From: Arnd Bergmann > Sent: 07 May 2021 23:08 ... > I don't know how the loads/store perform compared to the shift version > on a particular microarchitecture, but my guess is that the shifts > are better. What does the nios use? Shifts generate reasonable code for put_unaligned() but they get horrid for get_unaligned(). On the nios writing the 4 bytes to memory and reading back a 32bit value should generate shorter faster code. You do need to generate 4 byte loads, 4 bytes stores, 32bit load. (The load will cause a stall if the data is needed for one of the next two instructions, and there is a (undocumented) stall between a write and read to the same memory area. The shift version requires 3 shifts and 3 ors - but I think gcc makes a bigger pig's breakfast of it.) OTOH I'm not sure anyone in their right mind would run Linux on nios. It is a soft cpu for the altera (now intel) fpgas. We use them with 4k code and sub 64k data for real time processing. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
