[Bug 1783705] Re: clang errors with __float128 is not supported on this target on ppc64le

[William J. Schmidt]

FYI, Jonathan Wakely has now backported both fixes to the GCC 8 branch
in https://gcc.gnu.org/r263084.

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Title:
  clang errors with __float128 is not supported on this target on
  ppc64le

Status in gcc-8 package in Ubuntu:
  New
Status in gcc-8 source package in Bionic:
  New

Bug description:
  Running Ubuntu cosmic on ppc64le, since the GCC 8 update I am unable
  to compile programs with clang that include cmath:

  $ cat foo.cpp 
  #include <cmath>
  int main() { }

  $ clang++ foo.cpp 
  In file included from foo.cpp:1:
  In file included from /usr/bin/../lib/gcc/powerpc64le-linux-gnu/8/../../../../include/c++/8/cmath:47:
  /usr/bin/../lib/gcc/powerpc64le-linux-gnu/8/../../../../include/c++/8/bits/std_abs.h:102:7: error: 
        __float128 is not supported on this target
    abs(__float128 __x)
        ^
  /usr/bin/../lib/gcc/powerpc64le-linux-gnu/8/../../../../include/c++/8/bits/std_abs.h:101:3: error: 
        __float128 is not supported on this target
    __float128
    ^
  2 errors generated.

  GCC works fine. If I add -mfloat128, it fails with this error:

  $ clang++ -mfloat128 foo.cpp 
  In file included from foo.cpp:1:
  In file included from /usr/bin/../lib/gcc/powerpc64le-linux-gnu/8/../../../../include/c++/8/cmath:45:
  In file included from /usr/include/math.h:43:
  /usr/include/powerpc64le-linux-gnu/bits/floatn.h:72:52: error: unknown machine mode '__KC__'
  typedef _Complex float __cfloat128 __attribute__ ((__mode__ (__KC__)));
                                                     ^

  $ clang++ --version
  clang version 6.0.1-2ubuntu1 (tags/RELEASE_601/final)
  Target: powerpc64le-unknown-linux-gnu

  
  libc6: 2.27-3ubuntu1
  clang: 6.0-41ubuntu1
  gcc: 4:8.1.0-2ubuntu1

  ProblemType: Bug
  DistroRelease: Ubuntu 18.10
  Package: clang 1:6.0-41ubuntu1
  Uname: Linux 4.18.0-041800rc6-generic ppc64le
  ApportVersion: 2.20.10-0ubuntu5
  Architecture: ppc64el
  Date: Thu Jul 26 16:27:16 2018
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  ProcLoadAvg: 0.15 1.70 2.08 1/1654 18418
  ProcLocks:
   1: FLOCK  ADVISORY  WRITE 4151 00:32:46558 0 EOF
   2: FLOCK  ADVISORY  WRITE 3971 00:1a:62741 0 EOF
   3: FLOCK  ADVISORY  WRITE 3418 00:32:85157 0 EOF
   4: FLOCK  ADVISORY  WRITE 3104 00:17:44175 0 EOF
   5: POSIX  ADVISORY  WRITE 3109 00:17:39081 0 EOF
  ProcSwaps:
   Filename				Type		Size	Used	Priority
   /swapfile                               file		2097088	0	-2
  ProcVersion: Linux version 4.18.0-041800rc6-generic (kernel at tangerine) (gcc version 8.1.0 (Ubuntu 8.1.0-11ubuntu1)) #201807221830 SMP Sun Jul 22 23:58:55 UTC 2018
  SourcePackage: llvm-defaults
  UpgradeStatus: No upgrade log present (probably fresh install)
  VarLogDump_list: total 0
  cpu_cores: Number of cores present = 32
  cpu_coreson: Number of cores online = 32
  cpu_smt: SMT=4

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