[avr-gcc-list] Optimization around mul and restoring r1

2013-10-01 Thread Simon Kirby
Hello! How difficult would it be to convince avr-gcc to not re-zero r1 instantly after mul, but delay it until a zero is actually needed? For example, see this actual avr-gcc output: Vneutral = (uint16_t)Vbus * t >> 8; -> lds r25, 0x20FD mul r24, r25 movw

Re: [avr-gcc-list] Optimization around mul and restoring r1

2013-10-01 Thread Weddington, Eric
> -Original Message- > From: avr-gcc-list-bounces+eric.weddington=atmel@nongnu.org > [mailto:avr-gcc-list-bounces+eric.weddington=atmel@nongnu.org] On > Behalf Of Simon Kirby > Sent: Tuesday, October 01, 2013 9:42 AM > To: avr-gcc-list@nongnu.org > Subject: [avr-gcc-list] Optimiza

Re: [avr-gcc-list] Optimization around mul and restoring r1

2013-10-01 Thread David Brown
On 01/10/13 09:41, Simon Kirby wrote: > Hello! > > How difficult would it be to convince avr-gcc to not re-zero r1 instantly > after mul, but delay it until a zero is actually needed? For example, > see this actual avr-gcc output: > > Vneutral = (uint16_t)Vbus * t >> 8; > -> > lds

Re: [avr-gcc-list] Optimization around mul and restoring r1

2013-10-01 Thread Georg-Johann Lay
David Brown schrieb: On 01/10/13 09:41, Simon Kirby wrote: Hello! How difficult would it be to convince avr-gcc to not re-zero r1 instantly after mul, but delay it until a zero is actually needed? For example, see this actual avr-gcc output: Vneutral = (uint16_t)Vbus * t >> 8; ->