powerpc64-gcc unable to compile clang 3.8.0 from clang380-import -r294609 via buildworld
Mark Millard
markmi at dsl-only.net
Sun Jan 24 06:17:35 UTC 2016
I found a (the?) overall smoking gun: for powerpc64-gcc FreeBSD's /projects/clang380-import/contrib/libc++/include/__config is doing (for example):
#define _LIBCPP_HAS_NO_RVALUE_REFERENCES
(and other out of date classifications) for gcc5 vintages, and possibly for gcc49 and others as well.
This in turn means that other parts of libc++ are not providing modern definitions that modern enough gcc5 variations handle fine. Instead libc++ provides old definitions that are incorrect/incomplete for c++11 and later (despite use of -std=c++11 on the command line).
clang++ gets the modern definitions from libc++.
So: Not a gcc problem, a libc++ problem.
In the code that got the initial error report that I showed /projects/clang380-import/contrib/libc++/include/__config was using old definitions of std::begin(. . .) and std::end(. . .) for powerpc64-gcc and when the modern definitions are used instead under powerpc64-gcc the matching error report disappears.
Part of this may be that __config is still always expecting for g++ that __GXX_EXPERIMENTAL_CXX0X__ is defined if nearly any of the modern c++11 or later features exist at all. At this point various things are not experimental any more and -std=c++11 features likely are not considered experimental any more in more recent gcc5 and later vintages.
This __GXX_EXPERIMENTAL_CXX0X__ use is still true of __config at llvm's /libcxx/tags/RELEASE_380/rc1/include/__config and at llvm's /libcxx/trunk/include/__config too (head of trunk for the file).
Looking at the most recent content of FreeBSD's /projects/clang380-import/contrib/libc++/include/__config shows:
. . .
#elif defined(__GNUC__)
. . .
. . .
// GCC 5 will support variable templates
#define _LIBCPP_HAS_NO_VARIABLE_TEMPLATES
. . .
#ifndef __GXX_EXPERIMENTAL_CXX0X__
. . .
#define _LIBCPP_HAS_NO_RVALUE_REFERENCES
. . .
#else // __GXX_EXPERIMENTAL_CXX0X__
. . .
#if _GNUC_VER < 403
#define _LIBCPP_HAS_NO_RVALUE_REFERENCES
#endif
. . .
_LIBCPP_HAS_NO_RVALUE_REFERENCES being defined in turn causes /projects/clang380-import/contrib/libc++/include/iterator to define things like std::begin(. . .) in an old way, such as the following that was involved in the initial error report that I got:
> #else // !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES) && !defined(_LIBCPP_HAS_NO_TRAILING_RETURN)
>
> template <class _Cp>
> inline _LIBCPP_INLINE_VISIBILITY
> typename _Cp::iterator
> begin(_Cp& __c)
> {
> return __c.begin();
> }
>
> template <class _Cp>
> inline _LIBCPP_INLINE_VISIBILITY
> typename _Cp::const_iterator
> begin(const _Cp& __c)
> {
> return __c.begin();
> }
>
> template <class _Cp>
> inline _LIBCPP_INLINE_VISIBILITY
> typename _Cp::iterator
> end(_Cp& __c)
> {
> return __c.end();
> }
>
> template <class _Cp>
> inline _LIBCPP_INLINE_VISIBILITY
> typename _Cp::const_iterator
> end(const _Cp& __c)
> {
> return __c.end();
> }
Manually forced replacement with modern source:
> template <class _Cp>
> inline _LIBCPP_INLINE_VISIBILITY
> auto
> begin(_Cp& __c) -> decltype(__c.begin())
> {
> return __c.begin();
> }
>
> template <class _Cp>
> inline _LIBCPP_INLINE_VISIBILITY
> auto
> begin(const _Cp& __c) -> decltype(__c.begin())
> {
> return __c.begin();
> }
>
> template <class _Cp>
> inline _LIBCPP_INLINE_VISIBILITY
> auto
> end(_Cp& __c) -> decltype(__c.end())
> {
> return __c.end();
> }
>
> template <class _Cp>
> inline _LIBCPP_INLINE_VISIBILITY
> auto
> end(const _Cp& __c) -> decltype(__c.end())
> {
> return __c.end();
> }
eliminated the specific initial error report. (It is not a sufficient workaround to build clang as far as I know.)
The following code extracted from libc++ and simplified from the llvm code that got the initial error that I showed can be used to experiment with the definitions of std::begin(. . .) and std:end(. . .) for powerpc64-gcc vs. clang++ via commands like:
> /usr/local/bin/powerpc64-portbld-freebsd11.0-g++ -std=c++11 -I/usr/include/c++/v1/ func.cpp
vs.
> clang++ -std=c++11 -stdlib=libc++ func.cpp
with func.cpp being . . .
