diff options
Diffstat (limited to 'contrib/llvm/tools/clang/lib/Checker/CheckDeadStores.cpp')
| -rw-r--r-- | contrib/llvm/tools/clang/lib/Checker/CheckDeadStores.cpp | 289 |
1 files changed, 289 insertions, 0 deletions
diff --git a/contrib/llvm/tools/clang/lib/Checker/CheckDeadStores.cpp b/contrib/llvm/tools/clang/lib/Checker/CheckDeadStores.cpp new file mode 100644 index 0000000..d6ea187 --- /dev/null +++ b/contrib/llvm/tools/clang/lib/Checker/CheckDeadStores.cpp @@ -0,0 +1,289 @@ +//==- DeadStores.cpp - Check for stores to dead variables --------*- C++ -*-==// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This file defines a DeadStores, a flow-sensitive checker that looks for +// stores to variables that are no longer live. +// +//===----------------------------------------------------------------------===// + +#include "clang/Checker/Checkers/LocalCheckers.h" +#include "clang/Analysis/Analyses/LiveVariables.h" +#include "clang/Analysis/Visitors/CFGRecStmtVisitor.h" +#include "clang/Checker/BugReporter/BugReporter.h" +#include "clang/Checker/PathSensitive/GRExprEngine.h" +#include "clang/Analysis/Visitors/CFGRecStmtDeclVisitor.h" +#include "clang/Basic/Diagnostic.h" +#include "clang/AST/ASTContext.h" +#include "clang/AST/ParentMap.h" +#include "llvm/ADT/SmallPtrSet.h" + +using namespace clang; + +namespace { + +class DeadStoreObs : public LiveVariables::ObserverTy { + ASTContext &Ctx; + BugReporter& BR; + ParentMap& Parents; + llvm::SmallPtrSet<VarDecl*, 20> Escaped; + + enum DeadStoreKind { Standard, Enclosing, DeadIncrement, DeadInit }; + +public: + DeadStoreObs(ASTContext &ctx, BugReporter& br, ParentMap& parents, + llvm::SmallPtrSet<VarDecl*, 20> &escaped) + : Ctx(ctx), BR(br), Parents(parents), Escaped(escaped) {} + + virtual ~DeadStoreObs() {} + + void Report(VarDecl* V, DeadStoreKind dsk, SourceLocation L, SourceRange R) { + if (Escaped.count(V)) + return; + + std::string name = V->getNameAsString(); + + const char* BugType = 0; + std::string msg; + + switch (dsk) { + default: + assert(false && "Impossible dead store type."); + + case DeadInit: + BugType = "Dead initialization"; + msg = "Value stored to '" + name + + "' during its initialization is never read"; + break; + + case DeadIncrement: + BugType = "Dead increment"; + case Standard: + if (!BugType) BugType = "Dead assignment"; + msg = "Value stored to '" + name + "' is never read"; + break; + + case Enclosing: + BugType = "Dead nested assignment"; + msg = "Although the value stored to '" + name + + "' is used in the enclosing expression, the value is never actually" + " read from '" + name + "'"; + break; + } + + BR.EmitBasicReport(BugType, "Dead store", msg, L, R); + } + + void CheckVarDecl(VarDecl* VD, Expr* Ex, Expr* Val, + DeadStoreKind dsk, + const LiveVariables::AnalysisDataTy& AD, + const LiveVariables::ValTy& Live) { + + if (!VD->hasLocalStorage()) + return; + // Reference types confuse the dead stores checker. Skip them + // for now. + if (VD->getType()->getAs<ReferenceType>()) + return; + + if (!Live(VD, AD) && + !(VD->getAttr<UnusedAttr>() || VD->getAttr<BlocksAttr>())) + Report(VD, dsk, Ex->getSourceRange().getBegin(), + Val->getSourceRange()); + } + + void CheckDeclRef(DeclRefExpr* DR, Expr* Val, DeadStoreKind dsk, + const LiveVariables::AnalysisDataTy& AD, + const LiveVariables::ValTy& Live) { + if (VarDecl* VD = dyn_cast<VarDecl>(DR->getDecl())) + CheckVarDecl(VD, DR, Val, dsk, AD, Live); + } + + bool isIncrement(VarDecl* VD, BinaryOperator* B) { + if (B->isCompoundAssignmentOp()) + return true; + + Expr* RHS = B->getRHS()->IgnoreParenCasts(); + BinaryOperator* BRHS = dyn_cast<BinaryOperator>(RHS); + + if (!BRHS) + return false; + + DeclRefExpr *DR; + + if ((DR = dyn_cast<DeclRefExpr>(BRHS->getLHS()->IgnoreParenCasts()))) + if (DR->getDecl() == VD) + return true; + + if ((DR = dyn_cast<DeclRefExpr>(BRHS->getRHS()->IgnoreParenCasts()))) + if (DR->getDecl() == VD) + return true; + + return false; + } + + virtual void ObserveStmt(Stmt* S, + const LiveVariables::AnalysisDataTy& AD, + const LiveVariables::ValTy& Live) { + + // Skip statements in macros. + if (S->getLocStart().isMacroID()) + return; + + if (BinaryOperator* B = dyn_cast<BinaryOperator>(S)) { + if (!B->isAssignmentOp()) return; // Skip non-assignments. + + if (DeclRefExpr* DR = dyn_cast<DeclRefExpr>(B->getLHS())) + if (VarDecl *VD = dyn_cast<VarDecl>(DR->getDecl())) { + // Special case: check for assigning null to a