[cfe-commits] r153898 - /cfe/trunk/include/clang/Analysis/ProgramPoint.h

[Ted Kremenek]

Both suggestions sound reasonable to me.

On Apr 2, 2012, at 6:41 PM, Jordan Rose <jediknil at belkadan.com> wrote:

> 
> On Apr 2, 2012, at 17:44, Benjamin Kramer wrote:
> 
>> 
>> On 02.04.2012, at 23:24, Ted Kremenek wrote:
>> 
>>> Author: kremenek
>>> Date: Mon Apr  2 16:24:13 2012
>>> New Revision: 153898
>>> 
>>> URL: http://llvm.org/viewvc/llvm-project?rev=153898&view=rev
>>> Log:
>>> Reduce static analyzer memory usage by about 4% by packing the ProgramPoing 'Kind' field into the spare bits of other fields.
>>> 
>>> Modified:
>>>  cfe/trunk/include/clang/Analysis/ProgramPoint.h
>>> 
>>> Modified: cfe/trunk/include/clang/Analysis/ProgramPoint.h
>>> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Analysis/ProgramPoint.h?rev=153898&r1=153897&r2=153898&view=diff
>>> ==============================================================================
>>> --- cfe/trunk/include/clang/Analysis/ProgramPoint.h (original)
>>> +++ cfe/trunk/include/clang/Analysis/ProgramPoint.h Mon Apr  2 16:24:13 2012
>>> @@ -55,27 +55,59 @@
>>>             EpsilonKind};
>>> 
>>> private:
>>> -  std::pair<const void *, const void *> Data;
>>> -  Kind K;
>>> +  std::pair<uintptr_t, const void *> Data;
>>> 
>>> // The LocationContext could be NULL to allow ProgramPoint to be used in
>>> // context insensitive analysis.
>>> -  const LocationContext *L;
>>> +  uintptr_t L;
>>> const ProgramPointTag *Tag;
>>> 
>>> ProgramPoint();
>>> 
>>> +  static uintptr_t mangleUpperKindBits(Kind K, const void *p) {
>>> +    uintptr_t tmp = (uintptr_t) p;
>>> +    uintptr_t k_int = (uintptr_t) K;
>>> +    k_int >>= 3;
>>> +    assert((k_int & 0x3) == k_int);
>>> +    tmp |= k_int;
>>> +    return tmp;
>>> +  }
>>> +  
>>> +  static uintptr_t mangleLowerKindBits(Kind K, const void *p) {
>>> +    uintptr_t tmp = (uintptr_t) p;
>>> +    uintptr_t k_int = (uintptr_t) K;
>>> +    k_int &= 0x7;
>>> +    tmp |= k_int;
>>> +    return tmp;
>>> +  }
>> 
>> You could hide some of this nastiness by using 2 llvm::PointerIntPairs with 3 bits each.
>> 
>> - Ben
> 
> I'm actually wondering why we're using a std::pair at all here. It's not like it's visible outside of the implementation.
> 
> Also, I'd suggest mangling the bits into the /second/ data pointer, on the suspicion that if one of our ProgramPoint subclasses starts using a data field as a uintptr_t (or PointerIntPair), they'll probably mess with the first data pointer first. They may not even need the second pointer.
> 
> Jordy
>