[Icc-avr] Possible bug with post-increment?

[Thomas Schäfer]

Hi all,

after a two day debug session, I think I have found a bug:

I have a module global array of unsigned char and an index variable. I post
increment the index while write access to the array, but it seem to pre
increment the index.

Here are some snippets of the code and the assembler listing:

----
static volatile unsigned char *ucASCIIBuf = ucBinaryBuf; // Reuse binary buffer
static volatile unsigned int usBufferPos;


void writeBuffer(unsigned char value)
{
	ucASCIIBuf[usBufferPos++] |= value;
}

----
.lst

(0253)                 ucASCIIBuf[usBufferPos++] |= ucResult;
     77A 9180 0167 LDS	R24,ascii.c:usBufferPos
     77C 9190 0168 LDS	R25,ascii.c:usBufferPos+1
     77E 9601      ADIW	R24,1
     77F 9390 0168 STS	ascii.c:usBufferPos+1,R25
     781 9380 0167 STS	ascii.c:usBufferPos,R24
     783 9020 0133 LDS	R2,ascii.c:ucASCIIBuf
     785 9030 0134 LDS	R3,ascii.c:ucASCIIBuf+1
     787 9040 0167 LDS	R4,ascii.c:usBufferPos
     789 9050 0168 LDS	R5,ascii.c:usBufferPos+1
     78B 0C42      ADD	R4,R2
     78C 1C53      ADC	R5,R3
     78D 01F2      MOVW	R30,R4
     78E 8020      LDD	R2,Z+0
     78F 282C      OR	R2,R12
     790 8220      STD	Z+0,R2


If I explizit increment the index, everything works fine:

----
static volatile unsigned char *ucASCIIBuf = ucBinaryBuf; // Reuse binary buffer
static volatile unsigned int usBufferPos;


void writeBuffer(unsigned char value)
{
	ucASCIIBuf[usBufferPos] |= value;
	usBufferPos++;
}

----
.lst

(0253)                 ucASCIIBuf[usBufferPos] |= ucResult;
     77A 9020 0133 LDS	R2,ascii.c:ucASCIIBuf
     77C 9030 0134 LDS	R3,ascii.c:ucASCIIBuf+1
     77E 9040 0167 LDS	R4,ascii.c:usBufferPos
     780 9050 0168 LDS	R5,ascii.c:usBufferPos+1
     782 0C42      ADD	R4,R2
     783 1C53      ADC	R5,R3
     784 01F2      MOVW	R30,R4
     785 8020      LDD	R2,Z+0
     786 282C      OR	R2,R12
     787 8220      STD	Z+0,R2
(0254) 				usBufferPos++;
     788 9180 0167 LDS	R24,ascii.c:usBufferPos
     78A 9190 0168 LDS	R25,ascii.c:usBufferPos+1
     78C 9601      ADIW	R24,1
     78D 9390 0168 STS	ascii.c:usBufferPos+1,R25
     78F 9380 0167 STS	ascii.c:usBufferPos,R24

----

I use V7.14B standard.

regards,
Thomas