[Bug tree-optimization/64739] New: Spurious "array subscript is above array bounds" warning

["siddhesh at redhat dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64739

            Bug ID: 64739
           Summary: Spurious "array subscript is above array bounds"
                    warning
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: siddhesh at redhat dot com

Reduced Reproducer:

$ cat foo.c
void
foo (char **inptrp, char *inend, int *wch, int *cnt)
{ 
  int inlen = *cnt & 7;
  if (inlen != 0)
    { 
      char *inptr = *inptrp;
      char bytebuf[4];

      while (inptr < inend)
        bytebuf[inlen++] = *inptr++;

      *cnt = &bytebuf[inlen] - inptr;
      *wch = *inptr;
    }
}

$ gcc -O3 -Wall -o foo.s -S foo.c
foo.c: In function ‘foo’:
foo.c:11:16: warning: array subscript is above array bounds [-Warray-bounds]
         bytebuf[inlen++] = *inptr++;
                ^

The warning disappears when one adds -fno-tree-vrp to the compile command.

The actual error appears when building the iconv bits in glibc.
>From gcc-bugs-return-474491-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Fri Jan 23 08:13:57 2015
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From: "ebotcazou at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug ada/64712] [5 Regression] FAIL: gnat.dg/unchecked_convert1.adb execution test (x86_64/-m32)
Date: Fri, 23 Jan 2015 08:13:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd712

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|2015-01-22 00:00:00         |2015-01-23
     Ever confirmed|0                           |1

--- Comment #7 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
It's an uninitialized local variable.