo *DefBB;     // Block that defines the available value.
+    int BlkNum;        // Postorder number.
+    BBInfo *IDom;      // Immediate dominator.
+    unsigned NumPreds; // Number of predecessor blocks.
+    BBInfo **Preds;    // Array[NumPreds] of predecessor blocks.
+    PhiT *PHITag;      // Marker for existing PHIs that match.
+
+    BBInfo(BlkT *ThisBB, ValT V)
+      : BB(ThisBB), AvailableVal(V), DefBB(V ? this : 0), BlkNum(0), IDom(0),
+      NumPreds(0), Preds(0), PHITag(0) { }
+  };
+
+  typedef DenseMap<BlkT*, ValT> AvailableValsTy;
+  AvailableValsTy *AvailableVals;
+
+  SmallVectorImpl<PhiT*> *InsertedPHIs;
+
+  typedef SmallVectorImpl<BBInfo*> BlockListTy;
+  typedef DenseMap<BlkT*, BBInfo*> BBMapTy;
+  BBMapTy BBMap;
+  BumpPtrAllocator Allocator;
+
+public:
+  explicit SSAUpdaterImpl(UpdaterT *U, AvailableValsTy *A,
+                          SmallVectorImpl<PhiT*> *Ins) :
+    Updater(U), AvailableVals(A), InsertedPHIs(Ins) { }
+
+  /// GetValue - Check to see if AvailableVals has an entry for the specified
+  /// BB and if so, return it.  If not, construct SSA form by first
+  /// calculating the required placement of PHIs and then inserting new PHIs
+  /// where needed.
+  ValT GetValue(BlkT *BB) {
+    SmallVector<BBInfo*, 100> BlockList;
+    BuildBlockList(BB, &BlockList);
+
+    // Special case: bail out if BB is unreachable.
+    if (BlockList.size() == 0) {
+      ValT V = Traits::GetUndefVal(BB, Updater);
+      (*AvailableVals)[BB] = V;
+      return V;
+    }
+
+    FindDominators(&BlockList);
+    FindPHIPlacement(&BlockList);
+    FindAvailableVals(&BlockList);
+
+    return BBMap[BB]->DefBB->AvailableVal;
+  }
+
+  /// BuildBlockList - Starting from the specified basic block, traverse back
+  /// through its predecessors until reaching blocks with known values.
+  /// Create BBInfo structures for the blocks and append them to the block
+  /// list.
+  void BuildBlockList(BlkT *BB, BlockListTy *BlockList) {
+    SmallVector<BBInfo*, 10> RootList;
+    SmallVector<BBInfo*, 64> WorkList;
+
+    BBInfo *Info = new (Allocator) BBInfo(BB, 0);
+    BBMap[BB] = Info;
+    WorkList.push_back(Info);
+
+    // Search backward from BB, creating BBInfos along the way and stopping
+    // when reaching blocks that define the value.  Record those defining
+    // blocks on the RootList.
+    SmallVector<BlkT*, 10> Preds;
+    while (!WorkList.empty()) {
+      Info = WorkList.pop_back_val();
+      Preds.clear();
+      Traits::FindPredecessorBlocks(Info->BB, &Preds);
+      Info->NumPreds = Preds.size();
+      Info->Preds = static_cast<BBInfo**>
+        (Allocator.Allocate(Info->NumPreds * sizeof(BBInfo*),
+                            AlignOf<BBInfo*>::Alignment));
+
+      // Treat an unreachable predecessor as a definition with 'undef'.
+      if (Info->NumPreds == 0) {
+        Info->AvailableVal = Traits::GetUndefVal(Info->BB, Updater);
+        Info->DefBB = Info;
+        RootList.push_back(Info);
+        continue;
+      }
+
+      for (unsigned p = 0; p != Info->NumPreds; ++p) {
+        BlkT *Pred = Preds[p];
+        // Check if BBMap already has a BBInfo for the predecessor block.
+        typename BBMapTy::value_type &BBMapBucket =
+          BBMap.FindAndConstruct(Pred);
+        if (BBMapBucket.second) {
+          Info->Preds[p] = BBMapBucket.second;
+          continue;
+        }
+
+        // Create a new BBInfo for the predecessor.
