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 }
111