[Bug tree-optimization/59747] [4.9 Regression] wrong code at -Os and above on x86_64-linux-gnu in 64-bit mode

[mpolacek at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59747

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
I think the problem is in setting the value of e.  With -O in .gimple we have:
    e.2 = e;
    e.3 = e.2;   
    e.4 = e.3 + -1;
    e = e.4;
while with -O2:
    e.2 = e;
    e.3 = e.2;
    e.4 = (unsigned short) e.3;
    D.1762 = e.4 + 65535;
    e.5 = (short int) D.1762;
    e = e.5;

Wrt the weirdo shift: -1 >> 56 is implementation-defined behavior.