lib/Analysis/IteratedDominanceFrontier.cpp

   1 //===- IteratedDominanceFrontier.cpp - Compute IDF ------------------------===//
   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 // Compute iterated dominance frontiers using a linear time algorithm.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/Analysis/IteratedDominanceFrontier.h"
  15 #include "llvm/IR/CFG.h"
  16 #include "llvm/IR/Dominators.h"
  17 #include <queue>
  18
  19 namespace llvm {
  20
  21 template <class NodeTy, bool IsPostDom>
  22 void IDFCalculator<NodeTy, IsPostDom>::calculate(
  23     SmallVectorImpl<BasicBlock *> &PHIBlocks) {
  24   // Use a priority queue keyed on dominator tree level so that inserted nodes
  25   // are handled from the bottom of the dominator tree upwards. We also augment
  26   // the level with a DFS number to ensure that the blocks are ordered in a
  27   // deterministic way.
  28   typedef std::pair<DomTreeNode *, std::pair<unsigned, unsigned>>
  29       DomTreeNodePair;
  30   typedef std::priority_queue<DomTreeNodePair, SmallVector<DomTreeNodePair, 32>,
  31                               less_second> IDFPriorityQueue;
  32   IDFPriorityQueue PQ;
  33
  34   DT.updateDFSNumbers();
  35
  36   for (BasicBlock *BB : *DefBlocks) {
  37     if (DomTreeNode *Node = DT.getNode(BB))
  38       PQ.push({Node, std::make_pair(Node->getLevel(), Node->getDFSNumIn())});
  39   }
  40
  41   SmallVector<DomTreeNode *, 32> Worklist;
  42   SmallPtrSet<DomTreeNode *, 32> VisitedPQ;
  43   SmallPtrSet<DomTreeNode *, 32> VisitedWorklist;
  44
  45   while (!PQ.empty()) {
  46     DomTreeNodePair RootPair = PQ.top();
  47     PQ.pop();
  48     DomTreeNode *Root = RootPair.first;
  49     unsigned RootLevel = RootPair.second.first;
  50
  51     // Walk all dominator tree children of Root, inspecting their CFG edges with
  52     // targets elsewhere on the dominator tree. Only targets whose level is at
  53     // most Root's level are added to the iterated dominance frontier of the
  54     // definition set.
  55
  56     Worklist.clear();
  57     Worklist.push_back(Root);
  58     VisitedWorklist.insert(Root);
  59
  60     while (!Worklist.empty()) {
  61       DomTreeNode *Node = Worklist.pop_back_val();
  62       BasicBlock *BB = Node->getBlock();
  63       // Succ is the successor in the direction we are calculating IDF, so it is
  64       // successor for IDF, and predecessor for Reverse IDF.
  65       auto DoWork = [&](BasicBlock *Succ) {
  66         DomTreeNode *SuccNode = DT.getNode(Succ);
  67
  68         // Quickly skip all CFG edges that are also dominator tree edges instead
  69         // of catching them below.
  70         if (SuccNode->getIDom() == Node)
  71           return;
  72
  73         const unsigned SuccLevel = SuccNode->getLevel();
  74         if (SuccLevel > RootLevel)
  75           return;
  76
  77         if (!VisitedPQ.insert(SuccNode).second)
  78           return;
  79
  80         BasicBlock *SuccBB = SuccNode->getBlock();
  81         if (useLiveIn && !LiveInBlocks->count(SuccBB))
  82           return;
  83
  84         PHIBlocks.emplace_back(SuccBB);
  85         if (!DefBlocks->count(SuccBB))
  86           PQ.push(std::make_pair(
  87               SuccNode, std::make_pair(SuccLevel, SuccNode->getDFSNumIn())));
  88       };
  89
  90       if (GD) {
  91         for (auto Pair : children<
  92                  std::pair<const GraphDiff<BasicBlock *, IsPostDom> *, NodeTy>>(
  93                  {GD, BB}))
  94           DoWork(Pair.second);
  95       } else {
  96         for (auto *Succ : children<NodeTy>(BB))
  97           DoWork(Succ);
  98       }
  99
 100       for (auto DomChild : *Node) {
 101         if (VisitedWorklist.insert(DomChild).second)
 102           Worklist.push_back(DomChild);
 103       }
 104     }
 105   }
 106 }
 107
 108 template class IDFCalculator<BasicBlock *, false>;
 109 template class IDFCalculator<Inverse<BasicBlock *>, true>;
 110 }