On Mon, Jun 18, 2012 at 4:06 PM, Jordan Rose <[email protected]> wrote: > > On Jun 18, 2012, at 15:42 , Richard Smith <[email protected]> wrote: > >> On Mon, Jun 18, 2012 at 3:28 PM, Jordan Rose <[email protected]> wrote: >>> >>> On Jun 18, 2012, at 15:23 , Eli Friedman <[email protected]> wrote: >>> >>>> On Mon, Jun 18, 2012 at 3:09 PM, Jordan Rose <[email protected]> wrote: >>>>> Author: jrose >>>>> Date: Mon Jun 18 17:09:19 2012 >>>>> New Revision: 158683 >>>>> >>>>> URL: http://llvm.org/viewvc/llvm-project?rev=158683&view=rev >>>>> Log: >>>>> Support -Winternal-linkage-in-inline in C++ code. >>>>> >>>>> This includes treating anonymous namespaces like internal linkage, and >>>>> allowing >>>>> const variables to be used even if internal. The whole thing's been >>>>> broken out >>>>> into a separate function to avoid nested ifs. >>>> >>>> I think it's worth pointing out that in the C++ case, the given >>>> testcase doesn't strictly violate ODR because the definition of the >>>> function in question isn't actually used in multiple files. Because >>>> of that, it shouldn't be an error with -pedantic-errors (the >>>> diagnostic should use Warning rather than Extension/ExtWarn), and you >>>> should watch to see if there are any bug reports with false positives. >>>> (I think false positives are unlikely, but not impossible.) >>> >>> Ah, I see. Without cross-TU analysis, we can't tell if a function is used >>> in multiple files or not. I think it's valid to leave this as ExtWarn when >>> it's in a header file…it's kind of a ticking time bomb. >> >> -pedantic-errors shouldn't cause us to reject valid code, and not all >> #included files are intended to be included multiple times (we have >> several examples of this in Clang, with (for instance) files generated >> by tablegen). >> >> Have you considered implementing the check for whether a variable used >> within such an inline function has a literal type (or, in C++98, an >> integral or enumeration type), and checking whether the initializer is >> a constant expression? >> >> Checking whether the variable's address is used seems trickier, >> perhaps we can use the result of the odr-use checking mechanism? > > I skipped the literal type check; currently it allows all const variables > with initializers, literal or not. There's also no check for the address > clause (which I mistakenly interpreted as equivalent to "prvalue only", but > which allows references). Those checks won't cause us to reject valid code. > > The only valid code we will reject under -pedantic-errors here is code that > references internal linkage / anonymous namespace non-constant variables or > functions from a file that is included in one translation unit in the entire > compilation. From the perspective of perfection, this is technically > incorrect, and for -pedantic-errors that may be what we want. But there is > never a case where this is not fixable (by putting the offending > function/method in an anonymous namespace), and if someday the included file > shows up in two translation units you have a legitimate pedantic-error which > could affect the behavior of your program. > > I'm genuinely not sure which is worse: missing an error because we don't do > cross-TU checking, or preventing compilation on the case where something is > only included once. We'd warn whether it's ExtWarn or Warning, so that's not > the issue.
Changing ExtWarn -> Warning seems to have no downside. It just makes -pedantic-errors more pedantically correct, which is, after all, the point. If someone is using -pedantic-errors but not -Werror, they will get what they asked for -- allowing this code is not an extension, after all. _______________________________________________ cfe-commits mailing list [email protected] http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
