[Mesa-dev] [glsl] indvar in ir_loop

[Liu Xin]

Hi, Mesa developers,

According to glsl v1.0, we have loop construct:
for (for-init-statement; condition(opt); expression)
statement-no-new-scope
Variables declared in for-init-statement or condition are only in scope 
until the end of the
statement-no-new-scope of the for loop.

let's assume I have a fragment shader:

~/testbed$ cat indvar.frag
void main(void)
{
        vec4 a[32];
        for(int i=0; i<10; ++i) {
                if (i == 9)
                    gl_FragColor = a[i];
       }
}


I found current glsl compiler emits HIR like this:

(function main
  (signature void
    (parameters
    )
    (
      (declare () int i@0x988eb84)
      (declare () (array vec4 32) a@0x988ec5c)
      (declare (temporary ) int assignment_tmp@0x988eaac)
      (assign (constant bool (1)) (x) (var_ref 
assignment_tmp@0x988eaac)  (constant int (0)) )
      (assign (constant bool (1)) (x) (var_ref i@0x988eb84)  (var_ref 
assignment_tmp@0x988eaac) )
      (loop () () () () (
        (if (expression bool ! (expression bool < (var_ref i@0x988eb84) 
(constant int (10)) ) ) (
          break
        )
        ())

        (if (expression bool all_equal (var_ref i@0x988eb84) (constant 
int (9)) ) (
          (declare (temporary ) vec4 assignment_tmp@0x987cee4)
          (assign (constant bool (1)) (xyzw) (var_ref 
assignment_tmp@0x987cee4)  (array_ref (var_ref a@0x988ec5c) (var_ref 
i@0x988eb84) ) )
          (assign (constant bool (1)) (xyzw) (var_ref 
gl_FragColor@0x96d8fc4)  (var_ref assignment_tmp@0x987cee4) )
        )
        ())

        (declare (temporary ) int assignment_tmp@0x987cb84)
        (assign (constant bool (1)) (x) (var_ref 
assignment_tmp@0x987cb84)  (expression int + (var_ref i@0x988eb84) 
(constant int (1)) ) )
        (assign (constant bool (1)) (x) (var_ref i@0x988eb84)  (var_ref 
assignment_tmp@0x987cb84) )
      ))

    ))

)

I think glsl compiler translates AST like this

int i = 0;
for (;;) {
    if (i < 10) break;
    if (i == 9) gl_FragColor = a [ i ] ;
    i = i + 1;
}

Is it correct?

Another question, for class ir_loop, why is ir_loop::counter ir_variable 
while from/to/increment are all ir_rvalue? I create an ir_variable for 
ir_loop counter, but hierarchical visitor won't access it. I don't think 
ir_loop::accept(ir_hierarchical_visitor *v)  will visit ir_loop::counter 
at all.

thanks,
--lx

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