Steve,
at least the following code
struct __S {
char a[64],b[64];
int c[13];
};
struct __S *s;
struct __S * r(int i)
{
return s+i;
}
being evaluated to
.text
.p2align 1,0
.global _r
.type _r,@function
/***********************
* Function `_r'
***********************/
_r:
/* prologue: frame size = 0 */
.L__FrameSize_r=0x0
.L__FrameOffset_r=0x2
push r10
/* prologue end (size=1) */
mov r15, r10 ; 12 *movhi3/5 [length = 1]
mov #llo(154), r12 ; 13 *movhi3/8 [length = 2]
call #__mulhi3 ; 14 *mulhi3_call [length = 2]
mov r14, r15 ; 15 *movhi3/5 [length = 1]
add &s, r15 ; 16 *addhi3_3/5 [length = 2]
/* epilogue: frame size=0 */
pop r10
ret
/* epilogue end (size=2) */
/* function r size 11 (8) */
.Lfe1:
.size _r,.Lfe1-_r
/********* End of function ******/
.comm s,2,2
which seems to be correct...
Actually, multiplication vs. shifts&adds/subs being used upon max number of
iterations necessary for offset computation.
For example, if a structure size if 90, the multiplier being used to compute
indexing offset.
In general the decision about shifts&adds vs. multiplier is the following:
if total_sifts_and_adds_operations*operand_size_in_bytes > some_threshold then
use multiplier
otherwise
use shifts and tricks.
some_threshold == 10 now
for example :
a = b*65;
requires 6 shifts and 1 add operations.
cheers,
~d
On Tuesday 25 May 2004 16:22, Dmitry wrote:
> Hi Steve,
> Hm....
> Multiplier produces incorrect result?
> Or just an assembly output tricks registers?
> I had no probs with such structures...
>
> ~d
>
>
>
>
> -----Original Message-----
> From: mspgcc-users-ad...@lists.sourceforge.net
> [mailto:mspgcc-users-ad...@lists.sourceforge.net] On Behalf Of Steve
> Underwood
> Sent: Tuesday, May 25, 2004 3:52 PM
> To: mspgcc-users@lists.sourceforge.net
> Subject: [Mspgcc-users] compiler bug
>
> Hi Dimitry,
>
> I found a problem with the compiled code for GCC 3.2.3.
>
> If a structure is less than or equal to 128 bytes, an array of
> structures is accessed using shifts and adds to calculate the offset
> into the array. However, if the structure is more than 128 bytes the
> multiplier is used for these calculations. When shifts and adds are
> being used things work OK. When the multiplier is used the offset is
> calculated incorrectly.
>
> Regards,
> Steve
>
>
>
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