PR12214 - warn on suspicious self-compound-assignments

[nikola]

Summary

http://llvm.org/bugs/show_bug.cgi?id=12214

How about something as simple as this? Note that labels in the switch are no longer sorted but this isn't the only place.

[rsmith]

This approach looks good. Patch needs testcases :)

[nikola]

Are you happy with the message or should we go for something more specific mentioning bitwise operators?

[nikola]

Now with tests.

[rsmith]

Maybe tweak the diagnostic (for both this case and the normal self-assignment case) to:

explicitly assigning value of variable of type %0 to itself

(Adding the 'value of' makes this message work better for the compound-assignment case.)

Other than that, LGTM

[nikola]

Done in r209867.

lib/Sema/SemaExpr.cpp

       ResultTy = CheckAssignmentOperands(LHS.get(), RHS, OpLoc, CompResultTy);
     break;
   case BO_AndAssign:
+  case BO_OrAssign: // fallthrough
+    DiagnoseSelfAssignment(*this, LHS.get(), RHS.get(), OpLoc);
   case BO_XorAssign:
-  case BO_OrAssign:
     CompResultTy = CheckBitwiseOperands(LHS, RHS, OpLoc, true);
     CompLHSTy = CompResultTy;
     if (!CompResultTy.isNull() && !LHS.isInvalid() && !RHS.isInvalid())

test/SemaCXX/warn-self-assign.cpp

   b = a = b;
   a = a = a; // expected-warning{{explicitly assigning}}
   a = b = b = a;
+  a &= a; // expected-warning{{explicitly assigning}}
+  a |= a; // expected-warning{{explicitly assigning}}
+  a ^= a;
 }
 
 // Dummy type.