lib/CodeGen/LazyLiveness.cpp

   1 //===- LazyLiveness.cpp - Lazy, CFG-invariant liveness information --------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This pass implements a lazy liveness analysis as per "Fast Liveness Checking
  11 // for SSA-form Programs," by Boissinot, et al.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #define DEBUG_TYPE "lazyliveness"
  16 #include "llvm/CodeGen/LazyLiveness.h"
  17 #include "llvm/CodeGen/MachineDominators.h"
  18 #include "llvm/CodeGen/MachineRegisterInfo.h"
  19 #include "llvm/CodeGen/Passes.h"
  20 #include "llvm/ADT/DepthFirstIterator.h"
  21 #include "llvm/ADT/PostOrderIterator.h"
  22 using namespace llvm;
  23
  24 char LazyLiveness::ID = 0;
  25 static RegisterPass<LazyLiveness> X("lazy-liveness", "Lazy Liveness Analysis");
  26
  27 void LazyLiveness::computeBackedgeChain(MachineFunction& mf,
  28                                         MachineBasicBlock* MBB) {
  29   SparseBitVector<128> tmp = rv[MBB];
  30   tmp.set(preorder[MBB]);
  31   tmp &= backedge_source;
  32   calculated.set(preorder[MBB]);
  33
  34   for (SparseBitVector<128>::iterator I = tmp.begin(); I != tmp.end(); ++I) {
  35     assert(rev_preorder.size() > *I && "Unknown block!");
  36
  37     MachineBasicBlock* SrcMBB = rev_preorder[*I];
  38
  39     for (MachineBasicBlock::succ_iterator SI = SrcMBB->succ_begin(),
  40          SE = SrcMBB->succ_end(); SI != SE; ++SI) {
  41       MachineBasicBlock* TgtMBB = *SI;
  42
  43       if (backedges.count(std::make_pair(SrcMBB, TgtMBB)) &&
  44           !rv[MBB].test(preorder[TgtMBB])) {
  45         if (!calculated.test(preorder[TgtMBB]))
  46           computeBackedgeChain(mf, TgtMBB);
  47
  48         tv[MBB].set(preorder[TgtMBB]);
  49         SparseBitVector<128> right = tv[TgtMBB];
  50         tv[MBB] |= right;
  51       }
  52     }
  53
  54     tv[MBB].reset(preorder[MBB]);
  55   }
  56 }
  57
  58 bool LazyLiveness::runOnMachineFunction(MachineFunction &mf) {
  59   rv.clear();
  60   tv.clear();
  61   backedges.clear();
  62   backedge_source.clear();
  63   backedge_target.clear();
  64   calculated.clear();
  65   preorder.clear();
  66   rev_preorder.clear();
  67
  68   rv.resize(mf.size());
  69   tv.resize(mf.size());
  70   preorder.resize(mf.size());
  71   rev_preorder.reserve(mf.size());
  72
  73   MRI = &mf.getRegInfo();
  74   MachineDominatorTree& MDT = getAnalysis<MachineDominatorTree>();
  75
  76   // Step 0: Compute preorder numbering for all MBBs.
  77   unsigned num = 0;
  78   for (df_iterator<MachineDomTreeNode*> DI = df_begin(MDT.getRootNode()),
  79        DE = df_end(MDT.getRootNode()); DI != DE; ++DI) {
  80     preorder[(*DI)->getBlock()] = num++;
  81     rev_preorder.push_back((*DI)->getBlock());
  82   }
  83
  84   // Step 1: Compute the transitive closure of the CFG, ignoring backedges.
  85   for (po_iterator<MachineBasicBlock*> POI = po_begin(&*mf.begin()),
  86        POE = po_end(&*mf.begin()); POI != POE; ++POI) {
  87     MachineBasicBlock* MBB = *POI;
  88     SparseBitVector<128>& entry = rv[MBB];
  89     entry.set(preorder[MBB]);
  90
  91     for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(),
  92          SE = MBB->succ_end(); SI != SE; ++SI) {
  93       DenseMap<MachineBasicBlock*, SparseBitVector<128> >::iterator SII =
  94                                                          rv.find(*SI);
  95
  96       // Because we're iterating in postorder, any successor that does not yet
  97       // have an rv entry must be on a backedge.
  98       if (SII != rv.end()) {
  99         entry |= SII->second;
 100       } else {
 101         backedges.insert(std::make_pair(MBB, *SI));
 102         backedge_source.set(preorder[MBB]);
 103         backedge_target.set(preorder[*SI]);
 104       }
 105     }
 106   }
 107
 108   for (SparseBitVector<128>::iterator I = backedge_source.begin();
 109        I != backedge_source.end(); ++I)
 110     computeBackedgeChain(mf, rev_preorder[*I]);
 111
 112   for (po_iterator<MachineBasicBlock*> POI = po_begin(&*mf.begin()),
 113        POE = po_end(&*mf.begin()); POI != POE; ++POI)
 114     if (!backedge_target.test(preorder[*POI]))
 115       for (MachineBasicBlock::succ_iterator SI = (*POI)->succ_begin(),
 116            SE = (*POI)->succ_end(); SI != SE; ++SI)
 117         if (!backedges.count(std::make_pair(*POI, *SI)) && tv.count(*SI)) {
 118           SparseBitVector<128> right = tv[*SI];
 119           tv[*POI] |= right;
 120         }
 121
 122   for (po_iterator<MachineBasicBlock*> POI = po_begin(&*mf.begin()),
 123        POE = po_end(&*mf.begin()); POI != POE; ++POI)
 124     tv[*POI].set(preorder[*POI]);
 125
 126   return false;
 127 }
 128
 129 bool LazyLiveness::vregLiveIntoMBB(unsigned vreg, MachineBasicBlock* MBB) {
 130   MachineDominatorTree& MDT = getAnalysis<MachineDominatorTree>();
 131
 132   MachineBasicBlock* DefMBB = MRI->def_begin(vreg)->getParent();
 133   unsigned def = preorder[DefMBB];
 134   unsigned max_dom = 0;
 135   for (df_iterator<MachineDomTreeNode*> DI = df_begin(MDT[DefMBB]),
 136        DE = df_end(MDT[DefMBB]); DI != DE; ++DI) {
 137     if (preorder[DI->getBlock()] > max_dom) {
 138       max_dom = preorder[(*DI)->getBlock()];
 139     }
 140   }
 141
 142   if (preorder[MBB] <= def || max_dom < preorder[MBB])
 143     return false;
 144
 145   SparseBitVector<128>::iterator I = tv[MBB].begin();
 146   while (I != tv[MBB].end() && *I <= def) ++I;
 147   while (I != tv[MBB].end() && *I < max_dom) {
 148     for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(vreg),
 149          UE = MachineRegisterInfo::use_end(); UI != UE; ++UI) {
 150       MachineBasicBlock* UseMBB = UI->getParent();
 151       if (rv[rev_preorder[*I]].test(preorder[UseMBB]))
 152         return true;
 153
 154       unsigned t_dom = 0;
 155       for (df_iterator<MachineDomTreeNode*> DI =
 156            df_begin(MDT[rev_preorder[*I]]), DE = df_end(MDT[rev_preorder[*I]]);
 157            DI != DE; ++DI)
 158         if (preorder[DI->getBlock()] > t_dom) {
 159           max_dom = preorder[(*DI)->getBlock()];
 160         }
 161       I = tv[MBB].begin();
 162       while (I != tv[MBB].end() && *I < t_dom) ++I;
 163     }
 164   }
 165
 166   return false;
 167 }