[Bug tree-optimization/62033] New: okteta 4.13.97 error at -O3 -D_FORTIFY_SOURCE=2

[Bug tree-optimization/62033] New: okteta 4.13.97 error at -O3 -D_FORTIFY_SOURCE=2

[amodra at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62033

            Bug ID: 62033
           Summary: okteta 4.13.97 error at -O3 -D_FORTIFY_SOURCE=2
           Product: gcc
           Version: 4.10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: amodra at gmail dot com

Created attachment 33257
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33257&action=edit
delta+hand reduced testcase

Found on powerpc64le with 4.9, and then with x86_64 4.10.0 20140727

Due to __warn_memset_zero_len reference in object, we get
.../bytearraymodel_p.o: In function `memset':
.../bits/string3.h:81: warning: memset used with constant zero length
parameter; this could be due to transposed parameters
collect2: error: ld returned 1 exit status

Compile testcase with 
-O3 -fvisibility=hidden -Werror=return-type -fvisibility-inlines-hidden

[Bug tree-optimization/62033] okteta 4.13.97 error at -O3 -D_FORTIFY_SOURCE=2

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62033

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I don't see a bug here as there is one case where addSize can return 0 and with
jump threading and basic block copying, we get a zero size passed to memset.

[Bug tree-optimization/62033] okteta 4.13.97 error at -O3 -D_FORTIFY_SOURCE=2

[amodra at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62033

--- Comment #2 from Alan Modra <amodra at gmail dot com> ---
I can see where you're coming from Andrew, but what is disconcerting about this
is that the _FORTIFY_SOURCE warning is plainly incorrect here.  How is one
supposed to write a string.h memset macro using __builtin_constant_p() to
provide a useful _FORTIFY_SOURCE warning, in the face of this sort of
optimisation?

Users are going to see this as "__builtin_constant_p() is broken".

[Bug tree-optimization/62033] okteta 4.13.97 error at -O3 -D_FORTIFY_SOURCE=2

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62033

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

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

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Alan Modra from comment #2)
> I can see where you're coming from Andrew, but what is disconcerting about
> this is that the _FORTIFY_SOURCE warning is plainly incorrect here.  How is
> one supposed to write a string.h memset macro using __builtin_constant_p()
> to provide a useful _FORTIFY_SOURCE warning, in the face of this sort of
> optimisation?


This is why Jakub moved it to the front-end away from glibc (See PR 61294).

> 
> Users are going to see this as "__builtin_constant_p() is broken".

It is not.  It is working correctly as on that path, it is constant.

This is an exact duplicate of bug 61294 really.

*** This bug has been marked as a duplicate of bug 61294 ***