RE: Getting more information about functions arguments/locals inmachine description

RE: Getting more information about functions arguments/locals inmachine description

[Chris Lattner]

> I need to know how many arguments/local variables have
> being used and their starting offset on the stack (their size would
> actually help too)

DISCLAIMER: If there _is_ a right way to do it, this isn't it.  When I was
asking similar kinds of questions, there wasn't an "answer" persay, so
this is not much more than a hack.  That said here is what I'm doing to
get similar information (and it works great):

I added a hook earlier in GCC that grabs information from the function
tree as it's being compiled.  Because the arguments from the tree code
have all the information that you need, you can just grab it from there.
Since the argument allocation is target dependant, and this is target
dependant code, you just have to make sure that you transform them
consistently w.r.t the GCC backend.

For (stack allocated) local variables, you can use a function like this to
recursively traverse the blocks in the program, pulling out the
information you need:

static void PrintLocalVars(tree Block) {
  tree decl, subblocks;
  for (decl = BLOCK_VARS(Block); decl != NULL; decl = TREE_CHAIN(decl))
    debug_tree(decl);

  for (subblocks = BLOCK_SUBBLOCKS(Block); subblocks != NULL;
       subblocks = BLOCK_CHAIN(subblocks))
    PrintLocalVars(subblocks);
}

The RTL (accessible via DECL_RTL(decl) in the first loop), will tell you
enough information to know where on the stack it is located.  The type of
the variable will tell you alignment, size, or anything else you need.

Hope this helps,

-Chris

http://www.nondot.org/~sabre/os/
http://www.nondot.org/~sabre/Projects/

RE: Getting more information about functions arguments/locals inmachine description

[Alexandre Courbot]

> For (stack allocated) local variables, you can use a function like this to
> recursively traverse the blocks in the program, pulling out the
> information you need:
> 
> static void PrintLocalVars(tree Block) {
>   tree decl, subblocks;
>   for (decl = BLOCK_VARS(Block); decl != NULL; decl = TREE_CHAIN(decl))
>     debug_tree(decl);
> 
>   for (subblocks = BLOCK_SUBBLOCKS(Block); subblocks != NULL;
>        subblocks = BLOCK_CHAIN(subblocks))
>     PrintLocalVars(subblocks);
> }
> 
> The RTL (accessible via DECL_RTL(decl) in the first loop), will tell you
> enough information to know where on the stack it is located.  The type of
> the variable will tell you alignment, size, or anything else you need.
> 
> Hope this helps,

It does help, absolutely! :) I didn't want at first to deal with trees,
but it looks like I have no choice - and it's not as messy as I'd have
expected. Anyway, it does the job well.

One little question remains however: while your function is absolutely
clear, where to call it and what to give it as argument isn't completely
yet. Shall I give it the block of the function, in, say,
ASM_DECLARE_FUNCTION_NAME (as it is given the function's tree node as
argument), to output the locals later in FUNCTION_PROLOGUE? Or is there
a way to call it with the "root" of the program's tree, to retrieve all
the function's variables once and for all? As it makes use of recursion,
I guess the later is the good way, but I don't know when I could call
it, and how to get the program's tree - I'm not yet very familiar with
GCC's internals. Can you extend a little bit on how you use it? Or point
me to the source where you make use of it?

Anyway, thanks for the help - your reply has been a relief to me! :)
Alex.
-- 
http://www.gnurou.org