Re: New datatype addition to gcc

[Sriharsha <sriharsha.v@xxxxxxxxxxxxxxxxxx>]

Hi Michael,

Michael Meissner wrote:

> Note, GCC internally believes that all pointers are equal and are an integer
> type. 
That is known.

> If your port has two different types of address (ie, a pointer to 8 bit
> items would be different from a pointer to 16 bit items, either using a
> different format or a different sized item), it will be a long and difficult
> port.
My h/w personnel says that there will be TWO RAMs in the processor, one 
is 8-bit addressible while the other is 16-bit addressible. If the 
compiler has to do 8-bit data load/store, it uses the 8-bit RAM and if 
it has something to do with 16-bit, it uses that RAM. This sounded 
bizzare to me but, thats what they say (or atleast I've never come 
across such stuff).

>  I did the front end of the C compiler for Data General MV/Eclipse
> computers, which was originally a word machine that had byte modes grafted on
> (byte pointer was the word pointer shift left one bit).  At one point as we
> were doing the transition from MV/Eclipse to Motorola 8800, I looked at GCC,
> and concluded that it would be very difficult to support two types of pointer
> in the compiler.
>  
Completely agreed (though I have no clue how you do that)

> If your question is instead that you have a unifed pointer mode (word pointers
> having bottom bits zero), and you have load byte/store byte on the new machine,
> but no byte arithmetic, don't worry, most RISC machines have that restriction.
> GCC will just promote items to a larger integer type that does have arithmetic
> support.
>  
There we are. I was thinking exactly that. But again the problem of two 
RAM spaces is cropping up. Im totally stumped out here. I simply did not 
understand how the addresses are generated etc. (for eg. the arithmetic 
result of two 16-bit data can be 8-bit, then will it be stored in 8-bit 
RAM (thats what our ppl say))? And many such questions.

Im not sure if this is as unique a problem as I see or I'm still a 
novice in the processor world. Meanwhile our HW guys are busy with their 
works and have very less time for meetings on this issue.


Thanks again,
Sriharsha.