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Re^5: Perl 5 Optimizing Compiler, Part 5: A Vague Outline Emergesby dave_the_m (Prior)
|on Aug 31, 2012 at 13:36 UTC||Need Help??|
Consider the expression $x + $y * 3. This is compiled into an op tree, where (amongst other things) each op struct holds the info needed for that op, but also a pointer (op_next) to the next op in the execution sequence, and a pointer (op_ppaddr) to the C function that knows how to "execute" that op. So the op sequence for the above looks a bit like:
The pp_functions themselves look a bit like the following (hugely over-simplified of course):
And finally, the runops loop looks a bit like:
So the net effect is that perl is in a loop, calling various pp_* functions, whose job is to push and pull useful values onto the perl stack.
Now, under your proposal, you'll all have the pp functions (and all the functions they depend upon, such the hash library) compiled into IR and available to you. What do you do with the op tree? Yuval's proposal is to effectively compile the following C into IR:
except that he would use modified versions of the pp functions that take and return their args directly, rather than getting them on and off the stack. Then LLVM has access to IR version of the unrolled runops loop and all the functions in IR, and can do its funky stuff with them.
So, with that background, what would your IR generated from the op tree look like? Is it just an unrolled runops loop for a single sub, with lots of explicit calls to pp-ish functions, or would you try and unroll the pp functions themselves, or something completely different?