[analyzer] Refactor conditional expression evaluating code

Summary:
Instead of digging through the ExplodedGraph, to figure out which edge brought
us here, I compute the value of conditional expression by looking at the
sub-expression values.

To do this, I needed to change the liveness algorithm a bit -- now, the full
conditional expression also depends on all atomic sub-expressions, not only the
outermost ones.

Reviewers: jordan_rose

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1340

llvm-svn: 189090

clang/lib/Analysis/LiveVariables.cpp

@@ -212,6 +212,8 @@ class TransferFunctions : public StmtVisitor<TransferFunctions> {
   LiveVariables::LivenessValues &val;
   LiveVariables::Observer *observer;
   const CFGBlock *currentBlock;
+
+  void markLogicalExprLeaves(const Expr *E);
 public:
   TransferFunctions(LiveVariablesImpl &im,
                     LiveVariables::LivenessValues &Val,
@@ -368,9 +370,25 @@ void TransferFunctions::VisitBinaryOperator(BinaryOperator *B) {
         if (observer)
           observer->observerKill(DR);
       }
+  } else if (B->isLogicalOp()) {
+    // Leaf expressions in the logical operator tree are live until we reach the
+    // outermost logical operator. Static analyzer relies on this behaviour.
+    markLogicalExprLeaves(B->getLHS()->IgnoreParens());
+    markLogicalExprLeaves(B->getRHS()->IgnoreParens());
   }
 }
 
+void TransferFunctions::markLogicalExprLeaves(const Expr *E) {
+  const BinaryOperator *B = dyn_cast<BinaryOperator>(E);
+  if (!B || !B->isLogicalOp()) {
+    val.liveStmts = LV.SSetFact.add(val.liveStmts, E);
+    return;
+  }
+
+  markLogicalExprLeaves(B->getLHS()->IgnoreParens());
+  markLogicalExprLeaves(B->getRHS()->IgnoreParens());
+}
+
 void TransferFunctions::VisitBlockExpr(BlockExpr *BE) {
   AnalysisDeclContext::referenced_decls_iterator I, E;
   llvm::tie(I, E) =

clang/lib/StaticAnalyzer/Core/ExprEngine.cpp

@@ -1343,12 +1343,24 @@ void ExprEngine::processBranch(const Stmt *Condition, const Stmt *Term,
     return;
   }
 
+  SValBuilder &SVB = Pred->getState()->getStateManager().getSValBuilder();
+  SVal TrueVal = SVB.makeTruthVal(true);
+  SVal FalseVal = SVB.makeTruthVal(false);
 
   // Resolve the condition in the precense of nested '||' and '&&'.
   if (const Expr *Ex = dyn_cast<Expr>(Condition))
     Condition = Ex->IgnoreParens();
-
   Condition = ResolveCondition(Condition, BldCtx.getBlock());
+
+  // Cast truth values to the correct type.
+  if (const Expr *Ex = dyn_cast<Expr>(Condition)) {
+    TrueVal = SVB.evalCast(TrueVal, Ex->getType(),
+                           getContext().getLogicalOperationType());
+    FalseVal = SVB.evalCast(FalseVal, Ex->getType(),
+                            getContext().getLogicalOperationType());
+  }
+
+
   PrettyStackTraceLoc CrashInfo(getContext().getSourceManager(),
                                 Condition->getLocStart(),
                                 "Error evaluating branch");
@@ -1391,31 +1403,37 @@ void ExprEngine::processBranch(const Stmt *Condition, const Stmt *Term,
       }
     }
     
+    ProgramStateRef StTrue, StFalse;
+
     // If the condition is still unknown, give up.
     if (X.isUnknownOrUndef()) {
-      builder.generateNode(PrevState, true, PredI);
-      builder.generateNode(PrevState, false, PredI);
+
+      StTrue = PrevState->BindExpr(Condition, BldCtx.LC, TrueVal);
+      StFalse = PrevState->BindExpr(Condition, BldCtx.LC, FalseVal);
+
+      builder.generateNode(StTrue, true, PredI);
+      builder.generateNode(StFalse, false, PredI);
       continue;
     }
 
     DefinedSVal V = X.castAs<DefinedSVal>();
-
-    ProgramStateRef StTrue, StFalse;
     tie(StTrue, StFalse) = PrevState->assume(V);
 
     // Process the true branch.
     if (builder.isFeasible(true)) {
-      if (StTrue)
+      if (StTrue) {
+        StTrue = StTrue->BindExpr(Condition, BldCtx.LC, TrueVal);
         builder.generateNode(StTrue, true, PredI);
-      else
+      } else
         builder.markInfeasible(true);
     }
 
     // Process the false branch.
     if (builder.isFeasible(false)) {
-      if (StFalse)
+      if (StFalse) {
+        StFalse = StFalse->BindExpr(Condition, BldCtx.LC, FalseVal);
         builder.generateNode(StFalse, false, PredI);
-      else
+      } else
         builder.markInfeasible(false);
     }
   }

clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp

@@ -501,6 +501,33 @@ void ExprEngine::VisitDeclStmt(const DeclStmt *DS, ExplodedNode *Pred,
   }
 }
 
