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SF# 1409443: Expand comment to cover the interaction between f->f_lasti and the PREDICT macros.

This commit is contained in:
Raymond Hettinger 2007-01-06 01:14:41 +00:00
parent d14ef77ae1
commit 4bd97d4549
1 changed files with 10 additions and 1 deletions
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11
Python/ceval.c
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@ -741,7 +741,16 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
this wasn't always true before 2.3! PyFrame_New now sets
f->f_lasti to -1 (i.e. the index *before* the first instruction)
and YIELD_VALUE doesn't fiddle with f_lasti any more. So this
does work. Promise. */
does work. Promise.
When the PREDICT() macros are enabled, some opcode pairs follow in
direct succession without updating f->f_lasti. A successful
prediction effectively links the two codes together as if they
were a single new opcode; accordingly,f->f_lasti will point to
the first code in the pair (for instance, GET_ITER followed by
FOR_ITER is effectively a single opcode and f->f_lasti will point
at to the beginning of the combined pair.)
*/
next_instr = first_instr + f->f_lasti + 1;
stack_pointer = f->f_stacktop;
assert(stack_pointer != NULL);