[cfe-dev] Adding a new type qualifier

[kalyan ponnala]

Thanks for the reply john. What I want is something like the _global
qualifier of opencl. The hardware architecture that I am trying to support
with clang has this global address space. I am not sure about how to add an
address space qualifier and parse and generate IR all the way.
I looked into the embedded C "address space" type qualifier, Can an expert
who is familiar with openCL, tell me if this could be changed to act like
the _global type qualifier. If not, I can use some suggestions too.

The following link was posted in march about the address space qualifiers, I
would like to know if there was any progress on this topic.
http://lists.cs.uiuc.edu/pipermail/cfe-dev/2010-March/008252.html

Thanks a lot.

On Mon, May 10, 2010 at 4:28 PM, John McCall <rjmccall at apple.com> wrote:

> On May 10, 2010, at 11:50 AM, kalyan ponnala wrote:
> > I am trying to add a new qualifier to the existing clang architecture. So
> far I was looking into replacing one of the existing qualifiers "volatile or
> restrict" from the "fast qualifiers". Now I think its a bad idea to do that.
> Can someone tell me
> >
> > >> whats the best way to add a new type quailfier?
>
> The first question you should ask yourself is whether this is really a
> qualifier.  Does it need to apply to arbitrary types?  Is it more
> appropriately modeled as an attribute on specific type declarations, or
> possibly an independent type kind?  Does it behave like a normal C
> qualifier, e.g. it is lost during r-value conversion?
>
> Assuming that's true, read on.
>
> > >> Why are there only 3 fast qualifiers added to the qualtype?
>
> The fast qualifiers are mangled into the low bits of the type pointer;
>  that's why they're fast, because they don't need to be stored separately.
>  Other qualifiers are stored in a separately-allocated ExtQuals structure.
>
> If we allocate Types with 8-byte alignment, we have three bits available.
>  Currently only const and restrict are fast, and the third bit is used to
> indicate that the type has extended qualifiers.
>
> > >> How can I increase the size of the fast qualifiers, I mean how to add
> new qualifier to qualtype without actually disturbing the existing fast
> quals : const, volatile, restrict.
>
>
> I would strongly suggest that you avoid changing the fast-qualifiers
> representation.  Just add your new qualifier to the Qualifiers structure and
> make sure the Profile method includes it, and then you'll just need to worry
> about the N places in the code which assume they know about every qualifier
> (I consider such code to be buggy, but surprisingly that judgement doesn't
> by itself fix any bugs :) ).
>
> John.




-- 
Kalyan Ponnala
phone: 8163772059
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