[Bug ipa/66863] New: wrong code at -Os and above on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66863

            Bug ID: 66863
           Summary: wrong code at -Os and above on x86_64-linux-gnu
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ipa
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

The current gcc trunk mis-compiles the following code on x86_64-linux-gnu at
-Os and above in both 32-bit and 64-bit modes. 

This is a regression from 5.1.x.

$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-unknown-linux-gnu/6.0.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-trunk/configure --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 6.0.0 20150713 (experimental) [trunk revision 225727] (GCC) 
$ 
$ gcc-trunk -O1 small.c; ./a.out
$ gcc-5.1 -Os small.c; ./a.out
$ 
$ gcc-trunk -Os small.c
$ ./a.out
Floating point exception (core dumped)
$ 


---------------------------------


int a, b;

int
fn1 (int p1)
{
  if (p1 < -2147483647) 
    return 0;
  else 
    return 1;
}

int
fn2 (int p1, short p2)
{
  return p2 ? p1 % p2 : 0; 
}

int
main ()
{
  b = fn2 (fn1 (a), a);
  return 0;
}