[PATCH] [analyzer] Refactor conditional expression evaluating code

[Pavel Labath]

Hi jordan_rose,

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 depends on all atomic sub-expressions, not only the
outermost ones.

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

Files:
  lib/Analysis/LiveVariables.cpp
  lib/StaticAnalyzer/Core/ExprEngineC.cpp

Index: lib/Analysis/LiveVariables.cpp
===================================================================
--- lib/Analysis/LiveVariables.cpp
+++ lib/Analysis/LiveVariables.cpp
@@ -212,6 +212,8 @@
   LiveVariables::LivenessValues &val;
   LiveVariables::Observer *observer;
   const CFGBlock *currentBlock;
+
+  void MarkLogicalOpsLive(const Expr *E);
 public:
   TransferFunctions(LiveVariablesImpl &im,
                     LiveVariables::LivenessValues &Val,
@@ -368,9 +370,28 @@
         if (observer)
           observer->observerKill(DR);
       }
+  } else {
+    // All logical sub-operations are live until we reach the outermost
+    // operator. Static analyzer relies on this behaviour.
+    MarkLogicalOpsLive(B);
   }
 }
 
+void TransferFunctions::MarkLogicalOpsLive(const Expr *E) {
+  const BinaryOperator *BO = dyn_cast<BinaryOperator>(E);
+  if (!BO || !BO->isLogicalOp())
+    return;
+
+  const Expr *LHS = BO->getLHS()->IgnoreParens();
+  const Expr *RHS = BO->getRHS()->IgnoreParens();
+
+  val.liveStmts = LV.SSetFact.add(val.liveStmts, LHS);
+  val.liveStmts = LV.SSetFact.add(val.liveStmts, RHS);
+
+  MarkLogicalOpsLive(LHS);
+  MarkLogicalOpsLive(RHS);
+}
+
 void TransferFunctions::VisitBlockExpr(BlockExpr *BE) {
   AnalysisDeclContext::referenced_decls_iterator I, E;
   llvm::tie(I, E) =
Index: lib/StaticAnalyzer/Core/ExprEngineC.cpp
===================================================================
--- lib/StaticAnalyzer/Core/ExprEngineC.cpp
+++ lib/StaticAnalyzer/Core/ExprEngineC.cpp
@@ -501,72 +501,64 @@
   }
 }
 
+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 = cast_or_null<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.isUnknownOrUndef() && "Value should have already been computed.");
+
+  ProgramStateRef StTrue, StFalse;
+  llvm::tie(StTrue, StFalse) = State->assume(X.castAs<DefinedOrUnknownSVal>());
+
+  assert(!StTrue != !StFalse && "Value should be evaluate to true or false.");
+  if(!StFalse == (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 ||
          B->getOpcode() == BO_LOr);
 
   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;
-
-  // 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;
-    } 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());
+  state = EvaluateLogicalExpression(B, Pred->getLocationContext(), state);
+  SVal X = state->getSVal(B, Pred->getLocationContext());
+
+  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 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));
 }
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