(llvm's head-of-trunk iterator still has the same #if . . . #else . . . #endif structure)
> #include <__config>
>
> _LIBCPP_BEGIN_NAMESPACE_STD
>
> #if !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES) && !defined(_LIBCPP_HAS_NO_TRAILING_RETURN)
>
> template <class _Cp>
> inline _LIBCPP_INLINE_VISIBILITY
> auto
> begin(_Cp& __c) -> decltype(__c.begin())
> {
> return __c.begin();
> }
>
> template <class _Cp>
> inline _LIBCPP_INLINE_VISIBILITY
> auto
> begin(const _Cp& __c) -> decltype(__c.begin())
> {
> return __c.begin();
> }
>
> template <class _Cp>
> inline _LIBCPP_INLINE_VISIBILITY
> auto
> end(_Cp& __c) -> decltype(__c.end())
> {
> return __c.end();
> }
>
> template <class _Cp>
> inline _LIBCPP_INLINE_VISIBILITY
> auto
> end(const _Cp& __c) -> decltype(__c.end())
> {
> return __c.end();
> }
>
> #else // !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES) && !defined(_LIBCPP_HAS_NO_TRAILING_RETURN)
>
> template <class _Cp>
> inline _LIBCPP_INLINE_VISIBILITY
> typename _Cp::iterator
> begin(_Cp& __c)
> {
> return __c.begin();
> }
>
> template <class _Cp>
> inline _LIBCPP_INLINE_VISIBILITY
> typename _Cp::const_iterator
> begin(const _Cp& __c)
> {
> return __c.begin();
> }
>
> template <class _Cp>
> inline _LIBCPP_INLINE_VISIBILITY
> typename _Cp::iterator
> end(_Cp& __c)
> {
> return __c.end();
> }
>
> template <class _Cp>
> inline _LIBCPP_INLINE_VISIBILITY
> typename _Cp::const_iterator
> end(const _Cp& __c)
> {
> return __c.end();
> }
>
> #endif // !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES) && !defined(_LIBCPP_HAS_NO_TRAILING_RETURN)
>
> _LIBCPP_END_NAMESPACE_STD
>
> namespace ns {
> template <typename IteratorT>
> class iterator_range {
> IteratorT begin_iterator, end_iterator;
>
> public:
> iterator_range(IteratorT begin_iterator, IteratorT end_iterator)
> : begin_iterator(begin_iterator),
> end_iterator(end_iterator) {}
>
> IteratorT begin() const { return begin_iterator; }
> IteratorT end() const { return end_iterator; }
> };
>
> template <class T> iterator_range<T> make_range(T x, T y) {
> return iterator_range<T>(x, y);
> }
>
> template <typename ContainerTy>
> auto test( ContainerTy &&C
> ) -> decltype(make_range(std::begin(C),
> std::end(C))) {
> return make_range(std::begin(C),
> std::end(C));
> }
> };
>
> typedef int *const init_const_ptr;
> typedef int *const *init_const_iterator;
>
> int v;
> init_const_ptr cvp = &v;
> init_const_iterator pcpv = &cvp;
>
> typedef ns::iterator_range<init_const_iterator> init_const_range;
>
> void f(void) {
> for (auto *I : ns::test(init_const_range(pcpv,pcpv+1))) {
> }
> }
>
> int main(void)
> { return 0; }
Commenting out inside one branch of the #if . . . #else . . . #endif makes very clear if that part was in use or the other part. Switching compilers switches which part is used in my testing.
It also appears that /projects/clang380-import/contrib/libc++/include/__config has not been tracking various 3.8.0 changes. For example llvm's Log of /libcxx/tags/RELEASE_380/rc1/include/__config shows that its 2015-Dec-14 -r255585 version changed the _LIBCPP_HAS_NO_VARIABLE_TEMPLATES source that I quoted earlier to instead be:
> // GCC 5 will support variable templates
> #if !defined(__cpp_variable_templates) || __cpp_variable_templates < 201304L
> #define _LIBCPP_HAS_NO_VARIABLE_TEMPLATES
> #endif
(increasing the support for modern g++'s a little bit).
llvm's /libcxx/tags/RELEASE_380/rc1/include/__config is currently at -r258234 (2016-Jan-19) with about 8 checkins between the 2 versions.
Looking up /projects/clang380-import/contrib/libc++/include/iterator and others show they date back being copies made on 2015-Dec-30 of vintages from FreeBSD's 2015-Oct 3.7.0 materials as well. (For some files that may well be current for all I know.)
For all I know this status is deliberate for some reason. But it would seem that to expect modern gcc vintages to be supported well for modern libc++ uses probably has a necessary (but not sufficient) aspect of tracking llvm's updates that add handling of more modern gcc vintages.
