[analyzer] Construct a SymExpr even when the constraint solver cannot
reason about the expression.

This essentially keeps more history about how symbolic values were
constructed. As an optimization, previous to this commit, we only kept
the history if one of the symbols was tainted, but it's valuable keep
the history around for other purposes as well: it allows us to avoid
constructing conjured symbols.

Specifically, we need to identify the value of ptr as
ElementRegion (result of pointer arithmetic) in the following code.
However, before this commit '(2-x)' evaluated to Unknown value, and as
the result, 'p + (2-x)' evaluated to Unknown value as well.

int *p = malloc(sizeof(int));
ptr = p + (2-x);

This change brings 2% slowdown on sqlite. Fixes radar://11329382.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@155944 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/clang/StaticAnalyzer/Core/PathSensitive/SValBuilder.h b/include/clang/StaticAnalyzer/Core/PathSensitive/SValBuilder.h
index 4ad36f9..2acb5c1 100644
--- a/include/clang/StaticAnalyzer/Core/PathSensitive/SValBuilder.h
+++ b/include/clang/StaticAnalyzer/Core/PathSensitive/SValBuilder.h
@@ -107,12 +107,9 @@
   /// that value is returned. Otherwise, returns NULL.
   virtual const llvm::APSInt *getKnownValue(ProgramStateRef state, SVal val) = 0;
   
-  /// Handles generation of the value in case the builder is not smart enough to
-  /// handle the given binary expression. Depending on the state, decides to
-  /// either keep the expression or forget the history and generate an
-  /// UnknownVal.
-  SVal makeGenericVal(ProgramStateRef state, BinaryOperator::Opcode op,
-                          NonLoc lhs, NonLoc rhs, QualType resultTy);
+  /// Constructs a symbolic expression for two non-location values.
+  SVal makeSymExprValNN(ProgramStateRef state, BinaryOperator::Opcode op,
+                      NonLoc lhs, NonLoc rhs, QualType resultTy);
 
   SVal evalBinOp(ProgramStateRef state, BinaryOperator::Opcode op,
                  SVal lhs, SVal rhs, QualType type);
diff --git a/lib/StaticAnalyzer/Core/SValBuilder.cpp b/lib/StaticAnalyzer/Core/SValBuilder.cpp
index 9e97f5e..c1217e1 100644
--- a/lib/StaticAnalyzer/Core/SValBuilder.cpp
+++ b/lib/StaticAnalyzer/Core/SValBuilder.cpp
@@ -195,30 +195,26 @@
 
 //===----------------------------------------------------------------------===//
 
-SVal SValBuilder::makeGenericVal(ProgramStateRef State,
-                                     BinaryOperator::Opcode Op,
-                                     NonLoc LHS, NonLoc RHS,
-                                     QualType ResultTy) {
-  // If operands are tainted, create a symbol to ensure that we propagate taint.
-  if (State->isTainted(RHS) || State->isTainted(LHS)) {
-    const SymExpr *symLHS;
-    const SymExpr *symRHS;
+SVal SValBuilder::makeSymExprValNN(ProgramStateRef State,
+                                 BinaryOperator::Opcode Op,
+                                 NonLoc LHS, NonLoc RHS,
+                                 QualType ResultTy) {
+  const SymExpr *symLHS;
+  const SymExpr *symRHS;
 
