FIX: Optimization Bug Using Shift Operators and outp()

MORE INFORMATION

When compiled with /Ox, the following sample does not generate code for the line "addr >>= 8;"

NOTE: When the line of code marked "3" replaces the lines marked "1" and "2", "mov al,ah" is no longer incorrectly optimized out of the assembler listing produced by /Fc.

Sample Code

// Compile options needed: /c /Ox /Fc

   unsigned long test(char * baseport, unsigned long addr)
   {
       unsigned long   offset;

       offset = ((addr >> 3) & 0x00003fff);

       addr >>= 8;                     //Line 1
       outp(baseport + 4, addr);       //Line 2

// Replacing the above two lines of code with the line below
// fixes the problem.

//       outp(baseport + 4, addr >> 8);  //Line 3--okay with /Ox.

       return offset;
   }