On 05/10/2016 04:58 PM, Tom Udale wrote: > To my mind, the only reason that these would not be considered "memory > references" is because the compiler has already decided to put the > memory into registers (true these are mostly automatic variables so they > can easily be put into registers). But from an abstract machine > standpoint a=b is a memory read and a memory write is it not (or is that > a totally incorrect statement)? It seems odd therefore that a register > allocation choice can fundamentally alter program behavior. An auto variable is only considered to be "memory" if its address is taken with & . "memory" means that this object is reachable from some pointer somewhere. > It appears that the "memory" clobberer is operating at a level much > lower than the C statement which means you _really_ need to be careful > with it since what is memory and what is not could easily change with > the addition or removal of reference (i.e. something that once was held > in memory is not any longer because a removed reference made another > variable be better suited to the stack allowing the one-time memory > variable the better candidate for a register). Not really. If a variable is not addressable by any means then it can't be affected by a memory access. Whether the compiler spills that variable to a stack frame makes no difference. Andrew.
