Remove hack from LiveVariables analysis where variables whose address are taken

are considered 'live'. This hack isn't needed anymore because we have a
separation in the path-sensitive analyzer between variable names and bindings;
the analyzer can continue to reason about the storage of a variable after its
name is no longer directly referenced.  Now the live variables analysis literally means "is this name live".

Along this line, update the dead stores checker to explicitly look for variables
whose values have escaped.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@68504 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 38 insertions, 22 deletions

diff --git a/lib/Analysis/CheckDeadStores.cpp b/lib/Analysis/CheckDeadStores.cpp
index f75a96471a..69433d6396 100644
--- a/lib/Analysis/CheckDeadStores.cpp
+++ b/lib/Analysis/CheckDeadStores.cpp
@@ -17,9 +17,11 @@
 #include "clang/Analysis/Visitors/CFGRecStmtVisitor.h"
 #include "clang/Analysis/PathSensitive/BugReporter.h"
 #include "clang/Analysis/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"
 #include "llvm/Support/Compiler.h"
 
 using namespace clang;
@@ -30,16 +32,20 @@ class VISIBILITY_HIDDEN 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)
-    : Ctx(ctx), BR(br), Parents(parents) {}
+  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();
     
@@ -219,7 +225,35 @@ public:
 // Driver function to invoke the Dead-Stores checker on a CFG.
 //===----------------------------------------------------------------------===//
 
-void clang::CheckDeadStores(LiveVariables& L, BugReporter& BR) {  
-  DeadStoreObs A(BR.getContext(), BR, BR.getParentMap());
+namespace {
+class VISIBILITY_HIDDEN 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(LiveVariables& L, BugReporter& BR) {
+  FindEscaped FS(BR.getCFG());
+  FS.getCFG().VisitBlockStmts(FS);  
+  DeadStoreObs A(BR.getContext(), BR, BR.getParentMap(), FS.Escaped);
   L.runOnAllBlocks(*BR.getCFG(), &A);
 }
diff --git a/lib/Analysis/LiveVariables.cpp b/lib/Analysis/LiveVariables.cpp
index b8b0aaca18..b0eb37b065 100644
--- a/lib/Analysis/LiveVariables.cpp
+++ b/lib/Analysis/LiveVariables.cpp
@@ -74,28 +74,10 @@ public:
       AlwaysLive.push_back(VD);    
   }
   
-  void VisitUnaryOperator(UnaryOperator* U) {
-    // Check for '&'.  Any VarDecl whose value has its address-taken we
-    // treat as always being live (flow-insensitive).
-
-    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())) {
-          AD.Register(VD);
-          AlwaysLive.push_back(VD);
-          return;
-        }
-      
-    Visit(E);
-  }
-    
   CFG& getCFG() { return AD.getCFG(); }
 };
 } // end anonymous namespace
 
-
 LiveVariables::LiveVariables(ASTContext& Ctx, CFG& cfg) {
   // Register all referenced VarDecls.
   getAnalysisData().setCFG(cfg);