[LLVMdev] Extracting the global variables accessed by individual function with function pass

John Criswell criswell at illinois.edu
Fri Sep 6 08:41:38 PDT 2013

On 9/2/13 6:15 AM, Duncan Sands wrote:
> Hi,
>> Is there a way to dump the global variables, which are accessed 
>> (read/written
>> to) by each function within the LLVM function pass?
>> Any pointers on how that info can be extracted in LLVM for each 
>> function in the
>> application?
> you will have to write your own pass to do this.  For each global, 
> visit each
> of its uses (via use_begin, use_end).  If the use is a constant 
> (isa<Constant>),
> visit each of its uses too (do this recursively until you aren't visiting
> constants any more).  If a use isn't a constant, check whether it's 
> parent
> (getParent) is the function you are interested in.  The point of 
> recursing on
> constant uses is that the global may be used in a constant expression 
> (eg a
> constant bitcast) before actually being used by an instruction.

Note that this only finds globals that are directly accessed by the 
function.  It won't find globals that are accessed by the function due 
to the global being passed into the function as an argument or loaded 
from memory via an LLVM load instruction.  To find those, you'll need to 
use alias analysis or a points-to analysis.

-- John T.

> Ciao, Duncan.
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