1 //===- CFGReachabilityAnalysis.cpp - Basic reachability analysis ----------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file defines a flow-sensitive, (mostly) path-insensitive reachability
10 // analysis based on Clang's CFGs. Clients can query if a given basic block
11 // is reachable within the CFG.
12 //
13 //===----------------------------------------------------------------------===//
14
15 #include "clang/Analysis/Analyses/CFGReachabilityAnalysis.h"
16 #include "clang/Analysis/CFG.h"
17 #include "llvm/ADT/BitVector.h"
18 #include "llvm/ADT/SmallVector.h"
19
20 using namespace clang;
21
CFGReverseBlockReachabilityAnalysis(const CFG & cfg)22 CFGReverseBlockReachabilityAnalysis::CFGReverseBlockReachabilityAnalysis(
23 const CFG &cfg)
24 : analyzed(cfg.getNumBlockIDs(), false) {}
25
isReachable(const CFGBlock * Src,const CFGBlock * Dst)26 bool CFGReverseBlockReachabilityAnalysis::isReachable(const CFGBlock *Src,
27 const CFGBlock *Dst) {
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.
mapReachability(const CFGBlock * Dst)42 void 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 if (*i)
73 worklist.push_back(*i);
74 }
75 }
76 }
77