RE: [avr-gcc-list] Bug with -Os with constant multiplier of 3?

[Weddington, Eric]

Hi David,

Have you had a chance to take a look at the avr target bugs in the GCC Bugzilla 
database? This might have already been submitted, but if not, could you submit 
a bug to the GCC project? If you do this, please put my email address in the CC 
list.

Thanks,
Eric Weddington

> -----Original Message-----
> From: address@hidden
> [mailto:address@hidden On
> Behalf Of David Kopf
> Sent: Tuesday, December 21, 2010 8:02 AM
> To: address@hidden
> Subject: [avr-gcc-list] Bug with -Os with constant multiplier of 3?
> 
> Hi,
> 
> Using WinAVR avr-gcc 4.3.0 and 4.3.3, compiling 3*<uint8_t> with -Os calls
> __mulhi3 instead of the optimized *2+1 when no hardware
> multiply is present.  O1,O2,O3 does it right:
> 
> Target: ATTiny85
> 
> > uint8_t rssi;  //r24
> > -O1 -O2 -O3
> > rssi=3*rssi;
> >    aa: 28 2f        mov r18, r24
> >    ac: 22 0f        add r18, r18
> >    ae: 28 0f        add r18, r24
> >
> 
> > -Os
> > rssi=3*rssi;
> >    ae: 90 e0        ldi r25, 0x00 ; 0
> >    b0: 63 e0        ldi r22, 0x03 ; 3
> >    b2: 70 e0        ldi r23, 0x00 ; 0
> >    b4: 40 d0        rcall .+128     ; 0x136<__mulhi3>
> >
> 
> 
> 
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