On Wed, Oct 9, 2013 at 12:27 PM, Richard Trieu <[email protected]> wrote:
> > > > On Tue, Oct 8, 2013 at 9:09 PM, Arthur O'Dwyer > <[email protected]>wrote: > >> Really cool! I don't understand the template example, though... >> >> // sum<0>() is instantiated, does recursively call itself, but never >> runs. >> template <int value> int sum() { return value + sum<value/2>(); } >> // <== notice that your test is actually missing the (), so you've >> got a bogus syntax error in there >> template<> int sum<0>() { return 1; } >> > > My mistake. That should be int sum<1>(). For value > 1, it will > eventually call sum<1>(). But if sum<0>() is called, it just calls itself. > If the analysis is applied to template specializations, then, you'd only get this warning if your code lead to the instantiation of sum<0> - in which case the warning is correct and useful. I'm with Arthur - it's still not clear to me why this warning would need to avoid templates, as long as it ran on template specializations not template patterns. > >> You imply that Clang would get confused and think that sum<0> calls >> itself... but how can that be, since sum<0> simply returns 1? Or, if >> you mean that Clang would mistakenly try to instantiate the regular >> ("un-specialized"?) version of sum<i> with i=0... how can *that* be, >> since you could just as well make it >> >> template <int value> int sum() { static_assert( i != 0, "" ); >> return value + sum<value/2>(); } >> >> It would be great if the compiler could only choose to run on good code. > In practice, we need to look out for edgecases. > > >> ? Clang shouldn't be trying to static-analyze instantiations that >> aren't real. :P >> I'd like to see this patch fixed so that it works properly on >> templates, because that strikes me as exactly the case where this sort >> of warning would be most useful. We want to be able to distinguish the >> cases >> >> template <int value> int sum() { return value + sum<value/2>(); } >> // no warning >> template<> int sum<0>() { return 1; } >> void f() { sum<4>(); } >> >> and >> >> template <int value> int sum() { return value + sum<value/2>(); } >> // yes warning >> void f() { sum<4>(); } >> >> >> Also, FWIW, I see no reason to special-case infinite loops. >> >> void f() { while (true) f(); } >> >> is buggy enough to deserve a diagnostic, IMO. (Such a construct >> probably never happens in practice, but when it *does* happen, that >> one time in a million, and an engineer spends three hours tracking it >> down, he'll probably be annoyed that Clang specifically considered >> pointing out the problem and then silently swallowed it.) >> > > Except that there's plenty of reasons to allow this. Probably the most > common are programs that should never terminate and have a while(true) loop > in their main function. It's possible to make a list of the well-known > patterns to ignore [while(1), while(true), for(;;)] and warn on the rest. > >> >> my $.02, >> –Arthur >> >> >> On Tue, Oct 8, 2013 at 8:13 PM, Richard Trieu <[email protected]> wrote: >> > Implement a warning to detect when a function will call itself >> recursively on every code path. If a program ever calls such a function, >> the function will attempt to call itself until it runs out of stack space. >> > >> > This warning searches the CFG to determine if every codepath results in >> a self call. In addition to the test for this warning, several other tests >> needed to be fixed, and a pragma to prevent this warning where Clang really >> wants a stack overflow. >> > >> > Testing with this warning has already caught several buggy functions. >> Common mistakes include: incorrect namespaces, wrapper classes not >> forwarding calls properly, similarly named member function and data member, >> and failing to call an overload of the same function. When run outside of >> template instantiations, all true positives. In template instantiations, >> only 25% true positive. Therefore, this warning is disabled in template >> instantiations. An example of such a false positive is in the test cases. >> > >> > http://llvm-reviews.chandlerc.com/D1864 >> > >> > Files: >> > test/Analysis/inlining/test-always-inline-size-option.c >> > test/Analysis/misc-ps-region-store.cpp >> > test/Analysis/cxx11-crashes.cpp >> > test/FixIt/typo.m >> > test/FixIt/fixit.c >> > test/Sema/unused-expr-system-header.c >> > test/Sema/warn-unused-function.c >> > test/Sema/attr-deprecated.c >> > test/Parser/cxx-using-declaration.cpp >> > test/Parser/expressions.c >> > test/CodeGen/functions.c >> > test/SemaCXX/statements.cpp >> > test/SemaCXX/warn-bool-conversion.cpp >> > test/SemaCXX/warn-infinite-recursion.cpp >> > test/SemaCXX/MicrosoftCompatibility.cpp >> > test/Lexer/gnu-flags.c >> > include/clang/Basic/DiagnosticSemaKinds.td >> > include/clang/Basic/DiagnosticGroups.td >> > lib/Sema/AnalysisBasedWarnings.cpp >> > lib/Lex/Pragma.cpp >> > >> > _______________________________________________ >> > cfe-commits mailing list >> > [email protected] >> > http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits >> > >> > > > _______________________________________________ > cfe-commits mailing list > [email protected] > http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits > >
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