[LLVMdev] A very basic doubt about LLVM Alias Analysis

[ambika]

Hi,

I actually used the example mentioned by Török

int main(int argc, char **argv)
{
        int *i=0,*j=0,k;
        if (argc > 1) {
          i=&k;
        } else {
          j=&k;
        }
        k=4;
        printf("%d,%d,%d,%p,%p",*i,*j,k,i,j);
        return 0;
}



Duncan Sands wrote:
> Hi Ambika,
>
>> Using this option I do get all the vars as may alias ie
>>
>> MayAlias:    i32* %j.0, i32* %k
>> MayAlias:    i32* %i.0, i32* %k
>> MayAlias:    i32* %i.0, i32* %j.0
>>
>> Is there any other analysis which will give them as must aliases.
>
> at -O1 these variables are entirely eliminated here.  I'm surprised
> they aren't eliminated for you.
>
> Ciao,
>
> Duncan.
>
> PS:
>
> $ cat ambika.c
> int main()
> {
>        int *i,*j,k;
>        i=&k;
>        j=&k;
>        k=4;
>        printf("%d,%d,%d",*i,*j,k);
>        return 0;
> }
> $ llvm-gcc -S -O1 -emit-llvm -o - ambika.c
> ambika.c: In function ‘main’:
> ambika.c:7: warning: incompatible implicit declaration of built-in 
> function ‘printf’
> ; ModuleID = 'ambika.c'
> target datalayout = 
> "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64" 
>
> target triple = "x86_64-unknown-linux-gnu"
>
> @.str = private constant [9 x i8] c"%d,%d,%d\00", align 1 ; <[9 x 
> i8]*> [#uses=1]
>
> define i32 @main() nounwind {
> entry:
>   %0 = tail call i32 (i8*, ...)* @printf(i8* getelementptr inbounds 
> ([9 x i8]* @.str, i64 0, i64 0), i32 4, i32 4, i32 4) nounwind ; <i32> 
> [#uses=0]
>   ret i32 0
> }
>
> declare i32 @printf(i8* nocapture, ...) nounwind