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Workaround "error: ‘(9.223372036854775807e+18 / 1.0e+9)’ is not a constant expression" #39044
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The code is like it is because of #14093 ; so read that before attempting a fix. |
This worked for me to fix this. It is quite a minor change. |
*** Bug llvm/llvm-bugzilla-archive#40671 has been marked as a duplicate of this bug. *** |
Is the proper fix being worked on? |
The "proper fix" is for GCC to fix their PPC floating point codegen, because '(9.223372036854775807e+18 / 1.0e+9)' certainly is a constant expression. |
So we either use the latest GCC version which has the fix or we apply the patch on |
Here's a minimal reproducer on godbolt: https://godbolt.org/z/xFkZTR What confuses me is that the same expression that breaks with |
Here's my understanding: It's a very old deficiency in gcc's handling of a unique IBM format for long long floating point values. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=26374 A patch years ago was put it to indicate this type of folding could not be done: https://gcc.gnu.org/ml/gcc-patches/2005-01/msg01966.html And that code is more or less still in gcc8 in fold-const.c
There is some work being done to change things for PPCLE but not for PPCBE: https://fedoraproject.org/wiki/Changes/PPC64LE_Float128_Transition There is nobody I know of who knows more about gcc and PowerPC than Iain Sandoe, and his workaround was in the patch I referenced above. |
For what it is worth I patch-out the constexpr part (https://github.com/noloader/build-llvm/blob/master/build-llvm.sh#L566): THIS_FILE=include/thread I patch it out because my two choices are (1) broken compile an no compiler, or (2) lose constexpr on a function I probably won't use. The value still works, its just not constexpr. Patching-out the constexpr is a no brainer for me because I need a working compiler. |
The way I understand Iain's patch, it changes the thread to sleep from thousands of years to just hundreds of years. :> |
I'm wondering if replacing My understanding is that the GCC bug is only triggered when using the IBM long double ABI, and that other long double ABI's are available. Is these a GCC macro we can use to detect IBM's long double specifically? |
1 similar comment
I'm wondering if replacing My understanding is that the GCC bug is only triggered when using the IBM long double ABI, and that other long double ABI's are available. Is these a GCC macro we can use to detect IBM's long double specifically? |
As far as I can tell from https://github.com/llvm-mirror/libcxx/blob/master/src/condition_variable.cpp#L56 whatever superlong number we pass in here gets shortened down to "0x59682F000000E941" anyway. So Iain's 592 years is long enough to saturate the system. |
Am I correct this doesn’t happen when building LLVM |
That is my understanding. Building with LLVM is fine. |
By fully bootstrapped LLVM, it means that the linker also needs to be
|
This is a compile-time error; it hasn't gotten to the linker yet. |
A similar issue recently came up in gcc’s bug tracker https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88204 on their test suite, and the resolution was to disable the test. After 14 years, it would not seem very likely that gcc is going to fix this any time soon. Although it is undesirable to have one system working differently than all the others, for bootstrapping libc++ with gcc on powerpc there would not appear to be a lot of other available options than a patch something like Iain’s. Is there something about that patch (other than the systems test, which needs to be broadened out a bit) that I am missing that makes it unusable? |
Fixed in r357478. |
I don't see the Fix is in the llvm-project repo on GitHub, should I try |
And fixed correctly in https://llvm.org/r357540 |
On ppc64le, the code base which has the Fix doen's get build: $ cmake -G Ninja -DLLVM_ENABLE_PROJECTS="libcxx;libcxxabi" -DLLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN=TRUE -DCMAKE_C_COMPILER=/gpfs/software/opt/gcc/5.4.0/bin/gcc -DCMAKE_CXX_COMPILER=/gpfs/software/opt/gcc/5.4.0/bin/g++ ../llvm |
BTW, it builds fine on x86. |
I must be cross-eyed. To me the original commit looks correct, and the corrected fix now looks backwards. When building with gcc, on powerpc, don't we want to use _LIBCPP_CONSTEXPR duration _Max = duration(ULLONG_MAX/1000000000ULL) ; Because if so, we have that backwards now, don't we? |
This is the correct patch for ppc64el. I've tested this on a Raptor System Talos II Power9 workstation. diff --git a/libcxx/include/thread b/libcxx/include/thread
+#else |
Has this been landed on Trunk yet? |
And note that C++14 now that is a requirement. |
I confirm that I am able to build one of the LLVM projects, libcxx and libcxxabi on PowerPC natively for the first time ever. Time for changing the doc to Supported on Linux and PowerPC combination? |