-    if (const nonloc::ConcreteInt *rInt = dyn_cast<nonloc::ConcreteInt>(&RHS)) {
-      symLHS = LHS.getAsSymExpr();
-      return makeNonLoc(symLHS, Op, rInt->getValue(), ResultTy);
-    }
-
-    if (const nonloc::ConcreteInt *lInt = dyn_cast<nonloc::ConcreteInt>(&LHS)) {
-      symRHS = RHS.getAsSymExpr();
-      return makeNonLoc(lInt->getValue(), Op, symRHS, ResultTy);
-    }
-
+  if (const nonloc::ConcreteInt *rInt = dyn_cast<nonloc::ConcreteInt>(&RHS)) {
     symLHS = LHS.getAsSymExpr();
-    symRHS = RHS.getAsSymExpr();
-    return makeNonLoc(symLHS, Op, symRHS, ResultTy);
+    return makeNonLoc(symLHS, Op, rInt->getValue(), ResultTy);
   }
-  return UnknownVal();
+
+  if (const nonloc::ConcreteInt *lInt = dyn_cast<nonloc::ConcreteInt>(&LHS)) {
+    symRHS = RHS.getAsSymExpr();
+    return makeNonLoc(lInt->getValue(), Op, symRHS, ResultTy);
+  }
+
+  symLHS = LHS.getAsSymExpr();
+  symRHS = RHS.getAsSymExpr();
+  return makeNonLoc(symLHS, Op, symRHS, ResultTy);
 }
 
 
diff --git a/lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp b/lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp
index 45be5db..2522cbb 100644
--- a/lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp
+++ b/lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp
@@ -304,7 +304,7 @@
   while (1) {
     switch (lhs.getSubKind()) {
     default:
-      return makeGenericVal(state, op, lhs, rhs, resultTy);
+      return makeSymExprValNN(state, op, lhs, rhs, resultTy);
     case nonloc::LocAsIntegerKind: {
       Loc lhsL = cast<nonloc::LocAsInteger>(lhs).getLoc();
       switch (rhs.getSubKind()) {
@@ -327,7 +327,7 @@
               return makeTruthVal(true, resultTy);
             default:
               // This case also handles pointer arithmetic.
-              return makeGenericVal(state, op, lhs, rhs, resultTy);
+              return makeSymExprValNN(state, op, lhs, rhs, resultTy);
           }
       }
     }
@@ -389,9 +389,9 @@
             if (lhsValue == 0)
               // At this point lhs and rhs have been swapped.
               return rhs;
-            return makeGenericVal(state, op, rhs, lhs, resultTy);
+            return makeSymExprValNN(state, op, rhs, lhs, resultTy);
           default:
-            return makeGenericVal(state, op, rhs, lhs, resultTy);
+            return makeSymExprValNN(state, op, rhs, lhs, resultTy);
         }
       }
     }
@@ -406,7 +406,7 @@
             dyn_cast<SymIntExpr>(selhs->getSymbol());
 
         if (!symIntExpr)
-          return makeGenericVal(state, op, lhs, rhs, resultTy);
+          return makeSymExprValNN(state, op, lhs, rhs, resultTy);
 
         // Is this a logical not? (!x is represented as x == 0.)
         if (op == BO_EQ && rhs.isZeroConstant()) {
@@ -454,7 +454,7 @@
         // For now, only handle expressions whose RHS is a constant.
         const nonloc::ConcreteInt *rhsInt = dyn_cast<nonloc::ConcreteInt>(&rhs);
         if (!rhsInt)
-          return makeGenericVal(state, op, lhs, rhs, resultTy);
+          return makeSymExprValNN(state, op, lhs, rhs, resultTy);
 
         // If both the LHS and the current expression are additive,
         // fold their constants.
@@ -539,7 +539,7 @@
               resultTy);
         }
 
-        return makeGenericVal(state, op, lhs, rhs, resultTy);
+        return makeSymExprValNN(state, op, lhs, rhs, resultTy);
       }
     }
     }
diff --git a/test/Analysis/malloc.c b/test/Analysis/malloc.c
index 32c6171..1fc8743 100644
--- a/test/Analysis/malloc.c
+++ b/test/Analysis/malloc.c
@@ -776,6 +776,13 @@
   return p->n.m; // expected-warning {{leak}}
 }
 
+// Pointer arithmetic, returning an ElementRegion.
+void *radar11329382(unsigned bl) {
+  void *ptr = malloc (16);
+  ptr = ptr + (2 - bl);
+  return ptr; // no warning
+}
+
 // ----------------------------------------------------------------------------
 // Below are the known false positives.