[PATCH] D44883: [Sema] Extend -Wself-assign and -Wself-assign-field to warn on overloaded self-assignment (classes)

[Roman Lebedev via Phabricator via cfe-commits]

lebedev.ri added a comment.

Will do stage2 testing next..



================
Comment at: lib/Sema/SemaExpr.cpp:12087
+  case BO_AndAssign:
+  case BO_OrAssign:
+    DiagnoseSelfAssignment(S, LHS, RHS, OpLoc, /*IsBuiltin=*/false);
----------------
lebedev.ri wrote:
> rjmccall wrote:
> > Quuxplusone wrote:
> > > I understand why `x &= x` and `x |= x` are mathematically special for the built-in types, but surely `x -= x` and `x ^= x` and `x /= x` are just as likely to indicate programmer error. I would be happy if Clang either took the philosophical stance "We will diagnose `x = x` but uniformly //never// `x op= x`," or else took the pragmatic stance "We will diagnose any `x op= x` or `x op x` that seems likely to be a programming bug." This "middle way" of warning only for `&=` and `|=` is bothersome to me.
> > I think "we want to diagnose anything that seems likely to be a programming bug" is already our policy here.  It's inevitable that we'll overlook examples of that.  I agree that we should apply this warning to at least -=, ^=, and /=.
> Ok, will extend.
Would it make sense to also check `%=`?
It's a direct counterpart to `/=`, so i guess it would?


================
Comment at: lib/Sema/SemaExpr.cpp:12093
+    break;
+  }
+
----------------
rjmccall wrote:
> lebedev.ri wrote:
> > rjmccall wrote:
> > > lebedev.ri wrote:
> > > > rjmccall wrote:
> > > > > I think doing this here can result in double-warning if the overload resolves to a builtin operator.  Now, it might not actually be possible for that to combine with the requirements for self-assignment, but still, I think the right place to diagnose this for C++ is the same place we call DiagnoseSelfMove in CreateOverloadedBinOp.
> > > > > 
> > > > > Can CheckIdentityFieldAssignment just be integrated with DiagnoseSelfAssignment so that callers don't need to do call both?
> > > > > I think the right place to diagnose this for C++ is the same place we call DiagnoseSelfMove in CreateOverloadedBinOp.
> > > > 
> > > > ```
> > > >         switch (Opc) {
> > > >         case BO_Assign:
> > > >         case BO_DivAssign:
> > > >         case BO_SubAssign:
> > > >         case BO_AndAssign:
> > > >         case BO_OrAssign:
> > > >         case BO_XorAssign:
> > > >           DiagnoseSelfAssignment(Args[0], Args[1], OpLoc);
> > > >           CheckIdentityFieldAssignment(Args[0], Args[1], OpLoc);
> > > >           break;
> > > >         default:
> > > >           break;
> > > >         }
> > > > 
> > > >         // Check for a self move.
> > > >         if (Op == OO_Equal)
> > > >           DiagnoseSelfMove(Args[0], Args[1], OpLoc);
> > > > ```
> > > > 
> > > > 
> > > > ^ That does not appear to work. Pretty much all these tests start to fail.
> > > > 
> > > Okay.  It's possible that my suggestion is wrong.  Can you explain more how they fail?
> > Right, i should have been verbose :)
> > There are no test changes as compared to the current diff.
> > Here is the output of `$ ninja check-clang-sema check-clang-semacxx`
> > {F5920055}
> > It is also totally possible that i'm missing something obvious on my end...
> Oh, DiagnoseSelfAssignment disables itself during template instantiation, presumably because it's an easy syntactic check that will always warn on the parsed code and so doesn't need to warn again during instantiation.
> 
> In that case, I think the place you had the check is fine.
Am i correctly reading that as "ok, keep it as it is, in `BuildOverloadedBinOp()`" ?


Repository:
  rC Clang

https://reviews.llvm.org/D44883