[fpc-devel] Does FPC optimize unused parameters ?

Jonas Maebe jonas.maebe at elis.ugent.be
Wed Aug 8 16:55:47 CEST 2012

michael.vancanneyt wrote on Wed, 08 Aug 2012:

> On Wed, 8 Aug 2012, Jonas Maebe wrote:
>> After the body of the called routine has been parsed, it would be  
>> possible in theory (with indeed all the caveats the compiler would  
>> have to take care of such as side effects -- note that these may  
>> include non-obvious side-effects, such as potential overflow  
>> exceptions and invalid pointer accesses).
> You'd need to check the caller routine as well, values for parameters might
> still be used after the call to the function.

There's a difference between not loading/evaluating expressions passed  
as a parameter, and completely eliminating the program slice that  
contributed to calculating every value used in the parameter  
expression. Obviously, the latter has much more stringent requirements.

> I still use ifdefs for debug messages, and have a template to  
> quickly insert :
> {$ifdef debugmsg}SendDebug('|');{$endif debugmsg}
> This way, there is no extra code in my final build.

It's possible to do that in a more compact way with a macro (the  
following is used in a couple of places in the RTL):

{$macro on}
{$ifdef debugmsg}
{$define CallSendDebug:=SendDebug}
{$define CallSendDebug:=//}



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