topic Generated Assembly Code Inefficent in ColdFire/68K Microcontrollers and Processors

Generated Assembly Code Inefficent

KenH — Fri, 24 Aug 2007 01:45:39 GMT

Hi

I am using Metrowerks v6.4 compiling C code. I looked through the message board for a similar post and did not find one. My apoligies if this has already been discussed. This is for a 5270 micro, optimization level2 (doesn't matter as long as it is not level 0 ). My quesion is: Is there a way to get Metrowerks to generate for example (a0)+ (emphasis on the +) instruciton when imcrementing pointers?

Thank you.

I have this simple code (snippet)

char *ascii_data = cpe.data ; //(cpe.data is a structure array of 400 chars )

   *ascii_data++ = '0' ; // Group
   *ascii_data++ = '1' ; // Duration
   *ascii_data++ = '1' ; // default on pattern
   *ascii_data++ = '1' ; // default of pattern

I would expect something like this generated

move.b d1, (a0)+
move.b d0, (a0)+
move.b d0, (a0)+
move.b d0, (a0)+

I get this:

779:    *ascii_data++ = '0' ; // Group
;
0x000001B6 0x204E                   movea.l a6,a0
0x000001B8 0x528E                   addq.l   #1,a6
0x000001BA 0x1081                   move.b   d1,(a0)
;
; 780:    *ascii_data++ = '1' ; // Duration
;
0x000001BC 0x204E                   movea.l a6,a0
0x000001BE 0x528E                   addq.l   #1,a6
0x000001C0 0x1080                   move.b   d0,(a0)
;
; 781:    *ascii_data++ = '1' ; // default on pattern
;
0x000001C2 0x204E                   movea.l a6,a0
0x000001C4 0x528E                   addq.l   #1,a6
0x000001C6 0x1080                   move.b   d0,(a0)
;
;

====================

Re: Generated Assembly Code Inefficent

CompilerGuru — Thu, 29 Oct 2020 08:44:15 GMT

When I remember right there was once a thread where coding the post increment as separate statement did help, but that was for a loop and not for multiple assignments.

With this code I get that (with CF 6.3, not 6.4).

Code:

extern char array[];#pragma opt_propagation offvoid function(){    char *  ascii_data= array;    *ascii_data  = '0' ; ascii_data++;    *ascii_data  = '1' ; ascii_data++;    *ascii_data  = '1' ; ascii_data++;    *ascii_data  = '1' ; ascii_data++;    *ascii_data  = '1' ; ascii_data++;    *ascii_data  = '1' ; ascii_data++;    *ascii_data  = '1' ; ascii_data++;    *ascii_data  = '1' ; ascii_data++;    *ascii_data  = '1' ; ascii_data++;    *ascii_data  = '1' ; ascii_data++;    *ascii_data  = '1' ; ascii_data++;    *ascii_data  = '1' ; ascii_data++;    *ascii_data  = '1' ; ascii_data++;    *ascii_data  = '1' ; ascii_data++;    *ascii_data  = '1' ; ascii_data++;}

That generates

Code:

0x00000000                    _function:;                             function:0x00000000  0x41F900000000           lea      _array,a00x00000006  0x10FC0030               move.b   #48,(a0)+             ; '0'0x0000000A  0x7031                   moveq    #49,d00x0000000C  0x10C0                   move.b   d0,(a0)+0x0000000E  0x10C0                   move.b   d0,(a0)+0x00000010  0x10C0                   move.b   d0,(a0)+0x00000012  0x10C0                   move.b   d0,(a0)+0x00000014  0x10C0                   move.b   d0,(a0)+0x00000016  0x10C0                   move.b   d0,(a0)+0x00000018  0x10C0                   move.b   d0,(a0)+0x0000001A  0x10C0                   move.b   d0,(a0)+0x0000001C  0x10C0                   move.b   d0,(a0)+0x0000001E  0x10C0                   move.b   d0,(a0)+0x00000020  0x10C0                   move.b   d0,(a0)+0x00000022  0x10C0                   move.b   d0,(a0)+0x00000024  0x1080                   move.b   d0,(a0)0x00000026  0x11400001               move.b   d0,1(a0)0x0000002A  0x4E75                   rts