hm....
interesting.
i'll check this out later on today.
~d
Rick Jenkins wrote:
> 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
>
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