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 case Stmt::CXXForRangeStmtClass:
39 return cast<CXXForRangeStmt>(LoopStmt)->getCond();
40 }
41 }
42
43 namespace clang {
44 namespace ento {
45
getWidenedLoopState(ProgramStateRef PrevState,const LocationContext * LCtx,unsigned BlockCount,const Stmt * LoopStmt)46 ProgramStateRef getWidenedLoopState(ProgramStateRef PrevState,
47 const LocationContext *LCtx,
48 unsigned BlockCount, const Stmt *LoopStmt) {
49
50 assert((isa<ForStmt, WhileStmt, DoStmt, CXXForRangeStmt>(LoopStmt)));
51
52 // Invalidate values in the current state.
53 // TODO Make this more conservative by only invalidating values that might
54 // be modified by the body of the loop.
55 // TODO Nested loops are currently widened as a result of the invalidation
56 // being so inprecise. When the invalidation is improved, the handling
57 // of nested loops will also need to be improved.
58 ASTContext &ASTCtx = LCtx->getAnalysisDeclContext()->getASTContext();
59 const StackFrameContext *STC = LCtx->getStackFrame();
60 MemRegionManager &MRMgr = PrevState->getStateManager().getRegionManager();
61 const MemRegion *Regions[] = {MRMgr.getStackLocalsRegion(STC),
62 MRMgr.getStackArgumentsRegion(STC),
63 MRMgr.getGlobalsRegion()};
64 RegionAndSymbolInvalidationTraits ITraits;
65 for (auto *Region : Regions) {
66 ITraits.setTrait(Region,
67 RegionAndSymbolInvalidationTraits::TK_EntireMemSpace);
68 }
69
70 // References should not be invalidated.
71 auto Matches = match(
72 findAll(stmt(hasDescendant(
73 varDecl(hasType(hasCanonicalType(referenceType()))).bind(MatchRef)))),
74 *LCtx->getDecl()->getBody(), ASTCtx);
75 for (BoundNodes Match : Matches) {
76 const VarDecl *VD = Match.getNodeAs<VarDecl>(MatchRef);
77 assert(VD);
78 const VarRegion *VarMem = MRMgr.getVarRegion(VD, LCtx);
79 ITraits.setTrait(VarMem,
80 RegionAndSymbolInvalidationTraits::TK_PreserveContents);
81 }
82
83
84 // 'this' pointer is not an lvalue, we should not invalidate it. If the loop
85 // is located in a method, constructor or destructor, the value of 'this'
86 // pointer should remain unchanged. Ignore static methods, since they do not
87 // have 'this' pointers.
88 const CXXMethodDecl *CXXMD = dyn_cast<CXXMethodDecl>(STC->getDecl());
89 if (CXXMD && CXXMD->isImplicitObjectMemberFunction()) {
90 const CXXThisRegion *ThisR =
91 MRMgr.getCXXThisRegion(CXXMD->getThisType(), STC);
92 ITraits.setTrait(ThisR,
93 RegionAndSymbolInvalidationTraits::TK_PreserveContents);
94 }
95
96 return PrevState->invalidateRegions(Regions, getLoopCondition(LoopStmt),
97 BlockCount, LCtx, true, nullptr, nullptr,
98 &ITraits);
99 }
100
101 } // end namespace ento
102 } // end namespace clang
103