[sdcc-devel] Variables in code space on 8051

[Frieder F. <fri...@we...>]

Hi,

this patch saves a few cycles when accessing
variables in code space (on the 8051 port).
Hopefully I got it right.

Regards,

Frieder




With the patch the assignment i=c in the program:

--8<-----
long int i;
long int code c=0x01234567;

main()
{
  i=c;
}
-->8-----


compiles to:

;       test.c:6: i=c;
        mov     dptr,#_c
        clr  a
        movc    a,@a+dptr
        mov     _i,a
        mov     a,#0x01
        movc    a,@a+dptr
        mov     (_i + 1),a
        mov     a,#0x02
        movc    a,@a+dptr
        mov     (_i + 2),a
        mov     a,#0x03
        movc    a,@a+dptr
        mov     (_i + 3),a

before it was:

;       test.c:6: i=c;
        mov     dptr,#_c
        clr     a
        movc    a,@a+dptr
        mov     _i,a
        inc     dptr
        clr     a
        movc    a,@a+dptr
        mov     (_i + 1),a
        inc     dptr
        clr     a
        movc    a,@a+dptr
        mov     (_i + 2),a
        inc     dptr
        clr     a
        movc    a,@a+dptr
        mov     (_i + 3),a


patch to sdcc/src/mcs51/gen.c:


--- gen.c.orig  Wed Mar 20 23:26:16 2002
+++ gen.c       Wed Jul 31 01:13:08 2002
@@ -801,6 +801,15 @@
       return rs;

     case AOP_DPTR:
+
+      /* if possible use indexed addressing mode for code data access with positive byte offset */
+      if ( (aop->code) && (offset == (offset & 0xff)) )
+       {
+         emitcode ("mov", "a,#0x%02x", offset & 0xff);
+         emitcode ("movc", "a,@a+dptr");
+         return (dname ? "acc" : "a");
+       }
+
       while (offset > aop->coff)
        {
          emitcode ("inc", "dptr");