+        ValT PredVal = AvailableVals->lookup(Pred);
+        BBInfo *PredInfo = new (Allocator) BBInfo(Pred, PredVal);
+        BBMapBucket.second = PredInfo;
+        Info->Preds[p] = PredInfo;
+
+        if (PredInfo->AvailableVal) {
+          RootList.push_back(PredInfo);
+          continue;
+        }
+        WorkList.push_back(PredInfo);
+      }
+    }
+
+    // Now that we know what blocks are backwards-reachable from the starting
+    // block, do a forward depth-first traversal to assign postorder numbers
+    // to those blocks.
+    BBInfo *PseudoEntry = new (Allocator) BBInfo(0, 0);
+    unsigned BlkNum = 1;
+
+    // Initialize the worklist with the roots from the backward traversal.
+    while (!RootList.empty()) {
+      Info = RootList.pop_back_val();
+      Info->IDom = PseudoEntry;
+      Info->BlkNum = -1;
+      WorkList.push_back(Info);
+    }
+
+    while (!WorkList.empty()) {
+      Info = WorkList.back();
+
+      if (Info->BlkNum == -2) {
+        // All the successors have been handled; assign the postorder number.
+        Info->BlkNum = BlkNum++;
+        // If not a root, put it on the BlockList.
+        if (!Info->AvailableVal)
+          BlockList->push_back(Info);
+        WorkList.pop_back();
+        continue;
+      }
+
+      // Leave this entry on the worklist, but set its BlkNum to mark that its
+      // successors have been put on the worklist.  When it returns to the top
+      // the list, after handling its successors, it will be assigned a
+      // number.
+      Info->BlkNum = -2;
+
+      // Add unvisited successors to the work list.
+      for (typename Traits::BlkSucc_iterator SI =
+             Traits::BlkSucc_begin(Info->BB),
+             E = Traits::BlkSucc_end(Info->BB); SI != E; ++SI) {
+        BBInfo *SuccInfo = BBMap[*SI];
+        if (!SuccInfo || SuccInfo->BlkNum)
+          continue;
+        SuccInfo->BlkNum = -1;
+        WorkList.push_back(SuccInfo);
+      }
+    }
+    PseudoEntry->BlkNum = BlkNum;
+  }
+
+  /// IntersectDominators - This is the dataflow lattice "meet" operation for
+  /// finding dominators.  Given two basic blocks, it walks up the dominator
+  /// tree until it finds a common dominator of both.  It uses the postorder
+  /// number of the blocks to determine how to do that.
+  BBInfo *IntersectDominators(BBInfo *Blk1, BBInfo *Blk2) {
+    while (Blk1 != Blk2) {
+      while (Blk1->BlkNum < Blk2->BlkNum) {
+        Blk1 = Blk1->IDom;
+        if (!Blk1)
+          return Blk2;
+      }
+      while (Blk2->BlkNum < Blk1->BlkNum) {
+        Blk2 = Blk2->IDom;
+        if (!Blk2)
+          return Blk1;
+      }
+    }
+    return Blk1;
+  }
+
+  /// FindDominators - Calculate the dominator tree for the subset of the CFG
+  /// corresponding to the basic blocks on the BlockList.  This uses the
+  /// algorithm from: "A Simple, Fast Dominance Algorithm" by Cooper, Harvey
+  /// and Kennedy, published in Software--Practice and Experience, 2001,
+  /// 4:1-10.  Because the CFG subset does not include any edges leading into
+  /// blocks that define the value, the results are not the usual dominator
+  /// tree.  The CFG subset has a single pseudo-entry node with edges to a set
+  /// of root nodes for blocks that define the value.  The dominators for this
+  /// subset CFG are not the standard dominators but they are adequate for
+  /// placing PHIs within the subset CFG.
+  void FindDominators(BlockListTy *BlockList) {
+    bool Changed;
+    do {
+      Changed = false;
+      // Iterate over the list in reverse order, i.e., forward on CFG edges.
+      for (typename BlockListTy::reverse_iterator I = BlockList->rbegin(),
+             E = BlockList->rend(); I != E; ++I) {
+        BBInfo *Info = *I;
+
+        // Start with the first predecessor.
+        assert(Info->NumPreds > 0 && "unreachable block");
+        BBInfo *NewIDom = Info->Preds[0];
+
+        // Iterate through the block's other predecessors.
+        for (unsigned p = 1; p != Info->NumPreds; ++p) {
+          BBInfo *Pred = Info->Preds[p];
+          NewIDom = IntersectDominators(NewIDom, Pred);
+        }
+
+        // Check if the IDom value has changed.
