[Bug lto/63704] -flto internal compiler error: in mems_in_disjoint_alias_sets_p, at alias.c:398

[Bug lto/63704] -flto internal compiler error: in mems_in_disjoint_alias_sets_p, at alias.c:398

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63704

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |ice-on-valid-code, lto
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2014-11-03
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
That's odd.  Ah, no.  We're transfering compile-time -fno-strict-aliasing
by setting alias-sets to zero and as the link command-line doesn't use
-fno-strict-aliasing (and we don't force the option somehow) that assert
is "easy" to trigger (and broken).  We should simply remove it.

[Bug lto/63704] -flto internal compiler error: in mems_in_disjoint_alias_sets_p, at alias.c:398

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63704

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Oh, no.  It's actually a genuine bug.

__attribute__((optimize("O3"))) enables -fstrict-aliasing, so if the
rest of the TU is compiled with -fno-strict-aliasing it depends on
prue luck if 'int' (as in this case) gets alias-set zero (a function
compiled with -fno-strict-aliasing calls get_alias_set on it) or
a non-zero alias-set (the -O3 function calls get_alias_set on 'int').

Of course LTO just makes it more likely to trigger.

-> -fstrict-aliasing may not be altered via attribute((optimize())).

[Bug lto/63704] -flto internal compiler error: in mems_in_disjoint_alias_sets_p, at alias.c:398

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63704

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed.

[Bug lto/63704] -flto internal compiler error: in mems_in_disjoint_alias_sets_p, at alias.c:398

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63704

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Author: rguenth
Date: Thu Nov 27 09:51:32 2014
New Revision: 218114

URL: https://gcc.gnu.org/viewcvs?rev=218114&root=gcc&view=rev
Log:
2014-11-27  Richard Biener  <rguenther@suse.de>

    PR middle-end/63704
    * alias.c (mems_in_disjoint_alias_sets_p): Remove assert
    and instead return false when !fstrict-aliasing.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/alias.c

[Bug lto/63704] -flto internal compiler error: in mems_in_disjoint_alias_sets_p, at alias.c:398

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63704

--- Comment #5 from Martin Liška <marxin at gcc dot gnu.org> ---
Author: marxin
Date: Thu Jan 15 16:02:28 2015
New Revision: 219663

URL: https://gcc.gnu.org/viewcvs?rev=219663&root=gcc&view=rev
Log:
Backport from mainline

        2014-11-27  Richard Biener  <rguenther@suse.de>

    PR middle-end/63704
    * alias.c (mems_in_disjoint_alias_sets_p): Remove assert
    and instead return false when !fstrict-aliasing.


Modified:
    branches/gcc-4_8-branch/gcc/ChangeLog
    branches/gcc-4_8-branch/gcc/alias.c
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Subject: [Bug lto/63704] -flto internal compiler error: in mems_in_disjoint_alias_sets_p, at alias.c:398
Date: Thu, 15 Jan 2015 16:03:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63704

--- Comment #6 from Martin Liška <marxin at gcc dot gnu.org> ---
Author: marxin
Date: Thu Jan 15 16:03:05 2015
New Revision: 219664

URL: https://gcc.gnu.org/viewcvs?rev=219664&root=gcc&view=rev
Log:
Backport from mainline

        2014-11-27  Richard Biener  <rguenther@suse.de>

    PR middle-end/63704
    * alias.c (mems_in_disjoint_alias_sets_p): Remove assert
    and instead return false when !fstrict-aliasing.


Modified:
    branches/gcc-4_9-branch/gcc/ChangeLog
    branches/gcc-4_9-branch/gcc/alias.c
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Subject: [Bug c/64614] New: bogus used initialized warning (in gcc 4.9.2 not in 4.8.3); switch statement versus &
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64614

            Bug ID: 64614
           Summary: bogus used initialized warning (in gcc 4.9.2 not in
                    4.8.3); switch statement versus &
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
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          Assignee: unassigned at gcc dot gnu.org
          Reporter: dgilbert at redhat dot com

gcc t.c -O1 -Wall -Wextra

(Any -O value 1 or above)

t.c: In function ‘foo’:
t.c:15:15: warning: ‘tmp’ may be used uninitialized in this function
[-Wmaybe-uninitialized]
       tmp[11] = 15;
               ^
(This code is similar to qemu's arch_init.c/ram_load loop where I hit this)

Gcc doesn't seem to be spotting that the tmp = baz initialiser will always
happen for the switch cases that use tmp.

this is using the Fedora 21 gcc: gcc version 4.9.2 20141101 (Red Hat 4.9.2-1)
(GCC) 
package: gcc-4.9.2-1.fc21.x86_64
It doesn't trigger for me on gcc version 4.8.3 20140911 (Red Hat 4.8.3-9) (GCC) 


char *foo(int bar, char *baz)
{
  char *tmp;

  if (bar & 3) {
      tmp = baz;
  }

  switch (bar) {
  case 1:
      tmp[5] = 7;
      break;

  case 2:
      tmp[11] = 15;
      break;

  default:
      tmp = 0;
      break;
  }

  return tmp;
}
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd611

--- Comment #3 from J. van Oosten <jvoosten at bankai dot nl> ---
Yes, that works. Surprising simple solution, but I'm still wondering if this is
a bug or a feature....

Thanks for the reply.