1 //===--- LoopWidening.cpp - Widen loops -------------------------*- C++ -*-===//
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 contains functions which are used to widen loops. A loop may be
10 /// widened to approximate the exit state(s), without analyzing every
11 /// iteration. The widening is done by invalidating anything which might be
12 /// modified by the body of the loop.
13 ///
14 //===----------------------------------------------------------------------===//
15
16 #include "clang/AST/AST.h"
17 #include "clang/ASTMatchers/ASTMatchFinder.h"
18 #include "clang/StaticAnalyzer/Core/PathSensitive/ExplodedGraph.h"
19 #include "clang/StaticAnalyzer/Core/PathSensitive/LoopWidening.h"
20
21 using namespace clang;
22 using namespace ento;
23 using namespace clang::ast_matchers;
24
25 const auto MatchRef = "matchref";
26
27 /// Return the loops condition Stmt or NULL if LoopStmt is not a loop
getLoopCondition(const Stmt * LoopStmt)28 static const Expr *getLoopCondition(const Stmt *LoopStmt) {
29 switch (LoopStmt->getStmtClass()) {
30 default:
31 return nullptr;
32 case Stmt::ForStmtClass:
33 return cast<ForStmt>(LoopStmt)->getCond();
34 case Stmt::WhileStmtClass:
35 return cast<WhileStmt>(LoopStmt)->getCond();
36 case Stmt::DoStmtClass:
37 return cast<DoStmt>(LoopStmt)->getCond();
38 }
39 }
40
41 namespace clang {
42 namespace ento {
43
getWidenedLoopState(ProgramStateRef PrevState,const LocationContext * LCtx,unsigned BlockCount,const Stmt * LoopStmt)44 ProgramStateRef getWidenedLoopState(ProgramStateRef PrevState,
45 const LocationContext *LCtx,
46 unsigned BlockCount, const Stmt *LoopStmt) {
47
48 assert(isa<ForStmt>(LoopStmt) || isa<WhileStmt>(LoopStmt) ||
49 isa<DoStmt>(LoopStmt));
50
51 // Invalidate values in the current state.
52 // TODO Make this more conservative by only invalidating values that might
53 // be modified by the body of the loop.
54 // TODO Nested loops are currently widened as a result of the invalidation
55 // being so inprecise. When the invalidation is improved, the handling
56 // of nested loops will also need to be improved.
57 ASTContext &ASTCtx = LCtx->getAnalysisDeclContext()->getASTContext();
58 const StackFrameContext *STC = LCtx->getStackFrame();
59 MemRegionManager &MRMgr = PrevState->getStateManager().getRegionManager();
60 const MemRegion *Regions[] = {MRMgr.getStackLocalsRegion(STC),
61 MRMgr.getStackArgumentsRegion(STC),
62 MRMgr.getGlobalsRegion()};
63 RegionAndSymbolInvalidationTraits ITraits;
64 for (auto *Region : Regions) {
65 ITraits.setTrait(Region,
66 RegionAndSymbolInvalidationTraits::TK_EntireMemSpace);
67 }
68
69 // References should not be invalidated.
70 auto Matches = match(
71 findAll(stmt(hasDescendant(
72 varDecl(hasType(hasCanonicalType(referenceType()))).bind(MatchRef)))),
73 *LCtx->getDecl()->getBody(), ASTCtx);
74 for (BoundNodes Match : Matches) {
75 const VarDecl *VD = Match.getNodeAs<VarDecl>(MatchRef);
76 assert(VD);
77 const VarRegion *VarMem = MRMgr.getVarRegion(VD, LCtx);
78 ITraits.setTrait(VarMem,
79 RegionAndSymbolInvalidationTraits::TK_PreserveContents);
80 }
81
82
83 // 'this' pointer is not an lvalue, we should not invalidate it. If the loop
84 // is located in a method, constructor or destructor, the value of 'this'
85 // pointer should remain unchanged. Ignore static methods, since they do not
86 // have 'this' pointers.
87 const CXXMethodDecl *CXXMD = dyn_cast<CXXMethodDecl>(STC->getDecl());
88 if (CXXMD && !CXXMD->isStatic()) {
89 const CXXThisRegion *ThisR =
90 MRMgr.getCXXThisRegion(CXXMD->getThisType(), STC);
91 ITraits.setTrait(ThisR,
92 RegionAndSymbolInvalidationTraits::TK_PreserveContents);
93 }
94
95 return PrevState->invalidateRegions(Regions, getLoopCondition(LoopStmt),
96 BlockCount, LCtx, true, nullptr, nullptr,
97 &ITraits);
98 }
99
100 } // end namespace ento
101 } // end namespace clang
102