[Python-Dev] Store x Load x --> DupStore

Greg Ewing greg.ewing at canterbury.ac.nz
Mon Feb 21 04:32:11 CET 2005

Phillip J. Eby wrote:

> Hm, actually I think I see the answer; in the case of module-level code 
> there can be no "anonymous local variables" the way there can in 
> functions.

Why not? There's still a frame object associated with the call
of the anonymous function holding the module's top-level code.
The compiler can allocate locals in that frame, even if the
user's code can't.

> I guess you'd need to also have a "reset stack to 
> level X" opcode, then, and both it and the set-handler opcode would have 
> to be placed at every destination of a jump that crosses block 
> boundaries.  It's not clear how big a win that is, due to the added 
> opcodes even on non-error paths.

Only exceptions and break statements would require stack
pointer adjustment, and they're relatively rare. I don't
think an extra opcode in those cases would make much of
a difference.

Greg Ewing, Computer Science Dept, +--------------------------------------+
University of Canterbury,	   | A citizen of NewZealandCorp, a	  |
Christchurch, New Zealand	   | wholly-owned subsidiary of USA Inc.  |
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