Dan Sugalski wrote:At 5:34 PM +0200 10/21/04, Leopold Toetsch wrote:
The question is: is saveall supposed to copy registers or just prepare a fresh set of registers.
What about that?
Missed that, sorry. A copy.
and we see where we go from there. I'm not inclined, yet, to drop the register stacks and the push/pop ops as there are certainly times when it's useful, being a quick way to spill and unspill a set of registers for a basic block.
Not really IMHO. It doesn't get you more addressable registers, i.e. you can always access ony e.g. 2 x 16 at once. With spilling into an array the range of "registers" is extended.
If a basic block got such a behavior that it needs more registers locally then allocation of these registers isn't a problem. And in praxis you don't have that anyway, because a basic block is *branchless* per definition.
I realize that a basic block's branchless, Leo. What I was talking about was the *entry* (or exit) to a basic block. If you have a looping block construct:
FOO
|
V
BAR<-+
+---+
|
V
BAZwhere the BAR basic block either is entered from the beginning or looped into, the register coloring code is in a position to do some save optimizations. It *could* spill the used registers, or it could just push the whole set onto the register stack and start fresh, popping off the old set when the code's done.
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Dan
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