On Nov 13, 2004, at 11:16 AM, Matt Fowles wrote:
All~
On Sat, 13 Nov 2004 10:52:38 -0800, Jeff Clites <[EMAIL PROTECTED]> wrote:On Nov 13, 2004, at 8:53 AM, Leopold Toetsch wrote:We'd have just to force using lexicals for all vars
Having variable-size register sets would solve this, since you could have fixed assignments of variables to registers, and not have to suffer the overhead of moving data between registers and lexical pads over-and-over. Well, it doesn't really "solve" it--just makes it workable.
I like the idea of mandating lexicals vars. This would also eliminate the need for spilling (I think), as the register allocator would only need to refetch the lexical rather than save it off somewhere to be restored later.
In a way I feel like they're both same thing, just under a different description: spilling means moving data back-and-forth between registers and some other storage, and so does using lexicals.
But the only reason we have to do that sort of dance (under either description) is because we are RISC-ish: We have a limited number of registers, and calculations can only target registers (that is, you can't add 2 numbers directly in a lexical pad or other storage--they have to be moved to registers first). You don't have to move data back-and-forth if either you have an unlimited number of (preserved) registers, or you allow calculations to act directly on other memory locations. And I think this is again just two different ways of describing the same thing: you have an unlimited number of stable storage locations, and you do calculations directly from those locations. It's just that the former (unlimited preserved registers) feels cleaner, and doesn't require an explosion of op variants.
That's oversimplifying a bit, but I feel like those are the core issues (stemming from the observation of Leo's that continuations in effect give all variables a lifetime that extends to their entire block, in most cases).
JEff
