[Bug driver/21795] New: reordering/aliasing effect on ppc64

[Bug driver/21795] New: reordering/aliasing effect on ppc64

[hvr at gnu dot org]

when compiling the attached gcc4bug.c with

$ gcc -Wall -O2 -fno-strict-aliasing  gcc4bug.c -o gcc4bug;./gcc4bug ;echo $?
39

the assertion in line 39 gets triggered on ppc64, even though
-fno-strict-aliasing is used; looking at the assembler output, the 2 single-byte
stores (together with the assertion-checks before the call to _hexdump() that
got optimized away...) have been moved before the memcpy() 

        /* setting memory... */
#NO_APP
        li 0,-54
        ld 9,.LC3@toc(2)
        stb 0,120(1)     // m_b
        li 0,-2
        nop
        lhz 11,8(9)
        lwz 10,0(9)
        lwz 8,4(9)
        stb 0,121(1)     // m_c
        sth 11,120(1)
        stw 10,112(1)
        stw 8,116(1)
#APP
        /* done setting memory... */


interestingly, when enabling some of the commented out assert's in the .c file,
the code gets reordered to produce the expected result (i.e. all assertions to
hold, and the program to exit with a return code of 0)

(this behaviour wasn't present in gcc-3.4 yet)

$ gcc -v
Using built-in specs.
Target: powerpc64-linux
Configured with: ../src/configure -v
--enable-languages=c,c++,java,f95,objc,ada,treelang --prefix=/usr
--libexecdir=/usr/lib --enable-shared --with-system-zlib --enable-nls
--enable-threads=posix --without-included-gettext --program-suffix=-4.0
--enable-__cxa_atexit --enable-libstdcxx-allocator=mt --enable-clocale=gnu
--enable-libstdcxx-debug --enable-java-gc=boehm --enable-java-awt=gtk
--enable-mpfr --disable-nof --disable-softfloat --disable-werror
--enable-checking=release powerpc64-linux
Thread model: posix
gcc version 4.0.1 20050503 (prerelease) (Debian 4.0.0-2)

-- 
           Summary: reordering/aliasing effect on ppc64
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: driver
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hvr at gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: powerpc64-linux
  GCC host triplet: powerpc64-linux
GCC target triplet: powerpc64-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21795

[Bug driver/21795] reordering/aliasing effect on ppc64

[hvr at gnu dot org]

------- Additional Comments From hvr at gnu dot org  2005-05-28 07:50 -------
Created an attachment (id=8983)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=8983&action=view)
C file triggering the issue


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21795

[Bug middle-end/21795] reordering/aliasing effect on ppc64

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-05-28 08:08 -------
Note there is no C alias rules violating in the code as you can access anything via chars.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|driver                      |middle-end
           Keywords|                            |wrong-code


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21795

[Bug rtl-optimization/21795] reordering/aliasing effect on ppc64

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-05-28 14:01 -------
Note, you are violating not aliasing rules but rule of going over the bounds of the array which is 
undefined by the C standard.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|middle-end                  |rtl-optimization


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21795

[Bug rtl-optimization/21795] reordering/aliasing effect on ppc64

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-07-01 19:36 -------
This is still invalid as you are going passed the bounds which is undefined.

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21795