Jeremy Hylton wrote:
On Wed, May 7, 2008 at 11:43 AM, Thomas Lee <[EMAIL PROTECTED]> wrote:
Nick Coghlan wrote:
As Thomas mentions in a later message, making it possible to annotate
nodes would permit Functions to be annotated as being a generator at the AST
stage (currently it is left to the bytecode compiler's symtable generation
pass to make that determination).
Although I guess an alternative solution to that would be to have separate
AST nodes for Functions and Generators as well...
I've actually backtracked a little and gone back down the Const path again.
I know this is the third time I've changed my mind, but it's primarily
because annotations tend to get a little clunky (or my implementation was,
at least). Using Const nodes feels a lot more natural inside the optimizer.
I think it's going to stick, at least in the short term.
Rather than separate FunctionDef and GeneratorDef nodes, I think a new bool
attribute (is_generator?) on FunctionDef should do the job nicely. Further,
I'm thinking we can move the "generator detection code" from the symtable
into Python/ast.c so the generator/function information is available to the
optimizer.
Does the optimizer run after the symtable? I'd expect the symbol
table information to be essential for almost all analysis, so it
should be fine to wait until that pass to mark the generators.
There are a lot of micro-optimisations that are actually context
independent, so moving them before the symtable pass should be quite
feasible - e.g. replacing "return None" with "return", stripping dead
code after a return statement, changing a "if not" statement into an
"if" statement with the two suites reversed, changing "(1, 2, 3)" into a
stored constant, folding "1 + 2" into the constant "3".
I believe the goal is to see how many of the current bytecode
optimisations can actually be brought forward to the AST generation
stage, rather than waiting until after the bytecode symtable calculation
and compilation passes.
The current structure goes:
tokenisation->AST construction->symtable construction->bytecode
compilation->bytecode optimisation
My understanding of what Thomas is trying to do is to make it look more
like this:
tokenisation->AST construction->AST optimisation->symtable
construction->bytecode compilation
There may still be a direct bytecode optimisation step left at the end
if it turns out something relies on information that isn't worked out
until the symtable construction pass (and that can't easily be worked
out earlier, such as adding an 'is_generator' flag to the FunctionDef
AST node).
Cheers,
Nick.
--
Nick Coghlan | [EMAIL PROTECTED] | Brisbane, Australia
---------------------------------------------------------------
http://www.boredomandlaziness.org
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