DeadStoresChecker: Don't warn about dead stores into volatile variables

[sberg]

Committed revision 273689.

[zaks.anna]

Thanks!!!

lib/StaticAnalyzer/Checkers/DeadStoresChecker.cpp

if (const BinaryOperator* B = dyn_cast<BinaryOperator>(S)) {
         if (VarDecl *VD = dyn_cast<VarDecl>(DR->getDecl())) {
           // Special case: check for assigning null to a pointer.
           //  This is a common form of defensive programming.
           const Expr *RHS =
             LookThroughTransitiveAssignmentsAndCommaOperators(B->getRHS());
           RHS = RHS->IgnoreParenCasts();
 
           QualType T = VD->getType();
+          if (T.isVolatileQualified())
+            return;
           if (T->isPointerType() || T->isObjCObjectPointerType()) {
             if (RHS->isNullPointerConstant(Ctx, Expr::NPC_ValueDependentIsNull))
               return;
           }
 
           // Special case: self-assignments.  These are often used to shut up
           //  "unused variable" compiler warnings.
           if (const DeclRefExpr *RhsDR = dyn_cast<DeclRefExpr>(RHS))

test/Analysis/dead-stores.c

void testBOComma() {
   int m = getInt(), mm, mmm; //expected-warning {{Value stored to 'm' during its initialization is never read}} // expected-warning{{unused variable 'm'}} // expected-warning{{unused variable 'mm'}} // expected-warning{{unused variable 'mmm'}}
   int n, nn = getInt(); //expected-warning {{Value stored to 'nn' during its initialization is never read}} // expected-warning{{unused variable 'n'}} // expected-warning{{unused variable 'nn'}}
 
   int *p;
   p = (getPtr(), (int *)0); // no warning
 
 }
 
+void testVolatile() {
+    volatile int v;
+    v = 0; // no warning
+}