+        if (NewIDom != Info->IDom) {
+          Info->IDom = NewIDom;
+          Changed = true;
+        }
+      }
+    } while (Changed);
+  }
+
+  /// IsDefInDomFrontier - Search up the dominator tree from Pred to IDom for
+  /// any blocks containing definitions of the value.  If one is found, then
+  /// the successor of Pred is in the dominance frontier for the definition,
+  /// and this function returns true.
+  bool IsDefInDomFrontier(const BBInfo *Pred, const BBInfo *IDom) {
+    for (; Pred != IDom; Pred = Pred->IDom) {
+      if (Pred->DefBB == Pred)
+        return true;
+    }
+    return false;
+  }
+
+  /// FindPHIPlacement - PHIs are needed in the iterated dominance frontiers
+  /// of the known definitions.  Iteratively add PHIs in the dom frontiers
+  /// until nothing changes.  Along the way, keep track of the nearest
+  /// dominating definitions for non-PHI blocks.
+  void FindPHIPlacement(BlockListTy *BlockList) {
+    bool Changed;
+    do {
+      Changed = false;
+      // Iterate over the list in reverse order, i.e., forward on CFG edges.
+      for (typename BlockListTy::reverse_iterator I = BlockList->rbegin(),
+             E = BlockList->rend(); I != E; ++I) {
+        BBInfo *Info = *I;
+
+        // If this block already needs a PHI, there is nothing to do here.
+        if (Info->DefBB == Info)
+          continue;
+
+        // Default to use the same def as the immediate dominator.
+        BBInfo *NewDefBB = Info->IDom->DefBB;
+        for (unsigned p = 0; p != Info->NumPreds; ++p) {
+          if (IsDefInDomFrontier(Info->Preds[p], Info->IDom)) {
+            // Need a PHI here.
+            NewDefBB = Info;
+            break;
+          }
+        }
+
+        // Check if anything changed.
+        if (NewDefBB != Info->DefBB) {
+          Info->DefBB = NewDefBB;
+          Changed = true;
+        }
+      }
+    } while (Changed);
+  }
+
+  /// FindAvailableVal - If this block requires a PHI, first check if an
+  /// existing PHI matches the PHI placement and reaching definitions computed
+  /// earlier, and if not, create a new PHI.  Visit all the block's
+  /// predecessors to calculate the available value for each one and fill in
+  /// the incoming values for a new PHI.
+  void FindAvailableVals(BlockListTy *BlockList) {
+    // Go through the worklist in forward order (i.e., backward through the CFG)
+    // and check if existing PHIs can be used.  If not, create empty PHIs where
+    // they are needed.
+    for (typename BlockListTy::iterator I = BlockList->begin(),
+           E = BlockList->end(); I != E; ++I) {
+      BBInfo *Info = *I;
+      // Check if there needs to be a PHI in BB.
+      if (Info->DefBB != Info)
+        continue;
+
+      // Look for an existing PHI.
+      FindExistingPHI(Info->BB, BlockList);
+      if (Info->AvailableVal)
+        continue;
+
+      ValT PHI = Traits::CreateEmptyPHI(Info->BB, Info->NumPreds, Updater);
+      Info->AvailableVal = PHI;
+      (*AvailableVals)[Info->BB] = PHI;
+    }
+
+    // Now go back through the worklist in reverse order to fill in the
+    // arguments for any new PHIs added in the forward traversal.
+    for (typename BlockListTy::reverse_iterator I = BlockList->rbegin(),
+           E = BlockList->rend(); I != E; ++I) {
+      BBInfo *Info = *I;
+
+      if (Info->DefBB != Info) {
+        // Record the available value at join nodes to speed up subsequent
+        // uses of this SSAUpdater for the same value.
+        if (Info->NumPreds > 1)
+          (*AvailableVals)[Info->BB] = Info->DefBB->AvailableVal;
+        continue;
+      }
+
+      // Check if this block contains a newly added PHI.
+      PhiT *PHI = Traits::ValueIsNewPHI(Info->AvailableVal, Updater);
+      if (!PHI)
+        continue;
+
+      // Iterate through the block's predecessors.
+      for (unsigned p = 0; p != Info->NumPreds; ++p) {
+        BBInfo *PredInfo = Info->Preds[p];
+        BlkT *Pred = PredInfo->BB;
+        // Skip to the nearest preceding definition.
+        if (PredInfo->DefBB != PredInfo)
+          PredInfo = PredInfo->DefBB;
+        Traits::AddPHIOperand(PHI, PredInfo->AvailableVal, Pred);
+      }
+
+      DEBUG(dbgs() << "  Inserted PHI: " << *PHI << "\n");
+
+      // If the client wants to know about all new instructions, tell it.
