I notice we have a number of cases in LLVM source which allows
(optional) use of C++17, but it is never mandatory or assumed:
e.g StringRef.h
#if __cplusplus > 201402L
#include <string_view>
#endif
...
// Constexpr version of std::strlen.
static constexpr size_t strLen(const char *Str) {
#if __cplusplus > 201402L
return std::char_traits<char>::length(Str);
#elif __has_builtin(__builtin_strlen) || defined(__GNUC__) || \
(defined(_MSC_VER) && _MSC_VER >= 1916)
return __builtin_strlen(Str);
#else
const char *Begin = Str;
while (*Str != '\0')
++Str;
return Str - Begin;
#endif
}
According to https://llvm.org/docs/CodingStandards.html - we only accept
up to standard C++14 code that is supported by our minimum
gcc/clang/msvc versions.
Does anyone know what in particular is preventing us from bumping the
minimum compiler versions to make 'compiler supported' C++17 a similar
requirement to build LLVM at this time?
https://lists.llvm.org/pipermail/llvm-dev/2018-October/127045.html
https://reviews.llvm.org/D47073
AFAICT, the last time this was discussed (back in 2018/9), some
developers still had a dependency on Ubuntu 1604 LTS (and other old
distros), whose default gcc didn't have adequate C++17 support. Support
for 1604 has been extended to April 2026 - I'm guessing we're not going
to wait until then?
Cheers, Simon.
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There is a process for this that's documented here:
https://llvm.org/docs/DeveloperPolicy.html#id23
An RFC like this should be written:
https://lists.llvm.org/pipermail/llvm-dev/2019-January/129452.html
I don't think anything is blocking it except that someone needs to do
the work to investigate the different toolchains and summarize it in a
RFC email to the list.
-- Tobias