Creating a structure at compile time.

[Matt Davis]

On Fri, Dec 2, 2011 at 3:38 PM, Matt Davis <mattdavis9@gmail.com> wrote:
> I am working on a gcc-plugin where I need to create a structure at compile time.
> I have gleaned over one of the front ends to learn more about creating
> structures at compile time.  What I have thus far is a type node for my struct.
>
> I now need to create an instance of this struct.  For exemplary purposes we will
> call this type 'struct T' and we will call the instance of T, 'my_T'  By using
> the build_constructor() routine in GCC I create an instance, my_T, which I need
> to pass the address of to a function.  So, I take this decl, my_T, and pass it to
> build_fold_addr_expr().  The result of the latter is what I pass to the
> function 'fn()'.
>
> Yes, the function I am passing the reference to is expecting the proper type,
> that of address-to-T.  Running this presents me with an error in
> expand_expr_real_1() where "Variables inherited from containing functions should
> have been lowered by this point."
>
> So, I figure, if I create a temp variable, 'V', of type pointer-to-T, and run
> make_ssa_name() on that temp.  And then insert an assignment before the call to
> fn, so I get: 'V = &my_T;'  After looking at the GIMPLE dump, I see, 'V = &my_T;
> fn(V);'  Which is correct, however, in the type list of the caller, I only see:
> 'struct * V;'  Now, this concerns me, I would expect to see "struct T *V;"  As
> above, this case also fails.
>
> I am baffled, do I need to even be creating the ssa_name instance to pass to
> 'fn()', which is 'V' in the case above?  Or, will the build_constructor()
> produce a tree node that I can treat as a variable, that I can pass to 'fn()' ?
>
> -Matt

Well, I have successfully created and used an initialized structure.
Note that I do not need to run the make_ssa_name.  I can declare the
struct as TREE_STATIC and work from there.  Now, my problem with the
expand_expr_real_1 check failing is because some of the values I
initialize in my compile-time created struct can be different at
runtime.  Is there a way I can take this constructor tree node, and
have all of the values in it set in the middle of my function, where
those values are defined?   I do not need the structure initialized
upon function entry.  What I need is to have all of the values, which
I already setup when I am in the middle of the function being
processed.  I need these values actually filled-out in the middle of
function instead at function entry.  I am unsure how to do this.  The
constructor node exists, and I'm in the middle of an IPA pass.  I
assume I can call gimplify_expr() but I am thinking I need to pass it
something different than just a constructor tree node.

Thanks for any help

-Matt