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 template <class NodeTy, bool IsPostDom>
21 void IDFCalculator<NodeTy, IsPostDom>::calculate(
22     SmallVectorImpl<BasicBlock *> &PHIBlocks) {
23   // Use a priority queue keyed on dominator tree level so that inserted nodes
24   // are handled from the bottom of the dominator tree upwards.
25   typedef std::pair<DomTreeNode *, unsigned> DomTreeNodePair;
26   typedef std::priority_queue<DomTreeNodePair, SmallVector<DomTreeNodePair, 32>,
27                               less_second> IDFPriorityQueue;
28   IDFPriorityQueue PQ;
29 
30   for (BasicBlock *BB : *DefBlocks) {
31     if (DomTreeNode *Node = DT.getNode(BB))
32       PQ.push({Node, Node->getLevel()});
33   }
34 
35   SmallVector<DomTreeNode *, 32> Worklist;
36   SmallPtrSet<DomTreeNode *, 32> VisitedPQ;
37   SmallPtrSet<DomTreeNode *, 32> VisitedWorklist;
38 
39   while (!PQ.empty()) {
40     DomTreeNodePair RootPair = PQ.top();
41     PQ.pop();
42     DomTreeNode *Root = RootPair.first;
43     unsigned RootLevel = RootPair.second;
44 
45     // Walk all dominator tree children of Root, inspecting their CFG edges with
46     // targets elsewhere on the dominator tree. Only targets whose level is at
47     // most Root's level are added to the iterated dominance frontier of the
48     // definition set.
49 
50     Worklist.clear();
51     Worklist.push_back(Root);
52     VisitedWorklist.insert(Root);
53 
54     while (!Worklist.empty()) {
55       DomTreeNode *Node = Worklist.pop_back_val();
56       BasicBlock *BB = Node->getBlock();
57       // Succ is the successor in the direction we are calculating IDF, so it is
58       // successor for IDF, and predecessor for Reverse IDF.
59       for (auto *Succ : children<NodeTy>(BB)) {
60         DomTreeNode *SuccNode = DT.getNode(Succ);
61 
62         // Quickly skip all CFG edges that are also dominator tree edges instead
63         // of catching them below.
64         if (SuccNode->getIDom() == Node)
65           continue;
66 
67         const unsigned SuccLevel = SuccNode->getLevel();
68         if (SuccLevel > RootLevel)
69           continue;
70 
71         if (!VisitedPQ.insert(SuccNode).second)
72           continue;
73 
74         BasicBlock *SuccBB = SuccNode->getBlock();
75         if (useLiveIn && !LiveInBlocks->count(SuccBB))
76           continue;
77 
78         PHIBlocks.emplace_back(SuccBB);
79         if (!DefBlocks->count(SuccBB))
80           PQ.push(std::make_pair(SuccNode, SuccLevel));
81       }
82 
83       for (auto DomChild : *Node) {
84         if (VisitedWorklist.insert(DomChild).second)
85           Worklist.push_back(DomChild);
86       }
87     }
88   }
89 }
90 
91 template class IDFCalculator<BasicBlock *, false>;
92 template class IDFCalculator<Inverse<BasicBlock *>, true>;
93 }
94