Speedup Function::getIntrinsicID() with caching of result

[Jean-Luc Duprat]

As discussed, I will replace Module's destructor clear() call with a call to erase() in Function's destructor.
Thank you for the feedback, I'll send a revised patch out soon.

JL



On Feb 28, 2013, at 09:59 , Michael Ilseman <milseman at apple.com> wrote:

> 
> On Feb 28, 2013, at 9:34 AM, Duncan Sands <baldrick at free.fr> wrote:
> 
>> Hi Michael,
>> 
>> On 28/02/13 18:25, Michael Ilseman wrote:
>>> 
>>> On Feb 28, 2013, at 2:21 AM, Duncan Sands <baldrick at free.fr> wrote:
>>> 
>>>> Hi Jean-Luc,
>>>> 
>>>> On 28/02/13 02:16, Jean-Luc Duprat wrote:
>>>>> The attached patch caches the result of Function::getIntrinsicID() in a DenseMap attached to the LLVMContext.  This reduces the time actually spent doing string to ID conversion and shows a 10% improvement in compile time for a particularly bad case that involves ARM Neon intrinsics (these have many overloads).
>>>>> 
>>>>> This changes passes the regression tests and the nightly tests suite.
>>>> 
>>>> if you delete an intrinsic function declaration from the module, don't you get a
>>>> stale pointer to freed memory in the cache?  To avoid all such issues, maybe it
>>>> is simpler to have the cache map the name (a StringRef) to the intrinsic ID,
>>>> rather than mapping the function pointer to the intrinsic ID.  You probably lose
>>>> some of the speedup then though.
>>> 
>>> Can he instead have the destructor remove itself from the cache? This would preserve the speedups of key-ing off of the Function pointer directly.
>> 
>> this would also mean that the code that clears the cache when a module is
>> deleted wouldn't be needed.
> 
> Yes, I think the replacement is needed.
> 
>> 
>>> 
>>> Also, since it's the Function* that's the key, I believe the situation you described wouldn't provide an error so much as it would under-utilize the map by having extra meaningless entries. However, maybe there would be an error if anyone ever iterated over the cache. Replacing the Module's destructor clear() call with a Function's destructor erase() call might be a good way to go.
>> 
>> The problem is if that freed memory gets reallocated for another function.  Then
>> the cache lookup will wrongly think that the new function has the intrinsic id
>> of the freed function.
>> 
> 
> Ah, yes, of course.
> 
> Jean-Luc, do you think you could replace Module's destructor clear() call with a call to erase() in Function's destructor?
> 
>> Ciao, Duncan.
>> 
>>> 
>>>> 
>>>> Ciao, Duncan.
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>>> 
>> 
>