[analyzer] CStringChecker should not rely on the analyzer generating UndefOrUnknown value when it cannot reason about the expression.

We are now often generating expressions even if the solver is not known to be able to simplify it. This is another cleanup of the existing code, where the rest of the analyzer and checkers should not base their logic on knowing ahead of the time what the solver can reason about. 

In this case, CStringChecker is performing a check for overflow of 'left+right' operation. The overflow can be checked with either 'maxVal-left' or 'maxVal-right'. Previously, the decision was based on whether the expresion evaluated to undef or not. With this patch, we check if one of the arguments is a constant, in which case we know that 'maxVal-const' is easily simplified. (Another option is to use canReasonAbout() method of the solver here, however, it's currently is protected.)

This patch also contains 2 small bug fixes:
 - swap the order of operators inside SValBuilder::makeGenericVal.
 - handle a case when AddeVal is unknown in GenericTaintChecker::getPointedToSymbol.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@146343 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 5 insertions, 4 deletions

diff --git a/lib/StaticAnalyzer/Checkers/CStringChecker.cpp b/lib/StaticAnalyzer/Checkers/CStringChecker.cpp
index ff9d8689f6..49d8bf5388 100644
--- a/lib/StaticAnalyzer/Checkers/CStringChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/CStringChecker.cpp
@@ -532,10 +532,11 @@ const ProgramState *CStringChecker::checkAdditionOverflow(CheckerContext &C,
   const llvm::APSInt &maxValInt = BVF.getMaxValue(sizeTy);
   NonLoc maxVal = svalBuilder.makeIntVal(maxValInt);
 
-  SVal maxMinusRight = svalBuilder.evalBinOpNN(state, BO_Sub, maxVal, right,
-                                               sizeTy);
-
-  if (maxMinusRight.isUnknownOrUndef()) {
+  SVal maxMinusRight;
+  if (isa<nonloc::ConcreteInt>(right)) {
+    maxMinusRight = svalBuilder.evalBinOpNN(state, BO_Sub, maxVal, right,
+                                                 sizeTy);
+  } else {
     // Try switching the operands. (The order of these two assignments is
     // important!)
     maxMinusRight = svalBuilder.evalBinOpNN(state, BO_Sub, maxVal, left,