This demonstrates an apparent compiler bug in msp430-gcc, using a
compiler built 30 Sept 2003 from CVS. An older compiler version dating
from 31 March 2003 produced the same problem. The demonstration
routine is a hacked-out fragment from some real code, and makes little
sense in isolation, but is about the minimal code to show the bug.
The C source is:
###########################################################################
// BUG.C demonstrates a compiler bug
#define FULL_SCALE 4095
int p_offset, q_offset;
void set_offsets( int p_off, int q_off )
//
// Offsets in tenths of full scale
{
p_offset = ( p_off * FULL_SCALE ) / 10;
q_offset = ( q_off * FULL_SCALE ) / 10;
}
###########################################################################
Compiled with:
msp430-gcc -S -mmcu=msp430x149 -O2 bug.c
This produces correct code:
###########################################################################
.file "bug.c"
.arch msp430x149
/* Hardware multiplier registers: */
__MPY=0x130
__MPYS=0x132
__MAC=0x134
__MACS=0x136
__OP2=0x138
__RESLO=0x13a
__RESHI=0x13c
__SUMEXT=0x13e
.text
.p2align 1,0
.global set_offsets
.type set_offsets,@function
/***********************
* Function `set_offsets'
***********************/
set_offsets:
/* prologue: frame size = 0 */
.L__FrameSize_set_offsets=0x0
.L__FrameOffset_set_offsets=0x6
push r11
push r10
push r9
/* prologue end (size=3) */
mov r14, r9
push r2
dint
nop
mov r15, &__MPYS
mov #llo(4095), &__OP2
mov &__RESLO, r15
pop r2
mov r15, r12
mov #llo(10), r10
call #__divmodhi4
mov r12, &p_offset
push r2
dint
nop
mov r9, &__MPYS
mov #llo(4095), &__OP2
mov &__RESLO, r15
pop r2
mov r15, r12
mov #llo(10), r10
call #__divmodhi4
mov r12, &q_offset
/* epilogue: frame size=0 */
pop r9
pop r10
pop r11
ret
/* epilogue end (size=4) */
/* function set_offsets size 42 (35) */
.Lfe1:
.size set_offsets,.Lfe1-set_offsets
/********* End of function ******/
.comm p_offset,2,2
.comm q_offset,2,2
/*********************************************************************
* File bug.c: code size: 42 words (0x2a)
* incl. words in prologues: 3, epilogues: 4
*********************************************************************/
###########################################################################
Compiled with:
msp430-gcc -S -mmcu=msp430x149 -O2 -mnoint-hwmul bug.c
Which differs only in the addition of the -mnoint-hwmul switch, it
produces code which incorrectly sets the q_offset to the same value as
the p_offset. The calculation for q_offset starts correctly, but the
code to perform the division by ten is omitted, so that R12 still
contains the result of the previous calculation. The added comment
with all the queries pinpoints the error.
###########################################################################
.file "bug.c"
.arch msp430x149
/* Hardware multiplier registers: */
__MPY=0x130
__MPYS=0x132
__MAC=0x134
__MACS=0x136
__OP2=0x138
__RESLO=0x13a
__RESHI=0x13c
__SUMEXT=0x13e
.text
.p2align 1,0
.global set_offsets
.type set_offsets,@function
/***********************
* Function `set_offsets'
***********************/
set_offsets:
/* prologue: frame size = 0 */
.L__FrameSize_set_offsets=0x0
.L__FrameOffset_set_offsets=0x8
push r11
push r10
push r9
push r8
/* prologue end (size=4) */
mov r14, r8
mov r15, &__MPYS
mov #llo(4095), &__OP2
mov &__RESLO, r12
mov #llo(10), r10
call #__divmodhi4
mov r12, &p_offset
mov r8, &__MPYS
mov #llo(4095), &__OP2
/* ???????????????????????????????????????????????????????????????????
Some code was missed here
??????????????????????????????????????????????????????????????????? */
mov r12, &q_offset
/* epilogue: frame size=0 */
pop r8
pop r9
pop r10
pop r11
ret
/* epilogue end (size=5) */
/* function set_offsets size 30 (21) */
.Lfe1:
.size set_offsets,.Lfe1-set_offsets
/********* End of function ******/
.comm p_offset,2,2
.comm q_offset,2,2
/*********************************************************************
* File bug.c: code size: 30 words (0x1e)
* incl. words in prologues: 4, epilogues: 5
*********************************************************************/
###########################################################################
--
Rick Jenkins <r...@hartmantech.com>
Hartman Technica http://www.hartmantech.com
Phone +1 (403) 230-1987 voice & fax
221 35 Avenue. N.E., Calgary, Alberta, Canada T2E 2K5
