llvm dev - Mar 2009 - [LLVMdev] using alias-analysis

Hi together,

i want to create a map containing a set of aliases for each value.

For example, for a code like:

int main() {

    int i;
    int *p1 = &i;
    int *p2 = &i;
  
    return 0;
} 

the map should contain something like:

{i --> (p1, p2), 
.....
}

For that, i do followings in my pass:

AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
AliasSetTracker *tracker = new AliasSetTracker(AA);

for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
    tracker->add(*BB);
}

using the print-method of AliasSetTracker, i see:

Alias Set Tracker: 4 alias sets for 4 pointer values.
  AliasSet[0x8528d08,1] must alias, Mod       Pointers: (i32** %p1, 4)
  AliasSet[0x8528d48,1] must alias, Mod       Pointers: (i32** %p2, 4)
  AliasSet[0x8522d18,1] must alias, Mod/Ref   Pointers: (i32* %0, 4)
  AliasSet[0x8522d58,1] must alias, Mod/Ref   Pointers: (i32* %retval, 4)

can i create this map using the info in AliasSetTracker?


Regards
Raad


      
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On Mar 15, 2009, at 6:06 AM, RAAD B wrote:
> Hi together,
>
> i want to create a map containing a set of aliases for each value.
I'd suggest checking out the code in lib/Analysis/ 
AliasAnalysisEvaluator.cpp.  It does an all pairs query and prints out  
the result of each query.  Try "opt -aa-eval -print-all-alias-modref- 
info foo.bc".

>
> AliasSetTracker *tracker = new AliasSetTracker(AA);
I'd recommend against using the AliasSetTracker class if you want good  
precision.  It basically forces a unification approach on top of the  
underlying AA impl, which pessimizes the results when aliases are not  
transitive.

-Chris
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