Side note:
One revision in llvm's /libcxx/tags/RELEASE_380/rc1/include/ that I ran into that might be of note: -r257716 from 2016-Jan-13 says
> Fix PR#25973 : 'basic_string::assign(InputIt, InputIt) doesn't provide the strong exception safety guarantee'. This turned out to be a pervasive problem in <string>, which required a fair amount of rework. Add in an optimization for when iterators provide noexcept increment/comparison/assignment/dereference (which covers many of the iterators in libc++).
===
Mark Millard
markmi at dsl-only.net
On 2016-Jan-23, at 7:08 AM, Dimitry Andric <dim at FreeBSD.org> wrote:
On 23 Jan 2016, at 12:25, Mark Millard <markmi at dsl-only.net> wrote:
>
> I tried a buildworld that included building clang and lldb based on using powerpc64-xtoolchain-gcc/powerpc64-gcc as a cross compiler. It failed, see below. This might indicate a more general gcc 5.x vs. clang 3.8.0 source code mismatch. This was my first try. This could have been true for some time.
>
> --- CFG.o ---
> /usr/local/bin/powerpc64-portbld-freebsd11.0-g++ -isystem /usr/obj/xtoolchain/powerpc.powerpc64/usr/src/tmp/usr/include -L/usr/obj/xtoolchain/powerpc.powerpc64/usr/src/tmp/usr/lib --sysroot=/usr/obj/xtoolchain/powerpc.po
> werpc64/usr/src/tmp -B/usr/local/powerpc64-freebsd/bin/ -I/usr/obj/xtoolchain/powerpc.powerpc64/usr/src/tmp/usr/include/c++/v1 -std=gnu++11 -L/usr/obj/xtoolchain/powerpc.powerpc64/usr/src/tmp/../lib/libc++ --sysroot=/usr
> /obj/xtoolchain/powerpc.powerpc64/usr/src/tmp -B/usr/local/powerpc64-freebsd/bin/ -O2 -pipe -I/usr/src/lib/clang/libclanganalysis/../../../contrib/llvm/include -I/usr/src/lib/clang/libclanganalysis/../../../contrib/llvm
> /tools/clang/include -I/usr/src/lib/clang/libclanganalysis/../../../contrib/llvm/tools/clang/lib/Analysis -I. -I/usr/src/lib/clang/libclanganalysis/../../../contrib/llvm/../../lib/clang/include -DLLVM_ON_UNIX -DLLVM_ON_FREEBSD -D__STDC_LIMIT_MACROS -D__STDC_CONSTANT_MACROS -DCLANG_ENABLE_ARCMT -DCLANG_ENABLE_STATIC_ANALYZER -fno-strict-aliasing -DLLVM_DEFAULT_TARGET_TRIPLE=\"powerpc64-unknown-freebsd11.0\" -DLLVM_HOST_TRIPLE=\"powerpc64
> -unknown-freebsd11.0\" -DDEFAULT_SYSROOT=\"\" -MD -MP -MF.depend.CFG.o -MTCFG.o -fstack-protector-strong -Wno-error=unused-function -Wno-error=enum-compare -Wno-error=logical-not-parentheses -Wno-error=bool-compare -Wno-
> error=uninitialized -Wno-error=array-bounds -Wno-error=clobbered -Wno-error=cast-align -Wno-error=extra -Wno-error=attributes -Wno-error=inline -Wno-error=unused-but-set-variable -Wno-error=unused-value -Wno-error=strict
> -aliasing -Wno-error=address -std=c++11 -fno-exceptions -fno-rtti -c /usr/src/lib/clang/libclanganalysis/../../../contrib/llvm/tools/clang/lib/Analysis/CFG.cpp -o CFG.o
> . . .
> --- all_subdir_libclanganalysis ---
> /usr/src/lib/clang/libclanganalysis/../../../contrib/llvm/tools/clang/lib/Analysis/CFG.cpp: In member function 'std::__1::unique_ptr<clang::CFG> {anonymous}::CFGBuilder::buildCFG(const clang::Decl*, clang::Stmt*)':
> /usr/src/lib/clang/libclanganalysis/../../../contrib/llvm/tools/clang/lib/Analysis/CFG.cpp:1046:45: error: no matching function for call to 'reverse(clang::CXXConstructorDecl::init_const_range)'
> for (auto *I : llvm::reverse(CD->inits())) {
> ^
I just tried building clang 3.8.0 with gcc 5.3.0, but that went fine.
However, by default gcc uses its own copy of libstdc++. The above error
is most likely something caused by libc++ and gcc not playing well
together.
This kind of error is always hard to report upstream, since the gcc
maintainers obviously do not care that much about libc++, while the
libc++ maintainers do not care that much about gcc. :-)
-Dimitry
More information about the freebsd-toolchain
mailing list