eliminate dead stores across functions

[Bin.Cheng]

On Tue, Mar 6, 2018 at 4:50 PM, Bin.Cheng <amker.cheng@gmail.com> wrote:
> On Tue, Mar 6, 2018 at 4:44 PM, Martin Jambor <mjambor@suse.cz> wrote:
>> Hi Bin,
>>
>> On Tue, Mar 06 2018, Bin Cheng wrote:
>>> On Tue, Mar 6, 2018 at 2:28 PM, Richard Biener
>>>>
>>>> Do you think the situation happens often enough to make this worthwhile?
>>> There is one probably more useful case.  Program may use global flags
>>> controlling
>>> how it does (heavy) computation.  Such flags are only set couple of
>>> times in execution
>>> time.  It would be useful if we can (IPA) propagate flags into computation heavy
>>> functions by versioning (if necessary).  For example:
>>>
>>> int flag = 1;
>>> void foo ()
>>> {
>>>   //heavy computation wrto to flag
>>> }
>>> void main()
>>> {
>>>   flag = 2;
>>>   foo();
>>>   flag = 1;
>>>   foo();
>>> }
>>>
>>
>> So basically IPA-CP done on (not-addressable) static global variables.
>> Do you happen to know some real code which would benefit?  I'd like to
>> experiment with it but would like to have a real thing to look at, as
>> opposed to artificial test cases.
> As Richi pointed out, I think this is not rare in spec.  For this
> moment I only vaguely remember 544.nab_r for such issue, but I am sure
> there are other cases.
Sorry I forgot to mention it might not be static variables in file
scope, that's why I mentioned LTO previously.

Thanks,
bin
>
> Thanks,
> bin
>>
>> Thanks,
>>
>> Martin
>>
>>