Re: Representation clauses and records

[davidf@mks.com (David J. Fiander)]

Pascal MALAISE <malaise@alphalink.com.au> writes:
> As far as I know, this problem would not happen in full ADA because the
> instanciation of unchecked_conversion will be compiled as a call to
> something
> like memcpy, a procedure which does not make any assumption about
> alignment of arguments.
> We loose performance but gain reliability.

I've seen other comments that indicate that the runtime cost of a
call to Unchecked_Conversion is going to be a function call of
some sort, and I have just one question: "Why?"

It would seem to me that if I have an object of some sort, and I
call Unchecked_Conversion on it, if the type is small enough
(in C terms converting a pointer to an int), why shouldn't the
compiler just generate a "load ptr/store int" instruction
sequence?  Now, for larger objects, the compiler will have to
perform a block move to effect the conversion, either via a
runtime library call or by open-coding the block move, but that
depends entirely on the H/W support for block moves.

- David