cor3ntin added inline comments.
================ Comment at: clang/lib/Headers/stdckdint.h:13 + +#if defined(__GNUC__) +#define ckd_add(R, A, B) __builtin_add_overflow((A), (B), (R)) ---------------- aaron.ballman wrote: > hiraditya wrote: > > enh wrote: > > > hiraditya wrote: > > > > xbolva00 wrote: > > > > > yabinc wrote: > > > > > > enh wrote: > > > > > > > enh wrote: > > > > > > > > enh wrote: > > > > > > > > > ZijunZhao wrote: > > > > > > > > > > enh wrote: > > > > > > > > > > > is this ever _not_ set for clang? > > > > > > > > > > https://github.com/llvm/llvm-project/blob/main/clang/lib/Headers/stdbool.h#L23 > > > > > > > > > > I think it is set? > > > > > > > > > i get an error from > > > > > > > > > ``` > > > > > > > > > /tmp$ cat x.c > > > > > > > > > #if defined(__GNUC__) > > > > > > > > > #error foo > > > > > > > > > #endif > > > > > > > > > ``` > > > > > > > > > regardless of whether i compile with -std=c11 or -std=gnu11. > > > > > > > > > neither -ansi nor -pedantic seem to stop it either. > > > > > > > > it does look like it _should_ be possible to not have it set > > > > > > > > though? > > > > > > > > llvm/llvm-project/clang/lib/Frontend/InitPreprocessor.cpp has: > > > > > > > > ``` > > > > > > > > if (LangOpts.GNUCVersion != 0) { > > > > > > > > // Major, minor, patch, are given two decimal places each, > > > > > > > > so 4.2.1 becomes > > > > > > > > // 40201. > > > > > > > > unsigned GNUCMajor = LangOpts.GNUCVersion / 100 / 100; > > > > > > > > unsigned GNUCMinor = LangOpts.GNUCVersion / 100 % 100; > > > > > > > > unsigned GNUCPatch = LangOpts.GNUCVersion % 100; > > > > > > > > Builder.defineMacro("__GNUC__", Twine(GNUCMajor)); > > > > > > > > Builder.defineMacro("__GNUC_MINOR__", Twine(GNUCMinor)); > > > > > > > > Builder.defineMacro("__GNUC_PATCHLEVEL__", > > > > > > > > Twine(GNUCPatch)); > > > > > > > > Builder.defineMacro("__GXX_ABI_VERSION", "1002"); > > > > > > > > > > > > > > > > if (LangOpts.CPlusPlus) { > > > > > > > > Builder.defineMacro("__GNUG__", Twine(GNUCMajor)); > > > > > > > > Builder.defineMacro("__GXX_WEAK__"); > > > > > > > > } > > > > > > > > } > > > > > > > > ``` > > > > > > > /me wonders whether the right test here is actually `#if > > > > > > > __has_feature(__builtin_add_overflow)` (etc)... > > > > > > > > > > > > > > but at this point, you definitely need an llvm person :-) > > > > > > From > > > > > > https://clang.llvm.org/docs/LanguageExtensions.html#checked-arithmetic-builtins, > > > > > > we can check them with > > > > > > __has_builtin(__builtin_add_overflow) && > > > > > > __has_builtin(__builtin_sub_overflow) && > > > > > > __has_builtin(__builtin_mul_overflow). > > > > > > I saw some code also checks if __GNUC__ >= 5: > > > > > > > > > > > > // The __GNUC__ checks can not be removed until we depend on GCC >= > > > > > > 10.1 > > > > > > // which is the first version that returns true for > > > > > > __has_builtin(__builtin_add_overflow) > > > > > > #if __GNUC__ >= 5 || __has_builtin(__builtin_add_overflow) > > > > > > > > > > > > I guess we don't need to support real gcc using this header here. > > > > > > So maybe only checking __has_builtin is enough? > > > > > > > > > > > > By the way, if __builtin_add_overflow may not appear on some > > > > > > targets, do we need to modify tests to specify triple like "-triple > > > > > > "x86_64-unknown-unknown"" in > > > > > > https://github.com/llvm/llvm-project/blob/main/clang/test/CodeGen/builtins-overflow.c#L5 > > > > > > ? > > > > > > > > > > > #ifndef __has_builtin // Optional of course. > > > > > #define __has_builtin(x) 0 // Compatibility with non-clang > > > > > compilers. > > > > > #endif > > > > > > > > > > ... > > > > > #if __has_builtin(__builtin_trap) > > > > > __builtin_trap(); > > > > > #else > > > > > abort(); > > > > > #endif > > > > > /me wonders whether the right test here is actually #if > > > > > __has_feature(__builtin_add_overflow) (etc)... > > > > > > > > i think that should be added. > > > > > > > > I guess we also need a with `__STDC_VERSION__ > 202000L`? in princple > > > > we'd have a C23 number for it but i'm not sure if that has been added > > > > to clang yet. > > > > i think that should be added. > > > > > > i was advising the opposite --- now this is a standard C23 feature, any > > > architectures where __builtin_*_overflow doesn't work need to be found > > > and fixed. and we'll do that quicker if we unconditionally expose these > > > and (more importantly!) run the tests. > > > > > > > I guess we also need a with __STDC_VERSION__ > 202000L? > > > > > > _personally_ i think that's silly because you can't hide the header file, > > > so it doesn't make any sense to just have it empty if someone's actually > > > #included it. we don't do this anywhere in bionic for example, for this > > > reason. but obviously that's an llvm decision, and it does look like the > > > other similar headers _do_ have this check, so, yeah, probably. > > > i was advising the opposite -- now this is a standard C23 feature, any > > > architectures where __builtin > > > > you're right. it seems like `__builtin_add_overflow` is expected to be > > defined by default > > (https://github.com/llvm/llvm-project/blob/main/clang/test/Sema/builtins-overflow.c#L4). > > > > > and it does look like the other similar headers _do_ have this check, so, > > > yeah, probably. > > > > yeah, Several headers have checks for stdc_version that supported e.g., > > https://github.com/llvm/llvm-project/blob/main/clang/lib/Headers/stdint.h#L504. > > > > nit: It will be nice to add a reference to C23 that added this. i.e., 7.20. > > example: > > https://github.com/llvm/llvm-project/blob/main/clang/lib/Headers/stdint.h#L910 > Yeah, I think this should be guarded by `__STDC_VERSION__` and not `__GNUC__` > -- this is a C23 feature, not a GNU feature. > > We could expose these APIs in earlier C modes, but the macros defined here do > not use a reserved identifier and so we'd be stealing those names out from > under the user and so we might not want to. We don't expose `unreachable` in > earlier language modes (in `stddef.h`) or the width macros (in `stdint.h`), > so I lean towards not exposing this functionality in older language modes. > > We could also limit this functionality to just C (and not expose it in C++ > mode). We don't do that for any of the other C standard library headers, > however, so I think we should continue to expose the functionality in C++. > > Also, should we be falling back to the system-installed header if in hosted > mode and one exists? > > The file is missing the `__STDC_VERSION_STDCKDINT_H__` macro definition from > C2x 7.20p2 The content of C headers in C++ mode is dictated by http://eel.is/c++draft/support.c.headers#other-1. I think making them empty until WG21 has the opportunity to discuss a rebase of C++26 on top of C2x would make sense conservatively. The fact that these things are macros and that C++ is working on c++-specific solution to the same problem makes me think that being conservative is wise Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D157331/new/ https://reviews.llvm.org/D157331 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
