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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/67442] [5/6 Regression] GCC 5.2.0 on x86_64 creates invalid address on specific array index calculation through pointer
Date: Thu, 03 Sep 2015 08:24:00 -0000
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X-Bugzilla-Product: gcc
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X-Bugzilla-Version: 5.2.0
X-Bugzilla-Keywords: wrong-code
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67442

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
            Version|unknown                     |5.2.0
           Keywords|                            |wrong-code
   Last reconfirmed|                            |2015-09-03
          Component|target                      |middle-end
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org
     Ever confirmed|0                           |1
            Summary|GCC 5.2.0 on x86_64 creates |[5/6 Regression] GCC 5.2.0
                   |invalid address on specific |on x86_64 creates invalid
                   |array index calculation     |address on specific array
                   |through pointer             |index calculation through
                   |                            |pointer
   Target Milestone|---                         |5.3
      Known to fail|                            |5.2.0, 6.0

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed on x86_64 and the 5 branch with -O1 even:

main:
.LFB0:
        .cfi_startproc
        movabsq $foo+4294967408, %rax
        movswl  (%rax), %eax
        ret

.original has:

  short int value = *(bar + (sizetype) (((long unsigned int) i * (long unsigned
int) j) * 4294967292 + 16));

works correctly with -fstrict-overflow (or -O2).  Some bug in folding
somewhere.

4.8 and 4.9 have

  short int value = *(bar + (sizetype) (((long unsigned int) i * (long unsigned
int) j) * 18446744073709551612 + 16));