[LLVMdev] Using basicaa alias analysis pass

[Roel Jordans]

Hi Ahmed,

Yes, to do a new transformation using the alias analysis results you 
would need to write a pass.

I'd suggest you look at the "Writing an LLVM Pass" document [1] for 
information on how to get started with writing your pass and maybe have 
a look at the AliasAnalysisEvaluater pass [2] for an example on how you 
can extract information from the alias analysis.

Cheers,
  Roel

[1] http://llvm.org/docs/WritingAnLLVMPass.html
[2] 
http://llvm.org/docs/doxygen/html/AliasAnalysisEvaluator_8cpp_source.html

On 21/01/15 20:09, Sheng-Hsiu Lin wrote:
> Ahmed, Roel and Michael,
>
> Thank you so much for clarifying this for me.
>
> Now if I want to use the result of basicaa pass to do some
> transformation, I suppose I will need write a pass, correct?  Is there a
> good document on this (specifically on writing a pass to act on alias
> analysis results) that I could refer to?
>
> Thanks again!
>
> Sheng-Hsiu
>
> On Wed, Jan 21, 2015 at 11:58 AM, Kuperstein, Michael M
> <michael.m.kuperstein at intel.com <mailto:michael.m.kuperstein at intel.com>>
> wrote:
>
>     Specifying -basicaa only tells opt to run the basic alias analysis
>     pass. ____
>
>     However, since this is not a transformation pass, but, rather, an
>     analysis that is meant to be used by transformations, you will not
>     see any change in the bitcode.____
>
>     __ __
>
>     If you want to see the results in a human-readable form, you can try
>     something like:____
>
>     opt -basicaa -aa-eval -print-all-alias-modref-info < hello.bc____
>
>     __ __
>
>     Michael____
>
>     __ __
>
>     *From:*llvmdev-bounces at cs.uiuc.edu
>     <mailto:llvmdev-bounces at cs.uiuc.edu>
>     [mailto:llvmdev-bounces at cs.uiuc.edu
>     <mailto:llvmdev-bounces at cs.uiuc.edu>] *On Behalf Of *Sheng-Hsiu Lin
>     *Sent:* Wednesday, January 21, 2015 18:10
>     *To:* llvmdev at cs.uiuc.edu <mailto:llvmdev at cs.uiuc.edu>
>     *Subject:* [LLVMdev] Using basicaa alias analysis pass____
>
>     __ __
>
>     Hi____
>
>     __ __
>
>     I am completely new to LLVM, and I am trying to explore the alias
>     analysis part of it.  It seems to me that -basicaa is the most
>     simple alias analysis pass in LLVM.  So I would like to try and make
>     it work (to see some alias analysis results of some sample bit
>     code).____
>
>     __ __
>
>     What I have done is that I____
>
>     __ __
>
>     ---make lib/Analysis/BasicAliasAnalysis.cpp into a .so file____
>
>     ---write a sample c program, hello.c, with the following code____
>
>     __ __
>
>     #include<stdio.h>____
>
>     __ __
>
>     int main()____
>
>     {____
>
>          int a;____
>
>          int *p;____
>
>          p = &a;____
>
>          a = 10;____
>
>          printf("Hello World");____
>
>          return 0;____
>
>     }____
>
>     __ __
>
>     ---compile the c program into bit code by doing____
>
>     clang -c -emit-llvm hello.c -o hello.bc____
>
>     __ __
>
>     ---run the bit code through basicaa pass____
>
>     opt -load lib/AliasAnalysis.so -basicaa < hello.bc > result.bc____
>
>     __ __
>
>     ---display the resulted bit code____
>
>     llvm-dis result.bc -o -____
>
>     __ __
>
>     However, the resulted bit code result.bc is exactly the same as the
>     original bit code hello.bc.  That is no alias analysis information
>     is printed on the screen or recorded in the resulting result.bc
>     file.____
>
>     __ __
>
>     Could someone explain what I should do to get some results from
>     basicaa alias analysis pass?____
>
>     __ __
>
>     Thank you very much.  Your help is much appreciated!____
>
>     __ __
>
>     Sheng-Hsiu____
>
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