[llvm] r224058 - LeakDetector: Simplify code and fix comments, NFC

[Alexander Potapenko]

AFAIK neither Valgrind nor LSan are able to detect leaked objects that
reference each other.
Moreover, it is theoretically possible to get a false negative if
somewhere in the memory there's a value that looks like a pointer to a
leaked object (or a cluster of objects).
The leak detector built directly into IR can do a better job.

On Thu, Dec 18, 2014 at 10:14 PM, Duncan P. N. Exon Smith
<dexonsmith at apple.com> wrote:
> I guess I'm not sure.
>
> It's possible to set up orphaned cycles between metadata nodes.  If
> these are temporaries, and they never get deleted, that's a leak.
>
> Can asan/msan/etc. detect that situation?
>
> Are you suggested we kill the `LeakDetector` entirely?
>
> (Not that I'm against it...)
>
>> On 2014-Dec-17, at 19:52, Rafael Espíndola <rafael.espindola at gmail.com> wrote:
>>
>> Can this find bugs that asan/msan/valgrind cannot?
>>
>> Maybe it would be better to just delete it.
>>
>> On 11 December 2014 at 16:23, Duncan P. N. Exon Smith
>> <dexonsmith at apple.com> wrote:
>>> Author: dexonsmith
>>> Date: Thu Dec 11 15:23:43 2014
>>> New Revision: 224058
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=224058&view=rev
>>> Log:
>>> LeakDetector: Simplify code and fix comments, NFC
>>>
>>> Rather than requiring overloads in the wrapper and the impl, just
>>> overload the impl and use templates in the wrapper.  This makes it less
>>> error prone to add more overloads (`void *` defeats any chance the
>>> compiler has at noticing bugs, so the easier the better).
>>>
>>> At the same time, correct the comment that was lying about not changing
>>> functionality for `Value`.
>>>
>>> Modified:
>>>    llvm/trunk/include/llvm/IR/LeakDetector.h
>>>
>>> Modified: llvm/trunk/include/llvm/IR/LeakDetector.h
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/IR/LeakDetector.h?rev=224058&r1=224057&r2=224058&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/include/llvm/IR/LeakDetector.h (original)
>>> +++ llvm/trunk/include/llvm/IR/LeakDetector.h Thu Dec 11 15:23:43 2014
>>> @@ -34,7 +34,7 @@ struct LeakDetector {
>>>   /// pointers.  This should be called when objects are created, or if they are
>>>   /// taken out of an owning collection.
>>>   ///
>>> -  static void addGarbageObject(void *Object) {
>>> +  template <class T> static void addGarbageObject(T *Object) {
>>> #ifndef NDEBUG
>>>     addGarbageObjectImpl(Object);
>>> #endif
>>> @@ -44,7 +44,7 @@ struct LeakDetector {
>>>   /// our "garbage" objects.  This should be called when an object is added to
>>>   /// an "owning" collection.
>>>   ///
>>> -  static void removeGarbageObject(void *Object) {
>>> +  template <class T> static void removeGarbageObject(T *Object) {
>>> #ifndef NDEBUG
>>>     removeGarbageObjectImpl(Object);
>>> #endif
>>> @@ -63,25 +63,15 @@ struct LeakDetector {
>>> #endif
>>>   }
>>>
>>> -  /// Overload the normal methods to work better with Value*'s because they are
>>> -  /// by far the most common in LLVM.  This does not affect the actual
>>> -  /// functioning of this class, it just makes the warning messages nicer.
>>> -  ///
>>> -  static void addGarbageObject(const Value *Object) {
>>> -#ifndef NDEBUG
>>> -    addGarbageObjectImpl(Object);
>>> -#endif
>>> -  }
>>> -  static void removeGarbageObject(const Value *Object) {
>>> -#ifndef NDEBUG
>>> -    removeGarbageObjectImpl(Object);
>>> -#endif
>>> -  }
>>> -
>>> private:
>>> -  // If we are debugging, the actual implementations will be called...
>>> +  /// Overload the normal methods to work better with Value* because they are
>>> +  /// by far the most common in LLVM.
>>> +  ///
>>> +  /// Besides making the warning messages nicer, this hides errors by storing
>>> +  /// Value* in a different leak-detection container than other classes.
>>>   static void addGarbageObjectImpl(const Value *Object);
>>>   static void removeGarbageObjectImpl(const Value *Object);
>>> +
>>>   static void addGarbageObjectImpl(void *Object);
>>>   static void removeGarbageObjectImpl(void *Object);
>>>   static void checkForGarbageImpl(LLVMContext &C, const std::string &Message);
>>>
>>>
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>>> llvm-commits at cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>
>
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-- 
Alexander Potapenko
Software Engineer
Google Moscow