Tip: library size reduction
christoph at maxiom.de
Thu Jul 2 18:36:46 BST 2009
Hi there :)
Not that we run out of disk space, but now that KDE is more and more used on
embedded platforms, we could use a simple trick to save some space.
The problem is with class constructors. Imagine a simple dialog class that is
created from an .ui file:
Now, where would you save space? Obviously, you cannot write that any better
(except maybe doing the UI setup by hand to save some setObjectName() calls
on layouts, but this is not what I am after).
The problem is GCC "bug" 2163 (Code for constructors emitted twice). If you
objdump the generated code, you will indeed see the whole UI setup in the
binary twice, because gcc generates two constructors (and it generates three
destructors). And the larger your UI gets, the bigger the space wasting.
The solution is to use a simple trick that is used throughout in Qt library
code: use a private init() method to do the actual work for the constructor.
I did not check how many classes in KDE have "complex" constructors to measure
the actual savings we could get. But I guess there is several hundreds KB to
save in an KDE install.
Christoph Feck (kdepepo)
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