[Mesa-dev] [PATCH 07/11] glsl: Lower unconditional return statements.

[Kenneth Graunke]

On 07/07/2011 09:41 AM, Paul Berry wrote:
> On 7 July 2011 01:13, Kenneth Graunke <kenneth at whitecape.org> wrote:
>>>        visit_block(&ir->body);
>>>
>>> +      /* If the body ended in an unconditional return of non-void,
>>> +       * then we don't need to lower it because an unconditional
>>> +       * return of non-void at the end of a function is what returns
>>> +       * get lowered to.
>>
>> This comment doesn't make sense to me.  Are you trying to say that
>> unconditional all non-void returns were already lowered to variable
>> assignments and void returns?  Or...?
> 
> Hmm, let me try again in more words:
> 
> When we are lowering returns in a function whose return type is void,
> the goal is to rewrite the function so that it doesn't contain any
> return instructions at all.  However, when we are lowering returns in
> a function whose return type is non-void, the goal is to rewrite the
> function so that it contains a single return instruction, in canonical
> position.  (A return instruction is said to be in "canonical position"
> if it is the last instruction in the function, and it's not inside any
> ifs or loops).
> 
> If, after calling visit_block(&ir->body), the last instruction in the
> function is a return instruction, and the return type of the function
> is non-void, then we don't need to do anything, because the return
> instruction is already in canonical position.
> 
> Let me know if that makes more sense, and I'll rewrite the comment accordingly.

Ah, of course.  It's the one canonical return.  That makes sense.

--Kenneth