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c52edc7d30
handled cases where a block had zero predecessors, but failed to detect other cases like loops with no entries. The SSAUpdater is already doing a forward traversal through the blocks, so it is not hard to identify the blocks that were never reached on that traversal. This fixes the crash for ppc on the stepanov_vector test. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@103184 91177308-0d34-0410-b5e6-96231b3b80d8
470 lines
16 KiB
C++
470 lines
16 KiB
C++
//===-- SSAUpdaterImpl.h - SSA Updater Implementation -----------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file provides a template that implements the core algorithm for the
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// SSAUpdater and MachineSSAUpdater.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_TRANSFORMS_UTILS_SSAUPDATERIMPL_H
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#define LLVM_TRANSFORMS_UTILS_SSAUPDATERIMPL_H
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namespace llvm {
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template<typename T> class SSAUpdaterTraits;
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template<typename UpdaterT>
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class SSAUpdaterImpl {
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private:
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UpdaterT *Updater;
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typedef SSAUpdaterTraits<UpdaterT> Traits;
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typedef typename Traits::BlkT BlkT;
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typedef typename Traits::ValT ValT;
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typedef typename Traits::PhiT PhiT;
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/// BBInfo - Per-basic block information used internally by SSAUpdaterImpl.
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/// The predecessors of each block are cached here since pred_iterator is
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/// slow and we need to iterate over the blocks at least a few times.
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class BBInfo {
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public:
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BlkT *BB; // Back-pointer to the corresponding block.
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ValT AvailableVal; // Value to use in this block.
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BBInfo *DefBB; // Block that defines the available value.
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int BlkNum; // Postorder number.
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BBInfo *IDom; // Immediate dominator.
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unsigned NumPreds; // Number of predecessor blocks.
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BBInfo **Preds; // Array[NumPreds] of predecessor blocks.
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PhiT *PHITag; // Marker for existing PHIs that match.
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BBInfo(BlkT *ThisBB, ValT V)
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: BB(ThisBB), AvailableVal(V), DefBB(V ? this : 0), BlkNum(0), IDom(0),
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NumPreds(0), Preds(0), PHITag(0) { }
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};
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typedef DenseMap<BlkT*, ValT> AvailableValsTy;
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AvailableValsTy *AvailableVals;
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SmallVectorImpl<PhiT*> *InsertedPHIs;
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typedef SmallVectorImpl<BBInfo*> BlockListTy;
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typedef DenseMap<BlkT*, BBInfo*> BBMapTy;
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BBMapTy BBMap;
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BumpPtrAllocator Allocator;
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public:
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explicit SSAUpdaterImpl(UpdaterT *U, AvailableValsTy *A,
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SmallVectorImpl<PhiT*> *Ins) :
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Updater(U), AvailableVals(A), InsertedPHIs(Ins) { }
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/// GetValue - Check to see if AvailableVals has an entry for the specified
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/// BB and if so, return it. If not, construct SSA form by first
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/// calculating the required placement of PHIs and then inserting new PHIs
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/// where needed.
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ValT GetValue(BlkT *BB) {
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SmallVector<BBInfo*, 100> BlockList;
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BBInfo *PseudoEntry = BuildBlockList(BB, &BlockList);
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// Special case: bail out if BB is unreachable.
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if (BlockList.size() == 0) {
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ValT V = Traits::GetUndefVal(BB, Updater);
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(*AvailableVals)[BB] = V;
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return V;
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}
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FindDominators(&BlockList, PseudoEntry);
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FindPHIPlacement(&BlockList);
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FindAvailableVals(&BlockList);
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return BBMap[BB]->DefBB->AvailableVal;
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}
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/// BuildBlockList - Starting from the specified basic block, traverse back
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/// through its predecessors until reaching blocks with known values.
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/// Create BBInfo structures for the blocks and append them to the block
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/// list.
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BBInfo *BuildBlockList(BlkT *BB, BlockListTy *BlockList) {
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SmallVector<BBInfo*, 10> RootList;
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SmallVector<BBInfo*, 64> WorkList;
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BBInfo *Info = new (Allocator) BBInfo(BB, 0);
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BBMap[BB] = Info;
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WorkList.push_back(Info);
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// Search backward from BB, creating BBInfos along the way and stopping
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// when reaching blocks that define the value. Record those defining
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// blocks on the RootList.
