[LLVMdev] DCE and external function

[Duncan Sands]

>>> If I have:
>>>
>>> %x = call @externalFunc
>>> ... ; other codes where %x is not used
>>> ret ; assume void function
>>>
>>> and use dce optimization, will the call gets eliminated?
>>
>> only if the compiler can prove that the called function has
>> no side effects (such as modifying some global variables or
>> causing the program to exit).
>
> Wasn't there some efforts/investigation to support marking
> of (body-less) functions as 'pure'? Is this on the roadmap?

At the level of the original C source you can do this using gcc's "pure" and
"const" attributes.  At the level of LLVM IR, you can use the "readonly" and
"readnone" attributes.

Ciao,

Duncan.