Tcl Source Code

The patch defines 4 "constant" Tcl_Obj in the execution
environment: "zero", "one", "minus one" and "empty
object".
The purpose is to avoid some unnecessary object
creation/destruction, especially of boolean values.

There is a zero-to-minimal positive effect in tclbench
results; it may be larger for threaded builds.

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Parts of this have been incorporated into 8.5a3

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pushing this back to miguel due to the number of changes he 
has made to TEBC recently.

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Mhh ... the idiom is actually
  foreach $varNameList {{}} break
which sets the variables whose names are in $varNameList to
the empty object {}

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I do not expect a large memory effect either: most of the
things that are changed involve relatively short lived
Tcl_Obj. Boolean values for instance are typically consumed
right after creation.

One exception could be when setting large numbers of
variables to {} via the idiom
   foreach varName $someList {.} break
which sets the first variable to "." and the rest per
default to {}. This idiom is used in both implementations of
set operations in the wiki (soon in tcllib and tclbench?),
(see http://mini.net/tcl/271.html).

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My guess is this has minor benchmark effects because it 
only minorly affect small obj allocations.  However, it may 
be a more notable effect on mem usage (any good ways to 
check that in a practical manner?).

Anyway, this should be run through purify or efence before 
getting commited.

File Added - 8426: patch.txt

File Added - 8425: bench.const3