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SmallVector<BlkT*, 10> Preds;
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while (!WorkList.empty()) {
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Info = WorkList.pop_back_val();
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Preds.clear();
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Traits::FindPredecessorBlocks(Info->BB, &Preds);
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Info->NumPreds = Preds.size();
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if (Info->NumPreds == 0)
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Info->Preds = 0;
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else
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Info->Preds = static_cast<BBInfo**>
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(Allocator.Allocate(Info->NumPreds * sizeof(BBInfo*),
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AlignOf<BBInfo*>::Alignment));
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for (unsigned p = 0; p != Info->NumPreds; ++p) {
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BlkT *Pred = Preds[p];
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// Check if BBMap already has a BBInfo for the predecessor block.
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typename BBMapTy::value_type &BBMapBucket =
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BBMap.FindAndConstruct(Pred);
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if (BBMapBucket.second) {
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Info->Preds[p] = BBMapBucket.second;
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continue;
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}
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// Create a new BBInfo for the predecessor.
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ValT PredVal = AvailableVals->lookup(Pred);
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BBInfo *PredInfo = new (Allocator) BBInfo(Pred, PredVal);
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BBMapBucket.second = PredInfo;
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Info->Preds[p] = PredInfo;
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if (PredInfo->AvailableVal) {
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RootList.push_back(PredInfo);
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continue;
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}
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WorkList.push_back(PredInfo);
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}
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}
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// Now that we know what blocks are backwards-reachable from the starting
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// block, do a forward depth-first traversal to assign postorder numbers
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// to those blocks.
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BBInfo *PseudoEntry = new (Allocator) BBInfo(0, 0);
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unsigned BlkNum = 1;
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// Initialize the worklist with the roots from the backward traversal.
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while (!RootList.empty()) {
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Info = RootList.pop_back_val();
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Info->IDom = PseudoEntry;
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Info->BlkNum = -1;
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WorkList.push_back(Info);
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}
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while (!WorkList.empty()) {
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Info = WorkList.back();
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if (Info->BlkNum == -2) {
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// All the successors have been handled; assign the postorder number.
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Info->BlkNum = BlkNum++;
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// If not a root, put it on the BlockList.
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if (!Info->AvailableVal)
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BlockList->push_back(Info);
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WorkList.pop_back();
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continue;
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}
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// Leave this entry on the worklist, but set its BlkNum to mark that its
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// successors have been put on the worklist. When it returns to the top
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// the list, after handling its successors, it will be assigned a
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// number.
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Info->BlkNum = -2;
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// Add unvisited successors to the work list.
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for (typename Traits::BlkSucc_iterator SI =
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Traits::BlkSucc_begin(Info->BB),
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E = Traits::BlkSucc_end(Info->BB); SI != E; ++SI) {
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BBInfo *SuccInfo = BBMap[*SI];
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if (!SuccInfo || SuccInfo->BlkNum)
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continue;
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SuccInfo->BlkNum = -1;
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WorkList.push_back(SuccInfo);
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}
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}
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PseudoEntry->BlkNum = BlkNum;
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return PseudoEntry;
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}
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/// IntersectDominators - This is the dataflow lattice "meet" operation for
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/// finding dominators. Given two basic blocks, it walks up the dominator
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/// tree until it finds a common dominator of both. It uses the postorder
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/// number of the blocks to determine how to do that.
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BBInfo *IntersectDominators(BBInfo *Blk1, BBInfo *Blk2) {
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while (Blk1 != Blk2) {
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while (Blk1->BlkNum < Blk2->BlkNum) {
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Blk1 = Blk1->IDom;
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if (!Blk1)
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return Blk2;
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}
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while (Blk2->BlkNum < Blk1->BlkNum) {
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Blk2 = Blk2->IDom;
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if (!Blk2)
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return Blk1;
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}
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}
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return Blk1;
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}
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/// FindDominators - Calculate the dominator tree for the subset of the CFG
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/// corresponding to the basic blocks on the BlockList. This uses the
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/// algorithm from: "A Simple, Fast Dominance Algorithm" by Cooper, Harvey
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/// and Kennedy, published in Software--Practice and Experience, 2001,
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/// 4:1-10. Because the CFG subset does not include any edges leading into
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/// blocks that define the value, the results are not the usual dominator
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/// tree. The CFG subset has a single pseudo-entry node with edges to a set
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/// of root nodes for blocks that define the value. The dominators for this
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/// subset CFG are not the standard dominators but they are adequate for
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/// placing PHIs within the subset CFG.
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void FindDominators(BlockListTy *BlockList, BBInfo *PseudoEntry) {
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bool Changed;
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do {
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Changed = false;
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// Iterate over the list in reverse order, i.e., forward on CFG edges.
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for (typename BlockListTy::reverse_iterator I = BlockList->rbegin(),
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E = BlockList->rend(); I != E; ++I) {
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BBInfo *Info = *I;
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BBInfo *NewIDom = 0;
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// Iterate through the block's predecessors.
