[Bug libc/15605] New: gcc-4.8 + tree-loop-distribute-patterns breaks is unsafe for GLIBC

["azanella at linux dot vnet.ibm.com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=15605

            Bug ID: 15605
           Summary: gcc-4.8 + tree-loop-distribute-patterns breaks is
                    unsafe for GLIBC
           Product: glibc
           Version: 2.18
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: azanella at linux dot vnet.ibm.com
                CC: drepper.fsp at gmail dot com

GCC 4.8 now enables -ftree-loop-distribute-patterns at -O3 by default. This
optimization option may transform loops into memset/memmove call
(http://gcc.gnu.org/onlinedocs/gcc-4.8.1/gcc/Optimize-Options.html#Optimize-Options)
and without proper handling this may generate unexpected PLT calls on GLIBC
builds.

Carlos O'Donell raised his concerns
(http://sourceware.org/ml/libc-alpha/2013-02/msg00299.html), there is also
reports on recursive calls building the default memset/memmove implementations
(http://sourceware.org/ml/libc-alpha/2013-05/msg00731.html), and tt was
observed some PLT issues on PPC32/PPC64 builds as well
(http://sourceware.org/ml/libc-alpha/2013-04/msg00131.html).

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