Build clang-8.0.1 on linux shell script. |
I've attached a shell script for building clang-8.0.1 on linux. It's been test on a Power9 ppc64le system. |
Do you have build logs carried out on POWER9? |
I'll rebuild it again and attach the logs in an hour or so. What do you hope to see in the logs? |
I'd like to see the nightly build logs as I am on POWER8 and do build LLVM routinely by myself, when failture occurs I'd like to cross-check against it. |
201908190440 clang-8.0.1 build log on ppc64le - power9 |
I can confirm that as of now (SHA cda334b) this fix is still reversed on master. Adding a NOT for the if condition (or switching the bodies for if and else) would fix it |
I can also confirm that this is an issue in current master / trunk (llvm 10)
-#else
#endif |
We have recently encountered this bug and have found that the patch in #39044 #c38 fixes it. What stands in the way of this being pushed? Would it help if I created a phab review for it? |
Ping. |
Ping. What's the best way to move this forward? |
Ping.I suppose I should just take the patch to phabricator. |
mentioned in issue llvm/llvm-bugzilla-archive#40671 |
Extended Description
I'm trying to build LLVM and components on GCC112 from the compiler farm. GCC112 is ppc64-le, and ships with GCC 4.8.5:
$ gcc --version
gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-16)
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
LLVM configuration and build goes well for a while. Then it encounters https://bugzilla.redhat.com/show_bug.cgi?id=1538817:
[ 35%] Building CXX object projects/libcxx/lib/CMakeFiles/cxx_objects.dir//src/condition_variable.cpp.o
cd /home/noloader/llvm_build/projects/libcxx/lib && /usr/bin/c++ -DNDEBUG -D_DEBUG -D_GNU_SOURCE -D_LIBCPP_BUILDING_LIBRARY -D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/noloader/llvm_build/projects/libcxx/lib -I/home/noloader/llvm_source/llvm/projects/libcxx/lib -I/home/noloader/llvm_build/include -I/home/noloader/llvm_source/llvm/include -I/home/noloader/llvm_build/projects/libcxx/include/c++build -I/home/noloader/llvm_source/llvm/projects/libcxx/include -fPIC -fvisibility-inlines-hidden -std=c++11 -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wdelete-non-virtual-dtor -Wno-comment -g -DLIBCXX_BUILDING_LIBCXXABI -std=c++11 -nostdinc++ -fvisibility-inlines-hidden -Wall -Wextra -W -Wwrite-strings -Wno-unused-parameter -Wno-long-long -Werror=return-type -Wno-literal-suffix -Wno-c++14-compat -Wno-noexcept-type -Wno-error -fPIC -o CMakeFiles/cxx_objects.dir//src/condition_variable.cpp.o -c /home/noloader/llvm_source/llvm/projects/libcxx/src/condition_variable.cpp
In file included from /home/noloader/llvm_source/llvm/projects/libcxx/src/condition_variable.cpp:15:0:
/home/noloader/llvm_source/llvm/projects/libcxx/include/thread: In function ‘void std::__1::this_thread::sleep_for(const std::__1::chrono::duration<_Rep, _Period>&)’:
/home/noloader/llvm_source/llvm/projects/libcxx/include/thread:438:73: in constexpr expansion of ‘std::__1::chrono::duration(((const std::__1::chrono::duration<long long int, std::__1::ratio<1l, 1000000000l> >)(& std::__1::chrono::duration<_Rep, _Period>::max<long long int, std::__1::ratio<1l, 1000000000l> >())), 0u)’
/home/noloader/llvm_source/llvm/projects/libcxx/include/chrono:1055:68: in constexpr expansion of ‘std::__1::chrono::duration_cast<std::__1::chrono::duration, long long int, std::__1::ratio<1l, 1000000000l> >((* & __d))’
/home/noloader/llvm_source/llvm/projects/libcxx/include/chrono:907:72: in constexpr expansion of ‘std::__1::chrono::__duration_cast<std::__1::chrono::duration<long long int, std::__1::ratio<1l, 1000000000l> >, std::__1::chrono::duration, std::__1::ratio<1l, 1000000000l>, true, false>().std::__1::chrono::__duration_cast<_FromDuration, _ToDuration, _Period, true, false>::operator()<std::__1::chrono::duration<long long int, std::__1::ratio<1l, 1000000000l> >, std::__1::chrono::duration, std::__1::ratio<1l, 1000000000l> >((* & fd))’
/home/noloader/llvm_source/llvm/projects/libcxx/include/thread:438:73: error: ‘(9.223372036854775807e+18 / 1.0e+9)’ is not a constant expression
_LIBCPP_CONSTEXPR duration _Max = nanoseconds::max();
^
At global scope:
cc1plus: warning: unrecognized command line option "-Wno-noexcept-type" [enabled by default]
cc1plus: warning: unrecognized command line option "-Wno-c++14-compat" [enabledby default]
make[2]: *** [projects/libcxx/lib/CMakeFiles/cxx_objects.dir//src/condition_variable.cpp.o] Error 1
make[2]: Leaving directory
/home/noloader/llvm_build' make[1]: *** [projects/libcxx/lib/CMakeFiles/cxx_objects.dir/all] Error 2 make[1]: Leaving directory
/home/noloader/llvm_build'make: *** [all] Error 2
Failed to make LLVM sources
It would be nice if LLVM could work around the issue.
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