Bug fix to merging of data flow values (merge incorrectly made values

too "conservative").

Several revisions to UninitializedValues checker after testing.  We
now appear to be working correctly (probably some bugs still, but main
functionality appears to be there).  Implemented careful emitting of
warnings so that we wouldn't get a cascade of warnings for simply not
defining a single variable and using it everywhere.  This way the
warnings point closer to the root cause rather than "symptoms" from
using values derived from uninitialized variables.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@42067 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/Analysis/DataflowSolver.h b/Analysis/DataflowSolver.h
index 4a089dbcdc6ce05c40b46985c65933233c05859a..5266af3407cce99f3c2024fc36bc67bcad8b0352 100644 (file)
--- a/Analysis/DataflowSolver.h
+++ b/Analysis/DataflowSolver.h
@@ -85,6 +85,9 @@ public:
   ///  only be used for querying the dataflow values within a block with
   ///  and Observer object.
   void runOnBlock(const CFGBlock* B) {
+    if (D.getBlockDataMap().find(B) == D.getBlockDataMap().end())
+      return;
+      
     TransferFuncsTy TF (D.getAnalysisData());
     ProcessBlock(B,TF,AnalysisDirTag());
   }
@@ -118,14 +121,6 @@ private:
              I != E; ++I)
           WorkList.enqueue(*I);    
     }
-    
-    // For blocks that have no associated dataflow value, instantiate a
-    // default value.
-    BlockDataMapTy& M = D.getBlockDataMap();
-    
-    for (CFG::const_iterator I=cfg.begin(), E=cfg.end(); I!=E; ++I)
-      if (M.find(&*I) == M.end())
-        M[&*I].resetValues(D.getAnalysisData());
   }       
   
   /// SolveDataflowEquations (BACKWARD ANALYSIS) - Perform the actual
@@ -155,7 +150,7 @@ private:
   
   /// ProcessBlock (FORWARD ANALYSIS) - Process the transfer functions
   ///  for a given block based on a forward analysis.
-  bool ProcessBlock(const CFGBlock* B, TransferFuncsTy& TF, 
+  bool ProcessBlock(const CFGBlock* B, TransferFuncsTy& TF,
                     dataflow::forward_analysis_tag) {
     
     ValTy& V = TF.getVal();
@@ -164,9 +159,21 @@ private:
     V.resetValues(D.getAnalysisData());
     MergeOperatorTy Merge;
   
+    BlockDataMapTy& M = D.getBlockDataMap();
+    bool firstMerge = true;
+  
     for (CFGBlock::const_pred_iterator I=B->pred_begin(), 
-                                       E=B->pred_end(); I!=E; ++I)
-      Merge(V,D.getBlockData(*I));
+                                      E=B->pred_end(); I!=E; ++I) {
+      typename BlockDataMapTy::iterator BI = M.find(*I);
+      if (BI != M.end()) {
+        if (firstMerge) {
+          firstMerge = false;
+          V.copyValues(BI->second);
+        }
+        else
+          Merge(V,BI->second);
+      }
+    }
 
     // Process the statements in the block in the forward direction.
     for (CFGBlock::const_iterator I=B->begin(), E=B->end(); I!=E; ++I)
@@ -186,9 +193,21 @@ private:
     V.resetValues(D.getAnalysisData());
     MergeOperatorTy Merge;
     
+    BlockDataMapTy& M = D.getBlockDataMap();
+    bool firstMerge = true;
+
     for (CFGBlock::const_succ_iterator I=B->succ_begin(), 
-                                       E=B->succ_end(); I!=E; ++I)
-      Merge(V,D.getBlockData(*I));
+                                       E=B->succ_end(); I!=E; ++I) {
+      typename BlockDataMapTy::iterator BI = M.find(*I);
+      if (BI != M.end()) {
+        if (firstMerge) {
+          firstMerge = false;
+          V.copyValues(BI->second);
+        }
+        else
+          Merge(V,BI->second);
+      }
+    }
     
