From: Paul E. McKenney > Sent: 01 July 2020 17:06 ... > > Would an asm statement that uses the same 'register' for input and > > output but doesn't actually do anything help? > > It won't generate any code, but the compiler ought to assume that > > it might change the value - so can't do optimisations that track > > the value across the call. > > It might replace the volatile load, but there are optimizations that > apply to the downstream code as well. > > Or are you suggesting periodically pushing the dependent variable > through this asm? That might work, but it would be easier and > more maintainable to just mark the variable. Marking the variable requires compiler support. Although what 'volatile register int foo;' means might be interesting. So I was thinking that in the case mentioned earlier you do: ptr += LAUNDER(offset & 1); to ensure the compiler didn't convert to: if (offset & 1) ptr++; (Which is probably a pessimisation - the reverse is likely better.) David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
