[Mesa-dev] [PATCH 06/11] glsl: Refactor logic for determining whether to lower return statements.

[Ian Romanick]

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On 07/07/2011 01:16 AM, Kenneth Graunke wrote:
> On 07/05/2011 03:07 PM, Paul Berry wrote:
>> Previously, do_lower_jumps.cpp determined whether to lower return
>> statements in ir_lower_jumps_visitor::should_lower_jumps().  Moved
>> this logic to ir_lower_jumps_visitor::visit(ir_function_signature *),
>> so that it can be used in determining whether to lower a return
>> statement at the end of a function.
>> ---
>>   src/glsl/lower_jumps.cpp |   19 ++++++++++++-------
>>   1 files changed, 12 insertions(+), 7 deletions(-)
>>
>> diff --git a/src/glsl/lower_jumps.cpp b/src/glsl/lower_jumps.cpp
>> index da85c6b..fa247c6 100644
>> --- a/src/glsl/lower_jumps.cpp
>> +++ b/src/glsl/lower_jumps.cpp
>> @@ -210,16 +210,17 @@ struct function_record
>>      ir_function_signature* signature;
>>      ir_variable* return_flag; /* used to break out of all loops and
>> then jump to the return instruction */
>>      ir_variable* return_value;
>> -   bool is_main;
>> +   bool lower_return;
>>      unsigned nesting_depth;
>>
>> -   function_record(ir_function_signature* p_signature = 0)
>> +   function_record(ir_function_signature* p_signature = 0,
>> +                   bool lower_return = false)
>>      {
>>         this->signature = p_signature;
>>         this->return_flag = 0;
>>         this->return_value = 0;
>>         this->nesting_depth = 0;
>> -      this->is_main = this->signature&& 
>> (strcmp(this->signature->function_name(), "main") == 0);
>> +      this->lower_return = lower_return;
>>      }
>>
>>      ir_variable* get_return_flag()
>> @@ -398,10 +399,8 @@ struct ir_lower_jumps_visitor : public
>> ir_control_flow_visitor {
>>            /* never lower return at the end of a this->function */
>>            if(this->function.nesting_depth == 0&& 
>> ir->get_next()->is_tail_sentinel())
>>               lower = false;
>> -         else if (this->function.is_main)
>> -            lower = lower_main_return;
>>            else
>> -            lower = lower_sub_return;
>> +            lower = this->function.lower_return;
>>            break;
>>         }
>>         return lower;
>> @@ -833,9 +832,15 @@ lower_continue:
>>         assert(!this->function.signature);
>>         assert(!this->loop.loop);
>>
>> +      bool lower_return;
>> +      if (strcmp(ir->function_name(), "main") == 0)
>> +         lower_return = lower_main_return;
>> +      else
>> +         lower_return = lower_sub_return;
> 
> What exactly is the difference between lowering returns in "main" and
> lowering them in other subroutines?  void vs. non-void is definitely
> different, but I don't see why main is special.  Looking at the code, it
> doesn't actually seem to use lower_main_return anywhere...

The difference is that some architectures (e.g., i965!) *only* want
returns in main lowered.

> (I realize this code was already there, but as long as you're cleaning
> it up, maybe that can just get removed...)
> 
>>         function_record saved_function = this->function;
>>         loop_record saved_loop = this->loop;
>> -      this->function = function_record(ir);
>> +      this->function = function_record(ir, lower_return);
>>         this->loop = loop_record(ir);
>>
>>         assert(!this->loop.loop);
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