1 files changed, 247 insertions, 0 deletions
diff --git a/contrib/llvm/tools/clang/lib/StaticAnalyzer/Checkers/UnreachableCodeChecker.cpp b/contrib/llvm/tools/clang/lib/StaticAnalyzer/Checkers/UnreachableCodeChecker.cpp
new file mode 100644
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+++ b/contrib/llvm/tools/clang/lib/StaticAnalyzer/Checkers/UnreachableCodeChecker.cpp
@@ -0,0 +1,247 @@
+//==- UnreachableCodeChecker.cpp - Generalized dead code checker -*- C++ -*-==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// This file implements a generalized unreachable code checker using a
+// path-sensitive analysis. We mark any path visited, and then walk the CFG as a
+// post-analysis to determine what was never visited.
+//
+// A similar flow-sensitive only check exists in Analysis/ReachableCode.cpp
+//===----------------------------------------------------------------------===//
+
+#include "ClangSACheckers.h"
+#include "clang/StaticAnalyzer/Core/Checker.h"
+#include "clang/StaticAnalyzer/Core/CheckerManager.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/ExplodedGraph.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/SVals.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerHelpers.h"
+#include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
+#include "clang/AST/ParentMap.h"
+#include "clang/Basic/Builtins.h"
+#include "clang/Basic/SourceManager.h"
+#include "llvm/ADT/SmallSet.h"
+
+// The number of CFGBlock pointers we want to reserve memory for. This is used
+// once for each function we analyze.
+#define DEFAULT_CFGBLOCKS 256
+
+using namespace clang;
+using namespace ento;
+
+namespace {
+class UnreachableCodeChecker : public Checker<check::EndAnalysis> {
+public:
+  void checkEndAnalysis(ExplodedGraph &G, BugReporter &B,
+                        ExprEngine &Eng) const;
+private:
+  typedef llvm::SmallSet<unsigned, DEFAULT_CFGBLOCKS> CFGBlocksSet;
+
+  static inline const Stmt *getUnreachableStmt(const CFGBlock *CB);
+  static void FindUnreachableEntryPoints(const CFGBlock *CB,
+                                         CFGBlocksSet &reachable,
+                                         CFGBlocksSet &visited);
+  static bool isInvalidPath(const CFGBlock *CB, const ParentMap &PM);
+  static inline bool isEmptyCFGBlock(const CFGBlock *CB);
+};
+}
+
+void UnreachableCodeChecker::checkEndAnalysis(ExplodedGraph &G,
+                                              BugReporter &B,
+                                              ExprEngine &Eng) const {
+  CFGBlocksSet reachable, visited;
+  
+  if (Eng.hasWorkRemaining())
+    return;
+
+  const Decl *D = 0;
+  CFG *C = 0;
+  ParentMap *PM = 0;
+  const LocationContext *LC = 0;
+  // Iterate over ExplodedGraph
+  for (ExplodedGraph::node_iterator I = G.nodes_begin(), E = G.nodes_end();
+      I != E; ++I) {
+    const ProgramPoint &P = I->getLocation();
+    LC = P.getLocationContext();
+
+    if (!D)
+      D = LC->getAnalysisDeclContext()->getDecl();
+    // Save the CFG if we don't have it already
+    if (!C)
+      C = LC->getAnalysisDeclContext()->getUnoptimizedCFG();
+    if (!PM)
+      PM = &LC->getParentMap();
+
+    if (const BlockEntrance *BE = dyn_cast<BlockEntrance>(&P)) {
+      const CFGBlock *CB = BE->getBlock();
+      reachable.insert(CB->getBlockID());
+    }
+  }
+
+  // Bail out if we didn't get the CFG or the ParentMap.
+  if (!D || !C || !PM)
+    return;
+  
+  // Don't do anything for template instantiations.  Proving that code
+  // in a template instantiation is unreachable means proving that it is
+  // unreachable in all instantiations.
+  if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D))
+    if (FD->isTemplateInstantiation())
+      return;
+
+  // Find CFGBlocks that were not covered by any node
+  for (CFG::const_iterator I = C->begin(), E = C->end(); I != E; ++I) {
+    const CFGBlock *CB = *I;
+    // Check if the block is unreachable
+    if (reachable.count(CB->getBlockID()))
+      continue;
+
+    // Check if the block is empty (an artificial block)
+    if (isEmptyCFGBlock(CB))
+      continue;
+
+    // Find the entry points for this block
+    if (!visited.count(CB->getBlockID()))
+      FindUnreachableEntryPoints(CB, reachable, visited);
+
+    // This block may have been pruned; check if we still want to report it
+    if (reachable.count(CB->getBlockID()))
+      continue;
+
+    // Check for false positives
+    if (CB->size() > 0 && isInvalidPath(CB, *PM))
+      continue;
+
+    // It is good practice to always have a "default" label in a "switch", even
+    // if we should never get there. It can be used to detect errors, for
+    // instance. Unreachable code directly under a "default" label is therefore
+    // likely to be a false positive.
