[analyzer] Let ConstraintManager subclasses provide a more efficient checkNull.

Previously, every call to a ConstraintManager's isNull would do a full
assumeDual to test feasibility. Now, ConstraintManagers can override
checkNull if they have a cheaper way to do the same thing.
RangeConstraintManager can do this in less than half the work.

<rdar://problem/12608209>

llvm-svn: 167138

1 files changed, 25 insertions, 0 deletions

diff --git a/clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp b/clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp
index a4c841eb6ba..467abd08378 100644
--- a/clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp
+++ b/clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp
@@ -324,6 +324,7 @@ public:
                              const llvm::APSInt& Adjustment);
 
   const llvm::APSInt* getSymVal(ProgramStateRef St, SymbolRef sym) const;
+  ConditionTruthVal checkNull(ProgramStateRef State, SymbolRef Sym);
 
   ProgramStateRef removeDeadBindings(ProgramStateRef St, SymbolReaper& SymReaper);
 
@@ -347,6 +348,30 @@ const llvm::APSInt* RangeConstraintManager::getSymVal(ProgramStateRef St,
   return T ? T->getConcreteValue() : NULL;
 }
 
+ConditionTruthVal RangeConstraintManager::checkNull(ProgramStateRef State,
+                                                    SymbolRef Sym) {
+  const RangeSet *Ranges = State->get<ConstraintRange>(Sym);
+
+  // If we don't have any information about this symbol, it's underconstrained.
+  if (!Ranges)
+    return ConditionTruthVal();
+
+  // If we have a concrete value, see if it's zero.
+  if (const llvm::APSInt *Value = Ranges->getConcreteValue())
+    return *Value == 0;
+
+  BasicValueFactory &BV = getBasicVals();
+  APSIntType IntType = BV.getAPSIntType(Sym->getType());
+  llvm::APSInt Zero = IntType.getZeroValue();
+
+  // Check if zero is in the set of possible values.
+  if (Ranges->Intersect(BV, F, Zero, Zero).isEmpty())
+    return false;
+
+  // Zero is a possible value, but it is not the /only/ possible value.
+  return ConditionTruthVal();
+}
+
 /// Scan all symbols referenced by the constraints. If the symbol is not alive
 /// as marked in LSymbols, mark it as dead in DSymbols.
 ProgramStateRef