[Issue 8796] Optimizer bug on 64bit: *p++=1 where p is a parameter

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=8796


Don <clugdbug at yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Optimizer bug on 64bit      |Optimizer bug on 64bit:
                   |                            |*p++=1 where p is a
                   |                            |parameter


--- Comment #1 from Don <clugdbug at yahoo.com.au> 2012-11-05 11:43:22 PST ---
Reduced test case (applies to postfix ++ and --):

int* wrong8796(int* p)
{
    *p++ = 1;
    return p;
}

// The wrong code is generated in the function above, main() is just to
demonstrate

void main()
{
    int [3] arr;
    int * q = arr.ptr;
    q = wrong8796(q);
    assert(q != arr.ptr);
}

Without -O, wrong8796() compiles to:

        push    RBP
        mov    RBP,RSP
        sub    RSP,8
        mov    -8[RBP],RDI
        mov    RAX,-8[RBP]
        add    qword ptr -8[RBP],4
        mov    dword ptr [RAX],1
        mov    RAX,-8[RBP]
        leave
        ret

With -O:

        push    RBP
        mov    RBP,RSP
        mov    RAX,RDI
        mov    qword ptr [RAX],1
        add    RAX,4
        mov    RAX,RDI                <---- wrong
        pop    RBP
        ret

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