RE: [avr-gcc-list] Multiply improvement [1]

[Weddington, Eric]

Hi Anatoly,

Thanks for the patch!

Do you think that this patch is ok to put into the next WinAVR release?

Eric 

> -----Original Message-----
> From: 
> address@hidden 
> [mailto:address@hidden
> org] On Behalf Of Anatoly Sokolov
> Sent: Sunday, April 27, 2008 11:47 AM
> To: avr-GCC
> Subject: [avr-gcc-list] Multiply improvement [1]
> 
> Hello.
> 
> Now AVR-GCC for multiplication of two unsigned and two signed char 
> operands uses instructions 'MUL' and 'MULS' accordingly and is 
> 8x8=16bits operation. Multiplication signed on unsigned chars 
> is carried 
> out  as multiplication of two 16-bit values, though in AVR core there 
> is instruction MULSU. This patch adds a pattern usmulqihi3 for use 
> of instruction MULSU.
> 
> Testcase:
> extern unsigned char _a;
> extern          char _b;
> volatile extern          int _r;
> 
> int
> main (void) 
> {
>   _r = (unsigned int)_a * (int)_b;
>   return 0;
> }
> 
> Now:
>  lds r24,_b 
> 
>  clr r25  ;  6 extendqihi2/1 [length = 3]
>  sbrc r24,7
>  com r25
> 
>  lds r18,_a  ;  7 *movqi/4 [length = 2]
> 
>  ldi r19,lo8(0)  ;  28 *movqi/2 [length = 1]
> 
>  movw r20,r24  ;  26 *movhi/1 [length = 1]
> 
>  mul r20,r18  ;  9 *mulhi3_enh [length = 7]
>  movw r24,r0
>  mul r20,r19
>  add r25,r0
>  mul r21,r18
>  add r25,r0
>  clr r1
> 
>  sts (_r)+1,r25  ;  10 *movhi/3 [length = 4]
>  sts _r,r24
> 
> 
> With patch:
>  lds r18,_a  ;  5 *movqi/4 [length = 2]
> 
>  lds r20,_b  ;  6 *movqi/4 [length = 2]
> 
>  mulsu r20,r18  ;  7 usmulqihi3 [length = 3]
>  movw r18,r0
>  clr r1
> 
>  sts (_r)+1,r19  ;  8 *movhi/3 [length = 4]
>  sts _r,r18
> 
> Anatoly.
>