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for (unsigned p = 0; p != Info->NumPreds; ++p) {
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BBInfo *Pred = Info->Preds[p];
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// Treat an unreachable predecessor as a definition with 'undef'.
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if (Pred->BlkNum == 0) {
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Pred->AvailableVal = Traits::GetUndefVal(Pred->BB, Updater);
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(*AvailableVals)[Pred->BB] = Pred->AvailableVal;
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Pred->DefBB = Pred;
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Pred->BlkNum = PseudoEntry->BlkNum;
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PseudoEntry->BlkNum++;
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}
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if (!NewIDom)
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NewIDom = Pred;
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else
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NewIDom = IntersectDominators(NewIDom, Pred);
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}
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// Check if the IDom value has changed.
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if (NewIDom && NewIDom != Info->IDom) {
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Info->IDom = NewIDom;
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Changed = true;
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}
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}
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} while (Changed);
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}
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/// IsDefInDomFrontier - Search up the dominator tree from Pred to IDom for
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/// any blocks containing definitions of the value. If one is found, then
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/// the successor of Pred is in the dominance frontier for the definition,
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/// and this function returns true.
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bool IsDefInDomFrontier(const BBInfo *Pred, const BBInfo *IDom) {
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for (; Pred != IDom; Pred = Pred->IDom) {
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if (Pred->DefBB == Pred)
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return true;
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}
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return false;
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}
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/// FindPHIPlacement - PHIs are needed in the iterated dominance frontiers
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/// of the known definitions. Iteratively add PHIs in the dom frontiers
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/// until nothing changes. Along the way, keep track of the nearest
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/// dominating definitions for non-PHI blocks.
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void FindPHIPlacement(BlockListTy *BlockList) {
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bool Changed;
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do {
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Changed = false;
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// Iterate over the list in reverse order, i.e., forward on CFG edges.
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for (typename BlockListTy::reverse_iterator I = BlockList->rbegin(),
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E = BlockList->rend(); I != E; ++I) {
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BBInfo *Info = *I;
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// If this block already needs a PHI, there is nothing to do here.
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if (Info->DefBB == Info)
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continue;
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// Default to use the same def as the immediate dominator.
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BBInfo *NewDefBB = Info->IDom->DefBB;
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for (unsigned p = 0; p != Info->NumPreds; ++p) {
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if (IsDefInDomFrontier(Info->Preds[p], Info->IDom)) {
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// Need a PHI here.
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NewDefBB = Info;
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break;
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}
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}
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// Check if anything changed.
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if (NewDefBB != Info->DefBB) {
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Info->DefBB = NewDefBB;
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Changed = true;
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}
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}
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} while (Changed);
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}
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/// FindAvailableVal - If this block requires a PHI, first check if an
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/// existing PHI matches the PHI placement and reaching definitions computed
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/// earlier, and if not, create a new PHI. Visit all the block's
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/// predecessors to calculate the available value for each one and fill in
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/// the incoming values for a new PHI.
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void FindAvailableVals(BlockListTy *BlockList) {
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// Go through the worklist in forward order (i.e., backward through the CFG)
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// and check if existing PHIs can be used. If not, create empty PHIs where
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// they are needed.
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for (typename BlockListTy::iterator I = BlockList->begin(),
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E = BlockList->end(); I != E; ++I) {
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BBInfo *Info = *I;
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// Check if there needs to be a PHI in BB.
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if (Info->DefBB != Info)
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continue;
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// Look for an existing PHI.
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FindExistingPHI(Info->BB, BlockList);
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if (Info->AvailableVal)
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continue;
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ValT PHI = Traits::CreateEmptyPHI(Info->BB, Info->NumPreds, Updater);
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Info->AvailableVal = PHI;
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(*AvailableVals)[Info->BB] = PHI;
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}
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// Now go back through the worklist in reverse order to fill in the
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// arguments for any new PHIs added in the forward traversal.
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for (typename BlockListTy::reverse_iterator I = BlockList->rbegin(),
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E = BlockList->rend(); I != E; ++I) {
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BBInfo *Info = *I;
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if (Info->DefBB != Info) {
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// Record the available value at join nodes to speed up subsequent
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// uses of this SSAUpdater for the same value.
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if (Info->NumPreds > 1)
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(*AvailableVals)[Info->BB] = Info->DefBB->AvailableVal;
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continue;
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}
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// Check if this block contains a newly added PHI.
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PhiT *PHI = Traits::ValueIsNewPHI(Info->AvailableVal, Updater);
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if (!PHI)
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continue;
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// Iterate through the block's predecessors.
