On Thu, Jan 22, 2015 at 4:55 PM, Hans Wennborg <[email protected]> wrote: > On Thu, Jan 22, 2015 at 2:43 PM, David Blaikie <[email protected]> wrote: >> >> >> On Thu, Jan 22, 2015 at 2:11 PM, Hans Wennborg <[email protected]> wrote: >>> >>> Author: hans >>> Date: Thu Jan 22 16:11:56 2015 >>> New Revision: 226870 >>> >>> URL: http://llvm.org/viewvc/llvm-project?rev=226870&view=rev >>> Log: >>> Make the ?: precedence warning handle pointers to the left of ? >>> >>> Previously, Clang would fail to warn on: >>> >>> int n = x + foo ? 1 : 2; >>> >>> when foo is a pointer. >>> >>> Modified: >>> cfe/trunk/lib/Sema/SemaExpr.cpp >>> cfe/trunk/test/Sema/parentheses.c >>> >>> Modified: cfe/trunk/lib/Sema/SemaExpr.cpp >>> URL: >>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaExpr.cpp?rev=226870&r1=226869&r2=226870&view=diff >>> >>> ============================================================================== >>> --- cfe/trunk/lib/Sema/SemaExpr.cpp (original) >>> +++ cfe/trunk/lib/Sema/SemaExpr.cpp Thu Jan 22 16:11:56 2015 >>> @@ -6129,6 +6129,8 @@ static bool ExprLooksBoolean(Expr *E) { >>> return IsLogicOp(OP->getOpcode()); >>> if (UnaryOperator *OP = dyn_cast<UnaryOperator>(E)) >>> return OP->getOpcode() == UO_LNot; >>> + if (E->getType()->isPointerType()) >> >> >> Could we generalize this a bit further, somehow? (I haven't looked at the >> code in question, but it sounds like this should use some more general tool >> of "try to apply contextual conversion to bool" so that it matches the >> actual semantic situation we're interested in here) > > It's tricky, because we don't really want to match the actual > semantics, we want to figure out if the intention was to use 'foo' as > a conditional expression. That's what 'ExprLooksBoolean' does, and > it's erring on the side of caution. > > For example, we don't want to warn if 'foo' is int, even if that could > be used as a conditional expression. But we do want to warn if 'foo' > is 'a==b', even in C where the type of that expression is int. > > Having said that, I now realised I might have made the warning a > little too broad.. we want to warn here: > > int x = x + ptr ? 1 : 0; > > because 'x + ptr' seems like a pretty unlikely condition expression. > > But we don't want to warn here: > > int y = ptr1 - ptr2 ? 1 : 0; > > I'll think about that.
The last example actually showed up in code yesterday: http://git.savannah.gnu.org/cgit/emacs.git/tree/src/emacs.c?id=emacs-24.4#n2307 The reason I said I didn't want to warn here is because the expression can only be interpreted one way. For example, int y = ptr1 - (ptr2 ? 1 : 0); would not compile because the type has changed. On the other hand, parentheses would certainly make it more readable, and that is what the warning suggests: int y = (ptr1 - ptr2) ? 1 : 0; So I'm now thinking maybe warning here is the right thing, just as -Wparentheses warns about 'a && b || c'. - Hans _______________________________________________ cfe-commits mailing list [email protected] http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
