At 07:15 AM 6/12/2005, Chip Salzenberg wrote:
Therefore, register allocation must allow for implicit flow of control from *every* function call to *every* function return ... or, more precisely, to where *every* continuation is taken, including function return continuations.
Yes. But for casual readers, you might want to qualify that with: "For a given basic block..." Just a couple of thoughts to add: 1) As far as variable lifetime, the brute-force method would assume lifetime windows (du-chains) from the first definition of each variable to the last function call in a basic block. Horrible for optimization. 2) For languages without eval() it is possible simply to do compile time analysis of routines and associate an AST attribute with whether the routine captures or invokes a continuation, and for languages with Continuation Passing Style calls, you can analyze whether the function does anything but use Return Continuations. This would give the register allocator enough information to properly break down the basic blocks into correct DU-chains and allocate with confidence. However, given Parrot's intended target languages, I feel that (2) is going to be rarely applicable. -Melvin
