[cfe-dev] Dead stores of NULLs

Nikita Zhuk nikita at zhuk.fi
Thu Jun 19 17:40:37 PDT 2008

First I would like to express my appreciation for the great static  
analyzer, which is already producing useful results. I've been able to  
find several memory leaks and some dead stores. However, I would like  
to address an issue which produces some dead store reports which are  
technically correct (they really are dead stores), but I would still  
like to ignore them.

When I allocate an object (by using alloc & init* or one of the  
*Create* functions) and store it into a local variable inside some  
scope, I tend to set it to nil/NULL after the object has been  
released. This is an intentional dead store, which prevents any use of  
that released object later in the same scope. For example:

- (void)doSomethingWithFileExtension:(NSString *)ext
	CFStringRef fileUti =  
(CFStringRef)ext, NULL);

	// use 'fileUti'...

	fileUti = NULL; // Dead store, reported correctly by 'scan-build'

	// From now on, any unintentional use of 'fileUti' variable in this  
method will cause predictable runtime behaviour.
	// If it'll be passed to some other methods, precondition assertions  
of those methods will catch it early etc.

Would it be useful to add a flag to ignore nil/NULL dead stores?

- Nikita

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