+static ProgramStateRef evaluateLogicalExpression(const Expr *E,
+                                                 const LocationContext *LC,
+                                                 ProgramStateRef State) {
+  SVal X = State->getSVal(E, LC);
+  if (! X.isUnknown())
+    return State;
+
+  const BinaryOperator *B = dyn_cast<BinaryOperator>(E->IgnoreParens());
+  if (!B || (B->getOpcode() != BO_LAnd && B->getOpcode() != BO_LOr))
+    return State;
+
+  State = evaluateLogicalExpression(B->getLHS(), LC, State);
+  X = State->getSVal(B->getLHS(), LC);
+  QualType XType = B->getLHS()->getType();
+
+  assert(X.isConstant());
+  if (!X.isZeroConstant() == (B->getOpcode() == BO_LAnd)) {
+    // LHS not sufficient, we need to check RHS as well
+    State = evaluateLogicalExpression(B->getRHS(), LC, State);
+    X = State->getSVal(B->getRHS(), LC);
+    XType = B->getRHS()->getType();
+  }
+
+  SValBuilder &SVB = State->getStateManager().getSValBuilder();
+  return State->BindExpr(E, LC, SVB.evalCast(X, B->getType(), XType));
+}
+
 void ExprEngine::VisitLogicalExpr(const BinaryOperator* B, ExplodedNode *Pred,
                                   ExplodedNodeSet &Dst) {
   assert(B->getOpcode() == BO_LAnd ||
@@ -509,64 +536,25 @@ void ExprEngine::VisitLogicalExpr(const BinaryOperator* B, ExplodedNode *Pred,
   StmtNodeBuilder Bldr(Pred, Dst, *currBldrCtx);
   ProgramStateRef state = Pred->getState();
 
-  ExplodedNode *N = Pred;
-  while (!N->getLocation().getAs<BlockEntrance>()) {
-    ProgramPoint P = N->getLocation();
-    assert(P.getAs<PreStmt>()|| P.getAs<PreStmtPurgeDeadSymbols>());
-    (void) P;
-    assert(N->pred_size() == 1);
-    N = *N->pred_begin();
-  }
-  assert(N->pred_size() == 1);
-  N = *N->pred_begin();
-  BlockEdge BE = N->getLocation().castAs<BlockEdge>();
-  SVal X;
+  state = evaluateLogicalExpression(B, Pred->getLocationContext(), state);
+  SVal X = state->getSVal(B, Pred->getLocationContext());
 
-  // Determine the value of the expression by introspecting how we
-  // got this location in the CFG.  This requires looking at the previous
-  // block we were in and what kind of control-flow transfer was involved.
-  const CFGBlock *SrcBlock = BE.getSrc();
-  // The only terminator (if there is one) that makes sense is a logical op.
-  CFGTerminator T = SrcBlock->getTerminator();
-  if (const BinaryOperator *Term = cast_or_null<BinaryOperator>(T.getStmt())) {
-    (void) Term;
-    assert(Term->isLogicalOp());
-    assert(SrcBlock->succ_size() == 2);
-    // Did we take the true or false branch?
-    unsigned constant = (*SrcBlock->succ_begin() == BE.getDst()) ? 1 : 0;
-    X = svalBuilder.makeIntVal(constant, B->getType());
-  }
-  else {
-    // If there is no terminator, by construction the last statement
-    // in SrcBlock is the value of the enclosing expression.
-    // However, we still need to constrain that value to be 0 or 1.
-    assert(!SrcBlock->empty());
-    CFGStmt Elem = SrcBlock->rbegin()->castAs<CFGStmt>();
-    const Expr *RHS = cast<Expr>(Elem.getStmt());
-    SVal RHSVal = N->getState()->getSVal(RHS, Pred->getLocationContext());
-
-    if (RHSVal.isUndef()) {
-      X = RHSVal;
+  if (!X.isUndef()) {
+    DefinedOrUnknownSVal DefinedRHS = X.castAs<DefinedOrUnknownSVal>();
+    ProgramStateRef StTrue, StFalse;
+    llvm::tie(StTrue, StFalse) = state->assume(DefinedRHS);
+    if (StTrue) {
+      if (!StFalse) {
+        // The value is known to be true.
+        X = getSValBuilder().makeIntVal(1, B->getType());
+      } // else The truth value of X is unknown, just leave it as it is.
     } else {
-      DefinedOrUnknownSVal DefinedRHS = RHSVal.castAs<DefinedOrUnknownSVal>();
-      ProgramStateRef StTrue, StFalse;
-      llvm::tie(StTrue, StFalse) = N->getState()->assume(DefinedRHS);
-      if (StTrue) {
-        if (StFalse) {
-          // We can't constrain the value to 0 or 1.
-          // The best we can do is a cast.
-          X = getSValBuilder().evalCast(RHSVal, B->getType(), RHS->getType());
-        } else {
-          // The value is known to be true.
-          X = getSValBuilder().makeIntVal(1, B->getType());
-        }
-      } else {
-        // The value is known to be false.
-        assert(StFalse && "Infeasible path!");
-        X = getSValBuilder().makeIntVal(0, B->getType());
-      }
+      // The value is known to be false.
+      assert(StFalse && "Infeasible path!");
+      X = getSValBuilder().makeIntVal(0, B->getType());
     }
   }
+
   Bldr.generateNode(B, Pred, state->BindExpr(B, Pred->getLocationContext(), X));
 }
 

clang/test/Analysis/logical-ops.c

@@ -25,3 +25,15 @@ int testTypeIsInt(int i, void *p) {
     return 1;
   return 0;
 }
+
+// These crashed the analyzer at some point.
+int between(char *x) {
+  extern char start[];
+  extern char end[];
+  return x >= start && x < end;
+}
+
+int undef(void) {} // expected-warning{{control reaches end of non-void function}}
+void useUndef(void) { 0 || undef(); }
+
+void testPointer(void) { (void) (1 && testPointer && 0); }