On 08/28/2013 11:17 PM, Kenneth Graunke wrote:
On 08/27/2013 11:34 PM, Liu Xin wrote:
Hi, Mesa community,
I am not familiar with S-expression or other forms of lisp languages.
That's OK - the IR has no resemblance to actual Scheme or Lisp
programming. We just print and read the () syntax because it's simple.
indeed, I gradually realize glsl IR is not same from lisp at all. in
lisp, (if (cond) (then) (else)) is an expression. I found that ir_if in
is not a subclass of ir_rvalue.
it's a statement . that is to say, glsl IR is not functional language.
it's a procedural language with a lot of parentheses.
I am working on GLSL IR transformation. for example, i want to change a
variable to a array of same type.
By now , i can find the definition of a variable. How can i update all
uses of this variable in S-expression? I think all uses of this variable
are in the form of ir_dereference_variable.
That's right. ir_dereference_variable is an actual use of a variable.
The difficulty is how to collect d-u chain using hierarchical visitor.
Yeah...sadly, the compiler doesn't have UD chains. Ian was working on
those a few years back, but the code never landed.
I think some optimizer
authors must have the same problem. Could you give me a pass which
solved my problem? so I can take reference.
You might look at opt_array_splitting. It uses two visitors:
First, ir_array_reference_visitor walks over the IR and finds
variables it might want to transform, storing those in a hash table.
As a second pass, ir_array_splitting_visitor walks over the IR and
actually transforms things.
ir_array_splitting_visitor is also an ir_rvalue visitor, which is
useful for transforming expression trees. You get passed an ir_rvalue
** pointer, and can replace a whole subexpression tree with something
else. In your case, you'll probably find ir_dereference_variables and
replace them with ir_dereference_arrays. (In the printed IR, replace
(var_ref foo) with (array_ref (var_ref new_foo_array) ...subscript...).)
Good luck!
--Ken
yes, your pointers are really helpful. thank you.
--lx
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