CFGReachabilityAnalysis.cpp revision 263508 
1//==- CFGReachabilityAnalysis.cpp - Basic reachability analysis --*- C++ -*-==//
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 file defines a flow-sensitive, (mostly) path-insensitive reachability
11// analysis based on Clang's CFGs.  Clients can query if a given basic block
12// is reachable within the CFG.
13//
14//===----------------------------------------------------------------------===//
15
16#include "llvm/ADT/SmallVector.h"
17#include "clang/Analysis/Analyses/CFGReachabilityAnalysis.h"
18#include "clang/Analysis/CFG.h"
19
20using namespace clang;
21
22CFGReverseBlockReachabilityAnalysis::CFGReverseBlockReachabilityAnalysis(const CFG &cfg)
23  : analyzed(cfg.getNumBlockIDs(), false) {}
24
25bool CFGReverseBlockReachabilityAnalysis::isReachable(const CFGBlock *Src,
26                                          const CFGBlock *Dst) {
27
28  const unsigned DstBlockID = Dst->getBlockID();
29
30  // If we haven't analyzed the destination node, run the analysis now
31  if (!analyzed[DstBlockID]) {
32    mapReachability(Dst);
33    analyzed[DstBlockID] = true;
34  }
35
36  // Return the cached result
37  return reachable[DstBlockID][Src->getBlockID()];
38}
39
40// Maps reachability to a common node by walking the predecessors of the
41// destination node.
42void CFGReverseBlockReachabilityAnalysis::mapReachability(const CFGBlock *Dst) {
43  SmallVector<const CFGBlock *, 11> worklist;
44  llvm::BitVector visited(analyzed.size());
45
46  ReachableSet &DstReachability = reachable[Dst->getBlockID()];
47  DstReachability.resize(analyzed.size(), false);
48
49  // Start searching from the destination node, since we commonly will perform
50  // multiple queries relating to a destination node.
51  worklist.push_back(Dst);
52  bool firstRun = true;
53
54  while (!worklist.empty()) {
55    const CFGBlock *block = worklist.pop_back_val();
56
57    if (visited[block->getBlockID()])
58      continue;
59    visited[block->getBlockID()] = true;
60
61    // Update reachability information for this node -> Dst
62    if (!firstRun) {
63      // Don't insert Dst -> Dst unless it was a predecessor of itself
64      DstReachability[block->getBlockID()] = true;
65    }
66    else
67      firstRun = false;
68
69    // Add the predecessors to the worklist.
70    for (CFGBlock::const_pred_iterator i = block->pred_begin(),
71         e = block->pred_end(); i != e; ++i) {
72      worklist.push_back(*i);
73    }
74  }
75}
76