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

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

[siddhesh at redhat dot com]

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>
To: gcc-bugs@gcc.gnu.org
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.

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

[rth at gcc dot gnu.org]

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

Richard Henderson <rth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-01-23
                 CC|                            |rth at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Richard Henderson <rth at gcc dot gnu.org> ---
This seems to be related to induction variable elimination in some way,
because the VR for the offending unrolled iteration is [4,10].

Which is clearly silly.

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

[izamyatin at gmail dot com]

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

Igor Zamyatin <izamyatin at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |izamyatin at gmail dot com

--- Comment #2 from Igor Zamyatin <izamyatin at gmail dot com> ---
Looks quite similar to PR64277

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

[rth at gcc dot gnu.org]

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

Richard Henderson <rth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #3 from Richard Henderson <rth at gcc dot gnu.org> ---
Yes indeed, this does seem to have been fixed along with 64277.

*** This bug has been marked as a duplicate of bug 64277 ***