vc++ shift produces inconsistent result by PMacTensilica

Compile the code below with /O2 with vc2010 sp1. It produces the wrong result. see steps to reproduce for actual output.

vc2010sp1 x64 is correct
vc2008sp1 x86 is correct

vc2010 no sp x86 shows the bug
vc2010 sp1 x86 shows the bug

Q:\temp>type x.c

#include <stdio.h>
unsigned int tn6__o0 = 0xcd00abcd;
int main()
{
        unsigned int tn23__i0;
        tn23__i0 = ((((unsigned int)((((int)((tn6__o0) << 8))) >> 31)) & 0x7fffffU));
        printf("tn23 is 0x%x \n",tn23__i0);
}