+      if (InsertedPHIs) InsertedPHIs->push_back(PHI);
+    }
+  }
+
+  /// FindExistingPHI - Look through the PHI nodes in a block to see if any of
+  /// them match what is needed.
+  void FindExistingPHI(BlkT *BB, BlockListTy *BlockList) {
+    for (typename BlkT::iterator BBI = BB->begin(), BBE = BB->end();
+         BBI != BBE; ++BBI) {
+      PhiT *SomePHI = Traits::InstrIsPHI(BBI);
+      if (!SomePHI)
+        break;
+      if (CheckIfPHIMatches(SomePHI)) {
+        RecordMatchingPHI(SomePHI);
+        break;
+      }
+      // Match failed: clear all the PHITag values.
+      for (typename BlockListTy::iterator I = BlockList->begin(),
+             E = BlockList->end(); I != E; ++I)
+        (*I)->PHITag = 0;
+    }
+  }
+
+  /// CheckIfPHIMatches - Check if a PHI node matches the placement and values
+  /// in the BBMap.
+  bool CheckIfPHIMatches(PhiT *PHI) {
+    SmallVector<PhiT*, 20> WorkList;
+    WorkList.push_back(PHI);
+
+    // Mark that the block containing this PHI has been visited.
+    BBMap[PHI->getParent()]->PHITag = PHI;
+
+    while (!WorkList.empty()) {
+      PHI = WorkList.pop_back_val();
+
+      // Iterate through the PHI's incoming values.
+      for (typename Traits::PHI_iterator I = Traits::PHI_begin(PHI),
+             E = Traits::PHI_end(PHI); I != E; ++I) {
+        ValT IncomingVal = I.getIncomingValue();
+        BBInfo *PredInfo = BBMap[I.getIncomingBlock()];
+        // Skip to the nearest preceding definition.
+        if (PredInfo->DefBB != PredInfo)
+          PredInfo = PredInfo->DefBB;
+
+        // Check if it matches the expected value.
+        if (PredInfo->AvailableVal) {
+          if (IncomingVal == PredInfo->AvailableVal)
+            continue;
+          return false;
+        }
+
+        // Check if the value is a PHI in the correct block.
+        PhiT *IncomingPHIVal = Traits::ValueIsPHI(IncomingVal, Updater);
+        if (!IncomingPHIVal || IncomingPHIVal->getParent() != PredInfo->BB)
+          return false;
+
+        // If this block has already been visited, check if this PHI matches.
+        if (PredInfo->PHITag) {
+          if (IncomingPHIVal == PredInfo->PHITag)
+            continue;
+          return false;
+        }
+        PredInfo->PHITag = IncomingPHIVal;
+
+        WorkList.push_back(IncomingPHIVal);
+      }
+    }
+    return true;
+  }
+
+  /// RecordMatchingPHI - For a PHI node that matches, record it and its input
+  /// PHIs in both the BBMap and the AvailableVals mapping.
+  void RecordMatchingPHI(PhiT *PHI) {
+    SmallVector<PhiT*, 20> WorkList;
+    WorkList.push_back(PHI);
+
+    // Record this PHI.
+    BlkT *BB = PHI->getParent();
+    ValT PHIVal = Traits::GetPHIValue(PHI);
+    (*AvailableVals)[BB] = PHIVal;
+    BBMap[BB]->AvailableVal = PHIVal;
+
+    while (!WorkList.empty()) {
+      PHI = WorkList.pop_back_val();
+
+      // Iterate through the PHI's incoming values.
+      for (typename Traits::PHI_iterator I = Traits::PHI_begin(PHI),
+             E = Traits::PHI_end(PHI); I != E; ++I) {
+        ValT IncomingVal = I.getIncomingValue();
+        PhiT *IncomingPHI = Traits::ValueIsPHI(IncomingVal, Updater);
+        if (!IncomingPHI) continue;
+        BB = IncomingPHI->getParent();
+        BBInfo *Info = BBMap[BB];
+        if (!Info || Info->AvailableVal)
+          continue;
+
+        // Record the PHI and add it to the worklist.
+        (*AvailableVals)[BB] = IncomingVal;
+        Info->AvailableVal = IncomingVal;
+        WorkList.push_back(IncomingPHI);
+      }
+    }
+  }
+};
+
+} // End llvm namespace
+
+#endif