Split libAnalysis into two libraries: libAnalysis and libChecker.

(1) libAnalysis is a generic analysis library that can be used by
    Sema.  It defines the CFG, basic dataflow analysis primitives, and
    inexpensive flow-sensitive analyses (e.g. LiveVariables).

(2) libChecker contains the guts of the static analyzer, incuding the
    path-sensitive analysis engine and domain-specific checks.

Now any clients that want to use the frontend to build their own tools
don't need to link in the entire static analyzer.

This change exposes various obvious cleanups that can be made to the
layout of files and headers in libChecker.  More changes pending.  :)

This change also exposed a layering violation between AnalysisContext
and MemRegion.  BlockInvocationContext shouldn't explicitly know about
BlockDataRegions.  For now I've removed the BlockDataRegion* from
BlockInvocationContext (removing context-sensitivity; although this
wasn't used yet).  We need to have a better way to extend
BlockInvocationContext (and any LocationContext) to add
context-sensitivty.

llvm-svn: 94406

1 files changed, 279 insertions, 0 deletions

diff --git a/clang/lib/Checker/CheckDeadStores.cpp b/clang/lib/Checker/CheckDeadStores.cpp
new file mode 100644
index 00000000000..91c9bb30adb
--- /dev/null
+++ b/clang/lib/Checker/CheckDeadStores.cpp
@@ -0,0 +1,279 @@
+//==- 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/LocalCheckers.h"
+#include "clang/Analysis/Analyses/LiveVariables.h"
+#include "clang/Analysis/Visitors/CFGRecStmtVisitor.h"
+#include "clang/Checker/PathSensitive/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.
+          if (VD->getType()->isPointerType()) {
+            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;
+
+              // Special case: check for initializations from constant
+              //  variables.
+              //
+              //  e.g. extern const int MyConstant;
+              //       int x = MyConstant;
+              //
+              if (DeclRefExpr *DRE=dyn_cast<DeclRefExpr>(E->IgnoreParenCasts()))
+                if (VarDecl *VD = dyn_cast<VarDecl>(DRE->getDecl()))
+                  if (VD->hasGlobalStorage() &&
+                      VD->getType().isConstQualified()) 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);
+}