     // Process the statements in the block in the forward direction.
     for (CFGBlock::const_reverse_iterator I=B->begin(), E=B->end(); I!=E; ++I)

diff --git a/Analysis/UninitializedValues.cpp b/Analysis/UninitializedValues.cpp
index ce9454d0cc7d2b44ac63709a370ac0851130ed22..c5b13a4074af14fa547a59a397a62baee5830aa5 100644 (file)
--- a/Analysis/UninitializedValues.cpp
+++ b/Analysis/UninitializedValues.cpp
@@ -75,8 +75,8 @@ void UninitializedValues::InitializeValues(const CFG& cfg) {
       R.BlockStmt_Visit(*BI);
   
   // Initialize the values of the last block.
-  UninitializedValues::ValTy& V = getBlockDataMap()[&cfg.getEntry()];
-  V.resetValues(getAnalysisData());
+//  UninitializedValues::ValTy& V = getBlockDataMap()[&cfg.getEntry()];
+//  V.resetValues(getAnalysisData());
 }
 
 //===----------------------------------------------------------------------===//
@@ -88,8 +88,11 @@ namespace {
 class TransferFuncs : public CFGStmtVisitor<TransferFuncs,bool> {
   UninitializedValues::ValTy V;
   UninitializedValues::AnalysisDataTy& AD;
+  bool InitWithAssigns;
 public:
-  TransferFuncs(UninitializedValues::AnalysisDataTy& ad) : AD(ad) {
+  TransferFuncs(UninitializedValues::AnalysisDataTy& ad, 
+                bool init_with_assigns=true) : 
+    AD(ad), InitWithAssigns(init_with_assigns) {
     V.resetValues(AD);
   }
   
@@ -134,9 +137,21 @@ bool TransferFuncs::VisitBinaryOperator(BinaryOperator* B) {
       else if (DeclRefExpr* DR = dyn_cast<DeclRefExpr>(S))
         if (BlockVarDecl* VD = dyn_cast<BlockVarDecl>(DR->getDecl())) {
           assert ( AD.VMap.find(VD) != AD.VMap.end() && "Unknown VarDecl.");
-          return V.DeclBV[ AD.VMap[VD] ] = Visit(B->getRHS());
+          
+          if(InitWithAssigns) {
+            // Pseudo-hack to prevent cascade of warnings.  If the RHS uses
+            // an uninitialized value, then we are already going to flag a warning
+            // related to the "cause".  Thus, propogating uninitialized doesn't
+            // make sense, since we are just adding extra messages that don't
+            // contribute to diagnosing the bug.  In InitWithAssigns mode
+            // we unconditionally set the assigned variable to Initialized to
+            // prevent Uninitialized propogation.
+            return V.DeclBV[AD.VMap[VD]] = Initialized();
+          }
+          else 
+            return V.DeclBV[ AD.VMap[VD] ] = Visit(B->getRHS());
         }
-  
+
       break;
     }
   }
@@ -154,7 +169,8 @@ bool TransferFuncs::VisitDeclStmt(DeclStmt* S) {
                  AD.EMap.end() && "Unknown Expr.");
                  
         assert ( AD.VMap.find(VD) != AD.VMap.end() && "Unknown VarDecl.");
-        x = V.DeclBV[ AD.VMap[VD] ] = V.ExprBV[ AD.EMap[cast<Expr>(I)] ];
+        x = V.ExprBV[ AD.EMap[cast<Expr>(I)] ];
+        V.DeclBV[ AD.VMap[VD] ] = x;
       }
       
   return x;
@@ -246,7 +262,7 @@ struct Merge {
     assert (Dst.ExprBV.size() == Src.ExprBV.size()
             && "Bitvector sizes do not match.");
 
-    Dst.ExprBV |= Src.ExprBV;
+    Dst.ExprBV &= Src.ExprBV;
   }
 };
 } // end anonymous namespace