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Re: [gimplefe] Parsing PHI functions


On Fri, Jul 1, 2016 at 1:57 PM, Prasad Ghangal <prasad.ghangal@gmail.com> wrote:
> On 29 June 2016 at 12:42, Richard Biener <richard.guenther@gmail.com> wrote:
>> On Tue, Jun 28, 2016 at 4:16 PM, Prasad Ghangal
>> <prasad.ghangal@gmail.com> wrote:
>>> Hi,
>>>
>>> For handling PHI, it expects cfg to be built before. So I was
>>> wondering how are we going to handle this? Do we need to build cfg
>>> while parsing only?
>>
>> For handling PHIs we need to have a CFG in the sense that the GIMPLE PHI
>> data structures are built in a way to have the PHI argument index correspond
>> to CFG predecessor edge index.  As we'd like to parse phis with args
>> corresponding
>> to predecessor block labels, like
>>
>> a:
>>   i_1 = 1;
>>   goto p;
>>
>> b:
>>   i_2 = 2;
>>   goto p;
>>
>> p:
>>   i_3 = __PHI (a: i_1, b: i_2);
>>
>> I think that a possibility is to leave those PHIs as internal function
>> with label / arg
>> pairs and have CFG construction lower them to real PHIs.
>>
>> Of course the parser could as well build a CFG on its own but I think
>> we should use
>> the easy way out for now.
>>
>> Thus you'd have to modify CFG construction a bit to lower the internal
>> function calls.
>
> Currently I am just building internal call using
> gimple_build_call_internal_vec (), and detecting (and removing for
> now) it after edge creation in tree-cfg. I was observing
> internal-fn.def, do I need to make entry in internal-fn.def and write
> expand function?

You should add an entry and a stub expand function (like those
others that simply have gcc_unreachable in them).

Richard.

>>
>> Richard.
>>>
>>>
>>>
>>> Thanks,
>>> Prasad


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