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for (unsigned p = 0; p != Info->NumPreds; ++p) {
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BBInfo *PredInfo = Info->Preds[p];
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BlkT *Pred = PredInfo->BB;
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// Skip to the nearest preceding definition.
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if (PredInfo->DefBB != PredInfo)
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PredInfo = PredInfo->DefBB;
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Traits::AddPHIOperand(PHI, PredInfo->AvailableVal, Pred);
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}
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DEBUG(dbgs() << " Inserted PHI: " << *PHI << "\n");
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// If the client wants to know about all new instructions, tell it.
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if (InsertedPHIs) InsertedPHIs->push_back(PHI);
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}
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}
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/// FindExistingPHI - Look through the PHI nodes in a block to see if any of
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/// them match what is needed.
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void FindExistingPHI(BlkT *BB, BlockListTy *BlockList) {
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for (typename BlkT::iterator BBI = BB->begin(), BBE = BB->end();
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BBI != BBE; ++BBI) {
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PhiT *SomePHI = Traits::InstrIsPHI(BBI);
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if (!SomePHI)
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break;
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if (CheckIfPHIMatches(SomePHI)) {
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RecordMatchingPHI(SomePHI);
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break;
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}
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// Match failed: clear all the PHITag values.
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for (typename BlockListTy::iterator I = BlockList->begin(),
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E = BlockList->end(); I != E; ++I)
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(*I)->PHITag = 0;
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}
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}
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/// CheckIfPHIMatches - Check if a PHI node matches the placement and values
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/// in the BBMap.
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bool CheckIfPHIMatches(PhiT *PHI) {
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SmallVector<PhiT*, 20> WorkList;
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WorkList.push_back(PHI);
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// Mark that the block containing this PHI has been visited.
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BBMap[PHI->getParent()]->PHITag = PHI;
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while (!WorkList.empty()) {
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PHI = WorkList.pop_back_val();
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// Iterate through the PHI's incoming values.
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for (typename Traits::PHI_iterator I = Traits::PHI_begin(PHI),
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E = Traits::PHI_end(PHI); I != E; ++I) {
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ValT IncomingVal = I.getIncomingValue();
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BBInfo *PredInfo = BBMap[I.getIncomingBlock()];
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// Skip to the nearest preceding definition.
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if (PredInfo->DefBB != PredInfo)
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PredInfo = PredInfo->DefBB;
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// Check if it matches the expected value.
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if (PredInfo->AvailableVal) {
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if (IncomingVal == PredInfo->AvailableVal)
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continue;
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return false;
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}
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// Check if the value is a PHI in the correct block.
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PhiT *IncomingPHIVal = Traits::ValueIsPHI(IncomingVal, Updater);
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if (!IncomingPHIVal || IncomingPHIVal->getParent() != PredInfo->BB)
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return false;
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// If this block has already been visited, check if this PHI matches.
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if (PredInfo->PHITag) {
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if (IncomingPHIVal == PredInfo->PHITag)
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continue;
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return false;
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}
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PredInfo->PHITag = IncomingPHIVal;
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WorkList.push_back(IncomingPHIVal);
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}
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}
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return true;
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}
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/// RecordMatchingPHI - For a PHI node that matches, record it and its input
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/// PHIs in both the BBMap and the AvailableVals mapping.
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void RecordMatchingPHI(PhiT *PHI) {
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SmallVector<PhiT*, 20> WorkList;
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WorkList.push_back(PHI);
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// Record this PHI.
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BlkT *BB = PHI->getParent();
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ValT PHIVal = Traits::GetPHIValue(PHI);
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(*AvailableVals)[BB] = PHIVal;
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BBMap[BB]->AvailableVal = PHIVal;
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while (!WorkList.empty()) {
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PHI = WorkList.pop_back_val();
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// Iterate through the PHI's incoming values.
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for (typename Traits::PHI_iterator I = Traits::PHI_begin(PHI),
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E = Traits::PHI_end(PHI); I != E; ++I) {
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ValT IncomingVal = I.getIncomingValue();
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PhiT *IncomingPHI = Traits::ValueIsPHI(IncomingVal, Updater);
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if (!IncomingPHI) continue;
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BB = IncomingPHI->getParent();
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BBInfo *Info = BBMap[BB];
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if (!Info || Info->AvailableVal)
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continue;
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// Record the PHI and add it to the worklist.
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(*AvailableVals)[BB] = IncomingVal;
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Info->AvailableVal = IncomingVal;
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WorkList.push_back(IncomingPHI);
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}
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}
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}
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};
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} // End llvm namespace
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#endif
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