[Mesa-dev] [PATCH 03/38] i965/fs: Allocate a common IR builder object in fs_visitor.

[Francisco Jerez]

Francisco Jerez <currojerez at riseup.net> writes:

> Matt Turner <mattst88 at gmail.com> writes:
>
>> On Thu, Jun 4, 2015 at 9:04 AM, Francisco Jerez <currojerez at riseup.net> wrote:
>>> ---
>>>  src/mesa/drivers/dri/i965/brw_fs.cpp         | 11 +++++++++++
>>>  src/mesa/drivers/dri/i965/brw_fs.h           |  2 ++
>>>  src/mesa/drivers/dri/i965/brw_fs_visitor.cpp |  4 +++-
>>>  3 files changed, 16 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
>>> index 28a19bd..c1dd0a6 100644
>>> --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
>>> +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
>>> @@ -3986,6 +3986,17 @@ fs_visitor::calculate_register_pressure()
>>>  void
>>>  fs_visitor::optimize()
>>>  {
>>> +   /* bld is the common builder object pointing at the end of the program we
>>> +    * used to translate it into i965 IR.  For the optimization and lowering
>>> +    * passes coming next, any code added after the end of the program without
>>> +    * having explicitly called fs_builder::at() clearly points at a mistake.
>>> +    * Ideally optimization passes wouldn't be part of the visitor so they
>>> +    * wouldn't have access to bld at all, but they do, so just in case some
>>> +    * pass forgets to ask for a location explicitly set it to NULL here to
>>> +    * make it trip.
>>> +    */
>>> +   bld = bld.at(NULL, NULL);
>>
>> I like it. I know I've wasted a bunch of time in the last by
>> emit()'ing an instruction in an optimization instead of inserting it.
>> This should make that class of mistakes really simple to debug.
>>
>> But I'm not sure what your plan is for the builder in optimization
>> passes (I mean beyond this series)? I agree that it'd be nice to
>> separate the translation into the backend IR from the optimization
>> passes, but how could we ever remove access to the builder from the
>> optimization passes? They're of course going to need to insert
>> instructions.
>
> I had two possibilities in mind: We could pass the optimization passes a
> backend_shader pointer only, and let them create their own builder (what
> would require adding a dispatch_width field to backend_shader which
> seems like a good idea anyway), or we could pass them a builder pointing
> at the NULL instruction, kind of like what this patch does.

Hmm, I think I'm going to go change the constructor of fs_builder to
initialize cursor to NULL by default instead of to the end of the
program, in anticipation of these two possibilities.
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