[Icc-mot] Interesting Optimizations

[Gene Norris]

Richard,

Am I getting the correct results here?

; unsigned crc_calculation(unsigned irrelevant, unsigned useless)
  1662           ; {
  1662                   .dbline 1231
  1662           ;   unsigned i, j, k;
  1662           ;

  1662           ;   i = j = 0x0011;
  1662 1800820011        movw #17,2,S
  1667 1800840011        movw #17,4,S
  166C                   .dbline 1232

  166C           ;   i = i << 8;
  166C EC84              ldd 4,S             // D = 0x0011
  166E B710              tfr B,A             // D = 0x1111
  1670 C7                clrb                // D = 0x1100
  1671 B746              tfr D,Y             // Worked!
  1673 6D84              sty 4,S             // Back in original location
  1675                   .dbline 1233

  1675           ;   i = (i << 8) + 1;
  1675 A684              ldaa 4,S            // D = 0x1100 (from above)
  1677 C601              ldab #1             // D = 0x1101 (?!)
  1679 B746              tfr D,Y             // Fast? (but wrong)
  167B 6D84              sty 4,S             // Back to original spot
  167D                   .dbline 1234

  167D           ;   j = (j << 8) | 2;
  167D A682              ldaa 2,S            // D = 0x0001, ldaa 3,s?
  167F C602              ldab #2             // D = 0x0002, oops
  1681 B746              tfr D,Y             // Faster, but curiously,
  1683 6C82              std 2,S             // drastically incorrect
  1685                   .dbline -2