[Bug tree-optimization/59413] New: wrong code at -Os on x86_64-linux-gnu in both 32-bit and 64-bit modes

[su at cs dot ucdavis.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59413

            Bug ID: 59413
           Summary: wrong code at -Os on x86_64-linux-gnu in both 32-bit
                    and 64-bit modes
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

The current gcc trunk miscompiles the following code on x86_64-linux at -Os
(but not at the other optimization levels) in both 32-bit and 64-bit modes. 

It is interesting that the typedef appears necessary to trigger the
miscompilation. 

This is a regression from 4.8.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/4.9.0/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 4.9.0 20131206 (experimental) [trunk revision 205734] (GCC) 
$ 
$ gcc-trunk -O1 small.c; a.out
7
$ gcc-trunk -O2 small.c; a.out
7
$ gcc-4.8 -Os small.c; a.out
7
$ 
$ gcc-trunk -Os small.c; a.out
2
$ 


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


int printf (const char *, ...);

typedef unsigned int uint32_t;

uint32_t a;
int b;

int
main ()
{
  uint32_t c;
  for (a = 7; a <= 1; a++)
    {
      char d = a;
      c = d;
      b = a == c;
    }
  printf ("%d\n", a);
  return 0;
}