[Bug tree-optimization/100834] False positive of -Wstringop-overflow= with -Os

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100834

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:91f7d7e1bb6827bf8e0b7ba7eb949953a5b1bd18

commit r11-9731-g91f7d7e1bb6827bf8e0b7ba7eb949953a5b1bd18
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Mar 18 18:58:06 2022 +0100

    Allow (void *) 0xdeadbeef accesses without warnings [PR99578]

    Starting with GCC11 we keep emitting false positive -Warray-bounds or
    -Wstringop-overflow etc. warnings on widely used *(type *)0x12345000
    style accesses (or memory/string routines to such pointers).
    This is a standard programming style supported by all C/C++ compilers
    I've ever tried, used mostly in kernel or DSP programming, but sometimes
    also together with mmap MAP_FIXED when certain things, often I/O registers
    but could be anything else too are known to be present at fixed
    addresses.

    Such INTEGER_CST addresses can appear in code either because a user
    used it like that (in which case it is fine) or because somebody used
    pointer arithmetics (including &((struct whatever *)NULL)->field) on
    a NULL pointer.  The middle-end warning code wrongly assumes that the
    latter case is what is very likely, while the former is unlikely and
    users should change their code.

    The following patch adds a min-pagesize param defaulting to 4KB,
    and treats INTEGER_CST addresses smaller than that as assumed results
    of pointer arithmetics from NULL while addresses equal or larger than
    that as expected user constant addresses.  For GCC 13 we can
    represent results from pointer arithmetics on NULL using
    &MEM[(void*)0 + offset] instead of (void*)offset INTEGER_CSTs.

    2022-03-18  Jakub Jelinek  <jakub@redhat.com>

            PR middle-end/99578
            PR middle-end/100680
            PR tree-optimization/100834
            * params.opt (--param=min-pagesize=): New parameter.
            * builtins.c (compute_objsize_r) <case INTEGER_CST>: Use maximum
            object size instead of zero for pointer constants equal or larger
            than min-pagesize.

            * gcc.dg/tree-ssa/pr99578-1.c: New test.
            * gcc.dg/pr99578-1.c: New test.
            * gcc.dg/pr99578-2.c: New test.
            * gcc.dg/pr99578-3.c: New test.
            * gcc.dg/pr100680.c: New test.
            * gcc.dg/pr100834.c: New test.

    (cherry picked from commit 32ca611c42658948f1b8883994796f35e8b4e74d)