[Bug c/30724] New: Wrong code from -O2 taking ptr=(struct *)&int_proc_parm on x86_64

["schendel at kbcomputer dot com" <gcc-bugzilla at gcc dot gnu dot org>]

gcc -v
Using built-in specs.
Target: x86_64-suse-linux
Configured with: ../configure --enable-threads=posix --prefix=/usr
--with-local-prefix=/usr/local --infodir=/usr/share/info
--mandir=/usr/share/man --libdir=/usr/lib64 --libexecdir=/usr/lib64
--enable-languages=c,c++,objc,fortran,java,ada --enable-checking=release
--with-gxx-include-dir=/usr/include/c++/4.1.0 --enable-ssp --disable-libssp
--enable-java-awt=gtk --enable-gtk-cairo --disable-libjava-multilib
--with-slibdir=/lib64 --with-system-zlib --enable-shared --enable-__cxa_atexit
--enable-libstdcxx-allocator=new --without-system-libunwind --with-cpu=generic
--host=x86_64-suse-linux
Thread model: posix
gcc version 4.1.0 (SUSE Linux)
------------
Compile the following with cc -O2, gets wrong code.
If you use -fno-strict-aliasing or -fno-schedule-insns2 it works.
cc -O1 works.  cc -O1 -fstrict-aliaseing -fschedule-insns2 fails.
I might have prioritized this critical except I found the ref to
-fno-strict-aliasing in the 4.1.2rc1 thread...

/* -O2 compiles the fetch of lx_id->id_id before it stores
** external_lx_id into the stack:

        movzwl  6(%rsp), %eax   // oops, too soon
        movl    %edi, 4(%rsp)
        testw   %ax, %ax  //  tests garbage

*/

typedef int LG_LXID;
typedef int i4;
typedef unsigned short u_i2;
typedef struct _LG_ID {
    u_i2 foo;
    u_i2 id_id;
} LG_ID;


void
LGend(
LG_LXID             external_lx_id,
i4                  flag)
{
    LG_ID               *lx_id = (LG_ID*)&external_lx_id;

    if (lx_id->id_id == 0 || (i4)lx_id->id_id > flag)
        printf("barfo");
}


-- 
           Summary: Wrong code from -O2 taking ptr=(struct *)&int_proc_parm
                    on x86_64
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: schendel at kbcomputer dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30724