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Bug#906753: marked as done (GCC's -O2 optimization breaks floating point precision or something else)

Your message dated Tue, 21 Aug 2018 10:20:21 +0200
with message-id <a1aa0136-7a66-7be9-bb6b-1d96e885bc4c@debian.org>
and subject line Re: Bug#906753: Acknowledgement (GCC's -O2 optimization breaks floating point precision or something else)
has caused the Debian Bug report #906753,
regarding GCC's -O2 optimization breaks floating point precision or something else
to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

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-- 
906753: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=906753
Debian Bug Tracking System
Contact owner@bugs.debian.org with problems
--- Begin Message --- 
Package: g++-8
Version: 8.2.0-4
Severity: serious
Justification: -O2 results in different double precision number result.
Affects: 906708

This bug is found in package src:hepmc, which currently FTBFS on
i386, arm64, ppc64el and s390x.

https://buildd.debian.org/status/package.php?p=hepmc
 - arm64:
   difference is : 3.55271e-15
 - i386:
   difference is : 1.77636e-15
 - ppc64el:
   difference is : 3.55271e-15
 - s390x:
   difference is : 3.55271e-15

Data Matrix:

 * amd64 architecture
   + GCC-8:
     -O2 : OK
     -O0 : OK
   + Clang-6.0
     -O2 : OK
     -O0 : OK

 * ppc64el architecture
   + GCC-8:
     -O2 : FTBFS because floating point precision beyond tolerance
     -O0 : OK
   + Clang-6.0:
     -O2 : OK
     -O0 : OK

   + GCC-7:
     -O2 : FTBFS

   + GCC-6:
     -O2 : FTBFS

   + GCC-5:
     -O2 : FTBFS

 * i386, arm64, s390x not tested.

 * In testSimpleVector.cc, the expected result of
   v4.m2() and vector.m2() are both 2.4200000000000053 .

 * -O2 and -O0 can be specified in DEB_CXXFLAGS_MAINT_APPEND
 * default compiler can be switched by simply e.g.
   export CC=clang
   export CXX=clang++
   in debian/rules
   
I wanted to trace into testSimpleVector.cc with gdb to find out
what's going wrong. However this bug only occurs with -O2 option
with which gdb cannot trace the C++ code line by line.

Clang-6 doesn't FTBFS with the same compiler flags, so I
consider this bug is an RC bug of GCC.

I totally forgot how to dump the detail about gcc's -O2 option.
Hence I'm not sure if gcc -O2 used something like -ffast-math .

--- End Message ---
--- Begin Message --- 
and closed as invalid. See the upstream issue.

--- End Message ---
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