Re: [PATCH v2] ipa-inline: Add target info into fn summary [PR102059]

[Martin Jambor <mjambor@suse.cz>]

Hi,

On Fri, Sep 17 2021, Kewen.Lin wrote:
> on 2021/9/16 下午9:19, Martin Jambor wrote:
>> On Thu, Sep 16 2021, Kewen.Lin wrote:
>>> on 2021/9/15 下午8:51, Martin Jambor wrote:
>>>> On Wed, Sep 08 2021, Kewen.Lin wrote:
>>>>>
>>>>
>>>> [...]
>>>>
>>>>> diff --git a/gcc/ipa-fnsummary.h b/gcc/ipa-fnsummary.h
>>>>> index 78399b0b9bb..300b8da4507 100644
>>>>> --- a/gcc/ipa-fnsummary.h
>>>>> +++ b/gcc/ipa-fnsummary.h
>>>>> @@ -193,6 +194,9 @@ public:
>>>>>    vec<ipa_freqcounting_predicate, va_gc> *loop_strides;
>>>>>    /* Parameters tested by builtin_constant_p.  */
>>>>>    vec<int, va_heap, vl_ptr> GTY((skip)) builtin_constant_p_parms;
>>>>> +  /* Like fp_expressions, but it's to hold some target specific information,
>>>>> +     such as some target specific isa flags.  */
>>>>> +  auto_vec<HOST_WIDE_INT> GTY((skip)) target_info;
>>>>>    /* Estimated growth for inlining all copies of the function before start
>>>>>       of small functions inlining.
>>>>>       This value will get out of date as the callers are duplicated, but
>>>>
>>>> Segher already wrote in the first thread that a vector of HOST_WIDE_INTs
>>>> is an overkill and I agree.  So at least make the new field just a
>>>> HOST_WIDE_INT or better yet, an unsigned int.  But I would even go
>>>> further and make target_info only a 16-bit bit-field, place it after the
>>>> other bit-fields in class ipa_fn_summary and pass it to the hooks as
>>>> uint16_t.  Unless you have plans which require more space, I think we
>>>> should be conservative here.
>>>>
>>>
>>> OK, yeah, the consideration is mainly for the scenario that target has
>>> a few bits to care about.  I just realized that to avoid inefficient
>>> bitwise operation for mapping target info bits to isa_flag bits, target
>>> can rearrange the sparse bits in isa_flag, so it's not a deal.
>>> Thanks for re-raising this!  I'll use the 16 bits bit-field in v3 as you
>>> suggested, if you don't mind, I will put it before the existing bit-fields
>>> to have a good alignment.
>> 
>> All right.
>> 
>
> Sorry that I failed to use 16 bit-fields for this, I figured out that
> the bit-fields can not be address-taken or passed as non-const reference.
> The gentype also failed to recognize uint16_t if I used uint16_t directly
> in ipa-fnsummary.h.  Finally I used unsigned int instead.
>

well, you could have used:

  unsigned int target_info : 16;

for the field (and uint16_t when passed to hooks).

But I am not sure if it is that crucial.

Martin