+    if (const Stmt *label = CB->getLabel())
+      if (label->getStmtClass() == Stmt::DefaultStmtClass)
+        continue;
+
+    // Special case for __builtin_unreachable.
+    // FIXME: This should be extended to include other unreachable markers,
+    // such as llvm_unreachable.
+    if (!CB->empty()) {
+      bool foundUnreachable = false;
+      for (CFGBlock::const_iterator ci = CB->begin(), ce = CB->end();
+           ci != ce; ++ci) {
+        if (const CFGStmt *S = (*ci).getAs<CFGStmt>())
+          if (const CallExpr *CE = dyn_cast<CallExpr>(S->getStmt())) {
+            if (CE->isBuiltinCall() == Builtin::BI__builtin_unreachable) {
+              foundUnreachable = true;
+              break;
+            }
+          }
+      }
+      if (foundUnreachable)
+        continue;
+    }
+
+    // We found a block that wasn't covered - find the statement to report
+    SourceRange SR;
+    PathDiagnosticLocation DL;
+    SourceLocation SL;
+    if (const Stmt *S = getUnreachableStmt(CB)) {
+      SR = S->getSourceRange();
+      DL = PathDiagnosticLocation::createBegin(S, B.getSourceManager(), LC);
+      SL = DL.asLocation();
+      if (SR.isInvalid() || !SL.isValid())
+        continue;
+    }
+    else
+      continue;
+
+    // Check if the SourceLocation is in a system header
+    const SourceManager &SM = B.getSourceManager();
+    if (SM.isInSystemHeader(SL) || SM.isInExternCSystemHeader(SL))
+      continue;
+
+    B.EmitBasicReport(D, "Unreachable code", "Dead code",
+                      "This statement is never executed", DL, SR);
+  }
+}
+
+// Recursively finds the entry point(s) for this dead CFGBlock.
+void UnreachableCodeChecker::FindUnreachableEntryPoints(const CFGBlock *CB,
+                                                        CFGBlocksSet &reachable,
+                                                        CFGBlocksSet &visited) {
+  visited.insert(CB->getBlockID());
+
+  for (CFGBlock::const_pred_iterator I = CB->pred_begin(), E = CB->pred_end();
+      I != E; ++I) {
+    if (!reachable.count((*I)->getBlockID())) {
+      // If we find an unreachable predecessor, mark this block as reachable so
+      // we don't report this block
+      reachable.insert(CB->getBlockID());
+      if (!visited.count((*I)->getBlockID()))
+        // If we haven't previously visited the unreachable predecessor, recurse
+        FindUnreachableEntryPoints(*I, reachable, visited);
+    }
+  }
+}
+
+// Find the Stmt* in a CFGBlock for reporting a warning
+const Stmt *UnreachableCodeChecker::getUnreachableStmt(const CFGBlock *CB) {
+  for (CFGBlock::const_iterator I = CB->begin(), E = CB->end(); I != E; ++I) {
+    if (const CFGStmt *S = I->getAs<CFGStmt>())
+      return S->getStmt();
+  }
+  if (const Stmt *S = CB->getTerminator())
+    return S;
+  else
+    return 0;
+}
+
+// Determines if the path to this CFGBlock contained an element that infers this
+// block is a false positive. We assume that FindUnreachableEntryPoints has
+// already marked only the entry points to any dead code, so we need only to
+// find the condition that led to this block (the predecessor of this block.)
+// There will never be more than one predecessor.
+bool UnreachableCodeChecker::isInvalidPath(const CFGBlock *CB,
+                                           const ParentMap &PM) {
+  // We only expect a predecessor size of 0 or 1. If it is >1, then an external
+  // condition has broken our assumption (for example, a sink being placed by
+  // another check). In these cases, we choose not to report.
+  if (CB->pred_size() > 1)
+    return true;
+
+  // If there are no predecessors, then this block is trivially unreachable
+  if (CB->pred_size() == 0)
+    return false;
+
+  const CFGBlock *pred = *CB->pred_begin();
+
+  // Get the predecessor block's terminator conditon
+  const Stmt *cond = pred->getTerminatorCondition();
+
+  //assert(cond && "CFGBlock's predecessor has a terminator condition");
+  // The previous assertion is invalid in some cases (eg do/while). Leaving
+  // reporting of these situations on at the moment to help triage these cases.
+  if (!cond)
+    return false;
+
+  // Run each of the checks on the conditions
+  if (containsMacro(cond) || containsEnum(cond)
+      || containsStaticLocal(cond) || containsBuiltinOffsetOf(cond)
+      || containsStmt<UnaryExprOrTypeTraitExpr>(cond))
+    return true;
+
+  return false;
+}
+
+// Returns true if the given CFGBlock is empty
+bool UnreachableCodeChecker::isEmptyCFGBlock(const CFGBlock *CB) {
+  return CB->getLabel() == 0       // No labels
+      && CB->size() == 0           // No statements
+      && CB->getTerminator() == 0; // No terminator
+}
+
+void ento::registerUnreachableCodeChecker(CheckerManager &mgr) {
+  mgr.registerChecker<UnreachableCodeChecker>();
+}