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//==- 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/Analysis/LocalCheckers.h"
#include "clang/Analysis/Analyses/LiveVariables.h"
#include "clang/Analysis/Visitors/CFGRecStmtVisitor.h"
#include "clang/Analysis/PathSensitive/BugReporter.h"
#include "clang/Analysis/PathSensitive/GRExprEngine.h"
#include "clang/Basic/Diagnostic.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/ParentMap.h"
#include "llvm/Support/Compiler.h"
using namespace clang;
namespace {
class VISIBILITY_HIDDEN DeadStoreObs : public LiveVariables::ObserverTy {
ASTContext &Ctx;
Diagnostic &Diags;
DiagnosticClient &Client;
ParentMap& Parents;
public:
DeadStoreObs(ASTContext &ctx, Diagnostic &diags, DiagnosticClient &client,
ParentMap& parents)
: Ctx(ctx), Diags(diags), Client(client), Parents(parents) {}
virtual ~DeadStoreObs() {}
unsigned GetDiag(VarDecl* VD, bool inEnclosing = false) {
std::string name(VD->getName());
std::string msg = inEnclosing
? "Although the value stored to '" + name +
"' is used in the enclosing expression, the value is never actually"
" read from '" + name + "'"
: "Value stored to '" + name + "' is never read";
return Diags.getCustomDiagID(Diagnostic::Warning, msg.c_str());
}
void CheckVarDecl(VarDecl* VD, Expr* Ex, Expr* Val,
bool hasEnclosing,
const LiveVariables::AnalysisDataTy& AD,
const LiveVariables::ValTy& Live) {
if (VD->hasLocalStorage() && !Live(VD, AD)) {
SourceRange R = Val->getSourceRange();
Diags.Report(&Client,
Ctx.getFullLoc(Ex->getSourceRange().getBegin()),
GetDiag(VD, hasEnclosing), 0, 0, &R, 1);
}
}
void CheckDeclRef(DeclRefExpr* DR, Expr* Val,
const LiveVariables::AnalysisDataTy& AD,
const LiveVariables::ValTy& Live) {
if (VarDecl* VD = dyn_cast<VarDecl>(DR->getDecl()))
CheckVarDecl(VD, DR, Val, false, AD, Live);
}
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.
// FIXME: Make this optional?
Expr* Val = B->getRHS();
llvm::APSInt Result(Ctx.getTypeSize(Val->getType()));
if (VD->getType()->isPointerType() &&
Val->IgnoreParenCasts()->isIntegerConstantExpr(Result, Ctx, 0))
if (Result == 0)
return;
CheckVarDecl(VD, DR, Val, Parents.isSubExpr(B), AD, Live);
}
}
else if (UnaryOperator* U = dyn_cast<UnaryOperator>(S)) {
if (!U->isIncrementOp())
return;
Expr *Ex = U->getSubExpr()->IgnoreParenCasts();
if (DeclRefExpr* DR = dyn_cast<DeclRefExpr>(Ex))
CheckDeclRef(DR, U, 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 (ScopedDecl* SD = DS->getDecl(); SD; SD = SD->getNextDeclarator()) {
VarDecl* V = dyn_cast<VarDecl>(SD);
if (!V) continue;
if (V->hasLocalStorage())
if (Expr* E = V->getInit()) {
if (!Live(V, AD)) {
// 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->isConstantExpr(Ctx,NULL)) {
// Flag a warning.
SourceRange R = E->getSourceRange();
Diags.Report(&Client,
Ctx.getFullLoc(V->getLocation()),
GetDiag(V), 0, 0, &R, 1);
}
}
}
}
}
};
} // end anonymous namespace
//===----------------------------------------------------------------------===//
// Driver function to invoke the Dead-Stores checker on a CFG.
//===----------------------------------------------------------------------===//
void clang::CheckDeadStores(LiveVariables& L, BugReporter& BR) {
SimpleBugType BT("dead store");
DiagCollector C(BT);
DeadStoreObs A(BR.getContext(), BR.getDiagnostic(), C, BR.getParentMap());
L.runOnAllBlocks(*BR.getCFG(), &A);
// Emit the bug reports.
for (DiagCollector::iterator I = C.begin(), E = C.end(); I != E; ++I)
BR.EmitWarning(*I);
}
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