[LLVMdev] alias result

[Hal Finkel]

----- Original Message -----
> From: "Haopeng Liu" <hyliuhp at gmail.com>
> To: "Hal Finkel" <hfinkel at anl.gov>
> Cc: llvmdev at cs.uiuc.edu
> Sent: Monday, February 16, 2015 12:37:06 PM
> Subject: Re: [LLVMdev] alias result
> 
> t and t2 are two pointers defined in .c file.
> 
> The definitions in .bc are:
> %thd = alloc i64, align 8
> %t = alloca i64*, align 8
> %t2 = alloca i64*, align 8
> 
> .c file likes this:
> int thd;
> int *t = &thd;
> int *t2 = t;

Okay, those point to distinct local stack allocations. Why do you expect them to alias?

 -Hal

> 
> 
> On 2/16/15 12:28 PM, Hal Finkel wrote:
> > ----- Original Message -----
> >> From: "Haopeng Liu" <hyliuhp at gmail.com>
> >> To: llvmdev at cs.uiuc.edu
> >> Sent: Monday, February 16, 2015 12:12:18 PM
> >> Subject: [LLVMdev] alias result
> >>
> >> Hi all,
> >>
> >> I am implementing a pass which needs aliasanalysis in llvm.
> >>
> >> My pass firstly records all store or load instructions as follows:
> >> loc[cnt++] = AA.getLocation(si/li);
> >>
> >> Then, get each pairwise alias result.
> >> AliasAnalysis::AliasResult ar = AA.alias(loc[i], loc[j]);
> >> switch(ar){ case 0,1,2,3;}
> >>
> >> And the command is: opt -load mypass.so -mypass -basicaa test.bc
> >>
> >> The store/load in test.bc:
> >>
> >> (1): store i64* %thd, i64** %t, align 8    //int64 *t = &thd;
> >> (2): %1 = load i64** %t, align 8             //load t
> >> (3): store i64* %1, i64** %t2, align 8     //int64 *t2 = t;
> >> (4): %2 = load i64** %t, align 8             //load t
> >> (5): %3 = load i64** %t2, align 8           //load t2
> >>
> >> It seems that all these 5 instructions should be aliased to each
> >> other.
> >>
> >> But the result should that only (1,2) (1,4) (2,4) (3,5) are must
> >> alias.
> >> Others are no alias.
> > Where do %t and %t2 come from?
> >
> >   -Hal
> >
> >> Who can explain these results? Any hits would be appreciated.
> >> Thank
> >> you.
> >>
> >>
> >>
> >>
> >>
> >>
> >> _______________________________________________
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> >>
> 
> 

-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory