[LLVMdev] How to extend llvm IR and frontend?

[John McCall]

On Jan 21, 2011, at 10:23 AM, Frits van Bommel wrote:

> On Fri, Jan 21, 2011 at 4:32 PM, Aaron Myles Landwehr <snaphat at gmail.com> wrote:
>> Hypothetically, suppose I have a generic system with multiple address spaces
>> such that each address space is accessed using different instructions.
>> Now suppose, I wanted to add a new keywords 'foo' and 'bar' to the front of
>> c variables and function return types such that the following would be
>> valid:
>> foo void* a;
>> foo void* somefunc(){...}
>> bar int b;
>> int somefunc2(bar int*){...}
> 
> How about putting
> 
>  #define foo __attribute__((address_space(256)))
>  #define bar __attribute__((address_space(257)))
> 
> in some header? (Or on the command line, or in clang's default #defines, ...)
> Though maybe they'd need to be in a slightly different place; the
> example in the documentation
> (http://clang.llvm.org/docs/LanguageExtensions.html) is
> 
>  #define GS_RELATIVE __attribute__((address_space(256)))
>  int foo(int GS_RELATIVE *P) {
>    return *P;
>  }
> 
> so maybe it won't work if they're in front of the declaration.

That would work fine.  The attribute works like a normal qualifier:  just like 'int const *'
and 'const int *' both mean "pointer to const int", 'GS_RELATIVE int *' and
'int GS_RELATIVE *' both mean "pointer to int object in address space 256".
Whereas 'int * GS_RELATIVE *' means "pointer to pointer object in address
space 256 that points to int object in generic address space".

John.