[fpc-pascal] Remove unused functions in a class

JoshyFun joshyfun at gmail.com
Sun Apr 5 17:12:33 CEST 2009

Hello Jonas,

Sunday, April 5, 2009, 2:09:33 PM, you wrote:

JM> If you have a class hierarchy tbase->tderived1->tderived2 with a
JM> virtual method called "vmethod", and nowhere in the program there is a
JM> call to vmethod, then it is unused. Or if it is only called using
JM> tderived2 instances, then if the linker does not find any direct  
JM> references to tderived1.vmethod or tbase.vmethod (e.g., via  
JM> "inherited" calls from tderived2 methods), it knows that the VMT  
JM> entries for vmethod in tderived1 and tbase can be set to nil.

In fact I was thinking in something like this:

 procedure Myprocedure(); virtual;
 procedure MyProcedure(); override;

And in the code:

  MyObj: TCustomFoo;

Something like this could kill the dead code detection ? A simple
yes/no is enoght :)

>> JM> that produces an error if you try to link a unit compiled with the
>> JM> option using the external linker), but that hasn't been done yet.
>> Just for curiosity which is the parameter set ?

JM> Compile the compiler with -dvtentry. It's not been tested for a while
JM> though, as far as I know.

I'll play with it just for fun...

JM> I also made a mistake in my previous explanation: currently, the WPO
JM> does not yet perform the optimization the -dvtentry does. -dvtentry
JM> looks at which VMT entries of a class hierarchy are never accessed,
JM> and replaces those by nil. As a result, if those methods are not  
JM> referred directly, then they can be removed by the linker.

I understand it in that way already.

JM> The WPO looks at which class types can be instantiated in the program
JM> and at the inheritance tree, and based on this determines which  
JM> referenced directly, then they can be removed by the linker (and the
JM> ones that are referenced can be turned into normal function calls).

More or less I understand the WPO way of work. Thank you again.

Best regards,

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