GRExprEngine:
- Conjure symbols at '--' and '++' unary operations
- Add utility method SVal::GetConjuredSymbolVal() and constify some arguments
  along the way.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@67395 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/GRExprEngine.cpp b/lib/Analysis/GRExprEngine.cpp
index 1f47bc7..80467eb 100644
--- a/lib/Analysis/GRExprEngine.cpp
+++ b/lib/Analysis/GRExprEngine.cpp
@@ -2449,7 +2449,13 @@
       BinaryOperator::Opcode Op = U->isIncrementOp() ? BinaryOperator::Add
                                                      : BinaryOperator::Sub;
 
-      SVal Result = EvalBinOp(Op, V2, MakeConstantVal(1U, U));      
+      SVal Result = EvalBinOp(Op, V2, MakeConstantVal(1U, U));    
+      
+      // Conjure a new symbol if necessary to recover precision.
+      if (Result.isUnknown() || !getConstraintManager().canReasonAbout(Result))
+        Result = SVal::GetConjuredSymbolVal(SymMgr, Ex,
+                                            Builder->getCurrentBlockCount());
+      
       state = BindExpr(state, U, U->isPostfix() ? V2 : Result);
 
       // Perform the store.