[LLVMdev] Using basicaa alias analysis pass

[Sheng-Hsiu Lin]

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> 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] *On
> Behalf Of *Sheng-Hsiu Lin
> *Sent:* Wednesday, January 21, 2015 18:10
> *To:* 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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