[llvm-dev] GlobalVariable Recursive loop

[Johan Wehrli via llvm-dev]

Hi Mehdi,

> What about keeping track of “visited” global in a side structure (hash map…) and skip these?
> 
> Note also that only GlobalValue can create cycles, so you’d need only to track these, not all constant.

Thanks for the proposition, I will try that.

Greetings,

Johan

> On 28 Sep 2016, at 18:50, Mehdi Amini <mehdi.amini at apple.com> wrote:
> 
>> 
>> On Sep 28, 2016, at 9:35 AM, Johan Wehrli via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>> 
>> Hi,
>> 
>> I have implemented a recursive loop to go through all the user of a global variable but I have one issue left.
>> 
>> Depending the code, the global variable is using itself: 
>> 
>> @sSelectedAccount = internal constant %struct.KVObserver { %0* bitcast (%struct.__NSConstantString_tag* @_unnamed_cfstring_.744 to %0*), i8* bitcast (%struct.KVObserver* @sSelectedAccount to i8*), i32 3 }, align 4
>> 
>> With the IR code above, I am stuck in an infinite loop:
>> 
>> 	1) The global sSelectedAccount has the following user: "i8* bitcast (%struct.KVObserver* @sSelectedAccount to i8*)"
>> 	2) The bit cast has the following user: "%struct.KVObserver { %"type 0x7ff164027360"* bitcast (%struct.__NSConstantString_tag* @_unnamed_cfstring_.744 to %"type 0x7ff164027360"*), i8* bitcast (%struct.KVObserver* @sSelectedAccount to i8*), i32 3 }"
>> 	3) The previous has the user sSelectedAccount -> so this create the infinite loop.
>> 
>> I was looking for a way to detect the loop and I think there is two possibilities:
>> 	- from the global value, iterate through all the element and find the loop, but this need a lot of cast and another recursive loop (need to handle ConstantStruct, ConstantExpr, ConstantArray, etc.) Does anyone know if there is an easier way to do this?
>> 	-during the recursive loop, can I find the “main” global value? e.g: when I am on "i8* bitcast (%struct.KVObserver* @sSelectedAccount to i8*)”, how can I get the global variable sSelectedAccount ?
> 
> 
> What about keeping track of “visited” global in a side structure (hash map…) and skip these?
> 
> Note also that only GlobalValue can create cycles, so you’d need only to track these, not all constant.
> 
> — 
> Mehdi

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