Hi, On Mon, 30 Sep 2013, Jeff Law wrote:
> > - the compiler better do an awesome job of sharing stack space for > > user variables in a function... I wouldn't want to blow up the stack > > with a bazillion unrelatd temps each wit their own location. > If the objects have the same type and disjoint lifetimes, they can be easily > shared. > > Things are more difficult if the types are different Not anymore. We adjust the alias machinery when merging differently typed variables into the same stack slot, see update_alias_info_with_stack_vars. > -- IIRC, the root > of the problem is the optimizers can interchange a load of one type with > a later store of the other -- the aliasing code says "hey, they're > different types, so they don't alias, feel free to move them around as > desired" and all hell breaks loose. That was the problem once, yes. Meanwhile we should have fairly decent stack slot reuse, especially with variables declared in different scopes (since the end-of-scope CLOBBERs), for non-SSA_NAME temps that is. For the others it's the register allocator anyway that has to do a decent job (and it does). Ciao, Michael.
