Leo~ Thanks for the clarification.
Matt On Wed, 17 Nov 2004 08:48:58 +0100, Leopold Toetsch <[EMAIL PROTECTED]> wrote: > Matt Fowles <[EMAIL PROTECTED]> wrote: > > > ... Thus you can consider all of the > > following questions (even though they will be phrased as statements). > > > 1) After a full continuation is taken all of the registers must be > > considered invalid. > > Calling a subroutine allocates a new register frame, that subs register > frame pointer in the context points to these fresh registers. > > A continuation restores the context it captured, i.e. at the place, > where it was created. This is true for all continuations. Inside the > context there is a *pointer* to a register frame, which is therefore > restored too. > > The effect of taking a continuation is therefore to restore registers to > that state where the continuation was created. Due to calling conventions > a part of the registers is volatile (used during a call or as return > results), while the other part is non-volatile. > > Until here there is no difference between return or full continuation. > > The effect of a full continuation can be to create a loop, where the > known control flow doesn't show a loop. Without further syntax to denote > such loops 1) is true. This register invalidation happens, if a > preserved register was e.g. only used once after the call and then that > register got reassigned, which is allowed for a linear control flow but > not inside a loop. > > This has per se nothing to do with a continuation. If you got an opcode > that does *silently* a "goto again_label" the CFG doesn't cope with the > loop, because it isn't there and things start breaking. The effect of a > full continuation *is* to create such loops. > > > 2) After a return continuation is taken, the registers can be trusted. > > Yes, according to usage in pdd03. > > > 3) If someone takes a full continuation, all return continuations > > down the callstack must be promoted. > > If one *creates* a full continuation ... > > > 4) After a function call, some magic needs to happen so that the code > > knows whether it came back to itself via a return continuation and can > > trust its registers, or it came back via a full continuation and > > cannot trust them. > > No. It's too late for magic. Either the CFG is known at compile time or > refetching in the presence of full continuations is mandatory. For both > the code must reflect the facts. > > > Corrections welcome, > > Matt > > leo > -- "Computer Science is merely the post-Turing Decline of Formal Systems Theory." -???
