[Bug rtl-optimization/72488] New: wrong code (SIGFPE) at -Os and above on x86_64-linux-gnu (in the 64-bit mode)

["su at cs dot ucdavis.edu" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72488

            Bug ID: 72488
           Summary: wrong code (SIGFPE) at -Os and above on
                    x86_64-linux-gnu (in the 64-bit mode)
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

Created attachment 39012
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=39012&action=edit
test program

The current gcc trunk miscompiles the attached code (small.c) on
x86_64-linux-gnu at -Os and above in the 64-bit mode (but not in the 32-bit
mode).

This is a regression from 6.1.x. 

The code is extremely difficult to reduce, so the reported test is still rather
large (21709 bytes).  I am not certain, but fairly confident that it doesn't
have undefined behaviors as it passes UBSan, CompCert's reference interpreter,
the tis-interpreter, etc. 


$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/7.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-source-trunk/configure --enable-languages=c,c++,lto
--prefix=/usr/local/gcc-trunk --disable-bootstrap
Thread model: posix
gcc version 7.0.0 20160725 (experimental) [trunk revision 238706] (GCC) 
$ 
$ gcc-trunk -O1 small.c; ./a.out
507518-1357826554294967259-187769889781-5
$ gcc-6.1 -O2 small.c; ./a.out
507518-1357826554294967259-187769889781-5
$ 
$ gcc-trunk -Os small.c
$ ./a.out
Floating point exception (core dumped)
$