Speedup Function::getIntrinsicID() with caching of result

[Michael Ilseman]

r176365

Jean-Luc, for your test commit/first commits, can you do the cleanup Duncan mentioned? Also, as Duncan mentioned, could you add a unit test that checks that the cache behaves properly for Function and Module deletion?

If you look in llvm/unittests, you'll see where you can write C++ code as a unit test.

On Mar 1, 2013, at 12:25 AM, Duncan Sands <baldrick at free.fr> wrote:

> Hi Jean-Luc,
> 
> On 28/02/13 23:43, Jean-Luc Duprat wrote:
>> Attached is the revised patch, taking into account all the feedback received.
> 
> --- lib/IR/Module.cpp	(revision 176302)
> +++ lib/IR/Module.cpp	(working copy)
> @@ -13,6 +13,7 @@
> 
> #include "llvm/IR/Module.h"
> #include "SymbolTableListTraitsImpl.h"
> +#include "LLVMContextImpl.h"
> #include "llvm/ADT/DenseSet.h"
> #include "llvm/ADT/STLExtras.h"
> #include "llvm/ADT/SmallString.h"
> 
> I guess this bit isn't needed any more.  Also, did you check that when a module
> is deleted, the cache is cleared (i.e. that function destructors are run).
> 
> Ciao, Duncan.
> 
>> 
>> Thank you for your comments,
>> 
>> JL
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> On Feb 28, 2013, at 10:03 AM, Jean-Luc Duprat <jduprat at apple.com> wrote:
>> 
>>> 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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>>>>>> 
>>>>> 
>>>> 
>>> 
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>> 
>