[Bug tree-optimization/61277] New: Incorrect -Warray-bounds warning with 4.9.0

[akruppa at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61277

            Bug ID: 61277
           Summary: Incorrect -Warray-bounds warning with 4.9.0
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: akruppa at gmail dot com

The following code, when compiled with the gcc 4.9.0 release or with SVN branch
gcc-4_9-branch r210719, via

gcc -O2 -Wall -c bug.c

produces the warning

bug.c: In function ‘foo’:
bug.c:13:8: warning: array subscript is below array bounds [-Warray-bounds]
   if (s[n-1] != 2)
        ^

If foo() returns 2, the array accesses are not out of bounds.

Gcc 4.8.1 does not produce the warning. 
The gcc 4.9.0 and SVN builds were configured with

configure --prefix=install/dir/ --enable-languages=c,c++


int foo();
int s[2];
int bar()
{
  int n = foo();
  int i;

  for(i = 0 ; i < n ; i++)
    if ((i == 0) != (s[i] == 0))
      return 0;
  if (s[n-1] != 2)
      return 0;   
  for(i = 0 ; i < n ; i++)
      if (s[0])
        return 0;
  return 1;
}