[Bug c++/27045] New: c++ is generating incorrect optimized code for xor operations on long long

["l_heldt at poczta dot onet dot pl" <gcc-bugzilla at gcc dot gnu dot org>]

c++ is generating incorrect optimized code for xor operations on long long.
Version which is affected is:

g++ (GCC) 4.0.2 20051125 (Red Hat 4.0.2-8)

Following (proper) code is inlined into bad assembly when optimization is
turned on:

namespace __gnu_cxx
{
        /**
                hash specialization for uint64
        */
        template <>
        class hash<uint64>
        {
                public:
                        size_t operator()(uint64 const & number) const
                        {
                                hash<uint32> uint32Hasher;
                                uint32 const *p = (uint32 *)&number;

                                return uint32Hasher(p[0]) ^ uint32Hasher(p[1]);
                        }
        };

        /**
                hash specialization for RequestId
        */
        template<>
        class hash<RequestId>
        {
                public:
                        size_t operator()(RequestId const & requestId) const
                        {
                                hash<uint64> uint64Hasher;
                                return uint64Hasher(requestId.getV1()) ^
uint64Hasher(requestId.getV2());
                        }
        };
}


Part of bad assembly:

        call    _ZNK9RequestId5getV1Ev
        movl    -20(%ebp), %ebx
        movl    %esi, (%esp)
        movl    %eax, -24(%ebp)
        movl    -24(%ebp), %eax
        movl    %edx, -20(%ebp)
        xorl    %eax, %ebx
        call    _ZNK9RequestId5getV2Ev
        movl    -16(%ebp), %ecx
        movl    %eax, -16(%ebp)
        movl    -12(%ebp), %eax
        movl    %edx, -12(%ebp)
        xorl    %ecx, %eax

and it probably should be something like:

        call    _ZNK9RequestId5getV1Ev
        movl    %eax, -24(%ebp)
        movl    %edx, -20(%ebp)
        movl    -20(%ebp), %ebx
        movl    %esi, (%esp)
        movl    -24(%ebp), %eax
        xorl    %eax, %ebx
        call    _ZNK9RequestId5getV2Ev
        movl    %eax, -16(%ebp)
        movl    %edx, -12(%ebp)
        movl    -16(%ebp), %ecx
        movl    -12(%ebp), %eax
        xorl    %ecx, %eax

It seems that compiler reads values from stack before setting them after call
to getV1() or getV2().

Bug shows up only when optimization is turned on.

I am attaching simple demo program which should run when optimization is set to
0 and crash when it is set to 2 or 3.


-- 
           Summary: c++ is generating incorrect optimized code for xor
                    operations on long long
           Product: gcc
           Version: 4.0.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: l_heldt at poczta dot onet dot pl


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27045