REORDER Compiler Directive

The REORDER directive enables the compiler to reorder instructions to minimize wait states and pipeline stalls. REORDER is only useful for XC16x and Super-10 devices where the following instructions may cause stalls (wait states) when the register used in the instruction are set in the prior instruction.

• MOV Rn,[Rm]
• MOV Rn,[Rm+data16]
• MOV xxx,MDL
• MOV xxx,MDH

The following example:

stmt lvl  source
  1       unsigned int *p;
  2       unsigned int v;
  3
  4       unsigned int func (void)  {
  5   1     unsigned int i1, i2;
  6   1
  7   1     i1 = v * 4;
  8   1     i2 = *p << i1;
  9   1     return (i2);
 10   1   }

demonstrates code generated using the REORDER directive:

; FUNCTION func (BEGIN)
                  ; SOURCE LINE # 4
                  ; SOURCE LINE # 7

0000 F2F50000 R    MOV       R5,v
0004 5C25          SHL       R5,#02H
;---- 'i1' assigned to 'R5' ----
                  ; SOURCE LINE # 8
0006 F2F10200 R    MOV       R1,p
000A A841          MOV       R4,[R1]
000C 4C45          SHL       R4,R5
;---- 'i2' assigned to 'R4' ----
                  ; SOURCE LINE # 9
                  ; SOURCE LINE # 10
000E CB00          RET
; FUNCTION func (END)

; FUNCTION func (BEGIN)
                  ; SOURCE LINE # 4
                  ; SOURCE LINE # 7
0000 F2F10200 R    MOV       R1,p
0004 F2F50000 R    MOV       R5,v
0008 5C25          SHL       R5,#02H
;---- 'i1' assigned to 'R5' ----
                  ; SOURCE LINE # 8

000A A841          MOV       R4,[R1]
000C 4C45          SHL       R4,R5
;---- 'i2' assigned to 'R4' ----
                  ; SOURCE LINE # 9
                  ; SOURCE LINE # 10
000E CB00          RET
; FUNCTION func (END)

C166 EXAMPLE.C REORDER

#pragma reorder