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 /// \brief 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 using namespace llvm;
20
calculate(SmallVectorImpl<BasicBlock * > & PHIBlocks)21 void IDFCalculator::calculate(SmallVectorImpl<BasicBlock *> &PHIBlocks) {
22 // If we haven't computed dominator tree levels, do so now.
23 if (DomLevels.empty()) {
24 for (auto DFI = df_begin(DT.getRootNode()), DFE = df_end(DT.getRootNode());
25 DFI != DFE; ++DFI) {
26 DomLevels[*DFI] = DFI.getPathLength() - 1;
27 }
28 }
29
30 // Use a priority queue keyed on dominator tree level so that inserted nodes
31 // are handled from the bottom of the dominator tree upwards.
32 typedef std::pair<DomTreeNode *, unsigned> DomTreeNodePair;
33 typedef std::priority_queue<DomTreeNodePair, SmallVector<DomTreeNodePair, 32>,
34 less_second> IDFPriorityQueue;
35 IDFPriorityQueue PQ;
36
37 for (BasicBlock *BB : *DefBlocks) {
38 if (DomTreeNode *Node = DT.getNode(BB))
39 PQ.push(std::make_pair(Node, DomLevels.lookup(Node)));
40 }
41
42 SmallVector<DomTreeNode *, 32> Worklist;
43 SmallPtrSet<DomTreeNode *, 32> VisitedPQ;
44 SmallPtrSet<DomTreeNode *, 32> VisitedWorklist;
45
46 while (!PQ.empty()) {
47 DomTreeNodePair RootPair = PQ.top();
48 PQ.pop();
49 DomTreeNode *Root = RootPair.first;
50 unsigned RootLevel = RootPair.second;
51
52 // Walk all dominator tree children of Root, inspecting their CFG edges with
53 // targets elsewhere on the dominator tree. Only targets whose level is at
54 // most Root's level are added to the iterated dominance frontier of the
55 // definition set.
56
57 Worklist.clear();
58 Worklist.push_back(Root);
59 VisitedWorklist.insert(Root);
60
61 while (!Worklist.empty()) {
62 DomTreeNode *Node = Worklist.pop_back_val();
63 BasicBlock *BB = Node->getBlock();
64
65 for (auto Succ : successors(BB)) {
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 continue;
72
73 unsigned SuccLevel = DomLevels.lookup(SuccNode);
74 if (SuccLevel > RootLevel)
75 continue;
76
77 if (!VisitedPQ.insert(SuccNode).second)
78 continue;
79
80 BasicBlock *SuccBB = SuccNode->getBlock();
81 if (useLiveIn && !LiveInBlocks->count(SuccBB))
82 continue;
83
84 PHIBlocks.emplace_back(SuccBB);
85 if (!DefBlocks->count(SuccBB))
86 PQ.push(std::make_pair(SuccNode, SuccLevel));
87 }
88
89 for (auto DomChild : *Node) {
90 if (VisitedWorklist.insert(DomChild).second)
91 Worklist.push_back(DomChild);
92 }
93 }
94 }
95 }
96