[fpc-devel] Generated code of constant parameters of double type

Luiz Americo Pereira Camara pascalive at bol.com.br
Sun Nov 16 15:20:40 CET 2008

Jonas Maebe escreveu:
> On 16 Nov 2008, at 14:52, Florian Klaempfl wrote:
>> Luiz Americo Pereira Camara schrieb:
>>> Maybe the documentation 
>>> (http://www.freepascal.org/docs-html/ref/refsu50.html#x126-13300011.4.4) 
>>> can be modified to clarify this since the statement:
>>> "A constant argument is passed by reference if its size is larger 
>>> than a pointer."
>>> leads to the conclusion that double types (8 bytes) would be passed 
>>> as reference in 32bit code.
>> Well, the bigger problem is that this is target dependent.
> And calling convention dependent. In most cases, how exactly constant 
> and value parameters are handled by the compiler is a private 
> implementation detail. You cannot count on how it is exactly implemented.

Ok. I was not counting in implementation details.

My point was that this could be a missing optimization opportunity: pass 
by reference a 8 bytes parameter when the pointer size is 4. I also 
tested with TPoint (8 bytes) and it's passed by reference unlike double 
(also 8 bytes) that is passed by value always.

Probably i'm missing some information why double is treated differently 
of a record of same size. I don't have compiler knowledge. All my 
conclusions came from the documentation.


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