[OpenCL] __generic address space for CL2.0

[Sahasrabuddhe, Sameer]

Hello Anastasia,

Some comments below on the latest patch. Only a couple of nitpicks, really!

 > diff --git a/include/clang/Basic/AttrDocs.td 
b/include/clang/Basic/AttrDocs.td
<snip>
 > +def OpenCLAddressSpaceGenericDocs : Documentation {
 > +  let Category = DocOpenCLAddressSpaces;
 > +  let Heading = "__generic(generic)";
 > +  let Content = [{
 > +The generic address space attribute is only available with OpenCL 
v2.0 and later.
 > +It can be used with pointer types. Only local variables and function 
parameters
 > +in non-kernel functions can have generic address space type 
attributes. It is

It can be used *only* with pointer types. Is it not okay to declare 
(pointer) variables in program scope with a generic type attribute? 
Also, the sentence should use singular "attribute".

 > +intended to be a placeholder for any other address space except for 
'__constant'
 > +in OpenCL code which can be used with multiple address spaces.
 > +  }];
 > +}

<snip>

 > +def OpenCLAddressSpaceLocalDocs : Documentation {
 > +  let Category = DocOpenCLAddressSpaces;
 > +  let Heading = "__local(local)";
 > +  let Content = [{
 > +The local address space specifies that an object is allocated in the 
local (work
 > +group) memory area, which is accessible to all work items in the 
same work
 > +group. The content stored in this memory region is not accessible 
after the kernel
 > +execution ends. Pointer types to local address space are allowed as 
function
 > +parameters. In a kernel function scope any variable can be in the 
local address
 > +space. Local address space variables cannot have an initializer.
 > +  }];
 > +}

Variables declared in the local address space can only occur at kernel 
function scope. Only pointers to local address space can be declared in 
other places. I am not sure if a pointer to local address space can be 
declared at program scope. It doesn't sound very useful, but can't 
confirm if the spec disallows it.

 > +def OpenCLAddressSpacePrivateDocs : Documentation {
 > +  let Category = DocOpenCLAddressSpaces;
 > +  let Heading = "__private(private)";
 > +  let Content = [{
 > +The private address space specifies that an object is allocated in 
the private
 > +(work item) memory . Other work items cannot access the same memory 
area and
 > +its content is destroyed after work item execution ends. Local 
variables and
 > +function arguments can be in private address space. Kernel function 
arguments
 > +declared to be a pointer or an array type cannot point to the 
private address
 > +space.
 > +  }];

Function arguments are always in the private address space (stronger 
than just "can be").

Sameer.