[Bug c/59156] New: code miscompiled with -O2 -fpeel-loops

[mjt+gcc at tls dot msk.ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59156

            Bug ID: 59156
           Summary: code miscompiled with -O2 -fpeel-loops
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mjt+gcc at tls dot msk.ru

Created attachment 31231
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31231&action=edit
code demonstrating the issue

Attached is a code which shows different results when compiled with -O2 (wrong)
or -O1 (right).  Initially it was -O2 -funroll-loops which triggered the issue,
but after reducing the code further I managed to get the same result with -O1
vs -O2 without any additional options.

Tested with debian gcc 4.7.2-5 x86-65 (wheezy), confirmed with 4.8.1-10
(debian/testing, also 64bits).  32bit code is not affected.

The code does not have any preprocessor directives.

I tried to reduce it further but it is a bit fragile - for example, removing a
single call to free() makes the code generated to be correct.