Re: [gimple-ssa] result_decl and ssa_name

[Pierrick Philippe <pierrick.philippe@irisa.fr>]

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On 05/04/2024 14:46, Richard Biener wrote:
> On Fri, Apr 5, 2024 at 1:59 PM Pierrick Philippe
> <pierrick.philippe@irisa.fr> wrote:
>> Hi all,
>>
>> I do have a question regarding ssa_name and result_decl.
>>
>> For example on the following gimple function:
>>
>> int f ()
>> {
>>   int x;
>>   int D.2747;
>>   int _2;
>>
>>   <bb 2> :
>>   x_1 = 42;
>>   _2 = x_1;
>>
>>   <bb 3> :
>> <L0>:
>>   return _2;
>>
>> }
>>
>> On the above example, using the macro SSA_NAME_VAR() on _2 does not
>> yield anything usable.
>> Neither to call ssa_default_def() on the result of the result_decl
>> obtain through macro DECL_RESULT().
>>
>> Is there a way to get the ssa_name corresponding to the result_decl of a
>> function obtained through the use of macro DECL_RESULT() on a fn_decl?
>> And/or the other way around? I.e., from the returned ssa_name of a
>> function to the result_decl of that function?
>>
>> I totally might be missing something here, but I cannot figure out what.
> DECL_RESULT isn't always used (as in your example).  Not all SSA names
> have corresponding declarations, we have "anonymous" SSA names which
> have a NULL_TREE SSA_NAME_VAR (such as the _2 in your example).
I see, that makes so much more sense to me now.
> What do you try to find in the end?  If you want to find all returns you can
> walk predecessors of EXIT_BLOCK and look at their last stmt whether they
> are greturn statements.

I am implementing a state_machine within the analyzer, and I am trying
to understand where would be the best place to propagate the state of
the return value.
I intuitively thought it would be best to do so in the
state_machine::on_pop_frame() method, which is called by the analyzer
between the two frames of the caller and the callee. What I do have
access to is the struct function of the callee/caller, the gcall
instruction in the caller and the callee have been processed by my
analysis.

And to illustrate, here I do have the _2 ssa_name and its state which I
know in that case should be propagate to the lhs of the caller gcall
instruction.

Again I might be taking this in a wrong way.

> Richard.
>> Thanks for your time,
>>
>> Pierrick