pointer. + // This is a common form of defensive programming. + QualType T = VD->getType(); + if (T->isPointerType() || T->isObjCObjectPointerType()) { + if (B->getRHS()->isNullPointerConstant(Ctx, + Expr::NPC_ValueDependentIsNull)) + return; + } + + Expr* RHS = B->getRHS()->IgnoreParenCasts(); + // Special case: self-assignments. These are often used to shut up + // "unused variable" compiler warnings. + if (DeclRefExpr* RhsDR = dyn_cast<DeclRefExpr>(RHS)) + if (VD == dyn_cast<VarDecl>(RhsDR->getDecl())) + return; + + // Otherwise, issue a warning. + DeadStoreKind dsk = Parents.isConsumedExpr(B) + ? Enclosing + : (isIncrement(VD,B) ? DeadIncrement : Standard); + + CheckVarDecl(VD, DR, B->getRHS(), dsk, AD, Live); + } + } + else if (UnaryOperator* U = dyn_cast<UnaryOperator>(S)) { + if (!U->isIncrementOp()) + return; + + // Handle: ++x within a subexpression. The solution is not warn + // about preincrements to dead variables when the preincrement occurs + // as a subexpression. This can lead to false negatives, e.g. "(++x);" + // A generalized dead code checker should find such issues. + if (U->isPrefix() && Parents.isConsumedExpr(U)) + return; + + Expr *Ex = U->getSubExpr()->IgnoreParenCasts(); + + if (DeclRefExpr* DR = dyn_cast<DeclRefExpr>(Ex)) + CheckDeclRef(DR, U, DeadIncrement, AD, Live); + } + else if (DeclStmt* DS = dyn_cast<DeclStmt>(S)) + // Iterate through the decls. Warn if any initializers are complex + // expressions that are not live (never used). + for (DeclStmt::decl_iterator DI=DS->decl_begin(), DE=DS->decl_end(); + DI != DE; ++DI) { + + VarDecl* V = dyn_cast<VarDecl>(*DI); + + if (!V) + continue; + + if (V->hasLocalStorage()) { + // Reference types confuse the dead stores checker. Skip them + // for now. + if (V->getType()->getAs<ReferenceType>()) + return; + + if (Expr* E = V->getInit()) { + // Don't warn on C++ objects (yet) until we can show that their + // constructors/destructors don't have side effects. + if (isa<CXXConstructExpr>(E)) + return; + + if (isa<CXXExprWithTemporaries>(E)) + return; + + // A dead initialization is a variable that is dead after it + // is initialized. We don't flag warnings for those variables + // marked 'unused'. + if (!Live(V, AD) && V->getAttr<UnusedAttr>() == 0) { + // Special case: check for initializations with constants. + // + // e.g. : int x = 0; + // + // If x is EVER assigned a new value later, don't issue + // a warning. This is because such initialization can be + // due to defensive programming. + if (E->isConstantInitializer(Ctx)) + return; + + if (DeclRefExpr *DRE=dyn_cast<DeclRefExpr>(E->IgnoreParenCasts())) + if (VarDecl *VD = dyn_cast<VarDecl>(DRE->getDecl())) { + // Special case: check for initialization from constant + // variables. + // + // e.g. extern const int MyConstant; + // int x = MyConstant; + // + if (VD->hasGlobalStorage() && + VD->getType().isConstQualified()) + return; + // Special case: check for initialization from scalar + // parameters. This is often a form of defensive + // programming. Non-scalars are still an error since + // because it more likely represents an actual algorithmic + // bug. + if (isa<ParmVarDecl>(VD) && VD->getType()->isScalarType()) + return; + } + + Report(V, DeadInit, V->getLocation(), E->getSourceRange()); + } + } + } + } + } +}; + +} // end anonymous namespace + +//===----------------------------------------------------------------------===// +// Driver function to invoke the Dead-Stores checker on a CFG. +//===----------------------------------------------------------------------===// + +namespace { +class FindEscaped : public CFGRecStmtDeclVisitor<FindEscaped>{ + CFG *cfg; +public: + FindEscaped(CFG *c) : cfg(c) {} + + CFG& getCFG() { return *cfg; } + + llvm::SmallPtrSet<VarDecl*, 20> Escaped; + + void VisitUnaryOperator(UnaryOperator* U) { + // Check for '&'. Any VarDecl whose value has its address-taken we + // treat as escaped. + Expr* E = U->getSubExpr()->IgnoreParenCasts(); + if (U->getOpcode() == UnaryOperator::AddrOf) + if (DeclRefExpr* DR = dyn_cast<DeclRefExpr>(E)) + if (VarDecl* VD = dyn_cast<VarDecl>(DR->getDecl())) { + Escaped.insert(VD); + return; + } + Visit(E); + } +}; +} // end anonymous namespace + + +void clang::CheckDeadStores(CFG &cfg, LiveVariables &L, ParentMap &pmap, + BugReporter& BR) { + FindEscaped FS(&cfg); + FS.getCFG().VisitBlockStmts(FS); + DeadStoreObs A(BR.getContext(), BR, pmap, FS.Escaped); + L.runOnAllBlocks(cfg, &A); +} |
